A system solution for a 100 kA class High Temperature Superconducting line for HL-LHC and for wider energy applications

A system solution for a 100 kA class High Temperature Superconducting line for HL-LHC and for wider energy applications | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article A system solution for a 100 kA class High Temperature Superconducting line for HL-LHC and for wider energy applications Amalia Ballarino, Wendell Bailey, Christian Barth, Paul Cruikshank, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6629095/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted 11 You are reading this latest preprint version Abstract The powering of the High Luminosity magnets of the Large Hadron Collider relies on Cold Powering Systems incorporating direct current superconducting lines, called Superconducting Links, based on magnesium diboride cables. A Cold Powering System interconnects the magnets in the accelerator existing tunnel to the power converters in newly excavated galleries that are about 8 m higher than the accelerator tunnel and up to about 100 m distant from the magnets. It feeds circuits rated at different currents and is designed to transfer a total current of up to |117| kA with magnesium diboride and Rare-Earth-Barium-Copper-Oxide technologies. After about ten years of development, the first Cold Powering System was successfully constructed and tested at CERN. The Superconducting Link was measured in a geometrical configuration that included a vertical path simulating the final routing in the accelerator underground. The test campaign validated the mechanical, cryogenic and electrical performance of the system both in steady state conditions and under various transient scenarios. This paper reports on the results of the tests and details the performance of the first ever built magnesium diboride and Rare-Earth-Barium-Copper-Oxide 100 kA class superconducting system. Physical sciences/Engineering Physical sciences/Physics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction The High Luminosity Large Hadron Collider (HL-LHC) [ 1 ] is an upgrade of the LHC machine which aims at achieving instantaneous luminosities a factor of 5 to 7.5 larger than the LHC nominal value. This will allow attaining an integrated luminosity around ten times higher than the expected luminosity reach of the LHC after about 10 years of operation, and it will therefore bring new opportunities for physics discoveries. Planned to be operational as from 2030, the HL-LHC will rely on key innovative superconducting technologies. The final focusing magnets in the interaction regions close to the ATLAS and CMS experiments will consist of niobium-tin (Nb 3 Sn) quadrupoles reaching peak fields at operation of about 12 T, superconducting radio-frequency “crab” cavities will tilt the particle beams to enlarge the overlapping area of the incoming particle bunches, and the electrical transfer from the power converters to the magnets will be done via innovative Cold Powering Systems incorporating direct current (DC) superconducting lines, the so-called Superconducting Links, based on magnesium diboride (MgB 2 ) technology [ 2 ]. To enhance the accelerator’s availability and efficiency, the power converters of the HL-LHC magnets will be installed in newly excavated galleries, separated from and about eight meters above the LHC existing tunnel. This will facilitate access of personnel for maintenance and operational interventions that will take place in radiation free areas. The Superconducting Links will transfer the current from the power converters to the HL-LHC magnets. To interconnect the two different tunnel levels, they will pass through a purposely excavated, eight-meter high, vertical shaft (Fig. 1 ). A Superconducting Link consists of a flexible cryostat, made of two multi-layer-insulated (MLI) concentric corrugated pipes, and a multiplicity of electrically insulated MgB 2 cables in the inner pipe. These cables, which are grouped and twisted together to form a compact multi-cable assembly, feed the HL-LHC magnet circuits of the HL-LHC Triplets and Matching Sections. A Superconducting Link is connected at its warmer (∼ 20 K) end to a cryostat (DFHX for the Triplets and DFHM for the Matching Sections) that contains the High Temperature Superconducting (HTS) Rare-Earth-Barium-Copper-Oxide (REBCO) based current leads providing the electrical transfer to room temperature, and at its colder (4.5 K) end to a cryostat (DFX for the Triplets and DFM for the Matching Sections) that contains the Niobium Titanium (Nb-Ti) cables going to the magnets (Fig. 1 and Fig. 2 , left). The system of the Superconducting Link connected to a cryostat at each end is called Cold Powering System. A Cold Powering System provides the electrical transfer from room temperature to the liquid helium environment of the magnets. In total eight Cold Powering Systems of two different types are needed for HL-LHC: four for the powering of the magnets in the Triplets and four for the powering of the magnets in the Matching Sections. Two systems of different type will be located right and left of LHC Point 1 and Point 5 that house the ATLAS and CMS experiments. The Cold Powering Systems for the Triplets incorporate Superconducting Links that are 74.5 m long. They contain nineteen MgB 2 cables (Fig. 2 , right) rated at DC currents of 18 kA, 7 kA and 2 kA, and an equivalent number of HTS current leads and Nb-Ti cables. They can transfer a total DC current of up to |117| kA. The Cold Powering Systems for the Matching Sections incorporate Superconducting Links that are 120 m long. They require ten MgB 2 cables, and an equivalent number of HTS current leads and Nb-Ti cables rated at currents of 18 kA and 0.6 kA. They can transfer a total DC current of up to |40| kA. Following extensive research and development (R&D) as well as validation of individual components [ 3 ] [ 4 ], a Cold Powering System of the type needed for the HL-LHC Triplets has been constructed and extensively tested at CERN. This paper reports on the outcome of the room temperature, cryogenic, electrical and mechanical measurements performed on the first ever built 100 kA class MgB 2 and REBCO system. Methods Test bench The Cold Powering System was installed and tested at CERN in the SM-18 (Superconducting Magnet Test Facility). The Superconducting Link has a snaked geometry on the ground (Fig. 3 ): while this geometry does not reproduce the final configuration in the LHC underground, it meets the requirements of fitting the full length of 74.5 m within the available test area, coping with the thermal contraction and expansion of the system during cool-down and warm-up, and respecting the minimum bending radius of 2 m. To simulate the vertical path in the underground, where the Superconducting Link passes through the shaft connecting the HL-LHC new gallery to the LHC tunnel, a cable chain has been installed: it supports the Superconducting Link on the climb that leads to a vertical descent of about 2.5 meters (Fig. 4 ). At the end of the descent, the DFX cryostat receives the MgB 2 cables that are electrically connected in a vertical configuration to Nb-Ti cables. At the other side of the Superconducting Link, the MgB 2 cables are distributed inside the DFHX cryostat and are connected to the REBCO cables that are part of the HTS current leads. Each REBCO cable is connected to the resistive part of a current lead. The DFHX hosts, in a compact volume (∼ 5.5 m length, ∼ 1 m external diameter), the nineteen electrical joints (splices) between the MgB 2 and the REBCO cables and the nineteen HTS current leads. For the benefit of compactness, the current leads are not aligned vertically, one after the other, in the DFHX like in the LHC (Fig. 1 in [ 5 ]). They are instead grouped at two locations of the DFHX and are almost horizontal to the ground – the inclination ranges from about 6 to 15 degrees. Use of helium gas instead of liquid cryogen enables robust operation of the current leads in this configuration (Fig. 5 , left). Four power converters are available for the electrical tests: one 18 kA, one 15 kA and two 2 kA. Powering of an 18 kA circuit (Nb 3 Sn Quadrupole circuit in Table 1 ), of a 15 kA circuit (Nb-Ti Separation Dipole circuit in Table 1 ), and of two 2 kA circuits (Trim and Nb-Ti Corrector circuits in Table 1 , the latter all powered in series) is therefore possible. The powering scheme is reported in Fig. 6 . The routing of the room temperature water cooled 18 kA and 15 kA cables and of the air cooled 2 kA cables as well as their connection to the current leads are inside an ingress protection (IP) 2X rated cage, in front of the DFHX, that reproduces the final configuration in the HL-LHC gallery (Fig. 5 ). A dedicated cryogenic line transfers liquid helium from an available source, in the SM-18, to the DFX cryostat: a mix of liquid and gaseous helium is injected at 1.3 bara inside the DFX. Liquid helium fills the DFX cryostat and covers the electrical splices between MgB 2 and Nb-Ti. Two proportional-integral-derivative (PID) controlled 100 W electrical heaters inside the DFX vaporize the liquid helium to provide the gaseous mass flow rate required to cool the system. The gas flows along the Superconducting Link and reaches the DFHX where it is distributed among the nineteen MgB 2 to REBCO splices and the nineteen current leads before being recovered at room temperature. Recovery of helium gas on the DFHX side is managed by a purpose-built gas management system, which groups the helium gas return piping at room temperature and the valves used for the control of the flow through the current leads (Fig. 5 ). In the DFHX there is also a cryogenic by-pass line that recovers the excess of cold gas and warms it up to room temperature via a 15 kW electric heater. Operating conditions The number and type of HL-LHC circuits and the number of cables and current leads in the Cold powering System are listed in Table 1 . The current at which each circuit has been tested (test current), corresponding to the maximum current of the power converter, the current at which each circuit will operate in the LHC (nominal current), and the design currents are also reported. The design current of the superconducting cables is at least 10% higher than the nominal current. The total current is the sum of the absolute value of the current transferred by each polarity in the Cold Powering System. Table 1 Table 1 Number of HL-LHC circuits fed by the Cold Powering System, number of cables (MgB 2 or REBCO) and current leads per circuit type. Nominal currents during operation in the HL-LHC, test currents and design currents of the circuits are reported. Number of Circuits Number of Cables/Current Leads Nominal Current (kA) Test Current (kA) Design Current (kA) Nb 3 Sn Quadrupole 1 2 16.23 18 18 Nb-Ti Separation Dipole 1 2 12.11 15 18 Nb-Ti Trim 1 3* 2 2 7** Nb-Ti Corrector 2 4 1.74 2 2 Nb-Ti Corrector 2 4 1.34 2 2 Nb-Ti Corrector 2 4 1.59 2 2 Total 9 19 81.36 94*** 117**** The Cold Powering System should by design operate with a helium mass flow rate of not more than 5.5 g/s – when all circuits are operated at their nominal current. It must also be able to generate and transfer, in transient conditions, up to 10 g/s of helium gas produced in the DFX. The Superconducting Link operates in a temperature range from 4.5 K, in the DFX, to about 20 K, in the DFHX. The cryogenics of the Cold Powering System shall guarantee that: the Nb-Ti cables and their splices to the MgB 2 cables are submersed in a saturated liquid helium bath inside the DFX; the MgB 2 cables in the Superconducting Link operate at not more than 20 K; the REBCO cables in the current leads never exceed 60 K. These boundary conditions are by design defined as nominal cryogenic conditions. The static heat load of the Superconducting Link was specified and measured, in a previous test campaign at CERN, to be 1.6 ± 0.5 W/m [ 6 ]. The helium mass flow through each current lead is optimized for operation at the design current in Table 1 and shall be of the order of 0.055 g/(s⋅kA). The DFX internal vessel has a “fountain” configuration: there are two concentric volumes of saturated liquid helium. Helium is injected in the central volume, where the Nb-Ti cables and their splices to the MgB 2 cables are located, and overflows into the outer volume. The outer volume contains an electrical heater, which provides the helium mass flow rate required for the cooling of the system, and the level gauge used for liquid helium level control. This design enables meeting the requirement, imposed by cryogenic operating conditions, of maintaining the MgB 2 to Nb-Ti splices immersed in liquid helium during at least 10 minutes after an accidental stop of helium supply. The helium gas produced in the DFX warms up, while absorbing the static heat load of the Superconducting Link cryostat, from 4.5 K up to a maximum temperature of 20 K at the location of the splices between the MgB 2 and the REBCO cables. It then cools the nineteen current leads, at the exit of which it is recovered at room temperature. The temperature of the MgB 2 to REBCO splices (T MgB2 ≤ 20 K) and of the warm termination of the REBCO cables (T HTS ≤ 60 K) are monitored and the temperatures T HTS are controlled. Room temperature valves, one per current lead, control the helium mass flow rate passing through each lead so that T HTS stays at not more than 60 K. By design, T HTS is expected to be in the range 50 K – 60 K. Neither the Superconducting Link nor the DFX and the DFHX cryostats include a thermal shield. Insulation from thermal radiation from room temperature to the cryogenic environment is provided exclusively by 30 to 40 multi-layer insulation blankets located around the cold inner part of the cryostats that contains liquid or gaseous helium. This simplified design is made possible by the use of superconducting materials operated at temperatures higher than liquid helium. Electrical requirements and instrumentation The Cold Powering System includes high-current Nb-Ti, MgB 2 and REBCO cables. The splices between MgB 2 and REBCO are in helium gas in the DFHX, and those between MgB 2 and Nb-Ti are in liquid helium in the DFX (see Fig. 2 ). While the splices are not required to be superconducting, low resistance is necessary to avoid local thermal run-away and ensure efficient cryogenic cooling of the system with a minimum mass flow rate. Boundary conditions for the design were: electrical insulation among circuits and to ground of 2.3 kV when the system is in nominal cryogenic conditions; controlled cross talk among circuits, i.e. fast discharges generated by the resistive transition of the Nb-Ti Corrector magnets (see Table 1 ) should not trigger by electro-magnetic coupling the resistive transition of the other circuits. Circuits were therefore powered both individually and simultaneously with different ramp rates. If quench protection thresholds, i.e. the maximum allowed voltage drops along the superconducting parts of the system, are accidentally exceeded or nominal cryogenic conditions are lost, a discharge of the concerned circuit(s) is triggered. The temperature sensors and voltage taps required for monitoring and protection are incorporated in the system. All voltage taps used for quench protection are doubled for redundancy. Altogether, the system includes 304 voltage taps, 266 for protection and 38 for monitoring functionalities. An overview of the instrumentation is given in Fig. 7 . Data acquisition and quench detection are provided by twenty crates of the universal quench detection system (uQDS, [ 7 ]). The crates are equipped with 16 inputs each for a total of 320 channels. They are arranged in two redundant groups of ten crates. Each crate and its redundant twin monitor and protect the two polarities of a circuit and measure with two analog inputs the current signals stemming from two independent direct current transducers (DCCT) of the circuit. Protection thresholds are: 100 mV for the resistive part of each current lead, 5 mV for each REBCO cable, and 20 mV for each MgB 2 cable. Splices are also individually protected with voltage thresholds of 20 mV, for the MgB 2 to Nb-Ti splices, and 5 mV, for the MgB 2 to REBCO splices. The discrimination time of the quench detection system is 100 ms for the resistive part of the current leads and 20 ms for the REBCO and MgB 2 cables as well as for the splices. At low currents, defined as ≤ 10% of the design current of a circuit (see Table 1 ), the quench detection thresholds are increased by a factor ten to compensate for the higher ripple of the power converters in those current ranges. The Cold Powering System includes 105 temperature sensors (Fig. 7 ): sixty-one Platinum Resistance Temperature Detectors (RTD) Pt100 and forty-four Cernox®. The Pt100 sensors are located at the warm end of the REBCO cables (T HTS in Fig. 2 ) where they are connected to the resistive part of the current lead – one sensor and a redundant twin per cable. They are used for the control of the flow through each current lead and their set point is 50 K or 60 K. The Cernox® are located on the MgB 2 to REBCO splices (T MgB2 in Fig. 2 ) – one sensor and a redundant twin per splice. Both sensors are part of the interlock chain of the circuits: a power abort of a circuit (50 A/s to 100 A/s discharge, depending on the circuit) is triggered if a sensor exceeds by 5 K the nominal operating value, i.e. if the temperature of a MgB 2 to REBCO splice reaches 25 K or if the temperature of the REBCO reaches 55 K or 65 K. In addition, one Pt100 sensor is incorporated in the room temperature terminal of each current lead. The power abort of the concerned circuit is triggered if it exceeds 320 K or if is lower than 275 K. Below 275 K, the gas flow through the concerned current lead is also interlocked. This ensures that neither overheating nor overcooling of the current leads can take place in the system. The electrical tests aim at qualifying each circuit of the system. The test bench enables powering the circuits in Table 1 according to the following layout: the 18 kA circuit (Nb 3 Sn Quadrupole) is powered individually (the two polarities are electrically shorted inside the DFX via a Nb-Ti to Nb-Ti splice); the 15 kA circuit (Nb-Ti Separation Dipole) is powered individually (the two polarities are electrically shorted inside the DFX via a Nb-Ti to Nb-Ti splice); the 2 kA circuit (Nb-Ti Trim) is powered individually (two polarities plus one spare cable are electrically shorted inside the DFX via Nb-Ti to Nb-Ti splices and can be powered in pairs by changing the connections at the room terminal of the current leads); the 2 kA circuits of the corrector magnets (Nb-Ti Correctors) are powered all in series (the twelve polarities are electrically shorted inside the DFX via six Nb-Ti to Nb-Ti splices and at room temperature at the level of the current leads terminal). The powering layout is reported in Fig. 6 . The nineteen polarities – corresponding to nine circuits – could be powered individually via four power converters. Results Measured cryogenic performance The test campaign started with a pressure test of the Cold Powering System at 4.6 bara, followed by a helium leak test. Both tests were successful, and the helium leak rate was measured to be better than the specified value (≤ 1.0 × 10 − 8 mbar·l·s − 1 ). The cool down of the system was performed with a helium gas mass flow rate of 2 to 3 g/s. The thermal gradient between the helium supplied in the DFX and the helium recovered in the DFHX was limited to 50 K during the transient from room temperature to 160 K, and then increased to 70 K until the helium supplied in the DFX reached 15 K. This phase took about 3.5 days. Nominal cryogenic conditions – with liquid helium inside the DFX – were then reached in about eight hours (Fig. 8 , left). For dealing with the thermal contractions, the Superconducting Link was installed on the ground with a wavy shape that enables movements during cool-down/warm-up as well as during the pumping of the thermal insulating vacuum inside the flexible cryostat. The waves are fixed to ground at some locations and free to move thanks to dedicated guide rollers elsewhere (see Fig. 3 ). The amplitude and geometry of the waves were measured before and after vacuum pumping and cool down. Vacuum and cool down generated a maximum radial displacement of the peak of the free waves of 30 mm. After warm-up the Superconducting Link recovered its initial geometry with a maximum deviation of 10 mm due to stick-slip effect on the ground. During the electrical tests, the system was powered from 0 kA to |94| kA (see Table 1 ), with |94| kA DC current maintained up to eight hours. The helium mass flow rate required to cool the full system (DFH, Superconducting Link, DFHX and current leads) when operated at |94| kA was measured to be 4.9 g/s ± 0.1 g/s. Measured temperatures met nominal cryogenic conditions and no temperature drifts could be detected in the system. The total pressure drop of the helium was measured to be < 30 mbar during cool-down and < 10 mbar in nominal cryogenic conditions. This is well within the maximum acceptable value of 50 mbar. At zero current, a helium mass flow rate of 3.5 g/s was sufficient for cooling the system and maintaining it at nominal cryogenic conditions. In this operating mode, a flow of 5 g/s was generated in the DFX, and 1.5 g/s were extracted at the level of the cryogenic by-pass line in the DFHX. This is done to ensure a buffer of helium gas close to the current leads, to cope with a transient flow increase due to powering, and to guarantee a precise control of the liquid helium level (± 1 cm) inside the DFX, which implies continuous operation of the electrical heater in the DFX outer volume. A test with a reduced helium mass flow rate was also performed. The goal of this test was to define a cryogenically economic configuration that can be adopted during long periods with no liquid helium and no current in the system, i.e. during a stand-by mode usually corresponding to maintenance interventions in the accelerator. A mass flow of 3 g/s with helium gas entering the DFX at 20 K was able to maintain the REBCO in the current leads (T HTS ) at a temperature ≤ 100 K. The thermal performance of the Superconducting Link was quantified during five days of steady state cryogenic operation with 2 g/s of helium gas flowing through the system (Fig. 8 , right) and an inlet temperature of 15.8 K. The measured heat load is 2.0 W/m ± 0.5 W/m, in line with more precise measurements performed in the past [ 6 ]. A temperature mapping campaign with infrared camera enabled excluding presence of condensation or cold areas at any location along the external wall of the Superconducting Link cryostat and anywhere else in the system. The capability of generating and operating with a mass flow rate of 10 g/s was demonstrated. Two boil-off tests were performed, and it was shown that that such a flow can be produced by evaporation of liquid helium inside the DFX – with the level of liquid helium maintained within specification. It was also demonstrated that the MgB 2 to REBCO splices remain submersed in liquid helium if the supply is interrupted for 10 minutes. For the assessment of the cryogenic performance of the DFX cryostat, two boil-off tests (measurement of rate of decrease of the liquid helium level with no helium supply) were performed as well as a temperature mapping campaign of the external wall of the cryostat with a thermal imaging system. No condensation could be observed at any location, but some colder areas (15.4 °C to 19.1 °C) were identified (Fig. 9 ). The total static heat load was quantified to be 67 W, 55 W of which deposited into the liquid helium volume, at 4.5 K, and the remaining 12 W deposited into the helium gaseous volume above the liquid. This figure presents an extra 30 W with respect to the estimations [ 8 ]. It is considered that 10 W are due to a thermal shortcut through compacted MLI superinsulation blanket and 20 W are due to a non-optimised installation of MLI blankets. While optimal cryostat design is always a compromise between minimising heat inleak and adequate mechanical robustness, the mechanical design of the DFX cryostat had two unique challenges: (a) the inner helium vessel of the DFX cryostat has a design pressure of 3.5 bara (tested at 5 bara for European Conformity (CE) marking as a Category III Pressure Equipment) and is required to withstand high bending moment due to the L-shape (see Fig. 4 ) needed for keeping the MgB 2 to Nb-Ti splices in liquid helium and for transitioning the Superconducting Link from a vertical to an horizontal configuration; (b) the mechanical support for the 600 mm diameter vertical section of the inner vessel is restricted by the space available in the LHC tunnel to a short length of 300 mm between 4.2 K and 300 K to the detriment of thermal conduction. The test results fully validated the innovative structural design. For the remaining cryostats, the MLI installation will be further optimised with respect to the layout used in this test. During the powering tests, neither condensation nor cold areas could be observed on the DFHX external envelope or on the current leads. For the current leads, the temperature of the REBCO was set between 50 K and 60 K leading to the definition of the optimized operating temperatures: T HTS = 50 K for the 18 kA and for the 15 kA current leads, and T HTS = 50 K or 60 K for 2 kA current leads. The mass flow requirements of the current leads were measured to be: 0.81 ± 0.03 g/s for the 18 kA, 0.68 ± 0.01 g/s for the 15 kA, 111 ± 8 mg/s to 142 ± 8 mg/s for the 2 kA. The tests demonstrated the cryogenic efficiency of the system that was operated in DC mode with a helium mass flow rate of 4.9 ± 0.1 g/s at |94| kA and in nominal cryogenic conditions. The measured flow rate is well within the maximum value (≤ 5.5 g/s) defined acceptable during the design phase. Stability and robustness of the cryogenic control were also proven. High voltage electrical insulation tests Electrical insulation of the superconducting cables is provided by multi-layer wrapping of polyimide tape, while splices are insulated via machined glass-fibre-reinforced-plastic (G-10) and ULTEM™ parts. Insulators guarantee a minimum helium path in between non-insulated parts of 30 mm. A high voltage insulation test consists in measuring the electrical insulation between each polarity of a circuit and all the others and between each polarity of a circuit and the ground. The most critical part of the system with respect to the electrical insulation is the compact multi-cable assembly of the Superconducting Link. The electrical insulation of the MgB 2 cables was tested at up to 15 kV, at room temperature and in air, after production of the multi-cable assembly. After completion of the assembly of the Cold Powering System the following tests were performed: 5 kV at room temperature and in air before cool-down, 2.3 kV with the system in nominal cryogenic conditions, and 1.1 kV with the system filled with helium gas at 1.1 ± 0.015 bara and at room temperature after the completion of the powering tests and warm-up. The maximum leakage current for each circuit is specified to be 10 µA during the voltage plateaus (≥ 180 seconds) and 100 µA during the voltage ramps (50 V/s). The system passed successfully all high voltage insulation tests. The maximum leakage current measured during the 2.3 kV test in nominal cryogenic conditions was 104.0 nA – about 100 times lower than the maximum specified. Instrumentation signals, associated feedthroughs and temperature sensors all successfully passed the high voltage tests. Measured electrical performance The test sequence adopted for the powering tests can be summarized as follows: a) The nine electrical circuits were individually powered to their test current (18 kA, 15 kA, 2 kA and 2 kA, see Table 1 ). Nominal cryogenic conditions were ensured. The valves successfully controlled the helium mass flow through each current lead maintaining constant the T HTS of each REBCO cable (Fig. 10 ). Each circuit was brought individually from a low current plateau to the test current, which was initially held for about 10 minutes before ramping down. Ramp rates of 20 A/s were selected; b) The test current was then maintained for one hour (Fig. 10 ). For one hour, the system operated in nominal operating conditions with a total current of |94| kA, i.e. the maximum current that could be delivered by the four power converters, and a mass flow rate of 4.9 ± 0.1 g/s. Afterwards, each circuit was brought back to zero current with the same ramp rate and plateaus at lower currents. c) All circuits were ramped simultaneously with synchronized ramp rates ranging from 20 A/s to 100 A/s both in steps and from zero to their test current. The test currents were maintained constant in all circuits during eight hours with stable cryogenic conditions. Individual and simultaneous powering of all circuits were successfully repeated after a complete thermal cycle of the Cold powering System: the system was warmed-up to room temperature, cooled-down again to nominal cryogenic conditions, and powering tests were redone. During all tests no resistive transitions took place in the superconducting parts (Nb-Ti, MgB 2 and REBCO) of the circuits, no temperature or voltage drifts could be detected, voltage drops across resistive sections were within estimated values, temperatures and liquid helium level were stable and corresponding to those selected for nominal cryogenic conditions. Validation of the electrical splices was an important qualification step. Both REBCO tapes and MgB 2 wires contain high resistance metal in their matrix or substrate, Hastelloy® and Monel®, respectively, and optimization of the splices required a significant R&D effort. REBCO to MgB 2 splices are cooled by forced flow of helium gas at about 20 K inside the DFHX. They were measured to be in the range from 1.4 nΩ to 10.1 nΩ. MgB 2 to Nb-Ti splices are in liquid helium at 4.5 K inside the DFX. They were measured to be in the range from 1.4 nΩ to 2.4 nΩ. The electrical splices among Nb-Ti cables, used to create the electrical shorts in liquid helium inside the DFX, were less than 1.5 nΩ. All measured values matched with the estimated ones (see Table 2 ). They did not change after hundreds of electrical cycles and one complete thermal cycle (from room temperature to nominal cryogenic conditions) of the Cold Powering System. The evolution of the temperatures of the REBCO to MgB 2 splices during the current cycles are shown in Fig. 10 , left. The temperatures of all REBCO to MgB 2 splices remained at the nominal value (< 20 K) and are independent of the current. No indication of heating of the splices, during any phase of the test could be identified: both measured resistances and measured temperatures of the splices were stable. Table 2 Table 2 Measured and estimated resistance of the splices. Test Current (kA) REBCO to MgB 2 MgB 2 to Nb-Ti Nb-Ti to Nb-Ti R splice Measured (nΩ) R splice Estimated (nΩ) R splice Measured (nΩ) R splice Estimated (nΩ) R splice Measured (nΩ) R splice Estimated (nΩ) 18 1.4 ± 0.1 ≤ 2.2 1.4 ± 0.1 ≤ 1.8 0.9 ± 0.1 ≤ 2.0 15 1.7 ± 0.1 1.4 ± 0.3 0.9 ± 0.1 2 Trim 4.3 ± 0.8 ≤ 6.5 1.4 ± 0.2 ≤ 3.5 1.2 ± 0.1 2 Correctors 10.1 ± 1.1 ≤ 13.0 2.4 ± 1.4 ≤ 6.0 1.1 ± 0.3 Electro-magnetic compatibility Electro-magnetic cross talk among circuits, that could trigger the quench detection system, should be avoided during operation. More specifically, it is requested that in the case of quench of a corrector magnet in a 2 kA circuit, the resulting fast discharge of that circuit should not trip the quench protection of neither the Nb 3 Sn Quadrupole (18 kA) nor the Nb-Ti Separation Dipole (15 kA) circuits. Limitation of inductive couplings has therefore been addressed in the design of the Superconducting Link. This behaviour has been investigated by measuring the self-inductance of each circuit and the cross talk between circuits. Each circuit was powered with ramp rates of 50 A/s to 100 A/s and the voltage induced during the ramp in the other circuits was measured. The response of a circuit was found to be dependent on the relative position of the MgB 2 cables in the Superconducting Link and on the routing/location of the associated voltage signals. Measured inductive couplings between circuits and the self-inductance of each circuit are reported in Table 3 . The coaxial MgB 2 cable layout of the 2 kA circuits results in a very small inductive couplings of 0.02–0.03 µH towards the other circuits. A fast power abort in the HL-LHC configuration triggers a 6 kA/s discharge of the 2 kA corrector circuits. The measured maximum inductive coupling of 0.03 µH towards any other circuit implies induced voltages in the MgB 2 cables of the other circuits of 0.2 mV, a value about 100 times lower than the protection threshold of 20 mV. The test enabled concluding that in line with the design criteria of the Cold Powering System, a fast discharge of any 2 kA corrector circuit does not trip the electrical protection of any other circuit in the system. Table 3 Table 3 Measured inductive coupling and self-inductance for the 18 kA, 15 kA and 2 kA corrector circuits. Circuit Test current (kA) Ramp rate (A/s) Nb 3 Sn Quadrupole Nb-Ti Separation Dipole Nb-Ti Trim Nb-Ti Correctors Inductive coupling and self inductance (µH) Nb 3 Sn Quadrupole 18 100 31.0* 8.1 15.0 2.3 Nb-Ti Separation Dipole 15 100 0.1 0.1* 18.0 0.03 Nb-Ti Correctors 2 50 0.03 0.03 0.02 1.5* Current Leads The current leads consist of a resistive part, which is a heat exchanger cooled by forced flow of helium gas, and of a REBCO HTS part. The design is similar to that of the LHC current leads [ 9 ], with the difference that the HTS part consists of REBCO round cables [ 10 ] instead of stacks of Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) 2223 silver-gold (Ag-Au) tapes. The helium gas enters the resistive part of the current leads at a temperature which is expected to be in between 25 K to 35 K: after having passed through the Superconducting Link and cooled the MgB 2 to REBCO splices, which are at about 20 K, it cools the mechanical structure of the DFHX, the HTS parts of the current leads, the REBCO to copper splices at the cold end of the resistive heat exchanger, and it finally enters in and cools the resistive part of each current lead. The minimum mass flow rate for the resistive part of a current lead cooled with helium gas entering at about 25 K to 35 K is ranging from about 0.0048 g/s kA to 0.055 g/s kA [ 9 ]. The 18 kA and 15 kA current leads were able to operate at the test currents with the optimum rate. By design, the 18 kA and the 15 kA current leads are identical and optimized for operation at 18 kA. Figure 11 reports the voltage drop measured across the resistive parts of those current leads when operated at the test currents with T HTS equal to 50 K and mass flow rates of 0.81 ± 0.03 g/s and 0.68 ± 0.01 g/s respectively. The helium flow rates are stable with time. The resistive heat exchangers of the 2 kA current leads are all identical, while the HTS part of the Trim circuit is designed for 7 kA in order to cope with electrical transients in the magnets and currents of up to 7 kA with no resistive transition. Measurements in steady state at 2 kA with T HTS of 50 K or 60 K resulted in mass flow rates of 111 ± 8 mg/s and 142 ± 8 mg/s, respectively. Differently from the 18 kA and 15 kA current leads, where each resistive part is surrounded by a vacuum insulation jacket, the 2 kA current leads are grouped in assemblies of four inside a common vacuum insulated envelope. Two of the four 2 kA current leads have an inclination with respect to ground of about 6 degrees, while the other two on the same flange are inclined by about 15 degrees. The difference in mass flow rate is attributed to thermal coupling in between the gas flowing inside the leads and the static gas stratified inside the common vacuum insulating envelope. The two current leads with a higher inclination are expected to be surrounded by stratified gas at a slightly (5 K to 10 K) higher temperature (density of helium gas increases as temperature decreases), which impacts on the global performance by demanding an increased flow rate. There are in total three assemblies of four 2 kA current leads: the behaviour of the leads in the different assemblies and with the same geometrical configuration is identical. During operation no cold spots could be detected at any location along the currents leads, including the room temperature terminations where the room temperature cables are connected. Discussion A 100 kA class DC superconducting system, based on MgB 2 and REBCO technology, was designed, assembled and tested at CERN. The system successfully transferred a total DC current of up to |94| kA, the maximum current that could be delivered by the power converters, with MgB 2 at up to 20 K and REBCO at up to 60 K, and it passed the electrical insulation tests at the target voltage of 2.3 kV under nominal operating conditions. This is the first of eight systems that will be installed in the LHC underground as from 2028 for operation at the start of the LHC High Luminosity Upgrade in 2030. The Cold Powering System incorporates Nb-Ti cables in a saturated liquid helium bath at 4.5 K, a 74.5 m long Superconducting Link with MgB 2 cables in the temperature range from 4.5 K up to about 20 K, REBCO cables from about 20 K up to 60 K, and current leads providing the electrical transfer to room temperature. It is the first transmission system that relies on long and high current (up to 18 kA individually) MgB 2 cables. To our knowledge, the system transported the highest current ever reached in DC mode (|94| kA). The choice of the MgB 2 superconductor in the Superconducting Link was driven by the affordable cost of the conductor, its availability in kilometre lengths, its behaviour in case of resistive transition [ 11 ] that enables use of conventional and reliable quench protection methods and electronics [ 7 ], and the availability in the LHC of helium enabling operation at up to 20 K. Because of the requirement of feeding several superconducting magnet circuits, the Cold Powering System incorporates a multiplicity of cables and current leads, nineteen in total, that are tightly arranged inside the Superconducting Link flexible cryostat and in the DFX and DFHX termination cryostats. This adds challenges to the design for maintaining compactness, dealing with the electrical insulation of each polarity, avoiding electro-magnetic cross talks among circuits, ensuring the mechanical flexibility required for installing and spooling the Superconducting Link, implementing the instrumentation necessary for protecting and operating each circuit individually, and fitting a multiplicity of electrical splices, among different superconducting cables, in compact volumes. A single polarity 120 kA or two polarities each rated at 60 kA, applicable to DC superconducting power transmission for instance, would fit with ease in a Superconducting Link cryostat with the same dimensions, but all listed complexities would not apply or would be significantly reduced. From the point of view of cost and efficiency of the cryogenic cooling, the design of the system is such that the total helium mass flow rate corresponds to what is needed for operating the current leads. The Superconducting Link transfers both current and helium gas to the current leads, and the helium flow corresponds to that required for operating optimized current leads. To obtain this performance, a two-wall and low static heat load cryostat (≤ 2 W/m at any temperature in the range from 4.5 K to 20 K, with an external diameter of 220 mm and an inner diameter of 100 mm) was specifically developed for the Superconducting Link project in industry. The two-wall configuration was preferred to the four-wall configuration, which includes an actively cooled thermal screen, to enhance flexibility, simplify the design of the system and ease handling and installation aspects. The heat load of the Superconducting Link is mainly due to thermal radiation from room temperature to the cryogenic environment and thermal conduction through the vacuum insulation envelope, in between the two corrugated pipes, where MLI and spacers are located. Published values of static heat load for two-wall flexible cryostats with dimensions suitable for containing one, two or three electrical poles, are in the range of 1 W/m to 2.5 W/m at 77 K. These values are expected to increase by a factor of 4 to 6 with bends [ 12 ]. The 1.6 W/m at 4.5 K to 20 K of the Superconducting Link, operated in the convoluted geometry reported in Fig. 3 , represents therefore a remarkable performance when compared to what before available in industry. It should be noted that the static heat load was measured with the MgB 2 cables installed inside the cryostat. The design is such that the weight of the cables, which is of the order of 25 kg/m, did not impact on the thermal performance. The current leads define the mass flow rate for the system. Optimized self-cooled current leads, operating between room temperature and liquid helium, conduct about 1.1 W/kA at 4.5 K, corresponding to a mass flow rate of about 0.055 g/s kA, i.e. 5.2 g/s at |94| kA, and a similar flow of about 0.055 g/s kA is required for cooling the resistive part of the current leads when helium gas enters at a temperature in the range from 25 K to 35 K. The full Cold Powering System is cooled by a flow of 0.052 g/s kA, i.e. 4.9 g/s at |94|kA: the change in enthalpy of the gas from 4.5 K to 20 K is used to cool the Superconducting Link, while the change of enthalpy of the gas from about 20 K to room temperature is used to cool the current leads. The system is optimized in such a way that the Superconducting Link does not add cryogenic cost to the cooling of the system. By design the Superconducting Link can be spooled onto a large drum (radius of 2 m) after having been connected to the DFHX with the current leads. This enables implementing the strategy adopted for the transport and for the installation of the system in the LHC underground: a Cold Powering System is assembled, tested in nominal operating conditions in the configuration reported in Fig. 3 , spooled and finally transported. Such an operation has been successfully performed. Figure 12 left shows a Superconducting Link, attached to the DFHX, spooled onto a drum and being transported after completion of the qualification tests. This is an example of a 100 kA class transmission line transported together with the electrical terminations, ready to be installed and connected to the room temperature cables. After re-spooling (Fig. 12 right), the system successfully passed the high voltage and leak tightness tests. The developed system is cooled by a forced flow of helium gas generated inside the DFX. The cooling with gas is a reliable choice for a transmission system that has a long and convoluted geometry and that must operate, at a specific location, in a vertical configuration when it connects the HL-LHC new galleries to the LHC main tunnel. The use of MgB 2 and REBCO ensures a large temperature margin, i.e. a margin between the nominal operating temperature and the maximum operating temperature just below the critical temperature of the superconductor at the design current, of at least 5 K for MgB 2 and 10 K for REBCO. This margin is important since it eases cryogenic constraints and operation. Even if the nominal currents will never be exceeded during HL-LHC operation, by design the current margin for the MgB 2 and the REBCO, i.e. the margin between the nominal current and the maximum transportable current just below the critical current of the superconductor at 20 K for MgB 2 and at 60 K for REBCO, is at least 20%. Cooling of the high current MgB 2 and REBCO splices with forced flow of helium gas was proven to be effective. The available temperature margin makes the operation of the splices robust and reliable. Use of helium gas is the natural choice for the HL-LHC, where helium is available for the magnets. The Superconducting Link could, however, operate at 20 K in liquid hydrogen. Work in this direction was done by [ 13 ], where a 10 m long cable, in a cryostat with 40 mm external diameter, transported up to about 2.6 kA at 20 K. This cable was made with flat MgB 2 tape, which was at the time the only geometry of ex-situ MgB 2 conductor available in industry. The MgB 2 round wire used in the Superconducting Link has been developed for the project in industry, in collaboration with CERN. To date, the total quantity of wire needed for the ten Cold Powering Systems, about 1500 km, has been produced. The HL-LHC Cold Powering Systems represent the first large scale application of MgB 2 round wire, which is also for the first time successfully used in a large electrical transmission system. The developed MgB 2 technology finds applications for various uses in society. An initiative in this direction was taken by the IASS institute in Potsdam, under the scientific direction of Prof. Carlo Rubbia, where superconducting transmission was identified as an enabling technology for deployment of renewable electricity generation. The choice of MgB 2 was associated with liquid hydrogen as coolant, with the goal of simultaneous transmission of electric power and hydrogen fuel. A demonstrator in this direction was done at CERN, in the context of a collaboration agreement between CERN and IASS, where a 20 kA MgB 2 electrical transmission line was successfully constructed and qualified at 20 K [ 14 ]. This work continued with the BEST PATHS (acronym for “BEyond State-of-the-art Technologies for rePowering Ac corridors and multi-Terminal HVDC Systems”) project of the FP7 framework of the European Commission that demonstrated a DC monopole MgB 2 cable system operated in helium gas at 10 kA/320 kV, corresponding to a transmitted power of 3.2 GW [ 15 ]. The construction and qualification at CERN of the first Cold Powering System for HL-LHC demonstrate the feasibility and the potentials of very high DC current, 100 kA class, MgB 2 based electrical transmission lines operated at up to 20 K. Conclusions A complete system solution for a 100 kA class DC High Temperature Superconducting transfer line was developed and qualified at CERN. The system is cooled by a forced flow of helium gas. It incorporates MgB 2 and REBCO superconductors operated at up to 20 K and 60 K, respectively. The system successfully transported up to |94| kA in DC mode, the maximum current that could be delivered by the power converters, and it successfully underwent steady state and transient tests representative of different operating modes in the LHC. While the system was developed for use in the LHC accelerator, it is a potential platform for wider energy applications including long power transmission lines and industrial applications that can benefit from a sustainable transfer of high currents, possibly at low voltage. Declarations Data Availability Statement The datasets used and/or analysed during the current study are available from the corresponding author on request. Autor contributions statement Amalia Ballarino proposed, conceived and coordinated the research Paul Cruikshank, Yann Leclercq and Christian Barth coordinated experiments and contributed to the research Florian Pasdeloup contributed to design and assembly activities Vanessa Gahier coordinated the cryogenic tests and contributed to the analysis of the cryogenic test results Gerard Willering coordinated the powering tests and contributed to the analysis of the test results Yifeng Yang and Wendell Bailey designed and constructed the DFX cryostat and contributed to the analysis of the test results. Their work was performed in the framework of the CERN-UK1 HL-LHC collaboration agreement References Bruning, O. & Rossi, L. The High Luminosity Large Hadron Collider, Advanced Series on Directions in High Energy Physics 31, (2024). https://doi.org/10.1142/13487 Ballarino, A. Development of superconducting links for the Large Hadron Collider machine. Supercond Sci. Technol. 27 (7pp). 10.1088/0953-2048/27/4/044024 (2014). https:// home.cern/news/news/accelerators/superconductivity-sustainability-new-superconducting-link-high-luminosity Ballarino, A. New superconducting technologies for the HL-LHC and beyond, CERN Courier – Reporting on international high energy physics 63 Number 3, 37–41 (2023). Perin, A. et al. AIP Conference Proceedings 985, (747–754), DOI: AIP Conf. Proc. 985, 747–754, (2008). https://doi.org/10.1063/1.2908666 Fleiter, J. & Ballarino, A. Results of the Cold Powering Tests of the Demonstrators of HL-LHC SC-Links. IEEE Trans. Appl. Supercond . 32 10.1109/TASC.2022.3172053 (2022). Steckert, J. et al. Application of the Universal Quench Detection System to the Protection of the High-Luminosity LHC Magnets at CERN. IEEE Trans. Appl. Supercond . 32 10.1109/TASC.2022.3152125 (2022). Bailey, W. et al. Distribution Feedbox for the Superconducting Link (SCLink) and Magnets of HL-LHC. J. Phys. : Conf. Ser. 1559 10.1088/1742-6596/1559/1/012076 (2019). Ballarino, A., Leads, C., Buses, C. E. R. N. & Yellow Report Links and CERN-2014-005, (547–558) arXiv:1501.07166, (2015). https://doi.org/10.5170/CERN-2014-005.547 Barth, C., Saba, A., Leclercq, Y., Ballarino, A. & Development, F. Test of the Round, Multi-Layer REBCO Cables of the Cold Powering Systems of the HL-LHC. IEEE Trans. Appl. Supercond . 35 10.1109/TASC.2025.3537057 (2025). Giannelli, S., Montenero, G. & Ballarino, A. Quench Propagation in Helium-Gas-Cooled MgB 2 Cables. IEEE Trans. Appl. Supercond . 26 10.1109/TASC.2016.2524449 (2016). Gauge, M. J., Demko, J. A., Roden, M. L., Maguire, J. F. & Weber, C. S. Vacuum-Insulated Flexible Cryostats for Long HTS Cables: Requirements, Status and Prospects, AIP Conf. Proc. 985, (1343–1350, (2008). 10.1063/1.2908492 Kostyuk, V. V. et al. Experimental Hybrid Power Transmission Line with Liquid Hydrogen and MgB 2 Based Superconducting Cable, ISSN 10637850. Tech. Phys. Lett. 38 , 279–282 (2012). World-record current in a superconductor. https://cds.cern.ch/record/1693853?ln=it Ballarino, A. et al. The BEST PATHS Project on MgB 2 Superconducting Cables for Very High Power Transmission. IEEE Trans. Appl. Supercond . 26 10.1109/TASC.2016.2545116 (2016). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 01 Jul, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 05 Jun, 2025 Reviews received at journal 04 Jun, 2025 Reviews received at journal 29 May, 2025 Reviewers agreed at journal 21 May, 2025 Reviewers agreed at journal 19 May, 2025 Reviewers agreed at journal 15 May, 2025 Reviewers invited by journal 15 May, 2025 Editor assigned by journal 15 May, 2025 Editor invited by journal 15 May, 2025 Submission checks completed at journal 13 May, 2025 First submitted to journal 09 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6629095","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":457186239,"identity":"845805be-9f43-41c2-a8b3-70b1781ccd0a","order_by":0,"name":"Amalia Ballarino","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIie3OsUoDMRzH8X8I6HKQNbecr5ByIAilz5JwcF3KcXBLB4fIQd0cS8HBV6gIzoE/tMs9gBKHiuAsHIiCiNEWF0l0dMh3DPnw/wHEYv8zYiSAhH2qAQQA2z3LkNkSSrYk1X8h8E1cwvxC2Bw3ZnMMFWvJST+t77J8jau+hlHlI9yWwsgVNBxJm3biMT/syuJ8AUXjXWWlI3ugNBKdaoHq+ibJaQJGaY84sOMnI99BXbgrr5/kasH6IBF2IoyagVoimX1dWfKEBsnATmqjzngzcOTIkZx3pRsmCi/J7Pjy/uV5WGXrFm/1G2bsFB9oMh15yS7+Y3D4fywWi8XCfQAQBVyqxPOz3AAAAABJRU5ErkJggg==","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":true,"prefix":"","firstName":"Amalia","middleName":"","lastName":"Ballarino","suffix":""},{"id":457186241,"identity":"dd6c2106-926d-4945-b960-b1c04b4b8e58","order_by":1,"name":"Wendell Bailey","email":"","orcid":"","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Wendell","middleName":"","lastName":"Bailey","suffix":""},{"id":457186244,"identity":"ed583013-c6bf-4883-b826-5b4c7a16a6a2","order_by":2,"name":"Christian Barth","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Christian","middleName":"","lastName":"Barth","suffix":""},{"id":457186246,"identity":"e0a9f758-a898-4df4-8b70-613e5d9868e4","order_by":3,"name":"Paul Cruikshank","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Paul","middleName":"","lastName":"Cruikshank","suffix":""},{"id":457186247,"identity":"9444ba34-8ade-49f2-99e1-407c8a3772ad","order_by":4,"name":"Vanessa Gahier","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Vanessa","middleName":"","lastName":"Gahier","suffix":""},{"id":457186248,"identity":"bb44d3c8-4212-4063-9bb7-844c49d229e6","order_by":5,"name":"Yann Leclercq","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Yann","middleName":"","lastName":"Leclercq","suffix":""},{"id":457186249,"identity":"662ff037-4b2c-4d2b-9f68-783afe1ab289","order_by":6,"name":"Florian Pasdeloup","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Florian","middleName":"","lastName":"Pasdeloup","suffix":""},{"id":457186250,"identity":"691c51e9-31c5-4d58-b04c-6679c9635b22","order_by":7,"name":"Gerard Willering","email":"","orcid":"","institution":"CERN, European Organization for Nuclear Research","correspondingAuthor":false,"prefix":"","firstName":"Gerard","middleName":"","lastName":"Willering","suffix":""},{"id":457186251,"identity":"57c52f85-4145-455c-9909-c5a030eec1f2","order_by":8,"name":"Yifeng Yang","email":"","orcid":"","institution":"University of Southampton","correspondingAuthor":false,"prefix":"","firstName":"Yifeng","middleName":"","lastName":"Yang","suffix":""}],"badges":[],"createdAt":"2025-05-09 13:23:45","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6629095/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6629095/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-08543-9","type":"published","date":"2025-07-01T15:57:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83081147,"identity":"eb3c0d96-31b0-4699-8ed0-316a468697bd","added_by":"auto","created_at":"2025-05-19 19:49:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":278350,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic view of the LHC underground with the LHC existing tunnel and the HL-LHC new gallery where the Cold Powering Systems will be installed. The two types of systems that will be installed right and left of ATLAS and CMS experiments, are shown. The height of the vertical shaft is about eight meters.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/b036615659332c0679054a5d.png"},{"id":83080990,"identity":"ce53c43e-05ca-4fd7-8404-5c808fc1756b","added_by":"auto","created_at":"2025-05-19 19:41:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":187778,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic layout of a Cold Powering System (left). Nb-Ti cables are in a saturated liquid helium bath at 4.5 K, MgB\u003csub\u003e2\u003c/sub\u003e cables operate between 4.5 K and about 20 K, and REBCO cables operate between 20 K and about 60 K. Layout of the |117| kA MgB\u003csub\u003e2\u003c/sub\u003e cable assembly of the Superconducting Link for the HL-LHC Triplets (right). There are in total nineteen cables: two 18 kA cables for the Nb\u003csub\u003e3\u003c/sub\u003eSn quadrupole magnets, two 15 kA cables for the Nb-Ti Separation Dipole magnet (rated at 18 kA), three 2 kA cables for the Trim circuit (rated at up to 7 kA), and six coaxial 2 kA cables, i.e. twelve 2 kA polarities. The maximum field experienced by the superconductor is 1 T. The total external diameter is about 90 mm. The weight is about 25 kg/m.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/ab1dd8d0c97962586d0dcde8.png"},{"id":83081394,"identity":"4756def9-cf1a-4368-8ce4-46419b21c51b","added_by":"auto","created_at":"2025-05-19 19:57:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":441849,"visible":true,"origin":"","legend":"\u003cp\u003eCold Powering System in the test configuration in the SM-18 (left). The minimum bending radius of the Superconducting Link is 2 m. Layout of Cold Powering System in the SM-18 (right). F are fix points.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/1f2a5ea4eaf2b2d5c400f4a8.png"},{"id":83081397,"identity":"00225a6e-d46a-4d45-a519-934969596a4d","added_by":"auto","created_at":"2025-05-19 19:57:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":678884,"visible":true,"origin":"","legend":"\u003cp\u003eVertical path of the Superconducting Link and DFX. The L-shape of the DFX cryostat is due to the presence of a horizontal part, with the Nb-Ti cables, and a vertical part where the MgB\u003csub\u003e2\u003c/sub\u003e cables are connected to the Nb-Ti cables.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/aacdb0f0d72a0eb57f357a24.png"},{"id":83081395,"identity":"09265347-50e5-479a-9f46-04faf994eb4b","added_by":"auto","created_at":"2025-05-19 19:57:29","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":676382,"visible":true,"origin":"","legend":"\u003cp\u003eDFHX and room temperature cables inside the IP2X yellow cage. Gas management system in front of the IP2X yellow cage with the room temperature cables distributed and connected to the current leads. It contains helium valves and helium gas recovery lines.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/c6bbbcca2ae576835f6086a3.png"},{"id":83080995,"identity":"8f44cf1b-6243-4166-b4f7-ff6b2716f8f3","added_by":"auto","created_at":"2025-05-19 19:41:29","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":129842,"visible":true,"origin":"","legend":"\u003cp\u003ePowering layout adopted for the tests. Four power converters (2 kA, 2 kA, 15 kA and 18 kA) are available. The number of electrical shorts inside the DFX at 4.5 K, between Nb-Ti cables, is also reported.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/d32476e5d736d26e9b53e9dc.png"},{"id":83081400,"identity":"5255c128-8c32-4193-a4f7-3dde572ed3ec","added_by":"auto","created_at":"2025-05-19 19:57:29","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":86596,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of voltage taps and temperature sensors in each circuit. The total number of voltage taps (304) and temperature sensors (105) for all circuits is also reported.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/babbaade2d39ebcdcd1ff78a.png"},{"id":83081679,"identity":"cdc1c94d-4250-45f8-b4fb-1fd2cc6b1044","added_by":"auto","created_at":"2025-05-19 20:13:29","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":97267,"visible":true,"origin":"","legend":"\u003cp\u003eCool-down of the Cold Powering System from room temperature to about 15 K inside the DFHX (left). The decrease in helium gas flow after about 1.5 days is a cryogenic control transient not impacting on the cool-down of the system. Stable cryogenic conditions maintained during about 5 days for the measurement of the thermal performance of the Superconducting Link (right).\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/1af9a11dc245e6fcebc3d135.png"},{"id":83081403,"identity":"45f6eadf-d8b8-41c4-aeba-f5e91c7d58e5","added_by":"auto","created_at":"2025-05-19 19:57:29","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":730383,"visible":true,"origin":"","legend":"\u003cp\u003eThermal mapping of DFX cryostat in nominal cryogenic conditions and during powering.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/652d99b0705d5d6682917d14.png"},{"id":83081149,"identity":"258e1c86-16e6-4976-b6f4-42d53f29f24b","added_by":"auto","created_at":"2025-05-19 19:49:29","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":125213,"visible":true,"origin":"","legend":"\u003cp\u003eOne-hour steady state test current in all circuits (2 kA in the Trim circuit, 2 kA in the Corrector circuits, 15 kA in the Separation Dipole circuit and 18 kA in the Quadrupole circuit). The mass flow rate through the system in nominal operating conditions is 4.9 ± 0.1 g/s. On the left the total current is reported. On the right the individual current in each circuit is reported.\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/b16c7dd64511ba4cdfb857ae.png"},{"id":83081157,"identity":"90e37ce0-4e3c-4876-9896-cd70dff239ae","added_by":"auto","created_at":"2025-05-19 19:49:29","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":81941,"visible":true,"origin":"","legend":"\u003cp\u003eVoltage drop measured across the resistive parts of 18 kA and 15 kA current leads when operated at the test currents with T\u003csub\u003eHTS\u003c/sub\u003e equal to 50 K and mass flow rates of 0.84 g/s and 0.69 g/s, respectively.\u003c/p\u003e","description":"","filename":"Figure11.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/bdce3dd9628939039d5d4c2e.png"},{"id":83081159,"identity":"53e6d462-d387-4a3e-99bb-db36158d2960","added_by":"auto","created_at":"2025-05-19 19:49:29","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":593410,"visible":true,"origin":"","legend":"\u003cp\u003eTransport of the Cold Powering System (left) and respooling after transport (right). The radius of the spool onto which the Superconducting Link is wound is 2 m.\u003c/p\u003e","description":"","filename":"Figure12.png","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/29706a6d51bad6a5afc9ddee.png"},{"id":86179379,"identity":"52208940-f4ce-4206-ad69-efbd58075d2f","added_by":"auto","created_at":"2025-07-07 16:17:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5370392,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6629095/v1/85c42001-6ff3-41a1-bda2-22404c5d8338.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"A system solution for a 100 kA class High Temperature Superconducting line for HL-LHC and for wider energy applications","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe High Luminosity Large Hadron Collider (HL-LHC) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e] is an upgrade of the LHC machine which aims at achieving instantaneous luminosities a factor of 5 to 7.5 larger than the LHC nominal value. This will allow attaining an integrated luminosity around ten times higher than the expected luminosity reach of the LHC after about 10 years of operation, and it will therefore bring new opportunities for physics discoveries. Planned to be operational as from 2030, the HL-LHC will rely on key innovative superconducting technologies. The final focusing magnets in the interaction regions close to the ATLAS and CMS experiments will consist of niobium-tin (Nb\u003csub\u003e3\u003c/sub\u003eSn) quadrupoles reaching peak fields at operation of about 12 T, superconducting radio-frequency \u0026ldquo;crab\u0026rdquo; cavities will tilt the particle beams to enlarge the overlapping area of the incoming particle bunches, and the electrical transfer from the power converters to the magnets will be done via innovative Cold Powering Systems incorporating direct current (DC) superconducting lines, the so-called Superconducting Links, based on magnesium diboride (MgB\u003csub\u003e2\u003c/sub\u003e) technology [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo enhance the accelerator\u0026rsquo;s availability and efficiency, the power converters of the HL-LHC magnets will be installed in newly excavated galleries, separated from and about eight meters above the LHC existing tunnel. This will facilitate access of personnel for maintenance and operational interventions that will take place in radiation free areas. The Superconducting Links will transfer the current from the power converters to the HL-LHC magnets. To interconnect the two different tunnel levels, they will pass through a purposely excavated, eight-meter high, vertical shaft (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). A Superconducting Link consists of a flexible cryostat, made of two multi-layer-insulated (MLI) concentric corrugated pipes, and a multiplicity of electrically insulated MgB\u003csub\u003e2\u003c/sub\u003e cables in the inner pipe. These cables, which are grouped and twisted together to form a compact multi-cable assembly, feed the HL-LHC magnet circuits of the HL-LHC Triplets and Matching Sections. A Superconducting Link is connected at its warmer (\u0026sim; 20 K) end to a cryostat (DFHX for the Triplets and DFHM for the Matching Sections) that contains the High Temperature Superconducting (HTS) Rare-Earth-Barium-Copper-Oxide (REBCO) based current leads providing the electrical transfer to room temperature, and at its colder (4.5 K) end to a cryostat (DFX for the Triplets and DFM for the Matching Sections) that contains the Niobium Titanium (Nb-Ti) cables going to the magnets (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, left). The system of the Superconducting Link connected to a cryostat at each end is called Cold Powering System. A Cold Powering System provides the electrical transfer from room temperature to the liquid helium environment of the magnets.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn total eight Cold Powering Systems of two different types are needed for HL-LHC: four for the powering of the magnets in the Triplets and four for the powering of the magnets in the Matching Sections. Two systems of different type will be located right and left of LHC Point 1 and Point 5 that house the ATLAS and CMS experiments. The Cold Powering Systems for the Triplets incorporate Superconducting Links that are 74.5 m long. They contain nineteen MgB\u003csub\u003e2\u003c/sub\u003e cables (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, right) rated at DC currents of 18 kA, 7 kA and 2 kA, and an equivalent number of HTS current leads and Nb-Ti cables. They can transfer a total DC current of up to |117| kA. The Cold Powering Systems for the Matching Sections incorporate Superconducting Links that are 120 m long. They require ten MgB\u003csub\u003e2\u003c/sub\u003e cables, and an equivalent number of HTS current leads and Nb-Ti cables rated at currents of 18 kA and 0.6 kA. They can transfer a total DC current of up to |40| kA.\u003c/p\u003e \u003cp\u003eFollowing extensive research and development (R\u0026amp;D) as well as validation of individual components [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e] [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], a Cold Powering System of the type needed for the HL-LHC Triplets has been constructed and extensively tested at CERN. This paper reports on the outcome of the room temperature, cryogenic, electrical and mechanical measurements performed on the first ever built 100 kA class MgB\u003csub\u003e2\u003c/sub\u003e and REBCO system.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eTest bench\u003c/h2\u003e \u003cp\u003eThe Cold Powering System was installed and tested at CERN in the SM-18 (Superconducting Magnet Test Facility). The Superconducting Link has a snaked geometry on the ground (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e): while this geometry does not reproduce the final configuration in the LHC underground, it meets the requirements of fitting the full length of 74.5 m within the available test area, coping with the thermal contraction and expansion of the system during cool-down and warm-up, and respecting the minimum bending radius of 2 m. To simulate the vertical path in the underground, where the Superconducting Link passes through the shaft connecting the HL-LHC new gallery to the LHC tunnel, a cable chain has been installed: it supports the Superconducting Link on the climb that leads to a vertical descent of about 2.5 meters (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). At the end of the descent, the DFX cryostat receives the MgB\u003csub\u003e2\u003c/sub\u003e cables that are electrically connected in a vertical configuration to Nb-Ti cables. At the other side of the Superconducting Link, the MgB\u003csub\u003e2\u003c/sub\u003e cables are distributed inside the DFHX cryostat and are connected to the REBCO cables that are part of the HTS current leads. Each REBCO cable is connected to the resistive part of a current lead. The DFHX hosts, in a compact volume (\u0026sim; 5.5 m length, \u0026sim; 1 m external diameter), the nineteen electrical joints (splices) between the MgB\u003csub\u003e2\u003c/sub\u003e and the REBCO cables and the nineteen HTS current leads. For the benefit of compactness, the current leads are not aligned vertically, one after the other, in the DFHX like in the LHC (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e in [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]). They are instead grouped at two locations of the DFHX and are almost horizontal to the ground \u0026ndash; the inclination ranges from about 6 to 15 degrees. Use of helium gas instead of liquid cryogen enables robust operation of the current leads in this configuration (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, left).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFour power converters are available for the electrical tests: one 18 kA, one 15 kA and two 2 kA. Powering of an 18 kA circuit (Nb\u003csub\u003e3\u003c/sub\u003eSn Quadrupole circuit in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), of a 15 kA circuit (Nb-Ti Separation Dipole circuit in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), and of two 2 kA circuits (Trim and Nb-Ti Corrector circuits in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the latter all powered in series) is therefore possible. The powering scheme is reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The routing of the room temperature water cooled 18 kA and 15 kA cables and of the air cooled 2 kA cables as well as their connection to the current leads are inside an ingress protection (IP) 2X rated cage, in front of the DFHX, that reproduces the final configuration in the HL-LHC gallery (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA dedicated cryogenic line transfers liquid helium from an available source, in the SM-18, to the DFX cryostat: a mix of liquid and gaseous helium is injected at 1.3 bara inside the DFX. Liquid helium fills the DFX cryostat and covers the electrical splices between MgB\u003csub\u003e2\u003c/sub\u003e and Nb-Ti. Two proportional-integral-derivative (PID) controlled 100 W electrical heaters inside the DFX vaporize the liquid helium to provide the gaseous mass flow rate required to cool the system. The gas flows along the Superconducting Link and reaches the DFHX where it is distributed among the nineteen MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices and the nineteen current leads before being recovered at room temperature.\u003c/p\u003e \u003cp\u003eRecovery of helium gas on the DFHX side is managed by a purpose-built gas management system, which groups the helium gas return piping at room temperature and the valves used for the control of the flow through the current leads (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In the DFHX there is also a cryogenic by-pass line that recovers the excess of cold gas and warms it up to room temperature via a 15 kW electric heater.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eOperating conditions\u003c/h3\u003e\n\u003cp\u003eThe number and type of HL-LHC circuits and the number of cables and current leads in the Cold powering System are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The current at which each circuit has been tested (test current), corresponding to the maximum current of the power converter, the current at which each circuit will operate in the LHC (nominal current), and the design currents are also reported. The design current of the superconducting cables is at least 10% higher than the nominal current. The total current is the sum of the absolute value of the current transferred by each polarity in the Cold Powering System.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eNumber of HL-LHC circuits fed by the Cold Powering System, number of cables (MgB\u003csub\u003e2\u003c/sub\u003e or REBCO) and current leads per circuit type. Nominal currents during operation in the HL-LHC, test currents and design currents of the circuits are reported.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNumber of Circuits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNumber of Cables/Current Leads\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNominal Current\u003c/p\u003e \u003cp\u003e(kA)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTest Current\u003c/p\u003e \u003cp\u003e(kA)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDesign Current\u003c/p\u003e \u003cp\u003e(kA)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eSn Quadrupole\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eSeparation Dipole\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eTrim\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7**\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eCorrector\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eCorrector\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eCorrector\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e81.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e94***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e117****\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe Cold Powering System should by design operate with a helium mass flow rate of not more than 5.5 g/s \u0026ndash; when all circuits are operated at their nominal current. It must also be able to generate and transfer, in transient conditions, up to 10 g/s of helium gas produced in the DFX. The Superconducting Link operates in a temperature range from 4.5 K, in the DFX, to about 20 K, in the DFHX. The cryogenics of the Cold Powering System shall guarantee that: the Nb-Ti cables and their splices to the MgB\u003csub\u003e2\u003c/sub\u003e cables are submersed in a saturated liquid helium bath inside the DFX; the MgB\u003csub\u003e2\u003c/sub\u003e cables in the Superconducting Link operate at not more than 20 K; the REBCO cables in the current leads never exceed 60 K. These boundary conditions are by design defined as nominal cryogenic conditions.\u003c/p\u003e \u003cp\u003eThe static heat load of the Superconducting Link was specified and measured, in a previous test campaign at CERN, to be 1.6 \u0026plusmn; 0.5 W/m [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The helium mass flow through each current lead is optimized for operation at the design current in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and shall be of the order of 0.055 g/(s\u0026sdot;kA).\u003c/p\u003e \u003cp\u003eThe DFX internal vessel has a \u0026ldquo;fountain\u0026rdquo; configuration: there are two concentric volumes of saturated liquid helium. Helium is injected in the central volume, where the Nb-Ti cables and their splices to the MgB\u003csub\u003e2\u003c/sub\u003e cables are located, and overflows into the outer volume. The outer volume contains an electrical heater, which provides the helium mass flow rate required for the cooling of the system, and the level gauge used for liquid helium level control. This design enables meeting the requirement, imposed by cryogenic operating conditions, of maintaining the MgB\u003csub\u003e2\u003c/sub\u003e to Nb-Ti splices immersed in liquid helium during at least 10 minutes after an accidental stop of helium supply.\u003c/p\u003e \u003cp\u003eThe helium gas produced in the DFX warms up, while absorbing the static heat load of the Superconducting Link cryostat, from 4.5 K up to a maximum temperature of 20 K at the location of the splices between the MgB\u003csub\u003e2\u003c/sub\u003e and the REBCO cables. It then cools the nineteen current leads, at the exit of which it is recovered at room temperature. The temperature of the MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices (T\u003csub\u003eMgB2\u003c/sub\u003e \u0026le; 20 K) and of the warm termination of the REBCO cables (T\u003csub\u003eHTS\u003c/sub\u003e \u0026le; 60 K) are monitored and the temperatures T\u003csub\u003eHTS\u003c/sub\u003e are controlled. Room temperature valves, one per current lead, control the helium mass flow rate passing through each lead so that T\u003csub\u003eHTS\u003c/sub\u003e stays at not more than 60 K. By design, T\u003csub\u003eHTS\u003c/sub\u003e is expected to be in the range 50 K \u0026ndash; 60 K.\u003c/p\u003e \u003cp\u003eNeither the Superconducting Link nor the DFX and the DFHX cryostats include a thermal shield. Insulation from thermal radiation from room temperature to the cryogenic environment is provided exclusively by 30 to 40 multi-layer insulation blankets located around the cold inner part of the cryostats that contains liquid or gaseous helium. This simplified design is made possible by the use of superconducting materials operated at temperatures higher than liquid helium.\u003c/p\u003e\n\u003ch3\u003eElectrical requirements and instrumentation\u003c/h3\u003e\n\u003cp\u003eThe Cold Powering System includes high-current Nb-Ti, MgB\u003csub\u003e2\u003c/sub\u003e and REBCO cables. The splices between MgB\u003csub\u003e2\u003c/sub\u003e and REBCO are in helium gas in the DFHX, and those between MgB\u003csub\u003e2\u003c/sub\u003e and Nb-Ti are in liquid helium in the DFX (see Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). While the splices are not required to be superconducting, low resistance is necessary to avoid local thermal run-away and ensure efficient cryogenic cooling of the system with a minimum mass flow rate.\u003c/p\u003e \u003cp\u003eBoundary conditions for the design were: electrical insulation among circuits and to ground of 2.3 kV when the system is in nominal cryogenic conditions; controlled cross talk among circuits, i.e. fast discharges generated by the resistive transition of the Nb-Ti Corrector magnets (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) should not trigger by electro-magnetic coupling the resistive transition of the other circuits. Circuits were therefore powered both individually and simultaneously with different ramp rates.\u003c/p\u003e \u003cp\u003eIf quench protection thresholds, i.e. the maximum allowed voltage drops along the superconducting parts of the system, are accidentally exceeded or nominal cryogenic conditions are lost, a discharge of the concerned circuit(s) is triggered. The temperature sensors and voltage taps required for monitoring and protection are incorporated in the system. All voltage taps used for quench protection are doubled for redundancy. Altogether, the system includes 304 voltage taps, 266 for protection and 38 for monitoring functionalities. An overview of the instrumentation is given in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eData acquisition and quench detection are provided by twenty crates of the universal quench detection system (uQDS, [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]). The crates are equipped with 16 inputs each for a total of 320 channels. They are arranged in two redundant groups of ten crates. Each crate and its redundant twin monitor and protect the two polarities of a circuit and measure with two analog inputs the current signals stemming from two independent direct current transducers (DCCT) of the circuit. Protection thresholds are: 100 mV for the resistive part of each current lead, 5 mV for each REBCO cable, and 20 mV for each MgB\u003csub\u003e2\u003c/sub\u003e cable. Splices are also individually protected with voltage thresholds of 20 mV, for the MgB\u003csub\u003e2\u003c/sub\u003e to Nb-Ti splices, and 5 mV, for the MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices. The discrimination time of the quench detection system is 100 ms for the resistive part of the current leads and 20 ms for the REBCO and MgB\u003csub\u003e2\u003c/sub\u003e cables as well as for the splices. At low currents, defined as \u0026le;\u0026thinsp;10% of the design current of a circuit (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), the quench detection thresholds are increased by a factor ten to compensate for the higher ripple of the power converters in those current ranges.\u003c/p\u003e \u003cp\u003eThe Cold Powering System includes 105 temperature sensors (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e): sixty-one Platinum Resistance Temperature Detectors (RTD) Pt100 and forty-four Cernox\u0026reg;. The Pt100 sensors are located at the warm end of the REBCO cables (T\u003csub\u003eHTS\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) where they are connected to the resistive part of the current lead \u0026ndash; one sensor and a redundant twin per cable. They are used for the control of the flow through each current lead and their set point is 50 K or 60 K. The Cernox\u0026reg; are located on the MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices (T\u003csub\u003eMgB2\u003c/sub\u003ein Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) \u0026ndash; one sensor and a redundant twin per splice. Both sensors are part of the interlock chain of the circuits: a power abort of a circuit (50 A/s to 100 A/s discharge, depending on the circuit) is triggered if a sensor exceeds by 5 K the nominal operating value, i.e. if the temperature of a MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splice reaches 25 K or if the temperature of the REBCO reaches 55 K or 65 K. In addition, one Pt100 sensor is incorporated in the room temperature terminal of each current lead. The power abort of the concerned circuit is triggered if it exceeds 320 K or if is lower than 275 K. Below 275 K, the gas flow through the concerned current lead is also interlocked. This ensures that neither overheating nor overcooling of the current leads can take place in the system.\u003c/p\u003e \u003cp\u003eThe electrical tests aim at qualifying each circuit of the system. The test bench enables powering the circuits in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e according to the following layout: the 18 kA circuit (Nb\u003csub\u003e3\u003c/sub\u003eSn Quadrupole) is powered individually (the two polarities are electrically shorted inside the DFX via a Nb-Ti to Nb-Ti splice); the 15 kA circuit (Nb-Ti Separation Dipole) is powered individually (the two polarities are electrically shorted inside the DFX via a Nb-Ti to Nb-Ti splice); the 2 kA circuit (Nb-Ti Trim) is powered individually (two polarities plus one spare cable are electrically shorted inside the DFX via Nb-Ti to Nb-Ti splices and can be powered in pairs by changing the connections at the room terminal of the current leads); the 2 kA circuits of the corrector magnets (Nb-Ti Correctors) are powered all in series (the twelve polarities are electrically shorted inside the DFX via six Nb-Ti to Nb-Ti splices and at room temperature at the level of the current leads terminal). The powering layout is reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The nineteen polarities \u0026ndash; corresponding to nine circuits \u0026ndash; could be powered individually via four power converters.\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eMeasured cryogenic performance\u003c/h2\u003e \u003cp\u003eThe test campaign started with a pressure test of the Cold Powering System at 4.6 bara, followed by a helium leak test. Both tests were successful, and the helium leak rate was measured to be better than the specified value (\u0026le; 1.0 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;8\u003c/sup\u003e mbar\u0026middot;l\u0026middot;s \u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e).\u003c/p\u003e \u003cp\u003eThe cool down of the system was performed with a helium gas mass flow rate of 2 to 3 g/s. The thermal gradient between the helium supplied in the DFX and the helium recovered in the DFHX was limited to 50 K during the transient from room temperature to 160 K, and then increased to 70 K until the helium supplied in the DFX reached 15 K. This phase took about 3.5 days. Nominal cryogenic conditions \u0026ndash; with liquid helium inside the DFX \u0026ndash; were then reached in about eight hours (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, left).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor dealing with the thermal contractions, the Superconducting Link was installed on the ground with a wavy shape that enables movements during cool-down/warm-up as well as during the pumping of the thermal insulating vacuum inside the flexible cryostat. The waves are fixed to ground at some locations and free to move thanks to dedicated guide rollers elsewhere (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The amplitude and geometry of the waves were measured before and after vacuum pumping and cool down. Vacuum and cool down generated a maximum radial displacement of the peak of the free waves of 30 mm. After warm-up the Superconducting Link recovered its initial geometry with a maximum deviation of 10 mm due to stick-slip effect on the ground.\u003c/p\u003e \u003cp\u003eDuring the electrical tests, the system was powered from 0 kA to |94| kA (see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), with |94| kA DC current maintained up to eight hours. The helium mass flow rate required to cool the full system (DFH, Superconducting Link, DFHX and current leads) when operated at |94| kA was measured to be 4.9 g/s \u0026plusmn; 0.1 g/s. Measured temperatures met nominal cryogenic conditions and no temperature drifts could be detected in the system. The total pressure drop of the helium was measured to be \u0026lt;\u0026thinsp;30 mbar during cool-down and \u0026lt;\u0026thinsp;10 mbar in nominal cryogenic conditions. This is well within the maximum acceptable value of 50 mbar.\u003c/p\u003e \u003cp\u003eAt zero current, a helium mass flow rate of 3.5 g/s was sufficient for cooling the system and maintaining it at nominal cryogenic conditions. In this operating mode, a flow of 5 g/s was generated in the DFX, and 1.5 g/s were extracted at the level of the cryogenic by-pass line in the DFHX. This is done to ensure a buffer of helium gas close to the current leads, to cope with a transient flow increase due to powering, and to guarantee a precise control of the liquid helium level (\u0026plusmn; 1 cm) inside the DFX, which implies continuous operation of the electrical heater in the DFX outer volume. A test with a reduced helium mass flow rate was also performed. The goal of this test was to define a cryogenically economic configuration that can be adopted during long periods with no liquid helium and no current in the system, i.e. during a stand-by mode usually corresponding to maintenance interventions in the accelerator. A mass flow of 3 g/s with helium gas entering the DFX at 20 K was able to maintain the REBCO in the current leads (T\u003csub\u003eHTS\u003c/sub\u003e) at a temperature \u0026le; 100 K.\u003c/p\u003e \u003cp\u003eThe thermal performance of the Superconducting Link was quantified during five days of steady state cryogenic operation with 2 g/s of helium gas flowing through the system (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, right) and an inlet temperature of 15.8 K. The measured heat load is 2.0 W/m \u0026plusmn; 0.5 W/m, in line with more precise measurements performed in the past [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. A temperature mapping campaign with infrared camera enabled excluding presence of condensation or cold areas at any location along the external wall of the Superconducting Link cryostat and anywhere else in the system.\u003c/p\u003e \u003cp\u003eThe capability of generating and operating with a mass flow rate of 10 g/s was demonstrated. Two boil-off tests were performed, and it was shown that that such a flow can be produced by evaporation of liquid helium inside the DFX \u0026ndash; with the level of liquid helium maintained within specification. It was also demonstrated that the MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices remain submersed in liquid helium if the supply is interrupted for 10 minutes.\u003c/p\u003e \u003cp\u003eFor the assessment of the cryogenic performance of the DFX cryostat, two boil-off tests (measurement of rate of decrease of the liquid helium level with no helium supply) were performed as well as a temperature mapping campaign of the external wall of the cryostat with a thermal imaging system. No condensation could be observed at any location, but some colder areas (15.4 \u0026deg;C to 19.1 \u0026deg;C) were identified (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The total static heat load was quantified to be 67 W, 55 W of which deposited into the liquid helium volume, at 4.5 K, and the remaining 12 W deposited into the helium gaseous volume above the liquid. This figure presents an extra 30 W with respect to the estimations [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. It is considered that 10 W are due to a thermal shortcut through compacted MLI superinsulation blanket and 20 W are due to a non-optimised installation of MLI blankets. While optimal cryostat design is always a compromise between minimising heat inleak and adequate mechanical robustness, the mechanical design of the DFX cryostat had two unique challenges: (a) the inner helium vessel of the DFX cryostat has a design pressure of 3.5 bara (tested at 5 bara for European Conformity (CE) marking as a Category III Pressure Equipment) and is required to withstand high bending moment due to the L-shape (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) needed for keeping the MgB\u003csub\u003e2\u003c/sub\u003e to Nb-Ti splices in liquid helium and for transitioning the Superconducting Link from a vertical to an horizontal configuration; (b) the mechanical support for the 600 mm diameter vertical section of the inner vessel is restricted by the space available in the LHC tunnel to a short length of 300 mm between 4.2 K and 300 K to the detriment of thermal conduction. The test results fully validated the innovative structural design. For the remaining cryostats, the MLI installation will be further optimised with respect to the layout used in this test.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring the powering tests, neither condensation nor cold areas could be observed on the DFHX external envelope or on the current leads. For the current leads, the temperature of the REBCO was set between 50 K and 60 K leading to the definition of the optimized operating temperatures: T\u003csub\u003eHTS\u003c/sub\u003e = 50 K for the 18 kA and for the 15 kA current leads, and T\u003csub\u003eHTS\u003c/sub\u003e = 50 K or 60 K for 2 kA current leads. The mass flow requirements of the current leads were measured to be: 0.81 \u0026plusmn; 0.03 g/s for the 18 kA, 0.68 \u0026plusmn; 0.01 g/s for the 15 kA, 111 \u0026plusmn; 8 mg/s to 142 \u0026plusmn; 8 mg/s for the 2 kA.\u003c/p\u003e \u003cp\u003eThe tests demonstrated the cryogenic efficiency of the system that was operated in DC mode with a helium mass flow rate of 4.9 \u0026plusmn; 0.1 g/s at |94| kA and in nominal cryogenic conditions. The measured flow rate is well within the maximum value (\u0026le; 5.5 g/s) defined acceptable during the design phase. Stability and robustness of the cryogenic control were also proven.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eHigh voltage electrical insulation tests\u003c/h2\u003e \u003cp\u003eElectrical insulation of the superconducting cables is provided by multi-layer wrapping of polyimide tape, while splices are insulated via machined glass-fibre-reinforced-plastic (G-10) and ULTEM\u0026trade; parts. Insulators guarantee a minimum helium path in between non-insulated parts of 30 mm. A high voltage insulation test consists in measuring the electrical insulation between each polarity of a circuit and all the others and between each polarity of a circuit and the ground. The most critical part of the system with respect to the electrical insulation is the compact multi-cable assembly of the Superconducting Link.\u003c/p\u003e \u003cp\u003eThe electrical insulation of the MgB\u003csub\u003e2\u003c/sub\u003e cables was tested at up to 15 kV, at room temperature and in air, after production of the multi-cable assembly. After completion of the assembly of the Cold Powering System the following tests were performed: 5 kV at room temperature and in air before cool-down, 2.3 kV with the system in nominal cryogenic conditions, and 1.1 kV with the system filled with helium gas at 1.1 \u0026plusmn; 0.015 bara and at room temperature after the completion of the powering tests and warm-up. The maximum leakage current for each circuit is specified to be 10 \u0026micro;A during the voltage plateaus (\u0026ge;\u0026thinsp;180 seconds) and 100 \u0026micro;A during the voltage ramps (50 V/s). The system passed successfully all high voltage insulation tests. The maximum leakage current measured during the 2.3 kV test in nominal cryogenic conditions was 104.0 nA \u0026ndash; about 100 times lower than the maximum specified. Instrumentation signals, associated feedthroughs and temperature sensors all successfully passed the high voltage tests.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMeasured electrical performance\u003c/h3\u003e\n\u003cp\u003eThe test sequence adopted for the powering tests can be summarized as follows:\u003c/p\u003e \u003cp\u003ea) The nine electrical circuits were individually powered to their test current (18 kA, 15 kA, 2 kA and 2 kA, see Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Nominal cryogenic conditions were ensured. The valves successfully controlled the helium mass flow through each current lead maintaining constant the T\u003csub\u003eHTS\u003c/sub\u003e of each REBCO cable (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). Each circuit was brought individually from a low current plateau to the test current, which was initially held for about 10 minutes before ramping down. Ramp rates of 20 A/s were selected;\u003c/p\u003e \u003cp\u003eb) The test current was then maintained for one hour (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). For one hour, the system operated in nominal operating conditions with a total current of |94| kA, i.e. the maximum current that could be delivered by the four power converters, and a mass flow rate of 4.9 \u0026plusmn; 0.1 g/s. Afterwards, each circuit was brought back to zero current with the same ramp rate and plateaus at lower currents.\u003c/p\u003e \u003cp\u003ec) All circuits were ramped simultaneously with synchronized ramp rates ranging from 20 A/s to 100 A/s both in steps and from zero to their test current. The test currents were maintained constant in all circuits during eight hours with stable cryogenic conditions. Individual and simultaneous powering of all circuits were successfully repeated after a complete thermal cycle of the Cold powering System: the system was warmed-up to room temperature, cooled-down again to nominal cryogenic conditions, and powering tests were redone.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eDuring all tests no resistive transitions took place in the superconducting parts (Nb-Ti, MgB\u003csub\u003e2\u003c/sub\u003e and REBCO) of the circuits, no temperature or voltage drifts could be detected, voltage drops across resistive sections were within estimated values, temperatures and liquid helium level were stable and corresponding to those selected for nominal cryogenic conditions.\u003c/p\u003e \u003cp\u003eValidation of the electrical splices was an important qualification step. Both REBCO tapes and MgB\u003csub\u003e2\u003c/sub\u003e wires contain high resistance metal in their matrix or substrate, Hastelloy\u0026reg; and Monel\u0026reg;, respectively, and optimization of the splices required a significant R\u0026amp;D effort. REBCO to MgB\u003csub\u003e2\u003c/sub\u003e splices are cooled by forced flow of helium gas at about 20 K inside the DFHX. They were measured to be in the range from 1.4 nΩ to 10.1 nΩ. MgB\u003csub\u003e2\u003c/sub\u003e to Nb-Ti splices are in liquid helium at 4.5 K inside the DFX. They were measured to be in the range from 1.4 nΩ to 2.4 nΩ. The electrical splices among Nb-Ti cables, used to create the electrical shorts in liquid helium inside the DFX, were less than 1.5 nΩ. All measured values matched with the estimated ones (see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). They did not change after hundreds of electrical cycles and one complete thermal cycle (from room temperature to nominal cryogenic conditions) of the Cold Powering System.\u003c/p\u003e \u003cp\u003eThe evolution of the temperatures of the REBCO to MgB\u003csub\u003e2\u003c/sub\u003e splices during the current cycles are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, left. The temperatures of all REBCO to MgB\u003csub\u003e2\u003c/sub\u003e splices remained at the nominal value (\u0026lt;\u0026thinsp;20 K) and are independent of the current. No indication of heating of the splices, during any phase of the test could be identified: both measured resistances and measured temperatures of the splices were stable.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMeasured and estimated resistance of the splices.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTest Current\u003c/p\u003e \u003cp\u003e(kA)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003eREBCO to MgB\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eMgB\u003csub\u003e2\u003c/sub\u003e to Nb-Ti\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eNb-Ti to Nb-Ti\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eMeasured\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eEstimated\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eMeasured\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eEstimated\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eMeasured\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003eR\u003c/b\u003e\u003csub\u003e\u003cb\u003esplice\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eEstimated\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003e(nΩ)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;2.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;1.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;2.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003cp\u003eTrim\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003cp\u003eCorrectors\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;13.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026le;\u0026thinsp;6.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eElectro-magnetic compatibility\u003c/h3\u003e\n\u003cp\u003eElectro-magnetic cross talk among circuits, that could trigger the quench detection system, should be avoided during operation. More specifically, it is requested that in the case of quench of a corrector magnet in a 2 kA circuit, the resulting fast discharge of that circuit should not trip the quench protection of neither the Nb\u003csub\u003e3\u003c/sub\u003eSn Quadrupole (18 kA) nor the Nb-Ti Separation Dipole (15 kA) circuits. Limitation of inductive couplings has therefore been addressed in the design of the Superconducting Link. This behaviour has been investigated by measuring the self-inductance of each circuit and the cross talk between circuits. Each circuit was powered with ramp rates of 50 A/s to 100 A/s and the voltage induced during the ramp in the other circuits was measured. The response of a circuit was found to be dependent on the relative position of the MgB\u003csub\u003e2\u003c/sub\u003e cables in the Superconducting Link and on the routing/location of the associated voltage signals. Measured inductive couplings between circuits and the self-inductance of each circuit are reported in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The coaxial MgB\u003csub\u003e2\u003c/sub\u003e cable layout of the 2 kA circuits results in a very small inductive couplings of 0.02\u0026ndash;0.03 \u0026micro;H towards the other circuits.\u003c/p\u003e \u003cp\u003eA fast power abort in the HL-LHC configuration triggers a 6 kA/s discharge of the 2 kA corrector circuits. The measured maximum inductive coupling of 0.03 \u0026micro;H towards any other circuit implies induced voltages in the MgB\u003csub\u003e2\u003c/sub\u003e cables of the other circuits of 0.2 mV, a value about 100 times lower than the protection threshold of 20 mV. The test enabled concluding that in line with the design criteria of the Cold Powering System, a fast discharge of any 2 kA corrector circuit does not trip the electrical protection of any other circuit in the system.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMeasured inductive coupling and self-inductance for the 18 kA, 15 kA and 2 kA corrector circuits.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCircuit\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTest current\u003c/p\u003e \u003cp\u003e(kA)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eRamp rate\u003c/p\u003e \u003cp\u003e(A/s)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNb\u003csub\u003e3\u003c/sub\u003eSn Quadrupole\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNb-Ti Separation Dipole\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNb-Ti\u003c/p\u003e \u003cp\u003eTrim\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNb-Ti\u003c/p\u003e \u003cp\u003eCorrectors\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c7\" namest=\"c4\"\u003e \u003cp\u003eInductive coupling and self inductance (\u0026micro;H)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eSn Quadrupole\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e31.0*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e15.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti Separation Dipole\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.1*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e18.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNb-Ti\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eCorrectors\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e1.5*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eCurrent Leads\u003c/h2\u003e \u003cp\u003eThe current leads consist of a resistive part, which is a heat exchanger cooled by forced flow of helium gas, and of a REBCO HTS part. The design is similar to that of the LHC current leads [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], with the difference that the HTS part consists of REBCO round cables [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] instead of stacks of Bismuth-Strontium-Calcium-Copper-Oxide (BSCCO) 2223 silver-gold (Ag-Au) tapes. The helium gas enters the resistive part of the current leads at a temperature which is expected to be in between 25 K to 35 K: after having passed through the Superconducting Link and cooled the MgB\u003csub\u003e2\u003c/sub\u003e to REBCO splices, which are at about 20 K, it cools the mechanical structure of the DFHX, the HTS parts of the current leads, the REBCO to copper splices at the cold end of the resistive heat exchanger, and it finally enters in and cools the resistive part of each current lead. The minimum mass flow rate for the resistive part of a current lead cooled with helium gas entering at about 25 K to 35 K is ranging from about 0.0048 g/s kA to 0.055 g/s kA [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The 18 kA and 15 kA current leads were able to operate at the test currents with the optimum rate. By design, the 18 kA and the 15 kA current leads are identical and optimized for operation at 18 kA. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e reports the voltage drop measured across the resistive parts of those current leads when operated at the test currents with T\u003csub\u003eHTS\u003c/sub\u003e equal to 50 K and mass flow rates of 0.81 \u0026plusmn; 0.03 g/s and 0.68 \u0026plusmn; 0.01 g/s respectively. The helium flow rates are stable with time. The resistive heat exchangers of the 2 kA current leads are all identical, while the HTS part of the Trim circuit is designed for 7 kA in order to cope with electrical transients in the magnets and currents of up to 7 kA with no resistive transition. Measurements in steady state at 2 kA with T\u003csub\u003eHTS\u003c/sub\u003e of 50 K or 60 K resulted in mass flow rates of 111 \u0026plusmn; 8 mg/s and 142 \u0026plusmn; 8 mg/s, respectively. Differently from the 18 kA and 15 kA current leads, where each resistive part is surrounded by a vacuum insulation jacket, the 2 kA current leads are grouped in assemblies of four inside a common vacuum insulated envelope. Two of the four 2 kA current leads have an inclination with respect to ground of about 6 degrees, while the other two on the same flange are inclined by about 15 degrees. The difference in mass flow rate is attributed to thermal coupling in between the gas flowing inside the leads and the static gas stratified inside the common vacuum insulating envelope. The two current leads with a higher inclination are expected to be surrounded by stratified gas at a slightly (5 K to 10 K) higher temperature (density of helium gas increases as temperature decreases), which impacts on the global performance by demanding an increased flow rate. There are in total three assemblies of four 2 kA current leads: the behaviour of the leads in the different assemblies and with the same geometrical configuration is identical.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDuring operation no cold spots could be detected at any location along the currents leads, including the room temperature terminations where the room temperature cables are connected.\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eA 100 kA class DC superconducting system, based on MgB\u003csub\u003e2\u003c/sub\u003e and REBCO technology, was designed, assembled and tested at CERN. The system successfully transferred a total DC current of up to |94| kA, the maximum current that could be delivered by the power converters, with MgB\u003csub\u003e2\u003c/sub\u003e at up to 20 K and REBCO at up to 60 K, and it passed the electrical insulation tests at the target voltage of 2.3 kV under nominal operating conditions. This is the first of eight systems that will be installed in the LHC underground as from 2028 for operation at the start of the LHC High Luminosity Upgrade in 2030.\u003c/p\u003e \u003cp\u003eThe Cold Powering System incorporates Nb-Ti cables in a saturated liquid helium bath at 4.5 K, a 74.5 m long Superconducting Link with MgB\u003csub\u003e2\u003c/sub\u003e cables in the temperature range from 4.5 K up to about 20 K, REBCO cables from about 20 K up to 60 K, and current leads providing the electrical transfer to room temperature. It is the first transmission system that relies on long and high current (up to 18 kA individually) MgB\u003csub\u003e2\u003c/sub\u003e cables. To our knowledge, the system transported the highest current ever reached in DC mode (|94| kA).\u003c/p\u003e \u003cp\u003eThe choice of the MgB\u003csub\u003e2\u003c/sub\u003e superconductor in the Superconducting Link was driven by the affordable cost of the conductor, its availability in kilometre lengths, its behaviour in case of resistive transition [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] that enables use of conventional and reliable quench protection methods and electronics [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], and the availability in the LHC of helium enabling operation at up to 20 K.\u003c/p\u003e \u003cp\u003eBecause of the requirement of feeding several superconducting magnet circuits, the Cold Powering System incorporates a multiplicity of cables and current leads, nineteen in total, that are tightly arranged inside the Superconducting Link flexible cryostat and in the DFX and DFHX termination cryostats. This adds challenges to the design for maintaining compactness, dealing with the electrical insulation of each polarity, avoiding electro-magnetic cross talks among circuits, ensuring the mechanical flexibility required for installing and spooling the Superconducting Link, implementing the instrumentation necessary for protecting and operating each circuit individually, and fitting a multiplicity of electrical splices, among different superconducting cables, in compact volumes. A single polarity 120 kA or two polarities each rated at 60 kA, applicable to DC superconducting power transmission for instance, would fit with ease in a Superconducting Link cryostat with the same dimensions, but all listed complexities would not apply or would be significantly reduced.\u003c/p\u003e \u003cp\u003eFrom the point of view of cost and efficiency of the cryogenic cooling, the design of the system is such that the total helium mass flow rate corresponds to what is needed for operating the current leads. The Superconducting Link transfers both current and helium gas to the current leads, and the helium flow corresponds to that required for operating optimized current leads. To obtain this performance, a two-wall and low static heat load cryostat (\u0026le; 2 W/m at any temperature in the range from 4.5 K to 20 K, with an external diameter of 220 mm and an inner diameter of 100 mm) was specifically developed for the Superconducting Link project in industry. The two-wall configuration was preferred to the four-wall configuration, which includes an actively cooled thermal screen, to enhance flexibility, simplify the design of the system and ease handling and installation aspects. The heat load of the Superconducting Link is mainly due to thermal radiation from room temperature to the cryogenic environment and thermal conduction through the vacuum insulation envelope, in between the two corrugated pipes, where MLI and spacers are located. Published values of static heat load for two-wall flexible cryostats with dimensions suitable for containing one, two or three electrical poles, are in the range of 1 W/m to 2.5 W/m at 77 K. These values are expected to increase by a factor of 4 to 6 with bends [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The 1.6 W/m at 4.5 K to 20 K of the Superconducting Link, operated in the convoluted geometry reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, represents therefore a remarkable performance when compared to what before available in industry. It should be noted that the static heat load was measured with the MgB\u003csub\u003e2\u003c/sub\u003e cables installed inside the cryostat. The design is such that the weight of the cables, which is of the order of 25 kg/m, did not impact on the thermal performance.\u003c/p\u003e \u003cp\u003eThe current leads define the mass flow rate for the system. Optimized self-cooled current leads, operating between room temperature and liquid helium, conduct about 1.1 W/kA at 4.5 K, corresponding to a mass flow rate of about 0.055 g/s kA, i.e. 5.2 g/s at |94| kA, and a similar flow of about 0.055 g/s kA is required for cooling the resistive part of the current leads when helium gas enters at a temperature in the range from 25 K to 35 K. The full Cold Powering System is cooled by a flow of 0.052 g/s kA, i.e. 4.9 g/s at |94|kA: the change in enthalpy of the gas from 4.5 K to 20 K is used to cool the Superconducting Link, while the change of enthalpy of the gas from about 20 K to room temperature is used to cool the current leads. The system is optimized in such a way that the Superconducting Link does not add cryogenic cost to the cooling of the system.\u003c/p\u003e \u003cp\u003eBy design the Superconducting Link can be spooled onto a large drum (radius of 2 m) after having been connected to the DFHX with the current leads. This enables implementing the strategy adopted for the transport and for the installation of the system in the LHC underground: a Cold Powering System is assembled, tested in nominal operating conditions in the configuration reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, spooled and finally transported. Such an operation has been successfully performed. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e left shows a Superconducting Link, attached to the DFHX, spooled onto a drum and being transported after completion of the qualification tests. This is an example of a 100 kA class transmission line transported together with the electrical terminations, ready to be installed and connected to the room temperature cables. After re-spooling (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e right), the system successfully passed the high voltage and leak tightness tests.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe developed system is cooled by a forced flow of helium gas generated inside the DFX. The cooling with gas is a reliable choice for a transmission system that has a long and convoluted geometry and that must operate, at a specific location, in a vertical configuration when it connects the HL-LHC new galleries to the LHC main tunnel. The use of MgB\u003csub\u003e2\u003c/sub\u003e and REBCO ensures a large temperature margin, i.e. a margin between the nominal operating temperature and the maximum operating temperature just below the critical temperature of the superconductor at the design current, of at least 5 K for MgB\u003csub\u003e2\u003c/sub\u003e and 10 K for REBCO. This margin is important since it eases cryogenic constraints and operation. Even if the nominal currents will never be exceeded during HL-LHC operation, by design the current margin for the MgB\u003csub\u003e2\u003c/sub\u003e and the REBCO, i.e. the margin between the nominal current and the maximum transportable current just below the critical current of the superconductor at 20 K for MgB\u003csub\u003e2\u003c/sub\u003e and at 60 K for REBCO, is at least 20%. Cooling of the high current MgB\u003csub\u003e2\u003c/sub\u003e and REBCO splices with forced flow of helium gas was proven to be effective. The available temperature margin makes the operation of the splices robust and reliable. Use of helium gas is the natural choice for the HL-LHC, where helium is available for the magnets. The Superconducting Link could, however, operate at 20 K in liquid hydrogen. Work in this direction was done by [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], where a 10 m long cable, in a cryostat with 40 mm external diameter, transported up to about 2.6 kA at 20 K. This cable was made with flat MgB\u003csub\u003e2\u003c/sub\u003e tape, which was at the time the only geometry of ex-situ MgB\u003csub\u003e2\u003c/sub\u003e conductor available in industry. The MgB\u003csub\u003e2\u003c/sub\u003e round wire used in the Superconducting Link has been developed for the project in industry, in collaboration with CERN. To date, the total quantity of wire needed for the ten Cold Powering Systems, about 1500 km, has been produced. The HL-LHC Cold Powering Systems represent the first large scale application of MgB\u003csub\u003e2\u003c/sub\u003e round wire, which is also for the first time successfully used in a large electrical transmission system.\u003c/p\u003e \u003cp\u003eThe developed MgB\u003csub\u003e2\u003c/sub\u003e technology finds applications for various uses in society. An initiative in this direction was taken by the IASS institute in Potsdam, under the scientific direction of Prof. Carlo Rubbia, where superconducting transmission was identified as an enabling technology for deployment of renewable electricity generation. The choice of MgB\u003csub\u003e2\u003c/sub\u003e was associated with liquid hydrogen as coolant, with the goal of simultaneous transmission of electric power and hydrogen fuel. A demonstrator in this direction was done at CERN, in the context of a collaboration agreement between CERN and IASS, where a 20 kA MgB\u003csub\u003e2\u003c/sub\u003e electrical transmission line was successfully constructed and qualified at 20 K [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. This work continued with the BEST PATHS (acronym for \u0026ldquo;BEyond State-of-the-art Technologies for rePowering Ac corridors and multi-Terminal HVDC Systems\u0026rdquo;) project of the FP7 framework of the European Commission that demonstrated a DC monopole MgB\u003csub\u003e2\u003c/sub\u003e cable system operated in helium gas at 10 kA/320 kV, corresponding to a transmitted power of 3.2 GW [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe construction and qualification at CERN of the first Cold Powering System for HL-LHC demonstrate the feasibility and the potentials of very high DC current, 100 kA class, MgB\u003csub\u003e2\u003c/sub\u003e based electrical transmission lines operated at up to 20 K.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eA complete system solution for a 100 kA class DC High Temperature Superconducting transfer line was developed and qualified at CERN. The system is cooled by a forced flow of helium gas. It incorporates MgB\u003csub\u003e2\u003c/sub\u003e and REBCO superconductors operated at up to 20 K and 60 K, respectively. The system successfully transported up to |94| kA in DC mode, the maximum current that could be delivered by the power converters, and it successfully underwent steady state and transient tests representative of different operating modes in the LHC. While the system was developed for use in the LHC accelerator, it is a potential platform for wider energy applications including long power transmission lines and industrial applications that can benefit from a sustainable transfer of high currents, possibly at low voltage.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study are available from the corresponding author on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAutor contributions statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAmalia Ballarino\u003c/strong\u003e proposed, conceived and coordinated the research\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePaul Cruikshank, Yann Leclercq\u0026nbsp;\u003c/strong\u003eand \u003cstrong\u003eChristian Barth\u003c/strong\u003e coordinated experiments and contributed to the research\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFlorian Pasdeloup\u003c/strong\u003e contributed to design and assembly activities\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eVanessa Gahier\u0026nbsp;\u003c/strong\u003ecoordinated the cryogenic tests and contributed to the analysis of the cryogenic test results\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGerard Willering\u003c/strong\u003e coordinated the powering tests and contributed to the analysis of the test results\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eYifeng Yang and Wendell Bailey\u0026nbsp;\u003c/strong\u003edesigned and constructed\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003ethe DFX cryostat and contributed to the analysis of the test results. Their work was performed in the framework of the CERN-UK1 HL-LHC collaboration agreement\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBruning, O. \u0026amp; Rossi, L. The High Luminosity Large Hadron Collider, Advanced Series on Directions in High Energy Physics 31, (2024). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1142/13487\u003c/span\u003e\u003cspan address=\"10.1142/13487\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBallarino, A. Development of superconducting links for the Large Hadron Collider machine. \u003cem\u003eSupercond Sci. 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Supercond\u003c/em\u003e. \u003cb\u003e26\u003c/b\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1109/TASC.2016.2545116\u003c/span\u003e\u003cspan address=\"10.1109/TASC.2016.2545116\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2016).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6629095/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6629095/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe powering of the High Luminosity magnets of the Large Hadron Collider relies on Cold Powering Systems incorporating direct current superconducting lines, called Superconducting Links, based on magnesium diboride cables. A Cold Powering System interconnects the magnets in the accelerator existing tunnel to the power converters in newly excavated galleries that are about 8 m higher than the accelerator tunnel and up to about 100 m distant from the magnets. It feeds circuits rated at different currents and is designed to transfer a total current of up to |117| kA with magnesium diboride and Rare-Earth-Barium-Copper-Oxide technologies.\u003c/p\u003e \u003cp\u003eAfter about ten years of development, the first Cold Powering System was successfully constructed and tested at CERN. The Superconducting Link was measured in a geometrical configuration that included a vertical path simulating the final routing in the accelerator underground. The test campaign validated the mechanical, cryogenic and electrical performance of the system both in steady state conditions and under various transient scenarios. This paper reports on the results of the tests and details the performance of the first ever built magnesium diboride and Rare-Earth-Barium-Copper-Oxide 100 kA class superconducting system.\u003c/p\u003e","manuscriptTitle":"A system solution for a 100 kA class High Temperature Superconducting line for HL-LHC and for wider energy applications","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-19 19:41:24","doi":"10.21203/rs.3.rs-6629095/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-06-05T07:39:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-04T08:23:05+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-29T09:51:50+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"73736796605355177470186117351597287981","date":"2025-05-21T07:13:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"36347205950537278368777664024450110527","date":"2025-05-19T06:15:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"13343008888848760844635573046917214184","date":"2025-05-15T07:27:09+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-15T07:20:16+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-15T07:17:09+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-05-15T06:39:01+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-13T17:51:13+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-09T13:18:00+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e2f5859d-1a9f-465a-b227-ca298c080a76","owner":[],"postedDate":"May 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":48591453,"name":"Physical sciences/Engineering"},{"id":48591454,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2025-07-07T16:08:20+00:00","versionOfRecord":{"articleIdentity":"rs-6629095","link":"https://doi.org/10.1038/s41598-025-08543-9","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-07-01 15:57:24","publishedOnDateReadable":"July 1st, 2025"},"versionCreatedAt":"2025-05-19 19:41:24","video":"","vorDoi":"10.1038/s41598-025-08543-9","vorDoiUrl":"https://doi.org/10.1038/s41598-025-08543-9","workflowStages":[]},"version":"v1","identity":"rs-6629095","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6629095","identity":"rs-6629095","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}