Functional model of the measuring head for the plasma fusion reactor wall diagnostics using low pressure, laser induced breakdown setup at random positions

Functional model of the measuring head for the plasma fusion reactor wall diagnostics using low pressure, laser induced breakdown setup at random positions | 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 Research Article Functional model of the measuring head for the plasma fusion reactor wall diagnostics using low pressure, laser induced breakdown setup at random positions Milivoje Ivković, Nikola Vujadinović, Ivan Traparić, Biljana D. Stankov, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6212849/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Plasma Facing Components (PFC) diagnostics in fusion reactors require innovative and robust instrumentation capable of addressing the challenges of harsh operational environments. Hence, this work presents the design, construction, and testing of a functional model for a LIBS measuring head tailored for in-situ and post-mortem PFC analysis. The proposed system includes advancements in mechanical design, such as an adaptable measuring head configurations, which enable operation in low-pressure environments and random spatial positions within the reactor. By integrating spectroscopic techniques and remote control capabilities, the system demonstrates potential for real-time diagnostics with sensitivity comparable to state-of-the-art techniques. PFC diagnostics fusion LIBS plasma spectroscopy Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction During the preparation and operation of the fusion reactors, the plasma facing components PFC’s face significant challenges due to exposure to thermal loads, neutrons, and plasma. These conditions can lead to a range of detrimental effects, including recrystallization, cracks, melting, dust formation, defects, transmutation, sputtering, hydrogen retention, helium induced morphological changes etc. To minimize the risk of an unexpected PFC failure, it is crucial to conduct thorough material composition characterization. The diagnostics of PFCs is critically important for the safe and reliable operation of fusion reactors. There is substantial literature, and a variety of applied techniques published in this field. In this discussion, we will focus exclusively on state-of-the-art research, highlighting the most relevant and recent papers that describe primary approaches. Ion Beam Analysis (IBA) methods 1 are an ex-situ approach that involves the demounting or cutting of plasma-facing component (PFC) samples. This family of techniques encompasses nine major methods, including nuclear reaction analysis, elastic recoil detection analysis (with high-energy heavy ion variants), Rutherford backscattering spectrometry, non-Rutherford elastic backscattering spectrometry, medium energy ion scattering, particle-induced X-ray and gamma-ray emission, and accelerator mass spectrometry. Another ex-situ method is Thermal Desorption Spectroscopy (TDS), which involves placing mirror-finished disk-type tungsten samples at specific locations on the plasma-facing wall of devices like the Large Helical Device (LHD) at NIFS in Japan 2 , 3 . After demounting, these samples are analyzed using a quadruple mass spectrometer to evaluate the desorption behavior of hydrogen isotopes. Effective method for PFC characterization is Laser Induced Breakdown Spectroscopy, LIBS, which provides highly sensitive and rapid multi-element analysis with minimal destructiveness. This technique relies on the interactions of the focused laser beam with the material, which results in localized heating, melting and evaporation. The charged particles, present in the evaporated material, cause electric breakdown and formation of plasma. The created plasma emits radiation, having spectral lines of all target constituents. By recording this emitted radiation, LIBS enables detailed analysis of material composition, making it a valuable tool in the assessment of PFCs in fusion reactors. This analytical spectroscopy technique is well described in many books and review articles 4 , 5 , 6 , 7 , 8 , 9 , 10 . The distinctive attributes of laser radiation have significantly enhanced analytical methods for material characterization. LIBS is an elemental analytical technique that does not require any sample treatment, unlike inductively-coupled plasma–optical emission spectroscopy 11 . It can analyze non-conducting samples, which Spark Optical Emission Spectroscopy cannot, and it is not restricted to heavy elements, as is the case with X-ray fluorescence. Additionally, LIBS is considered an environmentally friendly analytical method, as it operates solely with light and collects only photons, eliminating the need for chemicals and producing no waste. Furthermore, as a minimally invasive and non-contact technique, LIBS allows for multi-element analysis and even depth profiling without the need for sample preparation, making it an appealing option for a wide range of applications. LIBS has a vast array of applications, including the preservation of cultural heritage, forensics, environmental protection (such as "contactless" waste sorting), and the analysis of biomaterials. Material characterization by the LIBS may enable prevention of fusion reactor damage by providing a tool for early detection of PFC defects caused by retention of reactor fuel and/or by neutron activation produced radio nuclides. Even though LIBS has been recognized as the strongest candidate for this demanding task, the configurations proposed so far do not fully meet the requirements for PFC diagnostics In-situ analyses using LIBS are conducted through a single port on the fusion reactor 12 . This technique utilizes a molybdenum mirror positioned inside the reactor, allowing the laser beam to be directed at different PFCs within a single poloidal cross-section of the machine. In-situ analysis of PFCs 13 can be achieved using a robotic arm (RA) as part of the Frascati Tokamak Upgrade (FTU) project. With an accuracy of approximately ± 1 mm, the robotic arm can probe any point within the vacuum vessel while maintaining consistent detection performance. It also has the capability to introduce gases to the sample surface, enabling measurements under varying background gas conditions. The aim of this work is to enhance the performance of the LIBS technique to achieve sensitivity levels comparable to those of IBA 1 and TDS 2 , 3 . Compared to these methods, LIBS offers more straightforward implementation, eliminating the need for complex computer codes essential for analyzing and interpreting IBA spectra, with possibility for in-situ operation. In this paper, we present a configuration with various adapters that are both more cost-effective and easier to operate than the robotic arm system 13 . Additionally, our approach allows for the use of gases at low pressures, which is more optimal for LIBS operation compared to the prior method of gas fluxing. The proposed LIBS configuration enables the examination of each component at any location on the PFC. This configuration could facilitate analysis of nearly the entire surface area of a fusion device. For tokamaks lacking toroidal symmetry—such as those with individual poloidal limiters—or for stellarators, analyzing multiple poloidal cross-sections may be necessary, a requirement that earlier approaches 12 cannot fulfill. Our proposed in-situ analysis will eliminate the need for extrapolation in toroidal symmetry tokamaks and enable comprehensive multi-point studies, even in stellarators. This improvement will enhance analytical performance compared to the robotic system, which requires significantly larger funding and research and development teams. The proposed system for post-mortem analysis of PFCs during maintenance periods utilizes an in-situ LIBS configuration, positioning the operator inside the fusion reactor. This work will provide detailed analysis of requirements for such a configuration, along with the construction, testing, and use of a functional model of measuring head. 2. LIBS system Considering the enhanced dimensions of new plasma fusion reactors, we propose an alternative to the previously used LIBS systems 12 , 13 , 14 , 15 . We advocate for a configuration operated by a person inside the reactor, enabling real-time in-situ diagnostics of PFCs at nearly any location, as depicted in Fig. 1 . Namely, having in mind dimensions of plasma fusion reactors (JET and bigger) the operator (instead of the robot) may move in device interior and visually inspect PFC to select for and perform the examination of any part (see also photos in Supplementary material). It must be underlined here that our ambition is not to enable in-situ operation without any protection, as somebody may conclude from the Fig. 1 . This figure only illustrates our configuration, showing comparison of the operator with the size of the JET (much smaller than ITER and not working with Be and T). Due to presence of the Be dust and radioactivity of tritium in PFC, the operators, who will probably use our configuration for in-situ operation, must wear air inflated hoods equipped with a filter, disposable coveralls, rubber boots with overshoes and several pairs of gloves including a sacrificial top layer which is changed periodically (as in handling Be or T contaminated PFC demounted from reactor). The proposed LIBS system, besides operator, includes a measuring head (MH), remote control (RC) and main unit (MU), marked in Fig. 1 . The operator positions the measuring head with the help of the telescopic arm, see photograph in Supplementary material. Construction of the measuring head is the main subject of this research, and it is described in Section 2.1 ., while the other LIBS system components necessary for MH operation are analyzed in Section 2.2 . 2.1. Measuring head construction In this work, a functional model of measuring head for work under low gas pressure conditions was constructed and shown in Fig. 2 . The MH consists of three parts: main chamber (1), adapter to the component being analyzed (2) and upper body with windows and connections (3), all marked in Fig. 2 . The role of the main chamber of the measuring head is to prevent air intake and establish low pressure conditions. The space in which the low-pressure conditions were established in this functional model has dimensions ϕ 5 cm x 4.5 cm, see Fig. 2 . The outer diameter of the main chamber is 10 cm. If the dimensions of the main chamber exceed those of the PFC to be analysed, the proposed adapter (2) must be redesigned to ensure proper vacuum sealing. Namely, the adapter (2) may also have two parts: one for threading into the main chamber and an additional one that can be rectangular and even have the curvature at the bottom (which will follow the curvature of the PFCs under analysis). At the upper end of adapter (2) there is a 5 mm annular rim that has a purpose to settle, easily removable metallic foil or glass or ceramic ring, (4) in Fig. 2 which covers main chamber inner wall. The purpose of these components is to prevent propagation of plasma to the sealing components on the chambers’ bottom and/or to prevent deposition of evaporated target on chamber walls. Namely, deposits on the wall may cause memory effects and wrong results of target analysis, if due to small chamber dimensions, plasma reaches and reacts with his walls. In the chamber wall there are two ports (PA and PB) for vacuuming, gas supply and gas pressure measuring instruments. The roles of PA and PB depend on the chosen sealing approach and will be detailed in Section 2.1.1 , along with the functions of the 30 mm deep and 5 mm wide groove G between components (1) and (2), as well as the two additional small grooves (A and B) at the bottom of the chamber (see Fig. 2 ). The MH chamber’s upper body (3 in Figs. 2 and 3 ) based on the standard DN63 vacuum connection flange, has one central opening and four radially spaced openings in Fig. 3 for carrying optical windows, (a) in Fig. 3 . Two of them are intended to be used for transmitting lasers radiation, one is for collecting emitted radiation and one for the illumination and observation using endoscope. The optical windows (a) are tightened using additional O ring and screws, while (c) are ferrules for fiber cable mounting. This flange (3) has also four additional ports (d in Fig. 3 ) with M6 metric screw thread. These ports can be used for: a) vacuum, b) gas supply, or c) high voltage connections, d) aiming beam entrances or e) spare. 2.1.1. Measuring head sealings The sealing mechanisms of the measuring head are critical to maintain the required low-pressure conditions and prevent contamination from external gases. At the beginning of each analysis, the measuring head should be positioned and roughly attached and sealed to the PFC. Several versions of the measuring head sealing mechanism for the PFC surface were constructed and tested in this work, as illustrated in Fig. 4 . Since these components are symmetric, only the left half of the cross-section is shown. The simplest configuration utilizes a thin gasket (highlighted in red in Fig. 4 ) with an inner diameter exceeding 50 mm and an outer diameter of up to 100 mm (see Fig. 4 a). This gasket design is primarily intended for use with surrounding gases other than air, at elevated pressures above 10 mbar or even exceeding one bar (as in 13 ), where small amounts of air inlet are not critical. In this configuration, it is important to apply additional force (indicated by the arrow in Fig. 4 a) to secure the measuring head against the PFC surface. The gas inlet is located at port PB, while port PA serves as the vacuum outlet. Tests of this setup, (by using both ports, PA and PB for vacuuming only) as shown in the Supplementary Material, demonstrated the ability to achieve pressures below 1 mbar within the main chamber, confirming its effectiveness. The sealing mechanism designed for situations where the PFC surface is uneven but lacks significant scratches or deep channels is illustrated in Fig. 4 b. In this design, the grooves at the bottom of the measuring head play distinct roles. The small outer groove (A, as shown in Fig. 2 ) houses the primary elastomer, effectively preventing the ingress of air and the egress of working gas. The smaller inner groove (B) accommodates an O-ring, which restricts gas flow from the vacuum chamber’s interior without directly contacting the PFC surface. Vacuuming is achieved through the main groove (indicated by the arrow in Fig. 4 b) and port PA, while gas supply is introduced via the outer port PB, similar to the configuration in Fig. 4 a. Low-pressure gas adjustment was carefully managed using a gas mass flow controller, with corrections applied based on voltage output from a capacitive manometer. This setup ensured optimal gas pressure within the measuring head, even when minor leakage occurred due to a rough PFC surface. The manometer connection was strategically placed at the center of the main chamber to ensure accurate pressure monitoring. Details of the specialized elastomer type and shape, critical to this configuration, will be discussed later in the text. In configuration, shown in Fig. 4 c, gas flow at pressure greater than atmospheric creates so-called “gas-curtain” and prevent air to reach main chamber. The elastomer in groove B, see Fig. 2 limits this high flow of gas to the main chamber and provides contact with the PFC surface, meaning it has a same purpose as in Fig. 4 b, but gas goes in opposite direction. The mass flow controller-manometer loop enables constant gas pressure inside the main chamber. Sometimes the PFC has such shape that MH cannot easily be attached to it. In that case, the plan is to use the inner component i.e. adapter which has upper part with screw for connection to the outer; see part 2 in Fig. 2 , while the bottom part has a shape, which corresponds to the PFC. Namely, not only the cross section of adapter should correspond to the dimensions of the PFC, but also should correspond to their curvature. Such version of MH can be used with any of the former gasket designs, but the distance between elastomer B must be carefully adjusted. In addition, adapters can be made to contain other components needed for spatially confined 16 , magnetically confined 17 , or discharge enhanced LIBS 18 . Adaptation of the proposed configuration of the measuring head to be used as a laser ablation cell, arc, glow discharge or similar analytical technology setups is also in progress. 2.1.2. Elastomer requirements In any of the studied versions of the measuring head the selection of the type and shape of the elastomer has a significant importance. The elastomer selection depends on several factors. These include temperature range, pressure range, integrity of sealing required, material of counter faces, life requirement, maintenance requirements, assembly methods, degree of flexibility and many others. Also, individual material classes achieve a satisfactory seal by quite different mechanisms, and it is necessary to take this into account at the selection and design stage. O-rings are by far the most common form of elastomer seal, and we use it at the inner part of the MH i.e. as adapter’s elastomer B, see Fig. 4 c. They are relatively easy to manufacture, readily available in standard sizes and there are many standards and guides to facilitate design. However, they do have several limitations, and hence an alternative style of seal is considered to achieve improved performance. The complex shape of the elastomer A, as well as the photograph of the used elastomers are shown in Supplementary material. The shape is chosen to satisfy the appropriate filling of gap A to enable sealing and to have as long possible tail (from gap A to the exterior of the main chamber) to enhance sealing capacity by prolonged contact to PFC surface. It should be stressed that for that purpose the tool for manufacturing such an elastomer shape from four different materials was also constructed. As an elastomer material we tested: silicone rubber, Q, having hardness of 40 Shore, nitrile butadiene rubber, NBR with 70 Shore hardness and two natural rubbers NR, with hardness of 45 and 55 Shore. All sealing rings B in this MH functional model have the same dimensions i.e. 118 x 83 x 8.5 mm. Elastomer B drawing and photograph of the realized sealant together with the tool for their production was presented in Supplementary material. Due to PFC surface roughness, the better results are performed with mandatory application of silicone, hydrocarbon or perfluoropolyether high vacuum grease. Choice of grease depends on PFC and analysis type. 2.2. Remote control and main unit design As can be seen from Fig. 1 , the main components besides measurement head are a telescopic arm, remote-control RC and main unit. The flexible telescopic arm carries tubing for a gas supply and vacuuming. The length of all cables (which may be even ten meters long) 19 , 20 should be changed, in accordance with the distance between operator and PFC under investigation. Therefore, the LIBS system must also have a winder for these tubing’s, as well as for the electric and fiber optic cables. The RC should enable wireless communication between the operator and the main control room. In addition, the RC should enable video surveillance, i.e. must have a display for receiving a picture from the endoscopic inspection camera, mounted on the measuring head. The endoscopic system should also have a possibility to illuminate the interior of the MH by corresponding LED's. Depending on the reactor and application, the main unit, MU can be installed in the fusion reactor control room or on the cart pulled by the operator. In both cases, the physical connection to the fusion reactor vacuum system, gas handling system and mains supply must be provided. As an option (due to the small MH volume) a small vacuum pump and one liter gas cylinder (enough due to the use of the low gas pressure) can be settled on the cart carrying other equipment. Besides these external connections, the lasers (one or two for double pulsed LIBS) with their power supplies and optics for coupling laser radiation to fiber optic cables, should be settled in the MU. The MU also should have a spectrometer equipped with a detection system (ICCD and/or CCD cameras), camera interface i.e. connections to the computer and corresponding optics for coupling optical radiation from fiber optic cable to spectrometer (F-matcher), AC and DC voltage power supply for all equipment etc. The principle and details about requirements on remote controlled power supply system and optimized control system for the laser can be found in Ref. 14. Depending on the application, various spectrometers can be used. For hydrogen isotope retention studies high resolution spectrometers (R > 20 000) must be used, while for other studies, echelle and segmented spectrometers have certain advantages due to covering a whole, or big part of the emitted spectrum. The simplest LIBS systems, capable of diagnosing the state of various components within plasma fusion reactors, can be based on field-portable (fpLIBS) or handheld (hLIBS) configurations 21 , 22 . However, the incorporation of a laser within these probes results in reduced sensitivity due to energy constraints linked to size and weight limitations. To enhance analytical capabilities, we propose a fiber optic LIBS configuration, omitting the laser from the measuring head, as referenced in [Ref. 23–28 and references therein]. In proposed main unit or measuring heads the optical setups are the same as used in fpLIBS and hLIBS probes, see Fig. 1 . in Ref. 24. The only difference between the optical setups for fpLIBS and hLIBS and the proposed one is the settling lasers in the MU (followed by) (and) the use of the fiber optic cable for transmitting laser radiation. The selection of fibers for collecting laser induced plasma radiation is a very common task and mainly depends on type of analysis. For example, for hydrogen isotope retention studies the necessity for high resolution (i.e. use of the narrow slit) and low intensity of Balmer alpha line favors the use of the fiber bundle with circular arrangement at the entrance and linear arrangement at the exit (to coincide with slit height). The selection of fiber for transmitting laser radiation is, on the contrary, a very demanding task. Namely, it is shown that coupling a laser beam to a fiber may produce permanent damage 29 even at laser energies 14 mJ (10 J/cm2) using hard clad quartz silica HCS fibers. Therefore, very low laser energies or complex fiber couplers and fibers having diameter at least 0.6 mm should be used 23 , 30 , 31 , 32 , 33 , 34 . The use of higher energies lasers requires fiber bundles with beam homogenizers in front of them, or use of hollow core fibers with gas circulation through them. Necessity for using diverging beams, i.e. focus position in front of fiber entrance also requires gas circulation to prevent formation of the laser induced spark, which may destroy fiber. For applications requiring higher Nd: YAG laser energies, or the use of TEA CO 2 lasers, an articulated arm with 6 to 8 rotatable joints becomes the most viable solution. Precise alignment of the laser beam at the fiber center is crucial and can be achieved using an x-y-z movable holder for accurate adjustments. The same fiber coupler design, excluding gas inlet and outlet features, should be employed at both ends of the irradiation and collection fibers, with identical x-y-z adjustment mechanisms to ensure optimal performance and alignment. 3. Experimental testing As discussed in Section 2.1 , LIBS achieves superior analytical performance when operating in a vacuum or at low gas pressures. Consequently, enabling low-pressure LIBS operation was a primary objective. To evaluate the effectiveness of this approach, experimental testing of the measuring head (MH) sealing was conducted using the configurations outlined in Fig. 4 . Sealant rings made from various elastomer materials were designed, manufactured, and tested. The testing involved determining the leakage rates of different elastomer types across various surface conditions to assess their sealing efficiency. Additionally, spectroscopic testing was performed to verify the absence of air within the MH chamber, estimate contamination levels, evaluate the analytical capabilities of the proposed setup, and investigate the potential for incorporating high-voltage discharges within the MH to enhance the LIBS signal. These evaluations provided valuable insights into the performance and reliability of the proposed low-pressure LIBS configuration. 3.1. Leakage rate testing For leakage rate testing the MH was connected at both PA and PB ports (see Figure 4a) to the rotary vane vacuum pump Alcatel 2012A having vacuuming speed of 15 m 3 /h. Then the MH was placed to different surfaces, evacuated to pressures less than 0.1 mbar and then disconnected from the vacuum pump using gate valve. The pressure was measured using the Leybold Heraeus DV 1000 manometer placed between MH and the valve. The time required for the pressure inside the chamber to increase to 10 mbar was measured for MH placed to the surfaces of the: a) brick, stone with and without vacuum grease, b) rough and c) polished metal and d) varnished wood. The results using red colored silicone Q rubber having hardness of 40 Shore and black colored nitrile butadiene rubber, NBR, having hardness of 70 Shore are presented in Table 1. The results for the other two elastomers are within experimental error and therefore are not presented in Table 1, thus also showing that for this application the elastomer hardness is a dominant parameter. The leakage rate in the table was estimated assuming the MH inner volume of 88 cm 3 . Table 1. Experimental testing of different elastomers. Elastomer type Surface time [s] cm 3 /s bar cm 3 /s Silicone rubber Q Red 40 Shore brick, stone 90 1 100 brick with grease 210 0.43 42.8 rough metal 270 0.33 33.3 wood varnished 300 0.3 30 polished metal 330 0.27 27.3 Nitrile butadiene rubber NBR black 70 brick, stone 10 9 900 wood varnished 310 0.29 29. rough metal 315 0.28 28.5 polished metal 330 0.27 27.27 From these measurements we concluded that, for the rough surfaces, the NBR 70 Shore is the better solution, and it was used in all further investigations. For the porous surfaces the rubber with a 40 Shore was the better solution. In addition, it is clear that the pumping speed of used vacuum pump may enable constant pressure inside the MH chamber. It is also concluded that usage of the high vacuum grease considerably decreases the leakage rate but should be used with precaution i.e. cleaned from the PFC to prevent possible reactor contamination. 3.2. Spectroscopic testing The prevention and testing of MH interior contamination was a more difficult problem. Namely, any leakage from the surrounding atmosphere may introduce air constituents (for example water vapor) which may influence measurement results. Therefore, spectral purity was studied. The configuration used for spectroscopical testing consists of the: a) Nd: YAG laser; b) optical elements for focusing the laser radiation onto the studied material surface, and for collecting emission from the created plasma, and c) spectrometer with camera for optical emission recording and saving by computer, see Fig. 5 . The Nd: YAG laser which was used for heating and ablating the target was Quantel model QSmart 450. This laser has maximal energy E YAG of 450 mJ, pulse duration of 6 ns and repetition frequency of 10 Hz. The beam diameter is 6 mm, while beam divergence is below 0.5 mrad. This laser was used with fundamental harmonic at 1064 nm. To increase the power density, i.e. laser fluence, to the level necessary for the realization of a breakdown in evaporated material and creation of plasma, the laser radiation was focused using a lens having focal distance f = 10 cm, settled at lens-target distance, 9 cm, to achieve laser spot diameter at the studied material surface of approximately 1 mm. Using double side glued tape, the copper target was attached to the flat rough plate set on the carrier (Pitch and roll platform AMS 027/M with the manually adjustable angle) connected to the XY stepper motor translation stage controlled by the computer, see photograph in Supplementary file. The MH was mounted onto the plate, evacuated, and a continuous flow of helium was initiated until the desired pressure was established and then maintained during the target irradiation. Following the application of the specified number of laser pulses, the target position was adjusted to expose a fresh surface for subsequent measurements. The dimensions of the created plasma must be small enough to avoid erosion of the in-situ measuring head walls, while ensuring that the plasma emission intensity is sufficiently high to enable reproducible measurements. The shape, position and size of the laser beam spot on the target was monitored using the endoscopic camera, equipped with 6 white LED diodes for illumination. The camera has a diameter of 7 mm and a 5 m long light guide and was connected to the computer. The resolution of the camera is 640 x 480 pixels. Using the collimator, emission from a plasma was collected and transferred to the entrance slit of the imaging spectrometer SOL Instruments MS7504i with a fiber cable. This spectrometer having a four grating turret was used for resolving plasma emission. Spectra recording was performed using CCD Proscan HS 101H camera mounted on the spectrometer direct exit adapter mount. This system enables spectrum recordings with time and spatial resolution needed for plasma diagnostics and LIBS performance studies. Typical spectra obtained in He at 10 mbar, using E = 179 ± 2 mJ at delay of 1 µs and gate of 1 ms with grating of 1200 lines/mm and input slit of 50 µm is presented in Fig. 6 a. It is evident that copper lines dominate the spectrum, while hydrogen lines are absent. Emission lines from Al were not detected in the spectrum also, what served as а clear indication that the plasma wasn’t interacting with the walls of the chamber made of aluminum alloy. The only noticeable helium line, He I at 587.6 nm, exhibits an intensity more than 20 times lower than that of the copper lines. From the spectral region between 740 and 785 nm, as shown in Fig. 6 b, it is evident that the most intense oxygen lines are 50 times weaker than the Cu I lines around 520 nm, while the nitrogen lines at 740 nm are entirely absent. This observation confirms that no detectable amount of air entered the MH interior when the configuration shown in Fig. 4 b was used. Recordings of the resonant copper lines at 520 nm, as shown in Figure 7, confirm that the LIBS plasma generated within the MH exhibits nearly identical analytical capabilities, intensities, and dependence on gas pressure as those observed in a standard LIBS configuration 35 . 3.3. Testing of the laser induced fast pulse discharge (LIFPD) use inside MH Inclusion of the magnets or other parts (for confining LIBS plasma propagation) inside adapter 2 in Fig. 2 is easy to perform. Inserting electrodes inside adapter 2 is, on the contrary, a more demanding task (see Fig. 2 b). MH with electrodes was used to analyze the potential enhancement of analytical capabilities through laser initiated high voltage discharge. The photographs of the: a) electrodes position (illuminated by the endoscopic apparatus) and b) HV discharge realized at voltage of 300 V by discharging capacitors of 6 nF in 10 mbar of He are presented in Supplementary material. The distance between electrodes was 4 mm, while the distance between electrodes and target surface was 6 mm. An eightfold enhancement in the Cu I line intensities in air at atmospheric pressure was observed when comparing LIBS and LIFPD setups (utilizing 100 nF capacitors charged to 5 kV). This significant enhancement is illustrated in Fig. 8 . 4. Conclusion In this work, we developed and tested a novel LIBS setup for in-situ, post-mortem diagnostics of plasma-facing components (PFCs) at random positions within the walls of fusion reactors. This innovative system, designed for larger installations such as those exceeding the size of the Joint European Torus (JET), utilizes a measuring head mounted on a telescopic arm, operated from inside the reactor in between the campaigns. The functional model of the measuring head was comprehensively analyzed, with particular emphasis on its capability to operate at low gas pressures. Three distinct configurations of gas supply and vacuum connections were implemented, supported by specialized elastomer designs for sealing, as detailed in Fig. 4 . Leak rate tests and spectroscopic measurements confirmed the effectiveness of the sealing mechanisms, including the gas curtain configuration, in preventing air ingress into the chamber. Spectroscopic validation, demonstrated by the resonant copper lines at 520 nm, revealed that the LIBS plasma generated within the measuring head achieves analytical performance comparable to that of conventional LIBS setups operating in standard vacuum chambers. Additionally, the system’s adaptability is enhanced by interchangeable adapters, allowing for customization based on the size and shape of the PFC. The incorporation of advanced components, such as electrodes for laser-induced fast pulse discharge, further expands its diagnostic capabilities. This work establishes a robust foundation for the proposed LIBS configuration, with potential extensions to other analytical applications such as laser ablation, arc discharge, and glow discharge setups. Future developments will focus on optimizing these configurations and exploring their application in real-world fusion reactor environments. Declarations Supplementary materials In Supplementary materials the figure of a human operator inside the vacuum vessel of larger fusion machines can be found. The proposed construction of the system incorporating the measuring head described in this work, measuring head during the leakage tests, sealing rings developed, the developed measuring head and photographs of measuring head with additional electrodes are also shown. Acknowledgement The research was funded by the Ministry of Science, Technological Development and Innovations of the Republic of Serbia, Contract numbers: 451-03-47/2023-01/200024, 451-03-47/2023-01/200017, 451-03-47/2023-01/200146, 451-03-66/2024-03/200107 and by the Science Fund of Republic Serbia through NOVA2LIBS4fusion project Grant no. 7753287 within call IDEAS. This work was carried out under the project: NIFS21KLPF087. We also acknowledge Stanko Milanović, our technical associate, who drew all schematic figures of the measuring head. Conflict of Interest Statement The author (authors) has (have) no conflicts to disclose. Author Contributions M. I. – Conceptualization, Funding Acquisition, Methodology, Supervision, Writing/Original draft Preparation N. V. – Investigation, Formal analysis, Writing/Review & Editing I. T. – Investigation, Formal analysis, Visualization, Writing/Review & Editing B. D. S. – Investigation, Writing/Review & Editing M. G. B. – Writing/Review & Editing M. K. – Writing/Review & Editing J. S. – Writing/Review & Editing Data Availability Statement The data that support the findings of this study are available from the corresponding author upon reasonable request. References Mayer M, Möller S, Rubel M, Widdowson A, Charisopoulos S, Ahlgren T, Alves E, Apostolopoulos G, Barradas NP, Donnelly S (2019) Ion Beam Analysis of fusion plasma-facing materials and components: Facilities and Research Challenges. Nucl Fusion 60:025001 Oya Y, Hu C, Fujita H, Yuyama K, Sakurada S, Uemura Y, Masuzaki S, Tokitani M, Yajima M, Hatano Y, Chikada T (2017) Development of H, D, T Simultaneous TDS measurement system and H, D, T retention behavior for DT gas exposed tungsten installed in LHD plasma campaign. Fusion Sci Technol 71:351–356 Kh V, Alimov M, Yajima S, Masuzaki, Tokitani M (2019) Analysis of mixed-material layers deposited on the toroidal array probes during the FY 2012 LHD plasma campaign. Fusion Eng Des 147:111228 Miziolek AW, Palleschi V, Schechter I (eds) (2006) Laser-Induced Breakdown Spectroscopy (LIBS). Fundamentals and Applications. Cambridge University Press, New York Cremers DA, Radziemski LJ (2006) Handbook of Laser-Induced Breakdown Spectroscopy. John Wiley & Sons Ltd, Chichester Noll R (2012) Laser-Induced Breakdown Spectroscopy, Fundamentals and applications. Springer-, Berlin Musazzi S, Perini U (eds) (2014) Laser-Induced Breakdown Spectroscopy Theory and Applications. Springer-, Berlin Heidelberg Singh JP, Thakur SN (2007) Laser-Induced Breakdown Spectroscopy. Elsevier Hahn DW, Omenetto N (2010) Laser-induced breakdown spectroscopy (LIBS), part I: review of basic diagnostics and plasma-particle interactions: Still-challenging issues within the analytical plasma community. Appl Spectrosc 64(12):335–366 Hahn DW (2012) Omenetto Laser-Induced Breakdown Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological Approaches to Material Analysis and Applications to Different Fields. Appl Spectros 66(4):347–419 Palleschi V (2017) If laser-induced breakdown spectroscopy was a brand: some market considerations. Spectrosc Eur 29:6–9 Cai L, Wang Z, Li C, Huang X, Zhao D, Ding H (2019) Development of an in situ diagnostic system for mapping the deposition distribution on PFC of the HL-2M tokamak. Rev Sci Instruments 90:053503 Almaviva S, Caneve L, Colao F, Lazic V, Maddaluno G, Mosetti P, Palucci A, Reale A, Gasior P, Gromelski W, Kubkowska M (2020) LIBS measurements inside the FTU vessel mock-up by using a robotic arm. Fusion Eng Des 157:111685 Zhao D, Li C, Hu Z, Feng C, Xiao Q, Hai R, Liu P, Sun L, Wu D, Fu C, Liu J, Farid N, Ding F, Luo G-N, Wang L, Ding H (2018) Remote in situ laser-induced breakdown spectroscopic approach for diagnosis of the plasma facing components on experimental advanced superconducting tokamak. Rev Sci Instruments 89:073501 Hu Z, Li C, Xiao Q, Liu P, Ding F, Mao H, Wu J, Zhao D, Ding H (2017) Luo and EAST team, Preliminary results of in situ laser-induced breakdown spectroscopy for the first wall diagnostics on EAST. Plasma Sci Technol 19:025502 Hao Z, Deng Z, Liu L, Shi J, He X (2022) Spatial confinement effects of laser-induced breakdown spectroscopy at reduced air pressures. Front Optoelectron 15:12200 Wu H, Wu D, Li C, Liu S, Hu Z, Li Y, Wang X, Bai X, Hai R, Ding H (2023) An approach for measurement of the magnetic field near the surface of plasma-facing components in tokamak by laser induced breakdown spectroscopy based on Zeeman effect. Spectrochim Acta B Spectrosc 207:106755 Vinic M, Ivkovic M (2014) Spatial and Temporal Characteristics of Laser Ablation Combined With Fast Pulse Discharge. IEEE Trans Plasma Sci 42:2598 Saeki M, Iwanade A, Ito C, Wakaida I, Thornton B, Sakka T, Ohba H (2014) Development of a fiber-coupled laser-induced breakdown spectroscopy instrument for analysis of underwater debris in a nuclear reactor core. J Nucl Sci Technol 51:930–938 Qiu Y, Wu J, Li X, Liu T, Xue F, Yang Z, Zhang Z, Yu H (2018) Parametric Study of Fiber-Optic Laser-Induced Breakdown Spectroscopy for Elemental Analysis of Z3CN20-09M Steel from Nuclear Power Plants. Spectrochim Acta B Spectrosc 149:48–56 Rakovský J, Čermák P, Musset O, Veis P (2014) A review of the development of portable laser induced breakdown spectroscopy and its applications. Spectrochim Acta B Spectrosc 101:269–287 Senesi GS, Harmon RS, Hark RR (2020) Field-portable and handheld LIBS: Historical review, current status and future prospects. Spectrochim Acta B Spectrosc 175:106013 Dumitrescu CE, Puzinauskas PV, Olcmen S (2008) Movable fiber probe for gas-phase laser-induced breakdown spectroscopy. Appl Opt 47:G88–G98 Lin Z, Zhang N, Xu Z, Liao J, Yuan H, Chenshen E, Liu J, Li J, Zhao N, Zhang Q (2022) Modified Iterative Wavelets for Background Removal in Laser-Induced Breakdown Spectroscopy Based on Fiber Laser Ablation. J Anal Spectrom 37:2082–2088 Lv C, Zhang N, Lin Z, Ou T, Li J, Zhao N, Yang X, Ma Q, Guo L, Zhang Q (2023) Determination of Copper, Magnesium, and Manganese in Aluminum Alloys Using Laser-Induced Breakdown Spectroscopy Based on Fiber Laser Ablation. J Laser Appl 35:012021 Hang Y-H, Qiu Y, Zhou Y, Liu T, Zhu B, Liao K, Shi M-X, Xue F (2022) Effects of Pulse Energy Ratios on Plasma Characteristics of Dual-Pulse Fiber-Optic Laser-Induced Breakdown Spectroscopy. Chin Phys B 31:024212 Yuan M, Zeng Q, Wang J, Li W, Chen G, Li Z, Liu Y, Guo L, Li X, Yu H (2021) Rapid Classification of Steel via a Modified Support Vector Machine Algorithm Based on Portable Fiber-Optic Laser-Induced Breakdown Spectroscopy. Opt Eng 60:124114 Rajavelu H, Vasa NJ, Seshadri S (2022) Hollow-Core Optical Fiber-Based Laser-Induced Breakdown Spectroscopy Technique for the Elemental Analysis of Pulverized Coal. Appl Phys A 128:868 Zhao Y, Yang H, Harilal SS (2024) Fiberoptic Laser-Induced Breakdown Spectroscopy System for in situ Measurement in a Hazardous Environment. Nucl Technol, 1–12 Allison SW, Gillies GT, Magnuson DW, Pagano TS (1985) Pulsed Laser Damage to Optical Fibers. Appl Opt 24:3140–3145 Pini R, Salimbeni R, Vannini M (1987) Optical Fiber Transmission of High Power Excimer Laser Radiation. Appl Opt 26:4185–4189 Schmidt-Uhlig T, Karlitschek P, Marowsky G, Sano Y (2001) New simplified coupling scheme for the delivery of 20 MW Nd:YAG laser pulses by large core optical fibers. Appl Phys B 72:183–186 Zeng Q, Guo L, Li X, He C, Shen M, Li K, Duan J, Zeng X, Lu Y (2015) Laser-induced breakdown spectroscopy using laser pulses delivered by optical fibers for analyzing Mn and Ti elements in pig iron. J Anal Spectrom 30:403–409 Sankhe ML, Favre A, Sirven J-B, Bultel A, L’Hermite D, Semerok A, Vartanian S, Grisolia C (2023) Development of fibered LIBS device for tokamak Plasma Facing Components characterization. Fusion Eng Des 197:114077 Ivkovic M, Savovic J, Stankov BD, Kuzmanovic M, Traparic I (2024) LIBS depth – profile analysis of W/Cu functionally graded material. Spectrochim Acta B Spectrosc 213:106874 Additional Declarations The authors declare no competing interests. Supplementary Files Supplementarymaterial1.docx Supplementary material Cite Share Download PDF Status: Posted Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6212849","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":427882361,"identity":"2240d9cc-566b-4df3-b8c2-a0d262a5a208","order_by":0,"name":"Milivoje Ivković","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAqklEQVRIiWNgGAWjYBACNiBk+GDAkECaFsYZJGkBaWLmYSBFC59EWuJjm4I7eQzshx8wV/whxg6JtMPGOQbPihl40gwYz7YRo4XneJt0jsHhxAaGHAbGxgbitLT/tgBp4X/DwNhAlMPY244xM4C0SABtaWAjTkuyZA/QL2wSzwwONhLjF/lmNsMPP/7cyePnT374kCiHQcEBUCIAkiQAkhSPglEwCkbBSAMAo24w8cAPnMgAAAAASUVORK5CYII=","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":true,"prefix":"","firstName":"Milivoje","middleName":"","lastName":"Ivković","suffix":""},{"id":427882362,"identity":"90fa7b31-b7fd-435d-b487-04db56552f19","order_by":1,"name":"Nikola Vujadinović","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Nikola","middleName":"","lastName":"Vujadinović","suffix":""},{"id":427882363,"identity":"5a5039a4-781d-4710-9b44-65d3147875f8","order_by":2,"name":"Ivan Traparić","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Ivan","middleName":"","lastName":"Traparić","suffix":""},{"id":427882364,"identity":"a929e86c-350b-4cf4-9dae-70f8bb4977d8","order_by":3,"name":"Biljana D. Stankov","email":"","orcid":"","institution":"Institute of Physics Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Biljana","middleName":"D.","lastName":"Stankov","suffix":""},{"id":427882365,"identity":"fa30b2d0-4066-43d9-ad10-e4fca954bd53","order_by":4,"name":"Marijana Gavrilović Božović","email":"","orcid":"","institution":"Faculty of Engineering, University of Kragujevac","correspondingAuthor":false,"prefix":"","firstName":"Marijana","middleName":"Gavrilović","lastName":"Božović","suffix":""},{"id":427882366,"identity":"4b04679f-2e41-4ea6-a2bb-146d60a36be4","order_by":5,"name":"Miroslav Kuzmanović","email":"","orcid":"","institution":"Faculty of Physical Chemistry, University of Belgrade","correspondingAuthor":false,"prefix":"","firstName":"Miroslav","middleName":"","lastName":"Kuzmanović","suffix":""},{"id":427882367,"identity":"5664ba9b-84f0-4a4d-8c16-f3103f8d6f3d","order_by":6,"name":"Jelena Savović","email":"","orcid":"","institution":"Vinca Institute of Nuclear Sciences","correspondingAuthor":false,"prefix":"","firstName":"Jelena","middleName":"","lastName":"Savović","suffix":""}],"badges":[],"createdAt":"2025-03-12 14:13:47","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6212849/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6212849/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":78637866,"identity":"b304775b-6519-48a2-b255-1ed50d74ee7a","added_by":"auto","created_at":"2025-03-17 05:42:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1091122,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eIn situ LIBS diagnostics of the first wall of the fusion reactor. MH - measuring head,\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eRC - remote control, MU - main unit carrying power supply.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig1MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/fb3b9c579b6ba30482e1c67b.png"},{"id":78637869,"identity":"9f29434b-6359-4fa2-a941-9014e625f535","added_by":"auto","created_at":"2025-03-17 05:42:29","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":939014,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMeasuring head schematics. (1) main chamber, (2) adapter to the component being analyzed and (3) upper body with windows and connections, (4) metallic foil or isolating ring, (5) isolator and (6) electrode connections used for discharge enhanced low-pressure operation testing. A) space for complex shape elastomer, B) space for O ring, G) groove between main chamber and adapter, while PA and PB are ports for gas inlet or vacuuming. Figure b) shows main chamber with additional electrodes from opposite cross section\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig2MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/42dbcf6de59618c06d21ded7.png"},{"id":78639356,"identity":"4d56573c-2d28-4163-b08b-0e8722d4d668","added_by":"auto","created_at":"2025-03-17 06:06:29","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":33791,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eUpper body of the measuring head schematics a) laser port windows, b) window tightening screw, c) fiber ferrules for fiber mounting and d) additional ports with M6 metric screw threads and 3) DN63 standard vacuum connection body.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig3MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/6bdfe77e2617126381048ff8.png"},{"id":78637871,"identity":"c5c66ec9-692d-4b77-9797-2df586e48ff2","added_by":"auto","created_at":"2025-03-17 05:42:29","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":931293,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eVersions of the measuring head main body connections to the PFC surface\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ea)\u003c/em\u003e \u003cem\u003egasket with force applied at the edge - vacuuming inside groove – PA in Fig 4.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eb)\u003c/em\u003e \u003cem\u003evacuuming through big groove PA and low p gas supply at top of vacuum chamber - PB\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ec)\u003c/em\u003e \u003cem\u003ehigh p gas through PA and big groove (gas curtain), vacuuming at top of chamber - PB\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig4MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/be7fb1b1f9a9294b40521900.png"},{"id":78640088,"identity":"220ae3bb-b104-4e3c-b027-8a70e5e92867","added_by":"auto","created_at":"2025-03-17 06:14:30","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":412208,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eExperimental setup used for the spectroscopic testing of the MH functional model.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig5MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/02f23e3b8951251f05933b74.png"},{"id":78639361,"identity":"ca84bf3b-fb92-4e93-a65e-18988d54a468","added_by":"auto","created_at":"2025-03-17 06:06:30","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":121920,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) The spectrum of the copper target recorded inside the MH (left) and (b) region of spectrum with strongest nitrogen and oxygen lines (right).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig6MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/5af33e44d648fd83a6fd7795.png"},{"id":78637876,"identity":"a627cd08-9d86-4b03-9a91-190d8cb6770c","added_by":"auto","created_at":"2025-03-17 05:42:30","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":1290875,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eRecordings of the resonant copper lines at 520 nm at various gas pressures.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"fig7MH.png","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/782c605bb1c85ad324c9970e.png"},{"id":78640091,"identity":"343789a5-723c-4f5e-bd7f-f1ef0d5c96b6","added_by":"auto","created_at":"2025-03-17 06:14:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4888872,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/4231e4bc-114a-4e83-8d82-d6d7f8fcfc4a.pdf"},{"id":78637873,"identity":"bed12e71-c40d-42d1-9797-3d3e9934a93b","added_by":"auto","created_at":"2025-03-17 05:42:30","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3801199,"visible":true,"origin":"","legend":"\u003cp\u003eSupplementary material\u003c/p\u003e","description":"","filename":"Supplementarymaterial1.docx","url":"https://assets-eu.researchsquare.com/files/rs-6212849/v1/288aca8767b93273ae1e9b64.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eFunctional model of the measuring head for the plasma fusion reactor wall diagnostics using low pressure, laser induced breakdown setup at random positions\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eDuring the preparation and operation of the fusion reactors, the plasma facing components PFC\u0026rsquo;s face significant challenges due to exposure to thermal loads, neutrons, and plasma. These conditions can lead to a range of detrimental effects, including recrystallization, cracks, melting, dust formation, defects, transmutation, sputtering, hydrogen retention, helium induced morphological changes etc. To minimize the risk of an unexpected PFC failure, it is crucial to conduct thorough material composition characterization.\u003c/p\u003e \u003cp\u003eThe diagnostics of PFCs is critically important for the safe and reliable operation of fusion reactors. There is substantial literature, and a variety of applied techniques published in this field. In this discussion, we will focus exclusively on state-of-the-art research, highlighting the most relevant and recent papers that describe primary approaches.\u003c/p\u003e \u003cp\u003eIon Beam Analysis (IBA) methods\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e are an ex-situ approach that involves the demounting or cutting of plasma-facing component (PFC) samples. This family of techniques encompasses nine major methods, including nuclear reaction analysis, elastic recoil detection analysis (with high-energy heavy ion variants), Rutherford backscattering spectrometry, non-Rutherford elastic backscattering spectrometry, medium energy ion scattering, particle-induced X-ray and gamma-ray emission, and accelerator mass spectrometry.\u003c/p\u003e \u003cp\u003eAnother ex-situ method is Thermal Desorption Spectroscopy (TDS), which involves placing mirror-finished disk-type tungsten samples at specific locations on the plasma-facing wall of devices like the Large Helical Device (LHD) at NIFS in Japan\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. After demounting, these samples are analyzed using a quadruple mass spectrometer to evaluate the desorption behavior of hydrogen isotopes.\u003c/p\u003e \u003cp\u003eEffective method for PFC characterization is Laser Induced Breakdown Spectroscopy, LIBS, which provides highly sensitive and rapid multi-element analysis with minimal destructiveness. This technique relies on the interactions of the focused laser beam with the material, which results in localized heating, melting and evaporation. The charged particles, present in the evaporated material, cause electric breakdown and formation of plasma. The created plasma emits radiation, having spectral lines of all target constituents. By recording this emitted radiation, LIBS enables detailed analysis of material composition, making it a valuable tool in the assessment of PFCs in fusion reactors. This analytical spectroscopy technique is well described in many books and review articles\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. The distinctive attributes of laser radiation have significantly enhanced analytical methods for material characterization. LIBS is an elemental analytical technique that does not require any sample treatment, unlike inductively-coupled plasma\u0026ndash;optical emission spectroscopy\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. It can analyze non-conducting samples, which Spark Optical Emission Spectroscopy cannot, and it is not restricted to heavy elements, as is the case with X-ray fluorescence. Additionally, LIBS is considered an environmentally friendly analytical method, as it operates solely with light and collects only photons, eliminating the need for chemicals and producing no waste. Furthermore, as a minimally invasive and non-contact technique, LIBS allows for multi-element analysis and even depth profiling without the need for sample preparation, making it an appealing option for a wide range of applications.\u003c/p\u003e \u003cp\u003eLIBS has a vast array of applications, including the preservation of cultural heritage, forensics, environmental protection (such as \"contactless\" waste sorting), and the analysis of biomaterials.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMaterial characterization by the LIBS may enable prevention of fusion reactor damage by providing a tool for early detection of PFC defects caused by retention of reactor fuel and/or by neutron activation produced radio nuclides. Even though LIBS has been recognized as the strongest candidate for this demanding task, the configurations proposed so far do not fully meet the requirements for PFC diagnostics\u003c/p\u003e \u003cp\u003eIn-situ analyses using LIBS are conducted through a single port on the fusion reactor\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e. This technique utilizes a molybdenum mirror positioned inside the reactor, allowing the laser beam to be directed at different PFCs within a single poloidal cross-section of the machine. In-situ analysis of PFCs\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e can be achieved using a robotic arm (RA) as part of the Frascati Tokamak Upgrade (FTU) project. With an accuracy of approximately\u0026thinsp;\u0026plusmn;\u0026thinsp;1 mm, the robotic arm can probe any point within the vacuum vessel while maintaining consistent detection performance. It also has the capability to introduce gases to the sample surface, enabling measurements under varying background gas conditions.\u003c/p\u003e \u003cp\u003eThe aim of this work is to enhance the performance of the LIBS technique to achieve sensitivity levels comparable to those of IBA\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e and TDS\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Compared to these methods, LIBS offers more straightforward implementation, eliminating the need for complex computer codes essential for analyzing and interpreting IBA spectra, with possibility for in-situ operation.\u003c/p\u003e \u003cp\u003eIn this paper, we present a configuration with various adapters that are both more cost-effective and easier to operate than the robotic arm system\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Additionally, our approach allows for the use of gases at low pressures, which is more optimal for LIBS operation compared to the prior method of gas fluxing. The proposed LIBS configuration enables the examination of each component at any location on the PFC. This configuration could facilitate analysis of nearly the entire surface area of a fusion device. For tokamaks lacking toroidal symmetry\u0026mdash;such as those with individual poloidal limiters\u0026mdash;or for stellarators, analyzing multiple poloidal cross-sections may be necessary, a requirement that earlier approaches\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e cannot fulfill. Our proposed in-situ analysis will eliminate the need for extrapolation in toroidal symmetry tokamaks and enable comprehensive multi-point studies, even in stellarators. This improvement will enhance analytical performance compared to the robotic system, which requires significantly larger funding and research and development teams. The proposed system for post-mortem analysis of PFCs during maintenance periods utilizes an in-situ LIBS configuration, positioning the operator inside the fusion reactor. This work will provide detailed analysis of requirements for such a configuration, along with the construction, testing, and use of a functional model of measuring head.\u003c/p\u003e"},{"header":"2. LIBS system","content":"\u003cp\u003eConsidering the enhanced dimensions of new plasma fusion reactors, we propose an alternative to the previously used LIBS systems\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e14\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. We advocate for a configuration operated by a person inside the reactor, enabling real-time in-situ diagnostics of PFCs at nearly any location, as depicted in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. Namely, having in mind dimensions of plasma fusion reactors (JET and bigger) the operator (instead of the robot) may move in device interior and visually inspect PFC to select for and perform the examination of any part (see also photos in Supplementary material). It must be underlined here that our ambition is not to enable in-situ operation without any protection, as somebody may conclude from the Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. This figure only illustrates our configuration, showing comparison of the operator with the size of the JET (much smaller than ITER and not working with Be and T). Due to presence of the Be dust and radioactivity of tritium in PFC, the operators, who will probably use our configuration for in-situ operation, must wear air inflated hoods equipped with a filter, disposable coveralls, rubber boots with overshoes and several pairs of gloves including a sacrificial top layer which is changed periodically (as in handling Be or T contaminated PFC demounted from reactor).\u003c/p\u003e\n\u003cp\u003eThe proposed LIBS system, besides operator, includes a measuring head (MH), remote control (RC) and main unit (MU), marked in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The operator positions the measuring head with the help of the telescopic arm, see photograph in Supplementary material.\u003c/p\u003e\n\u003cp\u003eConstruction of the measuring head is the main subject of this research, and it is described in Section \u003cspan class=\"InternalRef\"\u003e2.1\u003c/span\u003e., while the other LIBS system components necessary for MH operation are analyzed in Section \u003cspan class=\"InternalRef\"\u003e2.2\u003c/span\u003e.\u003c/p\u003e\n\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1. Measuring head construction\u003c/h2\u003e\n\u003cp\u003eIn this work, a functional model of measuring head for work under low gas pressure conditions was constructed and shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The MH consists of three parts: main chamber (1), adapter to the component being analyzed (2) and upper body with windows and connections (3), all marked in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n\u003cp\u003eThe role of the main chamber of the measuring head is to prevent air intake and establish low pressure conditions. The space in which the low-pressure conditions were established in this functional model has dimensions \u003cem\u003eϕ\u003c/em\u003e5 cm x 4.5 cm, see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e. The outer diameter of the main chamber is 10 cm. If the dimensions of the main chamber exceed those of the PFC to be analysed, the proposed adapter (2) must be redesigned to ensure proper vacuum sealing. Namely, the adapter (2) may also have two parts: one for threading into the main chamber and an additional one that can be rectangular and even have the curvature at the bottom (which will follow the curvature of the PFCs under analysis).\u003c/p\u003e\n\u003cp\u003eAt the upper end of adapter (2) there is a 5 mm annular rim that has a purpose to settle, easily removable metallic foil or glass or ceramic ring, (4) in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e which covers main chamber inner wall. The purpose of these components is to prevent propagation of plasma to the sealing components on the chambers\u0026rsquo; bottom and/or to prevent deposition of evaporated target on chamber walls. Namely, deposits on the wall may cause memory effects and wrong results of target analysis, if due to small chamber dimensions, plasma reaches and reacts with his walls. In the chamber wall there are two ports (PA and PB) for vacuuming, gas supply and gas pressure measuring instruments.\u003c/p\u003e\n\u003cp\u003eThe roles of PA and PB depend on the chosen sealing approach and will be detailed in Section \u003cspan class=\"InternalRef\"\u003e2.1.1\u003c/span\u003e, along with the functions of the 30 mm deep and 5 mm wide groove G between components (1) and (2), as well as the two additional small grooves (A and B) at the bottom of the chamber (see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eThe MH chamber\u0026rsquo;s upper body (3 in Figs.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) based on the standard DN63 vacuum connection flange, has one central opening and four radially spaced openings in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e for carrying optical windows, (a) in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Two of them are intended to be used for transmitting lasers radiation, one is for collecting emitted radiation and one for the illumination and observation using endoscope. The optical windows (a) are tightened using additional O ring and screws, while (c) are ferrules for fiber cable mounting. This flange (3) has also four additional ports (d in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e) with M6 metric screw thread. These ports can be used for: a) vacuum, b) gas supply, or c) high voltage connections, d) aiming beam entrances or e) spare.\u003c/p\u003e\n\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\n\u003ch2\u003e2.1.1. Measuring head sealings\u003c/h2\u003e\n\u003cp\u003eThe sealing mechanisms of the measuring head are critical to maintain the required low-pressure conditions and prevent contamination from external gases. At the beginning of each analysis, the measuring head should be positioned and roughly attached and sealed to the PFC. Several versions of the measuring head sealing mechanism for the PFC surface were constructed and tested in this work, as illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Since these components are symmetric, only the left half of the cross-section is shown. The simplest configuration utilizes a thin gasket (highlighted in red in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) with an inner diameter exceeding 50 mm and an outer diameter of up to 100 mm (see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea). This gasket design is primarily intended for use with surrounding gases other than air, at elevated pressures above 10 mbar or even exceeding one bar (as in\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e), where small amounts of air inlet are not critical. In this configuration, it is important to apply additional force (indicated by the arrow in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea) to secure the measuring head against the PFC surface. The gas inlet is located at port PB, while port PA serves as the vacuum outlet. Tests of this setup, (by using both ports, PA and PB for vacuuming only) as shown in the Supplementary Material, demonstrated the ability to achieve pressures below 1 mbar within the main chamber, confirming its effectiveness.\u003c/p\u003e\n\u003cp\u003eThe sealing mechanism designed for situations where the PFC surface is uneven but lacks significant scratches or deep channels is illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb. In this design, the grooves at the bottom of the measuring head play distinct roles. The small outer groove (A, as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) houses the primary elastomer, effectively preventing the ingress of air and the egress of working gas. The smaller inner groove (B) accommodates an O-ring, which restricts gas flow from the vacuum chamber\u0026rsquo;s interior without directly contacting the PFC surface.\u003c/p\u003e\n\u003cp\u003eVacuuming is achieved through the main groove (indicated by the arrow in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb) and port PA, while gas supply is introduced via the outer port PB, similar to the configuration in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea. Low-pressure gas adjustment was carefully managed using a gas mass flow controller, with corrections applied based on voltage output from a capacitive manometer. This setup ensured optimal gas pressure within the measuring head, even when minor leakage occurred due to a rough PFC surface. The manometer connection was strategically placed at the center of the main chamber to ensure accurate pressure monitoring. Details of the specialized elastomer type and shape, critical to this configuration, will be discussed later in the text. In configuration, shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec, gas flow at pressure greater than atmospheric creates so-called \u0026ldquo;gas-curtain\u0026rdquo; and prevent air to reach main chamber. The elastomer in groove B, see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e limits this high flow of gas to the main chamber and provides contact with the PFC surface, meaning it has a same purpose as in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb, but gas goes in opposite direction. The mass flow controller-manometer loop enables constant gas pressure inside the main chamber.\u003c/p\u003e\n\u003cp\u003eSometimes the PFC has such shape that MH cannot easily be attached to it. In that case, the plan is to use the inner component i.e. adapter which has upper part with screw for connection to the outer; see part 2 in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, while the bottom part has a shape, which corresponds to the PFC. Namely, not only the cross section of adapter should correspond to the dimensions of the PFC, but also should correspond to their curvature. Such version of MH can be used with any of the former gasket designs, but the distance between elastomer B must be carefully adjusted.\u003c/p\u003e\n\u003cp\u003eIn addition, adapters can be made to contain other components needed for spatially confined\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, magnetically confined\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, or discharge enhanced LIBS\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Adaptation of the proposed configuration of the measuring head to be used as a laser ablation cell, arc, glow discharge or similar analytical technology setups is also in progress.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003e2.1.2. Elastomer requirements\u003c/h2\u003e\n\u003cp\u003eIn any of the studied versions of the measuring head the selection of the type and shape of the elastomer has a significant importance. The elastomer selection depends on several factors. These include temperature range, pressure range, integrity of sealing required, material of counter faces, life requirement, maintenance requirements, assembly methods, degree of flexibility and many others. Also, individual material classes achieve a satisfactory seal by quite different mechanisms, and it is necessary to take this into account at the selection and design stage.\u003c/p\u003e\n\u003cp\u003eO-rings are by far the most common form of elastomer seal, and we use it at the inner part of the MH i.e. as adapter\u0026rsquo;s elastomer B, see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec. They are relatively easy to manufacture, readily available in standard sizes and there are many standards and guides to facilitate design. However, they do have several limitations, and hence an alternative style of seal is considered to achieve improved performance. The complex shape of the elastomer A, as well as the photograph of the used elastomers are shown in Supplementary material. The shape is chosen to satisfy the appropriate filling of gap A to enable sealing and to have as long possible tail (from gap A to the exterior of the main chamber) to enhance sealing capacity by prolonged contact to PFC surface. It should be stressed that for that purpose the tool for manufacturing such an elastomer shape from four different materials was also constructed.\u003c/p\u003e\n\u003cp\u003eAs an elastomer material we tested: silicone rubber, Q, having hardness of 40 Shore, nitrile butadiene rubber, NBR with 70 Shore hardness and two natural rubbers NR, with hardness of 45 and 55 Shore. All sealing rings B in this MH functional model have the same dimensions i.e. 118 x 83 x 8.5 mm. Elastomer B drawing and photograph of the realized sealant together with the tool for their production was presented in Supplementary material. Due to PFC surface roughness, the better results are performed with mandatory application of silicone, hydrocarbon or perfluoropolyether high vacuum grease. Choice of grease depends on PFC and analysis type.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2. Remote control and main unit design\u003c/h2\u003e\n\u003cp\u003eAs can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, the main components besides measurement head are a telescopic arm, remote-control RC and main unit. The flexible telescopic arm carries tubing for a gas supply and vacuuming. The length of all cables (which may be even ten meters long)\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e should be changed, in accordance with the distance between operator and PFC under investigation. Therefore, the LIBS system must also have a winder for these tubing\u0026rsquo;s, as well as for the electric and fiber optic cables.\u003c/p\u003e\n\u003cp\u003eThe RC should enable wireless communication between the operator and the main control room. In addition, the RC should enable video surveillance, i.e. must have a display for receiving a picture from the endoscopic inspection camera, mounted on the measuring head. The endoscopic system should also have a possibility to illuminate the interior of the MH by corresponding LED's.\u003c/p\u003e\n\u003cp\u003eDepending on the reactor and application, the main unit, MU can be installed in the fusion reactor control room or on the cart pulled by the operator. In both cases, the physical connection to the fusion reactor vacuum system, gas handling system and mains supply must be provided. As an option (due to the small MH volume) a small vacuum pump and one liter gas cylinder (enough due to the use of the low gas pressure) can be settled on the cart carrying other equipment.\u003c/p\u003e\n\u003cp\u003eBesides these external connections, the lasers (one or two for double pulsed LIBS) with their power supplies and optics for coupling laser radiation to fiber optic cables, should be settled in the MU. The MU also should have a spectrometer equipped with a detection system (ICCD and/or CCD cameras), camera interface i.e. connections to the computer and corresponding optics for coupling optical radiation from fiber optic cable to spectrometer (F-matcher), AC and DC voltage power supply for all equipment etc. The principle and details about requirements on remote controlled power supply system and optimized control system for the laser can be found in Ref. 14. Depending on the application, various spectrometers can be used. For hydrogen isotope retention studies high resolution spectrometers (R\u0026thinsp;\u0026gt;\u0026thinsp;20 000) must be used, while for other studies, echelle and segmented spectrometers have certain advantages due to covering a whole, or big part of the emitted spectrum.\u003c/p\u003e\n\u003cp\u003eThe simplest LIBS systems, capable of diagnosing the state of various components within plasma fusion reactors, can be based on field-portable (fpLIBS) or handheld (hLIBS) configurations\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. However, the incorporation of a laser within these probes results in reduced sensitivity due to energy constraints linked to size and weight limitations. To enhance analytical capabilities, we propose a fiber optic LIBS configuration, omitting the laser from the measuring head, as referenced in [Ref. 23\u0026ndash;28 and references therein]. In proposed main unit or measuring heads the optical setups are the same as used in fpLIBS and hLIBS probes, see Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. in Ref. 24. The only difference between the optical setups for fpLIBS and hLIBS and the proposed one is the settling lasers in the MU (followed by) (and) the use of the fiber optic cable for transmitting laser radiation.\u003c/p\u003e\n\u003cp\u003eThe selection of fibers for collecting laser induced plasma radiation is a very common task and mainly depends on type of analysis. For example, for hydrogen isotope retention studies the necessity for high resolution (i.e. use of the narrow slit) and low intensity of Balmer alpha line favors the use of the fiber bundle with circular arrangement at the entrance and linear arrangement at the exit (to coincide with slit height). The selection of fiber for transmitting laser radiation is, on the contrary, a very demanding task. Namely, it is shown that coupling a laser beam to a fiber may produce permanent damage\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e even at laser energies 14 mJ (10 J/cm2) using hard clad quartz silica HCS fibers. Therefore, very low laser energies or complex fiber couplers and fibers having diameter at least 0.6 mm should be used\u003csup\u003e\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e,\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. The use of higher energies lasers requires fiber bundles with beam homogenizers in front of them, or use of hollow core fibers with gas circulation through them. Necessity for using diverging beams, i.e. focus position in front of fiber entrance also requires gas circulation to prevent formation of the laser induced spark, which may destroy fiber. For applications requiring higher Nd: YAG laser energies, or the use of TEA CO\u003csub\u003e2\u003c/sub\u003e lasers, an articulated arm with 6 to 8 rotatable joints becomes the most viable solution. Precise alignment of the laser beam at the fiber center is crucial and can be achieved using an x-y-z movable holder for accurate adjustments. The same fiber coupler design, excluding gas inlet and outlet features, should be employed at both ends of the irradiation and collection fibers, with identical x-y-z adjustment mechanisms to ensure optimal performance and alignment.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Experimental testing","content":"\u003cp\u003eAs discussed in Section \u003cspan class=\"InternalRef\"\u003e2.1\u003c/span\u003e, LIBS achieves superior analytical performance when operating in a vacuum or at low gas pressures. Consequently, enabling low-pressure LIBS operation was a primary objective. To evaluate the effectiveness of this approach, experimental testing of the measuring head (MH) sealing was conducted using the configurations outlined in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. Sealant rings made from various elastomer materials were designed, manufactured, and tested. The testing involved determining the leakage rates of different elastomer types across various surface conditions to assess their sealing efficiency. Additionally, spectroscopic testing was performed to verify the absence of air within the MH chamber, estimate contamination levels, evaluate the analytical capabilities of the proposed setup, and investigate the potential for incorporating high-voltage discharges within the MH to enhance the LIBS signal. These evaluations provided valuable insights into the performance and reliability of the proposed low-pressure LIBS configuration.\u003c/p\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Leakage rate testing\u003c/h2\u003e\n \u003cp\u003eFor leakage rate testing the MH was connected at\u0026nbsp;both PA and PB ports (see Figure 4a) to the rotary vane vacuum pump Alcatel 2012A having vacuuming speed of 15 m\u003csup\u003e3\u003c/sup\u003e/h. Then the MH was placed to different surfaces, evacuated to pressures less than 0.1 mbar and then disconnected from the vacuum pump using gate valve. The pressure was measured using the Leybold Heraeus DV 1000 manometer placed between MH and the valve. The time required for the pressure inside the chamber to increase to 10 mbar was measured for MH placed to the surfaces of the: a) brick, stone with and without vacuum grease, b) rough and c) polished metal and d) varnished wood. The results using red colored silicone Q rubber having hardness of 40 Shore and black colored nitrile butadiene rubber, NBR, having hardness of 70 Shore are presented in Table 1. The results for the other two elastomers are within experimental error and therefore are not presented in Table 1, thus also showing that for this application the elastomer hardness is a dominant parameter. The leakage rate in the table was estimated assuming the MH inner volume of 88 cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eTable 1. Experimental testing of different elastomers.\u003c/em\u003e\u003c/p\u003e\n\u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElastomer type\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSurface\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003etime [s]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ecm\u003csup\u003e3\u003c/sup\u003e/s\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ebar cm\u003csup\u003e3\u003c/sup\u003e/s\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"5\"\u003e\n \u003cp\u003eSilicone rubber Q Red 40 Shore\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ebrick, stone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ebrick with grease\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e210\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e42.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erough metal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e270\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e33.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ewood varnished\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e300\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epolished metal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e330\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" rowspan=\"4\"\u003e\n \u003cp\u003eNitrile butadiene rubber\u003c/p\u003e\n \u003cp\u003eNBR black 70\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ebrick, stone\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ewood varnished\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e310\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erough metal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003epolished metal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e330\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eFrom these measurements we concluded that, for the rough surfaces, the NBR 70 Shore is the better solution, and it was used in all further investigations. For the porous surfaces the rubber with a 40 Shore was the better solution. In addition, it is clear that the pumping speed of used vacuum pump may enable constant pressure inside the MH chamber. It is also concluded that usage of the high vacuum grease considerably decreases the leakage rate but should be used with precaution i.e. cleaned from the PFC to prevent possible reactor contamination.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Spectroscopic testing\u003c/h2\u003e\n \u003cp\u003eThe prevention and testing of MH interior contamination was a more difficult problem. Namely, any leakage from the surrounding atmosphere may introduce air constituents (for example water vapor) which may influence measurement results. Therefore, spectral purity was studied. The configuration used for spectroscopical testing consists of the: a) Nd: YAG laser; b) optical elements for focusing the laser radiation onto the studied material surface, and for collecting emission from the created plasma, and c) spectrometer with camera for optical emission recording and saving by computer, see Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eThe Nd: YAG laser which was used for heating and ablating the target was Quantel model QSmart 450. This laser has maximal energy E\u003csub\u003eYAG\u003c/sub\u003e of 450 mJ, pulse duration of 6 ns and repetition frequency of 10 Hz. The beam diameter is 6 mm, while beam divergence is below 0.5 mrad. This laser was used with fundamental harmonic at 1064 nm. To increase the power density, i.e. laser fluence, to the level necessary for the realization of a breakdown in evaporated material and creation of plasma, the laser radiation was focused using a lens having focal distance f\u0026thinsp;=\u0026thinsp;10 cm, settled at lens-target distance, 9 cm, to achieve laser spot diameter at the studied material surface of approximately 1 mm. Using double side glued tape, the copper target was attached to the flat rough plate set on the carrier (Pitch and roll platform AMS 027/M with the manually adjustable angle) connected to the XY stepper motor translation stage controlled by the computer, see photograph in Supplementary file. The MH was mounted onto the plate, evacuated, and a continuous flow of helium was initiated until the desired pressure was established and then maintained during the target irradiation. Following the application of the specified number of laser pulses, the target position was adjusted to expose a fresh surface for subsequent measurements. The dimensions of the created plasma must be small enough to avoid erosion of the in-situ measuring head walls, while ensuring that the plasma emission intensity is sufficiently high to enable reproducible measurements. The shape, position and size of the laser beam spot on the target was monitored using the endoscopic camera, equipped with 6 white LED diodes for illumination. The camera has a diameter of 7 mm and a 5 m long light guide and was connected to the computer. The resolution of the camera is 640 x 480 pixels.\u003c/p\u003e\n \u003cp\u003eUsing the collimator, emission from a plasma was collected and transferred to the entrance slit of the imaging spectrometer SOL Instruments MS7504i with a fiber cable. This spectrometer having a four grating turret was used for resolving plasma emission. Spectra recording was performed using CCD Proscan HS 101H camera mounted on the spectrometer direct exit adapter mount. This system enables spectrum recordings with time and spatial resolution needed for plasma diagnostics and LIBS performance studies.\u003c/p\u003e\n \u003cp\u003eTypical spectra obtained in He at 10 mbar, using E\u0026thinsp;=\u0026thinsp;179\u0026thinsp;\u0026plusmn;\u0026thinsp;2 mJ at delay of 1 \u0026micro;s and gate of 1 ms with grating of 1200 lines/mm and input slit of 50 \u0026micro;m is presented in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea. It is evident that copper lines dominate the spectrum, while hydrogen lines are absent. Emission lines from Al were not detected in the spectrum also, what served as а clear indication that the plasma wasn\u0026rsquo;t interacting with the walls of the chamber made of aluminum alloy. The only noticeable helium line, He I at 587.6 nm, exhibits an intensity more than 20 times lower than that of the copper lines.\u003c/p\u003e\n \u003cp\u003eFrom the spectral region between 740 and 785 nm, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003eb, it is evident that the most intense oxygen lines are 50 times weaker than the Cu I lines around 520 nm, while the nitrogen lines at 740 nm are entirely absent. This observation confirms that no detectable amount of air entered the MH interior when the configuration shown in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb was used.\u003c/p\u003e\n \u003cp\u003eRecordings of the resonant copper lines at 520 nm, as shown in Figure 7, confirm that the LIBS plasma generated within the MH exhibits nearly identical analytical capabilities, intensities, and dependence on gas pressure as those observed in a standard LIBS configuration\u003csup\u003e35\u003c/sup\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Testing of the laser induced fast pulse discharge (LIFPD) use inside MH\u003c/h2\u003e\n \u003cp\u003eInclusion of the magnets or other parts (for confining LIBS plasma propagation) inside adapter 2 in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e is easy to perform. Inserting electrodes inside adapter 2 is, on the contrary, a more demanding task (see Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). MH with electrodes was used to analyze the potential enhancement of analytical capabilities through laser initiated high voltage discharge.\u003c/p\u003e\n \u003cp\u003eThe photographs of the: a) electrodes position (illuminated by the endoscopic apparatus) and b) HV discharge realized at voltage of 300 V by discharging capacitors of 6 nF in 10 mbar of He are presented in Supplementary material.\u003c/p\u003e\n \u003cp\u003eThe distance between electrodes was 4 mm, while the distance between electrodes and target surface was 6 mm. An eightfold enhancement in the Cu I line intensities in air at atmospheric pressure was observed when comparing LIBS and LIFPD setups (utilizing 100 nF capacitors charged to 5 kV). This significant enhancement is illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this work, we developed and tested a novel LIBS setup for in-situ, post-mortem diagnostics of plasma-facing components (PFCs) at random positions within the walls of fusion reactors. This innovative system, designed for larger installations such as those exceeding the size of the Joint European Torus (JET), utilizes a measuring head mounted on a telescopic arm, operated from inside the reactor in between the campaigns.\u003c/p\u003e \u003cp\u003eThe functional model of the measuring head was comprehensively analyzed, with particular emphasis on its capability to operate at low gas pressures. Three distinct configurations of gas supply and vacuum connections were implemented, supported by specialized elastomer designs for sealing, as detailed in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. Leak rate tests and spectroscopic measurements confirmed the effectiveness of the sealing mechanisms, including the gas curtain configuration, in preventing air ingress into the chamber.\u003c/p\u003e \u003cp\u003eSpectroscopic validation, demonstrated by the resonant copper lines at 520 nm, revealed that the LIBS plasma generated within the measuring head achieves analytical performance comparable to that of conventional LIBS setups operating in standard vacuum chambers. Additionally, the system\u0026rsquo;s adaptability is enhanced by interchangeable adapters, allowing for customization based on the size and shape of the PFC. The incorporation of advanced components, such as electrodes for laser-induced fast pulse discharge, further expands its diagnostic capabilities.\u003c/p\u003e \u003cp\u003eThis work establishes a robust foundation for the proposed LIBS configuration, with potential extensions to other analytical applications such as laser ablation, arc discharge, and glow discharge setups. Future developments will focus on optimizing these configurations and exploring their application in real-world fusion reactor environments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eSupplementary materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn Supplementary materials the figure of a human operator inside the vacuum vessel of larger fusion machines can be found. The proposed construction of the system incorporating the measuring head described in this work, measuring head during the leakage tests, sealing rings developed, the developed measuring head and photographs of measuring head with additional electrodes are also shown.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe research was funded by the Ministry of Science, Technological Development and Innovations of the Republic of Serbia, Contract numbers: 451-03-47/2023-01/200024, 451-03-47/2023-01/200017, 451-03-47/2023-01/200146, 451-03-66/2024-03/200107 and by the Science Fund of Republic Serbia through NOVA2LIBS4fusion project Grant no. 7753287 within call IDEAS. This work was carried out under the project: NIFS21KLPF087. We also acknowledge Stanko Milanović, our technical associate, who drew all schematic figures of the measuring head.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author (authors) has (have) no conflicts to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eM. I. – Conceptualization, Funding Acquisition, Methodology, Supervision, Writing/Original draft Preparation\u003c/p\u003e\n\u003cp\u003eN. V. – Investigation, Formal analysis, Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eI. T. – Investigation, Formal analysis, Visualization, Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eB. D. S. – Investigation, Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eM. G. B. – Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eM. K. – Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003eJ. S. – Writing/Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMayer M, M\u0026ouml;ller S, Rubel M, Widdowson A, Charisopoulos S, Ahlgren T, Alves E, Apostolopoulos G, Barradas NP, Donnelly S (2019) Ion Beam Analysis of fusion plasma-facing materials and components: Facilities and Research Challenges. Nucl Fusion 60:025001\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOya Y, Hu C, Fujita H, Yuyama K, Sakurada S, Uemura Y, Masuzaki S, Tokitani M, Yajima M, Hatano Y, Chikada T (2017) Development of H, D, T Simultaneous TDS measurement system and H, D, T retention behavior for DT gas exposed tungsten installed in LHD plasma campaign. Fusion Sci Technol 71:351\u0026ndash;356\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKh V, Alimov M, Yajima S, Masuzaki, Tokitani M (2019) Analysis of mixed-material layers deposited on the toroidal array probes during the FY 2012 LHD plasma campaign. Fusion Eng Des 147:111228\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMiziolek AW, Palleschi V, Schechter I (eds) (2006) Laser-Induced Breakdown Spectroscopy (LIBS). Fundamentals and Applications. Cambridge University Press, New York\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCremers DA, Radziemski LJ (2006) Handbook of Laser-Induced Breakdown Spectroscopy. John Wiley \u0026amp; Sons Ltd, Chichester\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNoll R (2012) Laser-Induced Breakdown Spectroscopy, Fundamentals and applications. Springer-, Berlin\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMusazzi S, Perini U (eds) (2014) Laser-Induced Breakdown Spectroscopy Theory and Applications. Springer-, Berlin Heidelberg\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh JP, Thakur SN (2007) Laser-Induced Breakdown Spectroscopy. Elsevier\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHahn DW, Omenetto N (2010) Laser-induced breakdown spectroscopy (LIBS), part I: review of basic diagnostics and plasma-particle interactions: Still-challenging issues within the analytical plasma community. Appl Spectrosc 64(12):335\u0026ndash;366\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHahn DW (2012) Omenetto Laser-Induced Breakdown Spectroscopy (LIBS), Part II: Review of Instrumental and Methodological Approaches to Material Analysis and Applications to Different Fields. Appl Spectros 66(4):347\u0026ndash;419\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalleschi V (2017) If laser-induced breakdown spectroscopy was a brand: some market considerations. Spectrosc Eur 29:6\u0026ndash;9\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai L, Wang Z, Li C, Huang X, Zhao D, Ding H (2019) Development of an in situ diagnostic system for mapping the deposition distribution on PFC of the HL-2M tokamak. Rev Sci Instruments 90:053503\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlmaviva S, Caneve L, Colao F, Lazic V, Maddaluno G, Mosetti P, Palucci A, Reale A, Gasior P, Gromelski W, Kubkowska M (2020) LIBS measurements inside the FTU vessel mock-up by using a robotic arm. Fusion Eng Des 157:111685\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao D, Li C, Hu Z, Feng C, Xiao Q, Hai R, Liu P, Sun L, Wu D, Fu C, Liu J, Farid N, Ding F, Luo G-N, Wang L, Ding H (2018) Remote in situ laser-induced breakdown spectroscopic approach for diagnosis of the plasma facing components on experimental advanced superconducting tokamak. Rev Sci Instruments 89:073501\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu Z, Li C, Xiao Q, Liu P, Ding F, Mao H, Wu J, Zhao D, Ding H (2017) Luo and EAST team, Preliminary results of in situ laser-induced breakdown spectroscopy for the first wall diagnostics on EAST. Plasma Sci Technol 19:025502\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHao Z, Deng Z, Liu L, Shi J, He X (2022) Spatial confinement effects of laser-induced breakdown spectroscopy at reduced air pressures. Front Optoelectron 15:12200\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu H, Wu D, Li C, Liu S, Hu Z, Li Y, Wang X, Bai X, Hai R, Ding H (2023) An approach for measurement of the magnetic field near the surface of plasma-facing components in tokamak by laser induced breakdown spectroscopy based on Zeeman effect. Spectrochim Acta B Spectrosc 207:106755\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVinic M, Ivkovic M (2014) Spatial and Temporal Characteristics of Laser Ablation Combined With Fast Pulse Discharge. IEEE Trans Plasma Sci 42:2598\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSaeki M, Iwanade A, Ito C, Wakaida I, Thornton B, Sakka T, Ohba H (2014) Development of a fiber-coupled laser-induced breakdown spectroscopy instrument for analysis of underwater debris in a nuclear reactor core. J Nucl Sci Technol 51:930\u0026ndash;938\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiu Y, Wu J, Li X, Liu T, Xue F, Yang Z, Zhang Z, Yu H (2018) Parametric Study of Fiber-Optic Laser-Induced Breakdown Spectroscopy for Elemental Analysis of Z3CN20-09M Steel from Nuclear Power Plants. Spectrochim Acta B Spectrosc 149:48\u0026ndash;56\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRakovsk\u0026yacute; J, Čerm\u0026aacute;k P, Musset O, Veis P (2014) A review of the development of portable laser induced breakdown spectroscopy and its applications. Spectrochim Acta B Spectrosc 101:269\u0026ndash;287\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSenesi GS, Harmon RS, Hark RR (2020) Field-portable and handheld LIBS: Historical review, current status and future prospects. Spectrochim Acta B Spectrosc 175:106013\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDumitrescu CE, Puzinauskas PV, Olcmen S (2008) Movable fiber probe for gas-phase laser-induced breakdown spectroscopy. Appl Opt 47:G88\u0026ndash;G98\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLin Z, Zhang N, Xu Z, Liao J, Yuan H, Chenshen E, Liu J, Li J, Zhao N, Zhang Q (2022) Modified Iterative Wavelets for Background Removal in Laser-Induced Breakdown Spectroscopy Based on Fiber Laser Ablation. J Anal Spectrom 37:2082\u0026ndash;2088\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLv C, Zhang N, Lin Z, Ou T, Li J, Zhao N, Yang X, Ma Q, Guo L, Zhang Q (2023) Determination of Copper, Magnesium, and Manganese in Aluminum Alloys Using Laser-Induced Breakdown Spectroscopy Based on Fiber Laser Ablation. J Laser Appl 35:012021\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHang Y-H, Qiu Y, Zhou Y, Liu T, Zhu B, Liao K, Shi M-X, Xue F (2022) Effects of Pulse Energy Ratios on Plasma Characteristics of Dual-Pulse Fiber-Optic Laser-Induced Breakdown Spectroscopy. Chin Phys B 31:024212\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan M, Zeng Q, Wang J, Li W, Chen G, Li Z, Liu Y, Guo L, Li X, Yu H (2021) Rapid Classification of Steel via a Modified Support Vector Machine Algorithm Based on Portable Fiber-Optic Laser-Induced Breakdown Spectroscopy. Opt Eng 60:124114\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRajavelu H, Vasa NJ, Seshadri S (2022) Hollow-Core Optical Fiber-Based Laser-Induced Breakdown Spectroscopy Technique for the Elemental Analysis of Pulverized Coal. Appl Phys A 128:868\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao Y, Yang H, Harilal SS (2024) Fiberoptic Laser-Induced Breakdown Spectroscopy System for in situ Measurement in a Hazardous Environment. Nucl Technol, 1\u0026ndash;12\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAllison SW, Gillies GT, Magnuson DW, Pagano TS (1985) Pulsed Laser Damage to Optical Fibers. Appl Opt 24:3140\u0026ndash;3145\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePini R, Salimbeni R, Vannini M (1987) Optical Fiber Transmission of High Power Excimer Laser Radiation. Appl Opt 26:4185\u0026ndash;4189\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSchmidt-Uhlig T, Karlitschek P, Marowsky G, Sano Y (2001) New simplified coupling scheme for the delivery of 20 MW Nd:YAG laser pulses by large core optical fibers. Appl Phys B 72:183\u0026ndash;186\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZeng Q, Guo L, Li X, He C, Shen M, Li K, Duan J, Zeng X, Lu Y (2015) Laser-induced breakdown spectroscopy using laser pulses delivered by optical fibers for analyzing Mn and Ti elements in pig iron. J Anal Spectrom 30:403\u0026ndash;409\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSankhe ML, Favre A, Sirven J-B, Bultel A, L\u0026rsquo;Hermite D, Semerok A, Vartanian S, Grisolia C (2023) Development of fibered LIBS device for tokamak Plasma Facing Components characterization. Fusion Eng Des 197:114077\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIvkovic M, Savovic J, Stankov BD, Kuzmanovic M, Traparic I (2024) LIBS depth \u0026ndash; profile analysis of W/Cu functionally graded material. Spectrochim Acta B Spectrosc 213:106874\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"0c4db099-2263-4f12-977a-786f00db9058","identifier":"10.13039/501100004564","name":"Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja","awardNumber":"451-03-47/2023-01/200024","order_by":0},{"identity":"c878bb95-f386-4061-b5b2-9982c18b7b49","identifier":"10.13039/501100004564","name":"Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja","awardNumber":"451-03-47/2023-01/200017","order_by":1},{"identity":"1319bbb0-dc92-44f0-b1aa-20edca8060d2","identifier":"10.13039/501100004564","name":"Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja","awardNumber":"451-03-47/2023-01/200146","order_by":2},{"identity":"42824505-d839-44a5-be9d-9eb959f0a11d","identifier":"10.13039/501100004564","name":"Ministarstvo Prosvete, Nauke i Tehnološkog Razvoja","awardNumber":"451-03-66/2024-03/200107","order_by":3},{"identity":"274dd197-3304-4112-8434-3f9ea2766200","identifier":"10.13039/501100016047","name":"Science Fund of the Republic of Serbia","awardNumber":"7753287 ","order_by":4}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Institute of Physics Belgrade","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"PFC diagnostics, fusion, LIBS, plasma spectroscopy","lastPublishedDoi":"10.21203/rs.3.rs-6212849/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6212849/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePlasma Facing Components (PFC) diagnostics in fusion reactors require innovative and robust instrumentation capable of addressing the challenges of harsh operational environments. Hence, this work presents the design, construction, and testing of a functional model for a LIBS measuring head tailored for in-situ and post-mortem PFC analysis. The proposed system includes advancements in mechanical design, such as an adaptable measuring head configurations, which enable operation in low-pressure environments and random spatial positions within the reactor. By integrating spectroscopic techniques and remote control capabilities, the system demonstrates potential for real-time diagnostics with sensitivity comparable to state-of-the-art techniques.\u003c/p\u003e","manuscriptTitle":"Functional model of the measuring head for the plasma fusion reactor wall diagnostics using low pressure, laser induced breakdown setup at random positions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-03-17 05:42:25","doi":"10.21203/rs.3.rs-6212849/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e6241d8f-acd2-40ba-a93a-f94b82eab167","owner":[],"postedDate":"March 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-04-23T09:30:44+00:00","versionOfRecord":[],"versionCreatedAt":"2025-03-17 05:42:25","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6212849","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6212849","identity":"rs-6212849","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}