Effects of applied magnetic fields on the performance of magnetoplasmadynamic thrusters

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Thrust, specific impulse, and ion energy distribution were measured under various operating conditions. The results indicate that the magnetic field configuration of permanent magnets with a magnetic null point may limit effective ion acceleration, leading to reduced thrust while the permanent magnet produces a stronger applied magnetic field ( B A : 0.175 T) than the electromagnet ( B A : 0.016–0.065 T). For the electromagnet configuration, thrust increased more significantly with discharge current at a lower flow rate (500 sccm) and a higher electromagnetic coil current (40 A). When the discharge current was increased to 300 A under the aforementioned conditions, the maximum thrust of 436 mN and the specific impulse of 2935 s were obtained. From these observations, the current-voltage (I–V) characteristics, which are strongly influenced by the magnetic field, appear to be closely linked to the thruster performance, as evidenced by the measured thrust and ion energy distributions. The findings highlight the dominant influence of the magnetic field geometry on the thruster performance, along with the contributions of the discharge current and the argon flow rate. Physical sciences/Engineering/Aerospace engineering Physical sciences/Physics/Plasma physics/Plasma based accelerators AF–MPD thruster Magnetic field Thruster performance Permanent magnet Electromagnet Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Space electric propulsion is crucial to advanced space exploration, offering a high specific impulse [ 1 , 2 ]. Among these technologies, magnetoplasmadynamic (MPD) thrusters are particularly promising due to their scalability from kW to MW power levels, high thrust density, and high specific impulse [ 1 – 7 ]. As the demand for reliable, high-power propulsion in deep-space missions continues to grow, further advancements in MPD thruster technology become increasingly critical [ 4 , 8 ]. However, progress in MPD thruster development has been relatively slow in recent decades, primarily due to the high power requirements for efficient operation [ 6 , 9 ]. Thus, resolving the challenges of supplying sufficient power to thruster systems is essential for the successful implementation of MPD thrusters [ 6 , 10 ]. Recent advancements in space nuclear fission power and nuclear-electric propulsion (NEP) systems have generated increasing interest in high-power electric propulsion technologies, including MPD thrusters [ 11 – 13 ]. In the United States, NASA and private companies such as Ultra Safe Nuclear Corporation are developing compact and highly efficient fission reactors [ 14 , 15 ]. Russia is advancing the Transport and Energy Module (TEM), a nuclear-powered space tug designed for long-duration interplanetary missions, and the European Space Agency is conducting research on NEP through projects such as RocketRoll (pReliminary eurOpean ReCKon on NuclEar ElecTric PROpuLsion for Space AppLications), which aims to assess the feasibility of nuclear-electric propulsion for space applications [ 16 , 17 ]. Ongoing developments in these technologies are expected to facilitate the effective implementation of MPD thrusters in deep-space missions [ 4 , 12 ]. MPD thrusters utilize magnetic fields to accelerate ionized propellants [ 1 , 7 ] with two primary methods for generating magnetic fields: permanent magnets and electromagnets [ 18 – 20 ]. Since the early stages of MPD thruster development in the 1960s, electromagnets have served as the primary means of generating applied magnetic fields in AF-MPD thrusters [ 21 ]. During the 1980s and 1990s, performance optimization efforts utilizing electromagnets were conducted through high-power MPD experiments. More recently, research on electromagnet-based AF-MPD thrusters has continued, including investigations into the Lorentz Force Accelerator (LiLFA) at Princeton University and the SX3 thruster at the University of Stuttgart [ 22 , 23 ]. Activate research on the application of permanent magnets began relatively later, around the 1990s, with experimental studies conducted by researchers at the University of Tokyo [ 19 ]. Due to limitations in magnetic field strength and controllability, permanent magnets have primarily been investigated for low- to mid-power MPD systems. Each method presents distinct advantages and limitations. Permanent magnets are structurally simple and do not require additional power during operation, making them well-suited for long-term missions [ 19 , 24 , 25 ]. However, their fixed magnetic field limits the ability to precisely control operational modes, constraining performance optimization in various missions. In contrast, electromagnets provide adjustable magnetic fields, allowing for precise control of thrust and specific impulse, but they necessitate significant electrical power input [ 23 , 26 , 27 ]. Another key distinction between these two types is the presence of a magnetic null. In contrast to an electromagnet, which primarily generates an axial magnetic field within the discharge channel, a ring-shaped permanent magnet with a magnetic null point produces a substantial radial magnetic field. As the geometry of the magnetic field influences the behavior of charged particles, it is expected to have a direct impact on both plasma characteristics and thruster performance. Despite its critical influence on thruster performance, detailed studies on the effects of permanent magnets and electromagnets in MPD thrusters remain limited. Most prior research has primarily focused on thruster performance in relation to magnetic field strength, without providing a comprehensive analysis of the impacts of magnetic field geometry on thrust. The objective of this paper is to conduct a comparative study on the performance of magnetic field configurations by permanent magnets and electromagnets in low-power MPD thrusters. Although the experiments were conducted using a low-power MPD thruster, the findings are expected to be applicable to high-power MPD thrusters due to their scalability. By evaluating thruster performance under various experimental conditions, the results are anticipated to offer valuable insights into the design of MPD thrusters for future space missions. Results The experiments carried out to evaluate the performance and discharge characteristics of the AF-MPD thruster using electromagnets and permanent magnets as external magnetic field sources. For the electromagnet configurations, experiments were conducted at argon flow rates of 500, 750, and 1000 sccm, with thruster performance evaluated at discharge currents ranging from 100 A to 300 A in 50 A increments. In the permanent magnet configuration, experiments were conducted at discharge currents ranging from 138 A to 290 A and argon flow rates of 600, 800, and 1000 sccm, covering a similar operational range to that of the electromagnet case. Discharge characteristics. The I–V curve characteristics as a function of discharge current were compared between the electromagnet and permanent magnet cases, as shown in Fig. 1 . Figures 1 (a)–(c) represent I–V curves obtained for the electromagnet cases, while Fig. 1 (d) presents the I–V curves measured for the permanent magnet case. In the region where the discharge current is below approximately 100 A, an increase in current enhances thermionic electron emission from the hot cathode, resulting in a decrease in voltage. However, when the discharge current exceeds 100 A, the voltage begins to increase again, indicating a transition from a non-thermal to a thermal arc. This trend aligns with the typical I–V characteristics of an arc plasma. In Figs. 1 (a)–(c), the I–V curves are compared based on Ar flow rates and electromagnetic coil currents. At flow rates of 750 sccm and 1000 sccm, the I–V curves exhibited similar characteristics under identical operating conditions. At the lowest flow rate of 500 sccm, a significant increase in voltage was observed as the electromagnetic coil current increased. Notably, when the electromagnet coil current was 40 A, the voltage exhibited a steeper rise as the discharge current increased compared to the other cases. For the permanent magnet configuration, at discharge currents exceeding 100 A, the voltage increased with rising current, while the effect of flow rate remained negligible, as shown in Fig. 1 (d). The permanent magnet configuration showed higher voltages at the same discharge current compared to the electromagnet configuration at 750 sccm and 1000 sccm. Thruster measurement results. In this subsection, the performance of the AF-MPD thruster was evaluated for different magnetic field configurations generated by the electromagnet and the permanent magnet. Thrust versus IB A (the product of discharge current and applied magnetic field) was selected for comparison, as previous studies have indicated that thrust in AF-MPDTs is proportional to this parameter [ 20 , 28 ]. Given that variations in Ar flow rate and the magnetic field structures affect the I–V curve characteristics, thrust curves as a function of input power are also presented. Figures 2 (a) and (b) present thrust as a function of IB A for configurations utilizing the electromagnet and the permanent magnet, respectively. While the operational discharge current range is comparable for both electromagnet and permanent magnet cases, the B A in the permanent case is approximately 3 to 10 times higher than that of the electromagnet, resulting in differences in the IB A regions. For the permanent magnet configuration, thrust exhibited a linear increase with IB A , and higher argon flow rates resulted in greater thrust, as shown in Fig. 2 (b). At a low electromagnet coil current ( I coil : 10 A), thrust also exhibited a linear increase with IB A , following a trend similar to that of the permanent magnet. Additionally, the higher flow rate (1000 sccm) led to a steeper increase in thrust compared to the lower flow rate (500 sccm). Interestingly, at a high coil current ( I coil : 40 A), thrust increased more sharply with IB A at a lower flow rate than at a higher flow rate. Moreover, when IB A exceeded 12 [N/m], thrust at the lower flow rate surpassed that at the higher flow rate case. Thrust and specific impulse I sp were evaluated as a function of input power, as shown in Fig. 3 . In both cases of the electromagnet and the permanent magnet, higher argon flow rates resulted in greater thrust at the same input power. For specific impulse, the permanent magnet configuration exhibited a linear increase with power, with no apparent dependence on flow rate. Similarly, in the electromagnet configuration at flow rates of 750 sccm and 1000 sccm, the effect of argon mass flow on I sp was negligible. However, at a lower flow rate of 500 sccm, I sp increased significantly at the same input power and showed a steep increase with increasing power. The maximum thrust of 436 mN and a maximum I sp of 2935 s were achieved at an argon flow rate of 500 sccm, I coil of 40 A, and an input power of 15 kW. Ion energy distributions measured by RPA. The ion energy distributions were measured using a retarding potential analyzer (RPA) for the electromagnet configurations. The normalized ion energy distribution function (IEDF) for each flow rate is presented in Fig. 4 . The peak ion energy exhibited an increasing trend with higher discharge current and electromagnet coil current. At a coil current of 10 A, the peak ion energy ranged between 21 eV and 35 eV across all flow rate cases. For a coil current of 40 A, the peak ion energy varied from 25 eV to 41 eV for the argon flow rates of 750 sccm and 1000 sccm. Notably, the peak ion energy increased as the argon flow rate decreased. In particular, at a flow rate of 500 sccm, the ion energy demonstrated a substantial increase compared to other flow conditions, with a maximum peak ion energy of 63 eV was obtained at a discharge current of 300 A and a coil current of 40 A. Thruster efficiency. Thruster efficiency under various experimental conditions is plotted against specific impulse I sp in Fig. 5 . Under comparable argon flow rate conditions, the efficiency and thrust density in the permanent magnet cases were lower than observed in the electromagnet cases. The efficiency and I sp for the permanent magnet case ranged between 3.4% and 19% and 401–1156 s, respectively, corresponding to an input power of 4–10 kW. The thrust-to-power ratio was primarily concentrated between 20 mN/kW and 40 mN/kW. Meanwhile, in magnetic field geometry of the electromagnet, the thrust-to-power ratio was slightly higher, typically ranging from 25 mN/kW to 45 mN/kW. The highest thrust-to-power ratio of 46.5 mN/kW was achieved at a high argon flow rate (1000 sccm) and low input power (2.1 kW), whereas the maximum efficiency of 42% was obtained at a low flow rate (500 sccm) and high input power (15 kW). Discussion As demonstrated in the results section, the performance characteristics of the thruster are significantly affected by the geometry of the external magnetic field, which varies depending on the type of magnet employed. Given that acceleration mechanisms in MPD thrusters are inherently interdependent on complex electromagnetic and gas-dynamic processes, a comprehensive understanding of how magnetic field configurations affect plasma behavior is essential for optimizing thruster performance [ 29 , 30 ]. Among the key factors determining thruster performance, the current-voltage (I–V) characteristics play a critical role, as they affecting thruster efficiency by governing the power consumption required for operation. In particular, the magnetic field geometry, along with discharge current and argon flow rate, significantly impacts plasma properties and the resulting I–V curve. Consequently, a comprehensive understanding of the I–V characteristics under various conditions is essential for optimizing thruster performance. The experimental results obtained under different magnetic field configurations indicate that, for the same input power, the electromagnet configuration generates higher thrust than the permanent magnet configuration. This difference can be attributed to the I–V characteristics, where the permanent magnet configuration results in a higher voltage being applied to the cathode at a given discharge current, as shown in Fig. 1 . Since thrust is primarily influenced by discharge current, the lower current levels observed in the permanent magnet case at the same input power lead to low thrust compared to the electromagnet case under similar mass flow rates (see Fig. 3 (a)). Additionally, these results can be interpreted in terms of particle behavior under different magnetic field configurations. In the permanent magnet configuration, despite its higher B A , the presence of a magnetic null point disrupts axial electron mobility, thereby weakening the induced electric field and impeding ion acceleration. Furthermore, a shorter field line length in the thruster channel may reduce the ionization rate, leading to lower plasma density. Consequently, the reduced ionization may lead to a lower local density, which ultimately disrupts efficient ion acceleration and degrades overall thruster performance [ 31 ]. As demonstrated in the results, across all magnetic field configurations, the total voltage exhibited an increasing trend with both the strength of the magnetic field and the discharge current in the primary operational regime above 100 A. In the thrust versus IB A graph for the electromagnet configuration, as depicted in Fig. 2 , thrust consistently increased with discharge current under all conditions for both the electromagnet and permanent magnet configurations. In addition, in most cases, for a given B A and discharge current, a higher flow rate resulted in greater thrust. A noteworthy observation is that under higher B A conditions ( I coil : 40 A), thrust exhibited a more pronounced increase with discharge current in the low mass flow rate case compared to the high mass flow rate case. Consequently, for discharge currents above 200 A, the thrust at a lower mass flow rate exceeded that at a higher mass flow rate for the same discharge current. The observed trend can be understood through the semi-empirical voltage model, which is mainly affected by the magnetic field [ 23 , 32 , 33 ]. Summary and Conclusion A comparative analysis of AF-MPD thruster performance using permanent magnets and electromagnets was conducted. Experimental investigations were carried out by varying discharge currents, flow rates, and magnetic field configurations to evaluate thruster performance, including ion energy distributions and thruster efficiency. The results indicated that while the permanent magnet configuration generated a higher B A , the presence of a magnetic null point restricted effective ion acceleration. In the electromagnet configuration improved thrust and efficiency, particularly at lower mass flow rates and higher applied magnetic fields. Additionally, the I–V characteristics, which varied with flow rate and magnetic field strength, played a crucial role in performance. The underlying physical interpretation is as follows [ 23 ]: as the discharge current and magnetic field strength increase, plasma pinching along the thruster centerline is enhanced, thereby reducing the flux of electrons entering the near-anode region. This effect becomes more pronounced at lower flow rates and stronger magnetic field strength, leading to enhanced thruster performance, as demonstrated by the semiempirical voltage model and the measured ion energy distributions. These findings highlight the critical role of magnetic field geometry in the design of MPD thrusters. While a stronger magnetic field generally enhances performance, the specific field topology has a significant influence on plasma behavior and ion acceleration efficiency. Thus, optimizing MPD thruster performance necessitates a careful selection of magnet type, discharge conditions, and system parameters to achieve an optimal balance among thrust, efficiency, and power consumption. Method MPD thruster and experimental setup. This section presents an overview of the low-power AF-MPD thruster used in this study, detailing its structural design, the magnetic field geometry generated by the permanent magnet or electromagnet, the thrust measurement setup, and the vacuum facility. Thruster discharge channel and magnetic field geometry. The AF-MPD thruster used in this work consists of a thoriated tungsten (2%) cathode, a copper anode, and three alumina insulators [ 34 , 35 ]. The cylindrical cathode, with an outer diameter of 12 mm, is enclosed by an anode with an inner diameter of 80 mm. The total length of the cathode is 110 mm, and its exposed length can be adjusted. Argon is used as the propellant gas and is supplied through the cathode. Both the anode and cathode are equipped with a water-cooling circuit to regulate temperature and dissipate the substantial heat generated by the DC power input. The schematic layout of the thruster is depicted in Fig. 6 (a). The electromagnet and the permanent magnet were utilized as sources of external magnetic fields to examine the effects of magnetic field geometry on thruster performance. Both magnets were designed in a ring shape with identical dimensions and were equipped with a water-cooling jacket on the plasma-facing side to protect them from the heat flux generated by the plasma. The axial positions of the magnet centers were aligned near the tip of the cathode. The electromagnet was constructed by winding 300 turns of AWG 7 wire, which has a cross-sectional area of 10 mm². To ensure stable operation, the current supplied to the electromagnetic coil was limited to 40 A in accordance with the ampacity of the wire. The thruster performance with the electromagnet was evaluated under three operating conditions, with coil currents of 10 A, 30 A, and 40 A. Figure 6 (b) presents a comparison of the calculated axial magnetic field generated by the permanent magnet and the electromagnet. In the case of the permanent magnet, the presence of a magnetic null point results in a different axial magnetic field profile compared to that of the electromagnet. The magnetic flux density at the cathode tip is 0.175 T for the permanent magnet, while for the electromagnet, it is 0.016 T, 0.049 T, and 0.065 T at coil currents of 10 A, 30 A, and 40 A, respectively. Figure 6 (c) illustrates the magnetic field distributions simulated using Finite Element Method Magnetics (FEMM) for both the electromagnetic and permanent magnet configurations. The results indicate that the axial magnetic field is dominant within the discharge channel in the electromagnet configuration, whereas in the permanent magnet configuration, the presence of a magnetic null point leads to an increased radial magnetic field near the magnet. Thrust measurement system and vacuum facilities. To evaluate the performance of the AF-MPD thruster, a plate spring-type thrust stand equipped with a load cell was used. The plasma source was mounted on the stand, which was supported by four plate springs [ 20 ]. The load cell was calibrated by hanging 10 g weights using a pulley system. When a thrust is generated in the direction opposite to the ion acceleration, the load cell converts this thrust into an electrical signal proportional to the applied thrust. The measurable thrust ranges from 0.1 N and 1 N. Calibration coefficients were calculated by averaging the results obtained from pre- and post-experiment calibrations. The experiments took place in a cylindrical vacuum chamber made of stainless steel, with a diameter and length of 1.5 m. The vacuum system consisted of four turbopumps and two cryopumps, with a pumping speed of 11,000 L/s for argon. During operation, the system maintained a pressure below 1.7 mTorr at an argon flow rate of 1000 sccm. Declarations Author contributions The original draft was written by H.S., who also conducted the methodology design, investigation, visualization, and data curation. Data curation support was provided by J.K., J.H., and K.C. Review and editing of the manuscript were performed by J.K., J.H., K.C., and H.K. Validation was carried out by K.C. and H.K. Methodology development was led by H.S. and H.K. Supervision and funding acquisition were provided by K.C. and H.K. All authors reviewed the first and final manuscript. Competing interests The authors declare no competing interests. Data availability The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. Acknowledgements This work was partially supported by National R&D program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2022-00155950) and by KAERI Institutional Program (524560-25). This work was also partially supported by “A Research on Critical Technology for Scalable Space Tug with Autonomy and Reconfigurability” of Korea Aerospace Research Institute (Grand No. FR25F00). References Goebel, D. M., Katz, I. & Mikellides, I. G. Fundamentals of Electric Propulsion (Wiley, 2023). Ahangar, M., Ebrahimi, R. & Shams, M. Numerical simulation of non-equilibrium plasma flow in a cylindrical MPD thruster using a high-order flux-difference splitting method. Acta Astronaut. 103 , 129–141 (2014). Albertoni, R., Paganucci, F. & Andrenucci, M. A phenomenological performance model for applied-field MPD thrusters. Acta Astronaut. 107 , 177–186 (2015). Krulle, G., Auweter-Kurtz, M. & Sasoh, A. Technology and application aspects of applied field magnetoplasmadynamic propulsion. J. Propuls. Power . 14 , 754–763 (1998). Sasoh, A. et al. Electrostatic-magnetic-hybrid thrust generation in central–cathode electrostatic thruster (CC–EST). Acta Astronaut. 152 , 137–145 (2018). Tauchi, S. et al. Analysis of thrust performance and cathode phenomena on a megawatt-class MPD thruster. AIAA SciTech 2019 Forum , 1241 (2019). Nerheim, N. M. & Kelly, A. J. A critical review of the magnetoplasmadynamic (MPD) thruster for space applications (Jet Propulsion Laboratory, California Institute of Technology, 1968). Brophy, J. Advanced ion propulsion systems for affordable deep-space missions. Acta Astronaut. 52 , 309–316 (2003). Mikellides, P. G. Modeling and analysis of a megawatt-class magnetoplasmadynamic thruster. J. Propuls. Power . 20 , 204–210 (2004). Patel, S., Bondugula, M. & Gorakula, S. MPD thruster technology and its limitations. Int. J. Sci. Adv. 2 , 578–585 (2021). Cassady, R. J. et al. Recent advances in nuclear powered electric propulsion for space exploration. Energy Convers. Manag . 49 , 412–435 (2008). La Rosa Betancourt, M. A. et al. Comparative overview of NEP programs and concepts for human exploration missions. ASCEND 2021 , 4075 (2021). McGuire, M. L., Borowski, S. K., Mason, L. M. & Gilland, J. High power MPD nuclear electric propulsion (NEP) for artificial gravity HOPE missions to Callisto. Space Technol. Appl. Int. Forum (2003). Gibson, M. A. et al. NASA's Kilopower reactor development and the path to higher power missions. IEEE Aerosp. Conf , 1–14 (2017). Venneri, P. & Eades, M. Space nuclear power and propulsion at USNC-Tech. Nucl. Technol. 207 , 876–881 (2021). La Luna, S., Sulpizi, R., Zuin, D. & Maggi, F. Nuclear propulsion technology for satellite applications: historical overview and current developments. 75th Int Astronaut. Congr (IAC) , 1–14 (2024). www.russianspaceweb.com. accessed (2025). Sasoh, A. & Arakawa, Y. Electromagnetic effects in an applied-field magnetoplasmadynamic thruster. J. Propuls. Power . 8 , 98–102 (1992). Arakawa, Y. & Sasoh, A. Steady-state permanent magnet magnetoplasmadynamic thruster. J. Propuls. Power . 5 , 301–304 (1989). Shin, H., Chai, K. B. & Kim, H. Performance and discharge characteristics of applied–field MPD thruster in accordance with ring magnet position. Vacuum 230 , 113674 (2024). Krülle, G. Characteristics and local analysis of MPD thruster operation. 6th Electr Propuls. Plasmadyn Conf , 672 (1967). Boxberger, A. & Herdrich, G. Experimental test campaign of gas-fed steady state applied-field magnetoplasmadynamic thruster SX3. IEPC Paper 251 , (2013). Lev, D. R. & Choueiri, E. Y. Scaling of efficiency with applied magnetic field in magnetoplasmadynamic thrusters. J. Propuls. Power . 28 , 609–616 (2012). Polzin, K. et al. Performance of a permanent-magnet cylindrical Hall-effect thruster. 45th AIAA Joint Propuls. Conf , 4812 (2009). Ferreira, J. L. et al. Permanent magnet Hall thruster development for future Brazilian space missions. Comput. Appl. Math. 35 , 711–726 (2016). Polzin, K. et al. Comparisons in performance of electromagnet and permanent-magnet cylindrical hall-effect thrusters. 46th AIAA Joint Propuls. Conf , 6695 (2010). Auweter-Kurtz, M., Kriille, G. & Kurtz, H. The investigation of applied-field MPD thrusters on the International Space Station. Proc. 25th Int. Electr. Propuls. Conf. , 721–727 (1997). Kodys, A. & Choueiri, E. A critical review of the state-of-the-art in the performance of applied-field magnetoplasmadynamic thrusters. 41st AIAA Joint Propulsion Conf. , 4247 (2005). Sun, Y. et al. Experimental investigation of the electromagnetic acceleration mechanisms in an applied-field magnetoplasmadynamic thruster. Plasma Sources Sci. Technol. 33 , 115016 (2024). Du, Y. et al. Theoretical research on magnetic confinement mechanism of applied-field magnetoplasmadynamic thruster. Aerospace 10 , 124 (2023). Kim, H., Doh, G. & Choe, W. Generation of multiply charged ions in accordance with geometry and magnetic field in Hall thruster plasmas. Curr. Appl. Phys. 51 , 8–12 (2023). Tikhonov, V., Semenikhin, S., Brophy, J. & Polk, J. Performance of 130 kW MPD thruster with an external magnetic field and Li as a propellant. Proc. 25th Int. Electr. Propuls. Conf. , 728–733 (1997). Mikellides, P. & Turchi, P. A theoretical model for the thrust and voltage of applied-field MPD thrusters. 34th AIAA Joint Propulsion Conf. , 3474 (1998). Chai, K. B. & Kwon, D. H. Heat and particle load test facility using an applied-field MPD thruster for studying fusion divertor technology. Plasma Phys. Control Fusion . 62 , 035007 (2020). Chai, K. B., Kwon, D. H. & Lee, M. Development of plasma beam irradiation facility using applied-field MPD thruster to study plasma–surface interactions. Plasma Phys. Control Fusion . 63 , 125020 (2021). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 06 Feb, 2026 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 13 Oct, 2025 Reviews received at journal 01 Oct, 2025 Reviewers agreed at journal 18 Sep, 2025 Reviews received at journal 01 Sep, 2025 Reviewers agreed at journal 21 Aug, 2025 Reviewers agreed at journal 03 Jun, 2025 Reviewers invited by journal 02 Jun, 2025 Editor assigned by journal 02 Jun, 2025 Editor invited by journal 02 Jun, 2025 Submission checks completed at journal 31 May, 2025 First submitted to journal 19 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6699652","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":465767816,"identity":"8e40aa32-e1cb-43e2-8fca-87c6d5994d74","order_by":0,"name":"Haewon Shin","email":"","orcid":"","institution":"Korea Atomic Energy Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Haewon","middleName":"","lastName":"Shin","suffix":""},{"id":465767820,"identity":"a4ccc319-ac6b-4ed7-8631-173ef6925037","order_by":1,"name":"Jeongho Kim","email":"","orcid":"","institution":"Pusan National University","correspondingAuthor":false,"prefix":"","firstName":"Jeongho","middleName":"","lastName":"Kim","suffix":""},{"id":465767821,"identity":"9ea4d72c-137c-4e4a-a99b-f6c19d328d05","order_by":2,"name":"Jaeyeon Hwang","email":"","orcid":"","institution":"Pusan National University","correspondingAuthor":false,"prefix":"","firstName":"Jaeyeon","middleName":"","lastName":"Hwang","suffix":""},{"id":465767822,"identity":"68fb5cfe-4c68-41db-bbd7-265c26806ffb","order_by":3,"name":"Kil-Byoung Chai","email":"","orcid":"","institution":"Korea Atomic Energy Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Kil-Byoung","middleName":"","lastName":"Chai","suffix":""},{"id":465767823,"identity":"c9677795-ffd0-4afe-9cc1-47ecd549fc82","order_by":4,"name":"Holak Kim","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYBACAwbmBsaGAxIM/AgxNkJaGCFaJBtI1AJkHCBWizl7Y+PHGWcsoo1v9xh/+LmDQZ6/gS3tAz4tlj0HmyU33JDI3XbnjJlk7xkGwxkH2A7PwOuwG4kNkg8+ALXcyDFj4G1jYNzAwN6M3y83Ept/grRsnpFj/PFvG4M9MVrawA7bIJFjIA20JXEDA9th/FrOHGyznHFGInfGnWNl0rJtEskzDrMl49dyvPnwzZ5jdbn9s5s3f3zbZmPb395mjFcLAkjASGYiNcC0jIJRMApGwSjABAC95U+VFqUHRAAAAABJRU5ErkJggg==","orcid":"","institution":"Pusan National University","correspondingAuthor":true,"prefix":"","firstName":"Holak","middleName":"","lastName":"Kim","suffix":""}],"badges":[],"createdAt":"2025-05-19 13:53:25","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6699652/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6699652/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-026-38380-3","type":"published","date":"2026-02-06T15:57:17+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84065179,"identity":"9989accf-c3ae-4d5e-bc13-6d4d34090825","added_by":"auto","created_at":"2025-06-06 10:58:06","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":116062,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the thruster I–V characteristics at different argon flow rates under various magnetic field configurations: (a) electromagnet configuration with coil current \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 10 A, (b) \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 30 A, (c) \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 40 A, and (d) the permanent magnet configurations. At 750 sccm and 1000 sccm flow rates, the I–V curves are similar. At 500 sccm, voltage increases significantly with coil current. The permanent magnet configuration shows minimal flow rate dependence at discharge currents above 100 A.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/3a48da87feb78857e17de1fb.png"},{"id":84065180,"identity":"2308ecdb-588b-469f-a4e0-daa42e075b55","added_by":"auto","created_at":"2025-06-06 10:58:06","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":90490,"visible":true,"origin":"","legend":"\u003cp\u003eThrust as a function of the product of magnetic field strength and discharge current (\u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e) for (a) the electromagnet and (b) the permanent magnet configurations. The permanent magnet provides a stronger magnetic field, resulting in higher \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e values. Thrust increases linearly with \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e in both configurations.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/227f92497fa8eb3eb36922d3.png"},{"id":84065182,"identity":"747220a2-a070-4793-b193-e68651b1c1a8","added_by":"auto","created_at":"2025-06-06 10:58:06","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":127533,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Thrust and (b) specific impulse (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e) as a function of input power for both electromagnet and permanent magnet configurations. Thrust increased with input power, and higher argon flow rates resulted in higher thrust. \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e showed a linear increase with power in the permanent magnet case, independent of flow rate. In the electromagnet case, \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e increased significantly with power only at the low flow rate of 500 sccm.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/bc44de85731d7319ce484610.png"},{"id":84065665,"identity":"4fef2dd3-c012-447f-a259-177276ae17b3","added_by":"auto","created_at":"2025-06-06 11:06:06","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":102135,"visible":true,"origin":"","legend":"\u003cp\u003eNormalized ion energy distribution functions (IEDFs) measured using a retarding potential analyzer (RPA) for the electromagnet configuration at various argon flow rates. Peak ion energy increased with both discharge current and coil current, and was highest at the lowest flow rate.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/f9943c18b700c184216fb363.png"},{"id":84065184,"identity":"0d9b678b-2d1d-446a-938c-35e90194335b","added_by":"auto","created_at":"2025-06-06 10:58:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":169094,"visible":true,"origin":"","legend":"\u003cp\u003eThruster efficiency of the low-power AF-MPD thruster plotted as a function of \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e. The electromagnet configuration exhibited higher efficiency and thrust-to-power ratios compared to the permanent magnet configuration.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/b24b9fe97ae732706f5ff1cd.png"},{"id":84065186,"identity":"3d1ca0fb-f68c-4428-9ac4-f409baec883a","added_by":"auto","created_at":"2025-06-06 10:58:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":301160,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Structure of the AF-MPD thruster, (b) axial magnetic flux density along the channel, and (c) magnetic field distributions for the electromagnet and permanent magnet configurations. The thruster consists of a water-cooled copper anode, thoriated tungsten cathode, and three alumina insulators. External magnetic fields are applied using either the electromagnet or the permanent magnet. FEMM simulations show an axially dominant field for the electromagnet configuration and a strong radial component near the null point in the permanent magnet configuration.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/31895ea940e2fa919fa73907.png"},{"id":102234001,"identity":"6f2a2071-b2e0-45dc-8442-fc9dd55411d8","added_by":"auto","created_at":"2026-02-09 16:02:49","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1334147,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6699652/v1/c001eda5-bd13-45a6-a096-ae72972d4b8e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of applied magnetic fields on the performance of magnetoplasmadynamic thrusters","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSpace electric propulsion is crucial to advanced space exploration, offering a high specific impulse [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Among these technologies, magnetoplasmadynamic (MPD) thrusters are particularly promising due to their scalability from kW to MW power levels, high thrust density, and high specific impulse [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. As the demand for reliable, high-power propulsion in deep-space missions continues to grow, further advancements in MPD thruster technology become increasingly critical [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, progress in MPD thruster development has been relatively slow in recent decades, primarily due to the high power requirements for efficient operation [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Thus, resolving the challenges of supplying sufficient power to thruster systems is essential for the successful implementation of MPD thrusters [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Recent advancements in space nuclear fission power and nuclear-electric propulsion (NEP) systems have generated increasing interest in high-power electric propulsion technologies, including MPD thrusters [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In the United States, NASA and private companies such as Ultra Safe Nuclear Corporation are developing compact and highly efficient fission reactors [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Russia is advancing the Transport and Energy Module (TEM), a nuclear-powered space tug designed for long-duration interplanetary missions, and the European Space Agency is conducting research on NEP through projects such as RocketRoll (pReliminary eurOpean ReCKon on NuclEar ElecTric PROpuLsion for Space AppLications), which aims to assess the feasibility of nuclear-electric propulsion for space applications [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Ongoing developments in these technologies are expected to facilitate the effective implementation of MPD thrusters in deep-space missions [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMPD thrusters utilize magnetic fields to accelerate ionized propellants [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] with two primary methods for generating magnetic fields: permanent magnets and electromagnets [\u003cspan additionalcitationids=\"CR19\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Since the early stages of MPD thruster development in the 1960s, electromagnets have served as the primary means of generating applied magnetic fields in AF-MPD thrusters [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. During the 1980s and 1990s, performance optimization efforts utilizing electromagnets were conducted through high-power MPD experiments. More recently, research on electromagnet-based AF-MPD thrusters has continued, including investigations into the Lorentz Force Accelerator (LiLFA) at Princeton University and the SX3 thruster at the University of Stuttgart [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Activate research on the application of permanent magnets began relatively later, around the 1990s, with experimental studies conducted by researchers at the University of Tokyo [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Due to limitations in magnetic field strength and controllability, permanent magnets have primarily been investigated for low- to mid-power MPD systems.\u003c/p\u003e \u003cp\u003eEach method presents distinct advantages and limitations. Permanent magnets are structurally simple and do not require additional power during operation, making them well-suited for long-term missions [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. However, their fixed magnetic field limits the ability to precisely control operational modes, constraining performance optimization in various missions. In contrast, electromagnets provide adjustable magnetic fields, allowing for precise control of thrust and specific impulse, but they necessitate significant electrical power input [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Another key distinction between these two types is the presence of a magnetic null. In contrast to an electromagnet, which primarily generates an axial magnetic field within the discharge channel, a ring-shaped permanent magnet with a magnetic null point produces a substantial radial magnetic field. As the geometry of the magnetic field influences the behavior of charged particles, it is expected to have a direct impact on both plasma characteristics and thruster performance.\u003c/p\u003e \u003cp\u003eDespite its critical influence on thruster performance, detailed studies on the effects of permanent magnets and electromagnets in MPD thrusters remain limited. Most prior research has primarily focused on thruster performance in relation to magnetic field strength, without providing a comprehensive analysis of the impacts of magnetic field geometry on thrust.\u003c/p\u003e \u003cp\u003eThe objective of this paper is to conduct a comparative study on the performance of magnetic field configurations by permanent magnets and electromagnets in low-power MPD thrusters. Although the experiments were conducted using a low-power MPD thruster, the findings are expected to be applicable to high-power MPD thrusters due to their scalability. By evaluating thruster performance under various experimental conditions, the results are anticipated to offer valuable insights into the design of MPD thrusters for future space missions.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe experiments carried out to evaluate the performance and discharge characteristics of the AF-MPD thruster using electromagnets and permanent magnets as external magnetic field sources. For the electromagnet configurations, experiments were conducted at argon flow rates of 500, 750, and 1000 sccm, with thruster performance evaluated at discharge currents ranging from 100 A to 300 A in 50 A increments. In the permanent magnet configuration, experiments were conducted at discharge currents ranging from 138 A to 290 A and argon flow rates of 600, 800, and 1000 sccm, covering a similar operational range to that of the electromagnet case.\u003c/p\u003e \u003cp\u003e \u003cb\u003eDischarge characteristics.\u003c/b\u003e The I\u0026ndash;V curve characteristics as a function of discharge current were compared between the electromagnet and permanent magnet cases, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Figures\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)\u0026ndash;(c) represent I\u0026ndash;V curves obtained for the electromagnet cases, while Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d) presents the I\u0026ndash;V curves measured for the permanent magnet case. In the region where the discharge current is below approximately 100 A, an increase in current enhances thermionic electron emission from the hot cathode, resulting in a decrease in voltage. However, when the discharge current exceeds 100 A, the voltage begins to increase again, indicating a transition from a non-thermal to a thermal arc. This trend aligns with the typical I\u0026ndash;V characteristics of an arc plasma.\u003c/p\u003e \u003cp\u003eIn Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)\u0026ndash;(c), the I\u0026ndash;V curves are compared based on Ar flow rates and electromagnetic coil currents. At flow rates of 750 sccm and 1000 sccm, the I\u0026ndash;V curves exhibited similar characteristics under identical operating conditions. At the lowest flow rate of 500 sccm, a significant increase in voltage was observed as the electromagnetic coil current increased. Notably, when the electromagnet coil current was 40 A, the voltage exhibited a steeper rise as the discharge current increased compared to the other cases. For the permanent magnet configuration, at discharge currents exceeding 100 A, the voltage increased with rising current, while the effect of flow rate remained negligible, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d). The permanent magnet configuration showed higher voltages at the same discharge current compared to the electromagnet configuration at 750 sccm and 1000 sccm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eThruster measurement results.\u003c/b\u003e In this subsection, the performance of the AF-MPD thruster was evaluated for different magnetic field configurations generated by the electromagnet and the permanent magnet. Thrust versus \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e (the product of discharge current and applied magnetic field) was selected for comparison, as previous studies have indicated that thrust in AF-MPDTs is proportional to this parameter [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Given that variations in Ar flow rate and the magnetic field structures affect the I\u0026ndash;V curve characteristics, thrust curves as a function of input power are also presented.\u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a) and (b) present thrust as a function of \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e for configurations utilizing the electromagnet and the permanent magnet, respectively. While the operational discharge current range is comparable for both electromagnet and permanent magnet cases, the \u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e in the permanent case is approximately 3 to 10 times higher than that of the electromagnet, resulting in differences in the \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e regions. For the permanent magnet configuration, thrust exhibited a linear increase with \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e, and higher argon flow rates resulted in greater thrust, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(b). At a low electromagnet coil current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 10 A), thrust also exhibited a linear increase with \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e, following a trend similar to that of the permanent magnet. Additionally, the higher flow rate (1000 sccm) led to a steeper increase in thrust compared to the lower flow rate (500 sccm). Interestingly, at a high coil current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 40 A), thrust increased more sharply with \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e at a lower flow rate than at a higher flow rate. Moreover, when \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e exceeded 12 [N/m], thrust at the lower flow rate surpassed that at the higher flow rate case.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThrust and specific impulse \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e were evaluated as a function of input power, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. In both cases of the electromagnet and the permanent magnet, higher argon flow rates resulted in greater thrust at the same input power. For specific impulse, the permanent magnet configuration exhibited a linear increase with power, with no apparent dependence on flow rate. Similarly, in the electromagnet configuration at flow rates of 750 sccm and 1000 sccm, the effect of argon mass flow on \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e was negligible. However, at a lower flow rate of 500 sccm, \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e increased significantly at the same input power and showed a steep increase with increasing power. The maximum thrust of 436 mN and a maximum \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e of 2935 s were achieved at an argon flow rate of 500 sccm, \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e of 40 A, and an input power of 15 kW.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eIon energy distributions measured by RPA.\u003c/b\u003e The ion energy distributions were measured using a retarding potential analyzer (RPA) for the electromagnet configurations. The normalized ion energy distribution function (IEDF) for each flow rate is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The peak ion energy exhibited an increasing trend with higher discharge current and electromagnet coil current. At a coil current of 10 A, the peak ion energy ranged between 21 eV and 35 eV across all flow rate cases. For a coil current of 40 A, the peak ion energy varied from 25 eV to 41 eV for the argon flow rates of 750 sccm and 1000 sccm. Notably, the peak ion energy increased as the argon flow rate decreased. In particular, at a flow rate of 500 sccm, the ion energy demonstrated a substantial increase compared to other flow conditions, with a maximum peak ion energy of 63 eV was obtained at a discharge current of 300 A and a coil current of 40 A.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eThruster efficiency.\u003c/b\u003e Thruster efficiency under various experimental conditions is plotted against specific impulse \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Under comparable argon flow rate conditions, the efficiency and thrust density in the permanent magnet cases were lower than observed in the electromagnet cases. The efficiency and \u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003esp\u003c/em\u003e\u003c/sub\u003e for the permanent magnet case ranged between 3.4% and 19% and 401\u0026ndash;1156 s, respectively, corresponding to an input power of 4\u0026ndash;10 kW. The thrust-to-power ratio was primarily concentrated between 20 mN/kW and 40 mN/kW. Meanwhile, in magnetic field geometry of the electromagnet, the thrust-to-power ratio was slightly higher, typically ranging from 25 mN/kW to 45 mN/kW. The highest thrust-to-power ratio of 46.5 mN/kW was achieved at a high argon flow rate (1000 sccm) and low input power (2.1 kW), whereas the maximum efficiency of 42% was obtained at a low flow rate (500 sccm) and high input power (15 kW).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eAs demonstrated in the results section, the performance characteristics of the thruster are significantly affected by the geometry of the external magnetic field, which varies depending on the type of magnet employed. Given that acceleration mechanisms in MPD thrusters are inherently interdependent on complex electromagnetic and gas-dynamic processes, a comprehensive understanding of how magnetic field configurations affect plasma behavior is essential for optimizing thruster performance [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong the key factors determining thruster performance, the current-voltage (I\u0026ndash;V) characteristics play a critical role, as they affecting thruster efficiency by governing the power consumption required for operation. In particular, the magnetic field geometry, along with discharge current and argon flow rate, significantly impacts plasma properties and the resulting I\u0026ndash;V curve. Consequently, a comprehensive understanding of the I\u0026ndash;V characteristics under various conditions is essential for optimizing thruster performance.\u003c/p\u003e \u003cp\u003eThe experimental results obtained under different magnetic field configurations indicate that, for the same input power, the electromagnet configuration generates higher thrust than the permanent magnet configuration. This difference can be attributed to the I\u0026ndash;V characteristics, where the permanent magnet configuration results in a higher voltage being applied to the cathode at a given discharge current, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Since thrust is primarily influenced by discharge current, the lower current levels observed in the permanent magnet case at the same input power lead to low thrust compared to the electromagnet case under similar mass flow rates (see Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a)). Additionally, these results can be interpreted in terms of particle behavior under different magnetic field configurations. In the permanent magnet configuration, despite its higher \u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e, the presence of a magnetic null point disrupts axial electron mobility, thereby weakening the induced electric field and impeding ion acceleration. Furthermore, a shorter field line length in the thruster channel may reduce the ionization rate, leading to lower plasma density. Consequently, the reduced ionization may lead to a lower local density, which ultimately disrupts efficient ion acceleration and degrades overall thruster performance [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs demonstrated in the results, across all magnetic field configurations, the total voltage exhibited an increasing trend with both the strength of the magnetic field and the discharge current in the primary operational regime above 100 A. In the thrust versus \u003cem\u003eIB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e graph for the electromagnet configuration, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, thrust consistently increased with discharge current under all conditions for both the electromagnet and permanent magnet configurations. In addition, in most cases, for a given \u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e and discharge current, a higher flow rate resulted in greater thrust. A noteworthy observation is that under higher \u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e conditions (\u003cem\u003eI\u003c/em\u003e\u003csub\u003e\u003cem\u003ecoil\u003c/em\u003e\u003c/sub\u003e: 40 A), thrust exhibited a more pronounced increase with discharge current in the low mass flow rate case compared to the high mass flow rate case. Consequently, for discharge currents above 200 A, the thrust at a lower mass flow rate exceeded that at a higher mass flow rate for the same discharge current. The observed trend can be understood through the semi-empirical voltage model, which is mainly affected by the magnetic field [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e"},{"header":"Summary and Conclusion","content":"\u003cp\u003eA comparative analysis of AF-MPD thruster performance using permanent magnets and electromagnets was conducted. Experimental investigations were carried out by varying discharge currents, flow rates, and magnetic field configurations to evaluate thruster performance, including ion energy distributions and thruster efficiency. The results indicated that while the permanent magnet configuration generated a higher \u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e, the presence of a magnetic null point restricted effective ion acceleration. In the electromagnet configuration improved thrust and efficiency, particularly at lower mass flow rates and higher applied magnetic fields. Additionally, the I\u0026ndash;V characteristics, which varied with flow rate and magnetic field strength, played a crucial role in performance. The underlying physical interpretation is as follows [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]: as the discharge current and magnetic field strength increase, plasma pinching along the thruster centerline is enhanced, thereby reducing the flux of electrons entering the near-anode region. This effect becomes more pronounced at lower flow rates and stronger magnetic field strength, leading to enhanced thruster performance, as demonstrated by the semiempirical voltage model and the measured ion energy distributions.\u003c/p\u003e \u003cp\u003eThese findings highlight the critical role of magnetic field geometry in the design of MPD thrusters. While a stronger magnetic field generally enhances performance, the specific field topology has a significant influence on plasma behavior and ion acceleration efficiency. Thus, optimizing MPD thruster performance necessitates a careful selection of magnet type, discharge conditions, and system parameters to achieve an optimal balance among thrust, efficiency, and power consumption.\u003c/p\u003e"},{"header":"Method","content":"\u003cp\u003e \u003cb\u003eMPD thruster and experimental setup.\u003c/b\u003e This section presents an overview of the low-power AF-MPD thruster used in this study, detailing its structural design, the magnetic field geometry generated by the permanent magnet or electromagnet, the thrust measurement setup, and the vacuum facility.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThruster discharge channel and magnetic field geometry.\u003c/b\u003e The AF-MPD thruster used in this work consists of a thoriated tungsten (2%) cathode, a copper anode, and three alumina insulators [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. The cylindrical cathode, with an outer diameter of 12 mm, is enclosed by an anode with an inner diameter of 80 mm. The total length of the cathode is 110 mm, and its exposed length can be adjusted. Argon is used as the propellant gas and is supplied through the cathode. Both the anode and cathode are equipped with a water-cooling circuit to regulate temperature and dissipate the substantial heat generated by the DC power input. The schematic layout of the thruster is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a).\u003c/p\u003e \u003cp\u003eThe electromagnet and the permanent magnet were utilized as sources of external magnetic fields to examine the effects of magnetic field geometry on thruster performance. Both magnets were designed in a ring shape with identical dimensions and were equipped with a water-cooling jacket on the plasma-facing side to protect them from the heat flux generated by the plasma. The axial positions of the magnet centers were aligned near the tip of the cathode. The electromagnet was constructed by winding 300 turns of AWG 7 wire, which has a cross-sectional area of 10 mm\u0026sup2;. To ensure stable operation, the current supplied to the electromagnetic coil was limited to 40 A in accordance with the ampacity of the wire. The thruster performance with the electromagnet was evaluated under three operating conditions, with coil currents of 10 A, 30 A, and 40 A. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b) presents a comparison of the calculated axial magnetic field generated by the permanent magnet and the electromagnet. In the case of the permanent magnet, the presence of a magnetic null point results in a different axial magnetic field profile compared to that of the electromagnet. The magnetic flux density at the cathode tip is 0.175 T for the permanent magnet, while for the electromagnet, it is 0.016 T, 0.049 T, and 0.065 T at coil currents of 10 A, 30 A, and 40 A, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c) illustrates the magnetic field distributions simulated using Finite Element Method Magnetics (FEMM) for both the electromagnetic and permanent magnet configurations. The results indicate that the axial magnetic field is dominant within the discharge channel in the electromagnet configuration, whereas in the permanent magnet configuration, the presence of a magnetic null point leads to an increased radial magnetic field near the magnet.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eThrust measurement system and vacuum facilities.\u003c/b\u003e To evaluate the performance of the AF-MPD thruster, a plate spring-type thrust stand equipped with a load cell was used. The plasma source was mounted on the stand, which was supported by four plate springs [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The load cell was calibrated by hanging 10 g weights using a pulley system. When a thrust is generated in the direction opposite to the ion acceleration, the load cell converts this thrust into an electrical signal proportional to the applied thrust. The measurable thrust ranges from 0.1 N and 1 N. Calibration coefficients were calculated by averaging the results obtained from pre- and post-experiment calibrations.\u003c/p\u003e \u003cp\u003eThe experiments took place in a cylindrical vacuum chamber made of stainless steel, with a diameter and length of 1.5 m. The vacuum system consisted of four turbopumps and two cryopumps, with a pumping speed of 11,000 L/s for argon. During operation, the system maintained a pressure below 1.7 mTorr at an argon flow rate of 1000 sccm.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe original draft was written by H.S., who also conducted the methodology design, investigation, visualization, and data curation. Data curation support was provided by J.K., J.H., and K.C. Review and editing of the manuscript were performed by J.K., J.H., K.C., and H.K. Validation was carried out by K.C. and H.K. Methodology development was led by H.S. and H.K. Supervision and funding acquisition were provided by K.C. and H.K. All authors reviewed the first and final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was partially supported by National R\u0026amp;D program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (RS-2022-00155950) and by KAERI Institutional Program (524560-25). This work was also partially supported by \u0026ldquo;A Research on Critical Technology for Scalable Space Tug with Autonomy and Reconfigurability\u0026rdquo; of Korea Aerospace Research Institute (Grand No. FR25F00).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGoebel, D. M., Katz, I. \u0026amp; Mikellides, I. G. \u003cem\u003eFundamentals of Electric Propulsion\u003c/em\u003e (Wiley, 2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhangar, M., Ebrahimi, R. \u0026amp; Shams, M. Numerical simulation of non-equilibrium plasma flow in a cylindrical MPD thruster using a high-order flux-difference splitting method. \u003cem\u003eActa Astronaut.\u003c/em\u003e \u003cb\u003e103\u003c/b\u003e, 129\u0026ndash;141 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlbertoni, R., Paganucci, F. \u0026amp; Andrenucci, M. A phenomenological performance model for applied-field MPD thrusters. \u003cem\u003eActa Astronaut.\u003c/em\u003e \u003cb\u003e107\u003c/b\u003e, 177\u0026ndash;186 (2015).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKrulle, G., Auweter-Kurtz, M. \u0026amp; Sasoh, A. Technology and application aspects of applied field magnetoplasmadynamic propulsion. \u003cem\u003eJ. Propuls. Power\u003c/em\u003e. \u003cb\u003e14\u003c/b\u003e, 754\u0026ndash;763 (1998).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSasoh, A. et al. Electrostatic-magnetic-hybrid thrust generation in central\u0026ndash;cathode electrostatic thruster (CC\u0026ndash;EST). \u003cem\u003eActa Astronaut.\u003c/em\u003e \u003cb\u003e152\u003c/b\u003e, 137\u0026ndash;145 (2018).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTauchi, S. et al. Analysis of thrust performance and cathode phenomena on a megawatt-class MPD thruster. \u003cem\u003eAIAA SciTech 2019 Forum\u003c/em\u003e, 1241 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNerheim, N. M. \u0026amp; Kelly, A. J. \u003cem\u003eA critical review of the magnetoplasmadynamic (MPD) thruster for space applications\u003c/em\u003e (Jet Propulsion Laboratory, California Institute of Technology, 1968).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBrophy, J. Advanced ion propulsion systems for affordable deep-space missions. \u003cem\u003eActa Astronaut.\u003c/em\u003e \u003cb\u003e52\u003c/b\u003e, 309\u0026ndash;316 (2003).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMikellides, P. G. Modeling and analysis of a megawatt-class magnetoplasmadynamic thruster. \u003cem\u003eJ. Propuls. Power\u003c/em\u003e. \u003cb\u003e20\u003c/b\u003e, 204\u0026ndash;210 (2004).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePatel, S., Bondugula, M. \u0026amp; Gorakula, S. MPD thruster technology and its limitations. \u003cem\u003eInt. J. Sci. Adv.\u003c/em\u003e \u003cb\u003e2\u003c/b\u003e, 578\u0026ndash;585 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCassady, R. J. et al. Recent advances in nuclear powered electric propulsion for space exploration. \u003cem\u003eEnergy Convers. Manag\u003c/em\u003e. \u003cb\u003e49\u003c/b\u003e, 412\u0026ndash;435 (2008).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLa Rosa Betancourt, M. A. et al. Comparative overview of NEP programs and concepts for human exploration missions. \u003cem\u003eASCEND 2021\u003c/em\u003e, 4075 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcGuire, M. L., Borowski, S. K., Mason, L. M. \u0026amp; Gilland, J. High power MPD nuclear electric propulsion (NEP) for artificial gravity HOPE missions to Callisto. \u003cem\u003eSpace Technol. Appl. Int. Forum\u003c/em\u003e (2003).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGibson, M. A. et al. NASA's Kilopower reactor development and the path to higher power missions. \u003cem\u003eIEEE Aerosp. Conf\u003c/em\u003e, 1\u0026ndash;14 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVenneri, P. \u0026amp; Eades, M. Space nuclear power and propulsion at USNC-Tech. \u003cem\u003eNucl. Technol.\u003c/em\u003e \u003cb\u003e207\u003c/b\u003e, 876\u0026ndash;881 (2021).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLa Luna, S., Sulpizi, R., Zuin, D. \u0026amp; Maggi, F. Nuclear propulsion technology for satellite applications: historical overview and current developments. \u003cem\u003e75th Int Astronaut. Congr (IAC)\u003c/em\u003e, 1\u0026ndash;14 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ewww.russianspaceweb.com. accessed (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSasoh, A. \u0026amp; Arakawa, Y. Electromagnetic effects in an applied-field magnetoplasmadynamic thruster. \u003cem\u003eJ. Propuls. Power\u003c/em\u003e. \u003cb\u003e8\u003c/b\u003e, 98\u0026ndash;102 (1992).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArakawa, Y. \u0026amp; Sasoh, A. Steady-state permanent magnet magnetoplasmadynamic thruster. \u003cem\u003eJ. Propuls. Power\u003c/em\u003e. \u003cb\u003e5\u003c/b\u003e, 301\u0026ndash;304 (1989).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShin, H., Chai, K. B. \u0026amp; Kim, H. Performance and discharge characteristics of applied\u0026ndash;field MPD thruster in accordance with ring magnet position. \u003cem\u003eVacuum\u003c/em\u003e \u003cb\u003e230\u003c/b\u003e, 113674 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKr\u0026uuml;lle, G. Characteristics and local analysis of MPD thruster operation. \u003cem\u003e6th Electr Propuls. Plasmadyn Conf\u003c/em\u003e, 672 (1967).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoxberger, A. \u0026amp; Herdrich, G. Experimental test campaign of gas-fed steady state applied-field magnetoplasmadynamic thruster SX3. \u003cem\u003eIEPC Paper\u003c/em\u003e \u003cb\u003e251\u003c/b\u003e, (2013).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLev, D. R. \u0026amp; Choueiri, E. Y. Scaling of efficiency with applied magnetic field in magnetoplasmadynamic thrusters. \u003cem\u003eJ. Propuls. Power\u003c/em\u003e. \u003cb\u003e28\u003c/b\u003e, 609\u0026ndash;616 (2012).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolzin, K. et al. Performance of a permanent-magnet cylindrical Hall-effect thruster. \u003cem\u003e45th AIAA Joint Propuls. Conf\u003c/em\u003e, 4812 (2009).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFerreira, J. L. et al. Permanent magnet Hall thruster development for future Brazilian space missions. \u003cem\u003eComput. Appl. Math.\u003c/em\u003e \u003cb\u003e35\u003c/b\u003e, 711\u0026ndash;726 (2016).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePolzin, K. et al. Comparisons in performance of electromagnet and permanent-magnet cylindrical hall-effect thrusters. \u003cem\u003e46th AIAA Joint Propuls. Conf\u003c/em\u003e, 6695 (2010).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAuweter-Kurtz, M., Kriille, G. \u0026amp; Kurtz, H. The investigation of applied-field MPD thrusters on the International Space Station. \u003cem\u003eProc. 25th Int. Electr. Propuls. Conf.\u003c/em\u003e, 721\u0026ndash;727 (1997).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKodys, A. \u0026amp; Choueiri, E. A critical review of the state-of-the-art in the performance of applied-field magnetoplasmadynamic thrusters. \u003cem\u003e41st AIAA Joint Propulsion Conf.\u003c/em\u003e, 4247 (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun, Y. et al. Experimental investigation of the electromagnetic acceleration mechanisms in an applied-field magnetoplasmadynamic thruster. \u003cem\u003ePlasma Sources Sci. Technol.\u003c/em\u003e \u003cb\u003e33\u003c/b\u003e, 115016 (2024).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDu, Y. et al. Theoretical research on magnetic confinement mechanism of applied-field magnetoplasmadynamic thruster. \u003cem\u003eAerospace\u003c/em\u003e \u003cb\u003e10\u003c/b\u003e, 124 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim, H., Doh, G. \u0026amp; Choe, W. Generation of multiply charged ions in accordance with geometry and magnetic field in Hall thruster plasmas. \u003cem\u003eCurr. Appl. Phys.\u003c/em\u003e \u003cb\u003e51\u003c/b\u003e, 8\u0026ndash;12 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTikhonov, V., Semenikhin, S., Brophy, J. \u0026amp; Polk, J. Performance of 130 kW MPD thruster with an external magnetic field and Li as a propellant. \u003cem\u003eProc. 25th Int. Electr. Propuls. Conf.\u003c/em\u003e, 728\u0026ndash;733 (1997).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMikellides, P. \u0026amp; Turchi, P. A theoretical model for the thrust and voltage of applied-field MPD thrusters. \u003cem\u003e34th AIAA Joint Propulsion Conf.\u003c/em\u003e, 3474 (1998).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChai, K. B. \u0026amp; Kwon, D. H. Heat and particle load test facility using an applied-field MPD thruster for studying fusion divertor technology. \u003cem\u003ePlasma Phys. Control Fusion\u003c/em\u003e. \u003cb\u003e62\u003c/b\u003e, 035007 (2020).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChai, K. B., Kwon, D. H. \u0026amp; Lee, M. Development of plasma beam irradiation facility using applied-field MPD thruster to study plasma\u0026ndash;surface interactions. \u003cem\u003ePlasma Phys. Control Fusion\u003c/em\u003e. \u003cb\u003e63\u003c/b\u003e, 125020 (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"AF–MPD thruster, Magnetic field, Thruster performance, Permanent magnet, Electromagnet","lastPublishedDoi":"10.21203/rs.3.rs-6699652/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6699652/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSince the performance of MPD thrusters is highly dependent on the applied magnetic field, we experimentally investigated the effects of magnetic field geometry. Thrust, specific impulse, and ion energy distribution were measured under various operating conditions. The results indicate that the magnetic field configuration of permanent magnets with a magnetic null point may limit effective ion acceleration, leading to reduced thrust while the permanent magnet produces a stronger applied magnetic field (\u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e: 0.175 T) than the electromagnet (\u003cem\u003eB\u003c/em\u003e\u003csub\u003e\u003cem\u003eA\u003c/em\u003e\u003c/sub\u003e: 0.016\u0026ndash;0.065 T). For the electromagnet configuration, thrust increased more significantly with discharge current at a lower flow rate (500 sccm) and a higher electromagnetic coil current (40 A). When the discharge current was increased to 300 A under the aforementioned conditions, the maximum thrust of 436 mN and the specific impulse of 2935 s were obtained. From these observations, the current-voltage (I\u0026ndash;V) characteristics, which are strongly influenced by the magnetic field, appear to be closely linked to the thruster performance, as evidenced by the measured thrust and ion energy distributions. The findings highlight the dominant influence of the magnetic field geometry on the thruster performance, along with the contributions of the discharge current and the argon flow rate.\u003c/p\u003e","manuscriptTitle":"Effects of applied magnetic fields on the performance of magnetoplasmadynamic thrusters","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-06 10:58:01","doi":"10.21203/rs.3.rs-6699652/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-13T17:40:01+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-02T03:45:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"333148960909434798316582967337155059390","date":"2025-09-18T06:48:22+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-02T03:38:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"113085021715877642332494726901022900562","date":"2025-08-22T03:12:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"14613187129529365081910768980124495701","date":"2025-06-03T07:23:54+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-02T12:50:54+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-02T12:47:40+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-06-02T11:49:34+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-31T10:04:11+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-19T13:50:02+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"389896c4-249d-454d-befb-1057455cc8a8","owner":[],"postedDate":"June 6th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":49445154,"name":"Physical sciences/Engineering/Aerospace engineering"},{"id":49445155,"name":"Physical sciences/Physics/Plasma physics/Plasma based accelerators"}],"tags":[],"updatedAt":"2026-02-09T16:00:49+00:00","versionOfRecord":{"articleIdentity":"rs-6699652","link":"https://doi.org/10.1038/s41598-026-38380-3","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-02-06 15:57:17","publishedOnDateReadable":"February 6th, 2026"},"versionCreatedAt":"2025-06-06 10:58:01","video":"","vorDoi":"10.1038/s41598-026-38380-3","vorDoiUrl":"https://doi.org/10.1038/s41598-026-38380-3","workflowStages":[]},"version":"v1","identity":"rs-6699652","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6699652","identity":"rs-6699652","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}