Design and Development of a High-Temperature Superconductor CCT Magnet for Research and Hadron Therapy Applications

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 36, NO. 3, MAY 2026 4400405 Design and Development of a High-Temperature Superconductor CCT Magnet for Research and Hadron Therapy Applications E. De Matteis ,A.Ballarino ,D.Barna ,M.Bartok ,E.Beneduce ,G.Crespi , A. Echeandia, G. Kirby , T. Lecrevisse ,J.Lucas , J. van Nugteren ,D.Pedrini ,L.Rossi , Fellow, IEEE,C.Senatore , and S. Sorti Abstract—The European I.FAST project’s Work Package 8 (WP8) initiative focuses on advancing Canted Cosine Theta (CCT) magnet technology using High-Temperature Superconductors (HTS). These magnets aim to revolutionize synchrotron and gantry designs by reducing their size and cost, offering transformative potential for research and hadron therapy. HTS materials enable higher magnetic fields and smaller cryogenic systems compared to Low-Temperature Superconductors (LTS). However, challenges such as cable production, magnet design, and cost-efficiency must be addressed. This work presents the design of a straight HTS CCT magnet capable of achieving a central dipole field of 4 T at an operating temperature of 20 K, using a cable configuration composed of two HTS tapes. A ramp rate of 0.4 T/s is targeted, with a lower initial ramp rate of 0.15–0.2 T/s deemed acceptable for early-stage development. The magnetic design was optimized to ensure high field quality under operational conditions. Heat extraction is managed through a closed-loop cooling system, with 20 K-helium gas flowing through channels digged directly in the body of the magnet. Thermal simulations demonstrate the effectiveness of this cooling approach, ensuring operational stability. Additionally, the paper highlights key assembly procedures and experimental tests conducted for qualifying critical fabrication steps, including cabling and winding. Results from these tests confirm the reliability and robustness of the developed methods, flooring the way for future HTS CCT magnet advancements. The progress Received 28 July 2025; revised 25 September 2025; accepted 13 October 2025. Date of publication 16 October 2025; date of current version 4 November 2025. This work was supported in part by European Commission H2020I.FAST under Grant 101004730 and in part by NextGeneration EU-funded Italian National Recovery and Resilience Plan under Project IR0000003 - IRIS. (Corresponding author: E. De Matteis.) E. De Matteis, G. Crespi, and D. Pedrini are with the Laboratory of Accelerators and Applied Superconductivity (LASA), National Institute for Nuclear Physics (INFN), Milan Section, 20054 Milano, Italy (e-mail: [email protected]). A. Ballarino is with CERN, CH-1211 Geneva 23, Switzerland. D. Barna and M. Bartok are with the HUN-REN Wigner Research Centre for Physics, 1525 Budapest, Hungary. E. Beneduce, L. Rossi, and S. Sorti are with the Laboratory of Accelerators and Applied Superconductivity (LASA), National Institute for Nuclear Physics (INFN), Milan Section, 20054 Milano, Italy, and also with the Department of Physics, University of Milan, 20133 Milan, Italy. A. Echeandia and J. Lucas are with Elytt Energy, 28020 Madrid, Spain. G. Kirby is with Magnet Consulting Services, Spain. T. Lecrevisse is with the Commissariat à l’énergie atomique et aux énergies alternatives, 91400 Saclay, France. J. van Nugteren is with Little Beast Engineering, 6021 RW Budel, Netherlands. C. Senatore is with the University of Geneva, 1205 Geneva, Switzerland. Color versions of one or more figures in this article are available at https://doi.org/10.1109/TASC.2025.3622552. Digital Object Identifier 10.1109/TASC.2025.3622552 presented here represents a significant step toward compact and efficient superconducting magnets, aligning with the project’s goal of fostering innovative solutions for next-generation synchrotrons and gantries. Index Terms—Superconducting magnets, HTS magnets, magnets for medical systems. I. INTRODUCTION THE I.FAST (Innovation Fostering in Accelerator Science and Technology) project [1], supported by the European Union under Horizon 2020, aims to boost innovation in accelerator technologies through close cooperation between research institutes, universities, and industrial partners. As part of this effort, WP8 focuses on developing new superconducting magnet concepts, in particular the use of High-Temperature Superconductors (HTS) in Canted Cosine Theta (CCT) geometries [2]. These magnets combine the mechanical simplicity and field control of the CCT layout [3] with the advantages of HTS conductors like REBCO, which allow for higher magnetic fields and reduced cooling requirements compared to traditional lowtemperature systems [4],[5]. This approach is especially relevant for applications where space and efficiency matter, such as in synchrotrons or compact gantry designs for hadron therapy [6], [7],[8],[9]. HTS-based accelerator magnets show great promise but still face key challenges—namely, cable fabrication, force management, thermal control at 15–20 K, and reliable protection systems. Similar developments in compact medical magnets [10], high-field dipoles [11],[12], and ongoing CCT R&D [13],[14] highlight the broader relevance of this work and its role in advancing HTS technologies for future accelerators. This paper presents the latest design and development of a straight HTS CCT dipole magnet, as a demonstrator within the I.FAST WP8 initiative [15],[16]. The magnet is designed to achieve a central dipole field of 4 T at 20 K, using a two-tape REBCO cable architecture and targeting an initial ramp rate between 0.15 and 0.2 T/s, with a final goal of 0.4 T/s. The study includes magnetic design optimization for field quality and a dual-channel helium gas cooling system for thermal stabilization. Furthermore, the paper reports on experimental results from cabling, splicing, and winding tests that validate key fabrication steps, and the winding of the first layer ongoing of the final 1051-8223 © 2025 IEEE. All rights reserved, including rights for text and data mining, and training of artificial intelligence and similar technologies. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: CERN. Downloaded on December 05,2025 at 16:15:50 UTC from IEEE Xplore. Restrictions apply. 4400405 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 36, NO. 3, MAY 2026 Fig. 1. 3D CAD model of the straight HTS CCT magnet, including winding grooves, inner (red) and outer (blue) formers, white and green external envelopes, cooling channels, and splice boxes, and 2-tape HTS cable layout. magnet. These results lay the groundwork for future curved HTS CCT magnets and contribute to the broader objective of developing compact, high-performance superconducting magnets for research and medical applications. II. MAGNET DESIGN The demonstrator magnet presented is a straight HTS CCT dipole, designed to generate a central magnetic field of 4 T at an operating temperature of 20 K. The magnet operates with a temperature margin greater than 10 K, ensuring robust thermal stability under both steady-state and transient conditions [17]. The magnet uses a compact two-tape cable architecture composed of 4 mm-wide REBCO tapes (Fig. 1with a nominal current of 980 A). To enhance both thermal stability and quench protection, the HTS stack is stabilized with two 0.2 mm thick copper tapes placed above and below the superconducting layer. This configuration promotes efficient heat conduction during transient events and contributes to the overall reliability of the magnet during fast ramping and potential quench scenarios. The coil layout uses the Frenet–Serret frame to define groove paths, ensuring proper tape alignment and avoiding hard-way bends. For this demonstrator, a straight design was chosen to simplify handling and validate construction steps ahead of future curved versions for gantry use. A key feature of the design is its closed-loop helium gas cooling system, built into the former. Helium at 20 K circulates through channels near the winding grooves, providing effective conduction cooling and keeping the temperature uniform across the coil. The construction of the magnet is currently underway in collaboration with the industry (Elytt Energy, Spain), representing a significant milestone toward the industrial validation of HTS CCT technology. The full assembly includes modular components such as splice boxes for cable interconnections, integrated cooling channels, and external supports for mechanical alignment and thermal anchoring. Fig. 1 shows the finalized 3D model of the magnet, including the winding grooves, helium channels, and terminal interfaces. The main design parameters are summarized in Table I, including field target, coil dimensions, cable specifications, and cooling configuration. A. Magnetic Design and Field Quality The magnetic design of the demonstrator was optimized using a full 3D field model, ensuring high field quality at the conductor TABLE I MAIN DESIGN PARAMETERS OF THE HTS CCT DIPOLE MAGNET Fig. 2. 3D magnetic field model of the HTS CCT magnet showing field strength on the conductor. The end parts represent the splice/current lead region with single cables, while the central part represents the stack of 23 cables. TABLE II INTEGRATED FIELD HARMONICS (NORMAL AND SKEW)ATREFERENCE RADIUS R0=26.6 MM (NORMALIZED TO MAIN FIELD) location and within the aperture. The geometry of the 23 cable grooves was individually tuned to minimize field harmonics and to account for the effect of Lorentz forces under operating conditions. A Fourier-synthesized axial excursion Z(ϑ)= Z1sin(ϑ)+Z2sin(2ϑ)+Z3sin(3ϑ)was implemented, with coefficients Zndetermined through systematic simulation studies. Corrections were found to be Z3=0.85 mm sextupole adjustment for both inner and outer formers, complemented by an additional Z2=0.1 mm quadrupole correction for the outer former. Fig. 2displays the magnetic field distribution in a cross-section of the coil, with field strength and orientation mapped over the conductor path. Table II reports the calculated integrated field harmonics (bn,an), demonstrating that the optimized groove layout results in excellent field uniformity across the aperture, suitable for beam transport applications. The results of this magnetic and mechanical design form the basis for subsequent fabrication and test phases, offering a robust and scalable platform for future HTS CCT magnets tailored to synchrotron and gantry environments. Authorized licensed use limited to: CERN. Downloaded on December 05,2025 at 16:15:50 UTC from IEEE Xplore. Restrictions apply. DE MATTEIS et al.: DESIGN AND DEVELOPMENT OF A HTS CCT MAGNET FOR RESEARCH AND HADRON THERAPY APPLICATIONS 4400405 Fig. 3. Enthalpy margin versus deposited power in the HTS conductor, illustrating thermal safety limits across ramping scenarios. III. THERMAL MANAGEMENT Effective thermal management is crucial for ensuring the safe and reliable operation of HTS magnets, particularly under ramping conditions and in conduction-cooled environments. The thermal design of the prototype CCT magnet leverages a forced-flow helium gas cooling system operating at 20 K and 5 bar, with channels drilled directly within the former structure. This enables efficient heat extraction and temperature uniformity along the length of the magnet. The coolant temperature is restored outside the cryostat by means of cryocoolers. Initial analysis showed that fast ramping from 0 to 1000 A over 10 s results in total dynamic losses of approximately 60 W— comprised of ∼50 W in the conductor and ∼10 W in the formers. To reduce the average heat load, an extended ramping cycle with 140s stabilization phase after each ramp (both up and down) has been considered. This approach reduces the average power dissipation to 4 W (3.3 W in the conductor and 0.7 W in the formers), making it compatible with the specifications of the cooling system operating at 20 K. In addition to dynamic AC losses, resistive heat generation in the splice regions was considered, with a resistance of 200 nΩ per junction and full current operation at 1000 A. This value is similar to the performance achieved in the first junction tests at LASA. As illustrated in Table IV, the best performance achieved up to now is more than an order of magnitude lower than that value. The total resistive heat load due to the 46 junctions reaches ∼9 W. To find out whether this still allows for operation within the temperature margin of the conductor, steady-state simulations with the time-averaged thermal loads where performed. The maximum time-averaged temperature was found to be in the splices junctions and smaller than 25 K, which falls within the admissible range. A key aspect of the thermal evaluation was estimating the temperature rise during ramping. By comparing the total energy dissipated during each ramp (∼50 W ·10 s =500 J, uniformly distributed on the conductor volume) with the calculated volumetric enthalpy of the REBCO conductor, the adiabatic increase in temperature was calculated to be less than 10 K. As a result, the maximum expected temperature in the conductor stays below 28 K–still offering a 2 K-margin. Fig. 3shows the calculated enthalpy margin as a function of deposited power, confirming robust thermal resilience under different operating scenarios. Fig. 4presents the average temperature distribution along the conductor path Fig. 4. Left: temperature distribution, obtained from a stationary simulation with heat loads corresponding to the average load over an operation cycle. Right: highlight of the conductor region. The total heat loads in the conductor and formers are distributed uniformly in each volume. The heat load on spliceboxes is concentrated in the junctions regions. Material is aluminum bronze except for the conductor which is a homogenized, non-isotropic mixture of copper, steel, kapton and wax resembling the real cables stack composition. Cooling channels are treated as 1D heat sinks at a reference temperature. Fig. 5. Custom winding machine with tilted shaft, enabling continuous former rotation and on-the-fly cable shaping. during nominal operation. The temperature gradient remains well-contained thanks to the efficient conduction cooling and careful positioning of the helium channels. IV. FABRICATION AND ASSEMBLY The fabrication of the HTS CCT prototype magnet involved the development and validation of multiple custom processes to ensure the mechanical integrity and electrical performance of the winding and splicing procedures. A key aspect of the manufacturing strategy was the in-house development of all tooling and techniques required for handling the composite conductor, formed by two REBCO tapes stabilized with copper layers and insulated with Kapton. The winding process was carried out using a dedicated machine specifically designed for this project (Fig. 5). The machine features a tilted shaft configuration to allow continuous rotation of the former during winding, enabling the conductor to be shaped and positioned with minimal mechanical stress. This setup also supports on-the-fly cabling and minimizes the need for manual tape handling, which is particularly important for preserving the critical current of the brittle HTS tapes. Fig. 5 shows the winding machine during cable layup and coil formation. To validate the mechanical and thermal design, a 6-turn mockup coil was fabricated using dummy copper tapes. The winding Authorized licensed use limited to: CERN. Downloaded on December 05,2025 at 16:15:50 UTC from IEEE Xplore. Restrictions apply. 4400405 IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 36, NO. 3, MAY 2026 Fig. 6. Winding of the first layer completed at Wigner RCP. The Kapton insulation of the HTS cable was separately tested up to 1 kV without damage, as reported in [18]. TABLE III CRITICAL CURRENT (Ic)MEASUREMENTS FOR DIFFERENT CABLING STAGES was performed on a test former with realistic rib thicknesses (0.5–0.9 mm), and the coil was subsequently wax-impregnated to assess mechanical stability and impregnation behavior. The successful completion of this mock-up demonstrated the feasibility of the proposed fabrication route and provided confidence for scaling up to the full prototype [18]. All critical manufacturing operations—including cable coating with indium-tin solder, in-situ soldering, winding, splicing, and impregnation—were validated without measurable degradation of the HTS conductor (see Section V). As shown in Fig. 6, the first-layer winding of the final prototype is underway at Wigner RCP, supported by Elytt Energy and INFN-LASA, and will serve as a foundation for future industrial production of HTS CCT magnets. V. CABLING AND SPLICING TESTS Extensive cabling and splicing tests were conducted to validate the reliability of the composite REBCO conductor under all fabrication steps [18]. The tests focused on assessing the impact of mechanical handling and soldering on the critical current, as well as evaluating the electrical performance of the splice joints. REBCO tapes (4 mm wide, from Faraday Factory, Japan) were tested in liquid nitrogen under different fabrication conditions. The results confirmed that there is no measurable degradation in critical current after solder-coating, winding, or cable assembly. A moderate ∼12% reduction in Icwas observed when comparing the two-tape stack to individual virgin tapes, attributed to self-field effects in the stacked configuration. Table III summarizes the critical current measurements. Splicing tests focused on a “crocodile” configuration (Fig. 7) with in-situ soldering at 140 °C, using Indium-Tin alloy. Contact pressure was applied during soldering to optimize joint quality. Tests demonstrated that increasing pressure from 1.5 MPa to 12 MPa significantly reduced joint resistance, achieving values below 10 nΩat 6 MPa, and a degradation in Icat 12 MPa or higher. This directly enhances quench protection by minimizing local heat generation. The splice resistance and performance data are reported in Table IV. Fig. 7. Sample holder and contact pressure system used for splice resistance tests. TABLE IV SPLICE RESISTANCE Rj,SPECIFIC RESISTANCE RSPEC ,CRITICAL CURRENT Ic,100 (@1µV/cm)AS A FUNCTION OF CONTACT PRESSURE Fig. 7shows the experimental setup used for the splice tests, including the sample holder and the pressure system. These results confirm that the cabling and splicing processes are welloptimized for the REBCO architecture adopted in the prototype magnet. VI. CONCLUSION The work presented here demonstrates significant progress toward the development of a high-performance HTS Canted Cosine Theta (CCT) dipole magnet for accelerator and hadron therapy applications. The development of the HTS CCT dipole magnet has successfully validated all key fabrication steps— from solder coating to winding and splicing—without degrading the conductor. The two-tape REBCO cable with copper stabilizers proved both robust and stable, while crocodile-type splices with indium-tin soldering achieved low contact resistance (<10 nΩ) under moderate pressure(<10 MPa). Thermal simulations confirm that the proposed dual-channel conduction cooling system enables safe operation at 20 K, even under high ramp rates (up to 0.4 T/s). Adiabatic heating and dynamic losses are well within the cooling budget of standard cryocoolers, with no quench risk identified during the expected operation cycle. The magnet is currently under construction, with winding and assembly in progress. The successful realization of this straight HTS CCT prototype will serve as a technological demonstrator, paving the way for future implementation of compact HTS magnets in synchrotron beamlines and gantry systems. The next phase—final assembly and cryogenic testing—will bring the project closer to its goal: enabling compact, industrial HTS magnets for future synchrotrons and gantries. ACKNOWLEDGMENT The authors gratefully acknowledge H2020-I.FAST Coordinator, Maurizio Vretenar, for his continuous support. Authorized licensed use limited to: CERN. Downloaded on December 05,2025 at 16:15:50 UTC from IEEE Xplore. Restrictions apply. 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