Construction of HTS CCT demonstrator

I.FAST Innovation Fostering in Accelerator Science and Technology Horizon 2020 Research Infrastructures GA n° 101004730 DELIVERABLE REPORT Construction of HTS CCT demonstrator DELIVERABLE: D8.5 Document identifier: IFAST-D8.5 Due date of deliverable: End of the Month 42 (October 2025) Justification for delay: Delivered on Month 54 (R&D complexity) Report release date: 28/10/2025 Work package: WP8: Innovative Superconducting Magnets Lead beneficiary: ELYTT ENERGY Document status: Final ABSTRACT This report presents the as-built details of the HTS Canted Cosine Theta (CCT) magnet demonstrator developed within Task 8.5 of WP8 – Innovative Superconducting Magnets in the I.FAST project. The demonstrator is a straight, two-layer HTS CCT magnet designed to achieve a central dipole field of 4 T at 20 K, using a two-tape HTS cable configuration and targeting a ramp rate of 0.4 T/s. The document describes the final design configuration, conductor and joint characteristics, manufacturing and assembly procedures. The report also summarizes the verification and quality control activities performed prior to testing and evaluates the compliance with design specifications, confirming the magnet’s readiness for cryogenic qualification at INFN. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 2 / 26 I.FAST Consortium, 2025 For more information on IFAST, its partners and contributors please see https://ifast-project.eu/ This project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement No 101004730. IFAST began in May 2021 and will run for 4 years. Delivery Slip Name Partner Date Authored by E. De Matteis, D. Barna, M. Bartok, E. Beneduce, G. Crespi, A. Echeandia, J. Lucas, D. Pedrini INFN, WIGNER, ELYTT ENERGY 20/10/2025 Edited by E. De Matteis INFN 28/10/2025 Reviewed by D. Barna, J. Lucas, M. Bartok WIGNER RCP, ELYTT ENERGY 23/10/2025 Approved by M. Vretenar CERN 28/10/2025 CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 3 / 26 TABLE OF CONTENTS 1. INTRODUCTION ......................................................................................................................................... 5 2. MAGNET DESIGN OVERVIEW ............................................................................................................... 6 A. FINAL ELECTROMAGNETIC DESIGN PARAMETERS .................................................................... 7 B. THERMAL DESIGN AND CRYOGENIC INTERFACES. ..................................................................... 8 3. CONDUCTOR AND SPLICES ................................................................................................................. 10 4. MAGNET FABRICATION AND ASSEMBLY PROCEDURES ........................................................... 13 5. VERIFICATION AND QUALITY CHECKS .......................................................................................... 23 6. CONCLUSIONS ......................................................................................................................................... 24 7. REFERENCES ............................................................................................................................................ 26 CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 4 / 26 Executive summary This report presents the design, fabrication, and assembly of the High-Temperature Superconducting (HTS) Canted Cosine Theta (CCT) dipole magnet demonstrator, developed within Work Package 8 (WP8) of the I.FAST project. The magnet represents the first complete realization of an HTS CCT concept using REBCO tapes, targeting a central dipole field of 4 T, and ramp rates of 0.4 T/s, at 20 K with conduction cooling. The demonstrator was designed to validate the feasibility of HTS CCT technology for accelerator and medical applications, with all components—mechanical, electrical, and cryogenic—developed in close collaboration between academic and industrial partners. The final design incorporates 20 two-tape REBCO composite cables, each stabilized with copper layers and insulated with a double Kapton layer to ensure robustness up to 1 kV. Three additional pickup coils made of insulated copper tape were included for field monitoring. The winding process required the development of a dedicated automated winding machine, capable of precisely guiding the flat HTS tapes into the CCT grooves while avoiding hard-way bending. The machine assembled the stacked cable in real time during winding and maintained uniform tension through computer-controlled motion. This process, combined with optimized alignment and controlled solder flux application, ensured consistent cable positioning and minimal mechanical strain throughout all turns. Following winding, in-situ soldering and splicing were carried out, producing stable and lowresistance joints in the nanohm range. The complete coil assembly was impregnated with paraffin wax under vacuum and controlled heating, ensuring full penetration and void-free insulation, as previously demonstrated in earlier prototypes. A streamlined instrumentation system was implemented, including PT100 sensors for temperature monitoring during fabrication, CERNOX sensors for cryogenic operation, and voltage taps across each splice for diagnostics. High-voltage tests conducted after each construction phase—from winding to final impregnation—confirmed full insulation compliance and electrical soundness. The HTS CCT demonstrator is now fully assembled and ready for cryogenic qualification, representing a crucial step toward industrializing HTS CCT technology and enabling future compact, high-field magnets for accelerator and hadron therapy applications. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 5 / 26 1. Introduction The Work Package 8 (WP8) – Innovative Superconducting Magnets of the H2020–EU project I.FAST [1] has the dual objective of fostering long-term strategic coordination among European laboratories and industries in the field of superconducting magnet technologies and of advancing the development of High-Temperature Superconductor (HTS) applications for accelerators. WP8 aims to establish a permanent European Strategy Group, open to worldwide collaboration, to define a coherent roadmap for HTS magnet technologies and to strengthen the involvement of industry in their design and fabrication. Within this framework, one of the main technological goals is to explore the Canted Cosine Theta (CCT) magnet concept using HTS conductors [2]. This activity follows a first phase based on LowTemperature Superconductor (LTS) technology, which served as a learning platform for industrial partners to acquire experience with the CCT architecture. The HTS CCT demonstrator thus represents a crucial step toward scalable, high-field accelerator magnets with simplified and more reliable manufacturing processes. The baseline magnet parameters were defined in coordination with the HITRIplus program, which focuses on the development of magnet technologies for hadron therapy applications [3, 4]. For both demonstrators, a straight geometry was selected to simplify design, fabrication, and testing while retaining the essential features of a curved accelerator magnet. Task 8.5, dedicated to the construction of the HTS CCT magnet demonstrator, was carried out by a consortium comprising ELYTT ENERGY (task leader), and several institutes as INFN-LASA, WIGNER RCP, CERN, and CEA. In this task, the partners transformed the conceptual design into a fully engineered and fabricated demonstrator. The demonstrator is designed to achieve a central dipole field of 4 T at an operating temperature of 20 K, using a two-tape HTS cable configuration. The design targets a field ramp rate of 0.4 T/s, with an initial operational ramp rate of 0.15–0.2 T/s considered acceptable for early development and stability validation. The demonstrator serves as a technological milestone toward scalable HTS magnet systems for accelerators. The work includes the preparation of detailed construction drawings, the definition of manufacturing procedures, and the design and production of dedicated tooling and components. Following the engineering design phase [5], the procurement of the key materials, and a mock-up coil fabrication[6], the final demonstrator was completed through two-layer winding, and mechanical assembly, followed by electrical qualification tests, manufactured by Wigner RCP and Elytt test facilities and coordination and technical support of the INFN-LASA team. This report presents the as-built details of the HTS CCT magnet demonstrator. It describes the final design configuration, the conductor and joint characteristics, the manufacturing and assembly procedures, and the main as-built parameters of the magnet. A summary of the verification activities performed prior to testing and the compliance with design specifications is also included, concluding with an assessment of the magnet’s readiness for cryogenic qualification. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 6 / 26 2. Magnet Design Overview The HTS Canted Cosine Theta (CCT) dipole magnet demonstrator (Tab. 1 and Fig. 1) developed within the I.FAST WP8 framework represents a major step toward industrially scalable accelerator magnets based on REBCO technology. Its design combines the CCT concept’s inherent geometric precision with the robustness and thermal margin offered by HTS conductors. The following sections summarize the final electromagnetic, and thermal design characteristics of the demonstrator. Table 1. Main Design Parameters of the HTS CCT Dipole Magnet: model vs as-built parameters. Parameter Model As-built Central field 4 T < 4 T Operating temperature 20 K Temperature margin 10 K Cable type 2-tape REBCO + Cu stabilizer Cable width 4 mm Nominal current 980 A Stack of cables per groove 23 20 Magnet aperture 80 mm Magnet length ≃ 1 m Cooling method conduction cooled Ramp rate (target) 0.4 T/s Figure 1. 3D model of the HTS CCT magnet demonstrator. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 7 / 26 a. FINAL ELECTROMAGNETIC DESIGN PARAMETERS [7] The demonstrator magnet is a straight HTS CCT dipole designed to generate a central field of 4 T at an operating temperature of 20 K. The magnet employs a two-layer, two-tape REBCO cable architecture stabilized with copper, optimized to operate at a nominal current of 980 A with a temperature margin exceeding 10 K. The total magnet length is approximately 1 meter, chosen to facilitate manufacturing and testing while maintaining relevance for scaling to 2–3 m class magnets in future accelerator and gantry applications. The CCT configuration offers intrinsic alignment precision and field quality by defining the conductor path analytically along helical grooves machined into a cylindrical former. The geometry of the grooves follows the Frenet–Serret frame, ensuring that each REBCO tape conforms naturally to the surface and avoids hard-way bending. This minimizes local strain on the HTS layer, preserving the conductor’s critical current and improving reproducibility during winding. Figure 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. The final coil layout consists of 23 two-tape stacks per groove in each layer, distributed symmetrically around the aperture. The reference radius of the magnetic aperture is 26.6 mm, corresponding to an 80 mm mechanical bore diameter. The optimized groove pattern ensures that the conductor path reproduces a nearly ideal cosine-theta current distribution, minimizing field harmonics. The magnetic optimization process was carried out using a full 3D finite element model, which allowed for precise control of local field strength and orientation along the conductor. To correct residual field distortions due to end effects and the finite thickness of the HTS cable stack, a Fourier-synthesized axial modulation of the groove position was implemented: 𝑍(𝜃)= 𝑍1sin(𝜃)+ 𝑍2sin(2𝜃)+ 𝑍3sin(3𝜃) CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 8 / 26 with optimized coefficients 𝑍2=0.1 mm (quadrupole correction) and 𝑍3=0.85 mm (sextupole correction). The quadrupole correction was applied only to the outer former, while the sextupole correction was applied to both inner and outer formers. These adjustments reduced the integrated field harmonics to below 5 units at the reference radius, as reported in Table 2. The resulting field quality is suitable for beam transport applications, validating the scalability of the HTS CCT architecture to larger accelerator systems. Table 2. Integrated Field Harmonics (Normal and Skew) at Reference Radius R0 = 26.6 mm (Normalized to Main Field) Order bn [units] an [units] 2 4.6 -0.2 3 -4.8 -0.1 4 -1.0 0.0 5 1.3 0.0 The target ramp rate of the magnet is 0.4 T/s, with an initial ramp rate of 0.15–0.2 T/s used during early operation to qualify the magnet’s stability. The conductor stack’s high current density and copper stabilization enable fast ramping with manageable AC losses, supported by efficient conduction cooling. b. THERMAL DESIGN AND CRYOGENIC INTERFACES [7] Thermal management is a critical aspect of HTS magnet operation, particularly under ramping conditions where dynamic AC losses and joint heating can compromise stability. The demonstrator employs an active conduction cooling scheme based on helium gas circulation at 20 K and 5 bar within channels integrated into the aluminum former. The cooling channels are drilled longitudinally near the winding grooves, ensuring uniform temperature distribution and effective heat removal from both coil layers. The helium gas is circulated in a closed-loop system, interfaced with external cryocoolers that restore the gas temperature before re-entry into the magnet. This design eliminates the need for liquid cryogens while maintaining excellent temperature control, a key requirement for industrial scalability. Thermal simulations predict an average heat load of approximately 60 W during fast ramping (0– 1000 A in 10 s), including ∼50 W in the conductor and ∼10 W in the formers. By adopting ramp cycles with stabilization phases of 140 s between successive ramps, the average thermal load is reduced to 4 W total—compatible with the available cryocooler capacity. Additional heat generation arises from resistive losses in splice regions, estimated at 200 nΩ per junction under full current operation, corresponding to a total of about 9 W distributed across the 46 joints. Steady-state simulations indicate that the maximum temperature in these regions remains below 25 K, comfortably within the conductor’s thermal margin. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 9 / 26 Figure 3. Left: temperature distribution, obtained from a stationary simulation with heat loads corresponding to the average load over an operation cycle. Right: Enthalpy margin versus deposited power in the HTS conductor, illustrating thermal safety limits across ramping scenarios. Transient analyses confirm that the adiabatic temperature rise in the conductor during a ramp cycle is less than 10 K, ensuring that the maximum local temperature does not exceed 28 K. The overall temperature margin remains above 2 K even under the most demanding ramp conditions, confirming robust thermal stability. The cryogenic interfaces are designed to integrate directly with the INFN test bench. They include vacuum feedthroughs for helium gas supply and return, mechanical supports for thermal anchoring, and electrical terminals compatible with the existing current leads and instrumentation systems. Temperature sensors and voltage taps are distributed along the magnet length to monitor the thermal gradient and detect any onset of quench or localized heating. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 16 / 26 Figure 9. Custom made winding machine. A dedicated winding machine was designed and built for this project to handle the composite cable structure and to ensure the correct tangential insertion of the cable into the CCT grooves (Fig.9). The machine consists of two main sub-assemblies: • a rotating support system holding the former, mounted on a shaft tilted by 30° with respect to the rotation axis, corresponding to the winding helix angle; • a translation frame carrying the conductor spools (HTS tapes, copper stabilizers, and Kapton insulation), capable of controlled motion in three orthogonal directions using stepper motors and precision ball screws. The composite cable, assembled “on the fly” during winding, consists of two HTS tapes sandwiched between two copper stabilizer tapes, insulated by a Kapton layer. Assembling the cable continuously during winding is essential, since the developed lengths of the individual tapes differ slightly due to geometry and bending, making pre-assembly over the full length impractical. The Kapton insulation is folded around the cable by a pair of rollers in the “Kapton folding tool.” Friction between the Kapton and the rollers provides adjustable cable tension, tuned by changing the preload on the tool’s springs. In this configuration, no flux paste is applied during winding. The flux paste was pre-applied to the conductor in an earlier preparation step to ensure adequate surface coating for soldering. During winding, the system instead incorporates a controlled removal of excess flux paste to prevent CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 17 / 26 accumulation within the grooves and to maintain consistent tape alignment and mechanical integrity throughout the process. A Raspberry Pi-based control system drives the five stepper motors, enabling precise motion coordination and real-time control of winding parameters via an intuitive graphical interface. The significant weight of the outer former (≈150 kg) and the moving frame requires careful safety management; the system is therefore operated through an uninterruptible power supply (UPS) to prevent back-driving of motors in the event of a power failure. The winding initially followed the baseline insulation scheme based on a single Kapton layer surrounding each cable. However, high-voltage tests at 1 kV performed after the first winding phase revealed insufficient insulation resistance, likely due to limited surface flatness of the former and localized mechanical contact points. To ensure robust electrical insulation, an additional Kapton layer was introduced around the cable, resulting in a double-Kapton insulation scheme. This modification increased the overall insulation thickness but was successfully accommodated within the groove dimensions without affecting the mechanical integrity. The final coil configuration consists of 20 active cable stacks (Fig. 10) and 3 pickup coils made of Kapton-insulated copper tapes, used for protection and measurement purposes. The reduction from the original 23 cable stacks was implemented to optimize layer closure and ensure uniform groove filling with the thicker insulation (Fig. 11). During the winding, each turn was laid under continuous optical monitoring to verify cable positioning and groove alignment. Tangential cable entry was maintained throughout to avoid mechanical stress or “hard-way” bending on the REBCO tapes. The customized winding machine and procedure developed in this project successfully demonstrated the feasibility of precise, reproducible winding of multi-tape HTS CCT coils, establishing a scalable manufacturing approach for future curved or larger-aperture HTS magnets. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 18 / 26 Figure 10. Left: outer former during the winding. Right: Inner former wound with Elytt and INFN-LASA teams at Wigner RCP. Figure 11. Fiber glass layers on the inner former. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 19 / 26 Current leads, In-situ Soldering and Splicing After the winding activities the two formers wound were sent to Elytt for finalizing the activities. The first one was to install the splice boxes (see Fig. 12), and verify the HV tests on all the cables. Figure 12. Splice boxes mounting at Elytt Energy with INFN-LASA team. The next passage was to install the two current leads (Fig. 13), soldering the tape on the copper block and then insert the assembled package into the dedicated pocket on the splice boxes. After another check of HV test up to 1 kV to verify if everything was ok, the adjustment of each cable was done on the splice boxes, in order to adapt the length of the cable, verify the couple for each splice, and prepare the crocodile configuration of the splices. The in-situ soldering procedure for the final HTS CCT magnet demonstrator was designed to ensure reliable electrical and mechanical bonding of the 20 stacked HTS composite cables during winding. During conductor preparation, the solder-coated tapes were assembled on the fly within the cabling head, maintaining controlled alignment and relative slippage among the constituent tapes. The tapes passed through a pocket filled with flux paste—a key step in the process. The flux acted both as a lubricant, preventing sticking and enabling differential motion between layers, and as a chemical agent, promoting effective bonding of the In52Sn48 solder layer during localized heating. Controlled mechanical pressure was applied at the cable entry point into the groove, ensuring intimate contact between the stacked layers. Local heating was provided through indirect thermal conduction from the former (Fig. 14), ensuring the solder reached the proper reflow temperature without exceeding limits that could damage the HTS tapes or Kapton insulation. The entire magnet was rotated around its axis back and forth by +/-180o during soldering so that the molten indium does not accumulate at the bottom extremities of the individual turns. Continuous monitoring of temperature, tension, and feed speed ensured homogeneous soldering conditions along the entire cable length. The in-situ CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 20 / 26 soldering approach thus produced continuous, well-bonded composite cables, reducing interfacial resistance and improving mechanical stability under Lorentz forces. Figure 13. Current lead installation. Figure 14. Soldering setup with heater strips around the magnet core. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 21 / 26 Coil impregnation Based on the positive experience gained with the mockup coil test former—whose winding showed excellent mechanical integrity — the final HTS CCT demonstrator was impregnated using paraffin wax, following the same proven technique adapted to the new geometry. In this process, the fully wound magnet was mounted vertically and sealed to create a closed volume for impregnation. A wax reservoir was hermetically attached to the top of the assembly, while liquid paraffin wax was injected from the bottom through a heated transfer line connected to an external melting pot. The magnet was equipped with a heater tape and thermal insulation jacket, allowing precise control of the temperature gradient during the process. Once the reservoir was filled, pumping was stopped and replaced by pressurized nitrogen at the top, while the bore of the magnet was cooled from below. This configuration ensured both vertical and radial temperature gradients, which are essential to achieve void-free impregnation throughout the winding volume [8]. Prior mock-up impregnation tests, conducted at Wigner RCP with participation from Elytt Energy and INFN-LASA, confirmed the wax’s ability to fully penetrate the grooves and cable insulation via capillary action, even through the double Kapton layer, ensuring complete filling of interstitial voids[6]. For the final demonstrator, special attention was given to controlled evacuation prior to wax injection, ensuring the removal of residual gases and moisture, and to the application of a mild overpressure during cooldown to maintain intimate contact between wax, insulation, and cables. This resulted in a homogeneously impregnated, mechanically consolidated winding, providing excellent dielectric strength and thermal contact, while maintaining the desired mechanical flexibility for differential contraction during cooldown. Instrumentation installed To enable precise monitoring during fabrication, assembly, and cryogenic testing, the HTS CCT magnet demonstrator was equipped with a comprehensive instrumentation system combining temperature and electrical diagnostics. Four instrumentation boxes were installed along the magnet structure, as highlighted in Figure 15. Each box houses a pair of temperature sensors — one PT100 thermometer and one CERNOX cryogenic sensor — carefully positioned to monitor thermal behavior during all critical phases of magnet preparation and testing (see Fig. 16). The PT100 sensors were primarily used during in-situ soldering, splice, and wax impregnation, providing accurate temperature readings up to several hundred kelvin. These sensors ensured proper control of heating profiles, preventing localized overheating that could damage the HTS tapes, solder joints, or insulation layers. The CERNOX sensors, on the other hand, will be employed during the cryogenic qualification, enabling reliable temperature measurement down to 20 K with low magnetic field dependence and high sensitivity. This combination ensured continuous temperature monitoring from room temperature through cooldown and operation. In addition to temperature sensors, voltage taps were installed across each splice to monitor the electrical performance of the joints during both room-temperature and cryogenic tests. These voltage CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 22 / 26 taps enable precise measurement of joint resistance and the detection of any degradation or abnormal voltage development during powering or quench tests. The voltage taps will also be employed in the quench detection/protection system. Together, the PT100 and CERNOX sensors — complemented by the voltage tap network — provide a complete diagnostic system for the demonstrator, ensuring accurate thermal and electrical characterization throughout all fabrication and test stages. This integrated approach supports both process validation (soldering, impregnation) and performance evaluation (cooldown, energization) of the HTS magnet. Figure 15. Positions of the temperature sensors pockets on the two formers. Figure 16. Temperature sensors: CERNOX sensors were clamped down by LakeShore's own clamps, and PT100 were glued into one of the tapped holes in each T-sensor pocket. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 23 / 26 5. Verification and Quality Checks High-voltage (HV) tests were performed at each key stage of the HTS CCT magnet demonstrator fabrication to verify the integrity of the insulation system (Fig. 17). Turn-by-turn tests during winding confirmed proper electrical separation between adjacent cables. After an initial breakdown at 1 kV, a double Kapton insulation layer was introduced, ensuring reliable performance in subsequent checks. Following the in-situ soldering and splicing, additional HV tests verified that local heating and soldering had not degraded insulation or introduced conductive residues. The Teflon-coated splice box surfaces effectively prevented solder bridges and ensured clean electrical separation. A final HV test after wax impregnation confirmed the overall dielectric integrity of the magnet. The combination of Kapton insulation and paraffin wax impregnation provided stable insulation resistance above 1 kV, validating the readiness of the demonstrator for cryogenic testing. Figure 17. High voltage tests after winding and travel from Wigner RCP to Elytt Energy. CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 24 / 26 6. Conclusions The construction of the HTS Canted Cosine Theta (CCT) dipole magnet demonstrator marks a major achievement within the I.FAST WP8 activities, representing the successful realization of the first fully assembled high-temperature superconducting CCT magnet designed for accelerator and medical applications. The project has demonstrated the feasibility of integrating REBCO-based composite cables into a complex CCT geometry, confirming the robustness of the design and fabrication processes required for this new class of magnets. The demonstrator magnet, designed to generate a 4 T central magnetic field at 20 K, has been fully assembled following extensive design optimization, mechanical verification, and testing of all key components. The mechanical structure, including the inner and outer formers, splice boxes, and external supports, was successfully verified through precise insertion and alignment checks. Teflon coating of the splice box interfaces ensured proper insulation and mechanical reliability during subsequent assembly stages. The winding process was completed using 20 REBCO-based cables and 3 pickup coils, with each composite cable consisting of two REBCO tapes and two copper stabilizers, insulated with a double Kapton layer to withstand up to 1 kV. The winding was carried out with the dedicated machine developed for this purpose, ensuring tangential insertion of the flat cable and smooth winding without hard-way bending. Following the winding, in-situ soldering of all turns and splices was performed, ensuring reliable electrical contact and uniform bonding of the stacked tapes. After electrical validation of each soldered joint and insulation layer, the magnet underwent wax impregnation using the proven paraffin-based method previously applied to the mockup-coil. This process ensured full filling of the winding grooves and cable interstices, providing excellent mechanical stability and dielectric insulation. The instrumentation was installed with a combination of PT100 and CERNOX sensors in the four instrumentation boxes, enabling continuous monitoring from soldering and impregnation phases down to cryogenic operation at 20 K. In addition, voltage taps were mounted across each splice to allow precise monitoring of resistive voltage and quench detection during future tests. Comprehensive high-voltage tests were carried out after each fabrication phase—winding, soldering, splicing, and impregnation—confirming the electrical integrity of the insulation system. The final HV test demonstrated insulation strength exceeding 1 kV, validating the overall reliability of the magnet before cryogenic operation. In conclusion, the HTS CCT magnet demonstrator has reached its final assembly stage and is now ready for cryogenic testing (Figs. 18 and 19). The successful completion of this magnet establishes a significant step forward in the practical development of compact, high-field, and conduction-cooled HTS magnets, laying the foundation for future applications in research accelerators and hadron therapy gantries. The results achieved confirm the maturity of the CCT architecture for HTS CONSTRUCTION OF HTS CCT DEMONSTRATOR Deliverable: D8.5 Date: 28/10/2025 Grant Agreement 101004730 PUBLIC 25 / 26 implementation and the strong collaborative effort across European laboratories and industry partners within the I.FAST framework. Figure 18. HTS CCT Magnet ready for tests with Elytt and LASA teams. Figure 19. HTS CCT magnet demonstrator ready for tests.