Test results and analysis of REBCO Subscale magnet 1 (RS1) in various cryogenic environments

The decreasing cost and expanding production of REBCO tapes make them promising candidates for accelerator magnets operating at high current density and high magnetic field. Within the CHART program supporting accelerator-magnet development, we perform electromagnetic and thermal analyses of the first REBCO subscale (RS1) magnet developed in the MagDev Lab at PSI, designed to enable direct experimental comparison between HTS and LTS technologies. The RS1 magnet adopts the same configuration as a previously tested LTS SMCC common-coil magnet, in which the Nb3Sn cable is replaced by a straight, soldered REBCO tape-stack cable with comparable geometric parameters. The magnet comprises four racetrack winding layers, with two layers located on each side of the aperture.We present models of resistive and AC-loss induced heating in the REBCO stack under operating conditions relevant to superconducting magnets: liquid helium (4.5 K), gaseous helium (20 K), and liquid nitrogen (77 K). Magnetic-field harmonics and transient behavior in the REBCO cables are computed using an H–A formulation in FEM. The analysis further includes predictions for REBCO magnet protection using a dump resistor as well as alternative protection strategies. Numerical results are compared with experimental data from the two-layer configuration and the full magnet tested in liquid nitrogen, and predictions are provided for liquid- and gaseous-helium tests upcoming at CERN in 2026. These results support the development of accelerator magnets at higher magnetic fields where REBCO conductors offer significant potential.