Hysteresis loss scaling of round REBCO cable towards 20 T

High Temperature Superconductor (HTS) cables are considered for use in tokamaks such as DEMO (EU) and Chinese next generation fusion device (CN) or compact fusion machines. HTS cables offer the advantage of increased operating temperature and field strength of the magnet coils. In particular for Central Solenoid (CS) coils, the HTS high current cabled conductor windings are exposed to fast ramping AC magnetic fields inducing AC losses. The AC loss in HTS cables for fusion is mainly explored at low magnetic field amplitudes due to lack of testing facilities at higher fields. However, since the operating field in CS coils may be up to 20 T, it is essential to obtain quantitative knowledge on the AC losses for the entire applied field range with reasonable accuracy. This is important for thermohydraulic analysis of the operating temperature margin in coil designs. A method is used here to scale the hysteresis loss of a REBCO cable without transport current, measured up to only 1.4 T, to the entire field and temperature range up to 20 T and 50 K respectively. The field shielding and penetration effects of a multi-layer REBCO CORC®-like cable are quantified by measurements on stacked tape samples with a Vibrating Sample Magnetometer (VSM) up to fields significantly higher than the round cable’s full penetration field, found to be at 4.2 T. For higher fields, using measured critical current ( I c ) data up to 19 T and an I c ( B , T ) scaling law for field ( B ) and temperature ( T ) serve to cover the required range of data within the window of coil operation parameters. Basic well-known theory on AC loss, particularly on the relation between hysteresis loss and critical current density against magnetic field, serves as a validation for this work.