Experimental Study on a Current Sweep Method Combined With Thermal Cycle for Mitigation of Screening Current-Induced Field in a Conduction-Cooled REBCO Magnet

Given that REBCO wire is typically manufactured as a tape, it is possible for REBCO magnets to exhibit a relatively larger screening current-induced field (SCF). It is well known that the SCF in an REBCO magnet can be effectively reduced by the so-called current sweep method. However, it requires an overshooting in the magnet current, often close to the magnet's critical current, to effectively suppress the SCF, which may not be favored in terms of operation reliability. In this study, we experimentally validated an alternative approach which mitigates the SCF using thermal cycling together with the current sweep reversal. Well known is the fact that the large load factor, defined as the ratio of operating current to critical current of an REBCO magnet, deteriorates the SCF impact on field uniformity. The key idea is to increase the magnet temperature to increase the effective load factor of the magnet close to its quench limit momentarily, minimize the SCF, and then return back to the nominal operating condition. The combined approach of the thermal cycling and the current sweep may be effective when attempting to eliminate the SCF without ramping an REBCO magnet to a current that may be dangerously high, especially when the magnet is operated at a high operating current. This paper presents the test results of the combined approach in the conduction-cooled REBCO magnet, and the results demonstrate the potential of the approach for more safe and effective elimination of the SCF.