In recent years, the applications of high-field REBCO coils have remarkably progressed towards NMR/MRIs, accelerators, and other devices. However, as numbers of experimental and simulated results have clarified that the screening current in REBCO coils poses a severe problem for the magnetic field quality and mechanical stress. In a circular REBCO coil, the center magnetic field generated by the screening current is in the opposite direction to the field generated by the transport current, thus reducing the magnetic field, deteriorating the field homogeneity, and affecting the time stability of the magnetic field. These problems of screening current have been discussed, and many researchers have been developing the simple or detailed numerical simulation techniques for an evaluation of screening-current-induced field [1-8]. Recently, studies have reported on the mechanical deteriorations or damages of the REBCO coils caused by a screening current [9,10]. In the upper half of the coil winding, the positive current on the conductor's upper part amplifies the outward force, while the negative current on the conductor's lower part intensifies the inward force. This phenomenon modifies the circumferential stress distribution, increasing the tensile stress on the conductor's upper part and the compressive stress on the conductor's lower part. Excessive tensile stress causes microcracks or fractures, damaging the conductor. Compressive stresses induce buckling, degrading the coil performance. The modified circumferential stress was numerically simulated based on the interaction between an axial magnetic field and the screening current [10-15].

In this presentation, we review the numerical simulation techniques for evaluation of screening-current-induced field and stress. Then we will compare the numerical simulation with the experimental results. Finally, we will discuss the adequate remedy of stress modification effect due to the screening current.

The part of this work was supported by JST-Mirai Program Grant No. JPMJMI17A2, Japan.

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Keywords: REBCO coil, screening-current-induced field, screening-current-induced stress