Screening-Current-Induced Strain Gradient on REBCO Conductor: An Experimental and Analytical Study with Small Coils Wound with Monofilament and Striated Multifilament REBCO Tapes

Screening currents in REBCO conductors, induced by time-varying magnetic fields, not only affect the field quality of HTS coils but also cause strain gradients along REBCO tape width that may overstress REBCO conductors used in NMR and other high-field magnets. In this paper, we present results of an experimental and analytical study on screening-current-induced strain gradients, performed with small REBCO pancake coils. Because we believe that screening current effect is reduced in multifilament conductor, we have studied 2 test coils, φ150 mm, one wound with monofilament and the other with 3-striate/4-filament REBCO tapes. A 5-T/ 300-mm room-temperature bore magnet was used not only to excite a strong screening current but also apply the nonuniform Lorentz force to each coil at 4.2 K. Our experiment and analysis have quantitatively demonstrated that we can effectively suppress the screening-current effect on strain gradient, not surprisingly, by using striated multifilament REBCO conductor.