Numerical Research of Potential Methods to Reduce Screening-Current-Induced Stress for No-Insulation REBCO Coils

Abstract

In recent years, the no-insulation REBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7−</sub> <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_x</i> (REBCO) (NI-REBCO) coils with self-protecting ability show remarkable attraction and potential in high magnetic field areas. As the study develops in-depth, it is widely recognized that the uneven stress/strain generated by screening current is a crucial concern for the NI-REBCO coils operating performance, especially for NI-REBCO insert coils under high background field. Therefore, effectively reducing screening-current-induced stress/strain (SCIS) is critical for NI-REBCO coils/magnet mechanical design and steady operation. In this article, we developed a new two-dimensional numerical model to analyze the mechanical responses caused by screening current in NI-REBCO coils using the T-A multiscale model for electromagnetic behavior and discrete contact model for stress/strain analysis. After verifying the model by comparing with previous experimental data, the effectiveness of three already-reported and potential methods of mitigating SCIS [i.e., 1) combining suitable winding tension and overband support in the fabrication of coils, 2) employing multifilamentary REBCO tape suppressing screening current, and 3) co-wound metal tape strengthening stiffness of coils] is revealed by comparing the strain/stress distribution with a designed benchmark NI-REBCO coils. Furthermore, by a parametric study of the aforementioned mitigating SCIS methods, a couple of novel conclusions were found. 1) The effect of overband support on reducing SCIS gradually weakens from the outer turn to the inner turn, and the SCIS decreases gradually as the overband metal tape thickness increases, whereas there is a critical value that the SCIS would no longer significantly decreases once exceeds it. 2) The more multifilaments in REBCO tape there are, the better the effect of mitigating SCIS. 3) The SCIS in NI-REBCO coils shows a clear decreasing trend with the increase of co-wound metal tape thickness, but the trend is gradually flattened. Finally, we summarized some feasible suggestions for the mechanical design of NI-REBCO coils to mitigate the SCIS.