A 78-mm/7-T Multi-Width No-Insulation ReBCO Magnet: Key Concept and Magnet Design

This paper presents a multi-width (MW) winding technique suitable for an HTS (high temperature superconductor) magnet comprising a stack of double-pancake (DP) coils. The main idea is to place DP coils wound with the narrowest-width ReBCO tape in the magnet center region and those of progressively wider tapes toward the magnet ends, where the "perpendicular field (parallel to the ReBCO c-axis)", a major limiting field of ReBCO current-carrying capacity, is at its peak. Analysis demonstrates the superior field performance of an MW ReBCO magnet to those of its single-width (SW) counterparts. Combined with the no-insulation (NI) technique, the NI-MW technique makes an HTS magnet self-protecting, highly compact, and mechanically robust. Appling the NI-MW technique, we have designed a 7-T/78-mm ReBCO magnet that will be built and operated under a 2-year program. Also, presented in the paper are electromagnetic and mechanical analyses, together with discussion on protection and charging delay issues. Sample MW ReBCO tapes were mechanically slit and their measured 77-K I-c data are presented.