Metal-as-insulation sub-scale prototype tests under a high background magnetic field

Abstract

The aim of the NOUGAT project is to design and realize a 10 T high temperature superconducting solenoidal insert able to operate in a 20 T background magnetic induction. Our design is based on the metal-as-insulation winding technique consisting of co-winding a bare REBCO high temperature superconducting tape with a stainless steel tape. The metal-asinsulation winding maintains the self-protection feature of the no insulation winding and helps to reduce current charging time constants-one of the major drawbacks of no insulation coils-by significantly increasing the turn-to-turn electrical resistance. First, we demonstrated the selfquench protective behavior at 4.2 K under a high field up to 17 T by testing a single-pancake prototype. Then, before fabricating the final insert, we designed, wound and tested a second prototype made of two double-pancakes. The purposes were three-fold: validating the winding and assembly process, confirming the operating margins and corroborating the mechanical study. In this article, we present the main results of the tests performed at 4.2 K on this sub-scale prototype in a high background magnetic field at

Screening current effect on the stress and strain distribution in REBCO high-field magnets: experimental verification and numerical analysis

“…Without reinforcement techniques such as overbanding [25] and co-winding [26], Lorentz force in radially outward direction could cause most threat to the outer turns in a solenoid coil winding. Based on previous models and analyses, we propose the following analytical expression to estimate this component of Lorentz force considering the screening current effect…”

Fast and accurate electromagnetic modeling of non-insulated and metal-insulated REBCO magnets

“…For high-field magnets, it has been found that enabling current sharing between turns highly improves the reliability against thermal quench [2,[17][18][19][20]. In addition, winding the coils without insulation (no-insulation (NI) coil [17,18]) reduces the coil volume, and hence it enhances engineering current density and generated magnetic field.…”

Topical Review: Multifilamentary coated conductors for ultra-high magnetic field applications

“…The schematic in figure 2 shows the three MIT REBCO double-pancake-based coils, designed to produce 18.8 T (800 MHz), embedded in a test cryostat. REBCO tapes are wound using the non-insulating (NI) winding technique and over-banded with stainless-steel tape [61,62] as shown in the inset of figure 2 presenting the largest of the three REBCO coils. These UHF magnet developments constitute state-of-theart systems for obtaining stable and very precise magnetic fields in small bore (centimeter-sized) magnets.…”

“…Stress management consequently constitutes one of the biggest challenges for UHF magnets. UHF CC coils are therefore typically carefully enforced employing, for example: co-winding with a highly resistive metal tape [62], overbanding with a high Young's modulus and yielding stress stainless-steel tape (6 mm overbanding radial build for the H800 coil in the MIT 1.3 GHz NMR using 76 µm tape) or epoxy impregnation [80].…”