Improved stability, magnetic field preservation and recovery speed in (RE)Ba₂Cu₃O_x-based no-insulation magnets via a graded-resistance approach

Abstract

The no-insulation (NI) approach to winding (RE)Ba2Cu3Ox (REBCO) high temperature superconductor solenoids has shown significant promise for maximizing the efficient usage of conductor while providing self-protecting operation. Self-protection in a NI coil, however, does not diminish the likelihood that a recoverable quench occurs. During a disturbance resulting in a recoverable quench, owing to the low turn-to-turn contact resistance, transport current bypasses the normal zone by flowing directly from the current input lead to the output lead, leading to a near total loss of the azimuthal current responsible for magnetic field generation. The consequences are twofold. First, a long recovery process is needed to recharge the coil to full operational functionality. Second, a fast magnetic field transient is created due to the sudden drop in magnetic field in the quenching coil. The latter could induce a global inductive quench propagation in other coils of a multi-coil NI magnet, increasing the likelihood of quenching and accelerating the depletion of useful current in other coils, lengthening the post-quench recovery process. Here a novel graded-resistance method is proposed to tackle the mentioned problems while maintaining the superior thermal stability and self-protecting capability of NI magnets. Through computational modeling and analysis on a hybrid multiphysics model, patterned resistive-conductive layers are inserted between selected turn-to-turn contacts to contain hot-spot heat propagation while maintaining the turn-wise current sharing required for self-protection, resulting in faster post-quench recovery and reduced magnetic field transient. Effectiveness of the method is studied at 4.2 and 77 K. Through the proposed method, REBCO magnets with high current density, high thermal stability, low likelihood of quenching, and rapid, passive recovery emerge with high operational reliability and availability.

Contact resistance between two REBCO tapes: the effects of cyclic loading and surface coating

“…To this end, the effect of 'insulation' by a metallic co-winding interlayer is also explored [13][14][15]. In addition, it is proposed that the conductor with graded R c is used to reduce the ramp loss [8] as well as to improve stability and recovery speed after a quench [16] in large NI REBCO magnets.…”

Ramping loss and mechanical response in a no-insulation high-temperature superconducting layer-wound coil and intra-layers no-insulation coil

“…Thus, the NI coil has a self-protecting feature during the local quench [8][9][10][11]. However, the current can also flow along the radial direction of the coil through low contact resistance during charging and discharging, which leads to a long magnetic field delay time [1, [12][13][14].…”

No-Insulation High-Temperature Superconductor Winding Technique for Electrical Aircraft Propulsion

“…The key idea of NI coil is to remove the turn-to-turn electrical insulation of traditional insulated coils. Transport current can bypass the local hot spot through turn-to-turn metallic contacts, so that the quench propagation is prevented and an enhanced thermal stability is achieved, which has been validated by both experiments and simulations [22][23][24][25][26]. Another advantage of the NI HTS coil is the enhanced power density since the elimination of turn-to-turn insulation increase the current density as well as the power density of the HTS machine.…”