Understanding quench in no-insulation (NI) REBCO magnets through experiments and simulations

Abstract

Present research on no-insulation (NI) rare earth barium copper oxide (REBCO) magnets have demonstrated their ability to produce high fields due to their compact nature. NI magnets have often been demonstrated to be self-protecting. However, evidence of mechanical damage in recent high field magnets, suggests that there are some issues about quench that must be resolved for this otherwise promising technology. This article attempts to explain multi-physics phenomena occurring during the quench of an NI magnet that can be used to elucidate quench behavior through experiments and simulations. A lumped circuit model is used for the circuit analysis where each coil is modeled as a single inductor with variable quench resistance in series and characteristic contact resistance in parallel. Three case studies have been analyzed: (1) a 3 double pancake (DP) standalone magnet, (2) a 2 DP coil in 31 T background, and (3) a high temperature superconductor/low temperature superconductor (HTS/LTS) hybrid user magnet that consists of a 13 T HTS insert and a 6 T LTS background magnet. Lessons learned from these analyses include: (1) characteristic resistance of NI coil rises during quench with the temperature rise; (2) influence of Hall effect exists on the voltage rise during quench; (3) over-current during quench can over-stress the coil; and (4) quench propagation from one end of the magnet generates significant unbalanced forces. This approach is expected to be used in the preliminary design of an ultra high field (>40 T) user magnet currently under design at the National High Magnetic Field Laboratory.

Scalability Analysis of Direct and Iterative Solvers Used to Model Charging of Non-insulated Superconducting Pancake Solenoids

“…We believe the most important future research avenue would be the incorporation of quench analysis [6] in our mathematical model and explore the charging behavior of non-insulated superconducting pancake solenoids. We will use the proposed efficient solver, FGMRES-GMRES, for problems with large degrees of freedom, and will continue to investigate further for a better preconditioner.…”

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

“…The upper boundary of the coil is assumed to be free because of the coil being in compression along with the height during the cooling and charging. Due to the self-supporting turn effect, the inner and outer boundaries of the coil are chosen to be free [39,48,49]. Since the number of layers along the radial direction is relatively less, the prestress during the winding is lower and neglected in the simulation.…”

“…Moreover, large hoop stress is generated by the prestress and strong electromagnetic force in a high magnetic field, which may affect the critical current of the coils [36,37]. The supporting structure might be damaged because of a large unbalanced axial force in the magnet [38,39]. Therefore, it is meaningful to clearly understand the distributions of the loss and stress in order to operate NI magnets safely.…”

Mechanical Damage Protection Method by Reducing Induced Current in NI REBCO Pancake Coils During Quench Propagation

“…Each turn is modeled as one element circuit [13], which is composed of the self and mutual inductances 𝐿𝐿, the equivalent REBCO layer resistance 𝑅𝑅 re the copper matrix resistance 𝑅𝑅 cu , and the turn-to-turn contact resistance 𝑅𝑅 cn . Here, 𝑅𝑅 re is obtained according to the index power model [17]. 𝑅𝑅 cu is computed using the copper resistivity shown in [18].…”