The characteristics of no-insulation hightemperature superconducting (HTS) manet is dominated by the magnitude of the turn-to-turn contact resistance. A few techniques have been proposed to increase the turn-to-turn contact resistance. The relation between the turn-to-turn contact resistance and the magnet stability has also been investigated in simulations. Although the turn-to-turn contact resistance measurement was only the sudden-discharging method before, we proposed a lowfrequency-AC current (LFAC) method. Using our proposed method, it is possible to measure the turn-to-turn contact resistance under various conditions. In a previous paper, we measured it when charging DC current to a single pancake coil. In this paper, the turn-to-turn contact resistance was measured by the LFAC method when an external field of 1-3 T was applied to a single pancake coil. The coil strain was also measured, and the relation of the turn-to-turn contact resistance and the coil strain was also discussed.

The no-insulation (NI) winding technique has been attracting attention, because NI Rare-Earth Barium Copper Oxide (REBCO) pancake coils have high thermal stability. It is an indispensable technology to generate an ultra-high magnetic field. In 2017, using the NI winding technique a world-record high magnetic field, 45.5 T, was generated by 12 insert single pancake coils with an outsert magnet, and it showed a high potential to generate 14.4 T inside a background field of 31.1 T. After the experiment, the REBCO tapes were mechanically damaged, so that the critical currents were deteriorated. A large current was induced in NI REBCO coils next to the quenched coil when one of multi-stacked NI REBCO pancake coils quenched, resulting in tape property degradation and irreversible mechanical damage. Therefore, in order to protect NI REBCO pancake coils during quench, it is desired to reduce the amount of induced current. To suppress an induced current, the idea of "magnetic dam" has been proposed previously. The idea is to use a copper pipe installed at the outside of NI REBCO pancake coils. However, the copper pipe just slowed the quench propagation. In this paper, we extended the method to decrease an induced current much more by installing extra NI REBCO windings instead of the copper pipe. The electromagnetic and stress behaviors of 6stacked NI REBCO coils with extra windings are simulated when one of the stacked NI REBCO coils transitions into a normal state. The ability of mechanical damage protection from a strong stress by an induced current during quench propagation is demonstrated through simulations.

Since the screening current induced in rare earthbarium-copper-oxide (REBCO) magnet generates an irregular magnetic field, a few screening current simulation methods have been proposed. For an insert REBCO magnet generating ultrahigh magnetic field, a new screening current method has been proposed with consideration of the coil-deformation effect.In this paper, we have developed a new screening current method based on a partial element equivalent circuit (PEEC) model coupling with a two-dimensional stress finite element analysis to accurately the time-transient distribution of accurate screening current. In the presented method, the changes of self/mutual inductances are considered due to the coil deformation. As the simulation results, it was found that the coil deformation affected the screening current distribution. When considering the coil deformations, the screening current-induced fields to operating current are different for charging cycles. It is necessary to simulate the coil deformation to accurately estimate the screening current and the screening current-induced field.

Ultra-high field superconducting magnets are facing a mechanical degradation problem. On 2017, a world-record high DC magnetic field of 45.5 T was generated by insert no-insulation (NI) Rare-Earth Barium Copper Oxide (REBCO) pancake coils (14.4 T), called "LBC3", and an outsert resistive magnet (31.1 T). Although the experiment showed a high potential of the NI REBCO magnets for ultra-high field generation, the insert NI REBCO pancake coils and the REBCO tapes were plastically deformed. The critical current properties of damaged REBCO tapes were degraded although the Hastelloy substrate of REBCO tapes is stiff and it has a high yield point of approximately 1 GPa. However, the mechanisms of the damaging REBCO tapes are not clarified. Therefore, it is necessary to clarify the mechanical phenomenon of REBCO tapes.In this paper, we model a REBCO tape with a smoothed particle hydrodynamics (SPH) method, which can represent plastic deformation. The SPH simulation is coupled with electromagnetic analysis with a partial element equivalent circuit (PEEC) model which we have previously developed. In the simulation, an external field, which linearly increases to 5 T and then decreases to 0 T, is applied to a short-length REBCO tape. The simulation results show that the REBCO tape largely deforms during the external field excitation and deexcitation.

In 2011, a no-insulation (NI) winding technique was first proposed. Rare-Earth Barium Copper Oxide (REBCO) pancake coils using the NI winding technique are promising to generate an ultrahigh magnetic field, because the NI winding technique drastically enhances the thermal stability. When a local hot spot appears on a turn of the NI REBCO pancake coil, the enforced current can bypass into the adjacent turns to suppress the Joule heat generation. Recently, different types of REBCO coils to enhance the thermal stability by escaping the current flow from a local hot spot have been researched and developed. A few years ago, a REBCO single pancake coil whose upper surface was coated with conductive epoxy resin was proposed as one kind of NI winding techniques. The high thermal stability of conductive-epoxy-resin-coated (CERC) REBCO single pancake coil was demonstrated through an overcurrent test. However, the current behavior in the coil is still unclear. Therefore, we have newly developed an equivalent circuit model for CERC REBCO pancake coils. The sudden discharging and overcurrent tests were simulated for CERC REBCO pancake coils, and the resistance parameters were varied to investigate the coil stability.  Index Terms-Conductive-epoxy-resin-coated REBCO coil, magnet stability, no-insulation winding technique, quench protection.