Development of Persistent-Current Mode HTS Coil for the RT-1 Plasma Device

Abstract

The plasma confinement device "RT-1" which had a high temperature superconducting (HTS) floating magnet was constructed for advanced high-beta plasma and fusion research at the University of Tokyo. The high temperature superconducting (HTS) floating magnet is magnetically levitated inside the plasma vacuum vessel. Plasma is confined by a magnetic dipole field around the HTS floating magnet. The HTS floating magnet is operated in persistent-current mode and it consists of an HTS coil, an HTS persistent-current switch (PCS), a pair of demountable joints of current leads, detachable joints of a cooling tube, a thermal shield and a vacuum vessel. The HTS coil and the PCS and the thermal shield are cooled below 20 K by a flow of helium gas through the cooling tube. The floating HTS magnet is designed to operate in the temperature range from 20 K to 30 K without being cooled while it is levitated. We fabricated a persistent-current HTS coil that consists of the HTS coil and the PCS. Persistent-current operations and protection tests were conducted with the persistent-current HTS coil before it was mounted in the floating magnet cryostat. The current-decay rate was 0.9% in an 8 hour operation. The coil energy was safely discharged by inducing PCS quench in a protection test.

A REBCO Persistent-Current Switch, Immersed in Solid Nitrogen, Operating at Temperatures Near 10 K

“…The results in Fig. 7 underscore the importance of protecting the PCS with parallel protection resistor as reported in [6], [8]. To incorporate a low-resistance protection resistor in parallel with our PCS we will need a significantly higher open-state PCS resistance than we designed to, which may require us to significantly revise our basic design approach.…”

“…Several examples of high-temperature superconductor (HTS) based PCS have been reported [5]–[14]. For instance, the bifilar-wound PCS, based on Bi-2223 tape, developed for the mini-RT experiment required 50-W heating power to open [7], while the PCS subsequently developed for the Ring Trap experiment, RT-1, using thick film REBCO deposited on sapphire substrate required 20-W heating power [8]. These heating powers are representative of most HTS PCS reported in the literature.…”

Construction and Operation of an Internal Coil Device, RT-1, with a High-Temperature Superconductor

“…The stored energy of the HTS coil should be damped by the resistance in the case of the HTS coil quench. A damping resistance of 60 mΩ is prepared inside the coil vacuum vessel and connected to the HTS coil in parallel with the PCS [19].…”

“…The coil's maximum current is approximately 1300 A, and the feedback control can apply ±150 A with a dynamic range of < 20 Hz (a switching regulator is used to control the current). Research and development of magnetic levitation systems have previously been carried out on the FB-RT and Mini-RT devices [19]. Since the HTS coil of RT-1 is suspended by a levitation coil located above the chamber, the floating coil is unstable in its vertical motion.…”

Influence of YBa 2 HfO 5.5 – ‘derived secondary phase’ on the critical current density and flux-Pinning force of YBa 2 Cu 3 O 7−δ thick films

“…High Temperature Superconductor (HTS) thick films are being engineered for high current applications in high magnetic fields such as in magnetic shielding, low phase noise oscillators, magnetic resonance imaging receiver coils, flux transformers, fault current limiter, filters, persistent-current and HTS magnets which need high critical current density (J c ) [1][2][3][4][5][6]. Since J c decreases with both thickness and magnetic field, artificial pinning centers (APC) in addition to conventional ones are required to keep J c high.…”