[AP3] Magnets (for accelerator, fusion)

5:30 PM - 5:45 PM JST(8:30 AM - 8:45 AM UTC)

[AP3-03] Experiment of a Double-Pancake Coil Wound by UROCOIC Conductor for Application in Helical Fusion Reactors

*Yoshiro NARUSHIMA^1,2, Yuta Onodera¹, Shinji Hamaguchi^1,2, Tomosumi Baba¹, Nagato Yanagi^1,2, Chikaraishi Hirotaka^1,2, Junichi Miyazawa³, Chikuma Hiroki³, Hitoshi Tamura³, Takuya Goto³ (1. NIFS (Japan), 2. SOKENDAI (Japan), 3. Helical Fusion Co., Ltd. (Japan))

Keywords:

Helical reactor,REBCO,Fusion magnet

High-temperature superconducting (HTS) magnets are promising candidates for magnetic confinement fusion reactors, particularly in helical configurations that support steady-state plasma operation. Among HTS materials, REBCO (Rare Earth Barium Copper Oxide) tape is a leading candidate. However, its helical winding is technically challenging due to its anisotropic bending properties [1]. To evaluate the feasibility of REBCO-based magnets for helical fusion reactors, we study a double-pancake (DP) coil using a UROCOIC (Unitized Reinforcing Outer Cover On Internal Components) conductor by the collaboration study between NIFS (National Institute for Fusion Science) and Helical Fusion Co., Ltd. The UROCOIC conductor’s flexibility is suitable for coils such as those in helical reactors. The coil uses a no-insulation design to improve thermal stability and allow current sharing during a normal-transition event. This design helps transient currents to bypass a locally normal-transitioned region and mitigates the risk of damage. As a first step, we performed an initial energization test at a temperature of 77 K using liquid nitrogen. The DP coil sustained a current of 0.8 kA for 300 seconds, generating a magnetic field that responded with a time constant of approximately 10 seconds. The steady-state magnetic field strength reached B ~ 12 mT, showing that the current remained within the superconducting region. This confirms that the no-insulation coil can generate a proper magnetic field. Although the field strength is modest, it serves as a proof-of-concept for magnetic field generation in this no-insulation coil. Electrical resistance at the joint sections also confirmed the mechanical and electrical integrity of the joints. Based on these results, we plan to conduct high-field current tests under fusion-relevant conditions, specifically approximately at 20 K and 8 T, with a target current of >20 kA. This experiment will provide critical insights into the performance and reliability of REBCO DP coils in extreme environments, contributing to the advancement of HTS magnet technology for future helical fusion reactors. References1) Y. Narushima et al. Plasma Fusion Research, Vol.15, 1405076, 2020