[AP8] Magnet science and technology 2

4:31 PM - 4:46 PM JST(7:31 AM - 7:46 AM UTC)

[AP8-08] E-J Characteristic of Damaged REBCO Tapes at 20 K and 77 K

*Shinsaku Imagawa¹, Masayoshi Ohya², Shinji Hamaguchi¹, Akifumi Iwamoto³, Hiroaki Kobayashi⁴ (1. National Institute for Fusion Science (Japan), 2. kwansei Gakuin University (Japan), 3. The University of Osaka (Japan), 4. Institute of Space and Astronautical Science (Japan))

Keywords:

Electric field,liquid hydrogen,liquid nitrogen,REBCO,thermal runaway

To determine design criteria for cryostable high-temperature superconducting coils, we have investigated the behavior of thermal runaway of locally damaged REBCO coils immersed in liquid nitrogen and hydrogen. The copper layers of 0.05 mm thick were plated on the both sides of the REBCO tape, and the testing part of 0.1 m long was damaged by being bent to both sides by a diameter of 6 mm. The critical current, I_C of the damaged part was less than 1/10 of the original value. The voltage-current (E-J) relation and cooling were key parameters for the thermal runaway. According to the power low scaling, E = E₀(I/I_C)ⁿ, n values around I_C of the damaged part of 0.1 m were 3 to 6 for four samples, and they were reduced to less than 3 near the thermal runaway for all the samples. Figures 1a and 1b show E-J curves of the 4th sample at 77 K and 20 K, respectively. Half 1 shows the voltage of a half of the damaged part, and Half 2 shows the voltage of another half part. I_C and n value at 77 K of Half 1 were 10.7 A and 6.7, while 3.4 A and 4.9 for Half 2. The voltage of Half 1 became higher than Half 2 at high current at 77 K. In the case of 20 K at 2.1 T of the external field, thermal runaway occurred before Half 1 exceeded Half 2. In reality, I_C and n-value should be distributed in the damaged part, and thermal runaway should occur at the point where the voltage drop is highest. Simulations of the voltage generation are underway, and the results will also be presented.