Status of the 25 T, 100 mm Bore HTS Solenoid for an Axion Dark Matter Search Experiment

This paper presents the design and test results of the pancake coils for the 25 T, 100 mm bore solenoid that Brookhaven National Laboratory (BNL) is building for the Institute for Basic Science (IBS) in Korea for an Axion dark matter search. The design is based on second-generation (2G) high-temperature superconducting (HTS) tape with no-insulation winding. The major challenges in the high-field, large aperture solenoid are the large stresses and the quench protection. Moreover, the design should be robust for reliable operation in a user facility environment. The paper will also present the construction and test results of two ∼100 mm bore double pancake coils creating a peak field of up to ∼17 T and similar hoop stresses as will be in the 25 T solenoid. The coils were subject to several severe tests, including the simulations of large defects and extended quench studies at ∼4 K. The most striking part of these studies was the demonstration of how fast (a few hundred milliseconds) these coils can turn from the superconducting state to the normal state (quench or thermal runaway). This removes the past concerns of protecting high-field HTS coils because of the low quench propagation velocities.