Design, construction, and operation of an 18 T 70 mm no-insulation (RE)Ba2Cu3O7−x magnet for an axion haloscope experiment
Jaemin Kim, Yungil Kim, Sangwon Yoon, Kanghwan Shin, Junghun Lee, Jong Seop Jung, Jung Tae Lee, Jin-Geun Kim, Donglak Kim, Jonghee Yoo, Hunju Lee, Seung-Hyun Moon, and Seungyong Hahn
Review of Scientific Instruments 91, 023314 (2020)
An 18 T 70 mm cold-bore no-insulation (NI) high temperature superconductor (HTS) magnet for an axion haloscope experiment was designed, constructed, and operated in a bath of liquid helium at 4.2 K. The magnet consisted of a stack of 44 double-pancake (DP) coils wound with multi-width REBa2Cu3O7−x tapes. Due to the limited conductor supply during construction, we were forced to use the multi-thickness tapes, which turned out to be effective in improving, though marginally, the spatial field uniformity and the operating current to the critical current margin of the 18 T magnet. The magnet generated a peak center field of 18.7 T at 207 A, yet it was operated at a reduced operating current of 200 A to generate the nominal target field of 18.2 T. The magnet met the spatial field uniformity requirement of >90% within the target cylindrical volume of 66 mm in diameter and 200 mm in length and provided an axion test environment of 0.22 T2 m3 within the volume. The first operation started in August 2017 as a user magnet of the Center for Axion and Precision Physics Research of the Institute of Basic Science (IBS). After the 14-month operation at the IBS user site, an excessive helium consumption was reported in October 2018. Maintenance was performed in December 2018, where DP coils and splices were replaced with new ones. Since then, the magnet continued operating as a user magnet at IBS to date. The magnet may represent the first HTS “user” magnet that performed a long-term operation for more than one year.
We report the design, construction, and operation results of an 18 T 70 mm cold-bore high temperature superconductor (HTS) no-insulation (NI) magnet, which is developed for an axion haloscope experiment. The magnet consists of 44 double-pancake coils wound with multiwidth and multi-thickness REBa2Cu3O7−x (RE = rare earth) tapes. Owing to the NI feature, the magnet is highly compact; is 162 mm in outer diameter and 476 mm tall; and provides an environment of 0.22 T2 m3 within the cold-bore target space of 66 mm in diameter and 200 mm in length. After an initial performance test at SuNAM Co. Ltd., the magnet was installed at the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science in Daejeon, South Korea, in August 2017. The magnet has been successfully operating at the CAPP since then, except for maintenance in October 2018. The magnet may represent the first high field HTS user magnet that experienced long-term operation of over one year.