Assembly and Test of a 3-Nested-Coil 800-MHz REBCO Insert (H800) for the MIT 1.3 GHz LTS/HTS NMR Magnet

We present assembly and test results of a 3-nested-coil 800-MHz (18.8 T) REBCO insert (H800) for the MIT 1.3 GHz LTS/HTS NMR magnet currently under completion. Each of the three H800 coils is a stack of no-insulation (NI) REBCO double-pancake coils (DPs). The innermost 8.7-T Coil 1 (26 DPs) was completed by mid-2016; the middle 5.6-T Coil 2 (32 DPs) was completed in mid-2017; while the outermost 4.5-T Coil 3 (38 DPs) was completed in early 2018. Coils 1, 2, and 3 were assembled together in early 2018 as a 3-nested-coil, the H800, and tested, first in liquid nitrogen to a power supply current of 20 A, followed by testing in liquid helium to a power supply current of 251.3 A, the H800's design operating current. After roughly five minutes settling time at 251.3 A, the H800 quenched. In this paper, we examine probable sources of quench initiation and simulate ensuing quench behavior. Remedial efforts to minimize the tendency toward quenching in the H800 are presented and discussed.