Metal-as-Insulation REBCO Insert: Simplified Protection Scheme and Investigation of Cooling Defect Under High-Field Operation

A refurbished metal-as-insulation (MI) HTS insert comprised of DP coils with replaced inner joints was charged under various magnetic field (B-ext) from 0 to 18 T at 4.2 K for testing. However, the refurbished insert could not be charged up to its maximum field, because the cryogenic condition tended to be unstable with a high helium boiling rate above 28 T. Therefore, to investigate the cooling issue, four Cernox sensors were installed in refurbished insert. The temperature of each position while powering the insert was measured under various B-ext. In addition, we qualified a new simplified protection scheme without the usual detection and dump circuit during a quench at B-ext = 9 T of the insert. Detailed experimental results about charging and quenching tests of the insert are presented and discussed in this paper.