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This paper presents the over-current quench test and post-quench operation results of a 7 T 78 mm winding diameter multi-width (MW), no-insulation (NI) magnet in a bath of liquid helium at 4.2 K. The MW-NI magnet consists of 13 double-pancake (DP) coils wound with GdBCO tapes having five different widths ranging from 4.1-8.1 mm. After the magnet reached 7.3 T at 253 A, the magnet current was further increased purposely until the magnet quenched at 312 A, corresponding to a current density of 895 A mm −2 for the central DP coils of the narrowest 4.1 mm tape. The NI DP coils showed a fast magnetically coupled quench propagation from the quenched DP to the rest of the 'healthy' DP coils. The stored magnetic energy of 25.4 kJ was completely dissipated in 0.3 s with an average dissipation power rate of 85 kW. The post-quench magnet, operated sequentially in baths of liquid nitrogen at 77 K and in liquid helium at 4.2 K, showed no discernable changes from the pre-quench magnet in their key parameters, except the magnet characteristic resistance, pre-1.4 mΩ versus post-3.6 mΩ. Thus, a forced quench of the magnet, thanks to the NI winding technique, kept the integrity-mechanical, electrical, and magnetic-of this NI magnet intact.

The partial insulation winding was examined to ameliorate the slow charge–discharge shown by coils wound without insulation. Single pancake coils of GdBCO coated conductor were wound without insulation, with kapton tape every five turns, and with the full use of kapton tape. They were characterized by charge–discharge, sudden discharge, and over-current testing. The improved charging and discharging and high thermal and electrical stabilities of the partially insulated coil demonstrate its potential for use in HTS power applications.

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