Construction and Test of 7-T/68-mm Cold-Bore Multiwidth No-Insulation GdBCO Magnet

As a sequel to our previous report on the key concept of the multiwidth (MW) no-insulation (NI) winding technique that applies the NI technique to a magnet assembly of double-pancake (DP) coils wound with varying tape widths (thus MW), this paper presents construction and test results of a 7-T/68-mm cold-bore MW-NI GdBCO magnet. A total of 13 DP coils were fabricated: five central DP coils were wound with 4.1-mm wide tape, while each of the remaining four pairs of DP coils, axially symmetric to the midplane, was wound, from center to end, with 5.1-, 6.1-, 7.1-, and 8.1-mm wide tapes. Each DP coil was tested in a bath of liquid nitrogen (LN2) at 77 K, to obtain its critical current and characteristic resistance. After stacking, the 13-DP magnet was tested in LN2 at 77 K. The key focuses of this paper are: 1) winding and testing of MW-NI DP coils; 2) DP-DP joints; 3) charging response of the magnet; 4) spatial field distribution; and 5) self-protecting feature in overcurrent operation.