No-Insulation (NI) Winding Technique for Premature-Quench-Free NbTi MRI Magnets

This paper describes and discusses a No-Insulation (NI) winding technique that, based on experiment results of two test NbTi coils, promises to significantly improve stability and ease protection of high performance magnets; if applied to those used in marketplace MRI magnets, it may eradicate premature quenches that still afflict these magnets, though much less frequently than in the past. The key idea is that a single turn in an NI winding can, upon a quench, share the copper stabilizers of neighboring turns through turn-to-turn contacts. To demonstrate the main features of the NI technique, two test coils
$({\mit\Phi}30\ {\rm mm})$
were wound with insulated (INS) and no-insulation (NI) NbTi wires, respectively. The results presented in this paper include: 1) charge-discharge test results and field analyses showing that the NI field performance is essentially identical to that of the INS coil except a charging delay; and 2) charging test results where coil voltages were measured during critical current tests to imply that the NI coil is charged more stably than its INS counterpart.