No abstract

The characteristic magnetic field delay time for a no-insulation (NI) REBCO layer-wound coil is three orders of magnitude longer than that for a NI REBCO double-pancake coil. In a NI layer-wound coil, the circumferential current firstly flows along the periphery of the coil winding, and then it diffuses from the top and bottom turns into the middle turns of the winding, resulting in a long characteristic magnetic field delay time due to the current diffusion process. In contrast, the characteristic magnetic field delay time for a NI double-pancake coil is dominated by the circumferential current decay in individual turns. On the basis of a derived scaling law, the characteristic magnetic field delay time for a NI REBCO layer-wound coil for a 400 MHz LTS/REBCO nuclear magnetic resonance (NMR) magnet is 37 h, while that for a NI REBCO double-pancake coil is only <1 min. Thus, it is demonstrated that a double-pancake-winding is greatly preferred to a layer-winding for NMR applications from the view point of the characteristic magnetic field delay time.

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REBCO high temperature superconductors are prom 孟 s 正 ng for various superconducting coil systems such as MR1 ， NMR and Superconducting Energy Storage Systems ， However， REBCO coils sometimes shows therma 正runaway ， rcs 山 ing in meltdown ofthe con in dle worst case ， In this paper， we investigate the effect of therma 且 grid method ， in which heat channel of high thcmlal conductivc metal are installed in the coi 正 winding ， on temperature increase of the REBCO じ oil due to thermal runaway ． We demonstrate that there is a time interval prior te therrnal runaway ， in which the normal conductive part shrinks if the eoil current dump starts．