1987 年 22 巻 3 号 p. 193-199
Experimental study was carried out on superconducting ac magnets with a high terminal voltage immersed in liquid helium. As a preliminary experiment, we measured ac breakdown voltage of liquid helium boiling at 4.2K under normal atmospheric pressure. Based on these data including the effects of the magnetic field or the bubbles boiling from the electrode surface on the breakdown voltage, we designed and made the 50kVA ac magnet wound by a multifilamentary wire with fine Nb-Ti filaments. The magnet has cooling channels in each layer which act as an electrical insulator as well as a conduit of coolant. This test magnet of a high voltage type was successively charged up by means of the resonance circuit with static condensers for various frequencies. The observed ac losses and quench currents of the magnet were in a good agreement with theoretical ones.