Breakdown characteristics of pressurized liquid helium under quench condition of superconducting wires

For practical insulation design of superconducting power apparatus, we have been studying quench-induced dynamic breakdown and prebreakdown characteristics of liquid helium (LHe). We have already pointed out that the insulation performance of LHe may be drastically degraded in thermal bubble disturbance. In this paper, we measured breakdown and prebreakdown characteristics of pressurized LHe under quench conditions and discussed the dynamic breakdown mechanism of pressurized LHe by thermal bubble behavior and partial discharge (PD) characteristics. Experimental results revealed that the dynamic breakdown voltage of LHe at 0.2 MPa increased as high as about 3 times of that at the atmospheric pressure with reduced PD charge in the quench-induced thermal bubbles.