Testing of the Ceramic Insulation Break for Fusion Device

Large magnet system is an essential component of most current or planned fusion devices. Axial insulation breaks are required in order to electrically isolate the cryogenic distribution system from the potential high voltage of the magnet system and bus bars. The epoxy resin based insulation break could be the weak link in magnet design, due to insulation sensitivity to high irradiation doses. The Al₂O₃ ceramic material instead of epoxy based material was used to manufacture the insulation break. Kovar alloy which has a similar mean coefficient of thermal expansion with Al₂O₃ ceramic in the temperature range of 300-1073 K was used as two ends of the insulation breaks. The ceramic tubes and Kovar alloy tubes were vacuum brazed together using silver-based filler at 1073 K. The helium tightness, the insulation resistances and dielectric breakdown were checked at room temperature and LN₂ temperature. Then 2 kN traction and compression were tested at room temperature and LN₂ temperature. The maximum tensile force of 8.62 kN and 8.18 kN were measured at room temperature and LN₂ temperature, respectively. The three point bending test was carried out. The test results of 4.5 kN and 3.6 kN were measured at room temperature and LN₂ temperature, respectively. The 50 thermal shock cycles were performed from 77 K to 300 K to ensure that the ceramic break could operate under rapid temperature change.