Paschen testing of ITER prototype cryogenic axial breaks

► Breakdown mechanisms in gas and vacuum are explained. ► Breaks and ITER arrangement are described. ► Test setup and test sequence for the breaks are shown. ► The results are presented. Axial insulation breaks are needed in forced cooled cryogenic high voltage devices for the separation of the high voltage area from the grounded pipe system. The ITER cryogenic axial breaks will be surrounded by good vacuum in case of normal operation but also under vacuum breakdown conditions sufficient dielectric strength is required for a reliable fast discharge of the coil system. A Paschen tight design of the ITER prototype breaks enables high voltage operation independent on the outer vacuum or gas conditions. Consecutively two pretested ITER prototype breaks were integrated in the insulation system of a Paschen test unit and high voltage tested. Two different ways to perform the Paschen testing were used for both breaks. The preparation of the breaks and the test setup are described and the test results are given.