A two-pulse method is used to determine the insulation recovery time of the gasspark gap switch with different types of gas applied in a high power accelerator with a waterdielectric pulse forming line.At the breakdown voltage of 450 kV,with the vacuum diode voltageof about 200 kV,and a current of 30 kA,recovery characteristics of H_2,N_2,SF_6 were studied.Therecovery percentages of the gas breakdown voltage and vacuum diode voltage were determined.The results show that hydrogen has the best recovery characteristics.At a pulse interval of8.8 ms,the recovery percentages of both the gas breakdown voltage and vacuum diode voltage forhydrogen exceed 95%.For SF_6 and N_2 with an interval of 25 ms and 50 ms respectively,a 90%voltage recovery was obtained.The experiments also proved that the repetitive rate of the highpower accelerator with a pulse forming line is mainly restricted by the gas switch repetitive rate;the recovery percentages of the vacuum diode voltage are limited by the recovery percentages ofthe gas switch breakdown voltage.The hydrogen switch can be employed for a high repetitiverate-high power accelerator with a pulse forming line.
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