pressure for 4 6 and 8 mm in pure sf 6 the system was limited in total voltage and so at the larger gaps only lower pressures could be investigated while the smaller gap would allow lower inductance the variations in self breakdown voltage were deemed unacceptably high for a stable low jitter system for that reason the preferred system in routine use employs 7 mm gaps and operates at 14 3 kv mm average field and 432 kpa pure sf 6 no prefires or misfires have been observed under these conditions in the course of approximately 10 000 shots quantifying the prefire probability of a gas switched system such as this is useful and can be done in at least three ways the first and most straightforward method is to operate the system normally and observe prefires over a number of shots this can be time consuming because of the number of shots required for systems with 10 u2212 1 or lower prefire probability the large number of shots may also cause significant conditioning or erosion and so could affect the results the second method is to operate the system at higher than normal voltage and characterize the self break distribution function at the operational pressure the rest of the system must be able to tolerate the higher voltages this can be a problem for low inductance designs where electric fields are relatively high during normal voltage operation the results at higher.