Experimental research on vacuum breakdown characteristics in a long gap under microsecond pulses

By conducting vacuum breakdown experiments under 30 μs pulses with a uniform field for gap separations d ranging from 2.5 to 5.5 cm, it is found that the dependence of the breakdown voltage U
b
on d obeys the total voltage effect (TVE) relation U
b
=Cd
^a
, where a ranges from 0.76 to 0.84. By fixing d as 3.5 mm, U
b
for stainless steel (304C), titanium (TC4), and aluminum (LY14) electrode materials are obtained, and it is found that U
b
(304C)b
(TC4)b
(LY14). Microscopic images of the electrode surfaces show the presence of melting traces coming from the opposite electrodes. By extending Farrall's model of vacuum breakdown under microsecond pulses, an expression for the power exponent of a in the TVE is derived as a=(5 − k)/6, where k is a parameter related to the uniformity of the field. In the experiments performed here, electrodes with the Bruce configuration are used, and k is close to 0. Therefore, a is close to 0.833, which agrees with the values of the power exponents found in the experiments.