It is well known that radio frequency breakdown is one of the main
limitations in high frequency accelerators. Similarities have been detected
between breakdowns in direct current vacuum gaps and those in superconducting
radio frequency cavities. Therefore, cavity break- downs due to electric
field phenomena can be understood by studying direct current vacuum
breakdowns. Significant irregularity of a surface and a variety of involved
processes objectively stipulate a number of factors which may lead to a
breakdown. In this paper, the effects of surface conditions, accelerator
gradient, pulse length, and operating frequency on the breakdown have been
studied by using COMSOL simulation package. It was found that the dependence
of breakdown rate on accelerating gradient and pulse length follows scaling
laws. Based on the time evolutions of electron density and the potential in
cone-cylinder electrode configuration at the pressure of 0.1 Pa, the time
scale of a vacuum breakdown has been established. It was also confirmed that
the emission from an electrode surface can be regarded as a major factor
leading to electrical breakdown in vacuum. The obtained results could be very
useful in high-gradient accelerating structures.
Simulation study of direct current vacuum breakdown and its application to high-gradient accelerating structures
