Breakdown in mm-sized discharges : discharge formation under high-frequency AC voltage

High-frequency AC breakdown covers a broad range of frequencies. The reakdown process in not the same in the whole frequency range, and the most attention has historically been given to low-frequency end where there is at least one breakdown per half voltage cycle, and to the high-frequency end, where the electron energy cannot follow the changes in electric ??eld. The mid-range, although it has been proven as technologically important, has not been extensively studied. The aim of this project was to examine the breakdown process in near-atmospheric pressure argon and xenon in an enclosed pin-pin geometry. The work was focused on 0.3 and 0.7 bar discharges in 4 mm and 7 mm gas gaps. The driving frequency was varied between 60 kHz and 1 MHz. We present several key features of breakdown in this combination of pressure, gap length and voltage frequency.