The low-pressure transition from diffusion-controlled to multipacting gas breakdown

Abstract

The transition region from diffusion-controlled to multipacting discharge conditions in a parallel geometry, when the gas pressure is decreased and attains values below the so-called mean-free-path limit, is investigated using a Monte Carlo simulation technique. An ideal gas, without excitation states at energies below the ionization level and with a velocity-independent electron-molecule collision frequency, is considered. The results are plotted as breakdown voltages, properly normalized to the electron energy for which the secondary-electron emission yield of the electrodes is unity, vs. the gas pressure, given as the ratio of the electron collision frequency over the applied electric field frequency. Curves for various sets of dimensionless variables, representing size, electrode and gas parameters, are given and interpreted in terms of the changing relative importance of electron collisions with gas molecules and with electrodes, when the gas pressure is decreased and vacuum conditions are approached.