Calculation Of Ionization Coefficient For Microscale Gas Breakdown In Ac Fields

Characterizing gas breakdown is critical for preventing breakdown, such as for MEMS and field emission devices, or inducing breakdown, such as for microplasma generation for medicine and combustion [1] . DC gas breakdown is typically driven by Townsend avalanche and mathematically described by Paschen’s Law (PL). For microscale gaps, the strong electric fields at the cathode strip electrons by field emission, causing a deviation from PL [2] . For both mechanisms, gas breakdown depends on the ionization coefficient. The ionization coefficient uses a semi-empirical model that is valid for a range of ratios of the electric field to the pressure [2] ; however, the breakdown conditions for microscale gaps fall outside of this range. While a semi-empirical relationship was derived to account for this, it was only derived for a narrow range of conditions [2] , [3] . We have recently used particle-in-cell (PIC) simulations to assess the semi-empirical behavior of the ionization coefficient over a broader range of pressures and gap distances [4] to ultimately apply to gas breakdown theories [2] . Here, we apply PIC to assess ionization coefficients for AC fields for a range of gap distances, pressures, and frequencies to ultimately incorporate into AC breakdown theories [5] . Additional scaling behavior with these parameters will be discussed.