HIGH-PRESSURE PULSED AVALANCHE DISCHARGES - FORMULAS FOR REQUIRED PREIONIZATION DENSITY AND RATE FOR HOMOGENEITY

The requirements on preionization for the formation of spatially homog eneous pulsed avalanche discharges are examined, We derive two formula s which apply in the case of a slowly rising electric field, one which gives the required preionization density at breakdown, and one which gives the required preionization rate, These quantities are expressed as functions of the electrochemical properties of the gas, the neutral density, and the electric field rise time, We also treat the statisti cal effect that the electrons tend to form groups, in contrast to bein g randomly distributed in space, during the prebreakdown phase, This p rocess is found to increase the required preionization rate significan tly, typically by a factor of five for a discharge at atmospheric pres sure.