Discharge development and minimum switching time in a kivotron

Experimental studies of the breakdown stage in a kivotron, a high-voltage switching device based on an open discharge with counterpropagating electron beams, are performed. It is demonstrated that a fast stage of the breakdown is provided by photoemission of resonance radiation of fast atoms with large Doppler shift with respect to the line center of thermal atoms. For working pressure $p_{\mathrm{He}}\approx$ 20 Torr, switching time $\tau_s\approx$ 80 ps is achieved. The estimated minimum switching time is $\sim$ 35 ps.