Breakdown of the heavy noble gases in a focused beam of powerful sub-THz gyrotron

The results of experimental investigations of heavy noble gas breakdown thresholds in a focused beam of powerful subterahertz radiation are presented. The gas discharge, maintained by the powerful radiation of the terahertz frequency band, is a new specific object of gas discharge physics. This paper presents the experiments with pulsed gyrotrons capable of generating a power of 250 kW at a frequency of 250 GHz. The gyrotron wave beam was focused by means of quasioptical mirrors into the spot with a diameter less than 3 mm that provided intensity into the focal spot up to 3.5 MW/cm2. The achieved electrical field intensity was enough for gas breakdown into the range of pressure values of 1–1500 Torr for heavy noble gases (argon and krypton). The boundary values of field intensity for discharge existence were measured. Experimental data were compared to the analytical model of Raizer and Vyskrebentsev for monatomic gases.