In this work gas discharge ignited by gyrotrone radiation with frequency 1THz were carried out. Breakdown curves were calculated both for selfignited and initiated discharges. There was shown that in case of breakdown by the pulse radiation with duration longest then several microseconds electric field threshold is the same as in case of continuous wave breakdown. Also the possibility of using a terahertz gyrotron as a radiation source for discharge in gas targets on installations for extreme ultraviolet photolithography was assessed.

The results of experimental studies on the breakdown of noble gases (argon and krypton) by terahertz radiation from the Novosibirsk free electron laser (NovoFEL) are presented. For the first time, the breakdown thresholds of noble gases by terahertz radiation were measured in a wide pressure range (0.2 – 1.5 bar). Previous experiments to measure breakdown thresholds in the THz range in various gases were carried out for hundreds of GHz or at atmospheric pressure. Experimental breakdown thresholds are compared with calculated data using various simplified models.