Threshold for a cumulative resonant microwave streamer discharge in a high-pressure gas

Results are reported from experiments aimed at investigating how the struct ure of a microwave streamer discharge depends on the gas pressure. The form ation of a bright core in the streamer channel is shown to be of a threshol d nature: in discharges initiated in the field of a standing electromagneti c wave of an open two-mirror cavity, a bright core forms in air and hydroge n in the pressure ranges p(0) greater than or equal to 540 +/- 50 torr and p(0) greater than or equal to 740 +/- 70 torr, respectively. Estimates are presented, according to which the appearance of a bright core can be attrib uted to the onset of a local microwave pinch effect. (C) 2000 MAIK "Nauka/I nterperiodica".