Triggering of the breakdown in a discharge tube by visible-spectrum light pulses

The influence of the pulses of visible-spectrum light on the breakdown in a discharge tube was studied experimentally. The tube of 80 cm length and 1.5 cm inner diameter contained neon at a pressure of 0.6 Torr. High-voltage rectangular or ramp pulses were applied to the anode. The light pulses of 0.1-100 mu s duration were produced by the light-emitting diode or laser diode at a wavelength of 460 and 407 nm, respectively. A small area of the tube wall near the anode was illuminated at different moments after or before the voltage pulse onset. It has been found that the light pulse exerts the strongest influence on the breakdown. In the case of rectangular pulse, it drastically decreases the statistical delay time of the breakdown. As a result, all the breakdowns, which did not happen before the light pulse, occur during several microseconds after its onset. The light pulse influences the breakdown delay time even if it terminates before the voltage pulse onset. This can be explained by the finite lifetime of the secondary electrons produced by the light. In the case of the ramp voltage pulse, an essential decrease in the breakdown voltage scatter is observed under illumination. The effect is especially pronounced if the light pulse is applied at the moment when the anode voltage is equal to or somewhat lower than the minimum breakdown voltage. For later moments, the breakdown voltages are strictly bounded by both sides. The average breakdown voltage decreases noticeably. As for the mechanism responsible for the observed effect, electron photodesorption from the tube wall is suggested. This process presumably occurs in dielectric barrier discharge at atmospheric pressure where it can influence the breakdown voltage and provide synchronous breakdown of micro discharges, thus causing the formation of multiple filaments.