Experimental Investigation of Ionization Waves in Fast Pulsed Capillary Discharges

Previous investigations show that the electric breakdown process in shielded capillary discharges with a hollow cathode geometry is characterized by the propagation of an anode directed high speed ionization wave (HSIW). To further investigate HSIW assisted capillary discharges with negative polarity, we have performed detailed experiments in argon, at pressures between 0.2 and 1.0 Torr. For these pressures, a characteristic ionization wave speed in the 0.1-3.0 x 107 m/s range is observed. The speed and amplitude of the wave are seen to decrease as the wave propagates along the capillary axis. As a result of these investigations, the role of the hollow cathode electron beams is clearly identified and the HSIW is established as the dominant mechanism for electric breakdown in low pressure capillary discharges, sharing most of the features previously observed in much larger coaxial discharge devices