Plasma jet emission in fast-pulsed capillary discharges

The properties of a plasma jet generated in low-pressure pulsed capillary discharge have been measured. The discharge operates in a 5 cm long and 1.6-mm-inner diameter alumina capillary, with argon in a pressure range between 20 and 100 Torr, at 11-kV applied voltage. The temporal and spatial evolutions of the plasma density in the plasma jets are measured close to the capillary end with a Michelson interferometry based on a 10-ns-pulse Nd:yttrium aluminum garnet laser. The maximum on-axis plasma density is of the order of 1017 cm-3 at the capillary output, with an ∼6-ns rise time to reach a significative electron density. At lower pressure the plasma density is seen to decay in a time scale of 50 ns and over an axial distance of the order of 0.5 mm, whereas at the higher pressure, 100 Torr, it remains more or less stationary for up to ∼300 ns. The discharge is characterized by a high efficiency in energy coupling, as the local-stored energy is much less than 1 J per pulse