Plasma-wall interaction in flashtubes

Abstract

A quasi-stationary arc has been established in a flashtube filled with a rare gas. The current intensity was varied in the range 1-3 kA and the arc lasted about 1 ms. The plasma parameters were determined spectroscopically and are typically N_e approximately 10¹⁸ cm^-3 and T approximately 1 eV. This allows the study of non-ideal plasma effects. The authors have investigated how the plasma fills the tube by means of an ultra-rapid camera either in streak or in framing mode. Two types of phenomena are found: (a) oscillations of the luminous boundary at the end of the expansion (this is usually ascribed to shock wave interaction); (b) dark contractions from place to place, restricting the current cross-section to a narrow channel. From the velocity measurements, and from the influence of the initial pressure, the energy and the nature of the gas, some conclusions can be made on the physical origin of these contractions. For the experimental determination of the electrical conductivity, the stability of the plasma must be carefully analysed.