Formation and dynamics of a Z pinch in a high current capillary discharge in initial vacuum

Abstract

Experimental conditions are presented for the formation of a Z pinch from ablated wall material in a high current, medium diameter capillary discharge without an initial filling gas. A hollow cathode geometry is used and electron beams, initiated by a laser spark, form a transient metallic plasma in the hollow cathode volume. The laser spark plasma initiates the preionization phase, whose conditions are essential for generating a stable Z pinch during the main conduction phase. During the preionizing phase wall plasma is ablated. The main discharge is derived from a small pulsed power generator, whose rate of rise of current may be varied, at current of 120 kA for 120 ns. The capillary has an internal diameter of 5 mm and length of 6 cm. From time, spatial and energy resolution of the axial soft x-ray emission, the optimum conditions of plasma formation are found to depend on the preionizing electron beams, current and the rate of rise of main discharge current applied. The temperature is obtained from soft x-ray spectra, and attains a maximum value of 80 eV. The relevance of these results in soft x-ray lasing capillary discharges is discussed. (C) 2003 American Institute of Physics.