X-ray spots emitted in a hollow cathode ns-discharge

Abstract

A hollow cathode discharge using a tungsten pointed anode is fed by a low power Marx generator (1 J, 70 kV, 50 ns). The x-ray emission duration varies from 20 to 10 ns in the pressure range 10 −6 -5 × 10 −1 mbar, in air. The spatial distribution of the emitting sites has been determined, using a sensitive imaging device with a 5 ns exposure time, in the same range of pressures. This emission is strongly influenced by the occurrence of the 'pseudo-spark' regime. X-rays are emitted by different mechanisms: (a) electron bremsstrahlung and by Auger cascade associated with particle emission from the Teflon insulator and also tungsten (L α and L β ) characteristic lines; (b) pinching and collapse of the hot plasma surrounding the anode and the insulator. X-ray spots are observed. Their number is about 200 per shot, their radius is less than 40 µm and their emission intensity is compatible with that of a dense plasma: N e = (1.3 ± 0.2) × 10 20 cm −3 with a temperature in the range 100 eV to 1 keV. Some of them are seen to follow linear trajectories, suggesting a 1 ns period wave propagation at 300 km s −1 which triggers the collapse.