Time-resolved hard X-ray emission from a small plasma focus

Abstract

Some results of an experimental study of the hard X rays emitted from a 15-kV, 3-kJ plasma focus operated in argon are reported. The temporal evolution of the hard X rays detected by a plastic scintillator-photomultiplier detector and the voltage across the focus tube measured by a resistive voltage divider are simultaneously recorded on a two-channel digitizing oscilloscope. Metal absorbers of various thicknesses are used to provide some indications of the energies of the X rays. When the time delay of the detector system with respect to the anode voltage is taken into account, the hard X rays are observed to be emitted about 15 ns before the peak of the anode voltage and last for about 100 ns. There are two periods of emission, the X rays emitted in the first period being more intense, more energetic, and more directional than the X rays emitted in the second period. The X rays are attributed to the bombardment of the anode by energetic electrons generated in the pinch and the disruption phases of the focus.