Effect of Wire Parameters on the Emission of Hard X Rays from Exploding Wires

Abstract

Tungsten wires, 20–80 mm in length and 0.05–0.20 mm in diameter, were exploded in vacuum (1×10−5 Torr) by means of a 0.4-μF capacitor charged to 30 kV. A pronounced dip and peak in the dI/dt and voltage oscillograms, respectively, corresponded in time to each other and to an ultrafast x-ray pulse. Calculations showed that the wire temperature reached melting point at the same moment. It was found that for a constant wire length, the magnitude of the voltage peak attained a weak maximum at a diameter of about 0.10 mm. In addition, for a constant wire diameter, this magnitude increased with increasing wire length. The x-ray output was measured by a scintillator-photomultiplier (PM) combination and an x-ray film. The PM pulses (half-width 20 nsec) depended only slightly on the wire parameters. Their peak values plotted against wire length and diameter showed the same feature as the peak voltage diagram did. Furthermore, studies of the film blackening indicated that various wire dimensions gave rise to various rates of blackening. It was also found that the higher the voltage peak (or PM pulse) the more dense the blackening on the film. A model, based on Ohmic heating of the wire with accompanying thermionic electron emission, which qualitatively explains the generation of the ultrafast x-ray pulse, is presented. In addition, it was found that the electron currents which gave rise to the x-ray burst were up to 10 times higher than those predicted by Richardson's formula.