Study of the x-ray production mechanism of a dense plasma focus

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Abstract
The x‐ray emission from a 375‐kJ plasma focus is reported as measured on a time‐resolved basis with Ross filters and silicon diode detectors. Thick‐target electron beam spectra are calculated with a Monte Carlo electron beam transport program and fit to the experimental time‐integrated x‐ray spectra. A good fit is obtained with a 2‐MA E−2 power law electron beam, with cutoff energies at 8 and 200 keV, incident normal to a thick tungsten target. The source of the beam is judged to be electrons which are accelerated under the influence of strong electric fields. A 20‐nsec Q‐switched ruby laser pulse injected tungsten ions via laser ablation prior to the initial dense pinch, and the x‐ray emission below 4 keV was enhanced and that above 10 keV was reduced. The enhanced low‐energy x‐ray emission is in agreement with calculated radiation for collisional M‐shell excitation of highly stripped tungsten in a 1.5‐keV thermal plasma. A 900‐ μsec ruby laser pulse injected sufficient tungsten ions to degrade greatly the initial dense plasma pinch and reduce the beam target x‐ray emission. The time‐resolved x‐ray emission from this configuration appeared as a smooth Gaussian function in time with FWHM∼200 nsec.