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

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.