Angular distribution measurements of energy spectra of protons emitted from hydrogen plasma focus

Abstract

The plasma focus is thought to be one of the most efficient pulsed neutron, X-ray and charged-particle beam sources. It is interesting phenomenon that high energy ions with an energy of more than one hundred times as large as the bank voltage are produced in plasma focus devices. The mechanism of the production of these ions, however, is not fully understood in spite of investigations from various points of view. Hence, the determination of ion beam characteristics is very important not only in understanding the mechanism of the production of high energy ions or neutrons, but also for their application. The characteristics of the ion beams produced in a Mather type plasma focus device were studied. The chamber was filled with hydrogen gas to 250∼350 Pa. The capacitor bank of 41.6 µF was charged to 30 kV to get a peak current of 550 kA. The distribution of ion current density was measured by a biased ion corrector. To evaluate the dependence of the angular distribution of ion energy spectrum on hydrogen gas pressure, the incident angle resolved energy spectrometer was used. The ion current density of 8 kA/cm2 with pulse duration of 60 ns was obtained at 110 mm downstream from the top of the anode on the axis. Experimental results for the energy spectrum showed that the proton beam energy was distributed from 0.1 MeV to 2 MeV and that ions with energies lower than 300 keV were distributed widely over emission angles ranging from −80° to 90°, with higher-energy ions (> 1 MeV) being confined to emission angles of −20°∼30°. In addition, the ion energy and the track density were found to decrease rapidly with increasing emission angle.