Experimental study of neutron emission characteristics in a compact sub-kilojoule range miniature plasma focus device

摘要

In order to gain insight into the possible neutron production mechanism in sub-kilojoule miniature plasma foci, the anisotropy in neutron and hard x-ray emissions from a newly developed fast miniature plasma focus device (2.4 mu F, 27 nH, T/4 similar to 400 ns, 12-15 kV, 170-270 J, total mass similar to 25 kg) is investigated. The system produces an average neutron yield of (1.2 +/- 0.2) x 10(6) neutrons/shot into 4 pi sr at similar to 80 kA peak discharge current and 5.5 mbar deuterium operation, as measured by a He-3 proportional counter. Relative measurements of radiation yields, to gauge the emission anisotropy, have been performed using a pair of fast scintillator-photomultiplier detectors placed along the axial (0 degrees) and radial (90 degrees) directions. The average forward to radial neutron yield anisotropy is found to be 1.3 +/- 0.2. The average peak neutron energy for the axial and radial directions is estimated to be (2.9 +/- 0.3) MeV and (2.6 +/- 0.1) MeV, respectively. The observed higher fluence along the anode axis and the coincidence between occurrence of maximum neutron yield and anisotropy at 5.5 mbar deuterium filling gas pressure, suggest that the neutron production mechanism in the sub-kilojoule range miniature plasma focus device FMPF-1 may be predominantly beam-target in nature.