Experimental observations of the spatial anisotropy of the neutron emission in a medium energy plasma focus

The results of experiments carried out on the DPF-78, a 60 kV, 28 kT plasma focus device are presented. The primary objective of these experiments was to investigate the spatial anisotropy of the neutron emission and to correlate the total neutron yield with hard X-ray emission and the presence of hot spots. To influence the plasma parameters, gas fillings of deuterium with doping of neon, argon, and krypton were used. An admixture of gases with an equivalent mass density of 5 mbar of D₂ was employed throughout the experiment. A novel technique for neutron detection was used, which allowed the recording of neutron signals at close distance to the focus (65 cm), with minimal dispersion of the signal due to time of flight and yet high X-ray rejection. A set of these detectors was placed at different angular positions to investigate the polar distribution in the neutron emission. It was identified for the first time that in a medium energy plasma focus device, the neutron emission is composed of two periods, similar to that reported in high energy devices. It was found that the first period occurs immediately before the maximum compression and lasts less than 50 ns while the second period lasts between 150 and 200 ns. It was found that the polar distribution of the neutron emission shows a strong anisotropy during the second period and depends on the Z of the doping gas. No correlation was found between the total neutron yield (about 10¹⁰) and the hard X-ray emission or appearance of hot spots