Neutron Production in a Plasma Focus Discharge with and without Axial Magnetic Field

Abstract

The D-D neutron emission from a 27-kJ plasma focus discharge was investigated with and without the effects of an applied axial magnetic field. With no applied field, the ratio of axial to radial neutron fluxes varied from 1.5 down to 1.2 for gas fillings of 4 to 10 Torr; the ratio of fluxes was greater for a round anode tip than for a flat end. An axial field of 1200 G (trapped flux of 57 000 Maxwells) reduced the average neutron yield from 1010 to 109, reduced the average energy of the axially emitted neutrons from 2.9 to 2.8 MeV, and caused the effective neutron source to shift away from the anode surface; the width of the neutron energy spectra remained about 500 keV. With an applied field, the ratio of axial to radial neutron fluxes increased from 1.2 early in the pulse to 1.5 at peak intensity. Streak photography with and without axial field revealed that neutron production began when the plasma column first pinched and that peak neutron emission occurred when the plasma luminosity faded; the axial field delayed the onset of peak emission by up to 80 nsec. The observations do not agree with a thermonuclear model of neutron production, but the results are consistent with a model of deuteron acceleration in crossed fields.