A Plasma Focus Electronic Neutron Generator

Abstract

An electronic neutron generator based on the dense plasma focus emits fast neutron pulses (~20 ns at the source) that allow for the time-of-flight detection of target materials at a standoff of ~3 m. Pulse-power-driven neutron generators have been considered unreliable due to the short lifetime of components such as gas switches and electrodes. The reliable operation of a plasma focus has been demonstrated for up to 25 000 shots at 1 Hz over several experiments with <; 25% variation in the mean neutron yield. The repetition rate is limited to 1 Hz for thermal management reasons. The peak current was 61 kA, with the neutron yield varying from 2.6 × 105 neutrons/pulse to 4.4 × 105 neutrons/pulse (a standard deviation of ~50%) within a given run. The neutron yield distribution variation more strongly correlates with the minimum in the time derivative of the current rather than the peak current in the narrow operating current window of 61 ± 2 kA. Each experiment used a fixed deuterium fuel gas charge. Insulator coating was shown not to be a problem after a total of 250 000 shots. The primary lifetime-limiting factor was a deep hole that was bored into the SS304 anode, eroding it at a rate of ≈6 μg/shot. With a refractory cooled anode, the source could realize an increase in electrode lifetime and a reduction in insulator coating, leading to a long lifetime (~106 pulse) and a fast pulse electronic neutron generator that operates at up to 100 Hz at 108-n/s D-D output.