Neutron Emission Characteristics of NX-3 Plasma Focus Device: Speed Factor as the Guiding Rule for Yield Optimization

Abstract

This paper reports the results of characterization and optimization experiments carried out on a newly developed NX-3 dense plasma focus device (20 kJ at 20 kV, a quarter time period of ~ 3 μs, and 10 kJ/600 kA at 14 kV) at the Plasma Radiation Source Laboratory, NIE, Nanyang Technological University, Singapore. Initial experiments were conducted with an electrode assembly configuration having anode radius and length of 20 and 160 mm, respectively, for detailed neutron emission characterization of NX-3 device followed by further optimization of neutron yield using various other electrode configurations designed using the Lee Code. At ≥10-kJ operation, the average neutron yield on the order of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> neutrons/pulse in 4πsr was obtained for the deuterium filling gas pressure range of 6-8 mbar. The neutron yield of ~ 4.6 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> neutrons/pulse at 10 kJ/6 mbar is the highest ever reported for a device with the same stored energy. The neutron anisotropy measurements point to the beam-target mechanism as the dominant neutron production mechanism for NX-3 plasma focus device. Further optimization of neutron yield in NX-3 was achieved with the peak average neutron yield being enhanced from ~ (2.38 ±0.31) ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> neutrons/shot for the initial electrode configuration to about ~ (3.40 ±0.43) ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> neutrons/shot for the electrode configuration with anode radius and length of 26 and 140 mm, respectively. The analysis of neutron yield results for various electrode assembly configurations demonstrates the speed factor as a key optimization tool for maximization of neutron yield.