Neutron Yield Optimization From a Palm Top Plasma Focus Device Using Lee Code

Abstract

A palm top plasma focus (PF) device (100 J, 5 kV, 59 kA, ~1.5 kg) with tapered anode was demonstrated in a study earlier by (Rout et al., 2013). To simulate that device, we use the Lee code (RADPFV5.16). The computed current trace is fit to Rout’s measured current trace at 2.25 Torr deuterium ( ${D} _{2}$ ) gas. The best-fit values of the model parameters are found as ${f}_{m} = 0.11, f_{c} = 0.73, f_{\text {mr}} = 0.245, f_{\text {cr}} = 0.78$ . Having fixed these parameters, the computed neutron yields ( ${Y} _{n}$ ) $6.12\times 10^{4}, 1.72\times 10^{4}$ , and $0.24\times 10^{4}$ neutrons/shot are found to be comparable with the measured values ( $5.2~\pm ~0.8$ ) $\times 10^{4}$ , ( $2~\pm ~0.5$ ) $\times 10^{4}$ , and ( $0.2~\pm ~0.1$ ) $\times 10^{4}$ at (2.25 Torr, 5 kV), (1.875 Torr, 4 kV), and (1.5 Torr, 3 kV), respectively. The remarkable agreement shows the reliability of the code. Numerical studies are extended with anode length and taper size optimization, corresponding to the pressure range (2–3.5) Torr of ${D} _{2}$ . The optimum ${Y} _{n}$ ( $1.56\times 10^{5}$ ) is found at 2.55 Torr which is three times greater than the highest measured value [( $5.2~\pm ~0.8$ ) $\times 10^{4}$ ] at 2.25 Torr, 5 kV. At this optimized configuration, using deuterium-tritium (1:1) as the operating gas, the neutron yield is computed to increase to $10^{7}$ , about 100 times greater than the computed yield with ${D} _{2}$ . In addition, we found that reducing the stray inductance ${L} _{0}$ of the device from its present value of 30 to 16 nH, the D-D neutron yield is increased from computed value of $1.56\times 10^{5}$ to $2.58\times 10^{5}$ .