Numerical Optimization of Neon Soft X-ray Emission in a Spherical Plasma Focus Device with Lee Code

Abstract

spherical

plasma focus (SPF) device using the Lee code. As a prerequisite for predictive modeling, the code was benchmarked

against the experimentally measured discharge current waveform of the 135 kJ SPF (N. V. Zavyalov et al., 2013). In this

numerical study using ‘equivalent straight length’ technique referred to ‘shortcut’ simply fits a straight length equivalent

to the curved run-down length of this SPF with the Lee code (for cylindrical electrodes), the computed current trace is

first fitted to the measured one at 14.3 Torr deuterium-tritium (D-T) gas and the obtained best-fitted values of the model

parameters are found as fm = 0.022, fc = 0.55, fmr = 0.14, fcr = 0.72 . These values were then adopted in a systematic

optimisation study of the pinch-plasma conditions. The simulations covered Ne fill pressures from 0.5 to 7 Torr,

anode and cathode radii at fixed ratios of b/a = 1.8125 and b/a = 1.41, and charging voltages from 15 to 30 kV. In all

the cases, the plasma pinch temperature was constrained to the characteristic Ne emission window of (2.3–5) × 106 K. For

each electrode geometry the code identified a unique combination of fill pressure and charging voltage that maximized

Ysxr. At moderate electrode sizes and bank voltages of 25 kV the SPF is predicted to deliver peak Ne soft X-ray (SXR)

yields exceeding 5 kJ per shot with efficiencies greater than 4%. In addition, our findings using the ‘shortcut’ method were

compared to the results obtained by (Y. Ay, 2021) using the spherical magneto-hydrodynamic model where the cylindrical

run-down section of the Lee code was modified to the spherical geometry. Indeed, both results overlap in some points,

which is a validation of the ‘shortcut’. And thus, the Lee code was established as a robust and quantitative tool for the

design and scaling of compact, high-performance Ne SXR sources.