Measurement of Model Parameters Versus Gas Pressure in High-Performance Plasma Focus NX1 and NX2 Operated in Neon

Abstract

Measured current waveforms at different neon pressures from two different plasma focus (PF) devices, namely, NX2 and NX1 are used for analysis using the Lee code. The model parameters of mass ( $f_{m}$ and $f_{{\text {mr}}}$ ) and current ( $f_{\text {c}}$ and $f_{\mathrm {cr}}$ ) in axial and radial phase, respectively, are obtained by fitting the computed current waveform to the measured current waveform for each pressure over a range of pressures in neon. The results show that the value of $f_{m}$ and $f_{\mathrm {mr}}$ ranges from 0.07 to 0.12 and 0.09 to 0.20, respectively, over the pressure range 1.0–5.0 Torr for NX2, whereas for NX1 it ranges from 0.020 to 0.024 and 0.048 to 0.08, respectively, over the pressure range 7.5–12 Torr. In all cases, the values of $f_{c}$ and $f_{\mathrm {cr}}$ are fixed at 0.7. Comparison of computed and measured soft X-ray (SXR) yield using fit model parameters for both devices shows good agreement. An important finding is that despite the noticeable variation of mass factors over the whole pressure range, a representative set of model parameters is found for each machine which may be taken as fixed over the range of pressures producing a good yield. In particular, for a high-performance PF using conventional electrode structure the representative set is: $f_{m} = 0.075$ , $f_{c} \,\, = \,\, 0.7$ , $f_{\mathrm {mr}} =0.1$ , and $f_{\mathrm {cr}}= \,\, 0.7$ . This is valuable information for neon SXR design purposes.