The Lee model couples the electrical circuit with plasma focus dynamics, thermodynamics, and radiation. It is used to design and simulate experiments. A beam-target mechanism is incorporated, resulting in realistic neutron yield scaling with pinch current and increasing its versatility for investigating all Mather-type machines. Recent runs indicate a previously unsuspected “pinch current limitation” effect. The pinch current does not increase beyond a certain value however low the static inductance is reduced to. The results indicate that decreasing the present static inductance of the PF1000 machine will neither increase the pinch current nor the neutron yield, contrary to expectations.

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Published literature shows that the neutron yield of the plasma focus has been modeled in two papers using a thermonuclear mechanism. However, it is more widely held that plasma focus neutrons are produced mainly by nonthermalized mechanisms such as beam-target. Moreover these papers use several parameters which are adjusted for each machine until the computed neutron yield Y n data agree with measured Y n data. For this paper numerical experiments are carried out, using the Lee model code, incorporating a beam-target mechanism to compute the Y n versus pressure data of plasma focus devices PF-400 J and FN-II. The Lee model code is first configured for each of these two machines by fitting the computed current waveform against a measured current waveform. Thereafter all results are computed without adjusting any parameters. Computed results of Y n versus pressure for each device are compared with the measured Y n versus pressure data. The comparison shows degrees of agreement between the laboratory measurements and the computed results.

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Contrary to the general expectation that performance of a plasma focus would progressively improve with progressive reduction of its static inductance L o , a recent paper suggests that there is in fact an optimum L o below which although the peak total current increases progressively the pinch current and consequently the neutron yield of that plasma focus would not increase, but instead decreases. This paper describes the numerical experiments and results that led to this conclusion.

A recent paper derived benchmarks for deuteron beam fluence and flux in a plasma focus (PF) [S. Lee and S. H. Saw, Phys. Plasmas 19, 112703 (2012)]. In the present work we start from first principles, derive the flux equation of the ion beam of any gas; link to the Lee Model code and hence compute the ion beam properties of the PF. The results show that, for a given PF, the fluence, flux, ion number and ion current decrease from the lightest to the heaviest gas except for trend-breaking higher values for Ar fluence and flux. The energy fluence, energy flux, power flow, and damage factors are relatively constant from H2 to N2 but increase for Ne, Ar, Kr and Xe due to radiative cooling and collapse effects. This paper provides much needed benchmark reference values and scaling trends for ion beams of a PF operated in any gas.

The total current I total waveform in a plasma focus discharge is the most commonly measured quantity, contrasting with the difficult measurement of I pinch . However, yield laws should be scaled to focus pinch current I pinch rather than the peak I total . This paper describes how I pinch may be computed from the I total trace by fitting a computed current trace to the measured current trace using the Lee model. The method is applied to an experiment in which both the I total trace and the plasma sheath current trace were measured. The result shows good agreement between the values of computed and measured I pinch .

Measurements on plasma focus ion beams include various advanced techniques producing a variety of data which has yet to produce benchmark numbers [A Bernard et al., J. Mosc. Phys. Soc. 8, 93-170 (1998)]. This present paper uses the Lee Model code [S Lee, http://www.plasmafocus.net (2012)], integrated with experimental measurements to provide the basis for reference numbers and the scaling of deuteron beams versus stored energy E 0. The ion number fluence (ions m À2) and energy fluence (J m À2) computed as 2.4À7.8 Â 10 20 and 2.2À33 Â 10 6 , respectively, are found to be independent of E 0 from 0.4 to 486 kJ. Typical inductance machines (33-55 nH) produce 1.2À2 Â 10 15 ions per kJ carrying 1.3%-4% E 0 at mean ion energy 50-205 keV, dropping to 0.6 Â 10 15 ions per kJ carrying 0.7% E 0 for the high inductance INTI PF. V