Numerical experiments on plasma focus pinch current limitation

Abstract

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.

Numerical Experiments Providing New Insights into Plasma Focus Fusion Devices

“…The code has been used extensively in several machines including UNU/ICTP PFF [2,7,8,10,11,[15][16][17], NX2 [9,12,18], and NX1 [18,19] and has been adapted for the Filippov-type plasma focus DENA [20]. A recent development is the inclusion of the neutron yield Y n using a beam-target mechanism [21][22][23][24][25], incorporated in recent versions [26,27] of the code (versions later than RADPFV5.13), resulting in realistic Y n scaling with I pinch [21,22]. The versatility and utility of the model are demonstrated in its clear distinction of I pinch from I peak [28] and the recent uncovering of a plasma focus pinch current limitation effect [23,24,29] as static inductance is reduced towards zero.…”

“…A recent development is the inclusion of the neutron yield Y n using a beam-target mechanism [21][22][23][24][25], incorporated in recent versions [26,27] of the code (versions later than RADPFV5.13), resulting in realistic Y n scaling with I pinch [21,22]. The versatility and utility of the model are demonstrated in its clear distinction of I pinch from I peak [28] and the recent uncovering of a plasma focus pinch current limitation effect [23,24,29] as static inductance is reduced towards zero. Extensive numerical experiments had been carried out systematically resulting in the uncovering of neutron [21][22][30][31][32][33] and SXR [30][31][32][33][34][35][36][37] scaling laws over a wider range of energies and currents than attempted before.…”

“…The beam interacts with the hot dense plasma of the focus pinch column to produce the fusion neutrons. The beam-target yield is derived [21][22][23][24]26] as:…”

“…The following parameters are kept constant : (i) the ratio c = b/a (kept at 1.5, which is practically optimum according to our preliminary numerical trials; (ii) the operating voltage V 0 (kept at 20 kV); (iii) static inductance L 0 (kept at 30 nH, which is already low enough to reach the I pinch limitation regime [23,24] over most of the range of E 0 we are covering) and; (iv) the ratio of stray resistance to surge impedance RESF (kept at 0.1, representing a higher performance modern capacitor bank). The model parameters [26,27] f m , f c , f mr , f cr are also kept at fixed values 0.06, 0.7, 0.16 and 0.7.…”

Optimizing UNU/ICTP PFF Plasma Focus for Neon Soft X-ray Operation

“…A recent development is the inclusion of the neutron yield Y n using a beam-target mechanism [23]- [27], incorporated in recent versions [8] of the code (versions later than RADPFV5.13), resulting in realistic Y n scaling with I pinch [23], [24]. The versatility and utility of the model are demonstrated in its clear distinction of I pinch from I peak [28] and the recent uncovering of a plasma focus pinch current limitation effect [25], [26]. The description, theory, code, and a broad range of results of this "Universal Plasma Focus Laboratory Facility" are available for download from [8].…”