Thermonuclearizing the plasma focus—converting plasma focus fusion mechanism from beam-gas target to thermonuclear

Abstract

Abstract It has been reported that over a range of 3–280 kJ, neutron-optimized deuterium plasma focus machines operate with a near constant speed factor S = 89 ± 8 kA cm−1 per (torr)0.5. This near-constant value of S is consistent with a narrow range of peak axial speeds approximately 10 cm μs−1 and peak radial speeds 20–30 cm μs−1, resulting in focus pinch temperatures less than 0.5 keV and inductively generated high voltages, producing deuteron beams with energies from high tens to hundreds keV. The low pinch temperatures and high beam-deuteron energies result in fusion neutrons predominantly from a beam-target mechanism. A converging taper ending in radius a e, is added to the end of the standard cylindrical anode of radius ‘a’. This taper converts the pinch from one with starting radius ‘a’ to one with a reduced starting radius a e. This increases the value of S and consequently the pinch temperature. This study examines the scaling of the end taper and finds that a taper ending in a radius, which is 1/20 that of the before-taper section increases the pinch temperature by a factor approximately 200, to above 20 keV. This increases the thermonuclear cross-sections by up to 14 orders of magnitude. Numerical experiments using the Lee code confirm that the thermonuclear component of the fusion yield becomes predominant. Such a taper may be considered as a thermonuclear converter.