Kinetic simulation of thermonuclear-neutron production by a 10{sup 7}-A deuterium Z pinch

Fully kinetic simulations have demonstrated that at sufficiently high currents, half of the neutrons produced by a deuterium Z-pinch are thermonuclear in origin. At 150-kA pinch current, O. A. Anderson et al. [Phys. Rev. 110, 1375 (1958)] clearly shows that essentially all of the neutrons produced by a deuterium pinch are not thermonuclear, but are initiated by an instability that creates beam-target neutrons. Since this paper, many subsequent authors have supported this result while others have claimed that pinch neutrons are, on the contrary, thermonuclear. To resolve this issue, fully kinetic, collisional, and electromagnetic simulations of the complete time evolution of a deuterium pinch have been performed. The simulations were performed with the implicit particle-in-cell code LSP, as described in D. R. Welch et al. [Phys. Rev. Lett. 103, 255002 (2009)]. At 10{sup 6} -A pinch currents, most of the neutrons are, indeed, beam-target in origin. At 15-MA current, half of the neutrons are thermonuclear and half are beam-target driven by instabilities that produce a power law fall off in the ion energy distribution function at large energy. Simulation results suggest that from 7- to 15-MA current, the fraction of thermonuclear neutrons is not sensitive to current and that the strong dependence of neutron yield on current will continue at currents greater than 15 MA.