Optimal conditions for efficient ion acceleration and neutron production in deuterium gas-puff z-pinches

Abstract

Deuterium gas-puff z-pinches are researched primarily as efficient sources of DD fusion neutrons. The first experiment with a deuterium gas jet was carried out in 1978 (Shiloh et al 1978 Phys. Rev. Lett. 40 515518). Since then, several D _2 gas-puff experiments have been performed on various pulsed-power generators. The highest, so far published, DD neutron yields of $4\times10^{13}$ were observed on the Z machine at Sandia National Laboratories around 2005 (Coverdale et al 2007 Phys. Plasmas 14 022706). More recently, z-pinch experiments with a plasma-shell on a deuterium gas puff were carried out on the GIT-12 higher-impedance pulsed-power generator at 3 MA currents. On GIT-12, unique results were high neutron and ion energies, which approached 60 MeV. Comparison of deuterium gas-puff experiments on different generators allows the identification of the parameters essential for optimizing neutron production. These parameters include the optimal mass, preionization, short deuterium gas-injection time, and zippering towards a cathode. Neutron yields appear to depend not only on a current, but also on other parameters of a generator, such as an impedance and the energy stored in a capacitor bank. Our conclusions regarding the optimal conditions were tested on the Hawk generator (NRL, Washington, DC). At a current of 0.7 MA, Hawk accelerated deuterons up to 15 MeV producing one neutron pulse with the yield of the order of 10 ^10 and a broad energy spectrum in the axial and radial direction. These results show that ion acceleration mechanisms in deuterium gas-puff z-pinches could be very efficient and attractive, with a variety of potential applications in high-energy-density physics, materials science, and controlled thermonuclear fusion research.

Keywords

• deuterium
• magneto-inertial fusion
• neutron diagnostics
• z-pinch
• optimization