paper

Nuclear probes of an out-of-equilibrium plasma at the highest compression

arXiv:1812.06868 · doi:10.1016/j.physleta.2019.04.048

Abstract

We report the highest compression reached in laboratory plasmas using eight laser beams, E $_{l a ser}$ $\approx$ 12 kJ, $I ¨ _{l a ser}$ =2 ns in third harmonic on a CD $_{2}$ target at the ShenGuang-II Upgrade (SGII-Up) facility in Shanghai, China. We estimate the deuterium density $I ¨ _{D}$ = 2.0 $\pm$ 0.9 kg/cm $^{3}$ , and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density $I^ I ¨ _{D}$ =4.8 $\pm$ 1.5 g/cm $^{2}$ was obtained from the measured ratio of the sequential ternary fusion reactions (dd $\to$ t+p and t+d $\to$ $I^\pm$ +n) and the two body reaction fusions (dd $\to$ $^{3}$ He+n). At such high densities, sequential ternary and also quaternary nuclear reactions become important as well (i.e. n(14.1 MeV) + $^{12}$ C $\to$ n'+ $^{12}$ C* etc.) resulting in a shift of the neutron (and proton) kinetic energies from their birth values. The Down Scatter Ratio (DSR-quaternary nuclear reactions) method, i.e. the ratio of the 10-12MeV neutrons divided by the total number of 14.1MeV neutrons produced, confirms the high densities reported above. The estimated lifetime of the highly compressed plasma is 52 $\pm$ 9 ps, much smaller than the lasers pulse duration.

6 pages, 5 figures, submit version