  We report the highest compression reached in laboratory plasmas using eight
laser beams, E$_{laser}$$\approx$12 kJ, $\tau_{laser}$=2 ns in third harmonic
on a CD$_2$ target at the ShenGuang-II Upgrade (SGII-Up) facility in Shanghai,
China. We estimate the deuterium density $\rho_D$= 2.0 $\pm$ 0.9 kg/cm$^{3}$,
and the average kinetic energy of the plasma ions less than 1 keV. The highest
reached areal density $\Lambda \rho_{D}$=4.8 $\pm$ 1.5 g/cm$^{2}$ was obtained
from the measured ratio of the sequential ternary fusion reactions
(dd$\rightarrow$t+p and t+d$\rightarrow$$\alpha$+n) and the two body reaction
fusions (dd$\rightarrow$$^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 $\rightarrow$ 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.

Plasma Physics;Nuclear Experiment