We report the highest compression reached in laboratory plasmas using eight laser beams, E ≈ l a s e r 12 kJ, τ l a s e r = 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 ρ D = 2.0 ± 0.9 kg/cm3, and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density Λ ρ D = 4.8 ± 1.5 g/cm2 was obtained from the measured ratio of the sequential ternary fusion reactions (dd→t+p and t+d→ α +n) and the two body reaction fusions (dd → 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 → 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 10-12 MeV neutrons divided by the total number of 14.1 MeV neutrons produced, confirms the high densities reported above. The estimated lifetime of the highly compressed plasma is 52 ± 9 ps, much smaller than the lasers pulse duration. • A very high compression stage can be reached by ten kilo joules nanosecond lasers hitting on a planar CD2 target. • The ratio between the secondary neutron yield and the primary one provides a robust probe for the density of the plasma. • Important non-equilibrium effects might change substantially the plasma dynamics resulting in an 'effective temperature' less than 1 keV. [ABSTRACT FROM AUTHOR]