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Experimental generation of ultrashort MeV positron beams with high intensity and high density using a compact laser-driven setup is reported. A high-density gas jet is employed experimentally to generate MeV electrons with high charge; thus, a charge-neutralized MeV positron beam with high density is obtained during laser-accelerated electrons irradiating high-Z solid targets. It is a novel electron–positron source for the study of laboratory astrophysics. Meanwhile, the MeV positron beam is pulsed with an ultrashort duration of tens of femtoseconds and has a high peak intensity of 7.8 × 1021 s−1, thus allows specific studies of fast kinetics in millimeter-thick materials with a high time resolution and exhibits potential for applications in positron annihilation spectroscopy.

We report the highest compression reached in laboratory plasmas using eight laser beams, E laser ≈12 kJ, τ 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 ρ D = 2.0 ± 0.9 kg/cm 3 , and the average kinetic energy of the plasma ions less than 1 keV. The highest reached areal density Λρ D =4.8 ± 1.5 g/cm 2 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 10-12MeV 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 ± 9 ps, much smaller than the lasers pulse duration.