We report on enhanced laser driven electron beam generation in the multi MeV energy range that promises a tremendous increase of the diagnostic potential of high energy sub-PW and PW-class laser systems. In the experiment, an intense sub-picosecond laser pulse of ∼1019 Wcm−2 intensity propagates through a plasma of near critical electron density (NCD) and drives the direct laser acceleration (DLA) of plasma electrons. Low-density polymer foams were used for the production of hydrodynamically stable long-scale NCD-plasmas. Measurements show that relativistic electrons generated in the DLA-process propagate within a half angle of 1 2 ± 1° to the laser axis. Inside this divergence cone, an effective electron temperature of 10–13 MeV and a maximum of the electron energy of 100 MeV were reached. The high laser energy conversion efficiency into electrons with energies above 2 MeV achieved 23% with a total charge approaching 1 μC. For application purposes, we used the nuclear activation method to characterize the MeV bremsstrahlung spectrum produced in the interaction of the high-current relativistic electrons with high-Z samples and measured top yields of gamma-driven nuclear reactions. The optimization of the high-Z target geometry predicts an ultra-high MeV photon number of ∼1012 per shot at moderate relativistic laser intensity of 1019 Wcm−2. A good agreement between the experimental data and the results of the 3D-PIC and GEANT4-simulations was demonstrated.

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Measurements of ion fluxes in close vicinity to Mars have been made by the space probes Mars 2 and Mars 3 during 1971-1972. Analysis of measurements confirms the earlier preliminary conclusion by these authors about the existence of bow shock wave near Mars. Seventeen crossings of the bow shock are used to obtain the mean location of the bow shock and to estimate the dimension of the obstacle. The mean distance to the bow shock subsolar point is estimated as • 1200 km, and the corresponding height of the stagnation point, as •400 km. Anomalously far positions of bow shock, •2800 km, have been observed by the two satellites. New features of the interaction region have been observed. This region is characterized by high-intensity fluxes of ions with temperatures of some tens of electron volts and convective velocities well below the convective velocity in the magnetosheath. This 'cushion' of hot ions is situated inside the magnetosheath but above the Martian ionosphere. Intercomparison of these measurements with magnetic field data shows that observations of decelerated hot ions usually coincide with an increase of the magnetic field up to 15-30 3•. A gradual change of the ion transport velocity at the transition from the magnetosheath to the cushion of hot ions favors the piling up model of magnetic field rather than the model of the internal dipole field of Mars.

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