High-current laser-driven beams of relativistic electrons for high energy density research
PLASMA PHYSICS AND CONTROLLED FUSION(2020)
摘要
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 similar to 10(19)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 12 +/- 1 degrees 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 mu C. 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 similar to 10(12) per shot at moderate relativistic laser intensity of 10(19)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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关键词
relativistically intense laser pulses,near critical electron density plasmas,long-scale plasma channel,direct laser acceleration,low-density polymer aerogels,super-ponderomotive electrons,nuclear reaction yields
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