Simultaneous stimulated Raman forward and backward scattering in hot, well-underdense plasmas

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Abstract
The competition of stimulated Raman forward scattering and backscattering in a hightemperature, underdense, nearly homogeneous plasma slab is investigated. In such plasmas Landau damping limits the growth of the Raman backscattering, and the weaker forward process may reach comparable levels. A modest seeding of one of the scattered electromagnetic waves influences the competition to a large extent. The conversion of the pump wave to scattered waves is calculated. The simultaneous operation of the two processes can lead to considerable modifications in the electron distribution; e.g., two hot tail components are formed because the plasma waves involved have different phase velocities. The generation regions of the scattering processes are spatially separated. Consequently, a large number of thermal electrons can be accelerated to very high energies in two stages. The backward plasmons preaccelerate the electrons and the faster plasmons, excited in the forward scattering, operate as a booster.