Examining the effects of variation of plasma conditions on the performance of high-energy long-pulse Brillouin amplifiers using one- and two-dimensional simulations

The plasma Brillouin amplifier uses an ion acoustic wave (IAW) to transfer energy from a "pump" laser to a "seed" laser, and can generate short, high-intensity pulses without being subject to the damage limits of conventional optical systems. The concept is the subject of a feasibility study at the National Ignition Facility (NIF), and we have developed a two-dimensional time-dependent simulation code for studying Brillouin amplification in such high-energy long-pulse systems. We apply our code to the NIF parameters and test the robustness of the amplification process to the variation of plasma and laser conditions expected around the nominal experimental parameters, with particular attention paid to the non-trivial spatial variation of plasma density and temperature. We compare our 2D simulations with the results of a standard three-wave 1D model, showing that for non-zero crossing angle between pump and seed beams the 2D overlap geometry produces strong transverse variation resulting from asymmetric amplification not seen in 1D. We report detailed simulations that can be used to inform the planned experiments at NIF.