Modeling of Two-Plasmon-Decay Instability in OMEGA Plasmas

The direct-drive inertial confinement fusion experiments on the OMEGA Laser System have identified the two-plasmon-decay (TPD) instability as a source of fast electrons that are important for target implosions.\footnote{ C. Stoeckl \textit{et al}., Phys. Rev. Lett. \textbf{90}, 235002 (2003).} In OMEGA experiments, TPD is driven by multiple laser beams that are spatially incoherent because of random phase plates. For this regime, the TPD instability thresholds and growth rates are calculated and compared with the results of the three-wave TPD model.\footnote{ A. Simon\textit{ et al}., RPhys. Fluids \textbf{26, }3107 (1983).} The saturation of the TPD instability caused by low-frequency plasma perturbations takes into account the perturbations driven by the laser beams and by the beating of plasma waves, including the Langmuir decay instability. The composition of multispecies plasmas modifies the properties of the low-frequency density perturbations and, therefore, the level of the TPD saturation. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.