Multibeam Two-Plasmon Decay: Experimental Signatures and Diagnostic Applications

Images and spectra at \textit{$\omega $}/2 and 3\textit{$\omega $}/2 along with 2-D and 3-D Zakharov simulations indicate that the two-plasmon-decay (TPD) instability operates primarily as a multibeam instability in direct-drive--implosion experiments. Simulations indicate that the instability enters the nonlinear regime within $\sim $1 ps and covers a large phase space volume within 10 ps, far beyond linear gain predictions. This largely explains the preponderance of 3\textit{$\omega $}/2 spectra seen in the past 40 years. The \textit{$\omega $}/2 and 3\textit{$\omega $}/2 images and spectra indicate the localized areas on the target surface where the TPD instability operates. The \textit{$\omega $}/2 spectra can be used as powerful $T_{e}$ measurement at $n_{c}$/4 as originally proposed in 1985. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.