Absorption by the Two-Plasmon-Decay Instability in Direct-Drive Implosions

There is mounting evidence that the two-plasmon-decay instability near $n_{c}$/4 absorbs non-negligible amounts of the incident laser energy in direct-drive implosion experiments. Most of this energy is deposited as thermal energy between 0.25 $\le \quad n_{c}$/$n_{e} \quad \le $ 0.2 (typical Landau cutoff location) with a small fraction going into energetic electrons. This conjecture is based on time-resolved 3\textit{$\omega $}/2 emission, scattered light at the laser wavelength, energetic-electron measurements, neutron and x-ray bang times, and comparison with hydrodynamic simulations. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC52-08NA28302.