Saturation of the two-plasmon decay instability in long-scale-length plasmas relevant to direct-drive inertial confinement fusion

Measurements of the hot-electron generation by the two-plasmon-decay instability are made in plasmas relevant to direct-drive inertial confinement fusion. Density-scale lengths of 400μm at n _cr/4 in planar CH targets allowed the two-plasmon-decay instability to be driven to saturation for vacuum intensities above ∼3.5×1014Wcm ^-2. In the saturated regime, ∼1% of the laser energy is converted to hot electrons. The hot-electron temperature is measured to increase rapidly from 25 to 90keV as the laser beam intensity is increased from 2 to 7×1014Wcm ^-2. This increase in the hot-electron temperature is compared with predictions from nonlinear Zakharov models.