Characterizing Laser-Plasma Interaction External to the Laser Entrance Hole of Ignition Scale Hohlraums*

Spatially resolved temperature measurements of plasma flowing from the laser entrance hole (LEH) of NIF hohlraums have allowed correlation of laser energy losses to plasma heating external to the LEH. The resolved temperatures agree with measurements from other diagnostics, including the equatorial hard x-ray imager and static x-ray imager, and were consistent with temperatures calculated using dot spectroscopy data. By asserting that inverse bremsstrahlung is the dominant laser energy loss mechanism, the relationship between the plasma temperature and laser energy absorption was determined. Data show an increase in plasma temperature which scales with laser energy. This analysis validates concern that plasma external to the LEH is contributing to laser energy losses and could be influencing drive symmetry, a critical feature in inertial confinement fusion experiments. The characterization of laser-plasma interaction external to the LEH provides insight for future symmetry tuning experiments, hohlraum structural designs, and refinement of simulation parameters.