Time- and space-resolved spectroscopy of dynamic hohlraum interiors

A dynamic hohlraum is created when an annular z-pinch plasma implodes onto a cylindrical 0.014 g/cc 6-mm-diameter CH2 foam. The impact launches a radiating shock that propagates toward the axis at w350 mm/ns. The radiation trapped by the tungsten z-pinch plasma forms a w200 eV hohlraum that provides X-rays for indirect drive inertial confinement fusion capsule implosion experiments. We are developing the ability to diagnose the hohlraum interior using emission and absorption spectroscopy of Si atoms added as a tracer to the central portion of the foam. Timeand space-resolved Si spectra are recorded with an elliptical crystal spectrometer viewing the cylindrical hohlraum endon. A rectangular aperture at the end of the hohlraum restricts the field of view so that the 1D spectrometer resolution corresponds approximately to the hohlraum radial direction. This enables distinguishing between spectra from the unshocked radiation-heated foam and from the shocked foam. Typical spectral lines observed include the Si Lya with its He-like satellites and the He-like resonance sequence including Hea, Heb, and Heg, along with some of their associated Li-like satellites. Work is in progress to infer the hohlraum conditions using collisionaleradiative modeling that accounts for the radiation environment and includes both opacity effects and detailed Stark broadening calculations. These 6-mm-scale radiation-heated plasmas might eventually also prove suitable for testing Stark broadening line profile calculations or for opacity measurements. 2005 Published by Elsevier B.V.