Using L-shell x-ray spectra to determine conditions of non-local thermal dynamic equilibrium plasmas.

K-shell x-ray spectra of Li- to H-like ions have long been used to determine plasma conditions. The ratio of integrated line intensities is used to determine the temperature. At the density of non-local thermal dynamic equilibrium (NLTE) plasmas (n ≈ 10 cm), the K-shell spectrum is not very sensitive to density.

Progress towards a more predictive model for hohlraum radiation drive and symmetry.

For several years, we have been calculating the radiation drive in laser-heated gold hohlraums using flux-limited heat transport with a limiter of 0.15, tabulated values of local thermodynamic equilibrium gold opacity, and an approximate model for not in a local thermodynamic equilibrium (NLTE) gold emissivity (DCA_2010). This model has been successful in predicting the radiation drive in vacuum hohlraums, but for gas-filled hohlraums used to drive capsule implosions, the model consistently predicts too much drive and capsule bang times earlier than measured.

X-ray observations of accreting white-dwarf systems.

Accretion in white-dwarf binary systems can occur through discs, accretion columns or a combination of these, depending on the magnetic field of the white dwarf. Recent high-quality X-ray observations with the XMM-Newton and Chandra observatories have significantly advanced our understanding of the physics of the accretion process, and place severe tests on our existing models. There have been some surprises, such as the strong dependence of atmospheric heating on accretion rate.

Reflectivity and scattering measurements of an Advanced X-ray Astrophysics Facility test coating sample.

Reflectivity and scattering profile measurements were made on a gold-coated witness sample produced to evaluate mirror coatings for the Advanced X-ray Astrophysics Facility program. Reflectivity measurements were made at Al K, Ti K, and Cu K energies as a function of incident graze angle. The results are fit to a model that includes the effects of roughness, particulate and organic contamination layers, and gold-coating density.