Gas Filled Halfraums on the First NIF Quad -- Radiation Hydrodynamics, Filamentation, and Spatial Diagnostics*

The Los Alamos gas-filled halfraum series on the first quad of NIF consisted of 4 laser shots at energies close to 15 kJ with nominal cylindrical symmetry. Lasnex modeling of halfraums with CO$_{2}$ as well as propane (C$_{3}$H$_{8})$ gas fill is consistent with peak power Dante experimental detector results. At the peak laser intensities of the shot ($>$ 2 x 10$^{15}$W/cm$^{2})$, filamentation is theoretically predicted, and more detailed simulations have suggested the possibility of conversion of the original f/8 laser beam profile into a beam with f-number as low as f/2. Simulations with laser beam profiles of f/8, f/4, f/3, and f/2 are available for both gas fills. Gated X-ray images of emission at energies above 10 keV probe the laser interaction with gold ablated from the rear wall of the halfraum. For CO$_{2}$, the axial variation in emission lies between the calculated results for the f/4 and f/8 simulations. For propane, the f/4 simulation provides the best fit to the data. Comparison at lower laser intensities, where the laser beam is expected to be f/8, clarifies the qualitatively different axial structuring observed for the two gases.