X-ray reemission from CH foils heated by laser-generated intense thermal radiation

Measurement of the absolute hohlraum-wall albedo under ignition foot drive conditions

We present measurements of the absolute albedos of hohlraums made from gold or from high-Z mixtures. The measurements are performed over the range of radiation temperatures (70-100 eV) expected during the foot of an indirect-drive temporally shaped ignition laser pulse, where accurate knowledge of the wall albedo (i.e., soft x-ray wall reemission) is most critical for determining capsule radiation symmetry. We find that the gold albedo agrees well with calculations using the supertransition array opacity model, potentially providing additional margin for inertial confinement fusion ignition.

Radiative ablation to low-Z matter

Eight beams of 0.35-microm laser with pulse duration of about 1.0 ns and energy of 260 J per beam were injected into a cylindrical cavity to generate intense x-ray radiation on the Shengguang II high power laser facility. Plastic foils with a thickness in the range of about 3.0-45 microm were attached on the diagnostic hole of the cavity and ablated by the intense x-ray radiation. The radiative energy transport through plastic foils with different thicknesses has been studied experimentally. The burn-through time of the plastic foils has been obtained. For comparison, we also simulated the experimental results with Planckian and non-Planckian x-ray spectrum source, respectively. It is shown that for thick plastic foil the simulation with non-Planckian x-ray spectrum source is in good agreement with the experiment.

Non-local-thermodynamical-equilibrium effects in the x-ray emission of radiatively heated materials of different atomic numbers

X-ray self-emission of radiatively heated materials with different values of Z has been investigated. Thin foils were uniformly heated by a 120-eV Hohlraum radiation of 400-ps duration in order to study the self-emission of a homogeneous, optically thin material. The x-ray emission spectra were followed for more than 2 ns. The spectrally integrated emission shows not only a strong Z dependence, but different temporal behaviors for different values of Z. The lower is the value of Z of the x-ray heated matter, the longer is the duration of self-emission. Theoretical comparison with a hydrocode and FLY post-processing shows a non-local-thermal equilibrium behavior caused by direct photoionization due to the thermal pumping radiation, which has a higher brightness temperature than the matter temperature of the heated material.