Refinements to the Opacity-on-NIF hohlraum*

The purpose of the Opacity-on-NIF experiments is to make LTE opacity measurements of iron at the same conditions as previous experiments on Sandia’s Z-facility: 156 eV and 190 eV. Iron opacities are important for understanding the structure of the sun, yet there is an ongoing disagreement between opacity theory and data that makes corroborating data highly important. Complex hohlraum geometries are required to achieve the necessary iron plasma conditions and minimize spectrometer background. We have begun taking data using the McFee-Apollo hohlraum. This hohlraum uses separate chambers to isolate the laser-driven gold from the iron sample with less surface area than previous designs, which leads to higher radiation temperatures. Different diameter laser entrance holes (LEH) and a slanted wall were added to block gold emission from the spectrometer’s line-of-sight and reduce background. We discuss additions to the initial Apollo work, including: a scaling of radiation temperature with incident energy and use of liners to better reduce background in the measured spectra.