Density measurements for the NIF Iron Opacity Campaign *

The Opacity Platform on the National Ignition Facility (NIF) has been developed to measure iron opacities at varying densities and temperatures relevant to the solar interior, and to verify recent experimental results obtained at the Sandia Z-machine, which diverge from theory.  The first set of NIF experiments collected iron opacity data at ~150-160 eV, and an electron density of ~7x10²¹ cm^-3, with a goal to study temperatures up to ~210 eV, with electron densities of up to ~3x10²² cm^-3.  The platform has a unique capability that allows an in-situ measurement of the sample expansion.  The sample expansion data is used to infer the sample density thorughout the duration of the laser drive.  We present the details of the density measurement technique, data analysis and recent results.