Core temperature and shape measurements from ignition implosions at the National Ignition Facility using multispectral x-ray imaging

Peak core temperature is an important measure of implosion performance, and will be a critical diagnostic of ignition implosion performance at the National Ignition Facility because peak temperatures must attain high values in order to form the hot-spot spark that ignites the main mass of deuterium-tritium fuel. We plan to measure peak core temperatures, resolved in space and time, using a gated pinhole camera that differentially filters the individual images in different continuum x-ray bands. Ross pair analysis allows the temperature profile to be measured directly. We describe the technique, the various challenges that include x-ray scattering, Abel inversion of noisy images that do not have perfect two-dimensional symmetry, calibrations, and background suppression, and we discuss how we expect to meet these challenges.