Time-Resolved Measurements of the Hot Spot Density and Temperature on the National Ignition Facility*

The electron density and temperature and their evolution in the hot spot of a Kr-doped, big-foot implosion target were measured for the first time using an absolutely calibrated, streaked, high-resolution x-ray spectrometer on the National Ignition Facility (NIF). Kr Heα and Heβ complexes near stagnation were recorded on a streak camera with a temporal resolution of  ~30 ps, with signal levels provided by a simultaneous time-integrated measurement on the image plate. The electron density was inferred through stark-broadened line shapes and the temperature was derived from the relative intensities of dielectronic satellites. The measurements are compared with hydrodynamic simulations of the big-foot implosion, as well as collisional-radiative calculations for line intensities and shapes.