TIME-RESOLVED X-RAY SPECTROSCOPY OF DEEPLY BURIED TRACER LAYERS AS A DENSITY AND TEMPERATURE DIAGNOSTIC FOR THE FAST IGNITER

The fast ignitor concept for inertial confinement fusion relies on the generation of hot electrons, produced by a short-pulse ultrahigh inte nsity laser, which propagate through high-density plasma to deposit th eir energy in the compressed fuel core and heat it to ignition. In pre liminary experiments designed to investigate deep heating of high-dens ity matter, we used a 20 joule, 0.5-30 ps laser to heat solid targets, and used emission spectroscopy to measure plasma temperatures and den sities achieved at large depths (2-20 microns) away from the initial t arget surface. The targets consisted of an Al tracer layer buried with in a massive CH slab; H-like and He-like line emission was then used t o diagnose plasma conditions. We observe spectra from tracer layers bu ried up to 20 microns deep, measure emission durations of up to 200 ps , measure plasma temperatures up to T-e = 650 eV, and measure electron densities above 10(23) cm(-3). Analysis is in progress, but the data are in reasonable agreement with heating simulations when space-charge induced inhibition is included in hot-electron transport, and this su pports the conclusion that the deep heating is initiated by hot electr ons.