ISOELECTRONIC X-RAY SPECTROSCOPY TO DETERMINE ELECTRON TEMPERATURES IN LONG-SCALE-LENGTH INERTIAL-CONFINEMENT-FUSION PLASMAS

We have successfully employed isoelectronic line ratios to measure the electron temperature in gas-filled Hohlraum targets and gas bags shot with the Nova laser. These targets produce millimeter-scale-length pl asmas with electron density N-e similar to 10(21) cm(-3) and electron temperature T-e similar to 3 keV. The Hohlraum targets can also produc e radiation temperature exceeding 200 eV. Isoelectronic line ratios ar e well suited to this measurement because they are relatively insensit ive to radiation field effects in Hohlraum targets; opacity, transient s, and variations in electron density compared to conventional line ra tios. We survey the properties of isoelectronic line ratios formed fro m ratios of n-to-1 resonance transitions in heliumlike Cr to the same transitions in Ti and compare with conventional ratios of n-to-1 trans itions in hydrogenlike Ti to the corresponding transitions in heliumli ke Ti, concentrating on plasma parameter ranges of interest to the Nov a experiments. We also consider the same ratios using K and Cl. Atomic kinetics are treated using collisional-radiative models and experimen tal data are analyzed with the aid of radiation-hydrodynamics calculat ions. When we apply isoelectronic techniques to the Nova experimental data, we find that the targets have electron temperatures of at least 3 keV.