A comparison of planar, laser-induced fluorescence, and high-sensitivity interferometry techniques for gas-puff nozzle density measurements.

The distribution of argon gas injected by a 12-cm-diameter triple-shell nozzle was characterized using both planar, laser-induced fluorescence (PLIF) and high-sensitivity interferometry. PLIF is used to measure the density distribution at a given time by detecting fluorescence from an acetone tracer added to the gas. Interferometry involves making time-dependent, line-integrated gas density measurements at a series of chordal locations that are then Abel inverted to obtain the gas density distribution. Measurements were made on nominally identical nozzles later used for gas-puff Z-pinch experiments on the Saturn pulsed-power generator. Significant differences in the mass distributions obtained by the two techniques are presented and discussed, along with the strengths and weaknesses of each method.

Efficient radiation production in long implosions of structured gas-puff Z pinch loads from large initial radius.

We have proposed and demonstrated successfully a new approach for generating high-yield K-shell radiation with large-diameter gas-puff Z pinches. The novel load design consists of an outer region plasma that carries the current and couples energy from the driver, an inner region plasma that stabilizes the implosion, and a high-density center jet plasma that radiates. It increased the Ar K-shell yield at 3.46 MA in 200 ns implosions from 12 cm initial diameter by a factor of 2, to 21 kJ, matching the yields obtained earlier on the same accelerator with 100 ns implosions. A new "pusher-stabilizer-radiator" physical model is advanced to explain this result.

Hot, dense, millimeter-scale, high-Z plasmas for laser-plasma interactions studies.

We have designed and produced hot, millimeter-scale, high-Z plasmas of interest for National Ignition Facility hohlraum target design. Using a high-Z gas fill produces electron temperatures in the 3.5-6-keV range, the highest temperatures measured to date for high-density (10(21) e/cm(3)) laser-heated plasmas, and much higher than the 3 keV found for low-Z (neopentane) fills. These measurements are in good agreement with the target design calculations, and the L-shell spectroscopic approach used to estimate the electron temperature has certain advantages over traditional K-shell approaches.

Absorption in high-z targets illuminated with 527-nm laser light at high intensity using induced spatial incoherence.

We have measured 527-nm absorption for induced spatial incoherence (ISI) and non-ISI illumination of high-Z targets over the 0.5-3.5 x 10(14)-W/cm(2) laser intensity range using energy balance with a custom designed 30-cm diam light integrating sphere. Induced spatial incoherence of the laser beam was produced by inserting echelons in the beam path and operating the laser at wide bandwidth (0.2%). To produce ISI and non-ISI data for comparison, we irradiated a large number of 180-microm diam gold disks with 0.5-1.5-ns pulses with echelons in the beam path with and without wide laser bandwidths. Our data show an increase in absorption of 5-11% for the ISI illuminated targets and also suggest a weaker dependence of absorption on laser intensity for ISI illumination than for non-ISI.