Time resolved measurements of radial implosion velocities, ion temperatures and implosion characteristics of double-shell argon gas-puff loads with on-axis jet

Abstract

Summary form only given. Tailoring the radial density profile of gas loads on radiation simulators is expected to increase the X-ray yield by mitigating the adverse effects of the Rayleigh-Taylor instability on axial uniformity of the current carrying sheath during the implosion phase of the load. Multi-shell gas puff loads, with and without on axis jets, have been studied to achieve this objective. The role of the inner shell and on-axis jet on the radiation characteristics of the pinch have been studied during the assembly phase of an argon load with a time resolved Johann spectrometer. The radial distribution of K-shell lines emitted by trace elements, added to the individual plenums, were recorded. The linear current ramp of the simulator imploded loads with a total mass of 325-375 mug/cm in 210 to 225 ns. The Si(III) spectrometer crystal was tuned to record the optically thin Lya line of S and He-like lines of Cl produced by 2% Freon and 2.5% hydrogen sulfide tracers. The micro channel plate strip lines were gated on with 5 ns pulses having an inter-frame time of 5 ns to obtain 3 radially resolved, but axially averaged, spectra. Spectra recorded during the rising edge of the X-ray pulse clearly show that the emission is from a thin cylindrical shell that is imploding with a radial velocity in the range of 24 to 42 cm/mus. Furthermore, the radial distribution from these trace elements is counter intuitive. The S Lya line is emitted from an on-axis region whose radius is approximately one half of that occupied by the Cl Hea line even though the S is initially in the inner shell and the Cl is in the on-axis jet. These measurements reveal detail features about the implosion, thermalization, and heating of Z-pinch gas puff loads as they assemble on axis. They can be compared with theoretical calculations to benchmark the latter and provide a better understanding of the physical processes involved