Optical spectroscopy measurements of shock waves driven by intense z-pinch radiation

Abstract

Z-pinches created using the Z accelerator generate -220 TW, 1.7 MJ radiation pulses that heat large (-10 cm3) hohlraums to 100-150 eV temperatures for times of order 10 nsec. We are performing experiments exploiting this intense radiation to drive shock waves for equation of state studies. The shock pressures are typically 1-10 Mbar with 10 nsec duration in 6-mm-diameter samples. In this paper we demonstrate the ability to perform optical spectroscopy measurements on shocked samples located in close proximity to the z-pinch. These experiments are particularly well suited to optical spectroscopy measurements because of the relatively large sample size and long duration. The optical emission is collected using fiber optics and recorded with a streaked spectrograph. Other diagnostics include VISAR and active shock breakout measurements of the shocked sample and a suite of diagnostics that characterize the radiation drive. Our near term goal is to use the spectral emission to obtain the temperature of the shocked material. Longer term objectives include the examination of deviations of the spectrum from blackbody, line emission from lower density regions, determination of kinetic processes in molecular systems, evaluation of phase transitions such as the onset of metalization in transparent materials, and characterization of the plasma formed when the shock exits the rear surface. An initial set of data illustrating both the potential and the challenge of these measurements is described.

An experimental platform for creating white dwarf photospheres in the laboratory

“…Each LOS has its own independent and identical system that collects visible light from the experiment using an optical fiber, transmitting the signal through a spectrometer and to a streak camera with a micro-channel plate intensifier. The setup is similar to that used previously at Z [45,46,47].…”

Diagnostics development plan for ZR.

“…The spectroscopy diagnostic requirements for ZR experiments must be met by development of instruments with improved spatial, time, and spectral resolution, and by instruments covering a broader spectral range, including UV, VUV, and XUV [36,37], to complement the very effective collection of instruments that have already been developed for visible and x-ray spectroscopy [38,39]. Note that optimized systems can be developed for visible or UV operation, but not both.…”