Visible Spectroscopy Studies in Gas Puff Z-Pinches at 1-Ma on Cobra

Abstract

Spectroscopy is the most established diagnostic method in astrophysics and plasma physics. Radiating ions can provide insight into z-pinch plasma parameters such as temperature, density, implosion velocity and magnetic field. Visible spectroscopy offers the possibility of accurate determinations of spectral line widths, shifts, polarization, and/or absolute intensity calibrations. In high current (>1MA) z-pinches, the plasmas are highly ionized and most of the emitted photons are in the XUV or x-ray region. It is a challenge to use visible spectroscopy there because there are not many detectable visible lines. We have identified several visible spectral lines in gas puff z-pinches on COBRA. These are pairs of lines at 5174 and 5193Å from Ar VIII 4d-4f transitions, as well as 5801.3 and 5812.0Å lines from C IV 3s-3p transitions, which are emitted from the imploding plasma shell. The Doppler shift due to the implosion is also observed. Zeeman splitting of these lines is measured to infer the magnetic field in the plasma. We have also observed several Ar II lines at a radius smaller than the imploding plasma shell, where both the Zeeman and Doppler shifts are absent. Using a triple-nozzle gas puff z-pinch on COBRA, we are able to measure the Zeeman splitting and Doppler broadening of the Ar VIII and C IV lines about 15 ns before the pinch time. After that, the plasma is so hot that the visible line radiation is washed out by the intense continuum radiation.