Doppler Shift and Broadening of K- and L-Shell x-ray Spectral Lines in Imploded Wire-Arrays on MAGPIE and COBRA Pulsers

Abstract

Summary form only given. Substantial broadening and clearly visible "red" and "blue" shifts of K-shell spectral lines as a function position along the axis of wire-array Z-pinches have been observed in the time-integrated X-ray spectra from 8-32 wire Al arrays in experiments on the MAGPIE (1 MA, 240 ns risetime) and COBRA (1 MA, 100 ns risetime) pulsed-power generators. To separate the spectral and spatial shift of the spectral lines, two wide-band spectrographs (WB-FSSR), each consisting of 3 spherically bent crystals with radius of curvature 182 mm, have been used in a mirror-symmetric configuration. In this configuration, the spatial shift of the spectral lines recorded by each spectrograph off the Rowland circle has the opposite sign and can therefore be distinguished from a spectral shift. K-shell X-ray spectra from Al-wire arrays and L-shell spectra from Ni and invar wire arrays have been studied. The measured Doppler shift of the spectral lines, Deltalambda/lambda, varied along the pinch axis and reached 0.015 corresponding to a radial plasma velocity of 5times107 cm/s. X-ray lines excited by energetic electrons show less broadening and more uniformity along the array axis. Spectroscopic data were compared with optical streak observation of implosion dynamics of different wire arrays. The average speed of implosion of the bulk of the array material as seen in visible light steak images is consistent with spectroscopic data.