X-ray absorption spectroscopy of exploding Al wire plasmas using X-pinch radiation sources

X-ray absorption spectroscopy is a powerful diagnostic technique useful for determining the charge state, temperature and density of plasmas under a wide range of conditions and situations. It has been employed for the last two decades to measure parameters of laser produced plasmas in the high energy density (HED) regime and to measure properties of the warm dense matter. Acquiring density, temperature and charge state information in a time and space resolved manner can shed much needed light on the properties of HED laboratory and astrophysical plasmas. In addition, if the spectral information is of sufficient quality, it can be used to better understand the atomic physics in relevant plasmas. Our particular interest was the study of the core-corona system generated in electrically exploded wires and wire array Z-pinches. This system is characterized by existence of a cold, <;5eV, dense, >;10
²¹
cm
^-3
, wire cores that ablatively supply mass to the surrounding relatively diffuse and higher temperature coronal plasma. The coronal plasma is optically thick to visible and extreme ultraviolet light and is too cold to emit x-rays. Therefore exploding wire plasmas provide perfect opportunities for the use of absorption spectroscopy. To develop this diagnostic we have implemented three types of x-ray spectrograph on the XP and COBRA pulsers at Cornell University, wide-bandwidth spectrographs with flat and concave cylindrically bent KAP crystals and high-resolution (λ/Δλ~5000) spectrographs with spherically bent quartz crystals
¹
. The hybrid X-pinch
²
was used as the continuum x-ray source in the photon energy range of interest for absorption spectroscopy with exploding wire experiments. This source is capable of producing broadband continuum x-ray pulses with about 1.5 μm source size and 100 ps duration. Absorption spectra of single exploded Al wires and 2 - 4 wire arrays were recorded with spatial resolution of 5-20 μm. The parameters of the plasma surrounding the dense cores and the ablating plasma streams were estimated under different experimental conditions. New spectral features in absorption spectra were observed and analyzed.