X-Ray Spectroscopy and Imaging of Tungsten Pulsed-Power Plasmas

We begin with a brief review of the work on x-ray spectroscopy and imaging of tungsten (W) single wires, wire arrays, X-pinches and their applications [1]–[6], and move on to the most recent results. Two sets of the new experiments performed in 2017 on two university-scale Z-pinch generators with different architecture will be considered: W Double Planar Wire Arrays (DPW A) at the University of Michigan's (UM) low-impedance Linear Transformer Driver (LTD) MAIZE generator and W X-pinches at the University of Nevada, Reno's (UNR) high-impedance Marx bank Zebra generator. Though a comprehensive set of diagnostics was implemented in both types of experiments, here we will focus mostly on x-ray spectroscopy and imaging results and their interpretation, as well as applications to electron beam studies and spectropolarimetry of W pulsed-power plasmas. Two axially-resolved spectrometers were implemented: the first was the x-ray convex crystal spectrometer with a potassium acid phthalate (KAP) crystal (2d = 26.63 A and R=51 mm) for the spectral region between 4 - 10A and another spectrometer with a lithium fluoride (LiF) convex crystal (2d = 4.027 A and R=25.4 mm) for hard x-ray radiation in a spectral band 1 - 2.4 A. X-ray time-integrated pinhole cameras recorded the images with cutoff energies of 1.4 and 3.5 keV. The very complex soft x-ray M-shell W spectra recorded by the KAP spectrometers are modeled and studied in detail to provide valuable information about “hot” W plasmas and electron beams. The analysis of the hard L-shell W spectra recorded by the LiF spectrometers from much cooler W plasma as well as from the anode is applied to the studies of electron beams, and to explore the possible development of hard x-ray spectropolarimetry of W plasmas. In this regard, the results for W DPW As on UM-MAIZE and W X-pinches on Zebra at UNR are evaluated, compared, and discussed.