Broadband X-Ray Imager for Spectroscopic Diagnostics
Project #: 22-123 | Year 2 of 3
Radu Presura,a Matthew S. Wallace,b Showera H. Haque,b Padrick A. Beggs,a Isiah D. Pohl,a James M. Heinmiller,b Alex L. Droemera
aNevada National Security Site, Sandia Operations; bLivermore Operations
Executive Summary
This project is exploiting the x-ray diffraction properties of convex bent crystals to develop a spectroscopic instrument where each spectral line, over a broad spectral range, is a 2D image of the x-ray source. When applied to mm- to cm-size plasmas, this will enable 2D space-resolved measurements of density and temperature, which will benefit the understanding and optimization of the plasma radiation sources, as well as the improvement of modeling codes.
Description
The hot and dense high energy density plasmas (HEDP) used as radiation sources for stockpile stewardship are highly inhomogeneous. Understanding and optimizing their performance requires knowledge of their density and temperature, including their spatial distributions. A common technique for these measurements is x-ray spectroscopy; which is typically used in space integrating, thus providing one average value for each plasma parameter. 2D space-resolved spectroscopy would provide the information needed to create 2D maps of plasma density and temperature, which are significantly more useful for understanding the plasmas directly and for improving the modeling codes used to predict the plasma behavior.
Our approach to this challenge uses a cylindrically bent convex crystal to produce a broad-band spectrum and for imaging in the spectral dispersion direction, along with a slit for imaging in the orthogonal direction. Based on analytical calculations and numerical ray tracing developed in the first year of the project, we designed and prototyped a fixture for controlled, progressive crystal bending. We initiated laboratory testing of the imaging properties of bent crystals with an example shown in the figure and used the same calculations to identify the spectral lines observed and the crystal planes responsible for their diffraction. The salient feature of the spectrum is that each spectral line is a quasi-monochromatic image of the x-ray source. Bending a crystal also leads to rocking curve broadening, an effect that can interfere with the imaging properties for smaller x-ray sources. We found that common diffraction curve models for bent crystals do not work well for the relatively small curvature radii required for this instrument. Comparisons with data from publications and with measurements performed by the Sandia collaborators showed limited success. The investigation of these discrepancies, of the models themselves, and of their numerical implementations will continue. A focus in the next year will be testing the instrument’s diagnostics quality with HEDP measurements using both laser-produced plasmas and z-pinch plasmas. Pending the success of these tests, we will explore adding time resolution by using a gated x-ray imager as a detector.
Conclusion
We have demonstrated experimentally that a spectroscopic instrument using a cylindrically bent convex crystal can produce a broad-band x-ray spectrum in which each spectral line is a 2D image of the x-ray source. The ray tracing code developed to model the instrument has proven to be useful and necessary for identifying the spectral lines observed and the crystal planes diffracting them. Work to understand and to model the diffraction curve of cylindrically bent convex crystals has progressed and will continue with further calculations and measurements. Moving forward, we plan to adapt and use the instrument for the diagnostics of HEDP, and to explore the possibility of adding time resolution by using an ultrafast x-ray imager.
Mission Benefit
Hot and dense high energy density plasmas produced in NNSA facilities are used to aid with stockpile stewardship and to develop neutron and x-ray sources for fundamental research. The broadband x-ray imager for spectroscopic diagnostics aims to improve the understanding of HED plasmas and their x-ray emission, and to help improve the plasma modelling codes.
Publications, Technology Abstracts, Presentations/Posters
Presura, R., M. S. Wallace, S. H. Haque, J. M. Heinmiller, P. A. Beggs, I. D. Pohl, A. L. Droemer, P. Lake, M. Wu. 2022. “Multi-Monochromatic Imaging with Cylindrically Bent Convex Crystals.” Poster presented at the High Temperature Plasma Diagnostics Conference, Rochester, NY.
Lake, P. W., G. P. Loisel, R. Presura, T. J. Webb, K. J. Moy, M. Wu. 2022. “Calibrations of Quartz (10-11) in both Laue and Bragg diffractions between 8-45 keV Using Micro-focusing X Ray Sources in Air.” Poster presented at the High Temperature Plasma Diagnostics Conference, Rochester, NY.
Presura, R. et al. Manuscript. “Multi-monochromatic Imaging with Cylindrically Bent Convex Crystals.” Review of Scientific Instruments.
This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy. DOE/NV/03624–1606.
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