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Engineering

Applying X-ray Imaging Crystal Spectroscopy for Use as a High Temperature Plasma Diagnostic

Published: August 25th, 2016

DOI:

10.3791/54408

1Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, 2Department of Physics, Massachusetts Institute of Technology, 3Plasma Science and Fusion Center, Massachusetts Institute of Technology

X-ray spectra provide a wealth of information on high temperature plasmas. This manuscript presents the operation of a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity with good spatial and time resolution. However, benchmarking atomic code modeling of X-ray spectra obtained from well-diagnosed laboratory plasmas is important to justify use of such spectra to determine plasma parameters when other independent diagnostics are not available. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a tokamak plasma. In addition, this manuscript covers a laser blow-off system that can introduce such ions to the plasma with precise timing to allow for perturbative studies of transport in the plasma.

X-ray spectra provide a wealth of information on high temperature plasmas; for example electron temperature and density can be inferred from line intensity ratios. By using a Johann spectrometer viewing the plasma off-axis, it is possible to construct profiles of plasma parameters such as density, temperature, and velocity inside the plasma with good spatial and time resolution1,2. This manuscript presents the operation of the High Resolution X-ray Crystal Imaging Spectrometer with Spatial Resolution (HIREXSR), a high wavelength resolution spatially imaging X-ray spectrometer used to view hydrogen- and helium-like ions of medium atomic number elements in a ....

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1. Choosing Appropriate Spectral Lines

  1. Choose appropriate emission lines that will determine the quality of obtained data. Figure 8 shows which noble gas emission lines will be relevant at different values for the electron temperature.
    1. Note that the ionization state and line ratios are determined by the competition of ionization, collisional excitation, radiative recombination and dielectric recombination. These processes can vary with plasma temperature and density. See F.......

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A representative data sample from the pixel detector for one time bin for the He-like argon spectrum is shown in Figure 17. The spectral lines, bent into an elliptical shape by the spherical crystal, are clearly visible. The top detector has a broken detector panel, and there are some dead pixels scattered across all of the detectors. Data from the broken detector panel should be ignored. Slices from the detector showing the measured spectra and results of the spectral fi.......

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The data generated by this technique can be used in a wide variety of experimental studies. Ion temperature and toroidal velocity profiles can be used in a wide range of transport studies, including intrinsic self-generated plasma rotation and non-local perturbative effects. Measuring spectra of injected impurities through laser blow-off can also provide important information about the transport of impurities in the plasma, as was done in Howard et al. 201110. At this time, no other plasma diagnostic .......

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The authors would like to thank Matt Reinke and the Alcator C-Mod team for designing, building, and testing HIREXSR. This work was supported by DOE Contract Nos. DE-FC02-99ER54512 and DE-AC02-76CH03073.

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Name Company Catalog Number Comments
PILATUS 100k Detector System DECTRIS 100k Superseded by newer PILATUS3 detectors
Bragg Crystals Kurchaov Institute Custom Part
CaF2 Slides LeBow Custom Part
High Purity Argon Airgas AR HP300 Any high purity argon should work
Be window Brush Wellman Electrofusion Products / Motion Hightech Custom part

  1. Reinke, M. L., et al. X-ray imaging crystal spectroscopy for use in plasma transport research. Rev. Sci. Instrum. 83 (11), 113504 (2012).
  2. Hill, K. W., et al. Development of a High Resolution X-Ray Imaging Crystal Spectrometer for Measurement of Ion-Temperature and Rotation-Velocity Profiles in Fusion Energy Research Plasmas. Plasma Fusion Res. 2, 1067-1067 (2007).
  3. Greenwald, M., et al. 20 years of research on the Alcator C-Mod tokamak. Phys. Plasmas. 21 (11), 110501 (2014).
  4. Rice, J. E., et al. X-ray observations of medium Z H- and He-like ions with satellites from C-Mod tokamak plasmas. J. Phys. B. 48 (14), 144013 (2015).
  5. Ince-Cushman, A. Rotation studies in fusion plasmas via imaging X-ray crystal spectroscopy. Rev. Sci. Instrum. 79, (2008).
  6. Zachariasen, W. H. . Theory of X-Ray Diffraction in Crystals. , (2004).
  7. Johann, H. H. Die Erzeugung lichtstarker Röntgenspektren mit Hilfe von Konkavkristallen. Zeitschrift für Physik. 69 (3-4), 185-206 (1931).
  8. Wang, E., et al. Calculation of the Johann error for spherically bent x-ray imaging crystal spectrometers. Rev. Sci. Instrum. 81 (10), (2010).
  9. Eikenberry, E., et al. PILATUS: a two-dimensional X-ray detector for macromolecular crystallography. Nucl. Instr. Meth. Phys. Res. A. 501 (1), 260-266 (2003).
  10. Howard, N. T., Greenwald, M., Rice, J. E. Characterization of impurity confinement on Alcator C-Mod using a multi-pulse laser blow-off system. Rev. Sci. Instrum. 82 (3), 1-6 (2011).
  11. Rice, J. E., et al. Non-local heat transport, rotation reversals and up/down impurity density asymmetries in Alcator C-Mod ohmic L-mode plasmas. Nucl. Fusion. 53, 033004 (2013).
  12. Reinke, M. L., Podpaly, Y., Gao, C., Science, P. . Operation and Validation of The HIREXSR Analysis COde MIT-Plasma Science and Fusion Center Alcator C-Mod. , (2013).
  13. Rosen, A. S., Reinke, M. L., Rice, J. E., Hubbard, A. E., Hughes, J. W. Validation of x-ray line ratios for electron temperature determination in tokamak plasmas. J. Phys. B. 47 (10), 105701 (2014).
  14. Delgado-Aparicio, L. F., et al. In-situ wavelength calibration and temperature control for the C-Mod high-resolution X-ray crystal imaging spectrometer. Bull. Am. Phys. Soc. 55, (2010).

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