Understanding the anomalous dispersion of doubly-ionized carbon plasmas near 47 nm

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Over the last several years we have predicted and observed plasmas with an index of refraction greater than one in the soft X-ray regime. These plasmas are usually a few times ionized and have ranged from low-Z carbon plasmas to mid-Z tin plasmas. Our main calculational tool has been the average atom code. We have recently observed C{sup 2+} plasmas with an index of refraction greater than one at a wavelength of 46.9 nm (26.44 eV). In this paper we compare the average atom method, AVATOMKG, against two more detailed methods, OPAL and CAK, for calculating the index of refraction ... continued below

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Nilsen, J; Castor, J I; Iglesias, C A; Cheng, K T; Dunn, J; Johnson, W R et al. April 15, 2008.

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Over the last several years we have predicted and observed plasmas with an index of refraction greater than one in the soft X-ray regime. These plasmas are usually a few times ionized and have ranged from low-Z carbon plasmas to mid-Z tin plasmas. Our main calculational tool has been the average atom code. We have recently observed C{sup 2+} plasmas with an index of refraction greater than one at a wavelength of 46.9 nm (26.44 eV). In this paper we compare the average atom method, AVATOMKG, against two more detailed methods, OPAL and CAK, for calculating the index of refraction for the carbon plasmas and discuss the different approximations used. We present experimental measurements of carbon plasmas that display this anomalous dispersion phenomenon. It is shown that the average atom calculation is a good approximation when the strongest lines dominate the dispersion. However, when weaker lines make a significant contribution, the more detailed calculations such as OPAL and CAK are essential. During the next decade X-ray free electron lasers and other X-ray sources will be available to probe a wider variety of plasmas at higher densities and shorter wavelengths so understanding the index of refraction in plasmas will be even more essential. With the advent of tunable X-ray lasers the frequency dependent interferometer measurements of the index of refraction may enable us to determine the absorption coefficients and line-shapes and make detailed comparisons against our atomic physics codes.

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PDF-file: 24 pages; size: 2.3 Mbytes

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  • Journal Name: High Energy Density Physics, vol. 4, N/A, October 1, 2008, pp. 107-113; Journal Volume: 4

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  • Report No.: LLNL-JRNL-403024
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 945127
  • Archival Resource Key: ark:/67531/metadc902712

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

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  • April 15, 2008

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  • Sept. 27, 2016, 1:39 a.m.

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  • Dec. 9, 2016, 12:09 a.m.

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Nilsen, J; Castor, J I; Iglesias, C A; Cheng, K T; Dunn, J; Johnson, W R et al. Understanding the anomalous dispersion of doubly-ionized carbon plasmas near 47 nm, article, April 15, 2008; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc902712/: accessed December 13, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.