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

Journal Article · Tue Apr 15 04:00:00 EDT 2008 · High Energy Density Physics, vol. 4, N/A, October 1, 2008, pp. 107-113

OSTI ID:945127

Nilsen, J; Castor, J I; Iglesias, C A; Cheng, K T; Dunn, J; Johnson, W R; Filevich, J; Purvis, M A; Grava, J; Rocca, J J

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.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 945127
• Report Number(s): LLNL-JRNL-403024
• Journal Information: High Energy Density Physics, vol. 4, N/A, October 1, 2008, pp. 107-113, Journal Name: High Energy Density Physics, vol. 4, N/A, October 1, 2008, pp. 107-113 Vol. 4
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
74 ATOMIC AND MOLECULAR PHYSICS
ABSORPTION
APPROXIMATIONS
ATOMIC PHYSICS
ATOMS
CARBON
FREE ELECTRON LASERS
INTERFEROMETERS
OPALS
PROBES
REFRACTIVE INDEX
WAVELENGTHS
X-RAY LASERS
X-RAY SOURCES