Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

Journal Article · Thu Oct 13 00:00:00 EDT 2011 · Review of Scientific Instruments

DOI: https://doi.org/10.1063/1.3647975 · OSTI ID:1076449

Vogman, G. V. ^[1]; Shumlak, U. ^[2]

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1. Univ. of California, Berkeley, CA (United States)
2. Univ. of Washington, Seattle, WA (United States)

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.

• Research Organization: University of California, Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• Grant/Contract Number: FG02-04ER54756; AC05-06OR23100
• OSTI ID: 1076449
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 10 Vol. 82; ISSN 0034-6748; ISSN RSINAK
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English