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Application of the wedge technique to the measurement of Start shifts of plasma lines

University of British Columbia

The ability of the GBKO Stark broadening theory to predict the position of the mean of a plasma spectral line is exper-imentally investigated for three isolated neutral helium lines at electron temperatures of about 1.5 eV and electron densities in the region of (0.5 to 2.0) x 10¹⁶ cm⁻³. General agreement was found between experimental and theoretical shifts of the mean of the lines Hel 5016, Hel 4713 and Hel 3889 from their unperturbed wavelengths. A semi-empirical relationship is derived which gives the shift of the mean in terms of the electron impact width, w, and shift, d, as well as in terms of the ion-broadening parameter, a, and the Debye-shielding parameter, r: Δλ ≃ [ d/w ± 4.1α(1 - 0.5r) ]w. This relationship estimates the shift of the mean within 5% of the width, w, over the ranges 0 ≤ α ≤ 0.4 and 0 ≤ r ≤ 0.8. The shifts in the means of the observed lines were measured by a new technique employing a linearly varying neutral density filter mounted in the exit plane of a monochromator. This "wedge technique" has a wide range of possible application from steady state to pulsed conditions for observation of Doppler shifts, van der Waals shifts, Stark shifts or Zeemann shifts. It requires that the line is reasonably isolated and it is useful when the shift to width ratio is either large or small. A complete discussion of the technique is presented along with the important design criteria for linearity, resolution and sensitivity.

Text

2011-03-09

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http://hdl.handle.net/2429/32257

Physics

University of British Columbia

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