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Direct extraction of coherent mode properties from imaging measurements in a linear plasma column
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10.1063/1.4818148
/content/aip/journal/pop/20/8/10.1063/1.4818148
http://aip.metastore.ingenta.com/content/aip/journal/pop/20/8/10.1063/1.4818148
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Time average profiles for plasma parameters. (a) and electron temperature profiles. The black solid line is a Gaussian fit to the data (gray dots). (b) Measured plasma potential and resulting azimuthal velocity.

Image of FIG. 2.
FIG. 2.

(a) Raw image example (single frame). White corresponds to zero intensity. (b) Normalized radial profiles of mean (solid black), RMS fluctuation amplitude (dotted black), and mean (solid gray).

Image of FIG. 3.
FIG. 3.

Comparison of (a) and (b) frequency spectra at various radii. The innermost radial trace is not shifted, while each successive radial trace is shifted downward by a factor of ten to allow all traces to be visible.

Image of FIG. 4.
FIG. 4.

The average coherence spectrum of the plasma column compared with the average power spectrum. Error bars in the cross-spectral power are statistical uncertainty in the discrete CSD estimate. Note that the power spectrum is plotted on a logarithmic scale. (a)–(d) are the four most prominent peaks, corresponding to the phase maps in Fig. 5 .

Image of FIG. 5.
FIG. 5.

Sample phase maps for the four most prominent coherent modes. Vertical bars in Fig. 4 highlight the frequency component corresponding to each map (a)–(d).

Image of FIG. 6.
FIG. 6.

Standard-deviation maps [Eq. (3) ] corresponding to Fig. 5 . Note that particularly asymmetric parts of the phase maps seem to coincide with high uncertainty.

Image of FIG. 7.
FIG. 7.

(a) Time-average frame. (b) RMS frame. (c) Azimuthal variation at for time-average (mean) , RMS , and the radial gradient (negative) of . Intensity is normalized to its maximum value in the image sequence.

Image of FIG. 8.
FIG. 8.

Normalized spectral density andmeasured dispersion relations at from (a) 2D auto-spectral density of image data, (b) average of 32 two-point estimates from pixel data, (c) two-point floating-potential data (probe), and (d) two-point pixel data. The color scale for each plot indicates the power relative to the total spectral power at the given radius. White circles represent the maxima of the k-spectra for frequencies where the total spectral power is more than 1% above background. The dashed line in (a) represents the raw theoretical expectation [Eq. (6) ] calculated from the profiles in Fig. ( 1 ). The hashed region in (a) indicates likely bounds for Doppler-shifted theory curves based on the profile of Fig. 1(b) . The solid line in each plot is the theoretical expectation including the best-fit Doppler shift for (a).

Image of FIG. 9.
FIG. 9.

Comparison of dispersion estimates at various radii: (a) , (b) , and (c) . The solid line is the theoretical curve from the Ellis model including the Doppler shift from the best-fit velocity. Best fit values for are , , . White circles represent the maxima of the k-spectra for frequencies where the total spectral power is more than 1% above background. The dashed line in (c) is the Kelvin-Helmholtz dispersion curve calculated from Eq. (7) .

Image of FIG. 10.
FIG. 10.

Frequency spectra of image sequences filtered in mode number, demonstrating shared frequency content. Shaded regions (a)–(c) correspond to the frequency pass bands used for the filtered sequences in Fig. 11 .

Image of FIG. 11.
FIG. 11.

Time evolution of  = 2 image component with various frequency filters applied. The rows (a,b,c) correspond to the pass-bands around the peaks distinguished in Fig. 10 . The color scale for each mode is normalized to the maximum intensity value in the entire image sequence.

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/content/aip/journal/pop/20/8/10.1063/1.4818148
2013-08-14
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Direct extraction of coherent mode properties from imaging measurements in a linear plasma column
http://aip.metastore.ingenta.com/content/aip/journal/pop/20/8/10.1063/1.4818148
10.1063/1.4818148
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