Direct extraction of coherent mode properties from imaging measurements in a linear plasma column

• Published in: Physics of plasmas 2013-08, Vol.20 (8)
• Main Authors: Light, A. D., Thakur, S. C., Brandt, C., Sechrest, Y., Tynan, G. R., Munsat, T.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ARGON; Argon plasma; CAMERAS; Coherence; Columns (structural); COMPARATIVE EVALUATIONS; Digital cameras; Dispersions; FLUCTUATIONS; FREQUENCY DEPENDENCE; HELMHOLTZ INSTABILITY; Imaging; PLASMA; Plasma (physics); PLASMA DIAGNOSTICS; PLASMA DRIFT; PLASMA WAVES; Spectra; VISIBLE RADIATION
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4818148

Spectral properties of coherent waves in an argon plasma column are examined using fluctuation data from fast imaging. Visible light from ArII line emission is collected at high frame rates using a high-speed digital camera. A cross-spectral phase technique allows direct visualization of dominant phase structures as a function of frequency, as well as identification of azimuthal asymmetries present in the system. Experimental dispersion estimates are constructed from imaging data alone. Drift-like waves are identified by comparison with theoretical dispersion curves, and a tentative match of a low-frequency spectral feature to Kelvin-Helmholtz-driven waves is presented. Imaging measurements are consistent with previous results, and provide non-invasive, single-shot measurements across the entire plasma cross-section. Implications of the measured spectral properties for imaging measurements of mode dynamics are explored.