ISSN:
1089-7666
Source:
AIP Digital Archive
Topics:
Physics
Notes:
CO2 laser scattering and correlation techniques are used to study low-frequency density fluctuations in plasmas in the Alcator C tokamak. Using crossed-beam correlation techniques, these fluctuations are found to have largest amplitudes near the plasma edge. In discharges with mean plasma densities n¯(approximately-greater-than)2×1014 cm−3, the normalized fluctuation amplitude is ñ/n(approximately-equal-to)0.5 and peaks at the limiter radius; however, at lower plasma densities, ñ/n peaks in the plasma interior at a normalized minor radius r/a(approximately-equal-to)0.75 (where a is the limiter radius). The radial and poloidal wave vectors of the fluctuations are comparable, with mean wavenumbers k¯∼20 cm−1. At any given k, the observed frequency spectrum is broad. For plasma densities n¯(approximately-less-than)1.5×1014 cm−3, the poloidal group propagation velocity vθ of the fluctuations is measured to be approximately 2×105 cm/sec in the electron diamagnetic drift direction, while at plasma densities n¯(approximately-greater-than)2×1014 cm−3, vθ(approximately-equal-to)9×104 cm/sec in the ion diamagnetic drift direction. The nature of these fluctuations is also studied in discharges exhibiting a boundary-layer instability (i.e., "marfes'').
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.865206
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