Analysis of the influence of external biasing on Texas Helimak turbulence

Journal Article · Fri Feb 15 00:00:00 EST 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4793732· OSTI ID:22113442

Toufen, D. L. ^[1]; Guimaraes-Filho, Z. O.; Caldas, I. L. ^[1]; Szezech, J. D. ^[2]; Lopes, S.; Viana, R. L. ^[3]; Gentle, K. W. ^[4]

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1. Institute of Physics, University of Sao Paulo, C.P. 66318, 05315-970 Sao Paulo, Sao Paulo (Brazil)
2. Department of Physics, State University of Ponta Grossa, 84030-900 Parana (Brazil)
3. Department of Physics, Federal University of Parana, 81531-990 Curitiba, Parana (Brazil)
4. Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)

We analyze alterations on the electrostatic turbulence in experiments with imposed bias to control the plasma radial electric field in Texas Helimak (K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)), a toroidal plasma device with a one-dimensional equilibrium, magnetic curvature, and shear. Comparing discharges from different biased potentials, we identify, in a roughly uniform gradient region, a continuous variation from low turbulence level and narrower frequency spectra, for negative bias, to high turbulence level and broadband spectra for positive bias. Overall, we distinguish two kinds of perturbed turbulence, classified according to their intensity, spectral, statistical, and recurrence properties. When the bias is positive, the turbulence shows enhanced and broadband spectra with non Gaussian probability distribution functions having noticeable long tails (extreme events) similar to the turbulence in tokamak scrape-off layer. On the other hand, negative bias reduces the turbulence level and decreases the spectrum widths. Also for negative bias, we found large frequency widths whenever the coupling between drift waves and the sheared plasma flow is fast enough to allow the enhancement of sidebands modes.

• OSTI ID: 22113442
• Journal Information: Physics of Plasmas, Vol. 20, Issue 2; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
DISTRIBUTION FUNCTIONS
ELECTRIC DISCHARGES
ELECTRIC FIELDS
EQUILIBRIUM
PLASMA
PLASMA DIAGNOSTICS
PLASMA DRIFT
PLASMA SCRAPE-OFF LAYER
PLASMA SHEATH
PROBABILITY
SHEAR
SPECTRA
TOKAMAK DEVICES
TURBULENCE
WAVE PROPAGATION