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Title: Electrostatic turbulence intermittence driven by biasing in Texas Helimak

We investigate changes in the intermittent sequence of bursts in the electrostatic turbulence due to imposed positive bias voltage applied 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. We identify the burst characteristics by analyzing ion saturation current fluctuations collected in a large set of Langmuir probes. The number of bursts increase with positive biasing, giving rise to a long tailed skewed turbulence probability distribution function. The burst shape does not change much with the applied bias voltage, while their vertical velocity increases monotonically. For high values of bias voltage, the bursts propagate mainly in the vertical direction which is perpendicular to the radial density gradient and the toroidal magnetic field. Moreover, in contrast with the bursts in tokamaks, the burst velocity agrees with the phase velocity of the overall turbulence in both vertical and radial directions. For a fixed bias voltage, the time interval between bursts and their amplitudes follows exponential distributions. Altogether, these burst characteristics indicate that their production can be modelled by a stochastic process.
Authors:
 [1] ;  [2] ; ; ;  [3] ;  [4]
  1. Federal Institute of Education, Science and Technology of São Paulo - IFSP, 07115-000 Guarulhos, São Paulo (Brazil)
  2. (Brazil)
  3. Institute of Physics, University of São Paulo, 05315-970 São Paulo, São Paulo (Brazil)
  4. Department of Physics and Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712 (United States)
Publication Date:
OSTI Identifier:
22403337
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 21; Journal Issue: 12; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DISTRIBUTION FUNCTIONS; ELECTRIC FIELDS; ELECTRIC POTENTIAL; LANGMUIR PROBE; ONE-DIMENSIONAL CALCULATIONS; PHASE VELOCITY; PLASMA; STOCHASTIC PROCESSES; TEXAS; TURBULENCE