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Title: Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas

Abstract

The combined effects of the electron-temperature (ET) and parallel electron velocity (PEV) gradients on electrostatic instabilities in a nonuniform magnetoplasma are investigated. For this purpose, a hybrid approach is used, in which the electrons are treated as a magnetized fluid, while the ions are described by means of a kinetic description. A new dispersion relation is derived, which shows how different plasma modes are linear coupled in the presence of the ET and PEV gradients. The dispersion relation is analyzed analytically (numerically) to demonstrate the instability of long- and short-wavelength electrostatic modes (to examine the combined effects of ET and PEV gradients) in nonuniform magnetoplasmas. The present results may be useful in understanding the salient features of nonthermal fluctuations and associated anomalous cross-field electron fluxes in forthcoming laboratory experiments.

Authors:
; ;  [1]
  1. Institut fuer Theoretische Physik IV and Centre for Plasma Science and Astrophysics, Fakultaet fuer Physik und Astronomie, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)
Publication Date:
OSTI Identifier:
20960133
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2430521; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; DISPERSION RELATIONS; ELECTRON TEMPERATURE; ELECTRONS; FLUCTUATIONS; ION TEMPERATURE; IONS; MAGNETOHYDRODYNAMICS; PLASMA; PLASMA INSTABILITY; PLASMA WAVES; TEMPERATURE GRADIENTS; VELOCITY

Citation Formats

Shukla, P. K., Coppi, B., and Eliasson, B.. Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas. United States: N. p., 2007. Web. doi:10.1063/1.2430521.
Shukla, P. K., Coppi, B., & Eliasson, B.. Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas. United States. doi:10.1063/1.2430521.
Shukla, P. K., Coppi, B., and Eliasson, B.. Mon . "Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas". United States. doi:10.1063/1.2430521.
@article{osti_20960133,
title = {Electron parallel velocity and temperature gradient driven electrostatic fluctuations in nonuniform magnetoplasmas},
author = {Shukla, P. K. and Coppi, B. and Eliasson, B.},
abstractNote = {The combined effects of the electron-temperature (ET) and parallel electron velocity (PEV) gradients on electrostatic instabilities in a nonuniform magnetoplasma are investigated. For this purpose, a hybrid approach is used, in which the electrons are treated as a magnetized fluid, while the ions are described by means of a kinetic description. A new dispersion relation is derived, which shows how different plasma modes are linear coupled in the presence of the ET and PEV gradients. The dispersion relation is analyzed analytically (numerically) to demonstrate the instability of long- and short-wavelength electrostatic modes (to examine the combined effects of ET and PEV gradients) in nonuniform magnetoplasmas. The present results may be useful in understanding the salient features of nonthermal fluctuations and associated anomalous cross-field electron fluxes in forthcoming laboratory experiments.},
doi = {10.1063/1.2430521},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • By employing the quantum magnetohydrodynamic-Poisson model, a general dispersion relation for low-frequency electrostatic ion-temperature-gradient (ITG) modes in a very dense Fermi plasma is derived. The growth rate is found to be higher in the presence of ion-temperature gradients and electron corrections due to quantum fluctuations. Two new ITG driven modes in the Fermi plasma are found. These ITG modes are associated with an electron density response that differs from the Boltzmann law. It is expected that newly found ITG modes can play an important role in anomalous cross-field ion energy transport in the next-generation laser-solid density plasma experiments as wellmore » as in dense astrophysical bodies (e.g., neutron stars and the interior of white dwarfs)« less
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  • Various theories and numerical simulations support the conjecture that the ubiquitous problem of anomalous electron transport in tokamaks may arise from a short-scale turbulence driven by the electron temperature gradient. To check whether this turbulence is present in plasmas of the National Spherical Torus Experiment, measurements of turbulent fluctuations were performed with coherent scattering of electromagnetic waves. Results from plasmas heated by high harmonic fast waves show the existence of density fluctuations in the range of wave numbers k(perpendicular to)rho(e) = 0.1-0.4, corresponding to a turbulence scale length of the order of the collisionless skin depth. Experimental observations and agreementmore » with numerical results from the linear gyro-kinetic GS2 code indicate that the observed turbulence is driven by the electron temperature gradient. These turbulent fluctuations were not observed at the location of an internal transport barrier driven by a negative magnetic shear.« less
  • Measurements with coherent scattering of electromagnetic waves in plasmas of the National Spherical Torus Experiment indicate the existence of turbulent fluctuations in the range of wave numbers k{sub perpendicular}{rho}{sub e}=0.1-0.4, corresponding to a turbulence scale length nearly equal to the collisionless skin depth. Experimental observations and agreement with numerical results from a linear gyrokinetic stability code support the conjecture that the observed turbulence is driven by the electron-temperature gradient.
  • Vortex structures and related heat transport properties in slab electron temperature gradient (ETG) driven turbulence are comprehensively investigated by means of nonlinear gyrokinetic Vlasov simulations, with the aim of elucidating the underlying physical mechanisms of the transition from turbulent to coherent states. Numerical results show three different types of vortex structures, i.e., coherent vortex streets accompanied with the transport reduction, turbulent vortices with steady transport, and a zonal-flow-dominated state, depending on the relative magnitude of the parallel compression to the diamagnetic drift. In particular, the formation of coherent vortex streets is correlated with the strong generation of zonal flows formore » the cases with weak parallel compression, even though the maximum growth rate of linear ETG modes is relatively large. The zonal flow generation in the ETG turbulence is investigated by the modulational instability analysis with a truncated fluid model, where the parallel dynamics such as acoustic modes for electrons is incorporated. The modulational instability for zonal flows is found to be stabilized by the effect of the finite parallel compression. The theoretical analysis qualitatively agrees with secondary growth of zonal flows found in the slab ETG turbulence simulations, where the transition of vortex structures is observed.« less