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Title: Modulational interaction between the short-wavelength lower-hybrid waves and slow, large-scale density fluctuations

Abstract

Conditions are formulated for modulational instability of two modes with disparate time and space scales, and the modulational interaction of fast and short-wavelength lower-hybrid waves with slow, large-scale inertial Alfven and ion-acoustic waves is analyzed. Instability is driven by Reynolds' stresses exerted on plasma by the lower-hybrid waves. Reynolds' stresses lead to the formation of background density modulations in which the lower-hybrid wave can be localized. It is concluded that the lower-hybrid solitary structures observed in the auroral ionosphere can be created by Reynolds' stresses of the lower-hybrid waves. In many respects, the observed structures exhibit properties of wave localizations that result from modulational instability.

Authors:
;  [1];  [2]
  1. Foundations Development, Sabanci University, Istanbul 34956 (Turkey)
  2. (United States)
Publication Date:
OSTI Identifier:
20782341
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 12; Journal Issue: 11; Other Information: DOI: 10.1063/1.2135770; (c) 2005 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; ALFVEN WAVES; FLUCTUATIONS; ION ACOUSTIC WAVES; IONOSPHERE; LOWER HYBRID CURRENT DRIVE; LOWER HYBRID HEATING; MODULATION; PLASMA; PLASMA DENSITY; PLASMA INSTABILITY; REYNOLDS NUMBER; SOLITONS; STRESSES; WAVELENGTHS

Citation Formats

Uecer, Defne, Shapiro, Vitali D., and Physics Department, University of California San Diego, La Jolla, California 92093. Modulational interaction between the short-wavelength lower-hybrid waves and slow, large-scale density fluctuations. United States: N. p., 2005. Web. doi:10.1063/1.2135770.
Uecer, Defne, Shapiro, Vitali D., & Physics Department, University of California San Diego, La Jolla, California 92093. Modulational interaction between the short-wavelength lower-hybrid waves and slow, large-scale density fluctuations. United States. doi:10.1063/1.2135770.
Uecer, Defne, Shapiro, Vitali D., and Physics Department, University of California San Diego, La Jolla, California 92093. Tue . "Modulational interaction between the short-wavelength lower-hybrid waves and slow, large-scale density fluctuations". United States. doi:10.1063/1.2135770.
@article{osti_20782341,
title = {Modulational interaction between the short-wavelength lower-hybrid waves and slow, large-scale density fluctuations},
author = {Uecer, Defne and Shapiro, Vitali D. and Physics Department, University of California San Diego, La Jolla, California 92093},
abstractNote = {Conditions are formulated for modulational instability of two modes with disparate time and space scales, and the modulational interaction of fast and short-wavelength lower-hybrid waves with slow, large-scale inertial Alfven and ion-acoustic waves is analyzed. Instability is driven by Reynolds' stresses exerted on plasma by the lower-hybrid waves. Reynolds' stresses lead to the formation of background density modulations in which the lower-hybrid wave can be localized. It is concluded that the lower-hybrid solitary structures observed in the auroral ionosphere can be created by Reynolds' stresses of the lower-hybrid waves. In many respects, the observed structures exhibit properties of wave localizations that result from modulational instability.},
doi = {10.1063/1.2135770},
journal = {Physics of Plasmas},
number = 11,
volume = 12,
place = {United States},
year = {Tue Nov 15 00:00:00 EST 2005},
month = {Tue Nov 15 00:00:00 EST 2005}
}
  • The linear and nonlinear dynamics of modulational interaction between small-scale drift waves and large-scale trapped ion convective cells are investigated. This example is a paradigm of the more general problem of describing the self-consistent interaction of small-scale fluctuations with mean sheared flows. The growth rate of modulational instability is determined by spectral properties of drift waves and can exceed the linear growth rate of the trapped ion mode. An anisotropic spectrum of drift waves is always modulationally unstable. The spatial orientation of the convective cell pattern and structure (i.e., shear strength) is determined by drift wave spectrum anisotropy and propagationmore » direction. In the presence of a sheared magnetic field, which pins small-scale drift waves to mode rational surfaces, the modulational growth rate becomes intrinsically anisotropic, on account of the modified radial structure of drift waves. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less
  • In the present paper, the perturbation of the launched power spectrum of the Lower Hybrid wave at the separatrix by electron density fluctuations in the scrape-off layer is investigated. Considering a slab geometry with magnetic field lines parallel to the toroidal direction, the full wave equation is solved using Comsol Multiphysics® for a fully active multi-junction like LH antenna made of two modules. When electron density fluctuations are incorporated in the dielectric tensor over a thin perturbed layer in front of the grill, it is shown that the power spectrum may be strongly modified from the antenna mouth to themore » plasma separatrix as the wave propagates. The diffraction effect leads to the appearance of multiple satellite lobes with randomly varying positions, a feature consistent with the recently developed model that has been applied successfully to high density discharges on the Tokamak Tore Supra corresponding to the large spectral gap regime [Decker J. et al. Phys. Plasma 21 (2014) 092504]. The perturbation is found to be maximum for the Fourier components of the fluctuating spectrum in the vicinity of the launched LH wavelength.« less
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  • Two different confinement transition discharges, the low-intermediate-high (L-I-H) and the low-intermediate-low (L-I-L) confinement transitions, respectively, have been obtained by lower hybrid current drive with lithium wall conditioning in the EAST superconducting tokamak. The dynamic features of short-scale turbulent fluctuations in the two discharges are investigated by a tangential CO{sub 2} laser collective scattering system. It is found that the great changes of broadband fluctuations in amplitude and structure characteristics are closely related to the choice of the final transition to H-mode. These results could shed light on the understanding of the L-H transition mechanism.
  • The results of theoretical and experimental studies on excitation of drift waves in a tokamak plasma under the conditions of experiments on lower-hybrid (LH) plasma heating and current drive are presented. It is shown that for sufficiently strong LH pump levels the main effect resulting in the drift wave excitation is the LH wave modulational instability. It is found that the modulational excitation of long-wavelength drift oscillations (with the wavelengths exceeding the length of the LH pump wave) is described by a dispersion equation similar to the equation for the usual hydrodynamical beam instability. This allows us to treat themore » excitation of the long-wavelength drift waves as modulational excitation by a beam of the LH waves. The theoretical results obtained are compared with the data of the tokamak Tore Supra [{ital Proceedings} {ital of} {ital the} 12{ital th} {ital International} {ital Conference} {ital on} {ital Plasma} {ital Physics} {ital and} {ital Controlled} {ital Nuclear} {ital Fusion}, Nice, 1988 (International Atomic Energy Agency, Vienna, 1989), p. 9] experiment. Qualitative accordance of the theoretical and experimental results is demonstrated. {copyright} {ital 1996 American Institute of Physics.}« less