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Title: Renormalized theory of MHD turbulence with electron compressibility

Abstract

Measurements of the power density spectrum for high frequency fluctuations in MST yield a spectrum decaying as k{sup -5/2} instead of the k{sup -3/2} spectrum long predicted to result from the high frequency Alfvenic excitations of MHD. It has been hypothesized that this behavior is due to diamagnetic effects introduced through electron density evolution. While MHD models with density evolution have a diamagnetic branch, it has not been clear what mechanism allows the small diamagnetic frequency to dominate the much larger Alfven frequency in the spectrum balances, as required for agreement with experiment. We detail here a closure calculation for the reduced three-field MHD model that verifies prior hypotheses and predicts spectra consistent with those of experiment. In the closure, the nonlinear response function must be solved as an eigenmode problem in which the driver fluctuations of all three fields are retained. There are three eigenfrequencies, two of which are an Alfvenic conjugate pair corresponding to Alfven waves propagating in either direction along the magnetic field, and one of which is a diamagnetic frequency. To lowest order in the ratio of diamagnetic frequency to Alfven frequency, this third branch is purely diamagnetic. The frequency spectrum is dominated by the nonlocalmore » Alfvenic interaction between high frequency fluctuations and the long wavelength magnetic field fluctuation. However, the triplet interactions that govern spectral transfer project onto both Alvenic and diamagnetic branches. A portion of each triplet correlation therefore decays at the slower diamagnetic time scale and survives longer that the Alfvenic components of each triplet correlation. The diamagnetic frequency thus dominates the spectrum balances.« less

Authors:
; ;  [1]
  1. Univ. of Wisconsin, Madison, WI (United States)
Publication Date:
OSTI Identifier:
489391
Report Number(s):
CONF-960354-
TRN: 97:011532
DOE Contract Number:  
FG02-89ER53291
Resource Type:
Conference
Resource Relation:
Conference: International Sherwood fusion theory conference, Philadelphia, PA (United States), 18-20 Mar 1996; Other Information: PBD: 1996; Related Information: Is Part Of 1996 international Sherwood fusion theory conference; PB: 244 p.
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; MST DEVICE; MHD EQUILIBRIUM; TURBULENCE; ALFVEN WAVES; WAVE PROPAGATION

Citation Formats

Terry, P W, Fernandez, E, and Ware, A S. Renormalized theory of MHD turbulence with electron compressibility. United States: N. p., 1996. Web.
Terry, P W, Fernandez, E, & Ware, A S. Renormalized theory of MHD turbulence with electron compressibility. United States.
Terry, P W, Fernandez, E, and Ware, A S. Tue . "Renormalized theory of MHD turbulence with electron compressibility". United States.
@article{osti_489391,
title = {Renormalized theory of MHD turbulence with electron compressibility},
author = {Terry, P W and Fernandez, E and Ware, A S},
abstractNote = {Measurements of the power density spectrum for high frequency fluctuations in MST yield a spectrum decaying as k{sup -5/2} instead of the k{sup -3/2} spectrum long predicted to result from the high frequency Alfvenic excitations of MHD. It has been hypothesized that this behavior is due to diamagnetic effects introduced through electron density evolution. While MHD models with density evolution have a diamagnetic branch, it has not been clear what mechanism allows the small diamagnetic frequency to dominate the much larger Alfven frequency in the spectrum balances, as required for agreement with experiment. We detail here a closure calculation for the reduced three-field MHD model that verifies prior hypotheses and predicts spectra consistent with those of experiment. In the closure, the nonlinear response function must be solved as an eigenmode problem in which the driver fluctuations of all three fields are retained. There are three eigenfrequencies, two of which are an Alfvenic conjugate pair corresponding to Alfven waves propagating in either direction along the magnetic field, and one of which is a diamagnetic frequency. To lowest order in the ratio of diamagnetic frequency to Alfven frequency, this third branch is purely diamagnetic. The frequency spectrum is dominated by the nonlocal Alfvenic interaction between high frequency fluctuations and the long wavelength magnetic field fluctuation. However, the triplet interactions that govern spectral transfer project onto both Alvenic and diamagnetic branches. A portion of each triplet correlation therefore decays at the slower diamagnetic time scale and survives longer that the Alfvenic components of each triplet correlation. The diamagnetic frequency thus dominates the spectrum balances.},
doi = {},
url = {https://www.osti.gov/biblio/489391}, journal = {},
number = ,
volume = ,
place = {United States},
year = {1996},
month = {12}
}

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