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Title: Existence and damping of toroidicity-induced Alfven eigenmodes

Abstract

A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.

Authors:
;
Publication Date:
Research Org.:
Texas Univ., Austin, TX (United States). Inst. for Fusion Studies
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10107738
Report Number(s):
DOE/ET/53088-531; IFSR-531
ON: DE92004250
DOE Contract Number:
FG05-80ET53088
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Dec 1991
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALFVEN WAVES; LANDAU DAMPING; EIGENVALUES; TOKAMAK DEVICES; WAVE FUNCTIONS; 700340; PLASMA WAVES, OSCILLATIONS, AND INSTABILITIES

Citation Formats

Mahajan, S.M., and Mett, R.R. Existence and damping of toroidicity-induced Alfven eigenmodes. United States: N. p., 1991. Web. doi:10.2172/10107738.
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Mahajan, S.M., & Mett, R.R. Existence and damping of toroidicity-induced Alfven eigenmodes. United States. doi:10.2172/10107738.
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Mahajan, S.M., and Mett, R.R. Sun . "Existence and damping of toroidicity-induced Alfven eigenmodes". United States. doi:10.2172/10107738. https://www.osti.gov/servlets/purl/10107738.
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@article{osti_10107738,
title = {Existence and damping of toroidicity-induced Alfven eigenmodes},
author = {Mahajan, S.M. and Mett, R.R.},
abstractNote = {A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.},
doi = {10.2172/10107738},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Dec 01 00:00:00 EST 1991},
month = {Sun Dec 01 00:00:00 EST 1991}
}
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Technical Report:
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DOI:  10.2172/10107738
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  • ;
    A new method of analyzing the toroidicity-induced Alfven eigenmode (TAE) from kinetic theory is presented. The analysis includes electron parallel dynamics non-perturbatively, an effect which is found to strongly influence the character and damping of the TAE -- contrary to previous theoretical predictions. The normal electron Landau damping of the TAE is found to be higher than previously expected, and may explain recent experimental measurements of the TAE damping coefficient. 11 refs., 1 fig., 1 tab.

  • ; ; ; ...
    The effect of resonant continuum damping is investigated for the low-mode-number, toroidicity-induced, global shear Alfven eigenmodes, which can be self-excited by energetic circulating alpha particles in an ignited tokamak plasma. Resonant interaction with the shear Alfven continuum is possible for these eigenmodes, especially near the plasma periphery, leading to significant dissipation, which is typically larger than direct bulk plasma dissipation rates. Two perturbation methods are developed for obtaining the Alfven resonance damping rate from the ideal fluid zeroth-order shear Alfven eigenvalue and eigenfunction. In both methods the real part of the frequency is estimated to zeroth order, and the imaginarymore » part, which includes the damping rate, is then obtained by perturbation theory. One method, which is applicable when the eigenfunction is nearly real, can readily be incorporated into general MHD codes. In the second method, the zeroth-order eigenfunctions may be complex; however, the application of this method to general MHD codes needs more detailed development. Also, an analytical estimate is found for the next-order real frequency shift of the fluid global Alfven mode. Analytical and numerical studies of this continuum damping effect indicate that it can substantially reduce the alpha particle-induced growth rate. Thus, either it is possible to prevent instability, or if unstable, to use the Alfven resonance damping to estimate the saturation amplitude level predicted from quasilinear theory. 44 refs., 13 figs., 1 tab.« less

  • ;
    The structure of toroidicity-induced Alfven eigenmodes (TAE) and kinetic TAE (KTAE) with large mode numbers is analyzed and the linear power transfer from energetic particles to these modes is calculated in the low shear limit when each mode is localized near a single gap within an interval whose total width {Delta}{sup out} is much smaller than the radius r{sub m} of the mode location. Near its peak where most of the mode energy is concentrated, the mode has an inner scalelength {Delta}{sup in}, which is much smaller than {Delta}{sup out}. The scale {Delta}{sup in} is determined by toroidicity and kineticmore » effects, which eliminate the singularity of the potential at the resonant surface. This work examines the case when the drift orbit width of energetic particles {Delta}{sub b} is much larger than the inner scalelength {Delta}{sup in}, but arbitrary compared to the total width of the mode. It is shown that the particle-to-wave linear power transfer is comparable for the TAE and KTAE modes in this case. The ratio of the energetic particle contributions to the growth rates of the TAE and KTAE modes is then roughly equal to the inverse ratio of the mode energies. It is found that, in the low shear limit the growth rate of the KTAE modes can be larger than that for the TAE modes.« less

  • ; ; ; ...
    Toroidicity induced Alfven Eigenmode (TAE) stability in National Spherical Torus Experiment (NSTX) is analyzed using the improved NOVA-K code, which includes finite orbit width and Larmor radius effects and is able to predicts the saturation amplitude for the mode using the quasilinear theory. Broad spectrum of unstable global TAEs with different toroidal mode numbers is predicted. Due to the strong poloidal field and the presence of the magnetic well in NSTX better particle confinement in the presence of TAEs in comparison with tokamaks is illustrated making use of the ORBIT code.

  • ; ; ; ...
    The toroidicity-induced Alfvin eigenmodes (TAE) with radially extended structure are found to be stable in the Tokamak Fusion Test Reactor Deuterium-Tritium plasmas. A core localized TAE mode is shown to exist near the center of the plasma at small magnetic shear and finite plasma beta, which can be destabilized by energetic alpha particles on TFTR. With additional instability drive from fast minority ions powered by ICRH, both the global and the core localized TAE modes can be readily destabilized.