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Title: Alpha particle effects on the internal kink modes

Abstract

The {alpha}-particle effects on the internal kink mode stability are studied. Finite Grad-Shafranov Shift, plasma {beta}, and plasma shape can significantly enhance the trapped particle drift reversal domain in pitch angle space and reduce average magnetic drift frequency. The drift reversal effect on the ideal kink mode is small, but the {beta}{sub {alpha}} threshold for the fishbone mode can be much lower than previously predicted. In addition, the ion diamagnetic drift has a stronger destabilizing effect.

Authors:
;
Publication Date:
Research Org.:
Princeton Univ., NJ (United States). Plasma Physics Lab.
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
10176063
Report Number(s):
PPPL-2979
ON: DE94017335; TRN: 94:016693
DOE Contract Number:
AC02-76CH03073
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: Aug 1994
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; TOKAMAK DEVICES; KINK INSTABILITY; ALPHA PARTICLES; DISTRIBUTION FUNCTIONS; MHD EQUILIBRIUM; DISPERSION RELATIONS; FISHBONE INSTABILITY; 700340; PLASMA WAVES, OSCILLATIONS, AND INSTABILITIES

Citation Formats

Wu, Yanlin, and Cheng, C.Z.. Alpha particle effects on the internal kink modes. United States: N. p., 1994. Web. doi:10.2172/10176063.
Wu, Yanlin, & Cheng, C.Z.. Alpha particle effects on the internal kink modes. United States. doi:10.2172/10176063.
Wu, Yanlin, and Cheng, C.Z.. Mon . "Alpha particle effects on the internal kink modes". United States. doi:10.2172/10176063. https://www.osti.gov/servlets/purl/10176063.
@article{osti_10176063,
title = {Alpha particle effects on the internal kink modes},
author = {Wu, Yanlin and Cheng, C.Z.},
abstractNote = {The {alpha}-particle effects on the internal kink mode stability are studied. Finite Grad-Shafranov Shift, plasma {beta}, and plasma shape can significantly enhance the trapped particle drift reversal domain in pitch angle space and reduce average magnetic drift frequency. The drift reversal effect on the ideal kink mode is small, but the {beta}{sub {alpha}} threshold for the fishbone mode can be much lower than previously predicted. In addition, the ion diamagnetic drift has a stronger destabilizing effect.},
doi = {10.2172/10176063},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Aug 01 00:00:00 EDT 1994},
month = {Mon Aug 01 00:00:00 EDT 1994}
}

Technical Report:

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  • The effects of alpha particles on the internal kink and fishbone modes are studied analytically. The nonadiabatic contribution from untrapped alpha particles is negligible. Finite inverse aspect ratio, plasma {beta} and plasma shaping effects can significantly enhance the trapped particle drift reversal domain in the pitch angle space and reduce the bounce-averaged magnetic drift frequency. The drift reversal effect on the ideal kink mode is small, but the {beta}{sub {alpha}} threshold for the fishbone mode can be much lower than previously predicted. Moreover, the fishbone mode could be excited by alpha particles even when the plasma is stable in themore » ideal MHD limit. In addition, the ion diamagnetic drift frequency (finite ion Larmor radius effect) has a strong destabilizing effect on the fishbone mode when it is comparable with the trapped alpha averaged precessional drift frequency, even though it stabilizes the plasma in the ideal MHD limit.« less
  • The influence of resistivity on energetic trapped particle-induced internal kink modes, dubbed ''fishbones'' in the literature, explored. A general dispersion relation, which recovers the ideal theory in its appropriate limit, is derived and analyzed. Implications of the theory for present generation fusion devices such as the Joint European Torus are discussed. 8 refs., 2 figs.
  • The effects of alpha particles on the internal kink and fishbone modes are studied analytically. The nonadiabatic contribution from untrapped alpha particles is negligible. Finite inverse aspect ratio, plasma [beta], and plasma shaping effects can significantly enhance the trapped particle drift reversal domain in the pitch angle space and reduce the bounce-averaged magnetic drift frequency. The decrease of the drift magnitude and drift reversal effects on the ideal kink mode is small, but the [beta][sub [alpha]] threshold for the fishbone mode can be much lower than previously predicted [B. Coppi, S. Migliuolo, F. Pegoraro, and F. Porcelli, Phys. Fluids Bmore » [bold 2], 927 (1990)]. Moreover, the fishbone mode could be excited by alpha particles, even when the plasma is stable in the ideal magnetohydrodynamic (MHD) limit. In addition, the ion diamagnetic drift frequency (finite ion Larmor radius effect) has a strong destabilizing effect on the fishbone mode when it is comparable with the trapped alpha-averaged precessional drift frequency, even though it stabilizes the plasma in the ideal MHD limit.« less
  • Global hybrid simulations of energetic particle effects on the n=1 internal kink mode have been carried out for tokamaks. For the International Thermonuclear Experimental Reactor (ITER) [ITER Physics Basis Editors et al., Nucl. Fusion 39:2137 (1999)], it is shown that alpha particle effects are stabilizing for the internal kink mode. However, the elongation of ITER reduces the stabilization effects significantly. Nonlinear simulations of the precessional drift fishbone instability for circular tokamak plasmas show that the mode saturates due to flattening of the particle distribution function near the resonance region. The mode frequency chirps down rapidly as the flattening region expandsmore » radially outward. Fluid nonlinearity reduces the saturation level.« less
  • The redistribution of alpha particles due to internal kink modes is studied. The exact particle trajectories in the total fields, equilibrium plus perturbation, are calculated. The equilibrium has circular cross section and the plasma parameters are similar to those expected in ITER. The alpha particles are initially distributed according to a slowing down distribution function and have energies between 18 keV and 3.5 MeV. The (1, 1), (2, 2), and (2, 1) modes are included and the effect of changing their amplitude and frequency is studied. When only the (1, 1) mode is included, the spreading of high energy (E≳1 MeV) alpha particlesmore » increases slowly with the energy and mode frequency. At lower energies, the redistribution is more sensitive to the mode frequency and particle energy. When a (2, 1) mode is added, the spreading increases significantly and particles can reach the edge of the plasma. Trapped particles are the most affected and the redistribution parameter can have maxima above 1 MeV, depending on the mode frequency. These results can have important implications for ash removal.« less