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Physics of Fluids B: Plasma Physics -- November 1992 -- Volume 4, Issue 11 pp. 3722-3734

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Excitation of high-n toroidicity-induced shear Alfvén eigenmodes by energetic particles and fusion alpha particles in tokamaks

G. Y. Fu and C. Z. Cheng
Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543

(Received 3 June 1992; accepted 20 July 1992)

The stability of high-n toroidicity-induced shear Alfvén eigenmodes (TAE) in the presence of fusion alpha particles or energetic ions in tokamaks is investigated. The TAE modes are discrete in nature, and thus can easily tap the free energy associated with energetic particle pressure gradient through wave particle resonant interaction. A quadratic form is derived for the high-n TAE modes using gyrokinetic equation. The kinetic effects of energetic particles are calculated perturbatively using the ideal magnetohydrodynamic (MHD) solution as the lowest-order eigenfunction. The finite Larmor radius (FLR) effects and the finite drift orbit width (FDW) effects are included for both circulating and trapped energetic particles. It is shown that, for circulating particles, FLR and FDW effects have two opposite influences on the stability of the high-n TAE modes. First, they have the usual stabilizing effects by reducing the wave particle interaction strength. Second, they also have destabilizing effects by allowing more particles to resonate with the TAE modes. It is found that the growth rate induced by the circulating alpha particles increases linearly with the toroidal mode number n for small kthetarhoalpha, and decreases as 1/n for kthetarhoalpha>>1. The maximum growth rate is obtained at kthetarhoalpha on the order of unity, and is nearly constant for the range of 0.7<=valpha/vA<=2.5. On the other hand, the trapped particle response is dominated by the precessional drift resonance. The bounce resonant contribution is negligible. The growth rate peaks sharply at the value of kthetarhoalpha, such that the precessional drift resonance occurs for the most energetic trapped particles. The maximum growth rate due to the energetic trapped particles is comparable to that of circulating particles. Finally, the effect of the two-dimensional wave structure of TAE modes is considered by using the Wentzel–Kramers–Brillouin (WKB) method. Physics of Fluids B: Plasma Physics is copyrighted by The American Institute of Physics.


DOI: 10.1063/1.860328
PACS: 52.35.Bj, 52.55.Fa        Additional Information


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Citing Articles

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  1. Hybrid magnetohydrodynamic-particle simulation of linear and nonlinear evolution of Alfvén modes in tokamaks
    S. Briguglio et al., Phys. Plasmas 5, 3287 (1998)
  2. Toroidal Alfvén eigenmodes in TFTR deuterium–tritium plasmas
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  3. Noncircular Triangularity and Ellipticity-Induced Alfvén Eigenmodes Observed in JT-60U
    G. J. Kramer et al., Phys. Rev. Lett. 80, 2594 (1998)

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