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Title: Stabilization of the quasi-interchange mode in tokamaks by circulating energetic ions

Abstract

The influence of the circulating energetic ions on the quasi-interchange (QI) mode in tokamak plasmas with a wide shearless core and the central safety factor close to unity is considered. It is found that these ions tend to stabilize the QI mode in the case of co-injection and balanced injection, whereas the influence of counter-circulating ions is typically destabilizing because of finite-orbit-width effects. Specific examples relevant to tokamaks with large and small aspect ratio of the torus are considered.

Authors:
; ; ;  [1];  [2]
  1. Institute for Nuclear Research, Prospect Nauky 47, Kyiv, 03680 (Ukraine)
  2. (United States)
Publication Date:
OSTI Identifier:
20960103
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 1; Other Information: DOI: 10.1063/1.2434791; (c) 2007 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; ASPECT RATIO; HEATING; ION BEAMS; PLASMA; PLASMA BEAM INJECTION; PLASMA CONFINEMENT; PLASMA INSTABILITY; SAFETY; STABILIZATION; TAIL IONS; TOKAMAK DEVICES

Citation Formats

Kolesnichenko, Ya. I., Lutsenko, V. V., Marchenko, V. S., White, R. B., and Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey, 08543. Stabilization of the quasi-interchange mode in tokamaks by circulating energetic ions. United States: N. p., 2007. Web. doi:10.1063/1.2434791.
Kolesnichenko, Ya. I., Lutsenko, V. V., Marchenko, V. S., White, R. B., & Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey, 08543. Stabilization of the quasi-interchange mode in tokamaks by circulating energetic ions. United States. doi:10.1063/1.2434791.
Kolesnichenko, Ya. I., Lutsenko, V. V., Marchenko, V. S., White, R. B., and Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey, 08543. Mon . "Stabilization of the quasi-interchange mode in tokamaks by circulating energetic ions". United States. doi:10.1063/1.2434791.
@article{osti_20960103,
title = {Stabilization of the quasi-interchange mode in tokamaks by circulating energetic ions},
author = {Kolesnichenko, Ya. I. and Lutsenko, V. V. and Marchenko, V. S. and White, R. B. and Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey, 08543},
abstractNote = {The influence of the circulating energetic ions on the quasi-interchange (QI) mode in tokamak plasmas with a wide shearless core and the central safety factor close to unity is considered. It is found that these ions tend to stabilize the QI mode in the case of co-injection and balanced injection, whereas the influence of counter-circulating ions is typically destabilizing because of finite-orbit-width effects. Specific examples relevant to tokamaks with large and small aspect ratio of the torus are considered.},
doi = {10.1063/1.2434791},
journal = {Physics of Plasmas},
number = 1,
volume = 14,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • The ELMO snaky torus concept (Furth and Boozer (private communication, 1983)) is investigated in a helically symmetric model with low beta and large aspect ratio (the curvature radius of the magnetic axis over the plasma radius). The equilibria are obtained by expansions in the inverse aspect ratio and plasma beta. Application of the energetic-particle- modified Mercier criterion (Zheng and Tsai, Phys. Fluids B {bold 4}, 1416 (1992)) to the analytical equilibria confirms that the interchange mode can be stabilized in helically symmetric systems in the low-beta regime by suitably introducing drift-nonreverse energetic particles. The results show that, for effective stabilization,more » it is better that the pressure profile of the energetic component depend on the radius quadratically, and peak at midplane in the poloidal angle, and the volume occupied by the energetic particles, the aspect ratio, and the ratio of the curvature to the torsion of the magnetic axis should be large when the energetic particles are drift nonreverse.« less
  • Toroidal Alfven eigenmodes are shown to be resonantly destabilized by {ital both} circulating {ital and} trapped energetic ions/alpha particles. In particular, the energetic circulating ions are shown to resonate with the mode not only at the Alfven speed ({ital v}{sub A}), but also at one-third of this speed, while for trapped ions, the dominant instability mechanism is shown to be due to the resonance between the precessional magnetic drift and the wave. Implications of the theory for present and future tokamaks are discussed.
  • The kinetic energy principle describing the interaction between ideal magnetohydrodynamic (MHD) modes with trapped energetic ions is revised. A model is proposed on the basis of the reduced ideal MHD equations for background plasmas and the bounce-averaged drift-kinetic equation for trapped energetic ions. The model is applicable to large-aspect-ratio toroidal devices. Specifically, the effect of trapped energetic ions on the interchange mode in helical systems is analyzed. Results show that the interchange mode is excited by trapped energetic ions, even if the equilibrium states are stable to the ideal interchange mode. The energetic-ion-induced branch of the interchange mode might bemore » associated with the fishbone mode in helical systems.« less
  • The influence of the well-circulating energetic ions on the ideal kink instability and the m=1 tearing instabilities (collisionless and semicollisional modes) is studied. It is found that the precession of these ions can be by an important stabilizing factor, especially when the balanced tangential neutral beam injection is used and/or in the presence of fusion-produced {alpha} particles.
  • A cylindrical plasma model is used to study the stabilizing effect of electromagnetic ion cyclotron frequency range (ICRF) waves on the m = 1 magnetohydrodynamic interchange mode. The fast wave eigenmodes of the column and the near-field antenna pattern are calculated numerically for a diffuse plasma profile when ..omega..>..cap omega../sub i/. The resulting ponderomotive force and sideband contributions to global interchange stability are then determined using a rigid shift trial function. For far-field stabilization it is verified that the direct ponderomotive and sideband contributions cancel exactly as the conducting wall supporting the fast wave eigenmode moves out to infinity. Themore » near-field stabilization effect is related numerically to the driven k/sub parallel/ spectrum of the waves and their radial profiles. The numerical model is employed to calculate threshold ICRF wave amplitudes for the stabilization experiments in the Phaedrus tandem mirror (Phys. Rev. Lett. 51, 1955 (1983)).« less