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Rotational stabilization of n=1 resistive wall modes in ITER advanced scenarios [K. Ikeda, Nucl. Fusion 47 (2007)] is investigated, where n is the toroidal mode number. In particular, we present numerical results for the ITER strongly reversed shear case, in comparison to the weakly reversed shear case. The rotation frequency is assumed to be modestly low. Our investigation employs the adaptive eigenfunction independent solution-kinetic (AEGIS-K) code [L. J. Zheng et al., “AEGIS-K code for linear kinetic analysis of toroidally axisymmetric plasma stability,” J. Comput. Phys. (to be published)], which provides a fully kinetic (nonhybrid) and self-consistent (nonperturbative) description. AEGIS-K includes wave-particle resonances, shear Alfvén continuum damping, trapped particle effects, and parallel electric effects, but not finite Larmor radius effects. In the case without rotation and kinetic effects included, we find that the strongly reversed shear configuration is more favorable for perfectly conducting wall stabilization of resistive wall modes, in that it has a higher conducting wall beta limit than the weakly reversed shear case. With sufficient rotation, the strongly reversed shear case can also achieve a higher beta limit for completely suppressing the resistive wall modes. However, the marginal rotation frequency required for complete resistive wall mode stabilization in the strongly reversed shear case is about twice as high as that required for the weakly reversed shear case. [ABSTRACT FROM AUTHOR]

Analytical expressions for the marginal stability boundary for resistive ballooning modes at high beta are obtained in the limits of both large and small global shear. These results confirm the recent numerical finding of Sykes et al. [Plasma Phys. Controlled Fusion 29, 719 (1987)] that resistive ballooning modes are stable throughout most of the regime corresponding to ideal ballooning ‘‘second stability’’ in high-beta tokamaks. [ABSTRACT FROM AUTHOR]

The stability of global Alfvén eigenmodes is investigated in the presence of super-Alfvénic energetic particles, such as fusion-product alpha particles in an ignited deuterium–tritium tokamak plasma. Alpha particles tend to destabilize these modes when ω[ATOTHER]@B|[/ATOTHER]α>ωA, where ωA is the shear-Alfvén modal frequency and ω*α is the alpha particle diamagnetic drift frequency. This destabilization due to alpha particles is found to be significantly enhanced when the alpha particles are modeled with a slowing-down distribution function rather than with a Maxwellian distribution. However, previously neglected electron damping due to the magnetic curvature drift is found to be comparable in magnitude to the destabilizing alpha particle term. Furthermore, the effects of toroidicity are also found to be stabilizing, since the intrinsic toroidicity induces poloidal mode coupling, which enhances the parallel electron damping from the sideband shear-Alfvén Landau resonance. In particular, for typical ignition tokamak parameters, global Alfvén eigenmodes are found to be completely stabilized by either the electron damping that enters through the magnetic curvature drift or the damping introduced by finite toroidicity. [ABSTRACT FROM AUTHOR]

The theory of energetic particle stabilization of ballooning modes in tokamaks is revisited. When the energetic particles are drift-reversed, a region of ballooning instability, akin to that which causes the Van Dam–Lee–Nelson limit [in Proceedings of the Workshop on EBT Ring Physics (Oak Ridge National Laboratory, Oak Ridge, TN, 1980), p. 471; Phys. Fluids 23, 1850 (1980)] in magnetic mirrors, is identified. At higher values of core poloidal beta a ‘‘third’’ region of stability is conjectured to occur. The inclusion of finite-aspect-ratio effects can eliminate ballooning instability completely when the energetic particles are non-drift-reversed, but the region of instability for drift-reversed particles persists. Requirements for energetic particle stabilization in large- and small-aspect-ratio tokamak experiments and reactors are discussed. [ABSTRACT FROM AUTHOR]

It is well known that the average favorable magnetic curvature of a tokamak is stabilizing with respect to pressure-driven magnetohydrodynamic instabilities at low beta and that self-stabilization occurs at finite beta in the so-called second stability regime. Here it is self-consistently investigated how these two effects, viz., the mean magnetic well and the self-stabilization, influence the energy confinement time in a tokamak, with the use of the ballooning mode transport model proposed by Connor, Taylor, and Turner [Nucl. Fusion 24, 642 (1984)]. [ABSTRACT FROM AUTHOR]

Modes have been observed near the frequency of the second Alfvén gap during off-axis H-minority heating experiments in the circular cross-section Tokamak Fusion Test Reactor. The observation of these modes is surprising in that the second gap, which is generally opened with ellipticity, is expected to be small, of order (r/R)[sup 2]. A model is proposed in which the second gap is opened by the fast ion beta, which is shown to be able to introduce mode coupling, much as toroidal effects introduce mode coupling for Toroidal Alfvén Eigenmodes (TAE). With the low inferred energy of the fast ion tail (30-50 keV), the fast ion bounce resonance condition is assumed to drive the modes. The modes are seen with and without accompanying TAE mode activity. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]