Author: G. RewoldtPublisher:
ISBN:
Category :
Languages : en
Pages : 17
Book Description
Influence of Hot Beam Ions on MHD Ballooning Modes in Tokamaks
Author: G. RewoldtInfluence of Hot Beam Ions on MHD Ballooning Modes in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
It has recently been proposed that the presence of high energy ions from neutral beam injection can have a strong stabilizing effect on kinetically-modified ideal MHD ballooning modes in tokamaks. In order to assess realistically the importance of such effects, a comprehensive kinetic stability analysis, which takes into account the integral equation nature of the basic problem, has been applied to this investigation. In the collisionless limit, the effect of adding small fractions of hot beam ions is indeed found to be strongly stabilizing. On the other hand, for somewhat larger fractions of hot ions, a new beam-driven mode is found to occur with a growth rate comparable in magnitude to the growth rate of the MHD ballooning mode in the absence of hot ions. This implies that there should be an optimal density of hot particles which minimizes the strength of the relevant instabilities. Employing non-Maxwellian equilibrium distribution functions to model the beam species makes a quantitative, but not qualitative, difference in the results. Adding collisions to the calculation tends to reduce considerably the stabilizing effect of the hot ions.
Energy Research Abstracts
Author: Fusion Energy Update
Author: Influence of Diamagnetic Drifts on Critical Beta in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
In specific cases the critical beta (.beta./sub c/) for stability against internal magnetohydrodynamic (MHD) ballooning modes can be improved significantly by taking into account the stabilizing influence of the ion diamagnetic drifts. This kinetic modification to the ideal MHD analysis together with radial corrections to the local theory are included in a calculation of .beta./sub c/ as a function of toroidal mode number (n) for a particular tokamak equilibrium sequence of interest.
Energy Research Abstracts
Author: Publisher:
ISBN:
Category : Power resources
Languages : en
Pages : 596
Book Description
Includes all works deriving from DOE, other related government-sponsored information and foreign nonnuclear information.
Kinetic Analysis of MHD Ballooning Modes in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
A comprehensive analysis of the stability properties of the appropriate kinetically generalized form of MHD ballooning modes together with the usual trapped-particle drift modes is presented. The calculations are fully electromagnetic and include the complete dynamics associated with compressional ion acoustic waves. Trapped-particle effects along with all forms of collisionless dissipation are taken into account without approximations. The influence of collisions is estimated with a model Krook operator. Results from the application of this analysis to realistic tokamak operating conditions indicate that unstable short-wavelength modes with significant growth rates can extend from .beta. = 0 to value above the upper ideal-MHD-critical-beta associated with the so-called second stability regime. Since the strength of the relevant modes appears to vary gradually with .beta., these results support a soft beta limit picture involving a continuous (rather than abrupt or hard) modification of anomalous transport already present in low-.beta.-tokamaks. However, at higher beta the increasing dominance of the electromagnetic component of the perturbations indicated by these calculations could also imply significantly different transport scaling properties.
Fusion Nucléaire
Author: Theory of Kinetic Ballooning Modes Excited by Energetic Particles in Tokamaks
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 19
Book Description
We have analyzed theoretically the resonant excitations of kinetic ballooning modes (KBM) by the energetic ions/alpha particles in tokamaks. Our theory includes finite-size orbit effects of both circulating and trapped particles. With energetic-particle contributions suppressed in the singular inertial layer, an analytic.dispersion relation can then be derived via an asymptotic matching analysis. The dispersion relation, in particular, demonstrates the existence of two types of modes; that is, the magnetohydrodynamic (MHD) gap mode and the energetic-particle continuum mode. Specific expressions for real frequencies, growth rates and threshold conditions are also derived for a model slowing-down beam ion distribution function.
Author: