Epithermal and Thermal Alpha-Particle Transport and Control

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Abstract
Alpha-particle ash accumulation in tokamaks and two possible ash control techniques are discussed. The effect of thermal alpha-particle ash accumulation on plasma performance is examined using a zero-dimensional analysis with profile corrections. Alpha-particle accumulation is shown to have serious effects on ignition requirements. An analytical model developed to predict the effect of sawtooth disruption on ash accumulation is discussed. The analytical results indicate that the sawtooth is effective when the temperature profile is parabolic or flatter. Alpha-particle ejection by a fishbone oscillation is envisaged to be helpful in ash control, and a model of the physics in a large-aspect-ratio approximation is discussed using an extended version of a Chen et al. formalism. The trapped particle destabilization of the internal kinks due to the alpha particles and a second hot-particle species is considered, and the expected oscillation frequency and growth rates are derived.