Alpha-particle effects on high-n instabilities in tokamaks

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Abstract
Hot alpha particles and thermalized helium ash particles in tokamaks can have significant effects on high toroidal mode number instabilities such as the trapped‐electron drift mode and the kinetically calculated magnetohydrodynamic ballooning mode. In particular, the effects can be stabilizing, destabilizing, or negligible, depending on the parameters involved. In high‐temperature tokamaks capable of producing significant numbers of hot alpha particles, the predominant interaction of the mode with the alpha particles is through resonances of various sorts. In turn, the modes can cause significant anomalous transport of the alpha particles and the helium ash. Here, results of comprehensive linear eigenfrequency–eigenfunction calculations are presented for relevant realistic cases to show these effects.