Revision of the theory of energetic-particle modes in tokamaks

Abstract

The investigation of instabilities driven by fast ions in tokamaks represents one of the central problems of the physics of collective processes in magneto-thermonuclear reactors. This area of physics has been developed in view of the design of the International Thermonuclear Experimental Reactor (ITER) [1]. In the framework of such an investigation, a class of instabilities called “energetic-particle modes” was predicted in [2‐6], whose authors stated that energetic ions not only drive these modes but are also responsible for their existence. In this work, we show that the theory of energetic-particle modes is invalid, because it is based on electrodynamic equations that disregard the effect of the drift of electrons in crossed fields, which compensate the electric charge of energetic ions. This effect was initially taken into account in [7], and its physical meaning was explained in [8], where it was noted that the effect under discussion is physically similar to the Varma‐ Shukla effect studied in the physics of dusty plasma [9]. As was mentioned in [4], energetic-particle modes are negative-energy waves. At the same time, according to the general concepts [10], such waves can exist only if the contribution of energetic ions to the equation for perturbations is not small as compared to other terms of this equation. We show that, in the approximation of large orbits of energetic particles, which is used in the theory of energetic-particle modes [2‐6], their contribution represents a small addition compared to the con