The kinetic theory of runaway electron beam instability in a tokamak

The paper considers the effects associated with the development of accelerated electron beam instability in a tokamak. The authors have investigated the microscopic stage of instability development in greater detail than in their earlier work. The instability threshold has been found by taking the actual distribution function into account. It is shown that the development of instability comprises two stages — isotropization of electrons due to the anomalous Doppler effect and subsequent formation of a plateau on the electron distribution function. It is at the second stage that oscillations of noticeable energy occur. It is demonstrated that the result of quasi-linear relaxation depends substantially on whether or not the oscillations pass out of the resonance region during instability development. The detailed picture which emerged made it possible to evaluate the basic macroscopic effects — the number of trapped electrons and their energy, the magnitude of ion heating and the sign and magnitude of spikes on the voltage curve. The evaluations obtained give a correct qualitative and, in some cases, quantitative description of the dependences measured experimentally.