Suppression of plasma instabilities by the feedback method
A new method of suppressing plasma instabilities with the aid of automatic control systems has been recently developed. The feasibility of using this method to stabilize a continuous medium is brought about by the fact that not all of the tremendous number of degrees of freedom of the medium are actually excited, but only several of the modes. The method is most suitable in practice for the suppression of large-scale oscillations. Two stabilization methods have been observed. An external control system can be used to alter the phase velocities of the waves in the plasma, thus upsetting their resonant interaction with the particles and with one another. This suppresses strong instabilities with large growth rates, particularly hydrodynamic ones (flute, helical, etc.). To eliminate instabilities of the dissipative type with small growth rates it suffices to use an external system to introduce additional damping of the plasma oscillations. The possibility of turning individual modes on or off makes feedback an outstanding tool for the study of nonlinear properties of oscillations, anoalous transport phenomena, and others. The first experiments in this direction have already been performed.