Turbulence

Abstract

It is striking to compare the predictions of plasma stability theory with experiment. In theory, almost every confined distribution of plasma is unstable to the exponential growth of a wide spectrum of modes of oscillation; in practice, most plasma physics experiments show a spectrum of random fluctuations which does not grow exponentially, and is indeed almost constant over the time scale suggested by the theoretical growth rates—rather they grow and decay on the much longer time scale of the existence of the plasma. It is reasonable to believe that these fluctuations represent the visible evidence of the theoretically predicted instability, but then we must suppose that the fluctuations themselves alter the properties of the plasma sufficiently to suppress the predicted growth. (For similar reasons, the identification of any observed mode of plasma oscillation with a predicted unstable mode requires rather more careful justification than is usually given.)