Fluctuations and Particle Collisions

Abstract

An important problem in plasma physics is the description of particle collisions and another problem is the question of what is the nature of the statistical fluctuations in a plasma when there are no external fields or strong collective oscillations. At first sight these two problems are unrelated but, in fact, they are related to one another. In discussing fluctuations when there are no fields present we shall consider the case of an arbitrary particle distribution which could be any non-equilibrium distribution. If the distribution is a thermal distribution function the fluctuations will be the thermal fluctuations. On the other hand, in the case of a non-equilibrium distribution the fluctuations are not thermal and we can call them the natural fluctuations of a large system of free particles. We shall define this term more precisely in what follows. For the moment we just mention that these fluctuations are closely connected with particle collisions in the plasma. We shall describe these relations in the present chapter and we shall show that collisions between particles in a plasma are quite different from collisions between particles in the absence of other plasma particles.