Is there a dynamic effect in the screening of nuclear reactions in stellarplasmas?

We investigate the following two questions of principle: (1) Does the ion's kinetic energy affect its electrostatic potential energy when the ion is in statistical equilibrium with the plasma? In other words , is there a difference between a potential energy of a test particle movin g in the plasma and the potential energy of a particle in statistical equil ibrium with the plasma? (II) Does the effect of the plasma on the rate of the nuclear reaction depe nd on kinetic energy? The two issues are important for evaluating the plasma effect on nuclear re actions in astrophysical plasmas. The first effect was calculated by Carrar o et al. (1988) and found to be significant. However, criticism by several authors (Brown and Sawyer, 1997; Weneser, 1996; Gruzinov, 1997) claim that there is no such effect. We examine the relevant statistical mechanics assu mptions and in the lack of a complete rigorous proof check them numerically . We find that the potential energy per particle for particles which are in statistical equilibrium is indeed independent of the potential energy of t he particle at least for particles with kinetic energy up to 10 kT. The sec ond question has to do with the kinetics of the collision between two parti cles in the presence of ambient plasma particles. We discuss this point and obtain the kinetic energy dependence of this interaction and relate it to the so-called 'screening effect'. The same numerical calculation which yields the result that the potential e nergy does not depend on the kinetic energy yields the result that the plas ma loses energy to relatively slow particles and vice versa. (C) 1999 Elsev ier Science B.V. All rights reserved.