Electrostatic-field fluctuations and form factors in multi-component non-equilibrium plasmas

Taking the Langevin approach to the evaluation of kinetic fluctuations with respect to a Maxwellian distribution characterized by different constant temperatures and mean velocities per species, the form factors and electrostatic field fluctuations of a multi-component plasma are derived. It is shown that the generalization of the Callen-Welton theorem for non-equilibrium systems, derived using thermodynamical arguments, has to be revised. Explicit values of the intensities of the electrostatic-field fluctuations are calculated, in the high-and low-frequency regimes. The former do not require any modelling of the collision integral. The latter have been calculated with a model that is more correct and simpler, than the Bhatnagar-Gross-Krook model. (author)