'Clumps' as enhanced correlations and turbulent Debye screening

Turbulent correlations in a collisionless plasma are calculated in the lowest approximation which goes beyond the Dupree-Weinstock description by taking trajectory correlations into account. For neighbouring particles in velocity space these effects are shown to reduce the relative diffusion process and to enhance the stationary correlations up to distances of 102 or 103 Debye lengths. Such effects were previously interpreted by Dupree et al. in terms of macroparticles called 'clumps'. Clumps lifetime and clump dimensions are compared with Dupree's result and are generalized to two and three dimensions where tensorial effects appear. It is shown that the clump size (for given lifetime) is much larger than predicted by Dupree. For such 'anomalous effects' a different physical explanation is proposed, where a 'clump' is interpreted as a turbulent generalization of the Debye sphere, rather than a discrete macroparticle. This interpretation of the turbulent screening seems to be in agreement with recent calculations of the effective turbulent potential by Tegeback and Stenflo. (author)