Nonlocal dc electrical conductivity of a Lorentz plasma in a stochastic magnetic field

The stochastic wandering of magnetic field lines allows momentum of even perfectly magnetized electrons to be transported across the mean B. We include this effect, along with the usual acceleration and scattering terms, in a spatially one-dimensional Boltzmann equation for the electron distribution function. For an electric field E/sub parallel/ (along local B) which varies versus position normal to B, the momentum transport leads to a nonlocal electrical conductivity. We apply the formalism to sheared, force-free magnetoplasmas, in which the E/sub parallel/ gradient is caused by variable twisting of B with respect to an externally applied uniform E. We examine in particular the experimentally documented phenomenon of field-aligned current density j/sub parallel/>0 in regions of the sheared magnetic field where E/sub parallel/roughly-equal0 or even E/sub parallel/<0. This phenomenon is in apparent violation of Ohm's law. Under suitable conditions of stochasticity and collisionality, we find that the spatial structure and temporal persistence of these force-free configurations can be directly caused by electron-momentum transport. This result is derived solely on the basis of electron dynamics. In contrast to fluid-turbulent models, our kinetic derivation requires no hypothetical ''plasma dynamo'' and no conjecture on the decay rates of magnetic helicity versus magnetic energy