POINCARE MAPS DEFINE TOPOGRAPHY OF VLASOV DISTRIBUTION-FUNCTIONS CONSISTENT WITH STOCHASTIC DYNAMICS

In a recent paper [A. D. Bailey et al., Phys. Rev. Lett. 34, 3124 (199 3)], the authors presented direct planar laser induced fluorescence me asurements of the oscillatory ion fluid velocity field in the presence of a large amplitude drift-Alfven wave. Surprisingly, the measured sp eeds were an order of magnitude lower than predicted by standard fluid theory, yet the flow pattern was consistent with the fluid theory. A new model, based on the connection between stochasticity and bull; beh avior, is presented which gives insights into the cause of this behavi or. It is shown that when particle motion is stochastic, invariant set s of a 'Poincare map' define a flat-topped particle distribution funct ion consistent with both the electromagnetic field driving the Vlasov equation and the fine-scale single particle dynamics. The approach is described for the general case and explored for a slab model of the ob served drift wave. (C) 1995 American Institute of Physics.