Properties of Low Beta, Saturated Drift Alfvén Microturbulence, P.W. Terry and E. Fernandez, to be presented at 1996 APS Division of Plasma Physics Meeting.
Power spectrum measurements of magnetic turbulence in the reversed field pinch and in low q tokamak discharges indicate that single fluid MHD is inadequate to recover the steep spectral decay rates (a » 2.6) observed in experiment. Examination of a two-fluid drift Alfvén model for low beta turbulence reveals the following properties: 1) in the regime where Alfvénic propagation yields the shortest correlation time, cross correlations of fluctuating fields govern saturation instead of the hyper-resistive damping (or other nonlinear damping rates proportional to fluctuation energy) often invoked in theory; 2) magnetic and kinetic energy transfers are controlled by disparate decorrelation rates, the former by Alfvénic propagation along large scale magnetic fields, the latter by fluid advection; 3) steep spectral decay rates like those of experiment are possible when the diamagnetic frequency is as large as eddy damping rates. These results indicate that the scaling of magnetic turbulence and transport with respect to parameters such as the Lundquist number must be revisited theoretically, that saturation and transport fluxes are more directly linked than they are in electrostatic turbulence, and that cross-correlation dynamics must be understood in order to accurately predict spectra and transport.