Stabilization of large-scale fluctuations in noise-driven plasmas by magnetic field

The stability of large-scale fluctuations in plasmas driven by the parity-nonconserving (PNC) noise is studied. The noise may model such short-scale turbulence as the drift waves of short wave lengths. It is known that the relative strength of the PNC noise greater than similar to ln R/R, where R is the ratio of the largest to the smallest scales, destabilizes the plasma. As a result, largescale fluctuations emerge and grow in time. It is shown that a homogeneous magnetic field, which exists either as a result of the growth of large scales or by external means, can stabilize the plasma. The stability diagram of the marginally unstable plasma is plotted in terms of the magnetic Prandtl number Pm and the Hartmann number H. It is found that the plasma is stable if Pm > (1 + root 5)/2 in the limit H -> 0. In another limit P-m -> infinity, the finite critical size of the magnetic field (i.e. H-c) is found to exist.