ROTATION SHEAR-INDUCED FLUCTUATION DECORRELATION IN A TOROIDAL PLASMA

The enhanced decorrelation of fluctuations by the combined effects of the ExB flow (V(E)) shear, the parallel flow (V(parallel-to)) shear, a nd the magnetic shear is studied in toroidal geometry. A two-point non linear analysis previously utilized in a cylindrical model [Phys. Flui ds B 2, 1 (1990)] shows that the reduction of the radial correlation l ength below its ambient turbulence value (DELTAr0) is characterized by the ratio between the shearing rate omega(s), and the ambient turbule nce scattering rate DELTAomega(T). The derived shearing rate is given by omega(s)2 = (DELTAr0)2[(1/DELTAphi2){(partial derivative/partial de rivative r)(qV(E)/r)}2 +(1/DELTAeta2){(partial derivative/partial deri vative r)(V(parallel-to)/qR)}2], where DELTAphi and DELTAeta are the c orrelation angles of the ambient turbulence along the toroidal and par allel directions. This result deviates significantly from the cylindri cal result for high magnetic shear or for ballooning-like fluctuations . For suppression of flute-like fluctuations, only the radial shear of qV(E)/r contributes, and the radial shear of V(parallel-to)/qR is irr elevant regardless of the plasma rotation direction.