PSFC/JA-06-20 Short wavelength effect on the collisionless neoclassical polarization and residual zonal flow level

Sheared zonal ‡ow helps to reduce the turbulent transport caused by the ion temperature gradient (ITG) mode. Rosenbluth and Hinton (R-H) calculated the residual zonal ‡ow level for radial wavelengths that are much larger than the ion poloidal gyroradius. Their calculation is extended to treat arbitrary radial wavelengths. For the radial wavelengths that approach the ion poloidal gyroradius, but are much larger than the ion gyroradius, an analytical formula is obtained. For radial wavelengths that are comparable or shorter than the poloidal ion gyroradius and the ion gyroradius a numerical solution is provided. These small radial wavelength results are then extended into the electron temperature gradient (ETG) regime, where the residual zonal ‡ow level is large but ine¤ective in regulating the turbulence, indicating that the conventional R-H explanation that zonal ‡ow regulates turbulence is incomplete.