A GENERAL EMPIRICALLY BASED MICROINSTABILITY TRANSPORT MODEL

A mixed Bohm-gyro-Bohm, shear dependent thermal diffusion coefficient to model the anomalous thermal transport in tokamaks is proposed. It i s derived on the basis of recent findings on the radial correlation le ngth of turbulent processes generated by small scale, collisionless, e lectrostatic microinstabilities (Romanelli, F., Zonca, F., Phys. Fluid s B 5 (1993) 4081). The model has been used to describe standard L and H mode discharges of the JET, DIII-D and TFTR devices and JET pellet enhanced performance (PEP) and hot ion mode discharges successfully.