A mixed Bohm-gyro-Bohm, shear dependent thermal diffusion coefficient to model the anomalous thermal transport in tokamaks is proposed. It is derived on the basis of recent findings on the radial correlation length of turbulent processes generated by small scale, collisionless, electrostatic microinstabilities (Romanelli, F., Zonca, F., Phys. Fluids 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.
Microinstability-based model for anomalous thermal confinement in tokamaks