The mixed Bohm/gyro-Bohm anomalous transport model (also called JETTO transport model) contains Bohm and gyro-Bohm contributions. The Bohm contribution, which is linear in the gyro-radius, is a non-local transport model, in which the transport thoughout the plasma depends on a finite difference approximation to the electron temperature gradient at the edge of the plasma. The gyro-Bohm contribution is a local transport model, which is porportional to the square of the gyro-radius. The version implemented in TRANSP is described in the work by Erba et al (Nucl. Fusion 38 (1998) 1013), while the magnetic and flow shear stabilization are described in the work by T. Tala (Plasma Phys. Controll. Fusion 44 (2002) A495).
The Bohm scaling term is expressed as:
where ΔTe is a finite difference approximation to the normalized electron temperature difference at the plasma edge
The gyro-Bohm scaling term is expressed as:
The resulting anomalous ion and electron thermal diffusivities are constructed from the sum of these Bohm and gyro-Bohm terms, with empirically determined coefficients. For JET:
and the hydrogenic charged particle diffusivity is given by:
