Expression for the ExB flow shear rate is improved in the XGC-0 code

The ExB flow shear rate has been implemented as simple derivative of the radial electric field with respect to minor radius:

$omega_{rm ExB}equivfrac{partial E_r}{partial r}.$

New implementation is according to Ref. [T.S. Hahm and K.H. Burrell Phys. Plasmas 2, 1648 (1995)]:

$omega_{rm ExB}equiv left|frac{R B_theta}{B_phi}frac{partial}{partial r} left(frac{E_r}{R B_theta}right)right|,$

where $B_theta$ and $B_phi$ are the poloidal and toroidal components of the magnetic field.

Integrated Modeling of Tokamak Plasmas