Parallel Viscous Force Densities

In the so-called *banana collisionality regime*,
[see Equation (2.95)], the flux-surface averaged parallel viscous force densities take the form [22,34,43]

(2.207) | ||

(2.208) |

In the banana collisionality regime, the parallel viscous force arises from collisional drag between passing and trapped particles [22,43]. The origin of this drag is the fact that, while passing particles can drift along magnetic field-lines in one direction, trapped particles are forced to periodically reverse direction. Not surprisingly, the viscous force density is proportional to the fraction of trapped particles, . [See Equation (2.203).]