Computation of the Spitzer function in stellarators and tokamaks with finite collisionality

The generalized Spitzer function, which determines the current drive efficiency in tokamaks and stellarators is modelled for finite plasma collisionality with help of the drift kinetic equation solver NE0-2 [1]. The effect of finite collisionality on the global ECCD efficiency in a tokamak is studied using results of the code NE0-2 as input to the ray tracing code TRAVIS [2]. As it is known [3], specific features of the generalized Spitzer function, which are absent in asymptotic (collisionless or highly collisional) regimes result in current drive from a symmetric microwave spectrum with respect to parallel wave numbers. Due to this effect the direction of the current may become independent of the microwave beam launch angle in advanced ECCD scenarii (02 and X3) where due to relatively low optical depth a significant amount of power is absorbed by trapped particles.