Evaluation of 1/nu neoclassical transport in stellarators

Using an analytic solution of the kinetic equation in the 1/nu regime, a ne w formula for the neoclassical transport coefficients is obtained which tak es into account all classes of trapped particles. This formula holds in any coordinate system and no simplifying assumptions about the magnetic field are needed. Therefore it is also applicable to complex magnetic fields give n in real space coordinates. The method and the results can be used to opti mize magnetic field configurations with respect to the 1/nu regime. The met hod is bench-marked against Monte Carlo calculation both for the l=3 classi cal stellarator model and also for the original Helias configuration [J. Nu hrenberg and R. Zille, Phys. Lett. A 114, 129 (1986)] with a more complex m agnetic field structure. Some features of transport for Helias are clarifie d by analyzing the bounce-averaged drift velocity. (C) 1999 American Instit ute of Physics. [S1070-664X(99)00412-7].