The Effect on Stellarator Neoclassical Transport of a Fluctuating Electrostatic Spectrum
Authors: H.E. Mynick and A.H. Boozer
Date of PPPL Report: November 2004
Published in: Physics of Plasmas 12:6 (June 2005) Article No. 062513 (9 pages)
We study the effect on neoclassical transport of applying a fluctuating electrostatic spectrum, such as produced either by plasma turbulence, or imposed externally. For tokamaks, it is usually assumed that the neoclassical and "anomalous" contributions to the transport roughly superpose, D = Dnc + Dan, an intuition also used in modeling stellarators. An alternate intuition, however, is one where it is the collisional and anomalous scattering frequencies which superpose, νef = ν + νan. For nonaxisymmetric systems, in regimes where ∂D/∂ν < 0, this "νef picture" implies that turning on the fluctuations can decrease the total radial transport. Using numerical and analytic means, it is found that the total transport has contributions conforming to each of these intuitions, either of which can dominate. In particular, for stellarators, the νef picture is often valid, producing transport behavior differing from tokamaks.