Verification of the classical theory of helical transport in stellarators

The apparent discrepancies of the classical theory of helical transport in stellarators, versus two recent numerical studies of stellarator transport, are investigated. Numerical results are presented, verifying the classical theory, when the model for the magnetic field has the simple form assumed by the classical theory. When the helical contribution to the total transport is isolated numerically, and the different energy dependence of the particle distribution is accounted for, the results of one of the numerical studies is brought into substantial agreement with theory. It is argued that the anomalously favorable low collisionality results of the second numerical study are due partially to numerical procedure, and partly to a more complicated spatial dependence of the magnetic field.