ORBIT CONFINEMENT AND NEOCLASSICAL TRANSPORT IN THE H-1 HELIAC

The neoclassical transport properties of the H-1 heliac are studied using data-parallel versions of guiding centre Monte Carlo techniques. Expressions for the neoclassical transport coefficients valid for electrons and ions over a wide range of plasma conditions are constructed from the Monte Carlo results. These expressions have the functional form of Shaing's analytic model for transport in simpler magnetic configurations, but with geometry dependent coefficients determined by fitting to the Monte Carlo results. The procedure used is quite general and could be used to construct expressions for transport coefficients in other stellarators. Estimates of the energy confinement times are made, and are found to be insensitive to changes in currents in the helical and vertical field coils. Calculations using model magnetic field spectra suggest that heliac configurations with more flexibility in the neoclassical transport properties may be possible, but independent control over currents in the toroidal field (TF) coils and more TF coils per field period would be required.