Neoclassical transport is studied for large helical device (LHD) configurations in which the magnetic axis has been shifted radially by determining the mono-energetic transport coefficient and the effective helical ripple. With respect to the transport in the long mean-free-path collisionality region—the so-called 1/ν transport—the optimum configuration is found when the magnetic axis has a major radius of 3.53 m, which is 0.22 m inward shifted from the `standard' configuration of LHD. In the optimized case, the effective helical ripple is very small, remaining below 2% inside (4/5) of the plasma radius. This indicates that a strong inward shift of the magnetic axis in the LHD can diminish the neoclassical transport to a level typical of so-called `advanced stellarators'.
Analysis of neoclassical transport in the banana regime with the DKES code for the Large Helical Device