Ion temperature gradient modes and neoclassical ripple transport in multiple-helicity fields

Effects of multiple-helicity magnetic fields oil ion temperature gradient (ITG) modes in toroidal helical systems like the Large Helical Device (LHD) are studied by means of the linear gyrokinetic theory. Especially, dependence of the real frequency, growth rate, and the eigenfunction of the ITG mode on sideband-helicity fields added to the main helical component is investigated in both unstable and stable regions. A comparison between multiple-helicity effects Oil the ITG mode with those on the neoclassical ripple transport is presented. and optimization of the magnetic configuration for better plasma confinement is discussed.