Gyrokinetic simulations of entropy transfer in high ion temperature LHD plasmas

Gyrokinetic simulations of the ion temperature gradient (ITG) turbulence in non-axisymmetric configurations modeled on the Large Helical Device (LHD) are performed with the entropy transfer analysis (Nakata et al 2012 Phys. Plasmas 19 022303). It is clarified that a fluctuation spectrum elongated in the radial wavenumber direction is formed in a neoclassically optimized field configuration with the inward-shifted magnetic axis position, where the zonal flows are more effectively generated than in the standard case. The strong interaction between zonal flows and turbulence causes the successive entropy transfer from low to high radial wavenumber space and the spectral broadening of ITG turbulence. (paper)