Electromagnetic gyrokinetic analysis of turbulent transport in finite-beta LHD plasmas

Turbulent transport in finite-beta Large Helical Device (LHD) plasmas is investigated by means of electromagnetic gyrokinetic simulations which enable us to elucidate the impact of the magnetic perturbation on microturbulence. It is found that (1) the ITG mode growth rate decreases with increasing beta, and the kinetic ballooning mode (KBM) becomes a dominant instability for local beta values larger than 2-3% in typical LHD configurations, (2) shearing between oppositely inclined convection cells newly found in the LHD configuration leads to saturation of the KBM instability which is hardly saturated in flux tube simulations of finite-beta tokamaks because of weak zonal flow generation, and (3) the efficiency of KBM turbulence in the transport is much smaller than that of ITG turbulence. (author)