Friday, September 29, 2017
Cross-scale interactions among turbulence and zonal flows involving multiple spatiotemporal scales have emerged as a key issue in transport studies of fusion plasma. In this talk, we would like to discuss three topics of homogeneous gyrokinetic turbulence simulations which have been carried out by use of peta-scale computers. Enhancement of the ion scale transport observed in the ion and electron temperature gradient (ITG and ETG) turbulence has been investigated by means of the entropy transfer analysis which confirms contribution of ETGs to zonal flow damping in a sub-ion gyroradius scale. Suppression of the micro-tearing mode (MTM) turbulence by the ETG mode growth is also found in our recent simulations, where current sheet structures of the MTM turbulence are destroyed by ETG fluctuations. The last topic is related to a multi-scale mode structure along toroidal field lines brought by low magnetic shear or by fast passing motions of electrons. Enhanced parallel correlation of drift wave turbulence fluctuations in a flux tube simulation leads to a lower saturation level of turbulence, and results in reduction of transport levels, suggesting that careful verification studies are necessary.