Understanding non-diffusive transport in gyro-kinetic simulations of electrostatic ITG turbulence in tokamak geometry R. Sanchez 1 , D.E. Newman 2 , J.N. Leboeuf 3 , V. Decyck 4 and B.A. Carreras 5 1 Oak Ridge National Laboratory, Oak Ridge, TN, USA 2 University of Alaska, Fairbanks, AK, USA 3 JNL Scientific Inc, Casa Grande, AZ, USA 4 University of California, Los Angeles, CA, USA 5 BACV Solutions Inc., Oak Ridge, TN, USA It is widely accepted that the rate at which particles, energy or any passive quantity are transported by turbulence can be significantly lowered in the presence of a perpendicular sheared flow. This is a situation of particularly relevance in tokamak plasmas, in which both externally-driven and self-consistently generated (by turbulence itself) sheared poloidal mean flows seem to be central to the formation of radial transport barriers. The reduction of turbulent fluxes along the direction perpendicular to the flow is ultimately related to the fact that the flow can somehow either reduce the amplitude of the fluctuations of the advecting and/or advected fields, or alter the cross-phase between them (or both) [1]. The way in which the flow achieves this suppression is still not well understood. However, it is customary to quantify it in practice by using reduced perpendicular diffusivities/conductivities. We have examined here whether this practice is appropriate and found that it fails to capture correctly the dynamics of transport across sheared flows [2]. These results may have implications not only for the theoretical understanding of the suppression, but for modeling purposes as well. 0 0.2 0.4 0.6 0.8 1 r/a 1.00 1.25 1.50 1.75 2.00 2.25 2.50 Safety factor q 0 5 10 15 20 25 30 35 η i Fig 1.-: (left) η i and safety factor (q) radial profiles used in the simulations; (right) geometry, coordinate definitions and snapshot of temperature fluctuation contours. 35th EPS Conference on Plasma Phys. Hersonissos, 9 - 13 June 2008 ECA Vol.32D, P-1.042 (2008)