Nonlocal effects in gyrokinetic simulations of turbulent transport in the edge pedestal

The local flux-tube formulation for gyrokinetic simulations, valid in the small rho-star limit, provides a robust and efficient method for understanding critical properties of anomalous plasma transport. However, for plasma regions where the density and temperature scale lengths are only a small fraction of the device size, the validity of the local model becomes questionable. The validity cannot be assessed by comparing local simulation with a nonlocal simulation that uses artificial sources and boundary conditions, as is done in most nonlocal gyrokinnetic simulations. We will use GEM to perform both local and nonlocal simulations for parameters representative of H-mode pedestal conditions. Preliminary results indicate that turbulence spreading, a process beyond the local model, frequently occurs in nonlocal simulations of pedestal. In order to assess the boundary effects in nonlocal simulations, we will implement arbitrary time-dependent Dirichlet boundary condition in GEM's ffield solvers to model the effects of the scrape-off layer turbulence on the pedestal. A buffer region outside the field solver boundary will be used to improve the boundary condition for the distribution function. Ad hoc particle and heat sources will be used to prevent profile relaxation and ensure steady-state transport. The effects of these sources, as well as the impact of shearing driven by a fixed Dirichlet radial boundary conditions, will be assessed.