Structure and transport of ion temperature gradient modes in global X-point geometry

Global simulations of ITG modes in X-point geometry are carried out using JOREK, including the scrape-off layer in the simulation domain. Using two-fluid equations, the model focuses on the effects of poloidal, m, and toroidal, n, mode coupling. Poloidal coupling is responsible for the ballooning structure, which along with toroidal coupling generates turbulence and permits the formation of large-scale structures, such as zonal flows. Simulations of several JET and COMPASS discharges show characteristic differences, originating largely from differing magnetic shear. In single-n simulations, where ballooning modes appear, they exhibit large ballooning angles, with a poloidal structure, m, radially shifted outwards by the distance of several rational surfaces. Several trends in this ballooning shift are shown (for both individual m, and the mode overall), and compared to theoretical models, previously expected to only generate much smaller shifts. Multi-n simulations detail qualitatively-different energy spectra, along with differing spatial distributions, and temporal variations in heat transfer, relating to the distinct parent mode structures from the single-n simulations.