Filament dynamics in presence of X-point in turbulence simulations

We investigate the impact on filamentary transport of the presence of X-points with turbulence simulations of the WEST tokamak using the TOKAM3X code. A blob recognition and tracking algorithm resolves the time evolution of the 3D filamentary structures, complemented by 2D and 3D conditional average sampling techniques. As a result, the single blobs exhibit complex trajectories with non-negligible mutual interactions in between filaments and with the turbulent background plasma. On average the blob dynamics are well described by the theoretically derived scalings of blob radial velocities against their size, showing a transition from the sheath connected regime to the ideal interchange one close to the separatrix, where the blobs disconnect from the target plates. In this work, we propose an additional mechanism for blob disconnection, namely the poloidal shear in radial EXB velocity, spontaneously arising in diverted plasmas at the X-point as the topology changes from closed to open field lines, and we compare it with the commonly accepted disconnection through high flux expansion and magnetic shear in the X-point region.