Blob dynamics in 3D BOUT simulations of tokamak edge turbulence

Propagating filaments of enhanced plasma density, or blobs, observed in 3D numerical simulations of a diverted, neutral-fueled tokamak are studied. Fluctuations of vorticity, electrical potential phi, temperature T-e, and current density J(parallel to) associated with the blobs have a dipole structure perpendicular to the magnetic field and propagate radially with large ExB drift velocities (>1 km/s). The simulation results are consistent with a 3D blob dynamics model that incorporates increased parallel plasma resistivity (from neutral cooling of the X-point region), blob disconnection from the divertor sheath, X-point closure of the current loops, and collisional physics to sustain the phi, T-e, J(parallel to) dipoles.