Three-dimensional simulations of blob dynamics in a simple magnetized torus

The propagation of blobs, structures of localized enhanced plasma pressure, is studied in global three-dimensional simulations of a simple magnetized torus. In particular, we carry out single-seeded blob simulations to explore the dependence of the blob velocity with respect to its size. It is found that the velocity scaling for two-dimensional blobs is satisfied in the parameter space where polarization currents are the dominant damping mechanism. On the other hand, three-dimensional blobs propagate faster than their two-dimensional counterparts in the parallel current damping regime. A detailed analysis of the charge and current balance reveals that, in fact, the difference in speed is due to an overestimation of the strength of the sheath current term in the two-dimensional model compared to the self-consistent three-dimensional model.