Merging dynamics of unidirectional current carrying filamentary plasma blobs in the edge region of a tokamak

We report on a model study of the merging of two electromagnetically interacting blobs, which have unidirectional currents and are located in the tokamak edge region in a high beta plasma. Unlike the conventional plasma blobs with dipolar currents that originate from resistive drift/interchange plasma turbulence, these unidirectional filamentary blobs arise from edge-localized mode ejection events. Two such blobs can interact strongly in the edge region to merge with each other in the poloidal direction. Our detailed simulations reveal that the blobs rotate about each other during the merging process and the merging occurs with a rate of acceleration in the poloidal direction that is directly proportional to the square of the current density of the blobs and inversely proportional to its density. We also derive an analytic condition for two poloidally separated plasma blobs to merge poloidally without a significant movement in the radial direction. Numerical simulations support this analytical condition. The separation distance between two high current density blobs is also seen to exhibit a sloshing behavior. For a given blob radius and density, the radial velocity during merging decreases with the strength of the unidirectional current density.