Plasma blobs in a basic toroidal experiment: Origin, dynamics, and induced transport

Detaching plasma blobs with very similar properties to tokamaks are observed in the basic toroidal plasma experiment TORPEX [ A. Fasoli et al., Phys. Plasmas 13, 055902 (2006) ]. The blobs originate from the breaking of wave crests of a drift-interchange wave, which span over regions characterized by strongly inhomogeneous background parameters. Once decoupled from the wave, the blobs follow a predominantly radial trajectory pattern. The blob-induced cross-field transport can instantaneously exceed the steady-state parallel fluxes by one order of magnitude, while accounting for only 10% of the time-average device losses. If the particles were confined in the parallel direction, as is the case in tokamaks, blobs would constitute the dominant loss mechanism in TORPEX. The presented results show that the presence of grad B is sufficient and neither a magnetic-topology change nor the presence of limiters, both absent in TORPEX, are necessary for the generation of blobs.