Tornado-like transport in a heated magnetized plasma*

A transient, large-scale, spiraling flow-pattern, akin to a tornado, is observed to spontaneously form in a transport experiment performed in the Large Plasma Device (LAPD) at UCLA in which a magnetized, ring-shaped region of elevated temperature is created within a large, pre-existing, cold plasma. The structure is generated by applying a voltage pulse (~15V) to a thermionic-emitting LaB₆ ring cathode during the afterglow phase of the main discharge. Significant density changes (~30%) are produced far from the heated region by the spiral arms. The presence of sheared flow introduces azimuthal phase-mixing that relaxes the tornado to an organized state of marginal stability, priming the plasma for future avalanche-like events. Detailed measurements of the spatio-temporal evolution of the tornado and its impact on cross-field transport are compared to the predictions of a Braginskii transport model that incorporates the self-consistent evolution of vorticity sourced by emissive-sheath boundaries.