Bremen 2017 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 13: Magnetic Confinement

P 13.14: Poster

Dienstag, 14. März 2017, 16:30–18:30, HS Foyer

Scaling of Zonal Flow Power with Shearing Rate — •Rafael Carmona Cabezas, Til Ullmann, and Mirko Ramisch — Institut für Grenzflächenverfahrenstechnik und Plasmatechnologie, Pfaffenwaldring 31, Stuttgart, Deutschland

In toroidal magnetic plasma confinement, zonal flows (ZF) play an important role in regulating drift-wave turbulence and, thus, edge cross-field transport. These flows are driven by gradients in turbulent Reynold stress, which is related with an average vortex tilt in the turbulent fluctuations. Thus, an already present background shear flow is expected to favour the ZF drive by tilting eddies.

In this work, the dependence of ZF amplitude on background ExB flow shear is investigated. To this end, the shearing rate of radially localized and stationary poloidal ExB flows are controlled via external plasma biasing. Different types of biasing electrodes are employed. Radial profiles of the ExB flow are measured by means of a movable emissive probe. At the same time, fluctuations in plasma density and potential are acquired using a poloidal 64-Langmuir probe array situated on one magnetic flux surface. The amplitude of the poloidally averaged potential fluctuations has proven useful as a good approximation for the time-varying ZF. This way, ZF power is detected, experimentally, and correlated with background flow shear.