Stefan Mueller
Centre de Recherches en Physique des Plasmas
Association EURATOM/Ecole Polytechnique
Lausanne, Switzerland

ABSTRACT:

Gradient driven electrostatic instabilities are investigated on the TORPEX toroidal device (R=1m, a=0.2m). Plasmas with ne"1017m-3 and Te=5eV are produced by injection of microwaves with f=2.45GHz, in the EC frequency range. The magnetic field is mainly toroidal (" 0.1T), with a small vertical component. A quasi-equilibrium is achieved via parallel flows that short circuit drift-induced charge separation. The related confinement time and the fluctuation properties depend strongly on the vertical field, which can thus be used as a control parameter. Fluctuation statistical and spectral properties are reconstructed over the whole plasma cross-section. Instabilities that can be generally identified as drift-interchange waves are observed, with more turbulent character as collisionality with neutrals is increased. An 86-tip probe is used to reconstruct the spatio-temporal evolution of turbulent structures across the plasma cross-section. The measured structures are characterized statistically, and the distribution of related quantitative observables, such as their position, size, velocity, and trajectories are evaluated. The algorithms to operate this characterization will be discussed, along with the adaptation of the two-fluid code ESEL for a comparison with TORPEX data.

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