Bochum 2015 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 22: Helmholtz Graduate School for Plasma Physics II

P 22.2: Fachvortrag

Mittwoch, 4. März 2015, 16:55–17:20, HZO 50

Study of the edge radial electric field during the L-H transition — •Marco Cavedon^1,2, Thomas Puetterich¹, Eleonora Viezzer¹, Gregor Birkenmeier^1,2, Tim Happel¹, Francois Ryter¹, Ulrich Stroth^1,2, and the ASDEX Upgrade Team¹ — ¹Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, D-85748 Garching — ²Physik-Department E28, TUM, D-85748 Garching

The access to the high confinement mode in fusion plasmas occurs through a transport barrier whereby plasma turbulence is reduced by the shear of the edge radial electric field (E_r). The neoclassical theory predicts E_r to be driven by the main plasma ions, as also suggested by experimental observations. A recent upgrade of the charge exchange recombination spectroscopy diagnostic (CXRS) in the ASDEX Upgrade tokamak (AUG) provides a full reconstruction of the impurity density, temperature and E_r profiles and allows us to address the fast dynamics of these quantities during the L-H transition. The characteristic time scale of the L-H transition can be associated to the typical frequency (1-10 kHz) of the fluctuating phases (often called limit cycle oscillations) observed before the L-H transitions. The new CXRS system has a time resolution of 50µs which allows to investigate these phenomena and analyze the causality of the transition mechanism. Correlations between turbulent fluctuations and changes in the edge profile gradients will be presented.