Aachen PK 2003 – wissenschaftliches Programm
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P: Plasmaphysik
P 4: Poster I
P 4.19: Poster
Montag, 17. März 2003, 17:45–19:15, Foyer
Self excitation of quasi-coherent modes in curved magnetic fields — •Franko Greiner1, Dietmar Block1, Alexander Piel1, Kristoffer Rypdal2, and Svetlana Ratynskaia2 — 1IEAP, Christian Albrechts Universit"at zu Kiel, 24098 Kiel, Germany — 2Department of Physics, University of Tromsø, Norway
The simple magnetised torus (SMT) seems to be the genereric configuration for self excited curvature driven instabilities. In fact, large scale stuctures are observed in the low frequency fluctuations of various SMT-configurations. We present a detailed investigations carried out in the BLAAMANN experiment at Tromsø University. We find, that the observed structures are flute-like quasi-coherent modes. They arise from the region of high density gradient on the weak field side of the torus, i. e. in regions with a predicted positive growth rate. The main charateristics of these modes do not depend on the specific plasma potential profile, which can be changed from a deep negative well (filament source) to a large positive hump (helicon source). The life time of the quasi coherent modes is much longer than the auto correlation time of the background fluctuations. The modes move arround the plasma column with local E× B-velocity following equi-potential lines. The phase between potential and density fluctuations is π/2 in all cases. The power spectra show the typical power law behavior of strong turbulence combined with a notable peak at the frequency of the flute modes.