Full Paper
Contents  Return  Previous Page  Next Page  Index

Return To: Session EX/S3 & IC & TH/6 - Helical
Prev Page: Session EX/S3 & IC & TH/6 - Helical
Next Page: (EX/S3-2) MHD Instabilities and Their Effects on Plasma

(EX/S3-1) Investigation of the Beta-Limit in the W7-AS Stellarator

A. Weller1), J. Geiger1), M. Zarnstorff2), E. Sallander1), S. Klose1), A. Werner1), J. Baldzuhn1), R. Brakel1), R. Burhenn1), H. Ehmler1), F. Gadelmeier1), L. Giannone1), D. Hartmann1), R. Jaenicke1), J. Knauer1), H.P. Laqua1), C. Nührenberg1), E. Pasch1), N. Rust1), E. Speth1), D.A. Spong3), F. Wagner1), U. Wenzel1), W7-AS Team1), NBI-Group1)
1) Max-Planck-Institut für Plasmaphysik, IPP-Euratom Association, Garching, Greifswald, Berlin, Germany
2) Princeton Plasma Physics Laboratory, Princeton, NJ, USA
3) Oak Ridge National Laboratory, Oak Ridge, TN, USA

Abstract.  Investigations of the performance and stability of high-beta plasmas have been restarted in W7-AS utilizing higher heating powers and the new divertor system. The combination of beneficial effects resulted in a significant increase of the volume averaged $ \beta$ from 2 % up to 3.1 % and in MHD-quiescent, quasi-stationary discharges at low radiation levels. Experimental studies of equilibrium effects and of MHD mode activity have been performed with the X-ray tomography system. In addition results of computational MHD stability studies are presented, which show an increase of the stability with increasing $ \beta$ due to the pressure induced deepening of the magnetic well in combination with increasing magnetic shear, in qualitative agreement with the experimental data. The maximum achieved $ \beta$ is limited by the available heating power and not by stability effects. The equilibrium $ \beta$-limit is approached in the case of low-iota configurations. Particularly with regard to current carrying stellarators and comparisons with tokamaks the modification of the stability of high-beta plasmas by significant OH-currents has been investigated.

Read the full paper in PDF format.

IAEA 2003