Full Paper
Contents  Return  Previous Page  Next Page  Index

Return To: Session EX/P3 - DIII-D, T10, HT-7, Small Stellarators,
Prev Page: (EX/P3-08) Modification of Boundary Plasma Behavior by Ion
Next Page: (EX/P3-10) New Results from Globus-M Spherical Tokamak

(EX/P3-09) Performance and Stability Limits at Near-Unity Aspect Ratio in the Pegasus Toroidal Experiment

R. J. Fonck1), S. Diem1), G. Garstka1), M. Kissick1), B. Lewicki1), C. Ostrander1), P. Probert1), M. Reinke1), A. Sontag1), K. Tritz1), E. Unterberg1)
1) University of Wisconsin, Madison, WI, USA

Abstract.  The Pegasus Toroidal Experiment is a mid-sized extremely-low aspect ratio (A) spherical torus (ST). It has the dual roles of exploring limits of ST behavior as A approaches 1 and studying the physics of ST plasmas in the tokamak-spheromak overlap regime. Major parameters are R = 0.25 - 0.45 m, A = 1.1 - 1.4, Ip $ \leq$ 0.15MA, and Bt < 0.07T. High beta plasmas are produced at very low toroidal field by ohmic heating. Values of toroidal beta up to 25% have been obtained, and the operational space of beta vs Ip/aBt is similar to that observed for NBI-heated START discharges. Achievable plasma current apparently is subject to a ``soft'' limit of Ip/Itf $ \leq$ 1. Access to higher-current plasmas appears to be restricted by the appearance of large internal MHD activity, including m/n=2/1 and 3/2 modes. Recent experiments have begun to access ideal stability limits, with disruptions observed as q95 approaches 5, in agreement with numerical predictions.

Read the full paper in PDF format.

IAEA 2003