Session RP1 - Poster Session VIII.
POSTER session, Thursday afternoon, October 30
Fran Hill Southeast Exhibit Hall, ACC
This work examines the impact of both the plasma current profile and external coil currents on ideal MHD stability in the Quasi-Poloidal Stellarator (QPS) [1]. The reference coil set for QPS contains 20 modular coils with 5 different coil shapes with each of the 4 coils of a given shape forming a group with a separate power supply. In addition to the modular coils, there are also a set of toroidal field coils and 3 pairs of vertical field coils. This coil set allows for flexible variation of the magnetic configuration. QPS has been designed to run with a bootstrap aligned current profile but will also have the capability of driving Ohmic current. By varying both the external coil currents and the plasma current profile, the ideal MHD stability properties of QPS can be greatly impacted. The infinite-n ballooning \beta limit can vary by a factor of ~2. The marginal ballooning \beta limit is lowest with an Ohmic current profile, highest with a bootstrap current profile, and can be varied between these limits with a combination of Ohmic and bootstrap current. As expected, finite-n ballooning modes (for n up to 19) have higher \beta limits, roughly 50-100% higher than the infinite-n limit for QPS. Kink and vertical modes are stable in QPS to much higher plasma \beta (> 5%). [1] J. F. Lyon, et al., “Physics and Engineering Design of a Very-Low-Aspect-Ratio Quasi-Poloidal Stellarator”, in preparation for Nucl. Fusion, (2003).