Negative magnetic shear modes of operation in the Alcator C-Mod tokamak near the beta limit

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Abstract
The stability properties of non-inductively driven, reversed-shear type current profiles that may be achieved for Alcator C-Mod tokamak-like parameters (aspect ratio R/a = 3) are examined. It is found that without a conducting wall, the best stability results ( up to 3.7) are achieved for highly triangular plasmas at , for relatively broad pressure profiles and large values of . For elliptical or circular cross-sectional plasmas with little triangularity, the stability limits are significantly lower ). Finally, more-peaked pressure profiles have lower beta limits than broader profiles.