Plasma studies for an upgraded TFTR experiment

During the summer of 1991 studies were requested and performed for the possibility of upgrading the TFTR plasma both in current capabilities and volume within the existing vacuum vessel. Additionally, many other constraints were imposed upon the problem description and possible solutions were investigated in turn incorporating the limitations necessitated by the existing TFTR facility. This paper formalizes the results obtained from this study. Several different plasma profiles were investigated and these are summarized in this paper. For plasma stability the q value at the plasma edge was never allowed to go below 3.0 in any of the different modes which were studied. These modes included: (1) A circular plasma which would effectively fill the entire vacuum vessel with the aim of achieving the highest plasma current within the q limitation. (2) A double nulled diverted D-shaped plasma to effectively use the vacuum vessel volume. (3) A single nulled diverted offset teardrop plasma to effectively use the vacuum vessel volume. In each of these cases the various input parameters were changed and the starting point, with respect to the poloidal coils, was to maintain the existing, though complicated, coil interconnection scheme for ease in reconfiguring of the TFTR device. If this proved impractical from a solution perspective the individual coils were then regrouped in order to minimize PF coil currents and maintain force limitations.