Configuration, Equilibrium, and Stability Studies for a Small-Aspect-Ratio Tokamak Stellarator Hybrid

A new class of small-aspect-ratio tokamak stellarator hybrids using modulated toroidal field coils(B. A. Carreras, et al, ORNL/TM-13252 (1996).) is investigated. A comprehensive study is underway to diagnose the vacuum, equilibrium, transport,(D. A. Spong, et al, this meeting.) and stability properties of these devices. These configurations have advantages in minimizing disruptions and reducing tokamak current drive needs, but they must also be optimized to reduce the amount of ripple transport and increase β_critical. Vacuum configurations have been found with robust flux surfaces and rotational transform close to that of a reverse-shear tokamak. With finite plasma current, equilibriums with <β > ~ 9% have been obtained. Results of these configuration and equilibrium studies will be reported along with initial stability studies using a 3D-ballooning code.