Dependence of Vertical Stability on Current Profile Peakedness and 3D Shaping in the Compact Toroidal Hybrid

Poloidally shaped, or elongated plasmas are desirable for tokamak operation in high-beta regimes but are susceptible to Vertical Displacement Events (VDE) resulting from n = 0 vertical motion, leading to disruptions. In the Compact Toroidal Hybrid (CTH) vertical drifts are minimized by the addition of external stellarator transform and the use of a radial field coil (RFC). A feed-back controlled power supply has recently been added to the RFC to be used in conjunction with a set of pickup coils mounted above and below the plasma volume for additional vertical control. Vertical drifts in CTH have been detected at varying elongations and fractional transforms using a set of poloidal pickup coils, an interferometer, and a SXR camera array. Additionally, a 3D Hall array consisting of 8 sensors spanning 45 mm has been installed and calibrated for internal field measurements to characterize the edge current gradient. Experimentally reconstructed magnetic field profiles are in good agreement with profiles from a Biot-Savart model. The effects of preprogrammed and feed-back controlled RFC on vertical drifts are investigated as a function of the current profile peakedness and 3D shaping in CTH.