Characterization of Current Profile Peakedness for Vertical Stability Studies of 3D Shaped Plasmas 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 resulting from n = 0 vertical motion, leading to disruptions. In the Compact Toroidal Hybrid (CTH) vertical drifts can be suppressed 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 for use in conjunction with real time measurements of the plasma’s vertical position. Vertical drifts in CTH have been detected for varying elongations and fractional transforms using a set of poloidal pickup coils, an interferometer, and a SXR camera array. The SXR cameras allow for characterization of the internal plasma current profile via V3FIT reconstructions, which sets constraints on the vertically stable equilibrium. To further aid in characterizing the edge current gradient, an 8-sensor 3D Hall array has been installed and calibrated for edge field measurements. Experimentally measured Hall array magnetic field profiles are in good agreement with profiles calculated from a Biot-Savart code. The effects of preprogrammed and feed-back controlled RFC currents on vertical drifts are investigated as a function of the current profile peakedness and 3D shaping in CTH.