Stability of 3D Shaped Vertically Drifting Plasmas in the Compact Toroidal Hybrid

Plasmas with vertically elongated cross sections have been shown to operate with higher beta limits but are susceptible to the axisymmetric (n = 0) MHD instability and vertical displacement events (VDEs) which can lead to major disruptions. Vertical drifts in the Compact Toroidal Hybrid (CTH) have been observed in current driven discharges at a range of elongations and fractional transforms using a set of poloidal pickup coils and a soft x-ray (SXR) camera array. Drifts in CTH are passively suppressed by nearby conducting structures and 3D shaping in the form of external stellarator rotational transform, as well as actively suppressed using a radial field coil (RFC). The use of SXR cameras allows for characterization of the internal plasma current profile via V3FIT reconstructions, which is known to affect the growth rate of the instability. To further aid in characterizing the edge current gradient, an 8-sensor 3D Hall array has been installed and calibrated for edge plasma magnetic measurements. The effects of plasma elongation, 3D shaping, and current profile peakedness on vertical drift rates are investigated and will be presented for varying amounts of external rotational transform and applied radial field.