Fast vertical control in superconducting tokamaks

For superconducting tokamaks like KSTAR, EAST and ITER the use of normal conducting coils internal to the vacuum vessel have been chosen as the actuator for fast vertical control. Modelling by the General Atomics control group and others have specified coil locations and power supplies for the internal vertical control (IVC) coils needed necessary for fast vertical control. Both EAST and KSTAR have used their IVC coils for vertical control since early in their operation. The control achieved early in their campaigns was limited by experimental realities. Conducting passsive plates used for stability control slow the response of the plasma to the IVC coils and the response of sensor coils to the plasma. Recent progress on identifying which sensors in KSTAR have both the sensitivity and fast response needed for feedback control is being extended to EAST. Both devices have implemented a separation of the time response to use the IVC coil for only fast deviations from the plasma vertical position determined by the plasma control system, primarily determined by the superconducting coils. The results of vertical control using the newly selected sensors for each machine will be discussed along with implications for ITER.