High performance plasma vertical position control system for upgraded MAST

•A control system for the vertical position of a high elongation tokamak is presented.•A closed loop model based on RZIp is validated against present day MAST discharges.•The limits of controllability are explored.•The power requirements for the new design are examined using the ‘maximum delta z’ method.

A plasma vertical control system able to control high elongation (∼2.5) plasmas at moderate internal inductance (∼0.9) is analysed, including both active and passive components in a closed loop system. The analysis is based on the RZIp rigid plasma model and this is extensively validated using present day MAST discharges, especially at the limits of controllability. Special consideration is given to the unusual MAST geometry (coils inside the main vacuum vessel) and general conclusions regarding system design are drawn wherever possible.