Plasma vertical stabilisation at JET using adaptive gain adjustment

The plasma vertical position at JET is stabilised using the Fast Radial Field Amplifier (FRFA). This amplifier applies voltage to the radial field coils in steps of 2.5 kV from -10 kV to 10 kV. It has a maximum current capability of 2.5 kA. The amplifier is controlled in a closed loop by the Vertical Stabilisation controller. The best settings of the gains in this controller depend on the plasma growth rate, which varies in an unpredictable manner during a JET pulse. An adaptive control algorithm based on measurements of the switching activity of the FRFA amplifier is used to adjust these settings in real time.