n=2 Compensation and variable gains for JET vertical stabilisation

In JET, the presence of an elongating quadrupolar field makes the plasma vertical position unstable. The vertical stabilisation (VS) system has been developed in order to keep plasmas for a time longer than the vessel field penetration time constant. Its present plasma vertical speed observer is affected by several problems, which reduce the operating range of the system. New hardware has been designed and is now being installed, aimed at solving some of these shortcomings. The main component is a new hybrid (digital–analogue) signal combination card, which should enable a better tuning of the VS system. In addition an increased set of magnetic measurements will be used.