Shape Controller Upgrades for the JET ITER-Like Wall
The upgrade of JET to a new all-metal wall will pose a set of new challenges regarding machine operation and protection. One of the key problems is that the present way of terminating a pulse, upon the detection of a problem, is limited to a predefined set of global responses, tailored to maximise the likelihood of a safe plasma landing. With the new wall, these might conflict with the requirement of avoiding localised heat fluxes in the wall components. As a consequence, the new system will be capable of dynamically adapting its response behaviour, according to the experimental conditions at the time of the stop request and during the termination itself. Also in the context of the new ITER-like wall, two further upgrades were designed to be implemented in the shape controller architecture. The first will allow safer operation of the machine and consists of a power-supply current limit avoidance scheme, which provides a trade-off between the desired plasma shape and the current distribution between the relevant actuators. The second is aimed at an optimised operation of the machine, enabling an earlier formation of a special magnetic configuration where the last plasma closed flux surface is not defined by a physical limiter. The upgraded shape controller system, besides providing the new functionality, is expected to continue to provide the first line of defence against erroneous plasma position and current requests. This paper presents the required architectural changes to the JET plasma shape controller system.