Fusion Science and Technology / Volume 59 / Number 2 / February 2011 / Pages 363-375
This paper describes the procedure adopted for the selection of an alternative controlled variable to be used for the vertical stabilization (VS) of elongated plasmas in the JET tokamak in the framework of the Plasma Control Upgrade (PCU) activities. The PCU enhancement project, aimed at increasing the capabilities of the VS system, explored the possibility of having a valid alternative to the controlled variable ZPDIP used for several years. The main motivation of this study was the need of operating JET in future campaigns with the new ITER-like wall, which is expected to significantly shield some magnetic diagnostics. This study was also aimed at improving the VS capabilities by reducing the effect of edge-localized modes on the vertical position estimator. The alternative controlled variable was also planned to play the role of backup solution in case of trouble with the standard one after the modifications of the radial field circuit. The selection was made paying particular attention to robustness, reliability, and reduced impact on the ongoing experimental campaigns. The new controlled variable, denoted OBS05, was successfully tested in JET in a variety of plasma scenarios and became the new vertical velocity estimator for the VS system.