JET Modelling and Control Analysis for POET (PFX Operating Early Task)
The aim of the PFX Operating Early Task (POET) was to obtain a highly shaped plasma and X-point formation in the early phases of the discharge. The PFX is an amplifier which feeds the central pancakes of the JET primary circuit. In the past it was possible to energize the PFX circuit only when the PFGC current, which feeds all the coils of the primary circuit, was already flowing in the same direction as the PFX current would have flowed, to avoid repulsive vertical forces which would tend to lift the top pancakes of the central solenoid, balanced only by the net weight of the upper part of the JET machine. In this paper the modeling activity performed to provide a more accurate estimate of the ejection forces acting on the upper coils in order to safely widen the operational space, by using two dimensional finite element electromagnetic models and the simulation of the performances of the actual controller algorithm on tracking the desired references of current are described. Finally the results of the implemented POET system, routinely used in JET, in the 2011/12 experimental campaigns, will be presented.