ELM Power Deposition Wetted Area and Temporal Shape in JET

Magnetic field perturbations which break the toroidal symmetries are inevitable in tokamaks due to imperfections in magnetic field coils and to the presence of magnetic materials. Magnetic islands arising from these asymmetries can cause the appearance of locked modes which, if uncontrolled, frequently lead to disruptions. One of the main goals of the Error Field Correction Coil (EFCC) systems in modern tokamaks is to alleviate this effect by applying magnetic perturbations that compensate the natural error field at the plasma boundary. Recently at JET, performance issues and practical limitations led to the decision of replacing the EFCCs voltage amplifiers. The opportunity was also taken to reformulate and improve the controller application by incorporating it into a new real-time software framework, developing a new control algorithm and revising the time synchronization mechanism whilst maintaining essentially the same VME based hardware components. Furthermore, a new graphical user interface configuration utility has been developed mainly to accommodate the new controller's waveform generator capability of nesting waveforms and enabling simultaneous sweeping in frequency, amplitude and osffet. In this paper, a global overview of the new controller application will be provided focusing mainly on the above mentioned improved elements. Preliminary results of the operation of this system during JET pulses will also be presented.
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