FPGA - based control system for piezoelectric stacks used for sc cavity´s fast tuner

The TESLA nine-cell SC cavities need a fast tuning system, which will be able to adjust its shape during the pulse operation. The first attempts were focused on the compensation of the repetitive and periodic distortion. The algorithms were implemented in Matlab and allow compensating only the Lorentz force detuning. However, the previous solution was too slow to be able to compensate the microphonics. The paper presents recent development in this field. The previously worked out algorithms are implemented in the FPGA-based control system. The SIMCON board is used, which allows to perform parallel, deeply pipelined calculations. The new approach allows integrating the algorithm dedicated for cavity shape control with the LLRF system used for vector sum control. Moreover, the new algorithm for online detuning calculation which is based on the electromechanical model of the cavity is presented. The system is tested with Module Test Stand (MTS) at DESY with the high gradient cavities (up to 37 MV/m). Two type of active elements are investigated the NOLIAC´s and PI´s - both multilayer, low voltage piezostacks. The paper will present the first results from carried out measurements.