• J. Alex, M. Bader, M. Iten, D. Reimann, J. Troxler
  Thomson Broadcast & Multimedia AG, Turgi
• S. Choroba, H.-J. Eckoldt, T. Grevsmühl
  DESY, Hamburg
• U. Gensch, M. Grimberg, L. Jachmann, W. Köhler, H. Leich, M. Penno, R.W. Wenndorff
  DESY Zeuthen, Zeuthen

The European XFEL project at DESY in Germany requires 27 RF stations capable of 10 MW RF power each. Each RF station needs one high voltage modulator that generates pulses up to 12 kV and 2 kA with a duration of 1.7 ms and a nominal repetition rate of 10 Hz. DESY decided to investigate new modulator prototypes and Thomson has been awarded to design and build one of these prototype modulators. The Thomson modulator is based on the pulse step modulator (PSM) principle. This technology allows the regulation of the pulse voltage during the pulses and by this achieving a good flatness. In addition to the common PSM technology this modulator design includes additional features. The first one is a constant power regulation system in order to prevent a 10 Hz loading of the mains. The second one is the extension of a part of the system to allow 2-quadrant mode in order to demagnetise the core of the pulse transformer between the pulses. The modulator has been delivered to DESY in July 2008 and is under testing at the modulator test facility in Zeuthen. The paper will give a detailed overview on the system and shows the results of the factory testing and of the testing at DESY.