World premiere: Ambitious European XFEL project with 27 klystron modulators by Ampegon brings technology breakthrough to the scientific world

Turgi, Switzerland, March 15, 2013. One of the most ambitious technology projects in Europe is well under way: Since the end of November 2012 every month two giant pulsed klystron modulators are leaving the Ampegon factory in Turgi with a heavy weight special transport to Hamburg, Germany. In March 2013 number seven and eight of the total 27 modulators will be ready for delivery. There at the Deutsche Electronen Synchroton (DESY) facility the European X-ray free electron laser project XFEL with a 3,4 km long superconducting linear electron accelerator is currently under construction, initiated in 2006 and due for completion by 2015. XFEL opens up new frontiers of research for scientists by allowing them for the first time to observe processes on the nanoscale in real time.


Ampegon’s Contribution

The European XFEL project at DESY 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 duration of 1.7 ms and a nominal repetition rate of 10 Hz. DESY has ordered 27 pulsed klystron modulators from Ampegon.

The commissioning of the first two modulators is planned for the 2nd quarter this year, whereas the entire queue of modulator, cables, pulse transformer with its matching network and the klystron will be thoroughly tested.

Josef Troxler, CEO of Ampegon AG states: “ Event though this is an entirely new experience for our company with regard to the production of such a number of modulators in series, our project is on time and the technical challenges have been fully mastered”


System Overview

The klystrons will be placed in the accelerator tunnel whereas all modulators will be placed in a central modulator hall. As the maximum distance will be 1700m, an impedance matched system is needed for the interconnection. This is achieved by using 4 coaxial cables, each with a nominal impedance of 28 ohms in parallel, resulting in an effective cable impedance of 7 ohms. EPSM (enhanced pulse step modulator) technology permits regulation of the pulse voltage during the pulse. This allows full compensation of the voltage droop on the storage capacitors.

The modulator is comprised of 24 active modules. The system is able to operate with 22 modules at full performance, resulting in a redundancy of 2 modules. The charging of the module capacitors is done with constant power consumption during the pulse pause, which is achieved with a boost converter.

For the demagnetization of the pulse transformer between the pulses and for dissipating the inductive stored energy under klystron arcing conditions 4 modules are paired with additional switching modules in a two phase configuration, allowing inverse voltage operation. This makes it possible to set a negative voltage of approximately 2 kV.

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