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PIEZO CONTROL FOR LORENTZ FORCE DETUNED SC CAVITIES OF DESY FLASH

DESY, Hamburg, Germany

ABSTRACT Free-Electron LASer in Hamburg (FLASH) accelerator is dedicated for various high energy physics experiments. The superconducting (SC) cavities, the main parts of RF linac, are Lorentz force detuned when operated in pulse mode with high accelerating field gradients. The cavities of FLASH linac have been equipped with piezo tuners allow compensating of dynamic detuning during the RF pulse. In order to assure the simultaneous control of all available piezo tuners a distributed, multi-channel digital and analog piezo control system was designed. The paper describes the main parts of the system as well as its efficiency measurements obtained during high current, high gradient beam acceleration (9 mA) performed in Deutsches Electronen SYnchrotron (DESY).

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Available from: Tomasz Pozniak, Apr 22, 2015
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    ABSTRACT: Pulsed operation of high gradient superconducting radio frequency (SCRF) cavities results in dynamic Lorentz force detuning (LFD) approaching or exceeding the bandwidth of the cavity of order of a few hundreds of Hz. The resulting modulation of the resonance frequency of the cavity is leading to a perturbation of the amplitude and phase of the accelerating field, which can be controlled only at the expense of RF power. The X-Ray Free Electron Laser (X-FEL) accelerator, which is now under development in Deutsches Elektronen Synchrotron (DESY), will consists of around 800 cavities with a fast tuner fixture including the actuator / sensor configuration. Therefore, it is necessary to design a distributed control system which could be able to supervise around 25 RF stations, each one comprised of 32 cavities. The Advanced Telecommunications Computing Architecture (ATCA) was chosen to design, develop, and build a Low Level Radio Frequency (LLRF) controller for X-FEL. The already performed tests of ATCA LLRF control system proofed the possibilities of usage of such a standard for high energy physics experiments. The paper presents the concept of integration of the piezo compensation system to the ATCA standards with special emphasis to the hardware part of the system. Moreover, the first results from carried out tests of the prototype power supply unit for piezo drivers integrated to ATCA board will be presented.
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