Abstract
At the ELBE Center for High-Power Radiation Sources, electrons are accelerated to an energy of up to 40 MeV in a superconducting linear accelerator that is operated in continuous wave (CW) mode. The acceleration is achieved using superconducting radio frequency (RF) cavities, which are driven by an analog low-level RF (aLLRF) system and solid-state-based RF amplifiers. The analog aLLRF system was transformed to a digital system based on the MicroTCA standard. It is in user operation since 2020. Here, the new digital system and its integration in the ELBE control system are described. Furthermore, the system is characterized by noise measurements and shows rms field stability of the digital LLRF (dLLRF) system of 0.01° in phase and 0.005% in amplitude. In addition, an algorithm for compensating long-term drifts is presented and characterized.
Highlights
M OST of today’s accelerator-based radiation sources, and especially light sources utilizing free electron lasers (FEL), are operated in pulsed mode
The data rate of 1 MB per macro pulse (25 MB/s for the maximum trigger rate used at ELBE) transferred from the field programmable gate array (FPGA) to the CPU is small compared to 640 MB/s [26], which is the maximum data rate of the advanced mezzanine card (AMC) (PCIe Gen I with 4 lanes)
At ELBE, for the first time, a digital level RF system (LLRF) system based on the MicroTCA.4 standard has been implemented on a machine operated in continuous wave (CW) mode at a high beam current of up to 1.6 mA and a high repetition rate of up to 26 MHz
Summary
M OST of today’s accelerator-based radiation sources, and especially light sources utilizing free electron lasers (FEL), are operated in pulsed mode. In the field of FEL experiments CW operation allows lock-in amplifier techniques to reduce the signal-to-noise ratio in measurements and to improve the FEL stability in general. The superconducting linac of ELBE [2] at HelmholtzZentrum Dresden-Rossendorf has operated in CW mode since 2001 to accelerate a high-power electron beam to drive several secondary radiation sources. It will allow implementation of advanced longitudinal feedback algorithms to achieve maximum beam stability. ELBE consists of two cryogenic modules each housing two 9-cell TESLA type superconducting resonant cavities [5] driven by a 1.3 GHz electro-magnetic field.
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