Recent Developments in Control Software for Optical Synchronization Applications at DESY

Abstract

Proper operation of FELs such as the Free-Electron Laser in Hamburg (FLASH)and the European X-Ray Free-Electron Laser (XFEL), which is currently under construction in Hamburg at DESY, requires many specific subsystems to be synchronized with a precision exceeding 10 femtoseconds. Those components are often separated by several hundred meters at FLASH or even kilometers in case of the European XFEL. Such distances mean that it is extremely difficult to use only conventional RF signal distribution in coaxial cables for synchronization because of high losses and excessive phase drifts, while electromagnetic interference is also an issue. Therefore, a laser-based synchronization scheme can be employed in parallel. In this case, the synchronization signals are transmitted via length-stabilized optical fibers. Such an architecture is currently being used at FLASH and will also be the main means of synchronization at the European XFEL. The hardware for such a synchronization system consists of many optical elements such as commercial lasers and self-built free-space and fiber optic setups. However, a significant part of it is also the electronics responsible for control, diagnostics and signal processing as well as high-level servers and front-end software running on those devices. Currently, the VME standard is used throughout FLASH as the basis for the control system digital hardware. For the European XFEL, however, an architecture with a high level of reliability and availability is required as well as one with higher data acquisition and processing rates. Because of that, the Micro Telecommunications Computing Architecture (μTCA) had been chosen. It is a fairly new standard, provides significantly better performance and employs modern technological solutions making it more suitable for modern accelerator applications than the older VME architecture. The paper presents the latest improvements in the control software for the optical synchronization system based on the VME standard. Servers for phase-locking the lasers as well as controlling the fiber link stabilization units are described in detail. Plans for migration to the new infrastructure are also outlined.