RF Backplane for MTCA.4-Based LLRF Control System

Low-level RF (LLRF) control systems developed for linear accelerator-based free electron lasers (FELs) require real-time processing of thousands of RF signals with very challenging RF field detection precision. To provide a reliable, maintainable, and scalable system, a new generation of LLRF control based on MTCA.4 architecture was started at DESY for the FLASH and European-XFEL facilities. In contrast to previous RF control systems realized in 19-in modules, we could demonstrate field detection, RF generation, RF distribution, DAQ system, and the high-speed real-time processing entirely embedded in the MTCA.4 crate system. This unique scheme embeds ultra-high-precision analog electronics for detection on the rear transition module (RTM) with powerful digital processing units on the advanced mezzanine card (AMC). To increase system reliability and maintainability and to reduce performance limitations arising through RF cabling, we developed and embedded in the MTCA.4 crate, a unique RF backplane for RTM cards. This backplane is used for distribution of high-performance local oscillator (LO), RF, and low-jitter clock signals together with low-noise analog power supply to analog RTM cards in the system. In this paper, we present the design and architecture of the MTCA.4 crate with the RF backplane and successful test results of the LLRF control system.