Conceptual LLRF Design for the European X-FEL

Abstract

The LLRF System for the superconducting cavities of the European X-FEL must support amplitude and phase stability of the accelerating fields of up to 0.01% and 0.01 deg. respectively. The stability must be achieved in pulsed operation with one klystron driving 32 cavities. This goal can only be achieved with low noise downconverters for field detection, high gain feedback loops and sophisticated feedforward techniques. State-of-the art technology including analog multipliers for downconversion, 100 MHz ADCs with high resolution up to 16 bit, and high performance data processing with FPGAs with a few hundred nanosecond latency allow to meets these goals. The large number of more than 100 input channels (including probe, forward and reflected signal of each of the 32 cavities) and more than 34 output channels combined with the tremendous processing power requires a distributed architecture using Gigalink interfaces for low latency data exchange.