Design and Integration of the Optical Reference Module at 1.3 GHz for FLASH and the European XFEL

Abstract

In this paper we present recent progress on the integration and implementation of the OPTical REFerence Module (REFM-OPT) for the free-electron lasers FLASH and the European XFEL. In order to achieve high energy stability and low arrival time jitter of the electron beam, the accelerator requires an accurate Low-Level RF (LLRF) field regulation and a sophisticated synchronization scheme for various devices along the facility. The REFM-OPT is a 19” module which is responsible for resynchronizing the 1.3 GHz reference signal for the LLRF distributed by coaxial cables to a phase-stable signal of the optical synchronization system. The module provides a 1.3 GHz output signal with low phase noise and high long-term stability. Several sub-components of the REFM-OPT designed specifically for this module are described in detail. The readout electronics of the highprecision Laser-to-RF (L2RF) phase detector are presented as well as the integration of this key component into the 19” module. Additionally, we focus on design solutions which assure phase stability and synchronization of the 1.3 GHz signal at several high power outputs of the module.