RF Connection from Master Oscillator to Phase Reference Line in European Spallation Source

The European Spallation Source (ESS) is a next-generation neutron source, under construction in Lund, Sweden. An important requirement for ESS is to assure a precise phase synchronization of LLRF and Beam Diagnostics systems. They are operating at frequencies of 352.21 MHz and 704.42 MHz. The phase stability along the machine is provided by the phase synchronization system. The main part of the system is a Phase Reference Line (PRL). It is an entirely passive system based on a single coaxial rigid line located in the tunnel, which distributes both reference frequencies. A source of the reference signals is a Master Oscillator (MO) located in the Klystron Gallery. High power amplifiers used at each frequency provide a power level of about +50 dBm. The output signals are combined in a custom made diplexer. The two-tone signal is distributed to the tunnel by a single 7/8" coaxial cable. Ambient temperature variations and humidity changes in the tunnel, STUB, and Klystron Gallery cause the phase drifts in the phase distribution system. An active drift compensation system was necessary to reduce those phase drifts. This paper shows the concept and block diagram of the RF connection from MO to PRL.