Concept of the phase reference line for the European Spallation Source

The 600 m long accelerator and beam transport of the European SpallationSource requires precise phase synchronizationof LLRF and Beam Diagnostics systems. Accelerator subsystems are operating at frequencies of 352 MHz and 704 MHz. The required phase accuracy at both frequencies is 0.1° for short term (during 3.5 ms pulse), 0.1° for long term between adjacent outputs and 2.0° for long term (hours to days) between any two points. The main part of the phase reference distribution system is a Phase Reference Line (PRL), which is a fully passive system based on a single 1–5/8” coaxial rigid line placed along the tunnel. The PRL was designed to distribute both reference frequencies from a Master Oscillator to 56 tap points in the tunnel. Each tap point has several (3 or 6) signal outputs. The total length of the PRL is around 580 meters and the total number of signal outputs equals 294. To achieve the best drift performance and fulfill ESS synchronization requirements, the PRL will be equipped with temperature stabilization system (+/-0.1 o C) and with an internal gas pressure stabilization system. This paper covers the concept of the PRL, technical assumptions, components selection considerations, general modeling results and initial tests of the ESS PRL prototype.