High-Level Software Tools for LLRF System Dedicated to Elliptical Cavities Management of European Spallation Source Facility

Abstract: The European Spallation Source (ESS) accelerator is composed of superconducting elliptical cavities. When the facility is running, the cavities are fed with electrical field from klystrons. Parameters of this field are monitored and controlled by the Low-Level Radio Frequency (LLRF) system. Its main goal is to keep the amplitude and phase at a given set-point. The LLRF system is also responsible for the reference clock distribution. During machine operation the cavities are periodically experiencing strain caused by the Lorentz force, appearing when the beam is passing through the accelerating structures. Even small changes of the physical dimensions of the cavity cause a shift of its resonance frequency. This phenomenon, called detuning, causes significant power losses. It is actively compensated by the LLRF control system, which can physically tune lengths of the accelerating cavities with stepper motors (slow, coarse grained control) and piezoelements (active compensation during operation state). The paper describes implementation and tests of the software supporting various aspects of the LLRF system and cavities management. The Piezo Driver management and monitoring tool is dedicated for piezo controller device. The LO Distribution application is responsible for configuration of the local oscillator. The Cavity Simulator tool was designed to provide access to properties of the hardware device, emulating behaviour of elliptical cavities. IPMI Manager software was implemented to monitor state of MicroTCA.4 crates, which are major part of the LLRF system architecture. All applications have been created using the Experimental Physics and Industrial Control System (EPICS) framework and built in ESS EPICS Environment (E3).