The ESS Synchronous Data Service (SDS) development and first results

The 5 MW proton linear accelerator of the European Spallation Source ERIC is designed to accelerate the beam at a repetition rate of 14 Hz, which dictates the refresh rate of most of the relevant data produced by acquisition systems. Each cycle of the 14 Hz timing structure receives a unique cycle ID from the ESS Timing System, which can be used as an index when data is collected and stored. The ESS Linac Synchronous Data Service (SDS) facilitates the collection of high-resolution data from various accelerator subsystems. Currently, SDS consists of an EPICS extension to be included in data acquisition IOCs and a client service (SDS Collector) that collects and stores the data produced by these IOCs. The novel features provided by the EPICS PVAccess protocol and libraries play a crucial role in this project by supporting structured data in the EPICS Process Variable data format. This paper outlines how SDS is designed, how it enables data-on-demand and post-mortem collection of large array datasets without overloading the network and describes the results of using SDS during the latest ESS beam commissioning campaign in 2025. From a broader perspective, SDS will be part of the ESS Data Framework, which comprises a set of tools to collect, store, catalog, retrieve, and analyze ESS Linac data to support advanced applications such as machine learning algorithms. This framework is briefly described in this paper.