Speaker
Description
The European Spallation Source (ESS) is one of the largest science and technology infrastructure project being built in Sweden. Protons at 2 GeV are delivered by a superconducting linear proton accelerator and are injected onto a rotating tungsten target. Neutrons via spallation reaction are moderated to cold thermal energies by two dedicated moderators. The cryogenic moderator system (CMS) was designed to remove both static heat load (2 kW) and dynamic heat load induced by the nuclear heating at the moderators, which is estimated to be 6.7 kW for a 5-MW proton beam power, by circulating subcooled liquid hydrogen at 17 K and 1.0 MPa. The liquid hydrogen is transferred from the CMS cold box (CBX) to a distribution box (DB) via a transfer line (HTL) and is split into each moderator transfer line. The CMS is cooled via a plate-fin type heat exchanger by a large-scale 20 K helium refrigeration system, referred to as the Target Moderator Cryoplant (TMCP), with a cooling capacity of 30.3 kW at 15 K. Two compressors are operated at a discharge pressure from 1.0 MPa to 2.0 MPa (HP) and a compression ratio (CR) of 4.1. A feed helium flow rate can be varied from 200 to 900 g/s when all the three expansion turbines are operated.
The CMS Process Control System is comprised of three Programmable Logic Controllers (PLCs) that manage a variety of equipment. Meanwhile, the TMCP PCS also includes three PLCs: one for business logic and one for each of the compressor skids. A direct data exchange between the two systems creates an interface that enables the integration and synchronization of their core functionalities.
A goal of the CMS Process Control System (PCS) is to establish automated operational controls for processes such as cooldown, warm-up, steady-state, beam injection modes and safe shut-down when failure event happens. In this study, additional device types were developed to provide various features, all accessible from the OPI block icons and faceplates, as well as the PLC logic. Most important ones are hydrogen pumps, vacuum pumps, valves, electric heaters, PID controllers with setpoint ramping and holding functionality, various feedback devices, tuning profile selection, and a customizable auto-profile selector for fast controller tuning. Subsequently, a custom device type was developed within the CMS PCS to manage the TMCP operation. This device offers several features, accessible via the Operator Interface (OPI), and PLC logic, which allow for control of the feed helium temperature using a split-range controller, a return helium temperature controller, and controlling the cooling capacity through a floating pressure process where the HP and CR controllers are directly manipulated by the CMS, alongside other functionalities.
Based on the results of the TMCP commissioning, setpoint ramping functions with various hold options have been implemented for cooldown and warm-up operations. These functions enable monitoring of the TMCP status during transient operations and intervene when necessary. It was helpful to ensure smooth operation during the CMS commissioning.
The basic functions of the CMS PCS together with the TMCP PCS were demonstrated to work effectively during the preliminary CMS commissioning using helium at 17 K, prior to hydrogen operation.
