Case Study: Integrating the European Spallation Source Accelerator Cryoplant into EPICS
Linde Kryotechnik was chosen to deliver a large and complex cryoplant to the European Spallation Source (ESS). For ESS it was important that the integration into EPICS was done in a way consistent with other subsystems. Cosylab was able to provide the missing link between cryoplant supplier and ESS, and thus adapt the industrial solution to the custom requirements of the ESS EPICS environment. Cosylab’s Senior software developer Ivana Mustac provides us with the details of the case.
Introduction
The European Spallation Source (ESS) will be the world’s most powerful pulsed neutron source to provide a means for multidisciplinary research in areas such as materials science, life sciences, energy, environmental technology, cultural heritage and fundamental physics. The first experiments are planned for 2023 with the commencement of the user programme.
The accelerator will contain three cryogenic refrigeration/liquefaction plants and an extensive cryogenic distribution system. The accelerator cryoplant (ACCP) is the largest of the ESS cryoplants. Its main purpose is to cool the superconducting RF cavities to a temperature of 2 K via saturated He-II baths through a number of cryomodules. Apart from that, a forced flow of 4.5 K Helium is supplied in a second circuit to cool the RF power couplers and a third circuit provides Helium at around 40 K to cool the thermal radiation shields. The ACCP provides cooling for all three of these circuits.
The two main ACCP subsystems are the warm compressor station and the coldbox. The warm compressor station consists of three oil lubricated compressor skids with a bulk oil removal system and oil and gas filters, a final oil removal system and a gas management panel (GMP) consisting of valves and pipe terminals for the process control. There is a single coldbox with a number of heat exchangers, expansion turbines, a cold compressor system, adsorbers, filters, electrical heaters and other equipment.
A number of manual and remote valves will be installed for different purposes, for example, to isolate specific loops, to protect the system against loss of oil or Helium and safety valves to protect the system against overpressure. Measuring points necessary for operation and protection of the equipment include Helium mass flow and water flow measurements, position measurements of all control valves, limit switches for manual valves, oil level measurements, oil and Helium pressure measurements, impurity measurements, Helium, water and oil temperatures, and others. These measurements, and control over the above-mentioned devices, will be exposed to the operators by the ESS control system.
Control System Architecture
The ACCP control system schema is shown below. Control over all functions with substantial technical safety requirements and deterministic sequence programs is carried out by a Siemens Step 7- 400 PLC. All relevant control points are collected and processed by the PLC and distributed and exposed to the operator via a dedicated IOC running EPICS. The interface between the PLC and the IOC is implemented through the s7plc EPICS driver, which is based on the Siemens send/receive protocol. Two touch panel PCs are installed as local displays, one in the compressor building and one in the coldbox building. The IOC and touch panel PCs run the standard ESS operating system with the ESS EPICS environent. Operator applications are implemented in Control System Studio (CS-Studio).
The EPICS database covers the input/output of all relevant control points and additional functionalities such as the communication logic with the PLC, recovery of set-points after a system shut down and locking access to a single workstation. Data that is sent from the PLC to the IOC is stored and recovered by the PLC while IOC set-points are stored on the IOC. The EPICS database provides the option to either initialize all data to their last values on the IOC, or to copy their respective readbacks from the PLC. Furthermore, since the ACCP graphical user interface (GUI) will run on several workstations, modification of set-points will only be possible after access has been locked to the current workstation. This prevents concurrent tuning of the system from separate workstations.
Graphical User Interface
An extensive graphical user interface has been produced that provides an overview of the several thousands of control points and grants control to operators with higher security privileges.
The GUI screens have been designed for a 1280x1024 touch panel PC. The design of the GUI screens has been optimized to take into account the need for quick navigation and other requirements for touch interfaces such as the size of elements and minimal spacing between elements. Additionally, clickable elements have been given a raised style.
Since the ACCP is a large and complicated system, the GUI has been structured hierarchically. At the top level, a process diagram of the whole system gives a quick overview of the cryoplant’s most important measuring points. The process diagram is reachable at all times by a single click.
From here, the operator can easily zoom into sections of the ACCP, for which 21 synoptic process screens have been developed, and navigate along the process lines in each direction.
Each screen is composed of two main sections, a header and a body. The header section contains a menu bar and displays important information on the communication with the PLC and gives an overview of the alarm status. The header also contains navigation buttons. The header is displayed at all times.
Control over what should happen after an IOC restart is granted to operators with appropriate access rights, who can decide whether to load the data recovered by the IOC or to copy read-backs from the PLC to the IOC set-points.
Control over parameters of individual instruments such as valves or pumps is achieved from the respective engineering screens, reachable by clicking the corresponding element on the process screen. These tabular screens appear in a new tab, in order to prevent the clutter of an uncontrolled number of separate open windows. Overall start-up control over individual subsystems is performed from start-up engineering screens, while another set of screens displays start-up and shut down conditions, all reachable from the menu bar in the header section.
Automation of Control System Development
Due to the complexity of the ACCP control system, extra attention has been paid to automate as much as possible. The PLC variables and all relevant information are parsed by appropriate Python scripts in order to create the EPICS database and configuration files for services such as the alarm handler and archiving service. This ensures that all services are up to date with the EPICS database. Templates were used, where possible, for the screen design. Apart from simplifying development, this approach reduces errors and simplifies testing of the GUI screens, since it is necessary to check only one instance of each template.
Conclusion
A large and complex system like the cryoplant is always customized by an experienced supplier, such as Linde Kryotechnik, the market leader for croygenic solutions. However, when considering a very large facility like ESS, it is extremely important that all systems get integrated into the central control system in the same way, i.e. to use the same technologies as are used for other subsystems. This is important for operators and becomes a necessity when considering maintenance throughout the system’s lifecycle.
Special emphasis was put on managing configuration of the devices in the cryoplant as this changes during development and testing. Also, all the complexity of the subsystem requires many GUI screens, the development of which was a major part of the project.
Cosylab was able to provide the missing link between cryoplant supplier and ESS, and thus adapt the industrial solution to the custom requirements of the ESS EPICS environment.
ABOUT THE AUTHOR
Ivana Mustac started working at Cosylab in 2015. She holds a Ph.D. in Physics with a topic in elementary particle physics. A major project she worked on is the ELI-NP in Romania (ELI-NP will study photonuclear physics, using two 10PW ultra-short pulse lasers and a very brilliant tunable gamma-ray beam). Ivana developed GUIs and applications of the gamma-ray beam EPICS-based control system. Now she works on the aforementioned ACCP EPICS integration project. Her hobbies are dancing and climbing.
This article is republished from our March 2018 edition of the Control Sheet newsletter. https://www.cosylab.com/our-newsletter/
