Conceptual design of the COMPASS-U control systems
Introduction
The COMPASS-U tokamak will be a new tokamak with toroidal magnetic field 5 T and plasma current up to 2 MA with flat-top duration 1 s [1,2]. The tokamak will have copper coils cooled to 80 K, but the vacuum vessel will operate up to 773 K. Therefore, the whole tokamak will be inside a vacuum cryostat.
The toroidal field coil will be powered by a thyristor power supply (2 × 12 pulse) and two new flywheel generators. The poloidal field coils will be powered using 12 IGBT power supplies with PWM at 1 kHz. Additional two fast power supplies will be available for vertical plasma position control. All poloidal power sources will utilize two existing (COMPASS) flywheel generators.
The COMPASS-U control systems must cover not only plasma discharge control but also all technological processes. This includes tokamak thermal management (including cooling down, warming up) of coils, vacuum vessel, and support structure, glow discharge, cryostat, and vacuum vessel vacuum control.
Important tasks are related to personnel safety and danger situation handling. The aim is to have a safe, fully operational tokamak with flexible and easily extensible control and data acquisition system.
Unlike the current COMPASS tokamak [3], the new tokamak system will produce ten times more data per discharge due to longer plasma discharge duration. Since it will include higher count of machine monitoring sensors (2000–4000), the amount of continuous data will increase significantly, too. This will increase demands on data storage and data handling.
The architecture of COMPASS-U systems divides individual systems into several categories based on their properties and responsibilities:
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Control systems consist of the Real-time plasma control system and Slow control and supervision system. The Real-time plasma control system controls plasma, minimizes delays in control loops, runs advanced control algorithms, is extendible, and allows control algorithms modification. The Slow control and supervision system controls and supervises tokamak all the time and provides a user interface to multiple users simultaneously. It integrates all systems, and therefore, it can perform actions across multiple systems. This will be used while handling failure.
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Protection systems consist of Personnel protection and Machine protection system. Both protection systems have to minimize risks for personnel and the tokamak, respectively. Their design will focus on reliability. The systems will operate independently to control systems in order to archive better resistance to failure.
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Acquisition systems consist of Machine monitoring system and Data acquisition system. The Data acquisition system automatically acquires experimental data, and provides data for plasma control. It allows easy and fast integration of new data acquisition devices. The Machine monitoring system continually and reliably acquires data from machine monitoring sensors. It serves as the data source for the protection systems.
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Databases include COMPASS-U database (CUDB), Machine monitoring database, and Machine configuration database. Databases store all data, make them accessible for users, and allow searching in data, and have an interface for easy data processing.
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Timing system and Triggering system have to provide accurate, reliable, and low noise and jitter signals to synchronize all COMPASS-U systems.
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Postprocessing system automatically runs user-defined tasks.
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Tokamak systems consist of Power supply system, Cryogenics system, Vacuum system, Additional plasma heating systems (e.g., NBI, ECRH). These systems will integrate with the Slow control and Supervision system.
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Building systems consist of heating, ventilation, air conditioning for server rooms, fire alarm, etc.
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The user interfaces are mainly parts of the Slow control and supervision system and database systems.
Systems are shown in Fig. 1, where categories are color coded.
Section snippets
Slow control and supervision system
The Slow control and supervision system is the main tokamak control system. It will control and supervise tokamak all the time except for plasma discharge. The plasma discharge will be controlled by the Real-time plasma control system. The Slow control and supervision system will use data supplied by the machine monitoring system and all other tokamak state relevant systems. This system will control devices and/or subsystems and their interaction. Moreover, it will provide cross-systems
Personnel protection system
The personnel protection system's only task is to protect personnel. Therefore, it has the highest priority in all situations. Handling some situations and requirements to some parts of the system is required by law. The regulations mainly cover fire safety, electrical safety, and radiation safety. The design prefers passive safety if possible, and it focuses on reliability and simplicity. Each subsystem will handle safety independently in order to improve resistance against failure.
Usually,
Data acquisition system
The Data acquisition system is intended for experimental data collection. Although it can be used for the tokamak checking, e.g. the magnetic diagnostic can be used for check of a magnetic field from coils and recognize an inter-turn short circuit.
The data acquisition system will be significantly extended during the tokamak lifetime. It will consist of many different types of devices with different interfaces. Therefore, the solution will use a multiplatform thin client with limited or no
COMPASS-U database
The COMPASS-U database (CUDB) is an evolution of the database currently used at COMPASS [9]. It is intended for experimental pulse data collected by the Data acquisition system and calculated data related to the experiment. Therefore, data are coupled with plasma discharge number and regime (experiment, calibration, test, pre-discharge check).
The CUDB avoids deleting or overwriting data. Everything is kept and updates are tracked through revisions. Metadata is stored in the relational database
Timing system
The timing system defines "a second" for all data acquisition devices and time for all computer systems. It provides a common reference to all tokamak systems continually with minimized outages. The configuration of the timing system will be mostly fixed. The Slow control and supervision system will set the variable part of the configuration.
The base is a stable and low phase noise oscillator that generates precise frequencies of 10 MHz and 100 MHz. The pulse per second (PPS) signal will be
Postprocessing system
This system will post-process data after discharge or periodically during the night or continuously. The start of processing can be triggered by an event generated from databases, e.g. “data are available” events. The system will allow the support of various tools and programming languages. It will process user-defined tasks. It is not necessary that all setting will be done via the Slow control and supervision system. It can overlap with the high-level part of the Machine protection system at
Tokamak systems
The tokamak systems are essential for tokamak operation including Power supply system, Cryogenics system, Vacuum system, additional plasma heating systems (NBI or ECRH), etc. Therefore, they must be integrated into COMPASS-U systems.
Each system will communicate with the Slow control and supervision system. They will not communicate directly with each other without the supervision of the Slow control and supervision system. Suppose the system has its own human-machine interface (HMI). In that
Building system
Building systems consist of systems that ensure the condition for tokamak operation such as heating, ventilation, air conditioning for server rooms, experimental area and technological rooms, pressurized air, water cooling, liquid nitrogen storage, and uninterruptible power system. There are also systems important for personnel safety such as the fire alarm system and an experimental hall access system.
The building systems are not so closely related to COMPASS-U systems. However, information
Conclusion
The new COMPASS-U control systems will enable achieving the full performance of the new COMPASS-U tokamak. The systems are designed with a focus on simple maintenance and extendibility, especially for the data acquisition system.
The Real-time plasma control system provides flexibility in plasma control that can be utilized by advanced control algorithms that will support plasma physic exploitation. The Real-time plasma control system architecture is designed to operate with short control cycle
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work has been carried out within the framework of the project COMPASS-U: Tokamak for cutting-edge fusion research No. CZ.02.1.01/0.0/0.0/16_019/0000768 and LM2018117 funded by Ministry of Education, Youth and Sports of the Czech Republic and co-funded from European Structural and Investment Funds.
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