We wanted to demonstrate fusion energy temperatures of 100 million degrees centigrade in a spherical tokamak, paving the way for consumable fusion energy generation by 2025.
We used CompactRIO hardware and LabVIEW software to create a modular, scalable control system with a centralised control room, which supports multiuser interfaces.
Lucy Scott - Tokamak Energy
Ed Pinkney - Tokamak Energy
Fusion is the reaction that powers the stars. At the centre of every star, two particles come together and fuse into one larger particle, which releases energy. In experiments on Earth, the nuclei of deuterium and tritium (types of heavy hydrogen) drive this process by fusing together to make a helium nucleus, a perfectly safe waste product. Fusion produces no greenhouse gases and no long-lived radioactive waste, yet it produces vast amounts of energy from very little fuel. As such it offers a clean, green, and plentiful energy solution if it can be harnessed on Earth, using the naturally present deuterium and tritium found in sea water.
For fusion reactions to occur, the deuterium and tritium must be very hot so particles can move at speeds high enough that they fuse upon collision. To safely create this fusion environment on Earth, we use specialised machines called tokamaks. Tokamaks use magnetic fields to keep the superheated fuel (now an electrically charged gas called plasma) from touching the walls of a vacuum chambers, keeping it hot enough for fusion to occur. If the plasma does hit the wall it is not dangerous, it simply cools down and stops the fusion process. Tokamak Energy aims to achieve these conditions in a spherical tokamak, which promises a smaller and cheaper solution than the larger tokamaks used in fusion experiments such as JET and ITER.
Since the possibility of controlled fusion was first demonstrated in the 1990s, the challenge to generate consumable energy for sustained periods using the fusion process has become an engineering challenge, rather than a physics problem. Tokamak Energy aims to accelerate the development of fusion energy by combining two emerging technologies: spherical tokamaks and high-temperature superconductors. Using this approach, we can design machines that are economical to build, run, and decommission.
We have broken down this huge challenge into the following five milestone stages:
We are currently at Stage 3 and are building a new tokamak, the ST40, at our facility at Milton Park, Oxfordshire. We want to demonstrate that we can achieve fusion temperatures in a small tokamak. Stage 4 (energy breakeven conditions) will be a world-changing technology breakthrough.
We are currently striving to build the ST40 from scratch. At this stage, we are building a tokamak that uses short bursts of the strong magnetic fields to create the conditions for fusion utilising super-capacitor power supplies and copper coils. We must complete this with only a few people, in a small building, and in a short time.
For the ST40 control system, we designed a scalable systems platform that integrates with our LabVIEW subsystems, CompactRIO systems, and third-party instrumentation. This gives us the option to increase functionality in the future. We use NI solutions throughout—from the implementation layer through to the server, data storage, and the control room screens. We want to oversee two control systems from the control room: the Machine Control System (MCS), and the Plasma Control System (PCS).
We are working to connect all our sub-systems to feed into a central control room. This will ensure we can efficiently operate and manage communications between all systems and manage data. It will also provide a platform for the control room equipment with many different screens and views.
Each time we drive the magnetics to create a fusion plasma is called a pulse. Before and during the pulse, the MCS monitors and controls almost all systems and displays them to the operations personnel using the control room screens. The MCS works between pulses to ensure the vacuum chamber is prepared and kept in a perfect state, ready for optimal plasma conditions.
Once everything is confirmed as ready, the MCS runs the pulse, managing all the peripheral systems and providing synchronised clocks to the diagnostics.
Our previous experience using LabVIEW was to control our previous Tokamak model (the ST25). We outline this in the case study titled “Using CompactRIO and LabVIEW to Monitor and Control a Compact Spherical Tokamak for Plasma Research.” From the start, we only considered NI technology. We have found that it delivers an incredibly scalable framework for building up a reliable control system that can communicate with a variety of controllers and sensors, as well as other more complicated or bespoke equipment. Our development team consists of two controls engineers (a Certified LabVIEW Architect and an experienced LabVIEW developer), working closely with a small physics and electrical team.
For our current work, we needed to measure all diagnostics with a synchronised clock. In this system, the plasma only gets hot for a few milliseconds and the complete pulse takes less than three seconds, so accurate and precise timing is critical. We currently use eight CompactRIO devices as our system controllers, with plans to include more in the future. With thousands of amps of current in our building, correct grounding is critical. Therefore, we placed the CompactRIO devices at various locations throughout our building.
Examples of our key systems include our system clock, the pulse control clock, and the vacuum vessel monitoring and control systems. The system clock and pulse control consist of two cRIO-9076 controllers. It uses several NI-9401 fast TTL modules connected to fibre optic converters for extremely accurate triggering. The vacuum vessel monitoring uses another CompactRIO controller with NI-9216 modules to simultaneously measure over 40 temperatures both inside the vessel and around the magnetic coils. This gives us excellent insight into conditions inside the vacuum chamber. Both during and outside of experimental runs, we use a system that includes a cRIO-9035 device to maintain chamber conditions through vacuum control, glow discharge cleaning and film deposition. This system operates firstly for long periods outside ‘pulses’ and secondly to control pre-ionisation during a pulse.
This project has aggressively short time frames and a small development team. We are currently preparing for our first full plasma trials and are confident in the solution we have chosen. By using LabVIEW and CompactRIO, we have designed a system that is scalable, reusable, and maintainable.
We have designed some special electronics ourselves, but there are many instances in which the ability to program the FPGA directly using a wide selection of standard I/O modules means that we can build high-speed solutions in hours, rather than weeks. By using standard components when possible, we simplified the solution. The flexibility of the CompactRIO platform will prove invaluable as we include new requirements in the project.
We have had help from NI support engineers, especially at the start of the project to review the original ST25 system and our proposed architecture. Because of this, we are pleased to be working with a reliable and responsive development environment as we commit to working at the cutting-edge of fusion research for a greener, sustainable future.
120A Olympic Avenue
Milton Park, Oxfordshire OX14 4SA, United Kingdom.