Rendering of SPARC, a compact, high-field DT-burning tokamak currently under development by a team at the Massachusetts Institute of Technology and Commonwealth Fusion Systems. Your mission is to create and contain a plasma that creates net fusion energy. Image Credit: CFS / MIT-PSFC – CAD rendering by T. Henderson
Seven studies describe the progress and challenges to date for a revolutionary emission-free power source.
Two and a half years ago WITH has entered into a research agreement with startup Commonwealth Fusion Systems to develop a next-generation fusion research experiment called SPARC as a precursor to a practical, zero-emission power plant.
After many months of intense research and engineering, the researchers charged with defining and refining the physics behind the ambitious reactor design have published a series of articles summarizing the advances made and outlining the key research questions that SPARC will enable .
Overall, according to Martin Greenwald, deputy director of the Plasma Science and Fusion Center at MIT and one of the leading scientists on the project, the work is proceeding smoothly and according to plan. This series of articles offers a great deal of confidence in plasma Physics and the performance predictions for SPARC, he says. No unexpected obstacles or surprises have arisen, and the challenges that remain appear manageable. According to Greenwald, this forms a solid foundation for the device to operate after construction.
Greenwald wrote the introduction for a series of seven research papers written by 47 researchers from 12 institutions and published today (29 September 2020) in a special issue of Journal of Plasma Physics. Together, the work outlines the theoretical and empirical physical basis for the new fusion system, the construction of which the consortium is expected to begin next year.
SPARC is said to be the first experimental device to ever achieve a “burning plasma” – ie a self-sustaining fusion reaction in which different isotopes of the element hydrogen fuse to form helium without the need for additional energy input. Studying the behavior of this burning plasma – something that has never been seen in a controlled manner on Earth – is seen as critical information in developing the next step, a working prototype of a practical power plant for generating electricity.
Such fusion power plants could significantly reduce greenhouse gas emissions from the power generation sector, one of the main sources of these emissions worldwide. The MIT and CFS project is one of the largest privately funded research and development projects ever undertaken in the merger area.
Visualization of the SPARC tokamak experiment. Using high field magnets built with newly available high temperature superconductors, this experiment would be the first controlled fusion plasma to produce a net energy output. Photo credit: Visualization by Ken Filar, PSFC research partner
The SPARC design would be about twice the size of MIT’s now decommissioned Alcator C-Mod experiment and is similar to several other research fusion reactors currently in operation. It would, however, be far more powerful and achieve fusion performance comparable to that of the much larger ITER reactor is being built in France by an international consortium. The high performance in a small size is made possible by advances in superconducting magnets, which allow a much stronger magnetic field to confine the hot plasma.
The SPARC project started in early 2018 and work on the first phase, the development of superconducting magnets that can be used to build smaller fusion systems, has progressed rapidly. The new set of papers is the first time the underlying physical basis for the SPARC machine has been fully described in peer-reviewed publications. The seven papers address the specific areas of physics that needed further refinement and further research to determine the final elements of the machine design, as well as the operating procedures and tests that will be required in the course of work on the power plant.
The articles also describe the use of computation and simulation tools to design SPARC that have been tested against many experiments around the world. The authors used state-of-the-art simulations on powerful supercomputers developed to aid in the design of ITER. The large multi-institutional research team represented in the new papers aims to provide the best consensus tools for SPARC machine design in order to build confidence that it will accomplish its mission.
The analysis carried out so far shows that the planned fusion energy release of the SPARC reactor should be able to meet the design specifications with a comfortable margin. It is designed to have a Q-factor – a key parameter that indicates the efficiency of a fusion plasma – of at least 2, which essentially means that twice as much fusion energy is produced as the amount of energy pumped into producing the reaction. This would be the first time that a fusion plasma of any kind produces more energy than it consumes.
The calculations at this point indicate that, according to the new releases, SPARC could actually achieve a Q ratio of 10 or more. While Greenwald warns that the team wants to be careful not to over-promise and that there is still much work to be done, results so far suggest that the project will at least achieve its goals, and specifically achieve its main goal of creating a burning plasma in which the self-heating dominates the energy balance.
The restrictions imposed by the Covid-19 pandemic have slowed progress somewhat, but not by much, he says, and researchers are back in the labs under new operating guidelines.
Overall, “we are still aiming for construction to start in June ’21,” says Greenwald. “The physical effort is well integrated into the technical design. We try to put the project on as solid a physical basis as possible so we are confident of how it will work, and then give guidance and answer questions for the technical design as it progresses. ”
Many of the fine details are still being worked out on the machine design, covering the best ways to inject energy and fuel into the device, turn off the power, deal with sudden heat or power transients, and measure key parameters to monitor the operation of the machine .
So far, only minor changes have been made to the overall design. The diameter of the reactor has been increased by about 12 percent, but little else has changed, says Greenwald. “There’s always a question of a little more of it, a little less of it, and there are a lot of things that affect it, technical problems, mechanical stresses, thermal stresses and also the physics – how does that affect the performance of ? The machine?”
The publication of this special edition of the journal is “a summary, a snapshot of today’s physical principles”. Although members of the team discussed many aspects of it at physics meetings, “this is our first opportunity to tell our story, have it reviewed, receive the seal of approval, and bring it to the community.”
According to Greenwald, there is still a lot to learn about the physics of burning plasmas, and once this machine is operational, important information can be gleaned that will pave the way for commercial, electricity-producing fusion devices whose fuel – the hydrogen isotopes deuterium and tritium – can be found in near-zero be made available in unlimited quantities.
The details of the burning plasma “are really new and important,” he says. “The great mountain that we have to overcome is to understand this self-heated state of a plasma.”
Overall, Greenwald said, the work that has gone into the analysis presented in this paper package helps “confirm our confidence that we will achieve the mission. We haven’t come across anything where we say, “Oh, that predicts we won’t get where we want to.” In short, he says, “One of the conclusions is that things are still on the right track. We believe it will work. ”
Reference: “Status of the SPARC physics base” by Martin Greenwald, September 29, 2020, September 29, 2020, Journal of Plasma Physics.
DOI: 10.1017 / S0022377820001063
