Two and a half years ago, MIT 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, emission-free power plant.
Now, after many months of intense research and engineering work, researchers tasked with defining and refining the physics behind the ambitious tokamak design have published a series of papers summarizing the progress they have made and outline the key research questions that SPARC will allow.
Overall, says Martin Greenwald, deputy director of MIT’s Plasma Science and Fusion Center and one of the lead scientists on the project, the work is progressing smoothly and on track. This series of articles provides a high level of confidence in plasma physics and performance predictions for SPARC, he says. No hindrances or unexpected surprises have emerged, and the remaining challenges appear to be manageable. This forms a solid foundation for the device to function once built, according to Greenwald.
Greenwald wrote the introduction to a series of seven research papers written by 47 researchers from 1
SPARC is designed to be the first ever experimental device to achieve a “fiery plasma” – a self-sustaining fusion reaction in which several isotopes of the element hydrogen fuse together to form helium, without the need for additional energy inputs. Studying the behavior of this burning plasma – something never seen before on Earth in a controlled way – is seen as crucial information for the development of the next step, a working prototype of a practical powerhouse for producing energy.
Such fusion plants could significantly reduce greenhouse gas emissions from the power generation sector, a major source of these emissions globally. The MIT and CFS project is one of the largest privately funded research and development projects ever undertaken in the fusion field.
“The MIT group is pursuing a very compelling approach to fusion energy.” says Chris Hegna, a professor of engineering physics at the University of Wisconsin at Madison, who was unrelated to this work. “They realized that the emergence of high-temperature superconductor technology allows a high magnetic field approach to produce net energy gain from a magnetic confinement system. This work is a potential game changer for the international fusion program. “.
The SPARC project, although roughly double the size of MIT’s now retired Alcator C-Mod experiment and similar to many other research fusion machines currently in operation, would be much more powerful, achieving fusion performance comparable to that expected in ITER. much larger tokamaks under construction in France by an international consortium. The high power in 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 was launched in early 2018 and work on its first phase, the development of superconducting magnets that would allow the construction of smaller fusion systems, is proceeding apace. The new series of articles represents the first time that the physical underpinnings of the SPARC machine have been outlined in detail in peer-reviewed publications. The seven articles explore specific areas of physics that needed to be further refined and which still require ongoing research to define the final elements of the machine design and the operational procedures and tests that will be involved as work progresses to the power plant. .
The papers also describe the use of calculations and simulation tools for the design of SPARC, which have been tested in many experiments around the world. The authors used state-of-the-art simulations, run on powerful supercomputers, which were developed to aid in the design of ITER. The large, multi-institutional team of researchers represented in the new series of papers aimed to bring the best consensus tools to the design of the SPARC machine to increase confidence in achieving its mission.
The analysis carried out so far shows that the planned fusion power production of the SPARC tokamak should be able to meet the project specifications with a comfortable margin of reserve. It is designed to achieve a Q factor – a key parameter denoting the efficiency of a fusion plasma – of at least 2, which essentially means that double the fusion energy is produced compared to the amount of energy pumped to generate the reaction. . It would be the first time that a fusion plasma of any type produces more energy than it consumes.
Calculations at this point show that SPARC could actually achieve a Q ratio of 10 or more, according to the new documents. While Greenwald warns that the team wants to be careful not to promise too much, and much work remains, the results so far indicate that the project will at least achieve its goals, and in particular will achieve its key goal of producing a fiery plasma, in which the self – heating dominates the energy balance.
The limits imposed by the Covid-19 pandemic slowed progress a little, but not by much, he says, and researchers are back in the labs with new operational guidelines.
Overall, “we’re still aiming to start construction around June ’21,” says Greenwald. “The physical exertion is well integrated with the engineering design. What we’re trying to do is put the design on the strongest physical foundation possible, so we can be confident in how it will work, and then provide guidance and answer engineering design questions as it goes. “
Many of the finer details are still being worked out on the car’s design, covering the best ways to get power and fuel into the device, pull power, deal with any sudden thermal or power transients, and how and where to measure key parameters for monitor the operation of the machine.
So far, there have been only minor changes to the overall design. The diameter of the tokamak has been increased by about 12 percent, but little else has changed, Greenwald says. “There’s always the question of a little more than that, a little less than that, and there are a lot of things that weigh in on that, engineering problems, mechanical stresses, thermal stresses and there’s physics too: how do you affect the performance of the machine? “
The publication of this special issue of the magazine, he says, “represents a summary, a snapshot of the physical basics as they are today.” Although team members discussed many aspects of this in physics meetings, “this is our first opportunity to tell our story, get it reviewed, get the stamp of approval, and spread it to the community.”
Greenwald says there is still a lot to learn about the physics of plasma combustion, and once this machine is up and running, key information can be obtained that will help pave the way for commercial energy-producing fusion devices, the fuel of which – the hydrogen isotopes deuterium and tritium – can be made available in almost unlimited quantities.
The details of the burning plasma “are really new and important,” he says. “The great mountain we have to overcome is to understand this self-heated state of a plasma.”
“The analysis presented in these papers will provide the worldwide fusion community with an opportunity to better understand the physical underpinnings of the SPARC device and assess for themselves the remaining challenges that need to be solved,” says George Tynan, professor of mechanics and aerospace engineering at the University of California at San Diego, which was not connected with this work. “Their publication marks an important milestone on the road to the study of burning plasma and the first demonstration of net production of controlled fusion energy, and I applaud the authors for making this work available to all.”
Overall, says Greenwald, the work done in the analysis presented in this package of documents “helps validate our confidence in achieving the mission. We don’t come across anything where we say, “oh, that’s predicting we’re not going to get where we want to.” In short, he says, “one of the conclusions is that things are still going well. We believe it will work. “