Negative Triangularity – A Positive for Tokamak Fusion Power Reactors

The Science

Tokamak devices use strong magnetic fields to confine and shape the plasma that contains the fuel that achieves fusion. The shape of the plasma affects the ease or difficulty of achieving a viable fusion power source. In a conventional tokamak, the cross-section of the plasma is shaped like the capital letter D. When the straight part of the D faces the “donut hole” side of the donut-shaped tokamak, this shape is called positive triangularity.

When the plasma cross-section is in a backwards D shape and the curved part of the D faces the “donut hole” side, then this shape is called negative triangularity. New research shows that negative triangularity reduces how much the plasma interacts with the plasma-facing material surfaces of the tokamak. This finding points to critical benefits for achieving nuclear fusion power.

Tokamaks, such as the Tokamak à Configuration Variable (TCV) shown here, are donut-shaped devices that confine plasma to produce fusion reactions. The shape of the plasma cross-section affects the quality of the containment. Credit: Image courtesy of CRPP-EPFL, Association Suisse-Euratom

The Impact

One of the challenges in fusion energy science and technology is how to build future power plants that control plasmas many times hotter than the sun. At these extreme temperatures, interactions of the plasma with the material walls of the power reactor must be controlled and minimized. Unwanted interactions occur due to turbulence in the boundary region of the plasma.

This research shows that the boundary turbulence in negative triangularity plasmas is much reduced when compared with that occurring in plasmas with a positive triangularity shape. As a result, the unwanted interactions with the plasma-facing walls are also much reduced, leading in principle to longer lifetimes for the wall and a reduction in the risk of damage to the wall, something that could shut down a reactor.


Scientists know that, in tokamak fusion devices, core plasma shapes with negative triangularity exhibit a substantial increase in energy confinement compared to plasmas with positive triangularity. Negative triangularity plasma shapes also show reductions in the fluctuation levels of the core electron temperature and density. This by itself makes negative triangularity plasmas promising candidates for a future fusion power reactor.

The new research reported here shows that the sign and degree of triangularity also have a large effect on plasma edge dynamics and power and particle exhaust properties, but scientists know relatively little about such effects. These experiments at the Tokamak à Configuration Variable (TCV), located at the École polytechnique fédérale de Lausanne (EPFL) in Lausanne, Switzerland, revealed a strong reduction of boundary-plasma fluctuations and plasma interaction with the facing wall for sufficiently negative triangularity values.

The researchers observed the effects across a wide range of densities in both inner-wall-limited and diverted plasmas. This strong reduction in plasma-wall interaction at sufficiently negative triangularity strengthens the prospects of negative triangularity plasmas as a potential reactor solution.

Reference: “Suppression of first-wall interaction in negative triangularity plasmas on TCV” by Woonghee Han, Nico Offeddu, T. Golfinopoulos, Christian Theiler, C.K. Tsui, J.A. Boedo, E.S. Marmar and the TCV Team, 19 February 2021, Nuclear Fusion.
DOI: 10.1088/1741-4326/abdb95

This work was supported by the Department of Energy Office of Science, Fusion Energy Sciences program, and the Swiss National Science Foundation. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training program.

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  • David Dundas

    The instabilities at the outer edge of a Tokamak plasma are largely due to the non-linear magnetic field across the torus, the strongest field being close to the central magnet. Negative triangularity of the torus will help, but a potentially better approach is to eliminate the central magnet as in the Wendelstein 7-AS Stellerator of the Max Plank Institute

  • Rod

    The naive public are being swindled again! It doesn’t matter if they have a billion tesla they will never produce fusion. The science is Voodoo!

    • Eric

      The science is “voodoo”? No, the science is very well understood and has been for decades. It is the engineering that has been lagging and this should be no surprise when you understand the level of difficulty being undertaken. Basically, we have to find a way to heat up hydrogen isotopes to a temperature far above that found on our Sun. But we are getting closer to that reality. I don’t know if we will achieve it in 10 years or 30, but fusion is the future of energy production.

      If you have an alternate viewpoint, and it appears that you do, please list the reasons you think the science is “voodoo”. Also, address how the science is voodoo we have already achieved fusion reactions many, many times with increasing duration and returns on energy put in.

      Thanks and have a great day!

  • Vernon Brechin

    Those, who work in the fusion energy field tend to be highly focused upon their technical specialty. Few have a holistic view of the technology that they often view as our savior. Typically, nuclear power advocates continue to believe that we have 20-30 years to scale up their favorite technology to a point where it can almost totally replace our long-time addiction to fossil fuel based energy resources. They tend to be clueless regarding the following statements and serious criticisms of the technologies that they adore.

    Most popular fusion energy breakthrough article are highly hyped while missing descriptions of the many key problems still requiring a solution.

    UN chief: World has less than 2 years to avoid ‘runaway climate change’

    UN Chief warns countries that the ‘point of no return’ on climate change is fast approaching

    UN warns that world risks becoming ‘uninhabitable hell’ for millions unless leaders take climate action

    ITER is a showcase … for the drawbacks of fusion energy

    List of fusion experiments

    • Eric

      I am not exactly sure what the point of your comment is. No one in the fusion field is saying that we should just sit on our hands and wait for fusion power to become commercially viable. We do need to invest heavily in solar and wind generation and shut down coal plants as soon as possible.

      But solar and wind suffer from a really bad problem… they don’t produce energy when there is no sun and no wind. This means you rely on fossil fuels for those periods, or you invest in massive batteries which are very expensive and also very bad for the environment.

      Fusion will be the solution longer term. No, we likely won’t have commercially viable fusion power plants for a couple decades, but it doesn’t mean we don’t continue to research it. The science is well understood and once our engineering capabilities catch up to theory, we will finally have a clean and almost limitless source of energy. In a century, kids will be reading about coal power plants in their history books and unable to understand how we could just pollute our air and kill thousands in the name of producing power.

      So please don’t turn this into an either-or situation. We need solar and win now. We also need to keep pushing for fusion power for our future.

  • Alex

    There will be no hot fusion rectors producing electricity in our life time, they are 30 years away every 20 years.

    • Eric

      It is easy to be dismissive of fusion power. I mean, being cynical is easy. Putting in the research is much harder.

      The reality is that the science is well understood and it is the engineering that has to catch up to theory. The engineers have a very difficult task in front of them, but they have been overcoming the obstacles needed to achieve temperatures hotter that our Sun.

      I am not sure how long your lifetime is, so I cannot say if it will happen in yours, but I am confident we will see our first commercial reactor within thirty years. Investors seem to agree as we are seeing more companies getting involved in this area. And when you see rich people pouring money into an area, you know it is more than just a pipe dream.

      • John Jakson

        It’s funny that fusion advocates will mention the liabilities of solar and wind programs but never ever mention fission like it doesn’t exist. They must think that every fission reactor is a potential Fukashima event.

        We have in Molten Salt Reactors an incredibly elegant design that has relatively few engineering challenges save the often repeated one of corrosion. But in fusion we have an endless list of engineering challenges. While the plasma physics may be very interesting it requires levels of engineering that make MSRs a walk in the park.

        We have atleast one MSR design and many similar ones that promise high temp 2GW thermal reactors for about $1B a piece like in New Brunswick based on smaller scaleable blocks. But in France we have the ITER project that is nowhere near net even going on $60B and won’t be energy even for several more 30year prototype cycles. The ITER team lied by ommision, energy in was greatly understated, energy out was over stated, result 15 fold error.

        The previous poster Vernon mentioned the Jasby article for “the drawbacks of fusion energy” on the bulletin. Jasby outlined as an actual fusion physicist all the realities of ITER, it won’t ever work, period. I didn’t see you respond to that article because it is really damning of ITER. His comments on tritium esp alarming. Not only is there no meaningful supply of tritium, he says that 98% of the tritium injected will never be burned. The problem with fusion is that there is a remarkable amount of hand waving that someone else will figure out each new problem. In MSRs every design can be fully understood by a single engineer/scientist almost on the back of an envelope. The most interesting part of MSR is the fuel rod, it’s a passive device too. Storing heat in hot salt tanks for constant heat production but variable electrical output to follow the grid demand is brilliant and is now part of every MSR project.

        Since fusion clearly works in the stars, fusion science isn’t voodoo at all, but on earth, fusion is achieved by means that are off the scales in terms of practical engineering. It’s the entire economics of ITER as well as laser driven fusion that is voodoo. So why does humanity spend possibly $100B over the entire planet for fusion research for no near term gain when a few $billion would start to get MSRs up and running now when they are most needed.

        We had a credible MSR program running 50 years ago, killed off by clueless presidents. China is now talking about their TMSR clone which the Obama gov gave them gratis. That project was only $150M iirc. It’s just a 2MW thermal prototype based on the original ORNL design. And thorium as well as uranium fuel is available for millenia of use.

        Every $B wasted on ITER is a $B not used to build a 1GW MSR power plant today which allows coal plants to continue on until the perfect solution is achieved.

        • Eric

          You had a lot of points and cannot respond to them all, but I will pick out your last sentence:

          “Every $B wasted on ITER is a $B not used to build a 1GW MSR power plant today which allows coal plants to continue on until the perfect solution is achieved.”

          This is a false dichotomy. We have plenty of money to do both. The $100B you cite appears to be a world wide total spend, not an annual amount Get rid of our bloated (US) military budget, bring it down to half its current budget and it is still bloated and you could take that roughly $400B PER YEAR and get us on a path to zero carbon emissions in five years and still have the money for fusion research. It is not an either-or proposition, and should be a focus mostly on solar/wind now but also use money to research fusion.

          You say the engineering is off the charts, but I don’t think it will be for long. Fission may be better than coal, I’d agree but it has long term problems that just aren’t solvable. Even China has moved away from building new nuclear plants and they don’t have to deal with environmental groups that are misguidedly stopping them.

          If some other solutions, say the molten salt reactor you cite pans out, wonderful. We should be looking at a wide variety of solutions to our carbon problem. Even if I am wrong that fusion will be one of those solutions, I would not consider it money wasted as we need to fund many different ideas to tackle this huge problem. And if you are wrong and fusion has the potential to solve the world’s energy problems, it would be awful if we didn’t explore it.

          I’m willing to cut the US military budget in half to solve our real problem. What about you?

        • Eric

          One final point: fusion reactors do not require tritium, they can easily run from deuterium-deuterium which has a nice side-effect of producing tritium. D-T reactions, if I remember correctly produce roughly 10 times the energy per gram as do D-D reactions, but when you are talking about only needing a few hundred grams to supply the country’s energy needs, I am not sure it matters a lot. So I think you could have D-D reactors that breed tritium for D-T reactors.

          • John Jakson

            I read the UofCS book pages 89..end, mostly the section on MSRs, my own favourite amongst them being Moltex came out pretty well, I even learned a few things. The writer had the least to say about them and a whole lot to say about failed MIT startup Transatomic, plus Terrestial, Terrapower and all the Thorium variants which I’m not much interested in. Your writer MV Ramana had a lot to say but not very much is relevant to Moltex. I get it, he and the UoCS and all the renewable folks don’t like nuclear fission but they don’t even begin to understand the issues of a renewable only economy, it’s always about land area per energy unit produced. The UK for example doesn’t have enough land to RE its way out of climate change. The US has 8* the land per capita and may have to cover about 10% of it to go RE with enough over production to store in chemical energy for all year energy production.

            At the end of the UofCS book, they basically state that the US should stick with current gen PWRs rather than experiment with unknown MSRs, I could live with that if many more were built in French style. I don’t agree with the authors but I know perfectly well we won’t be extending the PWR fleet because they want to dismiss all the advantages that MSRs claim. And yet the anti nuclear types won’t even accept that advice. The paper ignores some pretty big benefits of MSR claiming them to be more dangerous.

            When you get rid of fossil fuels esp nat gas, RE will fall apart because storage will kill it. Nat gas is the battery effect that solar and wind hide behind. The irony is that solar/wind force the use of the least efficient kind of nat gas plant, the 40% eff peakers. If solar and wind were shut down, the much more efficient CCNG plants would run at 60% eff. They could even go to 70-80% efficient with oxygen burning and those could capture the CO2 since it’s not released in air.

            If you think RE can power the world you should read the MacKay book, “without the hot air”, it is a bit dated though and nothing about MSRs in it. I only read that twice. Bill Gates did a redo of it, I wonder how that went.

            All energy forms are dirty, greens worry too much about radioactive waste and nasty actors, while say France can store it’s entire nuclear waste stream in a football field. Germany on the other hand shut down nearly half it’s reactor fleet and carbon emissions never changed because those base load zero carbon plants were replaced by coal peakers and intermittent solar/wind. The RE part stole the CO2 non emissions from nuclear. That won’t be so easy if the remainder are shut down, those will just go to coal.

            If we have the Biden solar plan go full steam ahead, you can imagine what the electronic waste stream will look like after 20 years. US total primary energy use is comparable to 300 solar panels per person ie 300GJ/yr, add Li ion batteries and that is one hell of a waste stream several orders greater than the current computer eWaste stream. And most of that is not going to be properly recycled, maybe some batteries.

            And as I always say fusion plants are never going to work, maybe in a hundred years. Those have way more issues in design and hand waving than fission, and those pesky neutrons will essentially destroy and irradiate the containment vessel. You might want to read the Jasby paper also at TheBulletin org site which was mentiooned above. He was also a fusion physicist.

            Have a nice day

  • John Jakson

    FWIW, DD produces He3 and tritium but its not likely to be useful, it will get burnt up in side reactions. All of the tritium currently comes from fission reactors and the half life is 12 years so it’s always going away. The other source is to process Li7 into tritium but I don’t think it’s ever been done, just more hand waving.

    You think fission is barely better than coal, you have got to be frickin kidding. The problems you allude to are nothing compared to the damage done by coal. It is because of fusion/solar worshipers that we don’t move forward in MSRs always looking for the golden goose solution. Do you know what Death By Terrawatt hours is, look it up. Do you know what the neutron flux in a fusion reactor is going to do to the containment vessel? It will be quite the radioactive beast if it ever produces any net energy whether it’s DD or DT. It is the neutron flux that will heat and irradiate the vessel that is supposed to be turned into electricty. Only the PB11 reaction is very nearly neutron clean but the hardest of all reacton to achieve.

    I doubt you even read anything about fusion that is negative like the Jasby article, I dare you. You obviously have no idea what molten salt is either, but you don’t read about practical things. If you don’t know about MSRs, you have no business commenting on fission or fusion.

    As for DD vs DT, no I don’t think anyone is going to do DD at scale, it is always the stated goal to use DT because the temp needed is orders lower than DD.

    As for solar, US energy use is 100XJ/year. Per cap energy use is 100XJ/330M so 300GJ/year. One solar panel in the US NE makes about 1.1GJ/yr. That means about 300 solar panels per person for equal no of J of consumption. But the storage can only be solved by converting about half of the production into chemical energy and back to electrical at huge losses OR just rely on nat gas as the hidden battery. Forget about electrical batteries here. Convert 300GJ into KWhrs and about 1/6 of that would be seasonal storage per person.

    As for the $100B yea thats a wild assed guess for total spending over perhaps a decade or more.

    As for the military, more likely than not if the bases want to go carbon neutral at scale for the amount of primary energy they use, it would most likely be an MSR they would build for themselves since they won’t have greens on their backs.

    Since it likely represent (guess) 2% of the economy and energy use, it will have to go huge on energy investments and no, solar panels on a base is not going to scratch its energy problem. If the 2% estimate is right the Pentagon is going to need 20 1GW reactors just for itself, they might even have 20 bases to put them on without needing much new land.

    And the entire US economy can be powered by about 1000 1GWe reactors for the 100XJ/year. Most of those could be thermal to produce synfuels with 400+ for electrical.

    And 1 ton of Uranium or Thorium contains about 1GWYr of energy if fully fissioned in a breeder or MSR so 1000 tons of material per year could power the US. And fusion energy is about 4* energy denser so close to 250 tons per year of DT. As for a few hundred grams you are a million times off, you must be thinking of antimatter energy and you are still four orders off. You need to pay more attention in your wikipedia reading.

  • Eric

    “And fusion energy is about 4* energy denser so close to 250 tons per year of DT. You need to pay more attention in your wikipedia reading.”

    “You think fission is barely better than coal, you have got to be frickin kidding.”

    (I never said that, not even close. If you need to put words into my mouth, you have lost the argument.)

    “It is because of fusion/solar worshipers”

    “You need to pay more attention in your wikipedia reading.”

    “You obviously have no idea what molten salt is either, but you don’t read about practical things. ”

    (I have by the way, but…)

    At this point, you are simply having an emotional reaction, not one based on reason. Based on this, I am better of disengaging. You are simply too angry to be objective or to even read the words I write. You may want to work on your anger issues.

    The fact is that the world will continue to invest in fusion power and it will be replacing the very dirty coal and problematic fission plants at some point in the future.

    Have a nice day!

  • John Jakson

    Engineers are very blunt, we don’t take nonsense from folks that write nice words that have very little technical content. Have a nice day too.