New Mode Enables Four-Fold Increase in Tokamak Fusion Performance

Super-H Mode allows tokamaks to achieve higher fusion performance than previously possible. In recent experiments operating in and near the Super H-mode regime, researchers have achieved record-breaking values of fusion gain for a device of DIII-D’s size. Fusion gain is the ratio of fusion power generated to heating power.

Super-H Mode works by increasing temperature and pressure in the outer region of the plasma, called the pedestal. The experiments showed – as the theory predicted – that proper tuning of the plasma cross-sectional shape and density leads to pedestal temperatures and pressures that are more than twice as high as those of typical pedestals.

Because plasma conditions in the core – where fusion takes place – are dependent on conditions at the edge, Super-H Mode enables as much as a four-fold increase in fusion performance.

Nuclear Fusion Journal – High fusion performance in Super H-mode experiments on Alcator C-Mod and DIII-D

“Super-H Mode promises to reduce the cost and scale of future fusion reactors, thereby bringing the realization of fusion power closer,” said Steven Cowley, director of the Princeton Plasma Physics Laboratory who was not involved in the research. “It couldn’t be more significant.”

A tokamak is a doughnut-shaped device with strong magnetic fields that confine matter at temperatures exceeding 100 million degrees. Inside the tokamak, matter transitions to a plasma state where electrons are stripped from their nuclei. The resulting electrically charged plasma can be shaped and controlled by the magnetic fields. Within a sufficiently hot plasma, atoms collide and fuse together, producing fusion energy in a manner similar to the sun.

Abstract
The ‘Super H-Mode’ regime is predicted to enable pedestal height and fusion performance substantially higher than standard H-Mode operation. This regime exists due to a bifurcation of the pedestal pressure, as a function of density, that is predicted by the EPED model to occur in strongly shaped plasmas above a critical pedestal density. Experiments on Alcator C-Mod and DIII-D have achieved access to the Super H-Mode (and Near Super H) regime, and obtained very high pedestal pressure, including the highest achieved on a tokamak (p ped ~ 80 kPa) in C-Mod experiments operating near the ITER magnetic field. DIII-D Super H experiments have demonstrated strong performance, including the highest stored energy in the present configuration of DIII-D (W ~ 2.2–3.2 MJ), while utilizing only about half of the available heating power (P heat ~ 7–12 MW). These DIII-D experiments have obtained the highest value of peak fusion gain, Q DT,equiv ~ 0.5, achieved on a medium scale (R  less than 2 meter) tokamak. Sustained high performance operation (β N ~ 2.9, H98 ~ 1.6) has been achieved utilizing n  =  3 magnetic perturbations for density and impurity control. Pedestal and global confinement has been maintained in the presence of deuterium and nitrogen gas puffing, which enables a more radiative divertor condition. A pair of simple performance metrics is developed to assess and compare regimes. Super H-Mode access is predicted for ITER and expected, based on both theoretical prediction and observed normalized performance, to allow ITER to achieve its goals (Q  =  10) at I p  less than  15 MA, and to potentially enable more compact, cost-effective pilot plant and reactor designs.

33 thoughts on “New Mode Enables Four-Fold Increase in Tokamak Fusion Performance”

  1. I think lithium ion got to utility storage first because we already had a large industry for portable devices. I’m agnostic about battery storage – whatever chemistry and technology works out the cheapest is fine with me.

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  2. This has been studied since the 1970’s, but launch cost has always been the roadblock. Compared to locations on Earth, solar flux in space is 4-10 times higher. That’s because no night, weather, or atmospheric absorption.

    Using the same technology as communications satellites (high frequency radio), transmission to the ground has about a 50% end-to-end efficiency. So the same solar panel in space delivers 2-5 times the net energy to the grid.

    The trick is putting it up there at an affordable cost. Cheap rockets is part of it, but also using off-planet resources (which is enabled by cheap rockets). 98-99% of the satellite mass can be made from materials already in space. That reduces what needs to be launched from Earth.

    The same high solar energy flux in space can power the machines and furnaces to convert lunar and asteroid rock into satellite parts. We just haven’t bootstrapped factory production in space yet.

    Space-based solar isn’t guaranteed to be a winner. Ground solar has gotten *very* cheap in the last decade. But it is an option worth considering. There is a reason 99% of satellites use solar power – it works and is reliable.

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  3. Right now, they have the scaling equation to tell them approximately what size reactor they need to build to get pass break even.

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  4. And rule breakers who get things done do the latter. If you listen to reason you never try hard enough. Engineers call it analysis paralysis.

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  5. Forever two decades down the line. Stop it already. If I was into conspiracies, I would swear the fossil power people are paying money to slow walk fusion.

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  6. I am actually surprise that some billionaire hasn’t taken on LFTR and Fusion. There is trillions to be made.

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  7. It doesn’t have to be a death ray, just a bounced sunbeam. Based on the Nanosail-D test you could get 2 square meters for 1 kg. So 160,000 square meters for 80,000kg launch. The Znamya experiment gives you insolation reflected for a 150 square meter piece of shiny mylar.
    So basically if you can get Spacex Superheavy launch costs down to $30 million each you can reflect enough sunlight to a large solar farm area (like 7 square kilometers) at $2 a watt nameplate such that you can boost capacity factor from like 25% to 75%. Night time power, no extra cost really. Cloud cover would still be an issue.
    This is based on current utility solar and storage project prices, which I expect will drop even more by the time a $30 million Superheavy launch is available, eroding the comparative economic feasibility. I’m also skeptical a solar mirror boosted farm would easily pass environmental review.

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  8. If you’re willing to put up with the 20% round trip loss, flow batteries already right now cost about 40% of lithium ion batteries once you start adding hours of storage past the first eight. It’s notable that matches the round trip efficiency of pumped hydro, and new flow batteries are actually now cheaper than new pumped hydro in California. Flow batteries will drop in price by about 50% 7 years based on current order pipeline and manufacturer projections. Retrofitting some existing hydro to have some reversibility is still likely to be cost effective in a lot of places going forward, though.

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  9. I don’t see how beaming it back to Earth could ever be worth the cost. Efficiency would be in the tank. And it would kill everything in its path.

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  10. New solar farms are being built with 4 hours of batter storage standard. As the price of storage comes down, they can afford to include more of it.

    Night-time demand is about half that of daytime. Other power sources can fill that need.

    It is always sunny in space. If SpaceX’s next generation rocket works as advertised, space-based solar will be feasible.

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  11. Hey, I wish that were the case, but once you start changing the magnets you need to start changing everything. The cryostats, first wall, etc etc – flexible tape isn’t going to make the thing appreciably better and increases the risk that unforseen ware or effect of neutrons degrades the tape.

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  12. The fusion reactor in the sky is great, it’s just too bad the transmission lines go down for about twelve hours every day.

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  13. By 2035 the world will be producing 3 TW of energy using that fusion reactor in the sky, at 2 cents/kWh. Terrestrial fusion will have lost the race, even if ITER works.

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  14. Using better magnets you could hit that goal at 1/6 the price on a rebuild (that’s a conservative number, likely better than that). I think starting over would just as likely accelerate the schedule. ITER won’t ignite tritium until 2035 by the current one.
    Also the new superconductor tapes are flexible so you can “pop open” a new build for easy upgrades, adjustment, and maintenance.

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  15. Redesigning ITER would create an even greater delay, and add to its cost. ITER is supposed to be used to study “burning plasmas” and to achieve Q = 10. It will probably be successful in that regard, but it will probably also prove to be an evolutionary dead end. I doubt a successful DEMO will look much like ITER. Although this research is directed towards ITER, I don’t see any reason a private company such as Tokamak Energy or Commonwealth Fusion systems couldn’t take advantage of it.

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  16. The assumption seems to be that there are two types of fusion reactors: those that we know won’t reach break even and those that we know will. I would submit that for now there is only one type of fusion reactor: those that we don’t know won’t reach break even. We don’t know for sure how successful an experimental fusion reactor is going to be until we’ve thoroughly tested it, which is why they’re called “experimental”.

    The TFTR tokamak was explicitly designed to reach break even, but it didn’t meet that goal during its operational life (1982-1997). It’s certainly not the only go-for-broke fusion reactor in the history of fusion research that went broke, which is not to say that we didn’t learn anything useful from it. The two tokamak reactors that contributed this paper are DIII-D, which has been operating since 1986, and Alcator C-Mod, which has been operating since 1991. Both are upgrades of even older reactors. ITER is the current (publicly-funded) go-for-broke tokamak design, but until it’s completed there aren’t any experiments that can be run on it. Which is why experiments are being run on older tokamaks. The more time that is spend running “endless” experiments now, the less time will probably be needed to run “endless” experiments after ITER is complete.

    As for non-tokamak reactors, in many cases there are big unknowns. It is usually extremely expensive to go for broke without minimizing those unknowns.

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  17. Because big reactors take a lot of money and a long time to build. We’ve been building ITER for twenty years.

    MIT published a paper a couple years ago saying we could speed up fusion development by using more small reactors, doing more experiments, instead of spending so much on a giant reactor that has to get everything right to avoid being a gigantic waste of money.

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  18. We do both, we have plenty of small reactors where many groups can test new theories, and a really big one (ITER) that goes for it using the methods developed by the small reactors.

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  19. The thinking has always been to demonstrate the physics on something easier to get funding for, rather than make the argument that you need 4x more money for a much larger device because you’re hoping you’ll get it to breakeven. Most of these physicists and post docs just want to figure out the physics problems, they’re not going to lose sleep over trying to get funding for a power production-level device on the first try. I see your point but the economic realities have never made that kind of thinking reasonable. Maybe in 10 years when he’s a predicted Trillionaire, it’ll get the ole Musk treatment and we’ll be done in 5 years.

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  20. Why do we build fusion reactors that we know won’t reach break even and run endless experiments? Scale the machines up and go for it. When the units are generating power there will be experiments that need doing also.

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  21. Nobody expects tokamaks that size to hit breakeven. They’re talking about maybe trying this on JET, which is about twice as big and achieved Q=0.67 in 1997.

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  22. I read another article that explained it much better. It had pictures and graphs which made it easier for ME to understand the principle behind it. 🙂

    They are getting there. I am excited about when they get a universal super quantum computer to figure out the cheapest, fastest, best way to create fusion using simulations. It would not surprise me in the least, if it spit out a way to create cold fusion. (Completely different then what they are trying to do now to create cold fusion.)

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