Clarifying What Commonwealth Fusion Systems Will Do

Steven B. Krivit points out that Commonwealth Fusion Systems will not get to true energy breakeven in 2025.

The plans for the SPARC reactor specify a fusion power output of 50 to 100 MW of heat. Thermal power to heat the fuel will be 30 MW. The goal is to do this for ten seconds. Krivit points out it will take 90MW of electricity to generate the 30 MW of input heat.

There is a 35-page report on the plans for the SPARC reactor that Commonwealth Fusion Systems will build.

Nextbigfuture noted that Commonwealth Fusion Systems might get some power generation system in 2033 if they maintain ambitious development and fundraising goals.

Commonwealth Fusion Systems has raised $50 million to prove out much more powerful superconducting magnets which are what will make their system 60 times smaller the the international Tokamak.

28 thoughts on “Clarifying What Commonwealth Fusion Systems Will Do”

  1. Not quite. It’s more like “we will make affordable fusion quickly by using a new technology (REBCO HTS tapes) and by iterating designs quickly”. Part of that iterative design strategy is concentrating on getting to Q>1 with as small a reactor as possible, using the high-field magnets.

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  2. SPARC isn’t trying to be a commercially viable reactor. That’s what ARC is for. But SPARC will cost a fraction of what ARC will. It’s the necessary proof-of-concept that will allow CFS to get the large-scale investments they’d need to build an ARC pilot plant, and then hopefully start building factory-produced operational plants.

    I’m not holding my breath yet, but this is one of the brighter spots in the private (or semi-private) fusion landscape.

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  3. Just to clarify Krivit’s big “expose” here:

    When plasma physicists talk about “breakeven plasmas”, they’re talking about a parameter conventionally called “Q”, which is (output power from the plasma) / (input power to the plasma). Q>1 means you’re better than breakeven.

    Q is not (output power from the facility) / (input power to the facility), which is what you need to gauge the commercial viability of a fusion reactor. There are all kinds of losses associated with delivering energy to a plasma. It’s likely that, to get to a commercially viable plant, you’d need a reaction where Q>20.

    One other thing to keep in mind is the length of the shot, i.e., the length of time each experiment lasts. Most tokamaks require “relaxation times” of minutes to even hours before the plasma is steady-state enough to extract data from it. SPARC has a relaxation time of about 10 seconds.

    But this also means that the whole commercial power generation argument is even sillier. In a commercial reactor, a “shot” would last for hours, days, or even weeks, and the burning plasma wouldn’t need any external power at all–it’d be heating itself. But with short shot lengths, most of the time the input power will be on. That makes any consideration of any (facility out) / (facility in) power balance completely irrelevant.

    Bottom line: SPARC is an experimental reactor. But the experiment is to gather the data necessary to go to commercial scale, not to learn stuff about plasmas.

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  4. CFS has been pretty up-front about what they intend to do. They’re making a lot of tradeoffs that make SPARC unusable for economical power generation, in favor of getting to Q>1 as quickly as possible, as cheaply as possible. The thinking is that being able to generate shots with net plasma energy generation will give CFS (and probably the rest of the commercial fusion industry) access to much larger pools of investment capital, which will give them the funds necessary to go off and build ARC as a prototype commercial plant.

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  5. D-T has 2500x the power density of p-B11. So, to get the same yield from the same sized machine as a D-T machine, a TAE machine would need a triple product (some combination of temperature, density, and confinement time) 2500x as large. So tack on another three orders of magnitude above and beyond the 4 or 5 orders of magnitude they need just to get close to Q>1 with D-T.

    It’s not happening any time soon.

    However, the answer is obvious: They’ll do experiments with D-D because it’s cheap, then go with D-T, just like everybody else.

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  6. I think that people are confusing SPARC with ARC. SPARC is an R&D project that is meant to demonstrate scientific break even and test various operating modes. The much larger (and steady state) ARC, will be the commercial reactor.
    So far no reactor experiment has demonstrated even scientific break even. So this would be an important next step.

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  7. Helion had enough funding to build their full scale prototype (~35 million) and they are already testing it as we speak, with good results, I hear. Though I do not have any numbers and we are likely not see them for a while. Helion has become very secretive after they got burned by news articles that overhyped their aspirational goals and timelines (which assumed ideal funding that was not available at the time) as a definitive statement. Either way, I think Helion is the team that I would bet my money on for getting there first.

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  8. Helion is now much further than that. They have a full scale prototyp in operation. I hear that results are encouraging. Seems to be enough for them to predict a first commercial reactor in 6 years.

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  9. I’ve seen the same materials. There is no straightforward path to increase heating to 2 billion degrees. That’s unrealistic optimism.

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  10. Helion is also funded but not with as much money – but also not boxed into having to go for the long shot boron fusion. TAE can’t viably do D-D and D-He hybrid fusion because their design can’t handle the 6% neutronicity.
    So your main argument seems to be they have more money? I predict they make D-D and D-He hybrid fusion near or past breakeven and then hit a wall reaching for boron and never achieve economic/commercial engineering relevance.

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  11. I saw a short presentation by one of their people a couple years ago. He said they’d shown stable plasma at 10M degrees, and their next goal was to use the bigger reactor to see whether it would remain stable at higher temperatures, targeting 100M degrees. Their simulation said stability would increase with higher temperature. If that worked out, they thought that was the last major milestone and it was a straightforward path to just add more heating.

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  12. They have a funded R&D program that they follow, with a singular goal of achieving economically feasible fusion within about 10 years. They achieve an intermediate goal and proceed to the next one. That makes them far ahead of every other project. No one else does that; at best, others are just research projects. A distant second, perhaps, is a barely known but long operational Russian project – slow but funded, selling TAE neutral beam injectors, and pursuing a rather modest goal of DD fusion in an open trap (with an awful lot of added magic). That would make an excellent bulk source of cheap neutrons (economic transmutation, cheap burning of nuclear waste, commercial isotope production, bulk tritium production, etc), but a power reactor is apparently not pursued. So who else is left? A few universities with their grand research programs. And the less said about ITER, the better.

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  13. That’s not how I interpreted the comment.

    My interpretation is that it takes 90MW of electrical power going into the system to create 30MW of heat energy in the actual plasma. Because you can’t just transfer energy to the plasma with 100% efficiency. Or not even 50% efficiency.

    Looking through the linked article I find:

    Coblentz told New Energy Times that 150 MW of electricity would be required to power the radio frequency and neutral beam injection systems that produce the 50 MW of heating power injected into ITER. If the conversion efficiency is the same with SPARC, it will require 90 MW of electricity to heat the fuel.

    So yes, it isn’t a 30MW for 3 seconds issue. It’s a question of the ratio between plasma heating and the supplied electrical power.

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  14. Yes but you could just use the energy to create heat in the first place without amortizing the cost of Mr Fusion.

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  15. Yeah Tri-Alpha is a bit odd. On the one hand they say that they are still going for p-B. On the other hand they don’t seem to be anywhere near the temperatures needed for p-B.

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  16. SPARC is impressive in terms of its goals and the possibility of making a fusion reactor that reaches breakeven.

    Not so impressive when you look to see how economical electricity would be from said reactor.

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  17. The fusion energy gain factor (Q), sometimes referred to as “scientific breakeven”, is the ratio of fusion power output to the power heating the plasma. It’s not the same thing as “engineering breakeven” or “wall plug efficiency”, but it’s a commonly-used metric and the next major milestone in fusion research. I don’t see that referring to Q>1 as “net energy gain” is intentionally misleading. However, I do think that fusion researchers should be aware that the metric that most members of the public are interested in (whether they know it or not) is engineering breakeven.

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  18. Didn’t Tri Alpha only reach 20 million degrees when they need to hit 3 billion? I guess I’m not getting the optimism.

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  19. I know I must sound like a squeaky door … But 30 MW for 3 seconds is 90 MJ, since a joule is one watt-second. Not 90 MW.  The original author could have said 90 MW-s, and that would have been the same thing. Thing is, power and energy, while intimately related, are NOT interchangeable.  

    Ah well … 

    I’m looking forward to the article (here?) that shows the 90 MJ input heating the plasma high enough that at least 90 more MJ of fusion product is produced. Still nowhere near enough to parlay into a working power reactor, but enough gain to get everyone’s attention.

    Just saying,
    GoatGuy ✓

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  20. So they want a fusion reactor for DT and DD fuel, which means mostly and much neutrons, respectively.

    At the same time Tri Alpha is already ahead with aneutronic machine. At the same time a modern PWR has up to ×50 net enegry gain (all-inclusive over entire fuel cycle and 80 years life cycle with proper centrifuges and decomissioning fund) with perfect neutron containment inside reactor (primarily a matter of economics). A smallish DD fusion machine with barely over break-even energy balance would be a candidate for spacecraft propulsion, but definitely not this design, as Tri Alpha beats them to it again.

    Dear investors, you never change. <double facepalm>

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  21. I read the report on SPARC from MIT and it looks very impressive but then again I am not a expert in any of the required fields. They want to use the latest type of superconducting magnets plus their whole fusion apparatus is reasonably small and can be easily dismantled for upgrades to the latest technologies.

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