Commonwealth Fusion Makes the Physics Case For Its 400 MW Reactor (arstechnica.com)
- Reference: 0183724156
- News link: https://hardware.slashdot.org/story/26/06/10/0319259/commonwealth-fusion-makes-the-physics-case-for-its-400-mw-reactor
- Source link: https://arstechnica.com/science/2026/06/__trashed-19/
> ARC will be a tokamak that hosts fusion between hydrogen's two heavier isotopes, deuterium and tritium. This reaction results in a helium nucleus and releases a neutron and radiation. The helium transfers heat to the plasma, maintaining the conditions needed for fusion, but it is otherwise a waste product, referred to as "ash" in the fusion context. The neutron and radiation, however, are put to use. Part of that use is simply imparting energy into a blanket of molten salt that surrounds the fusion chamber. That energy, in the form of heat, will be used to drive a turbine that produces the electricity. The molten salt includes lithium ions; when one lithium isotope absorbs a neutron, it decays into more helium, plus tritium that can be used as fuel for the reactor. There are isotopes present that will also release additional neutrons, allowing this process to generate sufficient fuel.
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> Overall, the present design of ARC is expected to produce about 1.13 GW of fusion power, with 500 MW of that extracted as electricity. Some of that (100 MW) will be needed to power the plant's operations, leaving 400 MW to be sent to the grid. The rest of the energy is either kept in the tokamak to maintain the fusion reactions or lost due to inefficiencies in the heat and energy transfer of the system. There's a lot of uncertainty about these numbers; the 1.13 GW is just the center of a range of potential values running from 900 MW to 1.3 GW, so the 400 MW output may need to be adjusted up or down accordingly.
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> Some of that 400 MW comes during periods where fusion is not occurring. The nuclear reactions will occur within 15-minute-long periods that will be interspersed with one minute resets. The resets are meant to be kept short enough that nothing has much of a chance to cool down before it gets heated up again -- thermal inertia will let it continue generating power. That will be one of the key differentiators with SPARC, which doesn't have the heat extraction needed to maintain stable fusion for these long time periods, and so can't maintain the near constant temperatures needed for reliable power generation.
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> It's inevitable that parts of the device will be exposed to radiation and perhaps fusion plasma. The inner walls of the reactor will be shielded by tungsten, which will limit erosion by the conditions. Meanwhile, the vacuum vessel is designed to be replaced every one to two years. The papers note that this flexibility will allow them to make some design changes even after ARC is built. To enable this, the whole tokamak is meant to split in half for maintenance.
[1] https://www.cambridge.org/core/journals/journal-of-plasma-physics/collections/arc-fusion-power-plant-physics-basis
[2] https://arstechnica.com/science/2026/06/__trashed-19/
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Pennsylvania, Massachusetts, Virginia, and Kentucky are commonwealths. Vermont and Delaware call themselves both commonwealths and states in their constitutions. Puerto Rico and the US Virgin Islands are commonwealths of a different sorts as well.
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from [1]https://en.wikipedia.org/wiki/... [wikipedia.org]:"The "commonwealth" appellation is merely stylistic and carries no legal or political significance. ", for Pennsylvania, Massachusetts, Virginia, and Kentucky,
[1] https://en.wikipedia.org/wiki/Commonwealth_(U.S._state)
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Candiakenvirchusevania?
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By your powers combined, I am... the British Colonies!
The papers suggest ARC could produce more energy t (Score:3, Interesting)
You have to be able to do much better than 'suggest' if you are going to be have any credibility: the controlled, net energy-yielding nuclear fusion field is littered with the corpses of entities who 'suggested' that much.
Re:The papers suggest ARC could produce more energ (Score:5, Interesting)
For YHVH's sake, first off "suggest" is not Commonwealth's wording, they wrote five bloody peer-reviewed papers. You're criticizing them based on a word that a Slashdot author chose, likely without even thinking about their wording.
Secondly, there's nothing mystical about tokamak fusion, it's the most well understood type of fusion out there. The scaling factors are well understood. What the "entities" whose "corpses" litter the field didn't have was high-temperature superconducting magnets , as commercial-scale availability of HTS tapes only emerged in relatively recent times. These let you double the field strength. Under tokamak scaling factors, doubling the field strength lets you get the same Q factor at around 1/10th the volume.
There's many other interesting aspects of note, but at a fundamental level, that's all you need to know.
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Also since a few years we have AI controlled super fast reacting field coils.
AI means, they are based on ANNs, of course, but learn the flukes of the specific reactor. Another break through in that area was better measuring methods of the actual fields and plasma!
Re:The papers suggest ARC could produce more energ (Score:5, Interesting)
Plus, pretty sure it's *not* littered with corpses. I think JET is the only reactor that was ever built so far with the goal of being energy positive (and even then, only in terms of fusion energy, not electrical, since it had no generation equipment). It got to a factor 0.72 in its final runs when they went balls to the wall since they didn't need to avoid damaging the machine. That's still a little way off, but it's also nearly 50 years old at this point. It uses copper (not even superconducting, let alone high temperature superconducting) magnets. It's substantially smaller than ARC, and it rarely ran using tritium due to the handling constraints.
Every other tokamak I can think of has been built with the explicit knowledge that it wasn't going to be able to reach break even, but would progress research. The amount of energy tokamaks produce has been going up faster than moore's law has been adding transistors to chips, or at least it had until around the year 2000, when we ran out of new magnet technology to squeeze everything in tighter. Thankfully, as you said, we've now got new magnet technology in CFS's HTS magnets that can roughly double the field strength.
Hopefully when SPARC breaks even some time in the next few years, we'll be able to more concretely tell the naysayers to shut up.
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All these commenters who think they're so smart coming out with the same "Fusion power is 20 years away and always will be, har har har!"-quip who don't know a damned thing about the field and its progression is so tiring. One error with neutron measurements at ZETA before we even knew what we were doing, and the entire field was turned into a permanent joke, even as Q factors continued to climb almost monotonically. The press had their story and now we're cursed with an endless stream of these people.
Re:The papers suggest ARC could produce more energ (Score:4, Interesting)
All these commenters who think they're so smart coming out with the same "Fusion power
is 20 years away and always will be, har har har!"-quip who don't know a damned thing
about the field and its progression is so tiring
Well I'm a physicist who has been writing about fusion since my 3rd year E&M thesis in the 1980s, and I say fusion power is 20 years away (at least).
But by all means, explain what makes you an expert on the topic and how I "don't know a damned thing" in comparison.
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I toured an experimental fusion reactor as a student around 1990.
They told us commercial fusion was 20 years away.
It's now nearly forty years later, the scientists and engineers I was talking to have retired (and probably half of them are dead), and commercial fusion is STILL probably 20 years away.
Fusion research has been a huge boondoggle where scientists and engineers have spent their entire career not making working reactors. Probably got decent pensions though.
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> I think JET is the only reactor that was ever built so far with the goal of being energy positive
Nope, JET, TFTR and JT-60 were all designed to hit breakeven, and such claims are widely found in 1980s documents. JT-60s original name was "breakeven test reactor". T-15 was also, although finding claims of that is not so easy.
> when we ran out of new magnet technology to squeeze everything in tighter
No, it's when we learned that the performance was nowhere near what we expected and we had no clear way
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"it's the most well understood type of fusion"
more like the type most understood to not work.
as Robert Bussard said in his famous Google TechTalk in Nov 2006, "we don't think it'll ever be economic but it's really good science" and "one of my friends Dr Nicholas Kroll, one of the top 3 theorists in the world said some years ago we've spent $15 billion studying tokamaks and what we know is they're no damned good".
[1]https://www.youtube.com/watch?... [youtube.com]
[1] https://www.youtube.com/watch?v=rk6z1vP4Eo8
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> more like the type most understood to not work.
Simply false. The Q factor is eminently predictable with scale. It is by far the most predictable form of high-Q factor fusion (outside of gravitational, and we're not going there any time soon ;) )
> as Robert Bussard said in his famous Google TechTalk in Nov 2006
What, you mean BEFORE we got commercial-scale HTS magnets that scale down the size requirements by an order of magnitude?
Also, pointing to things like ITER to say that cost-effective fusion is impossibl
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Oh, lol, I just noticed that the person you cited was BUSSARD .
Yes, I know most people here know him as the Bussard Ramjet guy. But he was also the Polywell guy ;) He's was hardly the guy you'd want to be citing for "mainstream" fusion commentary even back in 2006.
(Also for the record, Bussard Ramjets don't work either).
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"The Q factor is eminently predictable with scale"
i predict it'll scale eminently up to beyond brown dwarf scale before it's viable but that poses a slight problem for commercial deployment.
"single person's two decades-old view"
it's been nearly 6 decades since i 1st heard that commercial fusion was at most 20 years away.
given my family history it'll be nearly as miraculous as fusion if i have that many years left so i'm done sitting waiting & listening to more promises that'll never happen.
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> Also, pointing to things like ITER to say that cost-effective fusion is impossible is like pointing to the ISS and saying SpaceX is impossible.
The cost of a fission plant outside the nuclear island - that is all the things like steam generators, turbines, cooling loops, etc. - is about 60% of the total cost. Assuming MIT's ridiculously low estimates of reactor cost, $6.50/We, that makes just those portions of the system about $4/W. A fusion plant is basically identical to a fission one outside the isla
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Nick Kroll is also a physicist? And here I thought he was just funny.
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> You have to be able to do much better than 'suggest' if you are going to be have any credibility.
I don’t think that’s true. Do you have any idea of the power of suggestion?
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Meh, let them try. Personally, I would surf on the AI hype wave to draw in money. You need more energy? We have it*. It would be a good match. Two type of companies promising revolutions that will change our lives forever!
* No net gain in energy yet, but guaranteed** in two years!
What about the cost (Score:4, Insightful)
Assuming sparc (no power) costs $1 billion, then guessing that arc costs $5 billion and makes 400MW. You could install about 2GW of sea based wind for the same. With such a huge power surplus over fusion you could probably melt rocks to store power for the still days
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Tokamaks also have no solution to the fast-neutron problem, which "embrittles" the core components of the reactor itself into powder over a few years of operation.
Only magnetized target fusion, like what General Fusion is pursuing, solves that problem.
I'm not sure that fusion will ever reach economic viability. But they're literally the only ones that even have a chance.
Re:What about the cost (Score:4, Informative)
Fission isn't economical either, but still money get poured into rehashing a known dead end. At least fusion is something of an unknown so deserves some rope still.
Re:What about the cost (Score:5, Interesting)
Yes they do. The high temperature superconducting magnets that commonwealth fusion systems have solve the problem.
The primary problem with the embrittlement is that you need to somehow get the damaged sections of reactor out from between magnets that wrap entirely around them, but you also need to not go anywhere near those damaged bits of reactor, because they're radioactive. Taking it apart with robots between the magnets and the reassembling the reactor has always seemed like a non starter that would take years.
CFS though have a solution... Specifically, the REBCO tapes that they use can be soldered together with non superconducting materials, and maintain their ability to generate extremely high field strengths. ARC is designed with soldered jumpers in a couple of locations around the magnets, allowing them to take the magnets apart easily. That allows them to remove the entire core of the reactor out, and remove it in one operation using a large gantry crane positioned over the reactor.. Yes, they get a chunk of radioactive waste to deal with, but the reactor gets to keep operating with a new core.
As for as the ecenomics go... well... I'm sure the very first ever fusion plant won't be ecenomical. However, it'll immediately start making the second one ecenomical, because it'll start producing the tritium that they previously had to buy. There's already a significant number of improvements that can be made documented in the literature. I'm sure the second one will be more ecenomically viable, and the third more so and so on and so forth.
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> Yes they do. The high temperature superconducting magnets that commonwealth fusion systems have solve the problem.
They do not. The magnets themselves are subject to neutron dislocations as well, and REBCO is worse than simpler magnets in that regard. CFS claims it's not that bad, but that's the mantra of fusion since the 1950s.
It also doesn't solve the *actual* problem that turning off the reactor to get at the deeper bits requires weeks of warming up and cooling down, which means there is no way the t
Re:What about the cost (Score:4, Informative)
Yeah, so, this is not true.
First off, turning it "to powder" is hyperbole; metals just become increasingly brittle.
Secondly, claiming that there's "no solution" is not just wrong (there are many), the particular solutions used by Commonwealth are literally discussed in the papers that this Slashdot article is about . Specifically, they use a molten FLiBe breeder blanket to absorb the fast neurons, which also breeds tritium. Since it's molten, there are no "structural" issues with it at all. The inner core (mainly tungsten) does need periodic replacements (every 1-2 years), but the reactor is designed to be easy to open up for swap-outs. It is treated as an expendable consumable, and is melted down and recast/rebuilt for the next replacement. In terms of complexity, cost, and downtime, it's probably roughly on par with fission reactor maintenance periods, perhaps superior.
Third, there are many types of magnetic confinement fusion, not just magnetized target fusion. These are less mature than tokamaks , and generally considered more longshots. Even ignoring that the fusion itself is more challenging, they trade something relatively simple - materials science and swapping - for something much harder (immense mechanical and fluid dynamics challenges)
Fourth, if you really hate neutrons, there are also aneutronic fusion designs . Again, though, less mature.
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> Assuming sparc (no power) costs $1 billion, then guessing that arc costs $5 billion and makes 400MW. You could install about 2GW of sea based wind for the same. With such a huge power surplus over fusion you could probably melt rocks to store power for the still days
1) ~$5B is about right for the first ARC plant, but that's to be expected, because first-of-a-kind plants are always much more expensive. Nth-of-a-kind for ARC is expected to be about $2B.
2) Wind is variable load, not baseload, not load followi
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China generated, not installed but actually generated, 500TWh extra electricity last year. Nearly all of it was renewable, from solar and wind. That's as much as the annual generation of Germany, and dwarfs the UK at just shy of 300TWh.
If you want cheap, abundant energy, that's how you do it. And then again, the next year. I hate to sound all "missile gap", but in this case we know it's definitely true (can see it from space) and one of the biggest issues in our economies is the cost of energy.
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> You could install about 2GW of sea based wind for the same
I believe the plan is to kick-start the Fusion market by creating a "good enough" plant and improving efficiency over time.
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Are you considering maintenance of undersea equipment, requiring dive-certified electricians for wave generators and the fact that wind only works when the wind blows and I don't think there's ever been a wind solution that cost less over time than it output worth of electricity. It's insanely inefficient.
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With wind you also have to include the cost of the battery, batteries add about ~60c per kwh. You do this because fusion is 24/7 and wind is not to compare the costs.
Children of the Atom (Score:1)
"Commonwealth" Nice Fallout reference.
1.21 Gigawatt !!! (Score:1)
(1.13, close enough, I guess)
Speculative fiction. (Score:2)
Key words in the article: "Both of those projects are predicated on using high-temperature superconductors".
Yeah, if we have a material which there is yet no evidence to suggest can actually exist, it's possible to generate net positive fusion energy. I won't be holding my breath.
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A full size working prototype of the HTS magnet has been built and tested successfully. There are plenty of papers about it. For instance see [1] here [ieee.org]. It is still cooled to very low temperatures but less cold than conventional superconducting magnets. They claim this is good enough for their designs.
[1] https://ieeexplore.ieee.org/document/10316632
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I think you are mixing up high temperature and room temperature superconductors. High temperature means liquid nitrogen temperature in this context rather than liquid helium temperature. They definitely do exist.
It's high relative to 4k, not high relative to 300k.
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> The EM drive is a thinly disguised perpetual motion machine. This really annoys some people so I made it my signature.
The EM drive was the wish-fulfilment gadget of the moment a decade ago. Martin Tajmar's meticulous testing pretty well showed the purported thrust as being false positives, and I don't see people talking about them anymore (although there are always some impossible-to-convince holdouts, I guess), but mostly the people pushing such things have moved on to other magical gadgets.
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HIGH temperature, not ROOM temperature.
*Facepalm*
God, Slashdot comments sections are so embarrassing these days.
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Perhaps you should read up what the term "High temperature super conductor" actually means.
Because we have them since decades!
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Yeh, they've already built the magnets. High temperature superconductors absolutely do exist - there's a whole category of them called REBCO (rare earth berillium copper oxides).
Commercial fusion is perpetually X years away (Score:3)
Renewables + BESS is so much cheaper, scalable, and ready to deploy compared to non-renewables and fusion that it doesn't make sense to risk much investment in deploying the latter. If/when some team realizes viable fusion, then maybe... but I bet it will still be capital-intensive, risky, and slow compared to renewables. If it happens, it will be cool but probably not a world-changing breakthrough. Solar's price decline by economies-of-scale is a real breakthrough we already have and should be using much more of; something Jimmy Carter should've pushed and invested in because the US is way, way behind but rapidly advancing with multi GW projects here and there.
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Fusion will be cool, when you can make a relatively small reactor, and use it as engine for space ships. Like overpowered plasma engine.
Re:Commercial fusion is perpetually X years away (Score:4, Interesting)
Well, good thing we're not risking much investment in it. Last year globally about $400bn was invested in deploying wind energy. Around $500bn was invested in solar deployments. CFS has so far attracted about $3bn. Taking a small punt on a company that has a technology that's very immature, but improving rapidly seems entirely reasonable to me.
History... (Score:4, Informative)
> Solar's price decline by economies-of-scale is a real breakthrough we already have and should be using much more of; something Jimmy Carter should've pushed and invested in because the US is way, way behind but rapidly advancing with multi GW projects here and there.
Not sure what you're referring to here; Jimmy Carter most definitely did push for and invest in solar. Pretty much all of the solar array technology we see today is the outgrowth of the Energy Research and Development Administration (ERDA)'s research program of the late '70s and '80s. Most particularly the Large Silicon Solar Array (LSSA; later Low Cost Solar Array, LSA, and then changed to the Flat Plate Solar Array, FPSA) initiative pushed the movement of research from single cell development to production lines to actual large fields of arrays.
Fusion is just around the corner... (Score:2)
...just around the corner - and has been for 50 years.
They not only need to show that they can generate net energy - a lot of net energy. For commercial success, they also need to show that the reactor can sustain that level of output for weeks, months, and years. That's an area that has not really been looked at, because no one has sustained a fusion reaction for longer than minutes. Personally, I expect that to be a huge hurdle, because of the temperatures involved.
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In your review of the papers, were any of those items addressed?
They couldn't get another 80 MW...? (Score:2)
Make it just a little bigger, for one point twenty-one jigawatts!! ...?
Untrustful (Score:3)
Fusion energy has being clearly extremely complicated.
Steady self-heating plasma for long duration hasn't being achieved yet. And we aren't fully sure if self-heating plasma will have the exact same behavior than external heated plasma. After all, how the energy reach the plasma is important.
Also the tritium feeding problem is not solved neither mentioned.
As the condition hasn't being achieved, there is no real data about the fatigue of materials under neutron leaks that won't be stopped at the shielding and fuel feeding.
In summary, nobody can ensure it's gonna work based on "papers". On paper you can propose an experiment with multiple goals and you declare success if most goals are reached. You don't propose a full reactor over exotic yet to prove concept full of problems yet to be solved.
This is just an operation to capture funding.
Still Makes Nucler Waste (Score:2)
Fusion reactors seem really cool, but they still produce nuclear waste. Now that Nevada doesn't want it all. Where are you going to put it?
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You're some special kind of mentally ill and paranoid/obsessed, huh?
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You need to be able to distinguish between nuclear and fusion, they are completely different processes.