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Progress toward fusion energy gain as measured against the Lawson criteria
232 sam 142 5/8/2025, 3:49:37 PM fusionenergybase.com ↗
Somewhat relevant, folks here might also be interested in a whitepaper we recently put up on arXiv that describes what we are doing at Pacific Fusion: https://arxiv.org/abs/2504.10680
Section 1 in particular gives some extra high-level context that might be useful to have while reading Sam and Scott's update, and the rest of the paper should also be a good introduction to the various subsystems that make up a high-yield fusion demonstration system (albeit focused on pulser-driven inertial fusion).
Any truth to that?
Modern lasers can also repeat shots much more quickly. Power gain on the capsules appears to scale faster than linear with the input power, so getting to practical gain might not be as far off as it appears at first glance.
These are some of the reasons that various fusion startups are pursuing laser fusion for power plants.
https://physicsworld.com/a/national-ignition-facilitys-ignit...
https://pubs.aip.org/physicstoday/Online/31501/The-commercia...
NIF's latest shot is 2 MJ in, 7 MJ out[1], for a 3.5X fusion gain. So they've got an order of magnitude to go before getting to modestly practical levels. NIF seems to scale much better than linear with respect to the laser power, so an order of magnitude better gain is probably not a big change to the device.
(This does neglect energy loss in the hohlraum, so it assumes that direct drive laser fusion will get similar results. There are several projects working on that. Based on another comment here[2], the main reason for the hohlraum was that it made the experiment more relevant to weapons.)
[1] https://physicsworld.com/a/fusion-industry-meets-in-london-t...
[2] https://news.ycombinator.com/item?id=43935891
Btw, NIF achieved those recent results by adding strong magnetic field around the target (penny-shrinkers knew that tech for 20+ years :). There are other things like this around that can potentially be similarly useful. Only if somebody had money and interest ...
I know motor windings have gotten pretty funky of late to do a little bit of this, but do they do multi tesla magnetic fields that use several different windings to create the same sorts of bias in field strength? The ITER windings seem to be an extremely mild form of this.
Bear in mind that I wasn't directly involved, and this my impression picked up from conversations during my time in fusion research, which was about 10 years ago.
https://lasers.llnl.gov/about/what-is-nif
>NIF is a key element of the National Nuclear Security Administration’s science-based Stockpile Stewardship Program to maintain the reliability, security, and safety of the U.S. nuclear deterrent without full-scale testing.
So it seems more likely to me that some physicists figured out how to get their fusion power research funded under the guise of weapons research, since that's where the money is. NIF's original intent was mostly weapons research but it's turned out to be really useful for both, and these days, various companies are attempting to commercialize the technology for power plants.[3]
[1] https://theaviationist.com/2025/04/26/us-nuclear-weapons-wil...
[2] https://www.fusionindustryassociation.org/congress-provides-...
[3] NYTimes: https://archive.is/BCsf5
The purpose of it is to show that the USA is still capable of producing advanced hydrogen bombs. More advanced then anybody else.
The '2.05 megajoules' is only a estimation of the laser energy actually used to trigger the reaction. It ignores how much power it took to actually run the lasers or reactor. Even if they update the lasers with modern ones there is zero chance of it ever actually breaking even. It is a technological dead end as far as power generation goes.
The point of the 'breakthrough' is really more about ensuring continued Congressional approval for funding then anything else. They are being paid to impress and certainly they succeeded in that.
However I suspect this is true of almost all 'fusion breakthroughs'. They publish updates to ensure continued funding from their respective governments.
People will argue that this is a good thing since it helps ensure that scientists continue to be employed and publishing research papers. That sentiment is likely true in that it does help keep people employed, but if your goal is to have a working and economically viable fusion power plant within your lifetime it isn't a good way to go about things.
If the governments actually cared about CO2 and man-made global warming they would be investing in fusion technology and helping to develop ways to recycle nuclear waste usefully. Got to walk before you can run.
There's "breakeven" as in "the reaction produces more energy than put into it", and there's breakeven as in "the entire reactor system produces more energy than put into it", which isn't quite the same thing.
Energy gain (in the general sense) is the ratio of fusion energy released to the incoming heating energy crossing some closed boundary.
The right question to ask is then: “what is the closed boundary across which the heating energy is being measured?” For scientific gain, this boundary is the vacuum vessel wall. For facility gain, it is the facility boundary.
On the other side of the coin, if you put 10kWh in and get 10kWh of fusion out, that's 20kWh to run a steam turbine, which nets you about 8kWh. So really you need to be producing 15kWh of heat from fusion for every 10kWh you put in to break even.
Availability (reliability engineering) https://en.wikipedia.org/wiki/Availability
Terms from other types of work: kilowatt/hour (kWh), Weight per rep, number of reps, Total Time Under Tension
Additionally the final plot of scientific gain (Qsci) vs time effectively requires the use of deuterium-tritium fuel to generate the amounts of fusion energy needed for an appreciable level of Qsci. The number of tokamak experiments utilizing deuterium tritium is small.
Here was my completely layman attempt to forecast fusion viability a few months ago. https://news.ycombinator.com/item?id=42791997 (in short: 2037)
Is there some semblance of realism there you think?
> The design operating current of the feeders is 68Ka. High temperature superconductor (HTS) current leads transmit the high-power currents from the room-temperature power supplies to the low-temperature superconducting coils 4K (-269°C) with minimum heat load.
Source: https://www.iter.org/machine/magnets
Mind you, it's not useless! It produced a TON of very useful fusion research: neutral beam injectors, divertors, construction techniques for complex vacuum chambers, etc. At this point, I don't think it's going to be complete by the time its competitors arrive.
One spinoff of this is high-temperature superconductor research that is now close to producing actually usable high-TC flexible tapes. This might make it possible to have cheaper MRI and NMR machines, and probably a lot of other innovations.
I'm sure there'll be plenty of fascinating applications of high-Tc tape, however I'm not sure MRI/NMR machines will be one of those. There would still be a lot of thermal noise due to the high temperature. Which is why MRI/NMR machines tend to use liquid helium cooling, not because superconductors capable of operating at higher temperatures don't exist.
ITER has been criticized since early days as a dead end, for example because of its enormous size relative to the power produced. A commercial follow-on would not be much better by that power density metric, certainly far worse than a fission reactor.
There is basically no chance than a fusion reactor operating in a regime similar to ITER could ever become an economical energy source. And this has been known since the beginning.
I call things like ITER "Blazing Saddles" projects. "We have to protect our phony baloney jobs, gentlemen!"
It does, for high-current buses that interface with regular resistive power distribution. They are also planned for some auxiliary components (like the neutral beam injectors).
> ITER has been criticized since early days as a dead end, for example because of its enormous size relative to the power produced.
ITER is NOT designed for power generation. It's essentially a lab experiment to see how plasma behaves in magnetic confinement and test various technologies.
That's why ITER was designed with a very conservative approach to reduce the technical risk. We don't need it to be compact, this can come later. We just need it to work.
And yes, it is necessary. Plasma behavior can't be simulated numerically or analytically. It always provides surprises, sometimes even good ones: https://en.wikipedia.org/wiki/High-confinement_mode
That's the go-to excuse. But if you look at DEMO, it's power density is not enormously greater. ITER is so far out of the running that DEMO (or PROTO, etc.) will be too.
We're learning a great deal about something that's largely irrelevant.
They're based on the state-of-the art from about 2005. Since then, a lot of improvements happened. A more realistic power plant design is going to use a thinner center column (because of better superconducting magnets), resulting in a smaller cryostat volume. Possibly high-TC magnets.
It can also be made more compact, if neutral beams can be used to suppress some plasma instabilities.
ITER is not only facility in france it is multitude of manufacturing capabilities all over the globe which build parts for ITER and all future power plants.
To solve the homogeneity problem, you need the central column to be as thin as possible. That's where a lot of the recent advancements can help.
Also, fission research and fusion are actually aligned in designing materials that can tolerate more displacements per atom.
> And in no future world is the power density of DEMO going to be anywhere close to that of a fission reactor.
That's for sure. Modern fission reactors are close to magic, with the amount of heat they produce for a given volume.
The comment about fission and neutron dpa is misleading. The neutron damage issue is much less bothersome in fission reactors.
Fission produces about 3% of its energy in neutrons, vs. 80% in the DT fusion reaction. The spectrum of fission neutrons is much softer, with a peak around 1 Mev, vs. 14 MeV for DT neutrons. The DT neutrons are above threshold for (n,2n) reactions in most materials, and have much higher cross section for (n,p) and (n,alpha) reactions. The latter is particularly troublesome, as helium accumulates inside materials, forming microscopic very high pressure bubbles that rip the materials apart.
But it's even comparatively worse for fusion than that. In a PWR (for example), the core is carefully designed so that the only parts exposed to unmoderated neutrons are the fuel rods and the replaceable parts of the fuel rod bundles. The latter provide structural support for the fuel rods and are removed along with the fuel rods when the fuel is spent. The actual core supports for the fuel bundles are well away from where the chain reaction is occurring, shielded by water. The mean free path of a fission neutron in water is just a few centimeters, so their energy is quickly dissipated before reaching these components.
So, exposure of permanent reactor components to fast neutrons is essentially a non-issue in PWRs. Even control rods are not exposed much; reactivity is controlled by boric acid dissolved in the water (BWRs do it somewhat differently.)
This same strategy cannot be used in a fusion reactor; the plasma facing surfaces are exposed to the full, unshielded brunt of the DT neutron flux. Maybe a few cm of liquid lithium could be flowed along some surfaces? This is a stretch, particularly in a toroidal reactor.
I think this is overly harsh and somewhat unfair. You could make the same argument that anything operating in a regime similar to the Chicago Pile 1 could never be an economical reactor nor a bomb, but that does not mean skipping that particular development step is viable.
As far as fusion reporting goes, articles are at least somewhat consistent on the fact that ITER is a pure research project/reactor, while every 10-man fusion startup is being hyped up beyond all reason even if there is not even a credible roadmap towards an actual reactor in the 100MW range at all.
Personally I don't see fusion being a mainstream energy source (or helpful against climate change) in this century at all and maybe never, but ITER (even with all the delays) is at least an honest attempt at a credible size, and being stuck on older technology is an unfortunate side-effect of that.
The initial cost figures for ITER were obviously deliberate lies. When the true costs inevitably came out (after commitment had been made) this led to alternative approaches being canned. ITER has done grievous damage to fusion as a field, in a way eerily similar to how the Space Shuttle and ISS have done damage to NASA.
The true purpose of ITER wasn't to achieve fusion or push forward fusion; it was to preserve funding until those making the decisions had retired. If this required sacrificing long term goals, like actually delivering competitive energy (or, really, delivering anything at all), so be it.
Was ITER overambitious? Timeline and budget unrealistic from the start? Maybe. But I'm fairly confident that most people involved had perfectly defensible intentions.
I also think that if the goal is commercial fusion, small reactors (100MW and below) are nothing but a stepping stone and inherently commercially useless; I don't see the output (hundreds of termal megawatts) ever justifying the "fixed" overhead costs, and a scale at least close to GW scale seems completely inevitable to me.
If you agree with that premise, then building a reactor that size has a lot of utility already that you'd never achieve from building Wendelstein 7x equivalents or whatever at 50 different university campuses (or however else you'd want to spend the funds instead).
> The true purpose of ITER wasn't to achieve fusion or push forward fusion; it was to preserve funding until those making the decisions had retired. If this required sacrificing long term goals, like actually delivering competitive energy (or, really, delivering anything at all), so be it.
This is what I most disagree with; if commercial fusion is viable (I believe it really isn't) then I think ITER (or an equivalent of its size) is a very necessary, if expensive, step to make, and spending the money on dozens of smaller projects is not an "obviously better long term approach" at all in my view.
I also think that speaking about "true purpose" of the whole project is personifying the output of a complex process way too much, where individual actors in that scheme just want to make ITER happen (for very defensible reasons IMO).
Chicago Pile 1 ran for 12 years, ITER started ~12 years ago and plans to run into the 2030s at least. Budget and headcount would likely be vastly different too, I’d welcome any educated guesses. Sometimes quantity has a quality of its own, as they say.
A more fitting comparison to ITER would be something like Fermi-1 or other prototype designs at almost commercial scale, IMO, and those were multi-year, large projects too (and fission is much simpler than fusion, which obviously also helps).
I looked hopefully at the HR report https://www.iter.org/sites/default/files/media/2024-11/rh-20... to see if there was some sort of job categorisation - scientist, engineer, management. Disappointingly scant. PhD heavy. Perhaps the budget would be more insightful.
"Execution not ideas" is a common refrain for startups.
I wonder how much of the real engineering for ITER is occurring in subcontractors?
Much of the interesting tokamak engineering ideas were on small (so low-power) machines or just concepts using high-temperature superconducting magnets.
There's the common joke that fusion is always 30 years away, but now with the help of ITER, it's always 10 years away instead.
This is why much of the fusion research community feel disillusioned with ITER, and so are more interested in these smaller (and supposedly more "agile") machines with high-temperature superconductors instead.
The idea of using literal guns (gunpowder, then light gas gun, then coil gun) to impact projectiles against each other seemed like it was probably ludicrous, but I haven't seen any critical media or numbers yet.
(it's been 30 years away for 50 years already, but as long as I'm not dead 30 years from now, it's still a good investment...)
I want to believe, but this does not make that easier.
(I work for one startup in the field, Commonwealth Fusion Systems. We're building our SPARC tokamak now to demonstrate net energy gain in a commercially relevant design.)
High density is actively bad, you want to maximize strength and minimize density for flywheel designs, and this makes you much more likely to end up with low density composites (rather than high density tungsten alloys or somesuch).
fission has relatively low temperature heat, i.e. no metal reduction, no "concrete" production. you can cook hot dogs with it. also electrification of heat can provide lower losses stemming from regulation or lack thereof. with electricity you can say i need 293.5 degrees C and you just type it somewhere and you get it for almost free (regulation).
Lithium ion batteries are light with a high energy density, so are great for cars.
Flow batteries have a low energy density, but increasing the duration means a bigger tank, and the cost of bigger tanks increases as a function of the cube root (?) of their volume Flow batteries are well over a century old, but I have been reading about improvements over the last two decades. Where are they?
It is the good old: Good enough beats theoretically perfect.
china makes all panels, asia is making all batteries. so US utilities / energy providers can not have harmful grip on PV + batteries.
US utilities / energy providers want to have docile customer who only pays every month. they do not want to invest money into grid and have customer not only demand but also supply grid. because they do not understand how to benefit from that. they can, it is just mental limit for them.
utilities / energy providers were too lazy to think about proper decentralized grid so every participant in us grid will suffer more because of that.
this will be flagged as conspiracy, be cause it is conspiracy, conspiracy against US citizen by US companies / US interests"
But flow batteries can be made with century old technology, so it cannot be the whole answer.
It is hard to tell the difference of a "confluence of interests" from a "conspiracy". Perhaps it is a distinction without a difference.
coal power plant needs to have 100 or so rail cars worth of material brought every single day. so you are simplifying too much.
every person doing anything with power generation should put into spreadsheet, what quantities of material is needed to provide power capacity for entire grid.
and you need people, infrastructure to bring, prepare, load that material. which adds COST OF LOCKING PEOPLE, locking workforce for nonsensical jobs. so if someone drives train supplying coal plant with coal he can not do programming job, job in services etc... labor/workforce "opportunity cost"
with PV + battery you bring material once per 10-15 years. and it is not in quantities as in fossil. and one coal plant worth of personnel can manage higher amount of generating capacity in PV/battery
Nuclear plant of ANY KIND will have to have even bigger workforce than whole coal plant, just to do NONTRIVIAL maintenance. just simple microcontroller, sensor.... used in nuclear power plant has to be made available for duration of plant lifetime 30-40 years. you can use any inverter, solar panel in pv, you can interchange them, mix them, this is not as simple with nuclear plant.
people involved in providing energy services and citizens drawing energy from grid, should start think like producers AND consumer, not only like consumers. that way a lot of "grid problem" will be easier to deal with.
There are any problems with fission that are all related to the extraordinary danger of handling the fuel, byproducts, and the sites themselves.
The cost of them is huge, some people are hoping that modularity will help with construction, but it is still astonishingly expensive.
The problems of handling the fuel has been solved, in theory and practise. Except when commerce is involved. When the money people get involved corners will get cut, and we are back to incredible danger. Technically solvable, but I would not go near it. I have known too many business people.
The problem of the long-term waste is entirely beyond us. There has been no practical progress on this front. Long term waste (including some parts of the assemblies themselves) are very dangerous for hundreds of thousands of years.
This is, with current technology that can be bought to bear, unsolvable.
The only thing we can do is put it in a stable site, be ready to move it when the site becomes unstable (nowhere on Earth is known to be stable on such time scales), and find a way of communication, across thousands of generations, just how poisonous this stuff is.
Maybe our ancestors will get lucky and find a way to safely dispose of it....
So fission power is making future generations pay for today's consumption.
Fortunately for us it is moot. The costs of renewables is dropped to the point that the only reason for fission is to build the capacity for nuclear weapons.
If fact more people die from falling off wind turbines during maintenance than have died from nuclear accidents on a per-TWh basis [1].
And there were greater health effects in Fukushima due to panic and unnecessary evacuation than from radiation [2].
Again I agree radioactivity = bad, but I think it needs to be put in context.
And as for the disposal of nuclear waste, yes it's a problem for thousands of years, but we don't need a thousand year solution, it's not like we're leaving the planet. One possible outcome there is that eventually we develop cheap enough neutron sources that we can bombard the waste with neutrons until the various atoms capture enough neutrons to become stable isotopes. Considering the technological progress over the last 300 years, maybe in another 300 such a feat will be economically feasible.
[1] https://ourworldindata.org/safest-sources-of-energy
[2] https://pmc.ncbi.nlm.nih.gov/articles/PMC8208296/
reprocess the dirty fuel and bury the actual waste deep underground like Finland is doing at the Onkalo spent nuclear fuel repository.
https://en.wikipedia.org/wiki/Onkalo_spent_nuclear_fuel_repo...
And there is still very much a need for zero-carbon DISPATCHABLE electricity of witch nuclear is the ONLY choice. You simply cannot have 100% of your electricity from only solar and wind because it is far too variable and we simply don't have the technology to store electricity cheaply enough.
Your attitude towards nuclear energy is as irrational as the average antivaxer towards vaccines.
How deep, to stay put thousands of generations?
A) The area is not known to be geologically stable over the extraordinarily long time periods necessary. (Nowhere is....)
B) There is no containment vessel that can last that long
I get tired of the wishful thinking. Being charitable as describing it as that.
In the future, 600 generations from now, when the poisons we lay down now are bubbling up, perhaps people then will have forgotten us. If not, they will not forgive us
And so unnecessary
This is the the lie that I'm really tired of people repeating. Nuclear waste isn't THAT dangerous and doesn't have to be kept perfectly isolated for THAT long.
"In the future, 600 generations from now, when the poisons we lay down now are bubbling up,"
You should really be more worried about the 36 billion tons of CO2 we are spewing into the atmosphere every year instead of a TINY amount of nuclear waste many thousands of years in the future.
You are like someone with a malignant tumor worrying about the risks of radiation therapy.
But there is still plenty that needs to be stored for hundreds of millennium
There is no answer to that, and no amount of arguing by analogy, argumentum ad hominem nor wishful thinking can make that go away
It is a very good thing we do not need nuclear power
Stop repeating this lie.
We absolutely need Nuclear. It is the only way to eliminate CO2 emissions from electricity production completely.
It is not a lie
https://en.m.wikipedia.org/wiki/Long-lived_fission_product
Wishful thinking on your part
You are like a firefighter who opposes using water (nuclear energy) to extinguish fires (reduce CO2 emissions) because people might drown.
https://www.metaculus.com/questions/9464/nuclear-fusion-powe...