Fusion happens when hot enough hydrogen ions (=hydrogen atoms with the electron stripped so only the nucleus is left) are running into each other often enough.
So you need a high enough density of those that stay hot enough for long enough (the triple product, vertical axis) at a high enough temperature (horizontal axis) for enough atoms to fuse.
At the boundary, enough energy will start being released from fusion reactions to keep the reaction going. at Q=1 you have theoretical break-even. Somewhere between Q=5 and Q=10 you could extract more heat than you put in. The heat produced by the reactions should be enough to sustain the reaction. At Q=inf it just keeps burning like a fancy camp fire. Just throw in fuel, remove ashes and enjoy the heat. Commercial fusion can only start being viable probably somewhere between Q=10 and Q=20.
Do note that the projected future in OP's gif should contain way more attempts from various companies to reach that limit. Just mentioning sparc is a bit selective.
Stars are at Q=inf, they don't have external heating. They are also on a weird place on this plot, considerably more to the top left side of the high Q's.
It's the theoretical breakeven event (Q=1) when you use high power lasers rather than the magnetic confinement of a tokamak. The NIF is doing research on this inertial confinement fusion, where they shoot a lot of power with lasers on a tiny pellet with hydrogen. So you get extreme densities and temperatures, but not a lot of confinement time, i.e. the ions cool down _really_ fast. That shifts the curve a little bit.
In my opinion, it is a bit misleading to add this to the plot, because for this laser-based fusion, the theoretical breakeven lies really far from the practical, commercial breakeven. But as shown there on the gif, the NIF did manage to cross the Q=1 for inertial confinement fusion last year!
Author here. The black curve represents the hot-spot ignition condition for a laser inertial confinement fusion (ICF) experiment (like the NIF). This means that during the short period of inertial confinement, the self-heating exceeds all losses in the hot spot leading to an increase in temperature due to self heating. It only applies to the black 'x' points.
The Q_sci^MCF contours correspond to scientific energy gain (ratio of fusion power to heating power crossing the vacuum vessel boundary) for a magnetic confinement experiment.
For ICF we can't draw simillar Q_sci^ICF contours because the total fusion energy released depends on the degree to which the ignited hot-spot propagates a burn in the surrounding cold fuel. And this depends on other variables like the symmetry of the implosion which are not captured in this plot.
If you're curious to read more about this check out Section III.F of the linked paper (pp.10-11).
So does eg Q=100 mean that it'll still go out on its own at some point? Ie is Q a measure of duration/total energy output for a given energy expenditure?
Yes, it means you will get out 100 times more energy than you put in, but at that point it does still go out if you don't keep supplying that external heat.
At Q=infinity, you get out as much energy as you want compared to what you put in initially, but it keeps burning (as long as you add fuel and remove ashes, that is). At that point you pay an initial start-up cost and can fuse as much as you want.
I see, thanks! So this doesn't take into account the hydrogen, just the external energy/heat you put in? I guess it must, otherwise Q=inf would be free energy.
You still have to run the cryogenic system for the superconductors and the pittance of power to keep the confinement coil power supplies. Q=inf means ignition: an entirely self-heated plasma. The collisions of the helium ash on the un-burnt fuel are enough to bring the fuel above the flash point. In this way it is like a campfire.
To keep operating you need to extract heat, make power, and drive it from that power, or it goes out or blows radioactive burning molten lithium all over.
In practice, no such plant will ever exist, because there is no plausible prospect of the power being competitively priced.
No, in the sense that the costs for the competition, renewables + storage, are still falling at a reliably exponential rate, leaving everything else far, far behind. There is no reasonable prospect of catching up even ignoring capital cost and just comparing operating expense. The cost of maintaining steam turbines will not be coming down at all, never mind going to zero.
Commercial fusion will not be competitively viable at any Q. Even unlimited free heat is not valuable if it costs too much to make power from it. A volcano, earthquake, or hurricane releases many TWh of energy, but not usefully so, for reasons.
Once you start to get enough neutron kinetic energy out, those neutrons have to be captured and their kinetic energy degraded to heat in thousands of tons of molten lithium pumped in big pipes snaking around inside your magnets, which you must then use to boil water and drive a turbine.
The cost of operating such a plant would be at least 10x the equivalent fission plant. But fission is already not competitive, and gets less so every day.
Part of operation would need to be purifying grams of tritium, daily, out of those thousands of tons of radioactive molten lithium, for the fuel needed to continue operating. That might not be possible. No one is even trying it yet.
The power density of your D-T plasma would be much less than fissioning uranium (Th, Pu, etc.), which means you need a great deal of it, and a huge plant. If superconducting magnets squeeze it smaller, you have the problem that all this neutron flux has to come through a wall of limited area, destroying it in short order. Magnets so strong would need thousands of tons of steel to hold them in place, which would weaken rapidly under heavy hot neutron bombardment.
So, the D-T fusion chased is a series of fascinatingly hard technical problems, but there is no plausible prospect of ever getting any commercially valuable power out. And, they are not even safer than a regular nuke; the thousand tons of molten radioactive lithium is hugely inflammable, even explosive, and the smoke turns into radioactive drain opener on contact with anything damp, e.g. lungs.
Are you suggesting that all those people doing fusion research don’t know about this, or that they make false promises to the public to fund their research?
At least many know and do not care. Many deceive themselves, as often seen here. Others don't think about it, considering it Somebody Else's Problem. Promises of commercial power are naked lies they will never be called to account for.
Probably a mix of both, and other stuff. For an example of other stuff, look at the inertial confinement fusion reactors. Those are only plausibly useful for fusion weapons research (as fusion-based nuclear weapons work on the same principle, but are somewhat harder to study up close).
However, that's unfashionable to talk about, so they are touted as a potential source of energy. Given that a single shot costs many tens of millions of dollars (because of the incredibly precisely machined piece of gold, called a target, that gets heated up by lasers until it emits X rays that cause the fuel pellet to implode in a perfectly symmetrical fashion), and is over in nanoseconds. So, a continously operating plant would literally spend millions of dollars per minute even with optimistic improvements in the cost of the targets - not exactly a promising new "free energy" generation technology.
Effectively harnessing volcanos and earthquakes really should be a milestone on our path to Kardashev status. Elon, if you are reading this, we need drone swarms that can eat and store explosive geoenergy release.
> A volcano, earthquake, or hurricane releases many TWh of energy, but not usefully so, for reasons.
> The cost of operating such a plant would be at least 10x the equivalent fission plant. But fission is already not competitive, and gets less so every day.
People keep repeating this (fission is not competitive) like it's a law of nature, but the reason they are not competitive are entirely human-made.
They don't repeat it "like a law of nature" but as an empirical description of our technological capacity. If there is a large advancement of construction productivity that may make nuclear more cost effective, it would be good to know about, but nobody who claims this is possible seems to have some sort of methodological description of this advancement. Similarly, those that claim that it's just regulations getting in the way of nuclear don't seem to have an answer for why Flamanville in France has issues, or have the specific change of regulations that will alleviate the construction issues that we regularly see in the Western Hemisphere.
Personally, I believe an advancement in construction productivity is quite possible, but that it will take an entirely new generation of bright, ambitious, and innovative individuals entering the field, as well as compensation to attract them from other fields that currently outpay construction by quite a bit. But that's a loooong and expensive change of economies.
For a quick overview, skip down to figure 12, which shows a plot of overnight construction costs across time and countries. Note that the bulk of them are below $3000/kW, quite a bit less than the most expensive reactors in the US.
So here's an optimizer that finds the lowest overall grid cost, based on various assumptions you can modify: https://model.energy/
Pick a country. "Show advanced assumption settings." Check the box for "dispatchable technology 2." Set the overnight cost down to $3000. The lifetime of 25 years is unrealistic, given that the average age of US reactors is 40 years. Set that to a more accurate value, like 60 years. Finally, give it the same discount rate as everything else.
You'll find that in many countries, nuclear does quite well. In countries without good wind/solar resources, even a higher capital cost can result in a 100% nuclear grid.
That paper is about historical costs, which is not informative for current costs.
Saying 60 years is "more accurate" is kind of putting one's thumb on the scale, as is putting an overnight cost at $3000/kW. These sorts of overly rosy and unrealistically optimistic assumptions are how we get into such terrible estimates for nuclear.
Even though MIT has been one of the sources of inaccurate nuclear optimism in the past, I think that this is perhaps the best assessment of how to make nuclear competitive again:
I still thinks it's somewhat overly optimistic, but it at least tried to address the real and deep issues within the industry instead of hand waving them away.
Until nuclear proponents both acknowledge the full reality of construction, in the 2020s, and the errors of the past, they will never be able to get to $10k/kW or even $5k/kW. A future at $3k/kW in the US is not worth even contemplating until we could reliably even hit $5k/kW, and a world with $5k/kW is currently not worth contemplating because we are so far away from that.
If it's been done before, then we don't need a "large advancement of construction productivity" to do it again. If, as the paper shows, other countries have managed lower costs recently, then we should look at what they're doing. If the average lifespan of our existing nuclear reactors is 40 years, then setting a lifespan of more than 40 years is indeed more accurate than setting it to 25 years.
We live in a different technological setting than we did in the past, and all sorts of skilled labor that was economical in the past is no longer economical. As parts of the economy become more productive, labor costs rise, and the less productive parts of the economy become more expensive in comparison.
We see this cost disease in all sorts of large construction projects, not just nuclear. Though nuclear seems to be particularly bad. And that's why we need breakthrough in productivity. Personally I think that such a construction productivity breakthrough would have its greatest impact on decarbonization through cheaper subway construction, high speed rail construction, and through increased urban density with cheaper big buildings. These type of construction projects have few realistic alternatives, whereas renewables plus storage are already a great way to power an energy system.
So if we can fix companies like Bechtel, we will see lots of improvement throughout our society far beyond nuclear construction.
Yet there's Japan, with low nuclear costs within the past couple decades. Were their skilled labor costs all that low?
High cost of large projects is certainly a general problem in the US, but it may not be due to labor costs alone. Here's a Bloomberg article that attributes it to "over-design, inefficient project management and misaligned politics." https://www.bloomberg.com/news/articles/2021-12-08/why-build...
I think it's entirely possible that in the US, where we have copious wind and solar resources and we've gotten bad at doing large projects economically, nuclear is not the best option. That says little about the rest of the world, though. And it's possible that small modular reactors would help even in the US, because while we suck at big infrastructure projects, we're not too bad at high-volume production in factories.
And that brings us back to fusion, because a lot of modern fusion designs would be more like factory-produced modular devices rather than large site-built infrastructure projects.
$3/W capex, even if it could be achieved, is well north of the current cost for renewables. It anyway fails to address extraction cost, for which there is no plausible means to match renewables' near zero cost.
By the time any new nukes could be brought online, capex and opex for renewables will have fallen far, far below even their most aspirational projections.
> advancement in construction productivity ... will take an entirely new generation of bright, ambitious, and innovative individuals
Lack of those is not the cause of construction cost overruns, so increasing their supply would not help. Cost overruns are a deliberate consequence of wholly-legal institutional corruption, which no one shows any appetite for rooting out. Ingesting exemplary individuals just generates disillusioned individuals out the other end.
> A volcano, earthquake, or hurricane releases many TWh of energy, but not usefully so, for reasons.
I don't quite follow your point here. Presumably the issue with earthquakes and hurricanes is that they aren't dispatchable and the work environment for operating a plant is quite hazardous. The issue with volcanoes (although I'd bet we already do use volcanoes for power) could very easily be as simple as that they tend to be in difficult to reach locations because of the plate tectonics (ie, mountains) & the hot parts take a lot of drilling to get to.
We do not try to capture and bank energy from more or less reliably annual hurricanes because we are not fucking insane. They are rightly classed as natural disasters, not resources. Nukes will rightly come to be seen much the same way, a phenomenon to hope people elsewhere suffer, if anyone must.
That isn't an argument or a reason. The problem is they aren't reliably available. If hurricanes were an ongoing phenomenon we would harvest the energy - like we do for wind. Using volcanoes for power is absolutely on the cards. Apparently the hard part is finding the magma chambers [0].
The barriers are entirely practical in that these power sources don't scale well and aren't easy to get on demand. None of the problems there are similar to having a tokamak - it isn't like we are going to struggle to find the tokamak (it will be marked on the map with something like "tokamak here") and it will likely have a big on/off switch.
We reliably get multiple hurricanes every year, each releasing far more energy than we could use. We do not, in fact, extract that energy.
We also never, ever drill into magma chambers. Drilling into a magma chamber is a good way to get a new, vitrified surface, several feet deep, for miles around what was once your drilling rig.
> Magnets so strong would need thousands of tons of steel to hold them in place, which would weaken rapidly under heavy hot neutron bombardment.
I'm just going to nitpick this part. In ARC, the magnets go outside the blanket, which is a molten salt, fully surrounding the inner wall. The salt has to absorb almost all the neutrons, to generate enough tritium. The steel outside of that shouldn't be getting many neutrons.
The ARC proposal argued for a cost per kWh of 26 cents, for a pilot plant not necessarily optimized to full commercial configuration. This requires a fairly revolutionary further advance for general commercial relevance but note that the current cost for ratepayers in Germany is 32 cents. A much cheaper or much stronger structural material than steel 216 would quickly change the cost as the strength determines the operating magnetic field which increases output to the fourth power. More interestingly there appears to be a similar revolution newly predicted. Based on a first principles simulation it was projected that density can be doubled over current limits in a reactor as powerful as ARC. I believe density translates directly to pressure which increases output to the second power - possibly quadrupling output over what was expected. Roughly speaking this should mean a cost of less than 10 cents for ARC if that pans out. Hinkley Point C is guaranteed a price of 14 cents, which is the world average for electricity. The doubled density prediction appears to bring a conventional tokamak in line with the projected costs of various alternative designs such as General Fusion's 8 cent projection. None of the alternatives have been tested at the scale of tokamaks but there are a few with the potential of a revolutionary price - Helion projects 1-6 cents based on reactor survivability, and don't use tritium. In fact they may be able to produce it fairly efficiently if they fall short of standalone electricity production. Fusion is generally a more expensive, more of a longshot competitor to SMRs, but with the very dramatic advantage of zero meltdown risk that makes it worth a shot
Cost to extract power does not scale with power density of plasma.
No optimistic projections for cost of extraction are better than idle speculation. Practicality of extracting diffuse 3H from a molten metal blanket, needed for fuel, is as previously noted purely speculative.
Renewables are driving cost per kWh well below any plausible, or even aspirational, figures.
The only fusion technology that has any chance of competitive extraction cost is Helion's, which does not depend on a round trip through heat. But it depends on a regular supply of 3He, a decay product of 3H which must be produced via operation, filtered from the working plasma, and then held for its 12y decay half life. It is anyway not clear if its process can be achieved at all.
SMRs depend on the round trip through heat and incur all the other costs of traditional nukes, so offer no prospect of keeping up with plummeting cost of renewables.
Fission's fuel rod meltdown is not the only catastrophic failure mode available. Fukushima demonstrated hydrogen detonation. Breached containment of thousand-ton inflammable, caustic, radioactive molten metal neutron absorption blanket would be adequately catastrophic.
For SPARC the big innovation sounds like it is being able to use some special superconducting electromagnets to generate the massive magnetic field in the tokamak -- since that part is such a critical part, it would seem like in the next say 5-10 years that it takes to get SPARC up and running there should be a parallel group just trying to improve that magnet design by say 2X, which would likely have a massive impact.. seems like a smart thing for National science foundation or darpa or whatever to be funding that.. (maybe already happening) but it would be a bummer to be talking about this in 2030 and them saying, ok now we just need to design a more powerful magnet..
Well SPARC and the planned successor ARC can successfully generate power without needing more powerful magnets. Assuming all goes to plan (lol) ARC will be commercially viable with existing magnet tech. They have said that as you go towards higher field strengths, the physical forces pushing and pulling between magnets gets so extreme that it is difficult to build a machine that doesn't tear itself apart. So stronger magnets are only useful in conjunction with an entire machine design that can handle them. It looks to me like a good path is to get commercially viable machines with existing magnets, and then iterate on the entire machine once they have learned the basics of operating commercial fusion.
But I am just a robotics engineer who has watched a lot of the SPARC lectures, so I have no domain expertise here.
This goes for permanent magnets as well. I've had a ceramic magnet and a neo explode on me and to say that I was surprised at the incredible forces unleashed would be an understatement. I'm a sucker for working with proper safety gear and if not for wearing very good safety glasses I'd have been in serious trouble, multiple magnet fragments sat embedded in the glasses and a couple in my skin where it wasn't covered by the glasses (easily removed with another magnet :) ).
The ceramic one was a 2x2" square 1/4" thick one that had one stuck corner, trying to remove it shattered it, the other was a neo that accidentally jumped up when I put down a heavy piece of steel and that in turn allowed the magnet to start flying towards it, it shattered on impact. That one was a lot larger (2"x2"x1"), and neos are a lot more powerful for the same size as ceramics. In both cases it was to test sets of magnets under controlled circumstances to see which ones I would order in bulk for the rotor of a windmill.
Lessons learned: make no assumptions on whether or not a magnet really is free to be released, do not place magnets loose on a workbench even if they are far away from your work area because when the friction unexpectedly disappears you are going to be in for a surprise.
Don't mess around with very large neos unless you know what you are doing, they can really hurt you. (And when you do know what you are doing: observe safety precautions religiously and always wear safety glasses until your whole rig is assembled and the magnets are safely enclosed).
I saw a PPPL group propose the use of permanent magnets to assist in stellarator geometry. My first and continued thought has been "this is completely insane". Permanent magnets are fragile, violent, and cannot be turned off. All engineering challenges aside, they propose making an industrially sized death machine that cannot be turned off.
That can provide shielding, but how does that turn off the permanent magnetic field when a human considers working on (maintenance or decommissioning) the machine?
Well, during decommissioning that would be a tricky thing to do, but during maintenance I could image a way to slide the mu metal in front of the magnets shunting the field away in a safe way. But you are right, working on such gear requires strict precautions and attention to safety detail.
Let me give you one example of how hard it is to work with these: while building the windmill I had decided on an 'inside out' model where the rotor rotates around the stator, this has a bunch interesting properties, such as pushing the magnets onto the drump while they rotate instead of trying to eject them from the rotor in the normal designs. And because magnets get hot any kind of glue or other adhesive would be subject to all kinds of thermal stresses, might let go or melt. So that was a pretty neat solution. My rig for installing the drum was a half ton crane over a very heavy steel workbench that had the stator mounted to it.
As I lowered the rotor suddenly the whole assembly, table and all lifted off the ground and perfectly centered itself around the rotor. I swear I never ever saw that one coming and it really scared the crap out of me because only minutes before then I was still fiddling with pushing some wires in place inside the stator while the rotor was already floating above it. A bit earlier and I could have easily gotten pinched, in spite of all my precautions.
That's basically what's going on with ITER, it needs to be so massive because the technology available at the time of conception was not capable of generating more intense magnetic field. There is a very strong relationship between the strength of the field and the required size of the tokamak (hence time and cost of construction). By the time you're done better technology will be available, but that's how progress goes.
Unfortunately, it's not so simple. SPARC is just the latest attempt to benefit from stronger magnet technology and thus smaller designs, but another big problem remains unsolved: turbulence. Since smaller designs and stronger magnets directly imply higher field strength gradients, the plasma becomes harder to control for the necessary burn time to achieve Q>1. Lockheed also thought they could simply use stronger magnets to build smaller reactors faster, but in the end they discovered that smaller is not automatically better. I wouldn't be surprised if we also see the eventual SPARC redesign that's 100 times more massive. Unless we get a major theoretical breakthrough in the near future, ITER will probably remain the most likely design candidate for near term net energy production.
See here for example: https://www-pub.iaea.org/mtcd/publications/pdf/csp_019c/pdf/... - but note that this stuff is not trivial. The intricacies of turbulence in MHD are incredibly complex and hard to study (near-impossible analytically and very hard numerically). Nevertheless, these scaling behaviours (see the figures in section 2) have been known for more than 20 years by now.
Also, beware that the head of MIT's fusion program (your source) is the head of SPARC. Since he siphoned a huge amount of money from gullible venture capitalists outside his field by now, you definitely shouldn't rely on him for an obective analysis of SPARC's fundamental design.
Well that paper is above my pay grade so I'll have to trust you on it.
I will push back on your second paragraph though. The presentation I linked was from two years before the founding of CFS. It seems likely to me that Whyte founded CFS because he believed in the physics he presented, rather than the reverse.
I see this sort of causation reversal and associated accusations all the time in internet discussions. For example, yesterday someone told me that Musk only likes electric cars because he owns lithium mining rights. Tesla bought those rights in 2020, because they produce lithium batteries.
SPARC is in fact a heavily marketed continuation of ARC, which has been around since 2014 (https://arxiv.org/abs/1409.3540 - note the same authors). So the commercialization ideas would have started way earlier. But a project lead believing in the project shouldn't matter in any objective analysis anyways. The guys over at Lockheed also certainly believed in their compact fusion reactor design when they started working on it (which was, incidentally, one year before ARC), but they too had to learn by now that belief alone is not enough when it comes down to the laws of physics.
Don't get me wrong, I'd love for SPARC to be a success. I just haven't seen any objective, external review that would confirm (or at least try to show) how they solved the problem of controlling turbulent plasma in a high gradient field. It's not even fully clear that ITER will be able to do that, and they'll have a much easier time due to the larger reactor radius.
The guys over at Lockheed weren't in charge of one of the leading academic fusion programs in the US. ARC in 2014 was just a design created by students in one of Whyte's classes.
At this point, as a woefully ignorant layman, I'm forced to weigh two contrary claims. One is by the head of MIT's fusion program. The other is by a commenter on HN, helpfully linking an impressive-looking paper I don't understand, which does not appear to say with layman-friendly clarity that higher magnetic fields make fusion plasmas less stable.
Hey, I'm not trying to convince you of anything. In fact I couldn't care less what people think of this specific project. It's not my money that these VC funds are spraying. I'm just trying to convey a modicum of common sense when it comes to evaluating sources for particularly extraordinary claims. I see Elon Musk get torn to shreds regulalry around here whenever he says something slightly optimistic about electric cars or rocket science, so I frankly find it astounding how easily people eat stuff that comes from guys behind private fusion companies. I guess plasma physics and continuum mechaniccs are less impugnable than rockets and cars for most people.
Well I was hoping you were trying to convince me, and would have an easier-to-digest source handy, or a simple explanation of the relevant part of the paper. You certainly don't owe me that, and I don't mean to doubt you, and for all I know you're a professional fusion researcher. Plenty of people like that are on HN. But I don't know, so I'm just muddling through as best I can, trying to get things right.
Personally, the claim that stronger fields make plasma more stable doesn't seem all that extraordinary to me, and certainly not one that's contrary to simple common sense. And when it comes to evaluating sources, Dennis Whyte seems like a fairly reputable one.
Is there an inverse of the Kardashev Scale i.e for energy production rather than energy consumption? If so, what Level would we be now vs the projected?
From the 60s to the 80s we got pretty good at tokamaks (stellarators have been catching up since we got computers) but Magnetic Confinement Fusion (MCF) triple product performance scales with major radius ^ 1.3 and confinement field strength ^ 3. Power density scales linearly with major radius and with the magnetic field strength ^ 4.
At some point increasing the major radius becomes extremely expensive, so pushing past the barrier of Q=1 has been a long, political process. At the same time a real burning plasma (Q>1) machine has a lot of added cost to operate a nuclear facility (tritium handling and neutron radiation).
So there has never been a physics barrier to Q>1, but an economic one. What's changed in the past year is that REBCO manufacturing and working matured to the point that confinement fields are now twice as strong as they used to be. Suddenly building a burning plasma machine isn't a 40 year international venture and economically viable MCF plants are in the crosshairs.
Infinite money is a weird concept. It doesn't matter how much money humans print, what matters is what humans can accomplish. If we eliminated the concept of money we still would not be able to power mankind on 100 meter tall machines because we don't have the resources to build them quickly. There are sound practical and theoretical reasons for keeping "minimize the levelized cost of electricity" be the first goal of any alternate power source.
My prognosis is that CFS is on a good track and that their state goals are achievable. There's going to be some big headlines in a few years. If other startups also hit their goals we'll likely see a race with private investment. Public interest and government funding will likely lag the private progress by a few years.
Existing industries and throughput. We could divert steel production (as an example, but applied to other raw materials) away from unnecessary (defense) applications, but even with monetary incentive you need to scale up the ability of humans to create megaprojects. Minimizing the size of the project not only minimizes the cost, but also maximizes our ability to make them faster. Given a choice between the two: I'd take the latter. We don't really have that choice though because we (humans) have not cracked the code to successful megaprojects on budget and on time every time.
I suppose if we were talking about infinite money and political will we might as well simplify the problem to an ideal spherical world in vacuum where there are no rogue dictators and the whole world cooperates (=> defense is unnecessary). Would we be able to build them then?
Organisational know-how. If economic entities make a habit of sinking huge amounts of money into ventures with a high risk of failure then they disappear quite quickly (even governments, if the costs are high enough). The economic system is optimised to reward well calculated risk & evidence based decisions.
Looking at the graph in the tweet, I'd bet the strategy is patience. It seems clear that current research efforts will eventually produce net-positive-energy fusion, then the capitalists will start to swarm in. No need for anyone to take a big gambit.
If it is 2022 solar and wind LCOE cost, and you are targetting, say, 20 years to build a plant, then those aren't viable targets. Solar and wind will probably drop another 50% or more by then in LCOE cost.
It's worth research, sure. But the same issues of new-gen nuclear are shared with any fusion, except fusion is way further down the prototype stage. Solar/Wind/Battery is already near-price competitive with natural gas turbine unsubsidized (and they never seem to account for all the hidden fossil fuel subsidies), and the curves are still in prime economies of scale improvement.
Thanks. We published a number of prepublication versions over the past year on arXiv to gather feedback from the physics community before submitting to Physics of Plasmas last December. The version linked to above (and in the tweet) is the peer reviewed version which was published yesterday.
Serious question, since this is being done by a US company: is high-end engineering like this done in metric - as surely all the science is done in metric - or is the machinery built in customary units?
I wonder the same about SpaceX and the other rocket companies… does US manufacturing mean you really have no choice but to operate in obsolete units, or are these things so “custom” that they get to be done in metric anyway?
It varies. Automotive is basically all metric now. Aviation is typically in customary units. SpaceX is doing their new vehicle in metric, but the Falcon 9 is in the old style. Manufacturing is varied.
My understanding is that there isn't a consistent standard (or enforcement) for metric versus imperial units in engineering. The US military uses a mash of the two, but prefers metric in many instances due to NATO. NASA uses metric internally (I believe), but famously lost the Mars Climate Orbiter[1] because a defense contractor used imperial units instead.
> because a defense contractor used [US customary] units
That is a common but very limited evaluation of what happened. The contractor ignored the specifications, no proper testing was done to make sure their component would do what it was supposed to before launch, and when someone noticed the issue in-flight they were ignored due to the bureaucratic process until it was too late. The exact same issue would have happened entirely in metric units if one side used CGS and the other used MKS.
It helps my layman's eyes clearly relate the trajectories of the various developmental processes of each approach. I wonder why SPARC and ITER are the only projected ones. Do the other reactors being built not have estimated yields? My favourite has long been the wendelstein, because of they way it looks and how it feels like its pathway to success might be software based. I like the way Tokamak Energy markets itself, and would have loved to see the ST25 and the ST40 in that image, but maybe they're not complete enough projects to be on there?
We only included projected values of SPARC and ITER because they're the only ones whose physics basis has been published in the peer-reviewed literature. We would certainly like to include other devices - hopefully this will encourage more teams to publish results in the literature from which we can extract the required parameters.
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[ 4.4 ms ] story [ 171 ms ] threadSo you need a high enough density of those that stay hot enough for long enough (the triple product, vertical axis) at a high enough temperature (horizontal axis) for enough atoms to fuse.
At the boundary, enough energy will start being released from fusion reactions to keep the reaction going. at Q=1 you have theoretical break-even. Somewhere between Q=5 and Q=10 you could extract more heat than you put in. The heat produced by the reactions should be enough to sustain the reaction. At Q=inf it just keeps burning like a fancy camp fire. Just throw in fuel, remove ashes and enjoy the heat. Commercial fusion can only start being viable probably somewhere between Q=10 and Q=20.
Do note that the projected future in OP's gif should contain way more attempts from various companies to reach that limit. Just mentioning sparc is a bit selective.
In my opinion, it is a bit misleading to add this to the plot, because for this laser-based fusion, the theoretical breakeven lies really far from the practical, commercial breakeven. But as shown there on the gif, the NIF did manage to cross the Q=1 for inertial confinement fusion last year!
The Q_sci^MCF contours correspond to scientific energy gain (ratio of fusion power to heating power crossing the vacuum vessel boundary) for a magnetic confinement experiment.
For ICF we can't draw simillar Q_sci^ICF contours because the total fusion energy released depends on the degree to which the ignited hot-spot propagates a burn in the surrounding cold fuel. And this depends on other variables like the symmetry of the implosion which are not captured in this plot.
If you're curious to read more about this check out Section III.F of the linked paper (pp.10-11).
At Q=infinity, you get out as much energy as you want compared to what you put in initially, but it keeps burning (as long as you add fuel and remove ashes, that is). At that point you pay an initial start-up cost and can fuse as much as you want.
In practice, no such plant will ever exist, because there is no plausible prospect of the power being competitively priced.
Once you start to get enough neutron kinetic energy out, those neutrons have to be captured and their kinetic energy degraded to heat in thousands of tons of molten lithium pumped in big pipes snaking around inside your magnets, which you must then use to boil water and drive a turbine.
The cost of operating such a plant would be at least 10x the equivalent fission plant. But fission is already not competitive, and gets less so every day.
Part of operation would need to be purifying grams of tritium, daily, out of those thousands of tons of radioactive molten lithium, for the fuel needed to continue operating. That might not be possible. No one is even trying it yet.
The power density of your D-T plasma would be much less than fissioning uranium (Th, Pu, etc.), which means you need a great deal of it, and a huge plant. If superconducting magnets squeeze it smaller, you have the problem that all this neutron flux has to come through a wall of limited area, destroying it in short order. Magnets so strong would need thousands of tons of steel to hold them in place, which would weaken rapidly under heavy hot neutron bombardment.
So, the D-T fusion chased is a series of fascinatingly hard technical problems, but there is no plausible prospect of ever getting any commercially valuable power out. And, they are not even safer than a regular nuke; the thousand tons of molten radioactive lithium is hugely inflammable, even explosive, and the smoke turns into radioactive drain opener on contact with anything damp, e.g. lungs.
However, that's unfashionable to talk about, so they are touted as a potential source of energy. Given that a single shot costs many tens of millions of dollars (because of the incredibly precisely machined piece of gold, called a target, that gets heated up by lasers until it emits X rays that cause the fuel pellet to implode in a perfectly symmetrical fashion), and is over in nanoseconds. So, a continously operating plant would literally spend millions of dollars per minute even with optimistic improvements in the cost of the targets - not exactly a promising new "free energy" generation technology.
> A volcano, earthquake, or hurricane releases many TWh of energy, but not usefully so, for reasons.
People keep repeating this (fission is not competitive) like it's a law of nature, but the reason they are not competitive are entirely human-made.
Personally, I believe an advancement in construction productivity is quite possible, but that it will take an entirely new generation of bright, ambitious, and innovative individuals entering the field, as well as compensation to attract them from other fields that currently outpay construction by quite a bit. But that's a loooong and expensive change of economies.
For a quick overview, skip down to figure 12, which shows a plot of overnight construction costs across time and countries. Note that the bulk of them are below $3000/kW, quite a bit less than the most expensive reactors in the US.
So here's an optimizer that finds the lowest overall grid cost, based on various assumptions you can modify: https://model.energy/
Pick a country. "Show advanced assumption settings." Check the box for "dispatchable technology 2." Set the overnight cost down to $3000. The lifetime of 25 years is unrealistic, given that the average age of US reactors is 40 years. Set that to a more accurate value, like 60 years. Finally, give it the same discount rate as everything else.
You'll find that in many countries, nuclear does quite well. In countries without good wind/solar resources, even a higher capital cost can result in a 100% nuclear grid.
Saying 60 years is "more accurate" is kind of putting one's thumb on the scale, as is putting an overnight cost at $3000/kW. These sorts of overly rosy and unrealistically optimistic assumptions are how we get into such terrible estimates for nuclear.
Even though MIT has been one of the sources of inaccurate nuclear optimism in the past, I think that this is perhaps the best assessment of how to make nuclear competitive again:
https://energy.mit.edu/research/future-nuclear-power/
I still thinks it's somewhat overly optimistic, but it at least tried to address the real and deep issues within the industry instead of hand waving them away.
Until nuclear proponents both acknowledge the full reality of construction, in the 2020s, and the errors of the past, they will never be able to get to $10k/kW or even $5k/kW. A future at $3k/kW in the US is not worth even contemplating until we could reliably even hit $5k/kW, and a world with $5k/kW is currently not worth contemplating because we are so far away from that.
We see this cost disease in all sorts of large construction projects, not just nuclear. Though nuclear seems to be particularly bad. And that's why we need breakthrough in productivity. Personally I think that such a construction productivity breakthrough would have its greatest impact on decarbonization through cheaper subway construction, high speed rail construction, and through increased urban density with cheaper big buildings. These type of construction projects have few realistic alternatives, whereas renewables plus storage are already a great way to power an energy system.
So if we can fix companies like Bechtel, we will see lots of improvement throughout our society far beyond nuclear construction.
High cost of large projects is certainly a general problem in the US, but it may not be due to labor costs alone. Here's a Bloomberg article that attributes it to "over-design, inefficient project management and misaligned politics." https://www.bloomberg.com/news/articles/2021-12-08/why-build...
I think it's entirely possible that in the US, where we have copious wind and solar resources and we've gotten bad at doing large projects economically, nuclear is not the best option. That says little about the rest of the world, though. And it's possible that small modular reactors would help even in the US, because while we suck at big infrastructure projects, we're not too bad at high-volume production in factories.
And that brings us back to fusion, because a lot of modern fusion designs would be more like factory-produced modular devices rather than large site-built infrastructure projects.
By the time any new nukes could be brought online, capex and opex for renewables will have fallen far, far below even their most aspirational projections.
Lack of those is not the cause of construction cost overruns, so increasing their supply would not help. Cost overruns are a deliberate consequence of wholly-legal institutional corruption, which no one shows any appetite for rooting out. Ingesting exemplary individuals just generates disillusioned individuals out the other end.
I don't quite follow your point here. Presumably the issue with earthquakes and hurricanes is that they aren't dispatchable and the work environment for operating a plant is quite hazardous. The issue with volcanoes (although I'd bet we already do use volcanoes for power) could very easily be as simple as that they tend to be in difficult to reach locations because of the plate tectonics (ie, mountains) & the hot parts take a lot of drilling to get to.
If there is energy, we can find a use for it.
The barriers are entirely practical in that these power sources don't scale well and aren't easy to get on demand. None of the problems there are similar to having a tokamak - it isn't like we are going to struggle to find the tokamak (it will be marked on the map with something like "tokamak here") and it will likely have a big on/off switch.
[0] https://www.science.org/content/article/could-volcanoes-powe...
We also never, ever drill into magma chambers. Drilling into a magma chamber is a good way to get a new, vitrified surface, several feet deep, for miles around what was once your drilling rig.
I'm just going to nitpick this part. In ARC, the magnets go outside the blanket, which is a molten salt, fully surrounding the inner wall. The salt has to absorb almost all the neutrons, to generate enough tritium. The steel outside of that shouldn't be getting many neutrons.
No optimistic projections for cost of extraction are better than idle speculation. Practicality of extracting diffuse 3H from a molten metal blanket, needed for fuel, is as previously noted purely speculative.
Renewables are driving cost per kWh well below any plausible, or even aspirational, figures.
The only fusion technology that has any chance of competitive extraction cost is Helion's, which does not depend on a round trip through heat. But it depends on a regular supply of 3He, a decay product of 3H which must be produced via operation, filtered from the working plasma, and then held for its 12y decay half life. It is anyway not clear if its process can be achieved at all.
SMRs depend on the round trip through heat and incur all the other costs of traditional nukes, so offer no prospect of keeping up with plummeting cost of renewables.
Fission's fuel rod meltdown is not the only catastrophic failure mode available. Fukushima demonstrated hydrogen detonation. Breached containment of thousand-ton inflammable, caustic, radioactive molten metal neutron absorption blanket would be adequately catastrophic.
But I am just a robotics engineer who has watched a lot of the SPARC lectures, so I have no domain expertise here.
Lessons learned: make no assumptions on whether or not a magnet really is free to be released, do not place magnets loose on a workbench even if they are far away from your work area because when the friction unexpectedly disappears you are going to be in for a surprise.
Don't mess around with very large neos unless you know what you are doing, they can really hurt you. (And when you do know what you are doing: observe safety precautions religiously and always wear safety glasses until your whole rig is assembled and the magnets are safely enclosed).
Something like this just scares me:
https://www.apexmagnets.com/magnets/6-x-2-disc-neodymium-mag...
https://en.wikipedia.org/wiki/Mu-metal
Let me give you one example of how hard it is to work with these: while building the windmill I had decided on an 'inside out' model where the rotor rotates around the stator, this has a bunch interesting properties, such as pushing the magnets onto the drump while they rotate instead of trying to eject them from the rotor in the normal designs. And because magnets get hot any kind of glue or other adhesive would be subject to all kinds of thermal stresses, might let go or melt. So that was a pretty neat solution. My rig for installing the drum was a half ton crane over a very heavy steel workbench that had the stator mounted to it.
As I lowered the rotor suddenly the whole assembly, table and all lifted off the ground and perfectly centered itself around the rotor. I swear I never ever saw that one coming and it really scared the crap out of me because only minutes before then I was still fiddling with pushing some wires in place inside the stator while the rotor was already floating above it. A bit earlier and I could have easily gotten pinched, in spite of all my precautions.
Also, beware that the head of MIT's fusion program (your source) is the head of SPARC. Since he siphoned a huge amount of money from gullible venture capitalists outside his field by now, you definitely shouldn't rely on him for an obective analysis of SPARC's fundamental design.
I will push back on your second paragraph though. The presentation I linked was from two years before the founding of CFS. It seems likely to me that Whyte founded CFS because he believed in the physics he presented, rather than the reverse.
I see this sort of causation reversal and associated accusations all the time in internet discussions. For example, yesterday someone told me that Musk only likes electric cars because he owns lithium mining rights. Tesla bought those rights in 2020, because they produce lithium batteries.
Don't get me wrong, I'd love for SPARC to be a success. I just haven't seen any objective, external review that would confirm (or at least try to show) how they solved the problem of controlling turbulent plasma in a high gradient field. It's not even fully clear that ITER will be able to do that, and they'll have a much easier time due to the larger reactor radius.
At this point, as a woefully ignorant layman, I'm forced to weigh two contrary claims. One is by the head of MIT's fusion program. The other is by a commenter on HN, helpfully linking an impressive-looking paper I don't understand, which does not appear to say with layman-friendly clarity that higher magnetic fields make fusion plasmas less stable.
Personally, the claim that stronger fields make plasma more stable doesn't seem all that extraordinary to me, and certainly not one that's contrary to simple common sense. And when it comes to evaluating sources, Dennis Whyte seems like a fairly reputable one.
From the 60s to the 80s we got pretty good at tokamaks (stellarators have been catching up since we got computers) but Magnetic Confinement Fusion (MCF) triple product performance scales with major radius ^ 1.3 and confinement field strength ^ 3. Power density scales linearly with major radius and with the magnetic field strength ^ 4.
At some point increasing the major radius becomes extremely expensive, so pushing past the barrier of Q=1 has been a long, political process. At the same time a real burning plasma (Q>1) machine has a lot of added cost to operate a nuclear facility (tritium handling and neutron radiation).
So there has never been a physics barrier to Q>1, but an economic one. What's changed in the past year is that REBCO manufacturing and working matured to the point that confinement fields are now twice as strong as they used to be. Suddenly building a burning plasma machine isn't a 40 year international venture and economically viable MCF plants are in the crosshairs.
So could we have had a working fusion machine with infinite money and political will? Also what is your prognosis of the next 5 or 10 years?
My prognosis is that CFS is on a good track and that their state goals are achievable. There's going to be some big headlines in a few years. If other startups also hit their goals we'll likely see a race with private investment. Public interest and government funding will likely lag the private progress by a few years.
Defense uses only 3% of US steel production. That’s not the problem, and arguably, necessary.
https://www.commerce.gov/sites/default/files/department_of_d...
Looking at the graph in the tweet, I'd bet the strategy is patience. It seems clear that current research efforts will eventually produce net-positive-energy fusion, then the capitalists will start to swarm in. No need for anyone to take a big gambit.
what is the price target here?
If it is 2022 solar and wind LCOE cost, and you are targetting, say, 20 years to build a plant, then those aren't viable targets. Solar and wind will probably drop another 50% or more by then in LCOE cost.
It's worth research, sure. But the same issues of new-gen nuclear are shared with any fusion, except fusion is way further down the prototype stage. Solar/Wind/Battery is already near-price competitive with natural gas turbine unsubsidized (and they never seem to account for all the hidden fossil fuel subsidies), and the curves are still in prime economies of scale improvement.
> Small, modular & economically attractive fusion enabled by high-field superconductors
https://www.youtube.com/watch?v=rY6U4wB-oYM
https://aip.scitation.org/doi/10.1063/5.0083990
I wonder the same about SpaceX and the other rocket companies… does US manufacturing mean you really have no choice but to operate in obsolete units, or are these things so “custom” that they get to be done in metric anyway?
[1]: https://en.wikipedia.org/wiki/Mars_Climate_Orbiter
That is a common but very limited evaluation of what happened. The contractor ignored the specifications, no proper testing was done to make sure their component would do what it was supposed to before launch, and when someone noticed the issue in-flight they were ignored due to the bureaucratic process until it was too late. The exact same issue would have happened entirely in metric units if one side used CGS and the other used MKS.
https://aip.scitation.org/na101/home/literatum/publisher/aip...
It helps my layman's eyes clearly relate the trajectories of the various developmental processes of each approach. I wonder why SPARC and ITER are the only projected ones. Do the other reactors being built not have estimated yields? My favourite has long been the wendelstein, because of they way it looks and how it feels like its pathway to success might be software based. I like the way Tokamak Energy markets itself, and would have loved to see the ST25 and the ST40 in that image, but maybe they're not complete enough projects to be on there?
https://twitter.com/jb_fusion/status/1506964692627034118