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Why is nuclear fusion so hard?
- deleted 8y ago[deleted]
- mannykannot 8y agoThis is somewhat tangential to the specific issue here, but I was surprised by this: At the center of the Sun, fusion power is estimated by models to be about 276.5 watts/m3. Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap, and is lower than the power density produced by the metabolism of an adult human.[1] So practical fusion power requires producing much higher power densities than are found in the Sun. [1] https://en.wikipedia.org/wiki/Solar_core#Energy_conversion https://en.wikipedia.org/wiki/Solar_core#Energy_conversion
- mikeash 8y agoThat also shows why fusion power always centers around exotic isotopes like deuterium and tritium rather than plain hydrogen. The reaction paths needed to fuse plain hydrogen are so improbable that they don’t happen fast enough to be useful.
- kamaal 8y agoIs this an another way of saying that the only way to fuse to Hydrogen is to create a structure as large and with gravitational features that of a star? Then a star/solar energy is the only way you will ever have large scale fusion energy generation and harvesting.
- DennisP 8y agoNo, it's saying that large-scale fusion using hydrogen fuel requires a star, because hydrogen fusion reactions are very improbable. That reaction only happens when four nuclei collide at once. Fortunately we have other fusion fuels that are much more likely to fuse, including deuterium, which makes up 1/2500 of the hydrogen atoms in the ocean. Most projects target the easiest fuel, deuterium-tritium; while tritium isn't naturally available on Earth, it can be bred from lithium.
- wbl 8y agoNope! The p-p chain only has pairwise interactions. The issue is the p+p->d step is very disfavored, thanks to the weak step. D+T is all strong interaction.
- bjelkeman-again 8y agoCould that be explained with less jargon? I’d like to understand it.
- ravar 8y agoThere is a chain of individual steps that need to happen to create the final product of hydrogen fusion, helium. One of the crucial steps is the production of deuterium from two protons. This step is incredibly slow and limits the rest of the chain. However if you skip the slow step and start by fusing deuterium and tritium you can have a much faster and efficient reactor.
- DennisP 8y agoThanks, that was interesting. Apparently the five-minute video I got my statement from led me astray.
- pfdietz 8y agoIndeed. After a D nucleus forms in the sun, it reacts (with a proton, to form 3He and a photon) within a few seconds. The 3He+3He reaction is also slow, but not as slow as that first step.
- simonh 8y agoI suppose the universe doesn't owe us a cheap, easy, unlimited source of energy. A lot of people seem to think that it's inevitable we will achieve amazing, magical feats of technology given sufficient time and effort that are unthinkable today. Maybe. But it's also just as possible that we already know most of the general parameters of what is possible in the universe, and the peak practical feats of technology that will ever be open to us are not all that far off from what we have now. How can we tell?
- narag 8y agoNuclear tech is not even a century old. The idea that we can't do any better in a thousand or a million years seems so improbable to me that I can't take it seriously. There is some kind of extrange pessimism around that mindset: that we will be extinct much sooner, or that the Sun will die and thus Humanity, as if there's no obvious way to escape that apocalypsis.
- peterashford 8y agoI think that significant swathes of human kind throughout history have assumed that their current state of existence is the peak and final form of humanity. While it is always logically possible that this is the case, it has never yet been true.
- rectangletangle 8y agoAgreed, the accepted models in physics are laughably incomplete. There is still a tremendous amount we still don't know. Although it's possible we've peaked, I have doubts. It is also a self fulfilling prophecy to declare that we have reached our technological apex, and not striving to progress further.
- Koshkin 8y ago> do any better in a thousand or a million years From what I can tell, there is a much bigger chance that we'll do much worse - and much sooner.
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- curtis 8y ago> Despite its intense temperature, the peak power generating density of the core overall is similar to an active compost heap... I've seen this comparison before and it also seemed quite surprising to me. But in hindsight maybe it shouldn't: The sun is already billions of years old and it hasn't burned out yet. Another way to think of it: A larger compost pile has to radiate more heat out of the same surface area as a smaller heap because of the Square–cube law [1]. Now imagine a compost heap more than 800,000 miles in diameter. [1] https://en.wikipedia.org/wiki/Square%E2%80%93cube_law https://en.wikipedia.org/wiki/Square%E2%80%93cube_law
- gattr 8y agoAh, one of my favorite astronomy-related trivia. It also shows how a supernova can (briefly) shine as brightly as its whole host galaxy (i.e. some 10-11 orders of magnitude stronger than an average dwarf star - like you wrote, those basically "smoulder").
- thomasahle 8y agoIt continues like this though: > The low power outputs occurring inside the fusion core of the Sun may also be surprising, considering the large power which might be predicted by a simple application of the Stefan–Boltzmann law for temperatures of 10 to 15 million kelvins. However, layers of the Sun are radiating to outer layers only slightly lower in temperature, and it is this difference in radiation powers between layers which determines net power generation and transfer in the solar core. So if a m^3 of sun core was moved to a powerplant it would generate a lot more energy.
- thaumasiotes 8y ago> So if a m^3 of sun core was moved to a powerplant it would generate a lot more energy. Would it? Or would it expand into basically normal hydrogen and helium?
- sova 8y agoProvided you could keep the plasma contained in magnetic fields, it would certainly generate plenty of free neutrons to provide heat for substantial power generation.
- voidmain 8y agoIf you let it cool, it would stop fusing. The fusion power wouldn't magically go up.
- sova 8y agofusion halts harmlessly when conditions are unmet
- thaumasiotes 8y agoHalting harmlessly is the opposite of "producing a lot more energy".
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- Creatccount 8y agoWould zero gravity be helpful in order to make it easier to get fusion working?
- ballenarosada 8y agoGood question. Under the influence of a magnetic field, charged particles do all sorts of counterintuitive things due to the Lorentz force, which acts at right angles to the particle velocity and the field. One example is a sideways precession due to the interaction between gravitational acceleration g and the Lorentz force. Fortunately this effect is basically negligible, because gravity is so much weaker than the electromagnetic forces operating on the particles. The difficulties tend to come from the geometry of the magnetic field itself. For example, in a torus shape, there is an unavoidable drift in the vertical direction due to the combination of centrifugal force in the big circumference, and the force implied by the gradient of the magnetic field.
- pontifier 8y agoMy understanding is that stellarators are designed in such a way that this sideways drift in one part of the device is canceled by opposite drift in another part due to the twisting of the field.
- hwillis 8y agoThe particles in a fusion reactor are moving at 10 km/s. They don't particularly care about gravity. For components of the reactor, gravity tends to be helpful. It's much harder to cool superconductors or generate steam if your liquids aren't flowing along the bottom. Turbines don't work nearly as well if their inlets are sputtering like a coffeemaker.
- pfdietz 8y agoThey are moving a lot faster than 10 km/s.
- the8472 8y agoSpace also comes with a natural vacuum, not just zero-g. That might be more interesting for a reactor since you would only have to care about shielding the magnetic coils instead of building and cooling a vacuum vessel at the same time.
- qrbLPHiKpiux 8y agoIt's hard now because we don't know how to do it well. In the future, we'll learn, then it will be easy. History tells us this.
- deleted 8y ago[deleted]
- kjar 8y agoFor most of my life fusion has been teased but not delivered. fission has been pimped for decades yet cannot get private funding, or build reactors in a decade, or provide solutions for the waste. Yet still the industries persist with their propaganda while renewables beat them in cost and time to operation. If I managed the funds I'd cut nuclear and redirect to wind and solar immediately.
- kjar 8y agomy point in short is we don't have time for this right now. we need to de-carbonize our energy system a decade ago. this tech. is not operational and will take a decade to be so - that's not time we have to avoid catastrophic climate destabilization.
- adrianmonk 8y agoIf the objection is that nuclear can't be built quickly enough, then the renewable options need to be judged against that same standard. Suppose everyone in the world already agreed to go a hundred percent renewable in 10 years. Effectively replacing the entire world's energy infrastructure is going to take a huge amount of raw materials and production capacity. Is there going to be enough? It's possible the answer is yes, but I wouldn't take it for granted. There will need to be a lot of battery storage, which means there needs to be a lot of lithium. Are there enough lithium mines? Have geologists identified enough deposits to cover that massive quantity? And are there enough factories that can build batteries? For wind, there will need to be neodymium permanent magnets. For solar, you need fabs to build it all. Maybe all those challenges can be solved, but maybe it's also possible to streamline the process of building nuclear fission power plants.
- sanxiyn 8y ago> There will need to be a lot of battery storage, which means there needs to be a lot of lithium. No, if we actually want this, pumped-storage hydroelectricity is a proven solution that works. There is actually no uncertainty regarding energy storage: we can do it.
- Michaelanjello 8y agoDelete.
- loblollyboy 8y agoLinks to whatever those are? I googled, couldn’t find
- deleted 8y ago[deleted]
- Michaelanjello 8y agoI detest the overall HN commenting community. You may be an exception. They're always downvoting and shadowbanning. I am reluctant to share much useful info here.
- sctb 8y agoPlease stop trolling. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html
- Michaelanjello 8y agoI wasn't, but you should. Calling me a middlebrow goes to show you don't know what you don't know.
- gahhebjjd 8y agoSo for the record, this comment that was deleted referred to "reservoir nets" and "spiking architectures" as ways researchers should control plasma instability and in a separate comment, the poster claimed to have "said more than I should already". There was also a disparaging comment about fusion researchers.
- dukoid 8y agoIf you understand German, trust me and listen to this podcast about Wendelstein 7-X O:) : https://alternativlos.org/36/ https://alternativlos.org/36/
- sschueller 8y agoThis is a really excellent podcast. Very informative.
- throwaway77384 8y agoAlmost trotted this one out myself. So good!
- openloop 8y agoWhy is letting go of religion so hards. Who knows.
- sudhirj 8y agoTry making a compressed, spherical ball of water using your two hands.
- deleted 8y ago[deleted]
- finnh 8y ago“Confining a plasma is like trying to keep water in an inverted cup by blowing on the water with fans.” That is fantastic analogizing right there.
- HocusLocus 8y agoQUOTE "I took this fusion class when I was at Georgia Tech and I will never forget it. We started studying and I go, "Man, this is really hard." Charged particles don't want to get near each other. Bare nuclei are both charged, positive charged, they want to avoid each other. And my professor had a really great way of putting it. "It's like going to the mini golf." He says, "You know how in mini golf you've got the volcano, and the volcano's got the hole at the very top, and you've got to putt your ball in a way that it goes all the way up the side of the volcano, and 'phwep!' falls in the hole." He goes, "OK. That's like fusion. The ball is like a nucleus, and the volcano is the scattering effect. So any time you want to have a nucleus go to another nucleus, it scatters; it rolls up the mountain and it rolls down the side, it rolls over here, over there... and only when you just perfectly get it on the right angle does it go in the volcano." Now, the problem with fusion, he goes, "You can't steer the ball, you have to have enough temperature so that it can make it all the way up the side of the volcano and fall in, and then you have to have enough balls because you can't steer them there at the mini golf park", that's density, "and then because they're flying all over the place, you've got to make sure that there's a fence around the mini golf park so that they don't get away." That's confinement. He said, "Those are your three things: density, temperature, and confinement, to make fusion happen." I said, "Dude, that's really hard!" So, I came up with another analogy, "So, I guess fission would be like the mini golf park except now the volcano was flush, the hole was about this big around, the balls are going slow, and every time the ball goes in the hole, two more balls come out." He goes, "Yeah, that's pretty good." ENDQUOTE Watch the whole thing. It's good. https://www.youtube.com/watch?v=lG1YjDdI_c8 https://www.youtube.com/watch?v=lG1YjDdI_c8
- selimthegrim 8y agoWhat point in the video is this quote?
- deleted 8y ago[deleted]
- HocusLocus 8y agohttps://www.youtube.com/watch?v=lG1YjDdI_c8&t=71m26s https://www.youtube.com/watch?v=lG1YjDdI_c8&t=71m26s
- yummybear 8y agoThis a totally ignorant question - can you add “something” to the plasma to achieve the “jello like” analogy to water?
- lisper 8y agoThat's actually a very reasonable question. The answer is: no, but explaining why is non-trivial. The short version is that at 10 million degrees, matter behaves so differently than it does at room temperature that none of your everyday intuitions apply.
- throwawayaway12 8y agoWarm Dense Matter can be thought of as ionized jello.
- lisper 8y ago> Some kinds of instability are slow enough that we can control them. For example bicycles are unstable, but many of us eventually learn to ride them. Actually, bicycles are only unstable when they are moving slowly (or stopped), and most people never learn how to stabilize one in this unstable regime. It can be done, but it's very, very hard.
- adrianmonk 8y agoNow, what would be great is if that analogy could be stretched further. It would pretty wonderful if someone found a way to do fusion where, like a bike, it's stable once it gets going.
- lisper 8y agoWell, that is actually possible. That's what happens in stars and hydrogen bombs. The problem, of course, is that "getting going" for fusion means getting very big. The reason fusion energy is hard is precisely because to be practical and safe we have to "ride slowly".
- fusiaoids 8y agoThese are called self-stable plasmas, and are already been explored. For example, TAE's field-reversed configuration.
- rkagerer 8y agoThis is probably another ignorant question, but why can't we "aim" and shoot protons at each other to make them smack together without requiring all that heat and pressure?
- apcragg 8y agohttps://en.wikipedia.org/wiki/CERN https://en.wikipedia.org/wiki/CERN
- abecedarius 8y agoI've wondered, aren't there any fusible elements that can be solids in vacuum? Then shoot pellets at each other at a sizable fraction of c. Way better density than a particle beam. For instance, lithium-6 is a stable solid metal with the right nucleon composition and binding energy to fuse into carbon-12. I have no idea if it actually would to a useful degree.
- Retra 8y agoSolid in a vacuum at what temperature?
- abecedarius 8y agoWhatever's practical for your giant pea-shooter and reaction chamber. But lithium is a soft metal at room temperature, so this part doesn't seem too constraining.
- Retra 8y agoIf you want to sustain a fusion reaction for generating power through heat, you're not going to do it at room temperature, and there're not many materials that will remain solid at fusion temperatures.
- abecedarius 8y agoI said "shoot pellets at each other at a sizable fraction of c". The point is to hold together before the splat, so that by high density enough nuclei actually hit each other. This is a bang-bang kind of thing, not a continuous reaction.
- aurizon 8y agoHere is a thought experiment( no cats harmed or wetted). Show a cat how the toilet flushes, then try to flush the cat. You have two hands, the cat has 4 paws, with sharp claws as well as teeth. This will give you an idea.... Stars have gravity and mass- we do not, so we must try and compress the plasma, heat it AND stops the paws from grabbing the exterior. In truth magnetic confinement is a poor way to constrain a plasma that wants to leave at high speed = quenches the reaction. There have been many avenues tried and they are making incremental advances, year by year. They say we are 5-10 yearsaway? The ITER Tokamak is well advanced. https://www.iter.org/mach/Tokamak https://www.iter.org/mach/Tokamak New approaches are being tried that might leap past the Tokamak.
- mdpopescu 8y agoControlled fusion has always been 5 to 10 years away, just as we've always been at war with Eurasia.
- aurizon 8y agoThat is partly true,but we ave advanced to the point where the next generation of machines take 5 years or more to build. They have reached the break even and gone substantially past it, but they have not been ablt to reduce it to the turn-key appliance stage.
- pfdietz 8y agoNo fusion reactor has reached breakeven.
- losteric 8y agoAll deadlines have an implied "with equivalently aggressive funding" addendum
- BurnGpuBurn 8y agoI remember distinctly reading a popular science magazine article when I was young (it had that great plasma picture with all the plasma arcs fizzing over the floor of a giant lab) that stated that we could have fusion power plants in 25 to 50 years. That was 30 years ago.
- schwarze_pest 8y agoWrong title. Fusion is easy, plasma physics isn't.
- pfdietz 8y agoFusion is likely to be a nonstarter even if the plasma physics issues are completely solved. It has fundamental engineering and cost problems.
- Animats 8y agoPlasma instability is just awful. See [1]. I thought he was going to go on about some approach to active stabilization of plasmas. But no. There's been work done on that, but it's been years. Anyone following that? Then there's the first wall problem.[2] Fusion generates heat and neutrons. Lots of neutrons, which break atoms apart. Finding something which will stand up to that in an experimental machine has been tough. Finding something which will stand up to that in a long term production environment is really tough. In a fission reactor, you can use water to slow and stop the neutrons, and you just get some tritium as a byproduct. A fusion reactor's first wall faces a vacuum, so that's out. [1] https://en.wikipedia.org/wiki/Plasma_stability https://en.wikipedia.org/wiki/Plasma_stability [2] https://en.wikipedia.org/wiki/Plasma-facing_material https://en.wikipedia.org/wiki/Plasma-facing_material
- cjslep 8y agoYep, studied Nuclear Engineering at NC State, didn't stick around for the grad program. My friend did, for plasma physics, and is now working at ITER. Plasma confinement is still improving.
- dangjc 8y agoDoes fusion still have much of a role now that renewables are increasingly competetive? We can pretty much already harness infinite energy for all our needs from an already working fusion generator our planet happens to orbit around.
- ethbro 8y ago> now that renewables are increasingly competetive... ... with legacy energy sources. When talking about fusion / nuclear vs renewables, think in terms of max energy produced per site, not cost per unit. Similar to total thrust vs specific impulse. The largest respective power generation stations by source -- Three Gorges Dam / Itaipu Dam (Hydro, 22,500 MW capacity, ~100 TWh/yr), Kashiwazaki-Kariwa (Nuclear, 7,965 MW capacity, 60 TWh/yr, currently suspended for earthquake-proofing), Tengger Desert Solar Park (Solar, 1,547 MW capacity, ? TWh/yr), Alta Wind Energy Center (Onshore Wind, 1,547 MW capacity, 2.68 TWh/yr, Gansu not included due to utilization issues), Walney Wind Farm (Offshore Wind, ~1,000 MW capacity, >1.3 TWh/yr?). And then realize that hydro & wind are both location-limited. And solar has a large footprint: Tengger is 43km^2. Nuclear (and eventually fusion) scales footprint much more slowly with capacity. Kashiwazaki-Kariwa is 4.2km^2.
- robertsteinhaus 8y agoMankind is currently in possession of a practical fusion technology. It might be worthwhile to remember that Ivy-Mike fission-fusion technology worked the very first time it was tried in 1952. Mike technology was the basis of the first thermonuclear weapons in the US arsenal. Adapting Mike technology to be pure hybrid DT-DD fusion opens up many new applications in economical power generation. In 60 years, no other fusion technology (Magnetic Confinement or Inertial Confinement) has ever produced any net energy (more energy out of the fusion reaction than it takes to get the fusion plasma to fusion conditions). In 60 years, all existing MCF and ICF fusion systems have never worked (in the sense that they have not produced more energy from fusion than it took to get the fusion plasma to fusion conditions). Mike fission-fusion technology worked the first time it was tried and produced huge amounts of net energy (and has never failed). Rather than placing our faith in scaling laws while we build ever larger and more expensive Magnetic Confinement fusion experiments (tokamaks and stellarators) while trying to achieve break even energy generation - why not go back to the field and adapt technology that has never failed to finally find success in fusion?
- mathw 8y agoSo, how do you turn a bomb into a practical source of power that doesn't destroy the surrounding area the moment you turn it on?
- pfdietz 8y agoThey looked at this. It's grossly uneconomical as a power source. "In a 1975 review of the various Plowshares efforts, the Gulf University Research Consortium (GURC) considered the economics of the PACER concept. They demonstrated that the cost of the nuclear explosives would be the equivalent of fuelling a conventional light-water reactor with uranium fuel at a price of $328 per pound."
- dTal 8y agoMaybe we just haven't tried hard enough. While researching a comment for another thread I discovered an interesting fact: the US has now spent approximately as much money on fusion research ever (since 1955) as it did on the Manhattan project, alone. Perhaps we shouldn't be so surprised that progress is so slow.
- lerno 8y agoThis is why I have little confidence that Tokamaks and similar will have much success. Instead of trying to prevent the non-linear behaviour of plasma it should be utilized. Look at (grossly underfinanced) attempts like focus fusion, where there is no attempt to confine the plasma, instead self-interacting nature of the plasma is used to focus high temperature regions to a small region where higher temperature fusion processes can occur. Long time plasma confinement is a dead end.
- kristianp 8y agoI'm a fan of IEC, what happened to the Polywell? https://en.m.wikipedia.org/wiki/Inertial_electrostatic_confinement https://en.m.wikipedia.org/wiki/Inertial_electrostatic_confi...