Here's a video lecture from the MIT Professor (Dennis Whyte) who was leading the research group that provided some of the key designs for the SPARC reactor. As the NYT article explains, that research has been spun out into a startup that raised $200M.
The key breakthrough is the advancement of REBCO tape superconductors which allow you to (1) generate record breaking magnetic field strengths (2) easily disassemble the super conducting loop for fast repairs / refuels / more modular design.
It's a long talk, but it's extremely fascinating. Basically everything becomes much easier once you can increase the magnetic field strength. This talk is fairly accessible to even relative laypeople who have a vague understanding of E&M physics.
00:01:00 - introducing Dennis Whyte, MIT department head for nuclear science
00:04:24 - presentation starts
00:06:00 - identifies breakthrough with REBCO magnets
00:07:25 - explains deuterium-tritium fusion
00:12:30 - basic metrics for reactor performance
00:17:15 - energy output of other previous fusion experiments
00:19:00 - examines ITER and the problems of its approach
00:22:00 - problems solved by high energy magnetic fields
00:28:15 - full scale reactor concept, teardown of REBCO magnets
00:37:00 - design limits and margins
00:39:00 - fixes plasma instabilities found in weaker magnetic chambers
00:40:00 - maintainability, lifespan, component replacement
00:45:00 - solution to neutron damage and energy capture
00:50:30 - cost and profitability
00:54:00 - full graph of field strength vs reactor scale (and thus funding requirements)
01:01:50 - Q&A
01:30:00 - question about the biggest risks
Also a more recent video, with more numbers and even more confidence than the first: https://www.youtube.com/watch?v=rY6U4wB-oYM
https://www.youtube.com/watch?v=L0KuAx1COEk
He goes into detail about SPARC as well and why a higher magnetic field using HTS superconductors enables performance that can otherwise be obtained by greater size as ITER is trying.
Important decisions about the future development of atomic power must frequently be made by people who do not necessarily have an intimate knowledge of the technical aspects of reactors. These people are, nonetheless, interested in what a reactor plant will do, how much it will cost, how long it will take to build and how long and how well it will operate. When they attempt to learn these things, they become aware of confusion existing in the reactor business. There appears to be unresolved conflict on almost every issue that arises.
I believe that this confusion stems from a failure to distinguish between the academic and the practical. These apparent conflicts can usually be explained only when the various aspects of the issue are resolved into their academic and practical components. To aid in this resolution, it is possible to define in a general way those characteristics which distinguish the one from the other.
An academic reactor or reactor plant almost always has the following basic characteristics: (1) It is simple. (2) It is small. (3) It is cheap. (4) It is light. (5) It can be built very quickly. (6) It is very flexible in purpose ("omnibus reactor"). (7) Very little development is required. It will use mostly “off-the-shelf” components. (8) The reactor is in the study phase. It is not being built now.
On the other hand, a practical reactor plant can be distinguished by the following characteristics: (1) It is being built now. (2) It is behind schedule. (3) It is requiring an immense amount of development on apparently trivial items. Corrosion, in particular, is a problem. (4) It is very expensive. (5) It takes a long time to build because of the engineering development problems. (6) It is large. (7) It is heavy. (8) It is complicated.
The tools of the academic-reactor designer are a piece of paper and a pencil with an eraser. If a mistake is made, it can always be erased and changed. If the practical-reactor designer errs, he wears the mistake around his neck; it cannot be erased. Everyone can see it.
Anyone could have said similar things about computers in 1953, and been just as correct.
Are nuclear reactors computers? Of course not, and neither have practical reactors kept pace in development with practical computers.
But neither is it inevitable that steady progress cannot grind down the latter set of characteristics into the former. Indeed, that's what I would bet on, and I think the Admiral would be disappointed in the progress we have(n't) made.
Many people could say similar things about software in 2020 and be just as correct. :) The good Admiral may be describing some timeless aspects of engineering, possibly related to the recently discussed observation that reality has a surprising amount of detail: https://news.ycombinator.com/item?id=16184255 .
Though, as you say, over time engineering can grind out some of the practical into practice.
For fusion, you need to achieve a high temperature. So "thermal insulation" of the centre of the plasma from the edge of the plasma is really important. The nice thing is, that since charged particles move along magnetic field lines, and magnetic field lines never cross each other, the thermal insulation of plasma made from charged particles is enormous. That would imply it is really easy to achieve really high temperatures.
However, in 1953 they overestimated the enormous "thermal insulation" at higher temperatures by 10 orders of magnitude. That is a ratio of 1e10 between the expected and the actual value. It is still enormous, mind you, but not that enormous.
If that estimation had been correct, we would have had fusion by 1973. However, in that period it gradually became clear that fusion that way was not going to happen as people found lower and lower thermal insulations in their plasmas.
The same thing might have happened with semiconductors. What if the thermal noise were off by 10 orders of magnitude at smaller scales, compared to what was expected in 1953? Computing would not be where it is today, although it would definitely still be a good possibility if we were only pushing harder in circumventing the noise.
Vaporware is a real problem in every discipline.
1. It is simple: no, nobody says here that fusion is simple.
2. It is small: well, this one is small compared to ITER, but nobody's saying it's small in an absolute sense.
3. It is cheap: sure, compared to the billions and billions poured into ITER, this is dirt, dirt cheap, but still, they have secured $200MM so far, and they will need more money until they build an actual reactor.
4. It is light: really not applicable here, since nobody's thinking of putting these reactors in submarines (which is what Rickover was really talking about).
5. It can be built very quickly: sure, the time horizon is less than the perpetual 30 years of the old fusion reactor proposals, but it's not going to be "very quick",
6. It is very flexible in purpose: no, for the time being, something that just works is fine, nobody cares about flexibility,
7. Very little development is required, it will use mostly off-the-shelf components: nope, there will be plenty of very custom made components developed for just this purpose, and lots and lots of development are required.
8. The reactor is in the study phase. it is not being built now: it is both in the study phase and being built.
In the end, what was Rickover's agenda: some people were competing with him for government funding for nuclear reactor R&D in general, and for naval nuclear reactors in particular. All those people were a nuisance to him, he had to go and plead for funds again and again, so he decided to write this letter to put this thing to rest once and for all. He managed.
But here it's fusion. Commonwealth Fusion is privately funded, they are not looking for government funding, and they are not making inflated representations to the public. They are actually keeping a low profile in general. The message of this article is simply "this time there is a glint of hope", nothing more.
First, the context. Rickover needed to get a reactor designed, series built, and operated right away. In that context, he was absolutely right.
Second, the PWR design works and it works very well for submarines. I don't know that there has been a better design concept for submarines (the USSR built a few liquid metal cooled reactors which caused them lots of problems). When you have a basic design that does work, then going ahead and building it is the right thing to do.
We can see the consequences of what that approach does to earlier stage research programmes as well because some of Rickover's people were put in charge of Argonne's reactor research programme which they did not understand and where they caused an immense amount of trouble by trying to duplicate this approach in a context where the basic approach had not been definitively decided. This lead, for instance, to spending an enormous amount of money and time pursuing an oxide fuel fast reactor concept despite being warned that there were fundamental problems with that design and that spending more time up front on metal fuel design work would be a better idea. They didn't want to hear it - oxide fuel works (which it does - in thermal PWR and BWR reactors) - so go with that and just build it.
Rickover was right of course about the principle of understanding technological predictions in the context of what we would now call Technological Readiness Levels and optimism bias but in understanding this we also have to keep in mind the other side of the coin which is not to entirely commit to premature optimisation.
https://en.wikipedia.org/wiki/Hyman_G._Rickover#Safety_recor...
> (3) It is requiring an immense amount of development on apparently trivial items. Corrosion, in particular, is a problem.
The design has molten fluoride salt circulating in a strong magnetic field. Molten salts, unlike molten metals, have low (but not zero) conductivity.
But the motion will still induce a voltage drop across the salt. If the walls are metal, there is the possibility of galvanic corrosion due to this potential. And there's the possibility that radiation could enhance this corrosion.
"Although many significant challenges remain, the company said construction would be followed by testing and, if successful, building of a power plant that could use fusion energy to generate electricity, beginning in the next decade."
In other words, "very likely" in this case means "if several roadblocks are overcome, it might be a net-positive power generator in a decade". Even so, this is still exciting given how anemic advancement in the fusion space has been for 50+ years.
https://physicsworld.com/wp-content/uploads/2004/01/pwhoa4_0...
From the article at :
https://physicsworld.com/a/controlled-fusion-the-next-step/
more information about the triple product and the Lawson Criterion.
"Nuclear fusion. 30 years away since 1950"
Joking aside. I too am glad to see some progress of any kind, and new (seemingly credible) initiatives being funded and pursued
Those projections usually include the caveat "if properly funded" - https://i.imgur.com/3vYLQmm.png
I feel like there should be bonus points for getting this quote to the top of every fusion article posted until there's an existing fusion reactor.
At the top of my list for when I'll be king for a day is - massive, national-scale investments (think: reaching towards one percent of GDP) in fusion research.
This is a major roadblock, but things look awesome on the other side. We just need to get our stuff together to hop over this fence somehow.
Let’s suppose this proposal works out, ITER will become a very expensive boondoggle. A technological dead end. But if you’d taken the ‘Manhattan Project’ approach and thrown 10x as much money at fusion research 20 years ago we’d most likely have spent most of it on a super-ITER. It might be operational by now and might even have reached break-even on power generation, but in the longer term would now be just as redundant and superseded by this new approach.
A reminder of what could have been:
https://upload.wikimedia.org/wikipedia/commons/a/ab/U.S._his...
The 2020s start 2020-01-01 (just as the century called "the 1900s" started 1900-01-01).
The 21st century started 2001-01-01.
The 203rd decade starts 2021-01-01 -- but nobody talks about the "203rd decade". That's the difference in terminology between decades and centuries; we don't refer to decades by their ordinal numbers.
Yes, it's confusing and inconsistent. If only Dionysius Exiguus had known about zero.
I quote ISO/WD 8601-2:
Representation of a decade must be exactly three digits, leading zeros, if any, must be included. Thus the time interval 200 through 209 is represented as ‘020’ and NOT ‘20’; the latter would represent the time interval 2000 through 2099.
Here you can clearly see that the ISO definition of a decade is in keeping with the common understanding, not whatever oddball misunderstanding you've chosen to promulgate.
Tritium, however, does NOT exist in nature, and can only be conceivably produced in three ways:
1. Inside thermonuclear bombs
2. In heavy-water reactors, e.g. CANDU design, which requires Uranium, so it is not fuel-independent and totally dependent on nuclear fission technology. Getting Tritium that way is also extremely, extremely expensive.
3. possibly, in a breeding blanket of a fusion reactor. This makes fusion technology reliant on breeding reactors which is much more complicated and has many completely unsolved questions in the materials part. Also, existing fission-breeding reactors are also less safe, for example, like the Japanese Monju plant, which was cooled with liquid sodium, a highly reactive metal, which got incensed in a fire. Fusion breeder reactors will probably also require something like sodium cooling because of the high energy densities required.
And the existing research projects like ITER have not even started to address these issues - they are purely plasma physics experiments.
Maybe I don't understand properly, but I'm watching the video linked in a previous comment (1) and around the minute 9:30 professor White says that "what comes into the plant is actually deuterium and lithium".
It seems he is saying that you need only an initial quantity of Tritium and then Helium and Lithium is used to created Tritium again. I suppose that it's what you refer as "breeding". He explain it as it's not a big deal.
Section 3.2 Test Blanket Module (TBM) Testing Program in ITER
https://www.iter.org/doc/www/content/com/Lists/ITER%20Techni...
Look even closer at the fusion energy research community and you will find a lot of work has already gone into this problem. Assuming physicists sit on their thumbs is a bad bet.
Not fissionable, but many are unacceptable due to formation of long lived activtion products.
One additional problem with the alloys used is the degradation of their mechanical properties under radiation exposure. They tend to become brittle.
Testing any of these materials will require something close to a working fusion reactor (nothing else duplicates the neutron environment), but that will require the materials. Working around this loop of circular development dependency will be time consuming.
Seems like they're meeting all their planned milestones and it's going well!
Excited for their next updates...
More from their project page: https://www.ipp.mpg.de/w7x
"Wendelstein 7-X is the world’s largest fusion device of the stellarator type."
It reminds me of the principle that one shouldn't start a space travel project that is estimated to take more than x years to complete, because by that time, technological progress will have surpassed its speed and capabilities, and would physically overtake it (the 'wait calculation').
Episode 22 is an intro to fusion power research and tokamaks.
Episode 157 is an interview of a director at ITER.
Episode 304 interviews the author of the book you’re reading.
Episode 312 is a set of interviews with experimentalists and computational theorists at W7-X.
It's great there are seven-peer reviewed articles about SPARC, but plasma was not my specialty in physics -- would any specialists care to comment on whether there is anything particularly exciting here?
1 - https://www.fusionenergybase.com/concept/rebco-high-temperat...
2 - really great talk from a few years ago about this from MIT's Plasma Science Fusion Centre: https://www.youtube.com/watch?v=L0KuAx1COEk (really, if you like this stuff, give the talk a watch. It's great.)
The problem is that all known superconducting materials known will lose their ability to superconduct when exposed to a sufficiently strong magnetic field. The large field strengths induce eddy currents in the material which disrupt the propagation of the cooper pairs in its superconducting mode. The current sufficient to self-induce this field is called the critical current.
Layered rebco tape appears to shield against this effect or otherwise trap the eddy currents in a way that superconductivity is preserved even in the presence of extremely strong fields. The critical current in REBCO tape is enormously higher than in previously known materials or winding configurations.
Obviously the bigger the reactor volume is, the smaller the magnetic field needed to steer and confine the plasma within it can be. So back when they were designing ITER, engineers figured out the strongest magnet they could make, then they designed the reactor to be small enough (lol) that said magnet could still sustain confinement.
However now that we have stronger magnets we can make reactors smaller. This is even something of an gross understatement as the relationship is cubic. For a doubling in field strength, the reactor can be 8 times smaller. That effect is very meaningful when considering that you are essentially talking about shrinking something the size of ITER's 28m main reaction vessel to something that might fit into a garage.
I'm not really any kind of expert on this, so please treat this explanation as very simplistic.
I have not yet personally seen anything about this new lattice confinement modality that seems to give me anywhere near the same level of confidence that they will see viable applications compared to the magnetic confinement approach. (NIF already stood down their tries at laser inertial confinement) Maybe someone has some good insight on whether or not this is all still speculative fanfare or if researchers are finding real meat.
They were specifically looking at the tapes ability to function in high magnetic environments such as a tokamak type reactor.
Good job recording MIT.
Why can't natural laws be more simple and linear? (joking, sure, but it does feel that way sometimes)
In the sun, isn't energy production occurring at something like 100-1000 W/m3? So, if you want to build a multiple MW fusion plant, shouldn't these plants be ridiculously huge compared to, say, a wind turbine rated at a couple of MW?
Is the density of the plasma so much higher in a fusion reactor?
Also, something else I never grokked, how do you get the power out? The plasma heats up, but how do you turn that into useful electrical energy?
Nevertheless of course I hope it does work as advertised... someday.
Edit: thanks everyone for the thoughtful, insightful replies!
The trick is in higher temperature plasma. The sun fuses protium (lone protons). We don’t have the confinement necessary on Earth to do this, so we fuse deuterium (1p+1n) and tritium (1p+2n). This reaction is more energetically favorable and is achievable on Earth. Coupled with giant microwave ovens and clever geometry and electromagnetic tricks, we can make plasmas much hotter (faster moving particles) than the sun can.
Once a plasma is fusing, it emits a lot of heat (alpha heating and fast neutrons). A plasma that requires no external heating (no microwave ovens) is said to be “ignited”. We don’t necessarily need or want ignition to have a successful reactor, but it’s a cool thought.
The major trouble with fusion reactors is keeping particles in the bottle long enough to fuse. Since they’re leaving anyway they have to go somewhere. You can tune vessel geometry and magnetic fields to have designated strike points where most of the plasma will exit confinement. These are called divertors. Run some coolant through your divertors and you have a heat source that can boil water and spin a turbine.
Here my knowledge gets shaky because I know that the fastest particles coming out of a D+T reaction are neutrons (they weigh much less than an alpha particle). Since neutrons are electrically neutral I think they are much less likely to become thermalized (they are not likely to bump into another particle on their way out). I’m not sure how neutron thermalization happens in reactor simulations, but I’m under the impression that it does.
Terrestrial reactors try for much higher reaction rates. But most designs still have power density issues that would make them uneconomical even if they could make net power. Net power is actually a very low bar, corresponding to an EROI of 1.
I appreciate that many people are commenting 'you couple the plasma to a working fluid', but I think the original comment was more along the line of how you couple a confined plasma to a working fluid. By definition the plasma is in a hard vacuum, magnetically bottled. What, then, is the coupling method? Thermal photons escaping confinement? I genuinely have no idea myself, but would really like to know.
I looked up the effects of neutron radiation on materials[]. Sounds like a hell of an engineering challenge to come up with a robust way of getting that energy out!
Radiation damage to materials occurs as a result of the interaction of a [neutron] with a lattice atom in the material. The collision causes a massive transfer of kinetic energy to the lattice atom, which is displaced from its lattice site, becoming what is known as the primary knock-on atom (PKA). [...] The magnitude of the damage is such that a single 1 MeV neutron creating a PKA in an iron lattice produces approximately 1,100 Frenkel pairs.
To collect energy, heat would be transferred to a working fluid (e.g., molten salt) by exposing that fluid to the hot plasma. Then the working fluid would be used to boil water and spin a turbine.
> Also, something else I never grokked, how do you get the power out? The plasma heats up, but how do you turn that into useful electrical energy?
Steam turbines; same as fission or coal. Or gas turbines, if you want to get fancy.
- fusion is developed
- b/c of fusion, the cheapest "rocket fuel" is basically water heated into steam by the fusion reactor
- people on Earth get upset about the "spacers" taking all of the "earthers" water
- the spacers then have to go to other sources of water in the solar system (I think it was either rings of Saturn or the asteroid belt)
The thing that struck me at the time was the "water as propellant" without the extra step of breaking H2O into hydrogen and oxygen.
It's just an average. Fusion occurs only in the core, which is pretty tiny, relatively speaking.
> The plasma heats up, but how do you turn that into useful electrical energy?
The same way you can turn any kind of heat into useful energy.
~250W/m3.
The whole research program gets its funding as what amounts to a jobs program to keep high-neutron-flux physicists employed and available to draw upon for weapons work. That is one reason why any fusion process that does not emit neutrons is not given any of the research funds: weapons work doesn't need high-alpha-flux physicists. (Secondarily, they have papers that purport to show e.g. p-B fusion could never work.)
If we ever do get practical fusion, it won't be in a Tokamak, it probably won't be on the Earth's surface, and it certainly won't help resolve global climate disruption.
The money being spent on Tokamaks, on the other hand, absolutely could help a great deal with global climate disruption. But not while also maintaining the all-important high-neutron-flux population.
So, is this ‘just’ a matter of ITER being obsoleted by improvements in magnet tech before it is completed, or is there more in this design than scaling down ITER?
https://arxiv.org/abs/1409.3540
Some additional features (besides the magnets) that jump out at me:
The reactor vessel has joints to allow it to open up for maintenance access (previous tokamak designs have a reactor vessel that cannot be opened up once constructed, so maintenance inside has to be done through small access ports using remote manipulators).
The external current drive for heating the plasma to ignition looks like it is more efficient than previous designs.
The blanket around the reactor vessel is liquid instead of solid, using a fluorine-lithium-beryllium compound.
The power density of the reactor is 0.5 MW/m^3, which is 1/40th the power density of a commercial PWR primary reactor vessel.
The reactor (a single one!) uses something like 40% of the world's current annual production of beryllium. If all the world's estimated resource of Be is used to make these reactors, it would be enough for reactors producing just 1% of world primary energy demand.
The remote manipulators are an amazing piece of technology; having the movements of your arms and hands replicated exactly by a robot is mind-blowing.
https://en.wikipedia.org/wiki/ITER#Criticism
"The project however was significantly delayed at the design stage as result of purposeful decision to decentralize its design and manufacturing among 35 participating states, which resulted in complexity that was unprecedented but consistent with the initial ITER goals of creating knowledge and expertise rather than merely producing energy."
It also says it can be built much cheaper than the total cost for ITER.
The article doesn’t say it, but I would guess that it also can be built for less money than the money needed to complete ITER.
If so, what’s not obsolete about ITER? Are there useful experiments that can be done with it that one can’t do with a more modern design?
I'd recommend watching the whole thing, I found it quite interesting.
here is the original presentation by Dr Whyte of MIT behind this Sparc project: https://youtu.be/KkpqA8yG9T4?t=1511
he talks about the impact of these newer magnets at around 26min mark.
https://www.psfc.mit.edu/files/psfc/imce/research/topics/spa...
It seems that if we can't make fusion work for SPARC it won't likely work in ITER either since they're both based on the same understanding of the physics. Am I wrong on that point? Is there some reason to think that ITER will succeed even if SPARC does not?
See my other brief comment: https://news.ycombinator.com/item?id=24634894
As far as "why", you can take your pick of:
- ITER's design is older, and maybe could be considered "lower risk" (that it will work at all)
- Sunk cost
- Academic jobs program
- Money has already been allocated to member states, and none are happy to give that up
- Big changes take time
I'm not optimistic on stuff like this, so IMO it's another JWST, but it's not totally crazy to keep working on a plan (for a while) when new avenues of research arise.
https://www.cambridge.org/core/journals/journal-of-plasma-ph...
[1] https://lockheedmartin.com/en-us/products/compact-fusion.htm...
If?
Like, in classical terms, you can get a repulsive force to come out of Newton's law of gravitation if you plug in a negative mass. But that doesn't mean you've designed a hoverboard.
The simple line of reasoning being that if energy becomes 100 times cheaper, humanity will fast find ways to consume 100 times the amount of energy. A high amount of that energy will end up as heat.
The second reason... and you'll find it apparent I'm not a physicist, but reading about fusion research always has me worried. We're basically talking about starting a "controlled" chain reaction at millions of degrees, "like the one on the sun". The sun isn't a nice place, and the sun's fusion happens to be controlled just because it's surrounded by lightyears of vacuum.
-Yeah but we'll have magnetic fields and super coils and stuff. It's totally safe. -Totally safe? -Yes, our calculations say its totally safe. -Your calculations based on current theory? Guess what, theory is a moving target. Just a few years ago you didn't even know if the Higgs particle exists?
Global warming isn't about heat generation. The sun (the free fusions reactor in the sky) sends more heat our way then we could ever hope to produce. It is heat dissipation that is the problem. Greenhouse gasses prevent the sun's heat from dissipating. This is the problem, we will only make it better by stopping greenhouse gas emissions.
Cities Snub Plan to Save Nuclear Power With Mini Reactors:
https://www.bloomberg.com/news/articles/2020-09-28/cities-sn...
Kaysville withdraws from nuclear power project:
Small Modular Reactor Decision Made With Inadequate Information:
https://losalamosreporter.com/2020/09/14/small-modular-react...
ITER and similar projects are abject failures from non-scientific perspectives, they fail to improve on the economic weaknesses of fusion (radiological waste, massive capital costs, scarcity of fuel, proliferation risk), and only deliver on issues that have become irelevant for modern fision, like the risk of a meltdown.
There is zero economic potential for any ITER direct descendant.
While I agree the quantity of waste is low, that doesn't really matter for the general public. We had for decades the technology to put fission waste in deep geological storage, what held it up were political concerns - the same for fast breeders that could burn the waste. So I cannot for the life of me understand how NIMBY-ism, the major cost driver of fission plants (via political challenges, court actions, schedule slips etc.), is allayed, when the plant will regularly ship out tons of hazardous materials through the communities they serve.
As for the fuel cost issue, you cannot use natural Lithium due to low cross section, but blankets made up of tons of enriched Lithium that has a large Li6 content, that are continually circulated and need to be topped off as H3 is bred. No estimate of cost for this feed-stock exists, but it is likely more expensive than natural uranium that can be burnt in a heavy water reactor, for example. (that reactor design has it's own issues with heavy water inventory costs, but this material is most probably easier to produce than enriched Li6, and is not consumed as a fuel)
When you draw the line, the best prospects of ITER derived fusion plants (not existing experiments, mind you, but the theoretical future, practical designs) is at best comparable to existing fusion plants. Why should we waste money on them, if they cannot improve on the current state of the art?
The hard part is getting more energy out than you put in.
The sun does this all the time, basically by having so much mass that hydrogen gets sucked in by gravity to collide with other particles. Keeping hydrogen close enough to smash into each other is hard, the sun is just so big that it can do that.
Hydrogen bombs do this by using other explosives to push hydrogen together. This isn't a good power source.
We can't use gravity to cause hydrogen to collide here on earth (we have no artificial gravity). But we have magnets, so we try to bounce hydrogen particles around super fast in a small space with magnets instead of using gravity.
Now getting more energy out is a bit like starting a fire. You need to apply heat for a while with a lighter before the fuel ignites, then the burning fuel keeps releasing energy.
Same basic idea with fusion. You put in energy to start fusing hydrogen. Once the hydrogen is releasing power, it will cause other hydrogen particles to bounce around super fast and continue fusing, releasing more energy.
The part that hasn't really been done yet is proving that the "fire" can stay lit, and that is what people are trying to do. It's hard for a bunch of reasons, but the theme is "making a tiny sun-like place on earth is challenging". When this article mentions "q" that is what it is referring to. q=2 means for every joule of energy put in you get 2 joules out.
(disclaimer: this is a quick version that omits a lot)
I thought this was impossible due to law of conservation of energy.
Well eventually we get lucky with things like gravity, and water cycles doing the work for us by giving us rivers and we build a dam around it.
But you can never design a process where you can take more than what you put in.
The hard part is getting the reaction to produce more energy than it requires to sustain. Given a breakthrough that solves that problem, fusion would be a really appealing energy source given the abundance of hydrogen.
“ The activation of the reactor’s structural material by intense neutron fluxes is another issue. This strongly depends on what solution for blanket and other structures has been adopted, and its reduction is an important challenge for future fusion experiments.”
Seriously though, the article reads like "Remember SPARC? We're still trying to build it." I wish them luck, but if past experience with fusion can be extrapolated, they will run into some unexpected, crippling problems.
If we could make efficient fusion reactors the size of a truck, the solar system will become our backyard.
https://en.wikipedia.org/wiki/Electrically_powered_spacecraf...
Realistically, if we had good electric propulsion we could just slap a conventional fission reactor in there. We already launch plutonium on many deep-space missions for steady nuclear power. For now chemical propulsion is simply faster and more reliable, electric propulsion is still in the early stages, and there are many other problems to solve in human spaceflight.
Who will pay for the cost overruns?
Just one of the big problems with nuclear is that it is very centralized and takes individual control away from the consumers, who foot the bill through increased taxes and fees, and who could otherwise be using their money to finance options that give them individual control over their energy costs.
Decommissioning costs should be negligible because the reactors won't generate radioactive fission byproducts. The reactor chamber is designed for a 10 year lifespan and easy replacement. The old chamber is slightly radioactive (due to neutron bombardment) for a few decades, which is much less of a problem than the highly radioactive waste from fission plants that has to be stored for thousands of years.
