Laser fusion facility heads back to drawing board
nature.com
nature.com
It's good to remind people about weapons research interests. It's less good to completely dismiss the interests concerning energy production, or basic scientific research. They don't go away just “omgz military funding!”
So this is weapons research and basic physics research caked in the language of power generation.
Edit: Wow, looks like they have improved considerably
https://www.laserfocusworld.com/lasers-sources/article/14186...
1: source: a seminar I attended last year
Note that I'm not saying that it isn't an interesting or useful scientific experiment - it's just not a promising power source.
where in the world have you seen anyone that is planning to try to use inertial confinement fusion for energy production?
ie an American nuclear weapons laboratory was doing it
The kid in me says this was/is the coolest option.
Regardless of outcome, I'm glad we were able to test the idea.
Sometimes it's just nice to have something to compare your simulation results to.
http://nuclearweaponarchive.org/Nwfaq/Nfaq4-2.html
In principle there isn't really a limit to how small you can make it, just with decreasing efficiency and (with traditional implosive designs) a higher detinator-to-fissile material ratio. Things like laser implosion remove this design constraint, however, and would let you consider things like millimeter-sized pellets.
I suspect the soda-can sized charges you recall were conventional explosives for the small, non-nuke prototype they tried out.
It really matters that nuclear weapons go bang when you want, but not when you don't.
An example of why one needs to care about such things in stockpile stewardship -- plutonium's own radioactivity means that helium is effectively being born within the crystal lattice, causing damage, distortion, and swelling. It isn't a guarantee that a bomb that worked 50 years ago will work today.
Would you prefer to know? Or go off a hunch?
Intuitively, simply not building a bomb seems sufficient to prevent any accidental detonations.
But I'm of course no expert.
The cores of these weapons are unlike any environment on Earth. Maintaining the stockpile without running simulations is negligent.
US ICBM silo map https://qph.fs.quoracdn.net/main-qimg-45b10c7543ed5219a77858...
> okay with nuclear weapons not working when someone wants them to
Obviously s/he hoped the weapons not to explode when fired.
GP wished for a (moderately) likely failure: failure to detonate. GP obviously didn't wish for unlikely failures, like spontaneous detonation, ICBMs all flying to Washington DC, etc.
There is the case of the Goldsboro B52 in 1961 crash in which three bombs could fell out of a plane and could have gone off but didn’t :
https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash
Edit: of the four bombs one was only very close to going off, and a lot of lessons were learnt from this event 60 years ago.
Of course this "safety" has absolutely nothing to do with what the public naturally assumes is meant, which is typically that it won't go bang when you don't push the button, or leak, or be hijacked, or fall out of a plane carrying it. The DoE considers none of those its responsibility under the law.
One might guess that going bang when the button is not pressed would be extremely unlikely. But when a B-52 crew made a booboo and dropped a pair of hydrogen bombs in a farmer's field, investigation showed that all of the processes that would have set them off completed; just not all on the same bomb.
Thanks.
In the longer term, who could have known then or even cared how to maintain the transition to a no-test regime? What the treaties' drafters might have been thinking is now moot. Those people are long gone, it's your problem now.
No, we got ones designed to work in nuclear submarines [1]. Civil reactors don’t make weapons-grade anything.
[1] https://www.sciencedirect.com/science/article/pii/0301421584...
Fusion would necessarily be a lot more expensive than fission. But fission is itself not competitive, and gets less so with each passing day. So, the longer it takes before fusion is actually, technically possible, the less value there is in it.
Plus, they have much more parasitic power loss (running the superconducting magnets and cooling them to keep them superconducting, plus keeping the vaccum in the reactor chamber all require massive power, and they scale with the size of the reactor). You need some extra power to produce hydrogen through electrolysis as well, though that is probably lower. Note that making the magnets stronger to keep the vessel lower (so that everything is more easily cooled) will not get you much more, since we are already nearing the limits of material resistance for the supporting steel structures in the presence of the extreme magnetic forces trying to crush the reactor together - especially given embrittlement.
Not to mention, you will always need at least a small fission reactor to breed some tritium, since the fusion reactor will always have some losses.
Finally, the much much higher neutron flux that fusion expels (32x or more neutrons, and much higher energy per neutron as well) means that everything close to the reactor becomes brittle in 2-4 years. This means that things like support beams and the magnets themselves need to be constantly replaced. Even worse, they become medium level radioactive waste, which needs to be stored.
These are all intrinsic limitations of fusion that fission reactors just don't have.
So if something is complex we shouldn't or can't build it? OK. I hope you aren't an engineer.
Energy is needed to perform electrolysis to create hydrogen. What about the energy needed to mine uranium? I think it might require quite a lot of effort, particularly once supplies get harder to reach and extract.
The parts get radioactive and need maintenance and storage. The radioactivity is much more short term than fission. Fission fuel needs stored away from all life for 100,000 years. It will be a miracle if we manage to achieve that.
I think small scale modular fission is a good option, but your arguements against fusion aren't good.
We were discussing why fusion plants are necessarily more expensive than fission plants - not whether they can (or even should) in principle be built.
> Energy is needed to perform electrolysis to create hydrogen. What about the energy needed to mine uranium? I think it might require quite a lot of effort, particularly once supplies get harder to reach and extract.
I listed many other energy costs - including some uranium to breed tritium.
> The radioactivity is much more short term than fission.
Sure, but that still means decades for tritium and centuries for the neutron-bombarded materials - more than enough to make it as big of a problem in our lifetimes per kg, just with many more kg of waste from fusion.
Fusion's going to have to go with advanced fuels to have a chance. For that and various related reasons, I consider Helion the least dubious of the fusion efforts.
All that could make that tolerable is that a 2MW package just produces a lot less of everything than a 2GW (or 20GW) monstrosity.
The idea for future designs is to breed Tritium in the blanket surrounding the vessel. This obviates the need for external sources.
> everything close to the reactor becomes brittle in 2-4 years
I'm no expert on solid state physics, but that seems a little short? JET is more than ten times as old, and as we speak it's in its second run of D-T experiments.
> These are all intrinsic limitations of fusion that fission reactors just don't have
To be clear these are limitations of a specific kinds of fusion reaction and/or reactor design, primarily that of Deuterium-Tritium in a solid-walled tokamak. This may be a nitpick as it's currently far and away the most promising for energy production, and the alternatives are much further from any sort of workable prototype, but I have heard of them undergoing active research: tri-alpha (aneutronic reaction, meaning no activation or embrittlement of reactor components), liquid metal for the walls and divertor (in effect, continuously replacing neutron-bombarded material), etc.
The problem is that, at best, you can create as much Tritium in the blanket as you put in as fuel (since every emitted neutron is coming from a Tritium atom). So, to be self-sustaining, every emitted neutron would have to be caught by the blanket to form a Tritium atom, and you would have to be able to extract every single atom of Tritium from the blanket back as usable fuel - and this is assuming 100% of the tritium you put in actually fuses, which is unlikely given how hard tritium is to contain (essentially every material is porous to Tritium). So, since there are losses at each of these levels, you need to inject new tritium into the cycle.
Also note that this entire blanket design is entirely theoretical at the moment: no fusion experiment has ever attempted to do anything with the fusion products other then measure the amount of heat generated.
> I'm no expert on solid state physics, but that seems a little short? JET is more than ten times as old, and as we speak it's in its second run of D-T experiments.
I'm no expert either, but these are the estimates I have read everywhere. JET is not in any way representative, as they do a handful of fusion events per year, for a few seconds - while a DEMO plant would be running continuously, 24/7. The amount of irradiation is incomparable.
> To be clear these are limitations of a specific kinds of fusion reaction and/or reactor design, primarily that of Deuterium-Tritium in a solid-walled tokamak.
These are all limitations of the only fusion electrical power-producing technology that is anywhere close to realistic.
All other fusion reactions require much, much higher temperatures and pressures to ignite, so they are many more decades away (regardless of what some snake oil start-ups are claiming).
All other magnetic confinement D-T fusion reactions have the same problems I discussed.
And inertial-confinement fusion approaches are much less likely to ever be economical given the huge costs of the actual fuel.
CFS for example uses beryllium in a FLiBe salt. General Fusion and Zap Energy use lead.
It is conceivable that fusion could be made to work in outer solar system spaceship propulsion, where the constraints are very different. It will never generate commercial power on Earth. The billionaires pumping cash into fusion startups are being taken for a ride. They can afford it.
By contrast, Bill Gates got US taxpayers to pony up fully half of the scratch on his pet SMR project, without giving up any ownership. So, we are the ones taken for a ride, instead.
And it has a thousand years of history.
ITER : https://www.iter.org
Take a small cylinder of pyrolytic graphite (it is diamagnetic, repelled by magnets) milled to be in the ideal axis and polystyrene layered in it. Then shoot it into a somewhat large ring of powerful magnets that have a trough in them to such a degree that it can trap the cylinder as it accelerates around the loop. The cylinder is propelled by successive shots of laser bursts that are not powerful enough to ablate (but close). One of the electromagnets can be quickly deactivated to allow for the cylinder to escape. Then it travels for a safe distance into very large lead target. Fusion could proceed if the speed is fast enough as the fuel is inertially kept together and friction should raise it’s temperature. If it produces neutrons, they will be absorbed by the lead. You can just collect the heat.
Edit. I think the lead target would be a no go. It would be no different than a bullet hitting a soft block of lead. Better would be a block of silicon carbide with some kind of borehole made of tungsten metal with fuel packed at the end of it. So the rice sized cylinder of nuclear fuel shoots right into the borehole and before the material can squeeze itself out, it has to overcome the enormous inertia keeping it going in one direction. Might be better though if the target itself was fuel. And it would be much easier to fuse lithium dueuteride than hydrogen and carbon.
I seem to recall a recent story on HN about something similar. So it isn't really a new idea. Perhaps making it run a circular course is different or that it doesn't use ablation for propulsion, it uses light pressure. I think the project was in the UK.
https://en.wikipedia.org/wiki/United_States_Department_of_En...
Who are in charge of nukes.
Sounds like what goes on at the focal point of the laser requires nanometers of accuracy in design, position and orientation. Perhaps part of the problem is that we abandoned physical engineering and manufacture in the west in favour of outsourcing it all?
And no, this has nothing to do with outsourcing. There are no outside experts in this field.
The engineering and fabrication side is just that precise.
In this facility they indirectly drive the target with the lasers. So instead of uniformly heating a sphere with lasers, they heat the inside of both ends of a gold tube (holhraum). This causes a bath of x-rays to uniformly heat a glass sphere that contains your fusion fuel. That glass sphere needs to be suspended in the center of the tube, but any inconsistency can cause huge knock on effects on yield. So they hold it between two <1um thick sheets of plastic. But if you can imagine, part of the sphere will be in contact with this plastic and part will not. That adds some reduction in how uniformly you heat the glass sphere.
But let's back up, how do they even make this perfect sphere of glass that is hollow? And how big is it? Well the sphere can be anywhere from 420um to 800+ um in diameter. From what I recall, the only way to make these is to drop small amounts of glass from a tall tower into water. Then do metrology on it, and toss away >90% of them right off the bat. Another issue is that some of the fuel leaks out of this hollow glass sphere over time. So timing from when you load the target from storage to actually firing the lasers can have non-zero effects on the yield.
Long story short. It's really hard to convey how close to the edge of precision ICF research is to the edge of micro fabrication. Now add the fact that some of these targets need to survive going from atmosphere to ultrahigh vacuum, and not break or tear... Remember that 1um thick plastic?
So yeah, no one is outsourcing this stuff. It's not being negatively effected by brain drain or lack of funding. It's just absurdly difficult to build to the designed tolerances the physics demands.
Fun fact, this is why a lot of physicists got behind the ITER project. The bigger you make something, the less important the minor fluctuations are to the overall yield. :D