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Nuclear fusion reaction releases almost twice the energy put in
(www.newscientist.com)
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this post was submitted on 06 Feb 2024
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15% return is still net energy positive isn't it? Or is that not 15% above the input?
From another article: "In an experiment on 5 December, the lab’s National Ignition Facility (NIF) fusion reactor generated a power output of 3.15 megajoules from a laser power output of 2.05 megajoules – a gain of around 150 per cent. However, this is far outweighed by the roughly 300 megajoules drawn from the electrical grid to power the lasers in the first place."
https://www.newscientist.com/article/2350965-nuclear-fusion-researchers-have-achieved-historic-energy-milestone/
That's worded strangely (powering the lasers takes both 300 and 2.05 megajoules?) but oof
Powering the laser takes 300 MJ but the actual laser power (the energy in the light) is only 2.05 MJ. The rest of the energy is lost to heat and other inefficiencies. If the laser could be created with 100% efficiency then the input energy would also be 2.05 MJ.
Energy can be measured as occurring in different physical phenomena. There is energy in sound waves/packets, energy in light waves/packets, energy in matter, etc.
The 300 MJ number refers to the electrical energy in the form of electromagnetic fields carried specifically through solid conductors via electron movement along the conductors.
The 2.05 MJ number refers to the radiative energy in the form of electromagnetic fields sent specifically through free space/a vacuum (I presume; I didn't read the article, so maybe the laser medium was a vacuum or something else) via photons/waves. No electrons, aside from those in the lasers that create the photons in the first place.
So there is a conversion from electric to radiative energy here.
Start Edit:
And as another commenter said, in this conversion there are losses because materials aren't perfect.
:End Edit
If the 3 MJ radiant energy from the nuclear material was then converted back into electric energy via steam processes, we'd get a comparable number compared to the 300 one.
This is also why you see nuclear/CSP plants quoted in MWt and MWe: there is a conversion that takes place from thermal energy (vibrations of atoms/compounds) into electric energy.
I can't read the full article (paywalled for me) but it references the National Ignition Facility so the way it goes is super lasers blast a tiny hydrogen thing and that creates a tiny bit of fusion that releases the energy. The energy of the laser blast is what's being called the input and the fusion energy released the output. What is misleading is that a greater amount of energy was used create the laser blast than the laser blast itself outputs. If you consider the energy that went into creating the laser blast the input (rather than the laser blast itself), then it's usually not a net positive energy release.
What other energy are you referring to? Like warming up the laser?
Remember when incandescent light bulbs were the norm? They worked by sending full line voltage through a tiny tungsten wire that would get so hot that it glows, making some light, but 95% of the energy that gets consumed is frittered away as heat? The high-power lasers needed to make fusion happen are a lot like that.
I believe all this article is saying is that 15% more energy than what came out of the lasers as useful laser light was liberated in the reaction.This completely ignores the energy it took to power those massively inefficient lasers.
I think it also ignores the fact that the 15% more energy liberated wasn't actually, like, harnessed by a generator. I believe (and I may be wrong) this was testing only the reaction itself. Actually hooking that up to a turbine and using it to create energy that is cost competitive with contemporary sources is still a completely unsolved problem.
pixelscript@lemmy.ml got it, but basically lasers are pretty inefficient. The article I just found said (in a different run of this facility) they put 400MJ into the laser to get 2.5MJ out of it. So that makes the whole firing system what, 0.6% efficient? Your fusion reaction would have to give more than 400MJ to truly be in the positive for this particular setup/method, but again this facility is a research one and not meant to generate power - there isn't even a way to harness/collect it here.
Oh so the laser's generating mostly heat and a little coherent radiation, and they're only referring to the coherent radiation as the "energy input" to the process.
Hmm. Kinda sketch.
Especially because that's not trivial. If we have no way of obtaining laser light other than that process, and the laser is the only way to feed the fusion reactor, then that's 100% on the balance books of this process.
Thx. Rip tho