When you consider that they laser they used consumed 300 megajoules from the wall plug, in order to send 1.8 megajoules to the target, the fact that they got 2.5 megajoules out looks puny in comparison. Even newer lasers only have 20% wall plug efficiency according to the press conference.
So the important point here is, there was no net energy gain. They spent 300 megajoules to get 2.5 out. The scientists only talk about the 1.8 megajoules of laser energy sent to the target, not about the 300 megajoules of electricity needed to send 1.8 megajoules to the target.
The NIF is not intended to be a power plant, and inertial containment in general is probably not a great design for producing power.
This is scientific breakthrough. The best point of comparison is probably a fusion bomb, which requires an initial fission detonation to create enough pressure and free neutrons to force a net-positive fusion reaction. But at the NIF they do it using only lasers… incredible.
Mass is energy. Add energy (in any form, such as heat) to a system and you increase its mass. Thus, in the NIF reaction, the mass lost from the pellet is mass imparted on the surrounding environment. Immediately after the fusion reaction, before the energy can dissipate further as heat, etc, the reaction chamber system has the same mass as before the ignition.
There are some nuances regarding the distinction between rest mass vs relativistic mass, but they're not really relevant in this context.
I think what trips people up here is confusing mass with matter. Matter is also subject to mass-energy equivalence, of course, but AFAIU in most common types of nuclear reactions little if any matter, per se, is transformed.
Power plants add energy to an electrical grid by converting external (chemical/nuclear/kinetic) energy into more electricity than they consume. There's no loss of energy/mass overall, but the amount of available electricity goes up. Since the laser would use electricity from the grid, that should be taken into account.
The point is to get some of it from somewhere cheaper/free - mass, or outside air as in heat pumps.
You can't run your laser on mass or air, if you need a coal firing power plant to run your fusion reactor, from which you get less than you consumed from the coal plant...
It's great progress, it's just not as close to viable as it might sound like - more breakthroughs needed.
I have yet to find someone saying it sounds like fusion power reactors are right around the corner, but I have found lots of people shadowboxing these people and attacking the scientists for misleading press releases.
Seems like an overcorrection to something I haven't even seen anyone here say.
I think to a lot of the technically minded, but non nuclear physicists here, it initially sounded like less (paid for/electricity) energy was used than was put out. That's extremely exciting, and the actual news is still fantastic, it's just that 'actually, we needed to pay for over 100x more energy than we counted as the "input" energy [and it's possible to do 10x but not 100x better than that]' is quite a massive caveat on a 3:2 or whatever yield.
I'm not saying they've claimed anything wrong or deliberately misleading, it's just a misunderstanding/misalignment and possibly made worse by the PR teams in the middle.
In other words, I don't think it's an angry 'well actually' type correction so much as it is disappointment - it initially sounded even greater.
Not necessarily, it depends on how the reaction scales. If the reaction does not scale linearly (as is claimed) you don’t necessarily have to get more efficient, you just have to up the power until the output curve has increased past the input scaling. How big that is is determined by the efficiency of the input device itself, but it isn’t a question of if it will ever happen.
Yes, sure, it's just still a breakthrough or so (or at least work, I don't know how within grasp it is) away from what one may have (as did I) initially assumed.
Tangentially, it does seem fairly intuitive that it should be non-linear in that 'jump start' as it were: a fire can be grown arbitrarily large having started from a single match (or flint or whatever).
You are correct: this is the important point. Until this is actually powering homes at scale and competitive price- which, clearly from these numbers is a fantasy- developments in this field should be dismissed. It's embarrassing to see HN so excited about what's really quite the failure.
As was pointed out in other comments, their lasers and electrical equipment were not efficient as it was not necessary to get the scientific knowledge.
In the press conference they mentioned that modern lasers have "20% wall plug efficiency". That means fusion has to generate 5x more energy than this experiment did, for you to get more energy out than you put in.
So the important point here is, there was no net energy gain. They spent 300 megajoules to get 2.5 out. The scientists only talk about the 1.8 megajoules of laser energy sent to the target, not about the 300 megajoules of electricity needed to send 1.8 megajoules to the target.