The NIF's reactor model doesn't need plasma stability, right? The article points out they're intending to use a similar principle to an internal combustion engine: put in a tiny amount of fuel, blow it up, capture the energy, repeat.
No, it very much does. Laser fusion relies on creation of a spherically symmetric shock wave, which in turn momentarily creates huge pressure and temperature in the center of a pellet, thus igniting the fusion reaction. Any asymmetry (caused either by miscalibration, setup design, pellet flaw or even simple thermal noise) gets amplified by plasma instability effects and results in huge energy losses. The wiki article [0] briefly covers some of such effects.
How does the level of precision here compare to the precision needed to design LIGO?
I remember reading the precision requirements for LIGO and then reading about the efforts needed to achieve that precision and it seemed like magic. e.g. IIRC LIGO has a precision of PORTIONS of a wavelength of light at the end of arms that are kilometers long.
Is the precision for plasma stability that much higher?
(I understand that these are very different systems so asking more from an overall "what can we currently achieve" perspective).
raziel below has an excellent response. To add to their comment, I'll say the difference here is the precision needed for LIGO is with a more or less static equipment you can tweak. This requires plasma stability during a dynamic, very chaotic system. You do tweak the static parts, the laser and related apparatus, the target and what holds it in place, various diagnostics, but the actual process itself is a very dynamic explosion that it itself is hard to understand or predict fully a priori, and certainly not to the degree we understand gravitational waves at the point of detection at LIGO.
I mean, as I said elsewhere, the reason we don't have fusion for any fusion experiment is plasma instabilities, at this point that fact is like saying the reason ice cream melts in the sun is because it's hot. It's a fact of all fusion experiments. The only system we know of that can achieve net gain fusion we know of is gravitational confinement which uses a big mass to contain the hot plasma, also known as a star.
It's kind of hard to compare, especially since I don't know what you mean by precision: the metrics on both projects are very different.
LIGO is all about minimizing losses as the laser light bounces back and forth the two mirrors. The losses here arise from the stack of materials that the mirrors are made out of, which are multilayers of different oxides plus/minus Si or Ge, I forget. So one metric of course is the surface roughness of the material, but then there are also energetic defects called two-level systems in which atoms can absorb a little bit of light to tunnel into another location and thus contribute to the losses by having absorbed laser energy. There's coefficients of thermal expansion, stresses, that all have to be taken into account and tested as you layer all these dissimilar materials that may behave ok at room temperature but not at cryogenic ones for instance.
So LIGO is a game of minimizing losses, because you're after detecting the faintest of signals: a gravitational wave. Their game is all about increasing the signal to noise ratio.
NIF is a monster of energy. There's the whole steering of an enormous laser pulse which is the addition of 192 beams that have to converge into a tiny area the size of a pencil eraser. There's the containment of all this energy into a steel capsule that looks like something out of a sci-fi piece. There's the manufacture of the 2 mm diameter capsule that starts as plastic but is then coated with diamond, beryllium or more plastic and that leads to inherent asymmetries because it's not easy to coat a non-planar geometry. Already this coating assymmetry is very likely to lead to the hydrodynamic instabilities (https://en.wikipedia.org/wiki/Rayleigh%E2%80%93Taylor_instab...) that are obstructing the path forward. The hole with which you fill up the capsule with DT is still a problem, but they try to sweep it under the rug. The surface roughness of the capsule is a problem, contaminants in the diamond or plastic is a problem, a few atomic percent is enough to significantly dampen the amount of X-ray absorption/transmission. Control of the material's density is another one. The work that goes on all of this is tricky because you can solve all of these and control them very well on a planar geometry, but the moment you want to take this onto a sphere it doesn't work as well, we cannot suspend something in Earth's gravity without using a string, which then introduces an asymmetry. So the best we use is we roll the sphere around, and it's not very good for the tolerances that the scientists think we need.
And NIF has a history of escalation. We are currently shooting 1.6 - 1.8 MJ, but the scientists' simulations had predicted kJ range shots in the beginning, and the estimate has continued to climb. You see it in the article itself that they're hoping to get funding to go to 3 MJ. But there are some studies (Halite-Centurion IIRC) from the 50s that showed you needed like 100 MJ to get inertial confinement fusion on a capsule, and I think we've been happily disregarding those results, because, well, politics, job-protection etc. It's a complicated story, shrouded in a lot of secrecy, so I'm glad to read that the NNSA is reviewing it.
So, precision in LIGO, I don't think translates to precision in NIF. LIGO feels more like golf, NIF feels, like some beasts fighting it out. Very different set of challenges, very different resource pools they can draw from (I would argue that NIF can draw more money but less talent because of security clearance requirements restricting employees to be US citizens).
"Capture the energy". They haven't even looked at that step.
Laser fusion is about the least promising, most impractical possible approach to building a power reactor, even if you do manage to get ignition. Since at least the early 1980s, the word on the street has been that the talk about power is just a politically palatable wrapper for the weapons application. And let's just say that some of the people I heard that from, back in the 1980s, were in enough of a position to know that they probably shouldn't have said anything to some random kid like me.
Not to say that there aren't a few benighted souls working on it who've managed to convince themselves it's a power source, but notice that nobody but Livermore has ever bothered to put much into inertial confinement... and Livermore is a weapons lab?
That's fair enough from a political perspective (after all, as they say in the article, >70% of NIF shots are going to [nuclear] stockpile stewardship now) -- but just to give NIF a bit of credit on the "basic science" front, it has turned out to be quite good for studying the properties of matter under extreme compression more generally.
Some mineral physicists I know have used this to write some cool papers about the properties of natural materials at conditions replicating those expected in the cores of giant exoplanets [1-3], for example.
Funny tidbit, there is a huge scramble and fight over these few shot days from different research groups across the US that can actually be used for non-nuke and non-fusion physics, they're called "Discovery Science" shots and there are only like a dozen or so each year. For example, last year 18 shot days were devoted to DS.[0]
