Comment by cpleppert | Hacker News Reader

Comment by cpleppert | Hacker News Reader

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The studies done ten years ago suggested that the best case scenario was about thirty years( one demonstration phase of 15 years and another development phase of 15 years). This was premised on the INF demonstrating ignition using indirect drive soon after operation. There was also an expectation that the INF would transistion to researching other, possibly more promising technologies like direct drive ignition.

Instead, it took over ten years to simply demonstrate ignition using the indirect drive method which was chosen specifically because it was seen as being more technologically viable. This "big breakthrough" was supposed to happen immediately after operation!

No one knows whether commercialization of inertial confinement fusion is even possible. Laser efficiency is just one small part; the work to produce and develop a system to reliably shoot hohlraum targets is an order of magnitude harder than shooting a static target in ideal conditions.

Compared to these engineering challenges demonstrating ignition is the easy part.

> Compared to these engineering challenges demonstrating ignition is the easy part.

Again, let's discuss what those challenges are. A bunch of talk about how hard it might be with no detail on what makes it hard isn't really informative to anyone.

> the work to produce and develop a system to reliably shoot hohlraum targets is an order of magnitude harder than shooting a static target in ideal conditions.

Please see my note #2 about EUV light sources and similar technology. My understanding is the timing and precision requirements are much higher here, but on the other hand the "rate" of fire would be necessarily much lower making something perhaps feasible.

From the presentation and panel today, one of the key drivers seems to be the purity of the capsules and the ability to correct for asymmetries in the implosion caused by them. The results announced today where not because of the purity of the capsule, but instead because of the correct prediction of the asymmetries in the implosion and the ability to counter that with modifications to the laser strength and timing.

The NIF isn't (as others have noted) necessarily focused on bettering these two factors.

What I'd like to understand is what are the major tradeoffs in ICF vs MCF that would drive pursuing the difficult engineering problems of one vs another.

>> My understanding is the timing and precision requirements are much higher here, but on the other hand the "rate" of fire would be necessarily much lower making something perhaps feasible.

Leaving aside rate of fire and energy efficiency you have to develop a system that can shoot the hohlraum into the reactor chamber such that the lasers can be steered onto the target with enough precision to produce ignition. I believe 100um is the miniumum for the type of targets used in the INF. This all needs to occur within the reaction chamber. Besides the thermal loads you also have residual gases within the chamber. These conditions somehow have to be accounted for or you won't get ignition.

The work they did in demonstrating ignition is great but the engineering challenges for commericalization are immense. EUV lithography took decades to develop and perfect.

>>What I'd like to understand is what are the major tradeoffs in ICF vs MCF that would drive pursuing the difficult engineering problems of one vs another.

MCF is generally seen as a much easier approach because you avoid the problems with repeatedly generating fusion conditions and you remain in the ballpark of what can be solved with better technology. You can come up with a tokamak that you can be absolutely sure will probably work with enough money; but I'm not sure the same is true with ICF.

https://www-pub.iaea.org/MTCD/Publications/PDF/TE_1704_web.p...

and

https://www-pub.iaea.org/MTCD/Publications/PDF/TE-1911_web.p...

actually layout some of the challenges. they are not as you state and there ARE tradeoffs between MCF and ICF. Most experts agree MCF is closer to realization, but that's a very well educated guess not a surity.

https://scientific-publications.ukaea.uk/wp-content/uploads/...

lays out some of the differences and tradeoffs

Even more interesting is to look at approaches which might combine the two: https://medium.com/fusion-energy-league/the-fundamental-para...

from a brief look, both publications prominently feature discussions about target survival within the reaction vessel.

Of course there are tradeoffs between MCF and ICF. They involve different sets of challenges to achieve viable fusion energy production. Neither has been demonstrated to have commercial viability to date. The consensus view that MCF is more viable is rooted in the much better understanding of how to comercialize a MCF reactor.

The issue is the NIF isn't trying to study power generation, their mission is determining the health of our weapons stockpile. This experiment is a lab where they can test different casings and different hydrogen mixtures and this probably feeds real-world data into their supercomputer models. All this to determine how a 50 year old h-bomb would operate now. They also can find out how they can improve them without being able to go to Nevada and detonate one underground.

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