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Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

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Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#151

Post by lazide »

HPsquared wrote: post #133
dotancohen wrote: post #108

Earlier quoted context omitted.

As I understand it - correct me if I'm wrong - one of the consequences of the December 5 experiment is that the engineering uncertainty was brought into the realm of "this now fits the progress of engineering, so we expect to be able to engineer the thing given sufficient capital and time", rather than the previous "we have no idea if we'll ever be able to engineer this thing".

It has always been a matter of building a machine with sufficient performance. That's engineering, by definition.

What kind of machine though is the point.

A bomb? Already done.

A fusion reactor? We’re still light years away from anything of the sort. This is only one tiny tiny step there, and we’ve got miles to go.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#152

Post by DennisP »

albertopv wrote: post #57
moffkalast wrote: post #53

Earlier quoted context omitted.

I've also been quite surprised watching that one, it's completely novel approach to fusion and it may be the best way to mass adoption. If they can make it work that is. What most surprised me about NIF's ignition announcement was that this was even news. I'd assumed for years that most if not all tokamaks and stellerators could already achieve at least some brief fusion, just not to a useful degree. Turns out they'r…

I'm very skeptical about those great announcements, even more when there's an announcement of the announcement. 300MJ in, 3MJ out, I wouldn't call it a breakthrough, maybe a milestone, nothing more.

That ratio is so bad only because they're using really inefficient decades-old lasers. Equivalent modern lasers have forty times better efficiency.

https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#153

Post by arethuza »

denton-scratch wrote: post #146
arethuza wrote: post #99

Earlier quoted context omitted.

"fusion-enhanced fission stage" The primary is fusion boosted fission, the core ("spark-plug") of the secondary is also fusion boosted fission surrounded by dry fusion fuel (lithium deuteride) and then a fissionable tamper. My understanding is that X rays from the primary compress the entire secondary package - which ignites the spark-plug and then the fusion fuel is caught between the incoming tamper and the explodi…

The cited article says: "Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces radioactive fission product fallout." The way I read that, even in a large H-bomb, little of the yield is the direct result of fusion reactions. Rather, the neutrons produced by the fusion reaction dramatically increase the efficiency of the fission reactions, wh…

There is still a considerable about directly from fusion e.g. in the Tsar Bomba the fusion stage produced about 47Mt of the 50Mt total (it had two smaller H-bombs as primaries for the fusion stage). The full design was 100+ Mt so about 50% from the final fission stage seems a rule of thumb, which is also mentioned in this article about "neutron bombs":

https://en.wikipedia.org/wiki/Neutron_bomb

Neutron bombs don't have fissile tampers on the secondary exposing the neutrons from fusion directly rather than using them to fission the tamper.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#154

Post by thereddaikon »

oblio wrote: post #51
Systemic33 wrote: post #50

Earlier quoted context omitted.

With regards to NIF being a military facility, I'd very much think that energy production (cheap, safe, limitless?) is very much a military needs as much as a civilian need. Even if said energy goes further to power laser weapons or other exotic power hungry systems; energy is energy, and something has to produce it.

The internet was a military need from what I remember. The military said something like: "Telephone routing is point to point and inflexible, if the enemy cuts out 1-2 lines of communication, an entire section is completely cut off. We need something better." That something better turned out to be packed switching where you just throw stuff along a network and the network ensures that the packet reaches the destinati…

It started as a way to network air defense bases for AESA radars, NORAD and Nike missiles together across CONUS. Feature creep and increased scope grew it into a general purpose data network that linked not only military sites but also research institutes by the 80's.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#155

Post by rz2k »

zmgsabst wrote: post #114
HPsquared wrote: post #97

Earlier quoted context omitted.

Parent was basically saying it has not been a physics problem for decades, it's already an engineering problem and there is no change there. The physics are known to work and have been demonstrated decades ago in a different engineering context (i.e. weapons).

We can debate the importance, but it’s clear that they’ve made a qualitative leap in their technology the past few years — a “breakthrough”. https://en.wikipedia.org/wiki/National_Ignition_Facility#/me...

And that graph does not include the 2022 experiment with 3.15, which also happened to be the first one with net positive output.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#156

Post by GuB-42 »

mikepurvis wrote: post #116
raverbashing wrote: post #113

Earlier quoted context omitted.

True. My crazy idea would be to use the heat and the pressure of these to pump water uphill. It is of course a crazy idea and you'd have to figure out a way to manage the pressure peak But it would be very interesting

Pumped hydro has been a concept for a while now for grid storage of power; one of the limitations of it is just the rather unique geography required. Most places with adjacent reservoirs and enough vertical separation between them also have cottages, roads, and other infra that make it hard to be constantly draining and filling.

It is not just a concept, it represent the vast majority of grid energy storage today, we are talking about gigawatts.

Hydro is the best, so good in fact that most of the good spots are already taken, because as you said, it requires a very specific geography.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#157

Post by walnutclosefarm »

bawolff wrote: post #39

Everything i have heard about this makes it sound more like a milestone than a breakthrough. I.e. its great it happened and an important step, but its not shocking that we eventually did it. When i hear breakthrough i think of something more unexpected. I.e. figuring out how to solve a problem we had no idea how to solve.

Exactly. If there was a breakthrough at all, it in 2021, when NIF finally reached the point of "burning plasma."

But breakthrough, or milestone, I fear it may all be for naught. The improvements over the last two years are essentially all due to changes in the hohlraum geometry and preparation. All good, if your goal is to get burning plasmas to study. But NIF is orders of magnitude away from anything useful for power production. They have a Q of 1.5, but need something more like 100. They have a cycle time of, maybe, .1 shot/hour, and need something like 10,000/hour. Some real breakthroughs in the lasers (or maybe particle beams instead), coupling, and scale, not fine tuning of hohlraum shape, are needed.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#158

Post by throwawaymaths »

rob74 wrote: post #43

Still unconvinced why this is such a major breakthrough - it may be the first net-positive controlled fusion, but the distinction between controlled and uncontrolled fusion is a bit academic in this case. In uncontrolled fusion ( https://en.wikipedia.org/wiki/Thermonuclear_weapon ), you are using a nuclear fission primary stage to generate enough energy to start the fusion reaction in the secondary stage. In the NIF,…

It's not even close to net positive. It's more energy out than the lasers put in. But the lasers take in WAAAAY more than they put in.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#159

Post by lazide »

mikepurvis wrote: post #116
raverbashing wrote: post #113

Earlier quoted context omitted.

True. My crazy idea would be to use the heat and the pressure of these to pump water uphill. It is of course a crazy idea and you'd have to figure out a way to manage the pressure peak But it would be very interesting

Pumped hydro has been a concept for a while now for grid storage of power; one of the limitations of it is just the rather unique geography required. Most places with adjacent reservoirs and enough vertical separation between them also have cottages, roads, and other infra that make it hard to be constantly draining and filling.

It’s less that (IMO) - cottages and roads are usually not as dense on steep hillsides and the like, though of course they can’t be ignored entirely. The pipes involved are usually not the big issue, and the pumping ops are usually not the big issue either.

The business model for pumped hydro requires relatively low cost to be economic and if it requires building a giant concrete water retention systems on top of large flat topped hills/mesas, near large drops in elevation, with water retention at the bottom of the large drop that is also really really expensive to build and requires specific geology to be economic.

And if something gets messed up, it’s a huge liability [https://en.m.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Powe...], as it can cause very damaging flooding and be expensive to repair/replace.

Worth doing when there is cheap power that can be stored and sold at higher rates later, but construction costs are really a huge part of it.

Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough

#160

Post by throwawaymaths »

tadfisher wrote: post #139
headsoup wrote: post #96

Earlier quoted context omitted.

But isn't the 'net positive', itself only a factor in the very last stage of all of the input energy required for ignition? So they need to factor in all other components before looking at these orders of magnitude being useful?

Yes, but that is still a breakthrough.

No, it's not. If you get to arbitrarily define at what point you count "energy in" (as the NIF people are), you could also define a clever spot for MCF to be net positive.
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