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Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
141–150 of 289 posts
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#142Everything 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.
> Everything i have heard about this makes it sound more like a milestone than a breakthrough.
I guess milestone assume you already know you will reach it.
I also think breakthrough as a lot of meaning and people would assume there is a few years before a real application.
In a sense it's probably a breakthrough within the scientific ring rather than from the people perspective.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#143Everything 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.
Breakthrough:
1. a sudden advance especially in knowledge or technique
2. an act or instance of moving through or beyond an obstacle
Milestone:
1. an action or event marking a significant change or stage in development.
I'm failing to see why labeling it one or the other even matters.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#144Everything 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.
I feel like HN is being especially pedantic and jaded about this specifically and I don't really get why. Scientifically this is absolutely a breakthrough, just like the detection of the Higgs boson was despite them already having expected it or just like LIGO's detections of gravitational waves were despite that being entirely what it was built for or just as JWST's detections of galaxies much older than those seen…
Responding in a pedantic/jaded manner is one way to assert a form of intellectual dominance. For this audience I feel like that sort of dominance is unsurprising.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#145Earlier quoted context omitted.
You greatly underestimate the order of magnitude difference of produced energy in these two examples. You can't contain a bomb's hydrogen fusion reaction in a chamber for the simple reason that you need a nuclear fission warhead just to ignite it. So if you want to produce useful, controlled energy outside of killing things, the lasers are your only shot for inertial confinement fusion. Yes they still get damaged, bu…
> You can't contain a bomb's hydrogen fusion reaction in a chamber You certainly can, if you use a large enough chamber. Pacer was exactly this. You just have to accept high proliferation risk.
Pacer took thinking about nuclear fuels in a lot of new and interesting directions. For the use case of interest, they really wanted to maximize the fusion yield fraction, minimize the radioactive products, and minimize the total yield. Had it ever been allowed to proceed to a commercial scale, these would have been very tight, very challenging, technical constraints.
If you relax one of those requirements, then it becomes instantly clear that limitless cheap energy is possible. For a somewhat absurd example, imagine that we build Pacer plants in space instead of on Earth. There's no longer any size constraint on the blast chamber. You can go to triple-stage (like Tzar Bomba) or more designs, at which point the fusion fraction gets extremely close to 100%, and the cost per unit energy becomes somewhat hard to fathom. But on Earth, it still would have been expensive.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#146Earlier quoted context omitted.
My understanding is that what you're referring to as a "fusion" stage is really a fusion-enhanced fission stage. All the stages of normal "H-bombs" are fission stages, using a small fusion core to generate a flood of neutrons, which results in the fission fuel combusting more completely. Pure fission bombs tend to disintegrate long before enough neutrons have been generated to achieve complete combustion. The inclusi…
"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, which on their own would not produce enough neutrons to fission more than a small part of the fissile material before the device disintegrates.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#147Earlier quoted context omitted.
It's better to focus on standardised production lines for small fission reactors currently if your goal is to produce energy for the power grid right now, but that's not what cutting-edge research or science is about. Whoever launched the first firework probably didn't see how people could walk on the moon either. Science is rarely a linear path. It's also rarely "I have this problem so I solved it this way." That's…
Nuclear fusion is stuck into an "early MASER/LASER phase". Laser was cool, but nobody knew what to do with it. These days we're at the stage where we're thinking: what can't we do with it??? But for about 3 decades (before CDs, basically) laser was a pop science laughing stock, more or less. And fusion is much harder plus has been talked about and hyped for at least as long.
> laser was a pop science laughing stock, more or less.
Yup:
In college English classes I took, they wanted the students to write term papers. Ah, sure, they expected some review of some case of belles lettres, maybe Medieval French romantic poetry!!!!
Instead, in one case, I picked the transistor and another, the laser.
For the laser, I had no idea of the applications. For the transistor, all I knew was, what it seemed was all Bell Labs had in mind -- replace their usage of vacuum tubes, that is, analog amplifiers and not digital, Nyquist sampling, etc., even though Shannon was at Bell Labs, etc.
The idea of a few billion transistors on a sheet of silicon about the size of a large postage stamp, 16 cores, 64 bit addressing, 4.0 GHz clock, etc. -- beyond all expectation or belief. The graphics processors -- still less belief! Lasers sending trillions of bits per second per hair-thin glass fiber -- not even ready for science fiction!
No doubt I picked the transistor and the laser out of media hype. So at least some people in the media expected something from those two. Here the media was not wrong, and in the long term the hype was way below the reality.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#148It’s practical proof that in a single pulse we can get more energy out than we put in. We do spend a shit ton of energy setting up the pulse, and we haven’t figure out how to get that energy out and make electrons move, but it’s been proven possible. The “breakthrough” is the proof that it’s possible. Everything else is now optimisation and engineering, and needs mostly time, sweat and money.
That was already proven in weapons tests in the 1950s (e.g. https://en.m.wikipedia.org/wiki/Castle_Bravo ). The hard part is always building the machine to produce net energy gain, which is still 2+ orders of magnitude away.
The reason it looks that far away is that NIF uses lasers from the 1990s with only 0.5% efficiency. Equivalent modern lasers are over 20% efficient, which would put overall net energy gain only one order of magnitude away.
https://physicstoday.scitation.org/do/10.1063/pt.6.2.2021102...
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#149Earlier 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).
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".
Not really because we have known for almost a century that nuclear fusion is a real thing that can release energy.
The problem is the engineering of how to actually do it in a useful way. They have made some progress towards that but it's still extremely unlikely that laser based fusion will ever work as a power source because: a) they're still two orders of magnitude from break-even from the input side, and b) they don't have a practical way of capturing the energy that's produced at all as far as I understand it.
None of that has changed.
Re: Nuclear physicist explains why fusion ignition is hailed as a major breakthrough
#150Real Engineering published a video about Helion Energy company. I don't have the tools to filter out commercial BS, still it seems to me to be most promising effort. The idea to get electricity directly from magnetic fields instead of boiling water is very intriguing.
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…
Tokamaks do fuse a lot of atoms, just not yet enough to get more energy out than they put in. The record so far is energy output at 70% of the energy input.
The output scales with the square of plasma volume and fourth power of magnetic field strength, which is why net power is expected from ITER (which is huge) and SPARC (which uses new superconductors for especially powerful magnetic fields).