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Yes, "earthbound" fusion reactors are attempting very different conditions from the sun: that's what I said. The sun is the only reason anyone thinks a sustaine

Yes, "earthbound" fusion reactors are attempting very different conditions from the sun: that's what I said. The sun is the only reason anyone thinks a sustained, controlled fusion reaction is possible: there are no other examples, and the idea that we can do arbitrary (and high) energy densities of sustainable controlled fusion is wishful thinking. All the results thus far are that we don't know how to do this. Nature may prevent it completely. If we do figure out how to do this, of course the possibility of a controlled fusion reactor can be used as an absurdly powerful weapon. You've basically invented something that can make gigawatts of energy appear in a small volume. Sure, a power-generating fusion reactor won't make as big a mess as a fission reactor if there is a fault. That's not the point. If you know how to do this, you can design a system where you can open a hole in one end and point it at things you don't like. And people most certainly will do this if they can. Making the non-proliferation aspects of such a postulated technology absurd. Imagine you could build a NIF type device that actually was sustainable, and you could fit into a truck. Just the neutron flux from the thing would be absurdly murderous, and even using NIF figures (~200MJ), being able to direct the energy of some fraction of a ton of TNT worth of energy at things you don't like, fueled by a tiny amount of hydrogen seems pretty dangerous to me.

pdonis 7y ago
> The sun is the only reason anyone thinks a sustained, controlled fusion reaction is possible No, it isn't. We think it's possible because we have extensive experimental data on fusion reactions from Earthbound experiments. From those experiments we know a wide range of possible conditions that can produce sustained, controlled fusion. The conditions inside the Sun are only a very narrow part of that range. > You've basically invented something that can make gigawatts of energy appear in a small volume. You do realize that any power plant that is making gigawatts of energy has the same amount of fuel energy content inside it as a fusion reactor, right? A coal plant that is making a gigawatt of energy has a ton or so of TNT's worth of fuel energy inside it at any given time, just like a fusion reactor. There is no difference between them in terms of weapon potential. It's true that the amount of fusion fuel needed to make a ton or so of TNT's worth of energy occupies a much smaller volume than the amount of coal or oil or natural gas needed to make that amount of energy, but so what? It's the energy content that matters, not the volume. > Imagine you could build a NIF type device that actually was sustainable, and you could fit into a truck. That means you're building a laser capable of short pulses of gigawatts of power that can fit into a truck. If you can build that, you don't need to include a pellet of fusion fuel with it to make it a weapon. Also, nobody is talking about building gigawatt fusion reactors that can fit into trucks. They're large facilities, just like other power plants. > being able to direct the energy of some fraction of a ton of TNT worth of energy at things you don't like We already have weapons that can do this, and are much cheaper than building a fusion reactor with a hole in the side of it would be. They're called missiles.
- scottlocklin 7y ago
  >No, it isn't. We think it's possible because we have extensive experimental data on fusion reactions from Earthbound experiments. From those experiments we know a wide range of possible conditions that can produce sustained, controlled fusion. There is zero evidence sustained, controlled, above break-even fusion works at the types of energy densities people talk about for power plants. None; keine, zero, zilch: there is arguably as much evidence for this as the existence of ghosts or leprechauns. The models don't work! I ain't saying we shouldn't try, but there are by now reasonable arguments to be made that it's a big waste of time and money better spent on something boring that we know will work, like thorium. To make another technological analogy from nature: if the earth's gravitational potential well were larger, we wouldn't have been able to achieve orbit using chemical rockets. The specific impulse of fuels which exist in the periodic table of the elements would have been insufficient to achieve this. For example: https://arxiv.org/abs/1804.04727 https://arxiv.org/abs/1804.04727 -similarly, the properties of plasmas may make it impossible to achieve controlled, above break-even nuclear fusion in a conveniently small and dense volume. There is at present no evidence that it can be achieved. They've been working on it for 65 or 70 years now depending on how you count things, you'd think there would be some positive indications by now beyond optimistic press releases. As for your wishful thinking that a controlled nuclear fusion technology couldn't be used as a weapon, well, there you go again with that wishful thinking. Controlled fusion is a non-proliferation nightmare. Should this actually come to pass and become routine enough to be a meaningful part of the power grid, it will be a hell of a lot easier to build a fusion howitzer than an ICBM with H bomb at the business end of it. I mean, you're a nuclear physicist, man!
  - pdonis 7y ago
    > There is zero evidence sustained, controlled, above break-even fusion works at the types of energy densities people talk about for power plants. This is just another way of saying we haven't gotten it to work yet. That's true, we haven't. The same could have been said about controlled fission in 1941. > there are by now reasonable arguments to be made that it's a big waste of time and money better spent on something boring that we know will work, like thorium. I agree there are reasonable arguments to be made about this. But comparing controlled fusion to ghosts and leprechauns is not one of them. > it will be a hell of a lot easier to build a fusion howitzer I have no idea where you're getting this from. Again, I really don't think you've grasped the implications of the fact that the energy content of the fuel inside a reactor producing, say, a gigawatt of power, is the same whether the reactor is fueled by coal, oil, natural gas, or fusion. So a "fusion howitzer" based on a fusion reactor would have no more explosive power than a chemical explosive howitzer (which is not based on a coal, oil, or natural gas plant anyway, it's a very different thing). Nuclear fission is a unique case here because of the historical accident of fission power developing in such a way that multiple years' worth of fuel, containing orders of magnitude more stored energy than was being burned at any given time, was all inside the reactor core at once, instead of the reactor having fuel continually injected just in time to be burned, like every other kind of reactor. All of the downsides of fission--the possibility of meltdown, decay heat removal, huge spent fuel pools containing lots of long-lived radioisotopes, even an accident like Chernobyl--are due to this unique attribute. Newer designs like pebble bed reactors have shown that this is not a necessary attribute of fission power. But it won't be an attribute of fusion power at all.

pdonis 7y ago

> The sun is the only reason anyone thinks a sustained, controlled fusion reaction is possible No, it isn't. We think it's possible because we have extensive experimental data on fusion reactions from Earthbound experiments. From those experiments we know a wide range of possible conditions that can produce sustained, controlled fusion. The conditions inside the Sun are only a very narrow part of that range. > You've basically invented something that can make gigawatts of energy appear in a small volume. You do realize that any power plant that is making gigawatts of energy has the same amount of fuel energy content inside it as a fusion reactor, right? A coal plant that is making a gigawatt of energy has a ton or so of TNT's worth of fuel energy inside it at any given time, just like a fusion reactor. There is no difference between them in terms of weapon potential. It's true that the amount of fusion fuel needed to make a ton or so of TNT's worth of energy occupies a much smaller volume than the amount of coal or oil or natural gas needed to make that amount of energy, but so what? It's the energy content that matters, not the volume. > Imagine you could build a NIF type device that actually was sustainable, and you could fit into a truck. That means you're building a laser capable of short pulses of gigawatts of power that can fit into a truck. If you can build that, you don't need to include a pellet of fusion fuel with it to make it a weapon. Also, nobody is talking about building gigawatt fusion reactors that can fit into trucks. They're large facilities, just like other power plants. > being able to direct the energy of some fraction of a ton of TNT worth of energy at things you don't like We already have weapons that can do this, and are much cheaper than building a fusion reactor with a hole in the side of it would be. They're called missiles.

scottlocklin 7y ago
>No, it isn't. We think it's possible because we have extensive experimental data on fusion reactions from Earthbound experiments. From those experiments we know a wide range of possible conditions that can produce sustained, controlled fusion. There is zero evidence sustained, controlled, above break-even fusion works at the types of energy densities people talk about for power plants. None; keine, zero, zilch: there is arguably as much evidence for this as the existence of ghosts or leprechauns. The models don't work! I ain't saying we shouldn't try, but there are by now reasonable arguments to be made that it's a big waste of time and money better spent on something boring that we know will work, like thorium. To make another technological analogy from nature: if the earth's gravitational potential well were larger, we wouldn't have been able to achieve orbit using chemical rockets. The specific impulse of fuels which exist in the periodic table of the elements would have been insufficient to achieve this. For example: https://arxiv.org/abs/1804.04727 https://arxiv.org/abs/1804.04727 -similarly, the properties of plasmas may make it impossible to achieve controlled, above break-even nuclear fusion in a conveniently small and dense volume. There is at present no evidence that it can be achieved. They've been working on it for 65 or 70 years now depending on how you count things, you'd think there would be some positive indications by now beyond optimistic press releases. As for your wishful thinking that a controlled nuclear fusion technology couldn't be used as a weapon, well, there you go again with that wishful thinking. Controlled fusion is a non-proliferation nightmare. Should this actually come to pass and become routine enough to be a meaningful part of the power grid, it will be a hell of a lot easier to build a fusion howitzer than an ICBM with H bomb at the business end of it. I mean, you're a nuclear physicist, man!
- pdonis 7y ago
  > There is zero evidence sustained, controlled, above break-even fusion works at the types of energy densities people talk about for power plants. This is just another way of saying we haven't gotten it to work yet. That's true, we haven't. The same could have been said about controlled fission in 1941. > there are by now reasonable arguments to be made that it's a big waste of time and money better spent on something boring that we know will work, like thorium. I agree there are reasonable arguments to be made about this. But comparing controlled fusion to ghosts and leprechauns is not one of them. > it will be a hell of a lot easier to build a fusion howitzer I have no idea where you're getting this from. Again, I really don't think you've grasped the implications of the fact that the energy content of the fuel inside a reactor producing, say, a gigawatt of power, is the same whether the reactor is fueled by coal, oil, natural gas, or fusion. So a "fusion howitzer" based on a fusion reactor would have no more explosive power than a chemical explosive howitzer (which is not based on a coal, oil, or natural gas plant anyway, it's a very different thing). Nuclear fission is a unique case here because of the historical accident of fission power developing in such a way that multiple years' worth of fuel, containing orders of magnitude more stored energy than was being burned at any given time, was all inside the reactor core at once, instead of the reactor having fuel continually injected just in time to be burned, like every other kind of reactor. All of the downsides of fission--the possibility of meltdown, decay heat removal, huge spent fuel pools containing lots of long-lived radioisotopes, even an accident like Chernobyl--are due to this unique attribute. Newer designs like pebble bed reactors have shown that this is not a necessary attribute of fission power. But it won't be an attribute of fusion power at all.