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> That's because the Sun is very different from an Earthbound fusion reactor. It runs at a very different temperature and density, using very different reaction

> That's because the Sun is very different from an Earthbound fusion reactor. It runs at a very different temperature and density, using very different reactions. The analogy you are trying to draw is invalid. No, the analogy he draws is the correct one: the sun actually works. "Earthbound" controlled nuclear fusion doesn't in any meaningful way relating to energy production. There's no reason physics should cooperate with us and make it possible; "wouldn't it be nice" wishful thinking isn't good enough, and the results thus far are all complete and total crap. It isn't that we haven't spent enough: we simply don't know how to do this -there is no reason to believe it is possible. All the results from inertial confinement, tokomaks, fusors, whatever indicates we really don't know WTF we're doing. His other concerns are legit as well. If you can do controlled nuclear fusion, you have a really, really scary weapon.

pdonis 7y ago
> the analogy he draws is the correct one: the sun actually works Under, as I said, very different conditions from those which Earthbound fusion reactors are attempting. The only meaningful similarity between the two is that both are fusion reactions. You certainly cannot use numbers for the Sun to make any valid estimates about Earthbound fusion reactors, as the poster I responded to was attempting to do. > Earthbound" controlled nuclear fusion doesn't in any meaningful way relating to energy production. It hasn't yet, but that doesn't mean it never will. If it does, it certainly will not be by reproducing conditions similar to those that produce fusion in the Sun. And if your criticisms of fusion power turn out to be valid and it never works, then everything the poster I responded to said is irrelevant anyway, since he was assuming fusion power would work. > If you can do controlled nuclear fusion, you have a really, really scary weapon. No, you don't, because, as I said, only a very small amount of fuel is in the reactor at any given time--enough for a few seconds' worth of energy production. That equates to the energy equivalent of a few tons of TNT, not a few megatons. And since the entire system is designed to remove that amount of energy at that rate, concerns about even that few tons of TNT energy equivalent "exploding" are invalid--that amount of fuel undergoing complete fusion and liberating all that energy is what the reactor is designed for, not an abnormal condition. And, as I said, all you need to do to stop energy production is stop injecting fuel, and the reactor shuts down. Again, a fusion reactor is very different from a fusion bomb.
- scottlocklin 7y ago
  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.

pdonis 7y ago

> the analogy he draws is the correct one: the sun actually works Under, as I said, very different conditions from those which Earthbound fusion reactors are attempting. The only meaningful similarity between the two is that both are fusion reactions. You certainly cannot use numbers for the Sun to make any valid estimates about Earthbound fusion reactors, as the poster I responded to was attempting to do. > Earthbound" controlled nuclear fusion doesn't in any meaningful way relating to energy production. It hasn't yet, but that doesn't mean it never will. If it does, it certainly will not be by reproducing conditions similar to those that produce fusion in the Sun. And if your criticisms of fusion power turn out to be valid and it never works, then everything the poster I responded to said is irrelevant anyway, since he was assuming fusion power would work. > If you can do controlled nuclear fusion, you have a really, really scary weapon. No, you don't, because, as I said, only a very small amount of fuel is in the reactor at any given time--enough for a few seconds' worth of energy production. That equates to the energy equivalent of a few tons of TNT, not a few megatons. And since the entire system is designed to remove that amount of energy at that rate, concerns about even that few tons of TNT energy equivalent "exploding" are invalid--that amount of fuel undergoing complete fusion and liberating all that energy is what the reactor is designed for, not an abnormal condition. And, as I said, all you need to do to stop energy production is stop injecting fuel, and the reactor shuts down. Again, a fusion reactor is very different from a fusion bomb.

scottlocklin 7y ago
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.