5 ms·

It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. How can we possibly know what we don't know

by eloff 5y ago

It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. How can we possibly know what we don't know yet. Not about how fusion works in theory, but about the limits of the economics of fusion reactors at any point in the future. What I'm saying is it's too soon to say what's possible with fusion and what isn't. We don't even have a break even reactor yet. We can even say for certain that we ever will.

ansible 5y ago
> It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Let's talk about the core of the Sun, where p-p fusion takes place. Remember, I said at the top: no new physics. The core of the Sun is hot, like really, really hot. How hot? 15 million Kelvin. So no solid material ... made of atoms ... can be anywhere close by because it would vaporize. You can talk about active cooling or whatever, and that's not going to help. But let's assume we have some magical material that can deal with that temperature, and keep going. We're going to skip the pressure that really hot plasma is under, and assume we have terrifically awesome magnetic confinement that can handle that. We don't actually, but let's move on. The other problem with 15 million K is that all that energy wants to radiate away. Yes, you want to absorb some of that radiation (hard gamma, by the way, very nasty) as part of the energy generation process, but if you let the plasma cool off, the reaction rate drops. "Cool" in this context is relative, at 7 million K, the reaction rate is very close to zero. The last problem we will talk about today is volume. The above conditions get us a fusion power density of... 276 watts / cubic meter. To have a fusion plant that generates 1GW of power, we'd need to contain a cube 153 meters on a side of 15 million Kelvin plasma. Oh, wait, that assumes the magnetic containment and everything else requires zero power to run. So we'll have to go bigger, much bigger. Are you starting to understand the scale of the problem... trying to design a proton - proton fusion reactor? I am not the arrogant one, I'm just listening to the fusion scientists who have been studying how all this works. > We don't even have a break even reactor yet. We can even say for certain that we ever will. And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We have achieved fusion, just to be clear. We can reach the temperatures and pressures to see some reactions. Assuming civilization does not collapse (climate change, war, etc) we will be able to engineer a fusion reactor that is some kind of practical. But it won't be proton-proton.
- ansible 5y ago
  Edit: Actually, the material issues mentioned above probably won't be an issue, as long as the confinement is good. You still have the issue of keeping the plasma hot enough for long enough. But the scaling issue doesn't go away unless you go with even higher temperatures and pressures.
- eloff 5y ago
  > I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Doesn't sound like an arrogant person to me... FYI I understand how magnetic confinement fusion works at a high-level, as a non-scientist. There's a lot of assumptions you're making here. First that we need hydrogen-hydrogen fusion. Many current reactor designs use deuterium and tritium (nasty stuff tritium.) It doesn't have to be plain hydrogen, it just has to be elements common enough that we won't run out (or that we can breed using neutrons - that gamma radiation you talk about - from the fusion reactor.) Some designs are more exotic with fuel using isotopes of helium, lithium, boron. Second many current reactor designs use a plasma temperature well above 15M K. I've heard of 100M K and that's not an upper limit. But you're also making assumptions about the volume of a reactor - we don't even know if magnetic confinement fusion will end up being the best design, but if we assume it does - then stronger magnetic fields really decrease the volume required. In fact development of stronger magnets based on high-temperature superconductors may be the biggest breakthrough in fusion research in the last decade - see https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusion-energy-0908 https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusio... > And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We don't have a break-even reactor yet by the way - we have achieved fusion for short periods of time and by putting in far more energy than could be produced. That milestone is probably still at least a decade away. My point again is that we don't know enough to be able to say what's possible and what isn't. History is littered with people arrogant enough to say what we can never achieve and humans keep surprising. Sometimes even things that seem impossible - like detecting planets around other stars when the physics of optics is very clear that an optical telescope could never directly image a planet in another solar system. That was wrong on two fronts, one it doesn't account for gravitational lensing, and two it didn't account that we might cheat and detect planets indirectly. And so the arrogant people were wrong again. Don't make that mistake.

by eloff 5y ago

ansible 5y ago

> It doesn't surprise me. Your arrogance does though, I didn't expect you to double down on an unreasonable position. I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Let's talk about the core of the Sun, where p-p fusion takes place. Remember, I said at the top: no new physics. The core of the Sun is hot, like really, really hot. How hot? 15 million Kelvin. So no solid material ... made of atoms ... can be anywhere close by because it would vaporize. You can talk about active cooling or whatever, and that's not going to help. But let's assume we have some magical material that can deal with that temperature, and keep going. We're going to skip the pressure that really hot plasma is under, and assume we have terrifically awesome magnetic confinement that can handle that. We don't actually, but let's move on. The other problem with 15 million K is that all that energy wants to radiate away. Yes, you want to absorb some of that radiation (hard gamma, by the way, very nasty) as part of the energy generation process, but if you let the plasma cool off, the reaction rate drops. "Cool" in this context is relative, at 7 million K, the reaction rate is very close to zero. The last problem we will talk about today is volume. The above conditions get us a fusion power density of... 276 watts / cubic meter. To have a fusion plant that generates 1GW of power, we'd need to contain a cube 153 meters on a side of 15 million Kelvin plasma. Oh, wait, that assumes the magnetic containment and everything else requires zero power to run. So we'll have to go bigger, much bigger. Are you starting to understand the scale of the problem... trying to design a proton - proton fusion reactor? I am not the arrogant one, I'm just listening to the fusion scientists who have been studying how all this works. > We don't even have a break even reactor yet. We can even say for certain that we ever will. And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We have achieved fusion, just to be clear. We can reach the temperatures and pressures to see some reactions. Assuming civilization does not collapse (climate change, war, etc) we will be able to engineer a fusion reactor that is some kind of practical. But it won't be proton-proton.

ansible 5y ago
Edit: Actually, the material issues mentioned above probably won't be an issue, as long as the confinement is good. You still have the issue of keeping the plasma hot enough for long enough. But the scaling issue doesn't go away unless you go with even higher temperatures and pressures.
eloff 5y ago
> I'd give your criticism some consideration if I thought you had even the slightest knowledge of what we're talking about. Doesn't sound like an arrogant person to me... FYI I understand how magnetic confinement fusion works at a high-level, as a non-scientist. There's a lot of assumptions you're making here. First that we need hydrogen-hydrogen fusion. Many current reactor designs use deuterium and tritium (nasty stuff tritium.) It doesn't have to be plain hydrogen, it just has to be elements common enough that we won't run out (or that we can breed using neutrons - that gamma radiation you talk about - from the fusion reactor.) Some designs are more exotic with fuel using isotopes of helium, lithium, boron. Second many current reactor designs use a plasma temperature well above 15M K. I've heard of 100M K and that's not an upper limit. But you're also making assumptions about the volume of a reactor - we don't even know if magnetic confinement fusion will end up being the best design, but if we assume it does - then stronger magnetic fields really decrease the volume required. In fact development of stronger magnets based on high-temperature superconductors may be the biggest breakthrough in fusion research in the last decade - see https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusion-energy-0908 https://news.mit.edu/2021/MIT-CFS-major-advance-toward-fusio... > And here you are expressing doubt that we'll achieve even the easiest kind of fusion reactor. We don't have a break-even reactor yet by the way - we have achieved fusion for short periods of time and by putting in far more energy than could be produced. That milestone is probably still at least a decade away. My point again is that we don't know enough to be able to say what's possible and what isn't. History is littered with people arrogant enough to say what we can never achieve and humans keep surprising. Sometimes even things that seem impossible - like detecting planets around other stars when the physics of optics is very clear that an optical telescope could never directly image a planet in another solar system. That was wrong on two fronts, one it doesn't account for gravitational lensing, and two it didn't account that we might cheat and detect planets indirectly. And so the arrogant people were wrong again. Don't make that mistake.