But even if you have a working stellarator that's a very long way from an economically viable energy source. You've still got to a) figure out how to cheaply convert the released energy into electricity (and the baseline way of doing that in D-T fusion is...a steam turbine), and b) figure out materials that can survive the radiation bombardment for a sufficiently long time.
In sunny places (and I fully acknowledge that's not all of the world) it's still going to be hard to beat sticking bits of special glass out in a field and connecting wires to it.
But we should sure as heck keep tinkering away at it!
“PPPL researchers say their simpler machine demonstrates a way to build stellarators far more cheaply and quickly, allowing researchers to easily test new concepts for future fusion power plants.”
This quote reminded of the SpaceX’s approach to engineering and why they have leapfrogged past Boeing. Instead of spending 10-20 years and billions into a single design, SpaceX iterates.
People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.
Roughly speaking energy can be mechanical, for particles or radiative, for photons. The first one is proportional to the temperature (the famous NRT) and the second is proportional to the fourth power of the temperature. The constant of proportionality is very small, and at regular temperatures we generally don't think of it that much. But at millions of degrees Kelvin, it starts to dominate all considerations.
The heat always moves form hot to cold. In the case of particles the heat flow is proportional to the difference in temperature, and in the case of radiation with the difference in temperature to the power 4. But heat also travels from particles to photons and vice-versa. It doesn't matter how.
The problem with fusion is now this. Suppose that you have a super-duper device, let's call it brompillator. It brings an amount of deuterium-tritium mix at the required temperature, let's say 10 million Kelvin. Now that volume of plasma is surrounded by cold stuff. You can imagine that you have some mirrors, or magnetic fields, or some magic stuff, but the cold hard stuff is that that plasma will want to radiate to the exterior and the flow of heat would be proportional to the surface area times the fourth power of the difference in temperature. Since for all practical purposes the outer temperature is zero, we are talking about the fourth power of 10 million Kelvin. Now that constant of porportionality is very small, it is called the Stefan-Boltzman constant and has a value of about 10^7 W m^-2 K^-4. Let's say the surface area is 1 square meter. So the heat loss happens at a rate of 10^-7 times (10^7)^4 = 10^21 Watts. That is 10^12 GigaWatts. One GW is the output of a decent sized nuclear power plant.
Of course, you can try to shield that plasma, but that shield has to be 99.99999....9% effective, where the number of 9s needs to be about 15 or so.
That is the immensity of the challenge that nobody is willing to tell you about.
How was this overcome in the case of the thermonuclear bomb? People imagine that once you have a fission bomb, you just put some deuterium-tritium mix next to it, and voila, you have a fusion bomb. No. The world's greatest minds have worked at this issue for about 5 years. The solution was something like this: if you first compress significantly the volume of fusion fuel, then the heat losses are much smaller (remember they are proportional to the area, and that's proportional to the square of the radius). They will still be tremendous, but you don't even aim to keep the reaction going for a long time. The duration of the fusion reaction in a thermonuclear bomb is still classified information, but public sources put it at the order of 1 microsecond. The heat losses are still tremendous, but for a short moment the heat gains from the fusion reaction are even greater, so ignition is achieved.
In the NIF experiment that achieved more than breakeven 2 years ago, the fusion lasted less than 10 nanoseconds [1].
If someone thinks the brompillator will achieve fusion and that will run for years, or even hours, or seconds, they don't understand the fundamental problem. Unfortunately, nobody is willing to ask hard questions about this, not even Sabine Hossenfelder.
> People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.
I'm not sure that's even true, because if you manage to crack that, you still have the problem that your sustainable reaction is pumping out most of its energy in the form of very fast neutrons, which are (a) very hard to harvest energy from and (b) extremely bad for people and materials if you don't. You could have a self-sustaining reaction that you can't actually use!
Cool.
But even if you have a working stellarator that's a very long way from an economically viable energy source. You've still got to a) figure out how to cheaply convert the released energy into electricity (and the baseline way of doing that in D-T fusion is...a steam turbine), and b) figure out materials that can survive the radiation bombardment for a sufficiently long time.
In sunny places (and I fully acknowledge that's not all of the world) it's still going to be hard to beat sticking bits of special glass out in a field and connecting wires to it.
But we should sure as heck keep tinkering away at it!
“PPPL researchers say their simpler machine demonstrates a way to build stellarators far more cheaply and quickly, allowing researchers to easily test new concepts for future fusion power plants.”
This quote reminded of the SpaceX’s approach to engineering and why they have leapfrogged past Boeing. Instead of spending 10-20 years and billions into a single design, SpaceX iterates.
I admittedly don't know much about fusion reactors, but I do love that the thing which you create a star within is called a "Stellarator".
People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.
Roughly speaking energy can be mechanical, for particles or radiative, for photons. The first one is proportional to the temperature (the famous NRT) and the second is proportional to the fourth power of the temperature. The constant of proportionality is very small, and at regular temperatures we generally don't think of it that much. But at millions of degrees Kelvin, it starts to dominate all considerations.
The heat always moves form hot to cold. In the case of particles the heat flow is proportional to the difference in temperature, and in the case of radiation with the difference in temperature to the power 4. But heat also travels from particles to photons and vice-versa. It doesn't matter how.
The problem with fusion is now this. Suppose that you have a super-duper device, let's call it brompillator. It brings an amount of deuterium-tritium mix at the required temperature, let's say 10 million Kelvin. Now that volume of plasma is surrounded by cold stuff. You can imagine that you have some mirrors, or magnetic fields, or some magic stuff, but the cold hard stuff is that that plasma will want to radiate to the exterior and the flow of heat would be proportional to the surface area times the fourth power of the difference in temperature. Since for all practical purposes the outer temperature is zero, we are talking about the fourth power of 10 million Kelvin. Now that constant of porportionality is very small, it is called the Stefan-Boltzman constant and has a value of about 10^7 W m^-2 K^-4. Let's say the surface area is 1 square meter. So the heat loss happens at a rate of 10^-7 times (10^7)^4 = 10^21 Watts. That is 10^12 GigaWatts. One GW is the output of a decent sized nuclear power plant.
Of course, you can try to shield that plasma, but that shield has to be 99.99999....9% effective, where the number of 9s needs to be about 15 or so.
That is the immensity of the challenge that nobody is willing to tell you about.
How was this overcome in the case of the thermonuclear bomb? People imagine that once you have a fission bomb, you just put some deuterium-tritium mix next to it, and voila, you have a fusion bomb. No. The world's greatest minds have worked at this issue for about 5 years. The solution was something like this: if you first compress significantly the volume of fusion fuel, then the heat losses are much smaller (remember they are proportional to the area, and that's proportional to the square of the radius). They will still be tremendous, but you don't even aim to keep the reaction going for a long time. The duration of the fusion reaction in a thermonuclear bomb is still classified information, but public sources put it at the order of 1 microsecond. The heat losses are still tremendous, but for a short moment the heat gains from the fusion reaction are even greater, so ignition is achieved.
In the NIF experiment that achieved more than breakeven 2 years ago, the fusion lasted less than 10 nanoseconds [1].
If someone thinks the brompillator will achieve fusion and that will run for years, or even hours, or seconds, they don't understand the fundamental problem. Unfortunately, nobody is willing to ask hard questions about this, not even Sabine Hossenfelder.
[1] https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.132.065...
> People don't understand the fundamental problem of fusion. It's a problem of energy loss. Of enormous energy losses.
I'm not sure that's even true, because if you manage to crack that, you still have the problem that your sustainable reaction is pumping out most of its energy in the form of very fast neutrons, which are (a) very hard to harvest energy from and (b) extremely bad for people and materials if you don't. You could have a self-sustaining reaction that you can't actually use!
Aneutronic fusion has been previously mentioned, specifically HB11.
https://en.m.wikipedia.org/wiki/Aneutronic_fusion