3 ms·

That depends on what you mean by "close" and "viable", imo. We know that tokamaks will work if we build them big enough. So it's essentially a matter of dumping

That depends on what you mean by "close" and "viable", imo. We know that tokamaks will work if we build them big enough. So it's essentially a matter of dumping sufficient billions into large construction projects, i.e. ITER and DEMO. There are of course some open engineering questions, but afaik, they mostly concern economic viability, e.g. durability of materials involved.

apendleton 5y ago
Big enough, or high-enough field strength. For a given power density, I think required radius scales inversely with the fourth power of the field strength, or something along those lines. ITER was designed when niobium-tin superconductors where the best available, which will limit their field strength to around 13T, but newer HTS magnets should allow some of the upstarts to achieve comparable power densities with much smaller reactors, which should help with at least the economic concerns (durability is still a big concern, though).
- ncmncm 5y ago
  That just transfers the problem from plasma density to reactor-wall area. "Durability is still a big concern" translates to "but it doesn't help, in the end."
  - DennisP 5y ago
    CFS has an interesting design for that, too. MIT demonstrated joints in REBCO tape that don't introduce significant resistance. By putting these joints in the coils, CFS has a design that will let them open up the reactor and replace the inner wall annually. The inner wall will be 3D-printed, and immersed in a pool of molten salt that functions as coolant and breeding blanket.
hutzlibu 5y ago
"We know that tokamaks will work if we build them big enough. " I think we know that they will work, once they actually work. And the main important question remains, if they will also work economically.
- ncmncm 5y ago
  We already know we won't get that.
simiones 5y ago
We definitely don't "know" that yet. There is for example no experiment that has ever actually tried to extract any energy from the fusion reaction - it's assumed that the lithium blanket idea will work, but this remains more or less purely theoretical. It's sound science, but we're nowhere near sound engineering there.

apendleton 5y ago

Big enough, or high-enough field strength. For a given power density, I think required radius scales inversely with the fourth power of the field strength, or something along those lines. ITER was designed when niobium-tin superconductors where the best available, which will limit their field strength to around 13T, but newer HTS magnets should allow some of the upstarts to achieve comparable power densities with much smaller reactors, which should help with at least the economic concerns (durability is still a big concern, though).

ncmncm 5y ago
That just transfers the problem from plasma density to reactor-wall area. "Durability is still a big concern" translates to "but it doesn't help, in the end."
- DennisP 5y ago
  CFS has an interesting design for that, too. MIT demonstrated joints in REBCO tape that don't introduce significant resistance. By putting these joints in the coils, CFS has a design that will let them open up the reactor and replace the inner wall annually. The inner wall will be 3D-printed, and immersed in a pool of molten salt that functions as coolant and breeding blanket.

hutzlibu 5y ago

"We know that tokamaks will work if we build them big enough. " I think we know that they will work, once they actually work. And the main important question remains, if they will also work economically.

ncmncm 5y ago
We already know we won't get that.

simiones 5y ago

We definitely don't "know" that yet. There is for example no experiment that has ever actually tried to extract any energy from the fusion reaction - it's assumed that the lithium blanket idea will work, but this remains more or less purely theoretical. It's sound science, but we're nowhere near sound engineering there.