4 ms·

Yep - we're still nowhere near break-even.

by q1w2 5y ago

DennisP 5y ago
We're not that far off. JET previously achieved Q=0.67, ie. two-thirds as much energy output as input. (The new result has higher output but lower Q.) For a practical reactor we need Q around 30, which might seem far away but tokamak output scales with the square of reactor volume and the fourth power of magnetic field strength. Double the field, 16X the output, and we can generate much more powerful magnetic fields with modern superconductors than we can with JET's copper coils.
- faeyanpiraat 5y ago
  So they just need to build the same thing, but make it gigantic in size? Why is it not yet done?
  - deleted 5y ago
    [deleted]
  - willis936 5y ago
    It is very expensive to do. HTS was known but not practical when ITER was planned, but it's almost done. ITER is almost large enough to be an LTS-based power plant. ITER will still produce a lot of useful science, but there is a now a potential class of mid-scale HTS machines that would help develop plasma models. These iterations seem frustrating and time consuming, but their results are lowering the cost of a hypothetical power plant until one day maybe society will decide they're worth making for power generation.
- andruby 5y ago
  Any source on that Q=30 requirement for practical reactors? I’d assume that anything >1 is theoretically “profitable” and something like 2~5 might already be economically viable.
  - skykooler 5y ago
    Q=1 just means that the plasma is putting out more energy then is put in. However, that doesn't mean you can recover all of that energy; you can't run a heat engine at millions of degrees, so energy generation has to be fairly indirect, which means you need about Q=30 to handle all the various conversion inefficiencies and still come out net positive enough to be practical.
- Aperocky 5y ago
  > For a practical reactor we need Q around 30 Did we figure out how we could harness the energy released? It appears to me that all current research are about maximizing Q without really looking at how the energy will be converted into usable form.
  - DennisP 5y ago
    For D-T fusion, the output is 80% neutrons, so the only option is to let them heat something to run a turbine. You also need the neutrons for breeding the tritium, so you let your breeding blanket heat up and run coolant pipes through that. Commonwealth plans to use molten FLiBe salt as the breeding blanket and first loop of coolant. Aneutronic fusion produces fast-moving charged particles instead of neutrons, so if anyone gets that working, we could extract electricity without a thermal cycle.

Yep - we're still nowhere near break-even.

by q1w2 5y ago

Yep - we're still nowhere near break-even.

We're not that far off. JET previously achieved Q=0.67, ie. two-thirds as much energy output as input. (The new result has higher output but lower Q.) For a practical reactor we need Q around 30, which might seem far away but tokamak output scales with the square of reactor volume and the fourth power of magnetic field strength. Double the field, 16X the output, and we can generate much more powerful magnetic fields with modern superconductors than we can with JET's copper coils.

faeyanpiraat 5y ago
So they just need to build the same thing, but make it gigantic in size? Why is it not yet done?
- deleted 5y ago
  [deleted]
- willis936 5y ago
  It is very expensive to do. HTS was known but not practical when ITER was planned, but it's almost done. ITER is almost large enough to be an LTS-based power plant. ITER will still produce a lot of useful science, but there is a now a potential class of mid-scale HTS machines that would help develop plasma models. These iterations seem frustrating and time consuming, but their results are lowering the cost of a hypothetical power plant until one day maybe society will decide they're worth making for power generation.
andruby 5y ago
Any source on that Q=30 requirement for practical reactors? I’d assume that anything >1 is theoretically “profitable” and something like 2~5 might already be economically viable.
- skykooler 5y ago
  Q=1 just means that the plasma is putting out more energy then is put in. However, that doesn't mean you can recover all of that energy; you can't run a heat engine at millions of degrees, so energy generation has to be fairly indirect, which means you need about Q=30 to handle all the various conversion inefficiencies and still come out net positive enough to be practical.
Aperocky 5y ago
> For a practical reactor we need Q around 30 Did we figure out how we could harness the energy released? It appears to me that all current research are about maximizing Q without really looking at how the energy will be converted into usable form.
- DennisP 5y ago
  For D-T fusion, the output is 80% neutrons, so the only option is to let them heat something to run a turbine. You also need the neutrons for breeding the tritium, so you let your breeding blanket heat up and run coolant pipes through that. Commonwealth plans to use molten FLiBe salt as the breeding blanket and first loop of coolant. Aneutronic fusion produces fast-moving charged particles instead of neutrons, so if anyone gets that working, we could extract electricity without a thermal cycle.