Why fusion, over everything else?

[u/Sun_In_A_Bottle]

$15.2 billion in private investment over the past 5 years!

For an industry that is projected to need 1 million workers by 2040, how is the global private workforce roughly ONLY 4,000?!

[u/imtoooldforreddit]

I'm a big technology guy, but I'm skeptical it will be cheap anytime soon even if they get it to work

Looking at something like iter, it still needs to scale up to be able to make any kind of meaningful power, and scaling it up would be insanely expensive.

I understand economies of scale, but even still, that reactor is insanely big and expensive already.

I totally believe it can work, I'm not convinced it will ever be cheaper than solar panels per kwhr, given how quickly they are getting cheaper

[u/Cruisin4Fusion → u/imtoooldforreddit]

ITER is not commercially relevant and never will be so it is a moot point of comparison. That design was created in the late 80s and was never planned to be cost effective. No modern fusion device will be as large or as expensive as ITER.

[u/imtoooldforreddit → u/Cruisin4Fusion]

That's actually the thing though, a commercial tokamak reactor would probably want to be even bigger. The fusion energy generation is proportional to the volume while the confinement energy is proportional to the surface area that has to maintain the magnetic confinement. So basically, the bigger, the more efficient. Iter already is pretty low on its Q factor, so getting smaller wouldn't really work.

[u/Sad_Dimension423 → u/imtoooldforreddit]

The argument you gave there is actually why commercial tokamaks would want to be as small as possible.

The cost of the reactor scales with volume, while the power it can produce (when limited by what the first wall can withstand) would scale only as the surface area. So, the cost per W is proportional to radius of the reactor.

[u/imtoooldforreddit → u/Sad_Dimension423]

No, that's the opposite, the cost is connected to the containment (surface area) while the energy generation is limited by the volume where the reactions are happening.

Bigger is more efficient.

There will be a limit because the generated energy can only be collected on the surface area, which might be what's tripping you up, but that's not the limiting factor of the design at these scales. Pumping the heat away is fairly easy compared to the plasma stability and containment issues

[u/Sad_Dimension423 → u/imtoooldforreddit]

In general, the cost of an object is (at least) proportional to its mass, and a large part of the mass of a fusion reactor will scale with its volume. In particular, the mass of the structure needed to resist JxB forces is proportional to the stored magnetic energy, which is proportional to volume x B².

If, as you said, the mass scaled only with surface area, then scale would be neutral; the cost per W would depend only weakly with size. But any component that scales with volume will tip the balance toward smaller reactors.

Notice this is fundamentally unlike fission reactors, where the surface area for heat transfer scales right along with volume. Fission reactors do show economies of scale, if not enormous ones.