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I'm probably asking something dumb, but for the little I think I know, I assume that the bigger the electromagnetism field, the bigger the energetic requirement.

I'm assuming that the square cube law would also apply for electromagnetic fields and thus, fusion reactors.

And so, wouldn't be more interesting to try and achieve nuclear fusion if the Tokamak space was tiny, but longer, like a really thin ring?

Of course, I'm no expert and if it was the case, they would already be doing that, but nevertheless, I still want to know about it.

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    $\begingroup$ the heat loss is proportional to surface but "useful" energy is proportional to volume; the larger the installation the smaller is the relative loss. $\endgroup$
    – hyportnex
    May 19 at 15:16

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And so, wouldn't be more interesting to try and achieve nuclear fusion if the Tokamak space was tiny, but longer, like a really thin ring?

Oh, if only we could!

The problem is this: the plasma can be modelled as little balls bouncing off each other, which once in a long while fuse.

So with all of these random collisions going on, the particles are undergoing a random walk process. Eventually they will reach the outside wall of the reactor and then it's game over - they immediately cool and lose all the energy you spent all that effort putting into them.

Random walks are purely geometric. The farther you have to walk, the longer it takes. So by scaling up the reactor, the ions remain in the plasma longer, which means you keep the energy in the plasma longer.

The whole idea of the Lawson criterion is to balance energy being lost with energy being created by the reactions. If you make the reactor smaller, more ions leave, and you need to run everything else harder to make up for it.

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