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It all looks very impressive, but why all the funky curves? I thought the idea is to create a magnetic field to contain a plasma. Could that not be done with a torus of circular cross-section? Instead we see a very complex undulating torus, what's the reason for that?

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A simple toroidal magnet creates a complicated field, while this complicated magnet creates a much simpler and more benign field.

AFAIK, in Tokamaks you need to permanently increase the plasma current to keep it stable, which puts an upper bound on the time you can sustain the plasma (you can't increase the current forever). In a Stellarator, by contrast, you can keep the current constant, and thus have plasma durations measured in hours instead of minutes.

When you use a true doughnut stuff drifts toward the outside of the doughnut. You have to up the current constantly to keep it from drifting toward the outside of the doughnut.

If you make a doughnut twizzler it doesn't happen.

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