Just curious as to why a Mobius strip type arrangement is better than a toroid? Is it anything to do with the turbulence in the plasma flow being easier to control?
Draw a torus and then draw rectangular "bands" across it, they will represent the containment magnets.
Due to pure geometry, the area closer to the center will have a smaller distance between bars. This means that the magnetic field will be stronger near the center.
This in turn means that particles will separate (depending on charge) and drift to the sides. It seriously interferes with the containment.
You can fix that by changing the torus into something resembling "8", so that particles move to one side when they fly through the upper part, but then they'll move back as they fly through the lower part.
Of course, you can't just do that in 2D because the part in the middle of "8" will have no magnetic field. You need something without self-intersections. You can try to move one side up and another down. But that doesn't quite work either because you will get another set of preferred directions.
So instead you go with the gentle twisting, resulting in the Möbius-looking shape.
That explains why folding is important, as for the mobius, I oversimplified a bit. The Wendelstein has 5 folds, making it a mobius, but I think I read about one in Spain that had only 4 folds. That would mean the mobius isn't imperitive, but I'm sure there is a good reason for it.
Really a stellerator doesn't need 'folding' at all, they can be as simple as a twisted torroid. I didn't want to go into excruciating detail though, the more in detail I go the more likely I am to say something that is wrong lol.
Edit: I looked it up, the one in spain is called "TJ-II"
That effect works both ways too, where a single wire with a digital signal will spew out radio waves, 2 wires with opposing signal cancel each other out and emit no em waves.
The effect with the stellarator is more like stirring a pot.
With mobius strip you regularly flip between inside and outside, so the plasma particles get more even force applied.