Very interesting interview about very interesting topic.
One minor complaint: answer to the second question seems to have missed/ignored the question? I assume the true answer lies in the fact that the technical realization of the stellarator are even more complex than that of a tokamak and there is more global experience with tokamaks.
I can give this a shot. There is a sort of simpler explanation of what happens in a stellarator, or at least, why the shape is so weird:
When a plasma is confined in a torus, it is spinning (naturally). However, this creates an effective centrifuge, which means that the hottest atoms -- which are also the "lightest" -- will move towards the outside of the ring, and ultimately will escape confinement. This cools the plasma.
The stellarator solution is basically to turn the torus into a Möbius strip, so that ions which have drifted outside are naturally shuttled to the inside (for the same reason that the "inside" and "outside" of a Möbius strip are the same). However, in order to retain rotational symmetry, the strip has five twists, rather than just one (the topology remains the same).
Unfortunately, calculating the dynamics of a plasma shaped like this is hard -- really hard. It requires good computers, so for many years stellarators were mostly an object of theoretical interest. Additionally in order to deal with other instabilities the Wendelstein has an even more refined shape than the five-twisted strip.
ITER was conceived in 1987, and at the time it was necessary to go with a technology that was well-tested and understood, and which people felt confident would perform as expected. At that time, using a stellarator made as much sense as writing Firefox OS in Rust or something.
Thanks for a layman-lucid explanation. Does the Polywell design also fit into the overall fusion research picture as yet another design that might one day contribute parts of itself to the final working design as the Max Planck director suggested would happen with the tokamak and stellarator designs?
The polywell is an interesting concept, but it is extremely different from every other confinement mechanism, so it's hard to see how the ideas could be incorporated. To be precise, there are two "shapes" of "electromagnetic fields": curl-free (electric (unless magnetic monopoles exist)) and divergence-free (magnetic or electric), and each kind of field lends itself to a different kind of degree of symmetry in a confinement mechanism. Specifically, a divergence-free field cannot admit a spherical confinement because of Green's theorem, whereas a curl-free field requires a very unrealistic charge configuration to generate a toroidal confinement.
Tokamaks use a combination of divergence-free magnetic fields and divergence-free electric fields to make a donut. Stellarators use only magnetic fields to make a twisted donut. The polywell uses curl-free electric fields generated by an electron gun to make a sphere. There are other variants of inertial electrostatic confinement fusion, including that currently under development by Lockheed Martin, but it's generally received less attention.
Nitpick: IIRC the stellarator is in fact the slightly older design. It's just that it was more or less given up on in favor of the tokamak, due to the design and construction issues.
One minor complaint: answer to the second question seems to have missed/ignored the question? I assume the true answer lies in the fact that the technical realization of the stellarator are even more complex than that of a tokamak and there is more global experience with tokamaks.