The Wendelstein 7-X concept proves its efficiency

And fusion is hardest of the wares.

One of the selling points of stellarators is that they can be operated without risk of disruption, but W7-X has done campaigns that push its operation to disrupt. A machine with dimensions similar to W7-X could be made with higher field magnets.

* Yes, higher field means larger machines are not needed to hit the same performance metrics, pushing down the minimum size (and cost) of a reactor. REBCO (HTS material of choice) is quite an expensive material to procure and work, so even modest sized research devices are more expensive than Uncle Sam is willing to gift right now. Private investment into SPARC is changing my opinion about what the future of fusion research will look like.

* The details of working HTS into confinement coils is an active area of discussion. HTS coils will be operated at liquid helium temperatures but won't stop superconducting until liquid nitrogen temperatures. The critical current limit decreases as temperature increases, so the risk of quench is still there when operated at near-boundary conditions. One thing that is discussed is whether to insulate the HTS tape or not. Conventionally, coils have insulation between the windings. In the case of superconductors it isn't strictly necessary. Superconductors are embedded in large copper jackets. When the core is superconducting the copper acts as a virtual open. When the core quenches the coil turns into a one turn copper ring and can dump all of the stored energy through the leads quickly without boiling cryogenics because the inductance is much lower.

High field magnets are useful, just not to many areas. MRI is the singular commercial application and they are more interested in lower cost (ie being able to run a superconducting magnet without liquid helium) than they are a higher field. NMR is the other big (but actually quite small) application for high field magnets. There are commercially available NMRs today with fields of 50 T.

After working with a 50 kW gyrotron and 1 m major radius machine, the raw industrial scale of the project is awe-inspiring [0]. ITER has 20x 1 MW gyrotrons and a 6 m major radius. Every system in the machine is fascinating.

All that said, it is a slow and expensive project. The issues are mostly political. The design is very old at this point. All of this is fine, but in the context of potentially scaling up HTS supply chains to make a reactor that is much smaller, it becomes clear that the ITER path is not the one the first generation reactors will take. It's an important stepping stone in terms of plasma science and public opinion. It's going to be a lot of fun to follow its successes.

0. https://youtu.be/cvsj0nqHwic

This 45-year old analysis [0] says that 15 Bn USD 1978 (63 Bn USD 2021) stands between us and a first gen reactor. Afaict that is still accurate as we have been on the Logic I path since then. How quickly you want to spend that 63 Bn USD dictates what logic (II-V) you're on.

0. https://fire.pppl.gov/us_fusion_plan_1976.pdf

We're only a bit over a hundred years from developing quantum mechanics and relativity, how can we possibly say anything about hundreds of years from now?

If something is well enough understood to accurately predict the timeline, we could do it much sooner.

If we have no idea how to do something, then "hundreds of years" means nothing, except maybe "not proven impossible yet".