[sam]

Author here - some other posters have touched on the reasons. Much of the focus on high performing tokamaks shifted to ITER in recent decades, though this is now changing as fusion companies are utilizing new enabling technologies like high-temperature superconductors.

Additionally the final plot of scientific gain (Qsci) vs time effectively requires the use of deuterium-tritium fuel to generate the amounts of fusion energy needed for an appreciable level of Qsci. The number of tokamak experiments utilizing deuterium tritium is small.

[satellite2]

Thanks a lot for this research. Seing the comments here I think it's really important to make breakthroughs and progress more visible to the public. Otherwise the impression that "we're always 50 years away" stays strong.

Here was my completely layman attempt to forecast fusion viability a few months ago. https://news.ycombinator.com/item?id=42791997 (in short: 2037)

Is there some semblance of realism there you think?

[mchusma]

In the 2037 timeframe, modeling trends doesn’t matter as much as looking at the actual players. I think odds are good because you have at least 4 very well funded groups shooting to have something before 2035: commercial groups including CFS, Helios, TAE, also the efforts by ITER. Maybe more. Each with generally independent approaches. I think scientific viability will be proven by 2035, but getting economic viability could take much longer.

[CGMthrowaway]

If ITER is where it's at why are we building commercial scale tokamak? https://en.wikipedia.org/wiki/Commonwealth_Fusion_Systems

[sam]

Companies like Commonwealth Fusion Systems are an example of those utilizing high-temperature superconductors which did not exist commercially when ITER was being designed.

[twothreeone]

ITER uses HTSs, just not for the coils:

> The design operating current of the feeders is 68Ka. High temperature superconductor (HTS) current leads transmit the high-power currents from the room-temperature power supplies to the low-temperature superconducting coils 4K (-269°C) with minimum heat load.

Source: https://www.iter.org/machine/magnets

[stshank]

HTS current feeds are a good idea (we also use them at CFS, my employer: https://www.instagram.com/p/DJXInDUuDAK/). It's HTS in the coils (electromagnets) that enables higher magnetic fields and thus a more compact tokamak.