Some context on why progress slowed:<p>From the 60s to the 80s we got pretty good at tokamaks (stellarators have been catching up since we got computers) but Magnetic Confinement Fusion (MCF) triple product performance scales with major radius ^ 1.3 and confinement field strength ^ 3. Power density scales linearly with major radius and with the magnetic field strength ^ 4.<p>At some point increasing the major radius becomes extremely expensive, so pushing past the barrier of Q=1 has been a long, political process. At the same time a real burning plasma (Q>1) machine has a lot of added cost to operate a nuclear facility (tritium handling and neutron radiation).<p>So there has never been a physics barrier to Q>1, but an economic one. What's changed in the past year is that REBCO manufacturing and working matured to the point that confinement fields are now twice as strong as they used to be. Suddenly building a burning plasma machine isn't a 40 year international venture and economically viable MCF plants are in the crosshairs.
For SPARC the big innovation sounds like it is being able to use some special superconducting electromagnets to generate the massive magnetic field in the tokamak -- since that part is such a critical part, it would seem like in the next say 5-10 years that it takes to get SPARC up and running there should be a parallel group just trying to improve that magnet design by say 2X, which would likely have a massive impact.. seems like a smart thing for National science foundation or darpa or whatever to be funding that.. (maybe already happening) but it would be a bummer to be talking about this in 2030 and them saying, ok now we just need to design a more powerful magnet..
I like this image even more than the one in the tweet:<p><a href="https://aip.scitation.org/na101/home/literatum/publisher/aip/journals/content/php/2022/php.2022.29.issue-6/5.0083990/20220608/images/large/5.0083990.figures.online.f3.jpeg" rel="nofollow">https://aip.scitation.org/na101/home/literatum/publisher/aip...</a><p>It helps my layman's eyes clearly relate the trajectories of the various developmental processes of each approach. I wonder why SPARC and ITER are the only projected ones. Do the other reactors being built not have estimated yields? My favourite has long been the wendelstein, because of they way it looks and how it feels like its pathway to success might be software based. I like the way Tokamak Energy markets itself, and would have loved to see the ST25 and the ST40 in that image, but maybe they're not complete enough projects to be on there?
These authors put out a paper last December that really kicks ass. It's linked in the tweet. It's worth flipping through.<p><a href="https://aip.scitation.org/doi/10.1063/5.0083990" rel="nofollow">https://aip.scitation.org/doi/10.1063/5.0083990</a>
Serious question, since this is being done by a US company: is high-end engineering like this done in metric - as surely all the science is done in metric - or is the machinery built in customary units?<p>I wonder the same about SpaceX and the other rocket companies… does US manufacturing mean you really have no choice but to operate in obsolete units, or are these things so “custom” that they get to be done in metric anyway?
If anyone wants to see how triple product performance relates to Q for DT MCF machines:<p><a href="https://twitter.com/jb_fusion/status/1506964692627034118" rel="nofollow">https://twitter.com/jb_fusion/status/1506964692627034118</a>
Is there an inverse of the Kardashev Scale i.e for energy production rather than energy consumption? If so, what Level would we be now vs the projected?