> As you noted, they’ve worked decades to achieve seconds.

Minutes now. Last year, EAST ran sustained reactions over a minute, and a long-period plasma pulse over 17minutes.

> It is not reasonable to assume that this technology will catch up to be a viable energy source in the timeframe they target for the reactor install.

The thing to bear in mind is that certain things are a function of size and dimension. We've learnt that a classic torus tokomak needs to be bigger than JET - in fact we reckon it needs to be about the size of ITER. Now we could have just built a big tokomak in the 90s, but we also knew we needed to do lots of research on materials which could withstand neutron bombardment. And methods of extracting heat and waste materials. And a million other things. Even if JET had found Q=1, it was never any good as a power station. We couldn't have started cookie-cuttering JET reactors around the UK. It was very firmly a research reactor.

All of those bits and pieces could be done on smaller, cheaper reactors with second-long pulses. Rigs that are cheaper to build, tear apart, modify and upgrade (as JET has been, multiple times). You don't test a new rocket engine design for the first time by attaching it to a rocket - you put it in an isolated test cell because it probably won't work first time.

We're bringing together those decades of research into a viable reactor. It's now that we're committing to building "the whole rocket" and trying to launch it. We understand the geometries, the materials and the chemistries.

Consider: Nobody had launched a payload to space until they actually did it. Until that day, it was speculative. It was all a lot of work with no proof it would actually work. It was a lot of piddling around in test cells working out why the last engine blew itself to pieces, or working out why it caught fire on the pad. And then Sputnik happened. And it was both scientific and engineering fact.

There will be more unforeseen challenges, and it could undoubtedly have gone quicker if governments were vaguely interested in funding Fusion research properly. But it's not impossible, and at least one of the DEMO reactors is going to work. The level of engineering has risen and the technical risk has fallen. There's a diversity of designs, which improves the odds of finding the sweet spot.