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Comment by cygx | Hacker News Reader

Just for the record, you don't re-create stellar-core conditions with earth-bound fusion devices: We don't have the means, and the yield would suck.

Now, it is true that there's still fundamental research to be done until energy production via nuclear fusion becomes a reality, but we're reasonably confident that we could make the conventional approaches work.

However, that research is Big Science, and there's no political will to fund it properly (the graph that people like to cite is https://commons.wikimedia.org/wiki/File:U.S._historical_fusi... ). ITER suffered from this as well, and W7-X basically only exists because German reunification happened, and the German government was looking for a big science project - any project - they could leverage to funnel money into East Germany. The plans for W7-X just happened to be ready at the right time.

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>>> However, that research is Big Science,

Not all of it. The big science approach is a function of "pure" fusion research done from the assumption that containment/ignition only comes from magnetic fields and particle collisions. Some are approaching it from different directions, even using physical forces to trigger ignition (ie slamming the hydrogen with a big hammer). This isn't crazy stuff, just a more practical approach from people who see the problems from a different perspective.

https://en.wikipedia.org/wiki/General_Fusion

https://www.canadianbusiness.com/technology-news/crazy-geniu...

"At the centre will be a sphere, three metres in diameter, inside which molten lead swirls at high speed creating a vacuum, or vortex, in the middle. Arrayed around it will be 200 to 300 pistons, each the size of a cannon. Firing in perfect harmony, they will create an acoustic wave that collapses the vortex at the very moment a plasma injector shoots hydrogen isotopes, the nuclear fuel, into it. If General Fusion has its physics right, the heat and pressure will ignite a fusion reaction that spins off countless neutrons which will heat the lead even more. Pumped through a heat exchanger, that hot lead will help generate steam just like a conventional thermal power plant."

Hence my qualifier 'conventional approaches'. I wish those working on alternative approaches the best of luck, and some of the experiments look like a lot of fun (they get to blow things up - I've seen videos where plastering was raining from the ceiling of the control room ;)).

I'd say that the "conventional" approach for triggering fusion is physical. We've been triggering fusion in nuclear weapons for many years and the physicalities of it are very well understood. What general fusion is doing is essentially a non-destructive nuclear secondary. Triggering fusion with magnets, without moving parts, is imho the unconventional way of getting to fusion. It is only conventional in comparison to fusion research. The practical users of fusion (the armed forces) don't use magnets.

General Fusion changed their plan last year. The acoustic compression scheme, and the use of a spheromak plasma, are out. They discovered they have to limit the magnetic field to about 100T or else the induced currents start vaporizing the surface of the imploding liquid metal. This would be a disaster, as the metal vapor would have poor electrical conductivity and would penetrate into the plasma.

Confinement in the spheromak was also unacceptable; fast electrons were lost too easily from the edge, causing too much cooling.

Instead, the new scheme compresses more slowly, and compresses a spherical tokamak plasma. This scheme will have a solid post running down the center of the plasma, and the metal will implode from the sides at lower speed. The burn will take about 1 millisecond.

I am skeptical of this approach, since the center post will be exposed to extreme conditions (average neutron fluence two order of magnitude higher than in conventional fusion reactor designs) without a thick layer of liquid metal to shield it. The non-acoustic compression scheme also means the reactor vessel will have to withstand extreme pressure.

>> and W7-X basically only exists because German reunification happened, and the German government was looking for a big science project - any project - they could leverage to funnel money into East Germany

That's the first time I've heard that. Brilliant!

It's wrong, though.

Well, it's wrong insofar that the federal government wasn't actively looking for projects to fund and then miraculously discovered W7-X in a drawer. Rather, W7-X people were looking for funding and shopping for locations, but failed to secure it until they stumbled onto this particular angle to push. It's no coincidence that a new branch of the Max Planck Institute was established in Greifswald, whereas all previous work was done in Garchingen.

At least, that's the story I've been told by one of the current top W7-X people over a glass of beer, though the main topic at the time was that the movers and shakers behind such big projects might not see them to completion due to retirement or even death.

> However, that research is Big Science

Some of the progress in recent years is from the development of ideas that can be tried at much smaller scales, like the ST40:

https://www.youtube.com/watch?v=Cjzok6h2-xA

This is something that spherical tokamak research has been hammering away at for years:

https://en.wikipedia.org/wiki/Spherical_tokamak

>Just for the record, you don't re-create stellar-core conditions with earth-bound fusion devices: We don't have the means, and the yield would suck.

See Inertial Confinement Fusion, The NIF, High-Energy-Density Physics, etc.

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