Unexpected electric current that could stabilize fusion reactions discovered | Hacker News Reader

Unexpected electric current that could stabilize fusion reactions discovered

phys.org

51 pointsbookofjoe24 comments

A big problem with fusion systems has always been stabilizing the plasma. Stars do it with gravity, which pulls inward only. Doing it with magnetic fields requires fancy geometry to try to get the effect of a uniform inward push. None of the approaches are all that great.

A few groups have tried active stabilization of plasma. It's being planned for China's new tokomak.[1] The instabilities are on the order of milliseconds, not too fast for active control. This new development may advance that work. Maybe. Possibly.

[1] https://www.sciencedirect.com/science/article/abs/pii/S09203...

What about using an electric field?

That's what a Farnsworth Fusor does. It does cause some fusion and makes some neutrons, but not enough to be anywhere near self-sustaining.

What is interesting is that one can use current in the plasma itself (which creates a magnetic field) to confine the plasma, if one can control the current well enough. This design [1] does that. Unfortunately DOE funding for new fusion concepts has been almost zero for many decades and ITER has further depleted the DOE research fusion. On the bright side there has been some recent VC funding in the space and CTFusion is working on this design concept[2].

[1] https://spectrum.ieee.org/energy/nuclear/inside-the-dynomak-... [2]https://ctfusion.net/technology/

ITER isn't the problem, our priorities are.

Yes, confinement by running a current through the plasma is well known. First use was by the ZETA experiment in 1957. https://en.wikipedia.org/wiki/Z-pinch

The eternal problem in science journalism: a scientist will explain how their machine works, and the journalist will get the impression that they have independently invented each part of the apparatus, with no prior art. The incentives encourage it: the scientist wants to take credit for everything possible, and the journalist wants to report on a maximally new and exciting machine.

I agree, a journalists description of such new fusion concept is unlikely to be useful to people trying to understand what is new about the concept. I am not a fusion scientist, but my dad is the "Tom Jarboe" in the article. From my limited understanding from talking to him, the main reason that they think the dynomak design has a chance of working is because they solved the problem of adding energy to a stable plasma without disrupting it by using a new type of helicity injector. Not sure if it would really work, but hopefully they can get enough funds to try.

The title is terrible, but what is interesting to me is whether this could allow the direct draw of power from a nuclear reactor, instead of just through heat.

My shortened to fit the 80-character-limit title or the Phys.Org one? or both?

>Researchers find unexpected electrical current that could stabilize fusion reactions

How much more power would you get from a direct draw vs just through heat?

Thermal efficiency in the Rankine cycle (which powerplants apparently leverage) is around 30%.

So it sounds like there's a lot of potential improvement. Of course, given we're talking fusion and not fission any power plants are purely hypothetical at the moment as all publicly known fusion facilities are for research.

>publicly known

Do you feel that this is an important qualifier?

I’m sure there are plenty of secret evil lairs powered by fusion reactors.

I doubt it because anyone with secret fusion could immediately dominate the energy sector and become much more powerful than they already are?

Given we are talking about nuclear technology, an area more secretive than most, i don't think its an utterly unreasonable qualifier

Energy generation is a national security concern. While all signs point to engineering issues preventing creation of a successful fusion plant, the reality is there are only a small handful of issues left that prevent energy generation from fusion.

The Lockheed SR-71 Blackbird first flew in 1964, the titanium used for its construction was purchased in secret via front operations by the CIA from the USSR. The Soviet Union was the only country that had enough titanium to build the SR-71.

The reason I reference this is because with enough money and resources anything is possible to do in secret. The SR-71 included some revolutionary technological innovations to solve the problems created by super-sonic flight. Energy viable controlled fusion is a little farther than the SR-71 was but not so much so that it is impossible.

Hence the qualifier.

Thanks for the interesting historical example!

There's already a technology that can do that - magnetohydrodynamic generation [1]. A conductive material moving through a magnetic field develops a voltage across it, which can be used to produce power; a hot plasma is a conductive material with lots of energy that can drive movement.

The problem is that most of the energy produced in fusion is in the kinetic energy of neutrons. To capture that energy, you need to slow the neutrons down by collisions with some material, turning the kinetic energy into heat in that material, and then harvest the heat. AIUI, neutrons being neutral, you need that material to be dense (lots of nuclei per unit volume) and have a high neutron cross-section. The plasma in a fusion reactor is neither, so you can't collect the neutron energy in the plasma. Rather, you have to let the neutrons hit some dense blanket surrounding the plasma, collect the energy as heat there, and then harvest that.

There are fusion reactions which don't produce neutrons [1], and so where the energy goes into the kinetic energy of charged particles, which is readily collected in the plasma, using MHD or direct conversion [3] (is MHD considered a kind of direct conversion?). But they are much harder to do than the reactions which do produce neutrons, and those are already hard enough!

[1] https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator

[2] https://en.wikipedia.org/wiki/Aneutronic_fusion

[3] https://en.wikipedia.org/wiki/Direct_energy_conversion

The writing is really horrible.

Interactions of waves in plasma "conspire" to produce effects.

Electrons ride waves like "surfers".

Interesting findings, extremely badly presented.

Phys.org is the Applebee's of science journalism -- they warm over some canned press release topped with a thin sauce of quotes from the co-authors (they can't be bothered to get someone independent to comment).

In fact, this wasn't even written by phys.org staff -- it was from the Princeton PR department.

What is a low and what is a high frequency. It would be nice if there would be some kind of numbers in such texts.

It's probably in the original paper if you have access

https://aip.scitation.org/doi/10.1063/5.0011516

Do we understand how the magnetic fields in stars work?

Depends on which stars. We recently discovered through relativistic ray tracing of x-rays that neutron stars may have more than two magentic poles and as such two poles may even be located quite close to one another in the same hemisphere. There really is much left to discover about them!

https://ui.adsabs.harvard.edu/abs/2019ApJ...887L..21R/abstra...

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