Fusion in a magnetically-shielded-grid inertial electrostatic confinement device | Hacker News Reader

Fusion in a magnetically-shielded-grid inertial electrostatic confinement device

arxiv.org

61 pointscarapace29 comments

As this paper is from 2015 and I can't claim to understand it, is the follow up paper by the first author [0] the reason why it actually doesn't work?

[0]: https://arxiv.org/abs/1808.00622

they are using electric charge to move plasma particles around, and a magnetic field to enclose the charged electrodes and protect them from the plasma.

the electrode setup was a concentric ring setup so it was simpler than a spherical setup like a fusor kind of device

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

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

the most common fusion concepts nowadays involve magnetic enclosure and or compression, of plasma, and electric charge based acceleration of the plasma.

At first glance, no.

(2015)

Abstract:

> Theory for a gridded inertial electrostatic confinement (IEC) fusion system is presented that shows a net energy gain is possible if the grid is magnetically shielded from ion impact. A simplified grid geometry is studied, consisting of two negatively-biased coaxial current-carrying rings, oriented such that their opposing magnetic fields produce a spindle cusp. Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales. The proposed device has the unusual property that it can avoid both the cusp losses of traditional magnetic fusion systems and the grid losses of traditional IEC configurations.

> Our analysis indicates that better than break-even performance is possible even in a deuterium-deuterium system at bench-top scales.

That means it should be relatively easy to verify in a laboratory, right?

Yes, that was my take on the paper.

That it hasn't since publication in 2015 indicates they missed something.

https://arxiv.org/abs/1808.00622 [2019]

" Equations describing plasma equilibria are derived from the total energy of the system. The MHD equilibrium is shown to hold even for systems where the magnetic field may locally vanish. Through conservation of helicity, confinement is shown to be intimately related to electromagnetic tension. For an axisymmetric device, the presence of a magnetic field or current circling the axis is shown to be destabilising. This provides a simple explanation for the poor performance of some devices for which MHD predicts stability"

there is a cadence between electric charge motion and magnetic flux, and a dynamic balance has to be manufactured.

the addendum describes the magnetic confinement of electrodes to be a source of instability in the reaction. as well as providing a corrective factor for the mathematics, describing the theory.

Fusion over breakeven releases a boatload of ionizing radiation. So, it’s not exactly a safe thing to put on a lab bench. As even a single watt of power requires the kind of wall you put on a nuclear power plant.

As a rule of thumb, fusion is only really vastly better than fission once you turn it off.

That said, I agree there is likely something wrong with the design.

Thats the thing, even if you get the technique down right, then the system has to be engineered to transduce that energy and other product into something we can use. such as mechanical motion or electromagnetic generation/propulsion, or harvesting products such as isotopic helium.

you can build your own fusion reaction in the comfort of your home. Apparently fusor devices [1] are hobbist level difficulty. They are nowhere near break even, but they do generate a lot of radiation which can still be contained safely on a benchtop apparently.

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

At the hobbyist level they are making detectable amounts of radiation, but only something like 1 trillionth of a watt worth of fast neutrons per second.

Right, I completely missed the point that you were concerned about the amount of radiation at break even.

I wonder whether you could detect the increased efficiency well before reaching break even (that wouldn't prove that you can reach break even of course)?

Starting with HH vs DD fusion gives you validation with orders of magnitude less radiation, lower pressures would be similarly useful. But, IMO partnering with someone in the nuclear industry is probably the best bet.

Really, if your not asking for money just a location that's a fairly easy sell. If it doesn't work at all that's no real cost to them. If it almost works that's a cheap neutron source that's easy to turn on and off which is valuable. And if it actually works that's one of those world changing things people are willing to support.

This design sure looks a lot like the illustrations I've seen for Lockheed's fusion reactor design. Scroll down on this article, for example:

https://www.forbes.com/sites/arielcohen/2018/08/01/will-lock...

Compare that to the paper's figures, starting on page 2.

Above the illustration in the text, the paper references work from 2001-2006 for motivating that geometry:

    [19]  J. Khachan and S. Collis, Phys. Plasmas8, 1299 (2001).
    [20]  J. Khachan, D. Moore, and S. Bosi, Phys. Plasmas10, 596 (2003).
    [21]  O.  Shrier,  J.  Khachan,  S.  Bosi,  M.  Fitzgerald,  and  N.Evans, Phys. Plasmas13, 012703 (2006)

In particular all three citations refer to Joseph Khachan's work:

https://sydney.edu.au/science/about/our-people/academic-staf...

And Bosi seems to have been at Sydney at the time as well:

https://www.une.edu.au/staff-profiles/science-and-technology...

I was under the impression that bremsstrahlung losses were the main barrier to breakeven in fusor-like devices. Is this not susceptible to that?

Answering my own question: apparently not per section E.

They're making the assumption that the ions and electrons can be held outside of thermal equilibirium (and provide no evidence for this). In reality thermalisation is likely to occur rapidly due to frequent collisions, once thermalised a normal Maxwell distribution will apply and Bremsstrahlung losses will return with a vengeance.

"... in a mysterious and highly fluid vacuum, the force is not very small; it only moves at the speed and frequency of the plasma from two to three orders of magnitude faster than the plasma of other electrons to three orders of magnitudes..."

This makes me wonder what would happen to this device? Is it a device like the SG?

Something has to hold the magnets and physical supports will cool the plasma. Also there is a non trivial amount of magnetic force to contend with.

So don’t bring your credit cards in to work!

Don't bring your dental fillings either.

You are probably joking, but just in case not: dental fillings are not magnetic. They are amalgams of mercury and silver.

Try dropping a neodymium magnet down a length of copper pipe sometime. I would think that sensation would be quite disturbing from something hugging a tooth.

And the dental posts that hold crowns? Or the metal pins that screw implants into jaws?

>> Projectile Accidents: This is the scariest type of interaction, in which the MRI’s magnetic field literally pulls a restoration out of the mouth. The projectile restoration can injure the person with the restoration or, possibly, others nearby.

>> Damaged or Dislodged Restorations: Magnetic fields may not interact strongly enough to actually remove a restoration. But they may still be strong enough to move, break, or deform restorations.

https://www.topdowndental.com/blog/mri-safety-with-dental-cr...

I’ve been wanting to research magnetically shielded grids since 2007, but I’m not formally trained in physics [0] and don’t know where to begin. Can anyone make any recommendations for well-documented MHD simulator libraries?

[0] Informally I watch PBS Space Time and similar channels, but good though that content is, it’s not the same as a real qualification.

someone did make a charged particle simulator for polywell. You might find it by searching talk-polywell.org

http://www.talk-polywell.org/bb/index.php

Thanks :)

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