MIT Talks Plasma Details

Discuss how polywell fusion works; share theoretical questions and answers.

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MSimon
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MIT Talks Plasma Details

Post by MSimon »

http://ssl.mit.edu/research/fusion.html
The inertial electrostatic confinement (IEC) concept is ideal for space travel since it sheds massive magnets in favor of lightweight spherical metal grids which confine the fusing ions with purely electric fields. Also, the concept is ideally suited for direct electric conversion for power at very high efficiencies, eliminating much of the massive radiator required by nuclear fission and standard fusion schemes.

MIT’s contribution to this concept lies in the drastic improvement of the ion confinement via the introduction of multiple grids to create a more ordered system. Also, operating at lower background pressure with particle injection via guns allows for much monger ion lifetimes. A 2-D Monte-carlo collision, particle-in-a-cell model is used to simulate the external and internal fields and the dynamics for hundreds of thousands of simulated particles. These investigations have verified the improved confinement characteristics of a multiple grid system. The code is also used as a predictive tool for examining grid configurations in support of an experimental verification effort in the lab.

Also, a curious synchronizing collective behavior is observed in simulation. Particles injected uniformly in 3 separate beam paths ‘clump’ and form pulses. As the simulation progresses, these pulses are observed to synchronize between the beam channels. The steady-state behavior under constant injection is then observed to be a global pulse with the majority of the confined ion arrived near the center of the device at the same time. Two snapshots from a steady-state plasma are shown below.
They have some very pretty pictures of the ouputs of their computer runs.

A very nice poster:

http://ssl.mit.edu/research/Posters/FPP ... r_2006.pdf

TallDave
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Post by TallDave »

Multi-gridded! Cool. And it seems to boost confinement. I wonder if this can be applied to Polywell setups.

Isn't laser induced fluourescence what they used to show the well forming in that Japanese study? Apparently it was too expensive for these guys.

MSimon
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Post by MSimon »

I haven't figured out how to apply the multigridded concept to Polywell yet.

Yes. Laser diagnostics was used by the Japanese team.

The difficulty is that it does not work well with very low density plasma.

Solo
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Post by Solo »

So what they are doing is putting multiple central grids in (the ones that create a potential well directly) but staging the voltage between them, and keeping them all in their own 'shadows' from a radial perspective, right? I'm not sure how that helps. I guess it allows them to either make a more transparent grid, or to avoid collisions with ions somehow, right?

Edit: hmm, oscillations in a supposedly steady-state system? That's interesting. I wonder if they might be harnessed for some purpose.

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Post by drmike »

It helps because they are trying to form beams of ions. The idea is to create a set of linear accelerators, but keep the whole thing inside a simple spherical tank. If the ions stay in the "beam path", they don't hit the grids and that improves efficiency a lot.

Keegan
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Post by Keegan »

^ almost there. The MIT guys use multiple grids with varying potential. They act as electrostatic lenses that keep the beams bunching back and forth and away from the grids. Whats exciting is they found the ion beams "synchronized" this is the same mechanism the POPS guys at Los Alamos are independently researching. So you know its the real deal.

Drmike, the set of converging linear accelerator ion beams is what the polywell needs. If anything polywell's electron and ion sources are looking to be its Achilles heels.
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drmike
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Post by drmike »

I want to combine a few ideas along the lines of POPS and accelerators.
But I want to see the math first before I open my mouth and prove I'm a fool :oops:

Solo
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Post by Solo »

Great explanation again, Keegan! So the beams oscillate back and forth, and they are centered somehow by the configuration. Looks like that might get around the need to have magnetically-shielded coils. I like that.

I suppose that this stuff and POPS is similar to Bussard's work in that they all rely on something more like an accelerator than a plasma 'oven' to get the required ion temperature. But the difference is that with Bussard's machine, the ions oscillate individually, where as the other approaches oscillate the entire plasma, or chunks of it, as a unit.

Oh, and I guess another difference is that instead of creating a negative potential well in the center with trapped electrons, these guys are still using girds. And instead of having a central potential high enough to cause fusion directly, they avoid that by pulsing the thing.

I think you might be able to run a Bussard reactor POPS style, but it looks like the MIT thing is a completely different animal, and not complimentary.

MSimon
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Post by MSimon »

Solo,

From what I can tell all spherical machines oscillate.

The grid losses are lower in the MIT configuration. They may not be low enough for a practical power generator.

POPS is probably applicable to all similar configurations.

Dr. B's idea that his reactor was quasi-steady state is probably wrong.

No matter. The big deal is that he figured out how to magnetically shield the grids.

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WIKI NEEDS TO BE UPDATED

Post by zbarlici »

:?: :arrow: IEC @ Wikipedia

http://en.wikipedia.org/wiki/Inertial_e ... -bussard_0

Todd Rider's 1994 Masters Thesis is listed under the EXTERNAL LINKS section. MIT`s recent thesis needs to be added to that section as well... anyone know how to do that???

MSimon
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Post by MSimon »

Look for the edit thingy on the right of the page. You edit sections.

I can add links or whatever if you post them here.

The Rostoker Monkton Paper should be added with a bit of explanation in the text after the reference to the Rider paper.
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zbarlici
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Post by zbarlici »

:arrow: Add to WIKI

http://ssl.mit.edu/publications/theses/ ... Thomas.pdf

http://ssl.mit.edu/publications/theses/ ... chCarl.pdf

...can`t open the PDF files right now so i`m not sure which one is more appropriate(if not both).

Also add the link to the Monkton paper like you said...

MSimon
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Post by MSimon »

zbarlici wrote::arrow: Add to WIKI

http://ssl.mit.edu/publications/theses/ ... Thomas.pdf

http://ssl.mit.edu/publications/theses/ ... chCarl.pdf

...can`t open the PDF files right now so i`m not sure which one is more appropriate(if not both).

Also add the link to the Monkton paper like you said...
Those papers are already added.

I added this:

Rider's chief criticism is related to the recirculating power required in a colliding beam machine: "In virtually all cases, this minimum recirculating power is substantially larger than the fusion power, so barring the discovery of methods of recirculating the power at exceedingly high efficiencies, reactors employing plasmas not in thermodynamic equilibrium will not be able to produce net power". This is a very valid criticism and is acknowledged by Robert Bussard. However, Bussard claims that by use of the discovery of what he terms the Wiffle Ball effect and by circulating electrons escaping from the Wiffle ball at high efficiencies he can get the total electron circulation efficiency into the 99.999% to 99.9999% range, making colliding beam machines of his proposed design viable for power production. Experiments are currently under way (Jan. 2008) by the US Navy to test Dr. Bussard's ideas.

We shall see if it lasts.
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scareduck
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Post by scareduck »

MSimon wrote:Experiments are currently under way (Jan. 2008) by the US Navy to test Dr. Bussard's ideas.
I hope and pray he was right.

zbarlici
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Post by zbarlici »

scareduck wrote:
MSimon wrote:Experiments are currently under way (Jan. 2008) by the US Navy to test Dr. Bussard's ideas.
I hope and pray he was right.
well one way or another he got extremely positive results with WB-6... either that or he was lying - and i don`t see what an 80-something year old has to gain by lying, moreover the older you get, the wiser you get and you learn that lies dont take you far.

The man was not lying, so SOMEHOW he got those results. It would be weird if they couldn`t be reproduced.

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