magrid configuration brainstorming

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

Moderators: tonybarry, MSimon

MSimon
Posts: 14331
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

jlumartinez wrote:Hanelyp, I think you are right. I figured exactly this last configuration, that you propos,e but my knowledge of electrical & magnetic fields and magrid are not any deep so I just skip to continue with it because it seem so simple that I told myself it is impossible that Bussard had not been implemented it yet if viable. But maybe is a fairly good design. ..who knows ...

Maybe this guys have a different configuration: http://www.fpgeneration.com/ I talked to them by mail and they said me that their reactor has opposite polarity to Polywell . They use POPS . I would like to have a look to their patent
That would mean they are confining electrons with the electrostatic field and accelerating ions. I think their losses will be higher because the magnetic fields do not do a good job of deflecting ions.

hanelyp
Posts: 2255
Joined: Fri Oct 26, 2007 8:50 pm

Post by hanelyp »

Solo wrote:Gotta remember that those things are going to intercept alpha's like crazy if they aren't in the shadow of the coils, though. It'll be a trade-off, I guess.
Note I said screens, not plates. I figure getting alpha interception by the screens down to ~10% or less. Getting alpha interception by the coils that low seems a more difficult challenge.

Solo
Posts: 261
Joined: Fri Jun 29, 2007 12:12 pm
Location: Wisconsin

Post by Solo »

@ Hanleyp: Ahh, tricky! Ok, that might work.

@MSimon: the Q&A section on that FPG website suggests that they are running the grid at negative bias but still expecting a virtual well due to the electron confinement. They *are* having ions go in and out of the grid as part of the oscillation, but they mentioned forming electrostatic lenses to protect the grid. If they've got what they claim to have, it sounds like they are making progess.

MSimon
Posts: 14331
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

Solo wrote:@ Hanleyp: Ahh, tricky! Ok, that might work.

@MSimon: the Q&A section on that FPG website suggests that they are running the grid at negative bias but still expecting a virtual well due to the electron confinement. They *are* having ions go in and out of the grid as part of the oscillation, but they mentioned forming electrostatic lenses to protect the grid. If they've got what they claim to have, it sounds like they are making progess.
So far it is a paper design plus they appear to be having trouble raising cash. Their initial objective is a simulation. Given the current environment for IEC it means there is not much confidence in their design.

BTW there is no need to magnetically shield the grid if the charge is negative. The negative charge will keep electrons away and the ions will not be deflected significantly compared to electrons. The magnetic shield for ions would require a field about 40X to 50X that for electrons. I.e 20 to 80T. That will be very tough.

Solo
Posts: 261
Joined: Fri Jun 29, 2007 12:12 pm
Location: Wisconsin

Post by Solo »

MSimon wrote: BTW there is no need to magnetically shield the grid if the charge is negative. The negative charge will keep electrons away
Actually, I think they are trying to use a magnetic field to confine electrons to produce an even higher negative potential inside the grid, not to shield the grid. But as you say, they haven't done much in the way off proof. It still gives some interesting ideas though.

TallDave
Posts: 3114
Joined: Wed Jul 25, 2007 7:12 pm
Contact:

Post by TallDave »

93143 wrote:The trouble with a tokamak configuration is that the centre of charge for the electron distribution is outside the confinement area (ie: in the hole in the middle of the donut).
This is the point Bussard kept making re Polywell vs tokamaks in his speech at Google: like gravity, the electrostatic force isn't a right-angle force. The vast majority of net power fusion reactors around (i.e. stars) aren't toroidal, which may say something about the efficacy of using magnetic forces to contain ions.

tombo
Posts: 334
Joined: Fri May 09, 2008 1:10 am
Location: Washington USA

Post by tombo »

MSimon wrote:
windmill wrote:That new MgB2 superconductor should be great for this app. I noticed the company that makes the wire supplies it in round section and in, I believe, kilometer-long continous lengths. I wonder how much wire we would need for a 4T, 3 meter diameter coil? It's ampere-turns that partially determine field strength, but how do you include the coil diameter in the calculation?
IIRC a .3 meter coil producing .45T requires 100,000 A turns. Something like that. A 3 m coil to produce the same field would require 1,000,000 A turns. So for 4.5T it would be 10,000,000 A turns.

The current MgB wire is good for 100 A. The .45T 3 m coil would require 10,000 turns. At 10m per turn (roughly) that is 100,000 m, 100 km.

I did talk to the head of an MgB superconductor company. He seemed willing to work with us if we ever got funded. He has other technologies besides MgB so we will probably get steered in the right direction if we ask the right questions.
This kind of length is commonplace in the submarine telephone cable industry.
And they are much more complex than a superconductor cable.
The tricks for the manufacturer are clean splices and good QA (and good preventative maintenance).

I worked on a cable line that used a process very similar to Hyper Tech Research's CTFF process as a part of the process.
We regularly produced 50km per day in a single piece. (not the first year though)
But, our limiting process steps are not needed in this case.

When they need to get to 100km+ lengths they will.
I speculate they simply have no need to go beyond a few km for current customers.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

tombo
Posts: 334
Joined: Fri May 09, 2008 1:10 am
Location: Washington USA

Post by tombo »

Dr Bussard said in the Google video at 20min 40sec
“In the 1985 patent we said the polyhedron must have an even number of faces around every vertex with faces of alternating polarity.
The cube does not satisfy this requirement. It has three.” (Paraphrased)

Why then did he continue to work on cubic configurations for another 22 years?
And why, even now, is the WB7 a dodecahedron? A dodecahedron has only 3 faces per vertex.

It reminds me of the old joke where:
A man is looking for his keys under a streetlamp.
Another man comes by and starts to help him look for a while, then asks “where did you lose them?”
The first man answers “over there in the dark.”
“Well then why are you looking over here?”
“The light is better over here.”

I’m new here.
Am I missing something blindingly obvious here?
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

tonybarry
Posts: 219
Joined: Sun Jul 08, 2007 4:32 am
Location: Sydney, Australia
Contact:

Post by tonybarry »

Hello Tombo,
The essential element for a polywell to confine a plasma in a stable way is to have a series of magnets whose North faces all point in (or perhaps out, I am not sure which is better, and Dr. Mike Rosen also would like to know!). Thus, in WB-6 and 7, there are six coils and six North faces pointing in.
The statement you mention by Dr. Bussard regarding alternating faces does not make sense to me, although you get functional alternating zones from the cusp points where three hoops touch. These cusps leak electrons until the wiffleball is established.
It may be that what you interpret as opposing faces actually means something else. Dr. Joe Khachan mentioned that he thought the alignment of the magnetic field coils might need to be a very precise arrangement to ensure symmetry of the resultant confinement zone. And in this case, the cubic (or dodecahedron) fits the bill, because faces oppose each other rather than a face opposing a vertex.
However, I would be grateful for further input on the subject.

Regards,
Tony Barry

Solo
Posts: 261
Joined: Fri Jun 29, 2007 12:12 pm
Location: Wisconsin

Post by Solo »

Tony, I think you are about right. I remember reading in one of Dr. B's patents that he thought he needed some special symmetry to produce these acoustic waves in the plasma that would compress the core. Sounds to me like he might have changed his mind about that; did he have any knowledge of the POPS work?

drmike
Posts: 825
Joined: Sat Jul 14, 2007 11:54 pm
Contact:

Post by drmike »

There's a lot we don't know about what Bussard was thinking. Or how often he changed his mind! But it's clear from the basics Krall has described that cusp like fields are stable and that mirrors can help with confinement.

I'm pretty sure field direction doesn't matter, so long as all the coils are wound the same direction! Although if you want to start silly rumors you could say that down under should be wound backwards from the northern hemisphere :D

If you combine strength of two coils, the vertex won't be the cusp. I think symmetry improves confinement - but we really need to prove this. 4, 6 or 12 coils is the best symmetric layout you can get - but I'm not totally convinced they are the only possible solutions. It would be really interesting to see how arbitrary fields help or hinder the confinement. Nature likes symmetry though, so it just seems like a good place to start.

MSimon
Posts: 14331
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

Solo wrote:Tony, I think you are about right. I remember reading in one of Dr. B's patents that he thought he needed some special symmetry to produce these acoustic waves in the plasma that would compress the core. Sounds to me like he might have changed his mind about that; did he have any knowledge of the POPS work?
Yes. He and Dr. Nebel knew each other well before Dr. Nebel came on board. I'm not sure Dr. B said anything about POPS before he died. Tom L. probably has more on that.
Engineering is the art of making what you want from what you can get at a profit.

tonybarry
Posts: 219
Joined: Sun Jul 08, 2007 4:32 am
Location: Sydney, Australia
Contact:

Post by tonybarry »

Dr. Mike,
The stability of North faces pointing inwards is kind of a leaky stability ... from Dr. Khachan's comments I am given to understand that the confinement leaks electrons all round the edges and right through the centre, until the wiffleball confinement takes over and closes off those holes (at least we presume this happens).

As I understand it, the stability is due to the fact that when you "push" against the magnetic field, you get stronger repulsion the closer you get to the magnet. That's a nice thing which I understand ITER (tokamaks) do not have. But it's not perfect; the magnetic field has a vector when you are off-axis, so the push goes sideways rather than being focused back on itself.

Dr. Khachan would like to know if confinement happens with magnetic systems like polywell. For him, that's the first step. If confinement is not observed, then polywell will not work.

I would really like to know the answer too.

Regards,
Tony Barry

MSimon
Posts: 14331
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

tony,

That seems to be Dr. Nebel's first concern given his comments here.
Engineering is the art of making what you want from what you can get at a profit.

Solo
Posts: 261
Joined: Fri Jun 29, 2007 12:12 pm
Location: Wisconsin

Post by Solo »

tonybarry wrote:But it's not perfect; the magnetic field has a vector when you are off-axis, so the push goes sideways rather than being focused back on itself.
That's another thing that Dr. B mentioned in the patents. I think he was proposing to put another layer of coils outside the primary magrid to correct for the unspherical magnetic field. Or to use a geometric figure with a large number of faces/coils.

MSimon: I don't know how much this is worth, but it sure looks like there's some confinement going on in the picture of WB-7 at the EMC2 webpage. The plasma brightness (and presumably density) seems to be in the center.

Post Reply