I Just Got An e-mail from a Tokamak Guy

Consider specific people in the fusion research community, business, or politics who should be made aware of polywell research, and how we might reach them.

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MSimon
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I Just Got An e-mail from a Tokamak Guy

Postby MSimon » Wed May 14, 2008 2:15 pm

I just got an e-mail from a tokamak guy. It is his day job.

However, he has some interesting ideas about improving the design of BFRs.

I can't quote the message but he did give some interesting links:

http://ci.nii.ac.jp/vol_issue/nels/AA0081640X_en.html

http://ci.nii.ac.jp/vol_issue/nels/AA00 ... 49_en.html

http://ci.nii.ac.jp/organ/journal/INT1000001383_en.html

http://ci.nii.ac.jp/search/servlet/Kens ... yword0=%2F
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Zixinus
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Postby Zixinus » Sat May 17, 2008 9:08 pm

Why can't you quote the e-mail?
"We should be open minded, but not so open minded that our brain falls out."
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MSimon
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Postby MSimon » Sat May 17, 2008 9:12 pm

Because I don't have permission and I'm not going to ask.

He visits here and if he wants to chime in he can.
Engineering is the art of making what you want from what you can get at a profit.

Zixinus
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Postby Zixinus » Sat May 17, 2008 9:44 pm

Because I don't have permission and I'm not going to ask.


You do have permission: that e-mail he sent to you is now yours and you can do whatever you want with it.

It would help allot to understand the context of the links.

He visits here and if he wants to chime in he can.


I am pretty sure he already knows that. Registration is free afterall.
"We should be open minded, but not so open minded that our brain falls out."

- Richard Dawkins

tonybarry
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Postby tonybarry » Sat May 17, 2008 10:21 pm

Zixinius wrote:You do have permission: that e-mail he sent to you is now yours and you can do whatever you want with it.


The essence of civilisation is respect for others wishes.

Regards,
Tony Barry

MSimon
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Postby MSimon » Sat May 17, 2008 10:26 pm

tony,

Right you are.
Engineering is the art of making what you want from what you can get at a profit.

Solo
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Postby Solo » Sun May 18, 2008 3:03 am

Those are some really interesting resources there. I don't quite understand the principle behind the rf plug for the cusp. Could someone dumb it down a bit for me? Anyway, MSimon, I take it your contact was thinking that the rf plug could be tuned to repell electrons rather than ions. That would require a higher frequency I guess. But, where would the rf signal be applied? We don't seem to have any place to put plates like that in a polywell. I guess you could just slap a couple around each cusp ... ?

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Postby MSimon » Sun May 18, 2008 12:18 pm

My contact didn't give much information with the links. (I'll go back and re-read the e-mail to be sure.) I think what he was hinting at was a confirmation of POPS in another setting.

The scheme is adiabatic - that means that the POPS idea that the energy of the fluid doesn't change from cycle to cycle (i.e. the distribution is constant if you measure at the same point in the cycle) is valid.

The other point that is useful is that it is a trapping method for ions - i.e. the ions do not gain energy and fly out of the machine - instead there is an exchange with the ions trying to escape and those returned to the machine. Annealing.

Which you would kind of expect due to the RF field retarding fast ions and speeding up slow ones. Assuming a Maxwellian distribution which the original POPS paper did.

So I wouldn't take the configuration as gospel (a 100 m long reaction space of about 1 larmour diameter? tough to build). What I think it confirms is the viability of POPS in a magnetic mirror machine. Which is not a bad description of a BFR.

Any way that is my take from a quick read. I may be all wet.
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drmike
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Postby drmike » Sun May 18, 2008 2:49 pm

Solo wrote:Those are some really interesting resources there. I don't quite understand the principle behind the rf plug for the cusp. Could someone dumb it down a bit for me? Anyway, MSimon, I take it your contact was thinking that the rf plug could be tuned to repell electrons rather than ions. That would require a higher frequency I guess. But, where would the rf signal be applied? We don't seem to have any place to put plates like that in a polywell. I guess you could just slap a couple around each cusp ... ?


You need motion perpendicular to the field line to help prevent the electrons from riding out on their loss cone. By putting in RF that matches the natural frequency (based on density and temperature) the electrons will move with the RF in sync. If it is perpendicular to the field lines, they will mirror more easily and fewer will escape the loss cone. A TE mode antenna applied over each cusp and face would do the trick.

Since the electrons are trapped on the field lines, the ions will tend to stick around as well. And so you have an effective "plug" - both the electons and ions don't want to leave out the mirror cusp and stay trapped. Since the MaGrid is positive, the ions want to leave the region and they will drag electrons along back to the center. Add POPS on top of it, and you can get a stable oscillation going with little loss.

Solo
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Postby Solo » Sun May 18, 2008 3:53 pm

Drmike: so basically the rf adds more perpendicular velocity component in the cusp region so that the particle is no longer in the loss cone? Ok, I can understand that.

MSimon: Hmm. I must not understand the POPS concept. I guess I've been imagining it acting kind of like the much-hyped sonofusion idea (high density at the point of collapse). But you seem to be saiyng that the real value is that it anneals the ion velocity, not pumping up the amplitude.

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Postby MSimon » Sun May 18, 2008 9:25 pm

Solo wrote:Drmike: so basically the rf adds more perpendicular velocity component in the cusp region so that the particle is no longer in the loss cone? Ok, I can understand that.

MSimon: Hmm. I must not understand the POPS concept. I guess I've been imagining it acting kind of like the much-hyped sonofusion idea (high density at the point of collapse). But you seem to be saiyng that the real value is that it anneals the ion velocity, not pumping up the amplitude.


Yes.

Think about an oscillating ion beam. It will have zero velocity just short of the grids and maximum velocity in the center. So in the center it will add to the collision energy (which may help lower the needed drive voltage some). What also happens is that the ions "bunch" according to the instantaneous electrostatic field of the RF. Look up klystrons for an example of this with electrons.

Now according to simulations done without RF this sort of happens naturally in the BFR. By applying a small drive voltage that is in tune with this natural bunching I expect that the bunches can be tightened, annealing improved, and collisions in the center area to be enhanced.

I also expect electrons to get dragged along.

Electrons that are in the loss cone should have two main modes (ions would also have two main modes - edge to edge and edge to center). The electrons not following the ions would have an "outside" to center mode and an outside to outside mode depending on energy. A lot would depend on the density in the center which would affect the collision frequency.

It should be possible to tune the frequency to enhance the mode that helped the most.

If all these frequencies could be harmonically related some really interesting things might happen - good or bad I couldn't say, definitely interesting.

Carl Willis over at fusor forums is setting up to do some POPS experiments with fusors. It may be a month or three before he gets any results. We shall see.

==

The difference compared to the sonofusion idea is that the POPS drive in a BFR would not have a full reversal of the field. It would be a modulation of the field. (of course in sonofusion the field is acoustic and in the BFR electrostatic). The POPS bunching would increase the density in the collision region. And from basic physics fusion reaction rates are dependent on density.

From the original POPS paper they got a density improvement of 6.7 with a single species gas. Deuterium, Argon and one other which I forget. They figured they needed a density improvement of 200 to get significant fusion. They thought that might be possible by tailoring the drive waveform.
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