Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Derek
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Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Derek » Thu Jan 10, 2008 1:42 am

OK, I've decided to stop lurking for a while.

Precisely why is everyone assuming that magnetic shielding of the grid (to prevent electron collisions) is necessarily associated with magnetic confinement of the electrons to the centre of the machine? Surely these can be seen as separate considerations: the gain from the (potentially) increased concentration of -ve charge may not be worth the effort. If we can prevent electrons being lost to grid collisions whilst they circulate freely, the centre density issue will resolve itself ... no? There seem to have been several good points made about the relatively low efficiency of magnetic confinement systems and the tendency of their proponents to therefore 'go big': why, given that fusors are essentially electrostatic devices, are we looking for magnetic electron containment?

In other words, do we require a 'polywell', 'magrid' or simply a magnetically shielded grid (which might, for all I know, be what a 'Magrid' was supposed to be)?

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull » Thu Jan 10, 2008 2:55 pm

Magnetic confinement of STUFF, plasma, electrons, etc., has been the absolute watchword for fusion since Lyman Spitzer's first little group toyed with the concept. It is a tough cycle to break with so much rich history of big bucks being offered up for net fusion failures.

Magnetically bottling, mirroring and confining things just seems like a great mindset and you will always be in good company should you decide to join in on the action.

The magnetic bottlers have always reminded me of the perpetual motion folks. ......" If I only had this monster magnet... or....If the magnets I have on my wheel were only a tiny bit stronger, this sucker would spin on its own, forever.....WOW!"

What seemed like a good idea in 1950 is now a mantra.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil » Thu Jan 10, 2008 4:17 pm

>Why, given that fusors are essentially electrostatic devices, are we looking for magnetic electron containment?

The magnets confine electrons and let them recirculate, creating a negative potential well. This well then attracts and traps the ions, which are heavy and otherwise would need a much stronger magnetic field to be trapped. The same could be done with electrostatic means alone, like in Farnsworth's multipactor design.

We'll have to see what is technically feasible and also efficient.
The "Polywell" is not a bad idea. It would be interesting to see if it works.

M. Simon wrote:
> Magnetic confinement of electrons is 40X more effective vs. magnetic confinement of protons.

The magnetic field would have to be ~60x stronger to confine deuterium ions (with ~3700 electron masses) instead of electrons. Otherwise, will not be effective at all.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Derek » Thu Jan 10, 2008 5:29 pm

As I understand it Bussard's device is/was an EXL machine with the refinement of magnetic shielding of the anode grid and some degree of magnetic confinement of the 'virtual cathode' electrons effected by the same magnets. I understand the point about the electrostatic ion trap and indeed that a magnetic ion trap would require much stronger magnetic fields.
My point is that since an EXL machine forms a perfectly good virtual cathode from recirculating electrons why bother trying to contain the electrons at all: why not just magnetically shield the anode grid to discourage electron strikes from the recirculating electrons?

BTW the magnetic confinement only lets the electrons recirculate in the sense that it leaks at the cusps: the recirculating mechanism is electrostatic.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull » Thu Jan 10, 2008 9:47 pm

I remember when Doc Bussard took me into his office with Tom and, having signed the non-dislosure agreement, he explained to me how his electron virtual cathode worked and how it would both obviate grid losses and sought to stop the bleed of the 50% electron losses encountered with the slamming into the walls in the simple fusor.

All well and good, but the other bleed is loss of non- productive ions through losses other than fusion. (recirculation is not and cannot be perfect in any real world device.)

My visit to work with Tom and Doc that day was very early in my fusor investigation with fusor II and was in 1998 just a few months before I actually did fusion. I was wide-eyed and hopeful as hell. In the years that followed, I became much jaundiced against fusion by magnetic schemes of any sort.

It seems that I had to actually do fusion to see just how crappy it was as a viable power source due to any number of natural barriers thrown up to keep the universe from going high order in seconds.

All we have to do is either totally overide natural urgings of heated matter or obtain total, intimate control over what we term gravitation.

Since those "anything is possible days", I have "groaned weary".

So even if Bussard's system works perfectly, we are looking at a system that is 50% better, energy-wise, than the simple fusor; how is it an improvement beyond reducing power input for what was and is normal ionic electrostatic fusion of the stock, simple Farnsworth device?

For a given ionic energy delivered to the device, you should be doing no more fusions or, certainly, not many more. It is still the same old crap shoot at 1/2 power and lots more expense and infrastructure. Recombination and lost ions will still be there.

As always, myself and others await real quantitative data from an ostensibly working device which runs for an extended period, (minutes), without self destruction, fully involving Bussard's principle as he envisioned it. A tall order, I am sure.

Richard Hull
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil » Thu Jan 10, 2008 10:03 pm

Apparently someone will try to tackle that. A proof of principle and repeatable data is certainly not too much to ask for.

If the physics behind it allows Bussard's Polywell to be an energy source as intended is an entirely different matter.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Thu Jan 10, 2008 10:06 pm

Magnetic confinement of electrons is 40X more effective vs. magnetic confinement of protons.

In any case physics simulations are being done plus the real thing is being tested in the lab as we speak.

http://powerandcontrol.blogspot.com/200 ... lasma.html

The requirement is to get electron losses down to the 1E-5 or 1E-6 range for net power.

Richard of course is convinced it is impossible. Men much smarter than I am are of a different opinion. We will have a pretty good idea who is right in about 70 to 120 days.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Carl Willis » Thu Jan 10, 2008 10:10 pm

Derek,

The point of the magnetic fields in these designs is to keep electron current from flowing to the anode, as you mentioned, but also to effect sufficient densification of charge in the intra-anode region by means of the so-called "Wiffle Ball" cusp confinement effect, essentially magnetic pinching-to-near-death of the electron leakage beams that exit the anode at its openings. These are complementary results produced by using the same magnets in the quasi-spherical anode. According to Bussard's papers, both effects--magnetic shielding of the anode AND the cusp-current-driven wiffle ball effect--are necessary to attain the purported revolutionary fusion efficiency of his design. This is my understanding. I hope I interpreted your question as you intended.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Thu Jan 10, 2008 10:16 pm

Carl,

That is my understanding as well. It is not just shielding but also raising the density in the reaction area vs the dead space. The density in the dead space is limited by arcing considerations so without higher density in the reaction space the net power out would be uneconomical.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Derek » Thu Jan 10, 2008 11:36 pm

Carl,

Yes, thanks, you have indeed interpreted the question as I intended. I have to admit that I must have missed the bit in Bussard's papers which stated that both effects were required. I can see that magnetic confinement would be helpful, I was interested to understand which of the two effects (screening of the anode or electron confinement) was felt to be most important ...

I guess I may have to give up on the old cars (yes Richard, I do rebuild old cars!) and build something to experiment with instead.

Derek

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