Electron Recirculation through different Cusps revisited

[D Tibbets]

There has been little in the Theory forum for a while, so I decided I would revisit an old topic, and wander into some vague and wild speculations. There has been a near concinsence here that electron recirculation occurs through the same cusp that the electrons exit from. Consider the picture on page 5 of this link-

http://www.askmar.com/Fusion_files/2008 ... isited.pdf

- which shows the burn marks on the outside faces of the perminate magnets of WB1. Also, I have seen in my demo fusor with perminate magnets in a similar arangement the plasma/ glow discharge wraping around the magnets and hitting the outside face where one of the poles are. How this compares to the conditions in which a Wiffleball may exist (internal field compressed and exterior field bloated) which would push the external field closer to the walls; and on the opposite side,I suspect that WB1 did not have a positive potential on the magnets (?), so it would be less attractive to the electronsand I would expect the electrons would have higher orbits. The contribution of these two opposing conditions may result in conditions similar to a Wiffleball (in terms of preferred cusp reentry) with cusp flows similar to the electromagnet powered machines, like WB2,3,4,6,7, etc. The percentage of electrons recirculating around between cusps is enough to be visualized and to burn the permainate magnet surface. Wheather this pathway is a significant percentage of the total is uncertain. I speculate that the higher energy escaping electrons (that are not very near the centerline of the cusps where the field line curvature is approaching infinity) might be more likely to take this route , as opposed to those electrons that are stoped and fall back through the same cusp due to the magrid positive potential. I would not expect the ions to show this behavior with positive magrids, and thier greater inertia. They would be be accelerated away from the magrid once outside, and if thay remained traped on a magnetic field line thay would orbit much (?) further out. But if there is enough space some of the least energetic ions might orbit back into the magrid through another cusp at the same energy that they left (not nessisarily good, though it does stimulate some thought).

If there is a second magrid outside the first, the 'external' magnetic field (outside the inner magrid) would not be as bloated. There might even be some increased compression/ strength on the internal field. If arranged properly the external magrid might be in the shadow of the first, and effectively increase the strength of the internal field. Could it possibly alter the size/ pinching of the cusps?
The outer magrid could be tuned to perhaps recirculate ions much as the electrons are recirculated by the inner magrid (any electrons reaching this height are already considered lost). This might conserve some of the escaping ions, though I don't know if it would effect the energy balance. Despite this though, it might give a two stage trapping mechanism and increase the density gradiant so that higher densities can be maintained inside the inner/ primary magrid without reaching the critical external density that could lead to arcing. The external magrid would also serve as the first (weak) power harvesting direct conversion grid.
In my convoluted brain I can even see a layering of containment . If ions and/or electrons accumilate in the areas of the cusps between the magrids, there may be knobs that can be used to create neutral or charged plasmas in these regions. Overall containment, trapping factors, and confusing interactions might be possible. Taking it to the extream there might even be the possibility of having multiple fusion cores in a matrix of magrids. The sphericity of all but the central core would suffer, but the complexity might be conterbalanced by better overall containment, density, and control (now I am getting really silly). Supporting and shielding the various support structures would be interesting. In some ways this might be similar to the POPS reactor drawing that had many cores clustered together in tubes, these presumably improved effective containment in at least one axis ( charged particles that were leaving one core region could travel to the next core in line). Imagine clustering magrids in layers like an onion, of string them like peas in a pod.


Dan Tibbets

[Nik]

All polywell magnets that I've seen have 'shallow' magnets. Extending them gives a solenoid. I suppose spreading the turns axially eases the cooling issues.

D'uh, this is drifting into linear magnetic confinement and classic 8-shaped 'Stellerator' country...

( Hey, if it works, I'm not going to argue !! )

[D Tibbets]

All polywell magnets that I've seen have 'shallow' magnets. Extending them gives a solenoid. I suppose spreading the turns axially eases the cooling issues.

D'uh, this is drifting into linear magnetic confinement and classic 8-shaped 'Stellerator' country...

( Hey, if it works, I'm not going to argue !! )

I may be confused, but lengtheng the axial thickness to allow more turns and therfore stronger magnetic fields (I'm not sure how the strength would vary in the cusp regions away from the concentration of the coils that extend further away from the center) is an option that might have merit. But, this is not what I am suggesting. The magnet arrangement I'm referring to is two seperate ring electromagnets, one outside (and proportionatly larger and possibly stronger) than the other. These magnets would have opposite polarity so that the magnetic fields would be squeezed between them. This would be similar to the opposing magnets on opposite sides of a single magrid. This would impead, and possiblactually compress the magnetic field outside the inner/ primary magrid. This would cause the magnetic fields withinin the primary magrid to be pushed inward more. This might allow more charged particle density buildup within the primary magrid before Beta=1 is reached. This would increase the fusion rate. In a way it is similar in effect to increasing the magnetic field strength of an isolated primary magrid. The advantage is that the two magrid approach (one within another) is that the outer grid is in the shadow of the primary grid and is further away from the core ( less x-rays, etc. hitting it despite its larger size). If a substantial amount of the nessisary magnetic field can be provided by the external magrid- through compressing the weaker(?) magnetic field of the primary coil, this would decrease demands on the primary magrid. This would have engeenering benifits in terms of insulating and cooling the inner coil (less windings needed, so more room for insulating layers and coolent flow).

The interaction of the cusps which would be symetrical (one more proximal to the core than the other) would modify the travel of ions and electrons exiting the primary magrid. I'm speculating that this would improve recirculation (through different cusps) of the electrons, and perhaps some of the upscattered ions, thereby increaseing the effective wiffleball trapping factor and possibly decreasing the electron input power. The cusps of the primary magrid might also be pinched to a greater extent, and possibly sphericity improved. The monoenergetic properties of the contained ions (plus the recirculated upscattered ions) may be harmed. Some knobs might need to be twisted to achieve a net benifit (if possible).

Somewhere in the forum there is a drawing of a similar arangement, though I beleive the discussion in that thread was about rotating magnetic fields.

Dan Tibbets

[D Tibbets]

Images showing what I'm triying to describe are at:

http://www.mare.ee/indrek/ephi/images.pdf

Here Indrek was using a inner grid to simulate the magnetic effects (wiffleball formation) of the contained plasma by substituting a virtual magrid to represent the plasma. To emmulate my idea, add a third grid to the picture.

Dan Tibbets

[rcain]

Hi Dan,

recirculation through different cusps - i had always wondered about the possibilities here also; indeed my original understanding of 'recirculation' had (mistakenly) been precisely that, until corrected to the consensus definition of 'internal''orbit/oscillation'.

two/three configurations i had wondered about:
- multiple concentric polywells
- cubical matrix configuration of multi-polywells
- single polywell with intentional cusp-to-cusp recirculation/diversion.

my tenuous/questionable rational, aimed at a staged, progressive amplification of effect toward the central active core cell (in the manner concentric multi-gridded IEC fusors, or perhaps methods of ultra-cooling).

either way, size and complexity increase, making it even more difficult to understand and engineer, towards highly questionable advantage, at least at this stage of research.

separately i also wonderd about recirculation within/about the wiffle ball separatrix region (if we might suppose there were such a thing).

...vague and wild speculations...

i wouldnt be worried about that on this forum.

[MSimon]

either way, size and complexity increase, making it even more difficult to understand and engineer, towards highly questionable advantage, at least at this stage of research.

I second that.

[D Tibbets]

It occurs to me that since the second magrid's purpose is to modify the fields of the first magrid, but not to provide recirculation by it'sself, it could be external to the vacuum chamber. Sort of like placing a WB5 around a WB6. IF there are sufficient benifits, this would be easier(?) with less clutter inside the vacuum chamber, and with cleaver engenering might also play a role in shielding componets of the collection grid and possibly directing/ focusing fusion product flows for convient harvesting (keeping the fusion ions from P-B11 from spreading out as much once they are past the cusps of the primary magrid. In this regard it would be similar to placing a magnetic nozzle around the magrid to direct the P-B11 fusion products out the back of a rocket engine.

Dan Tibbets

[Nik]

Uh, if you place the second magrid outside the vacuum chamber, doesn't that limit the chamber material to alumin(i)um ?

Or just the secondaries' 'branches' ??

[MSimon]

with cleaver engenering

I'll get some hackers I know on it ASAP.

[D Tibbets]

with cleaver engenering

I'll get some hackers I know on it ASAP.

You cut me to the quick


Dan Tibbets

[D Tibbets]

Uh, if you place the second magrid outside the vacuum chamber, doesn't that limit the chamber material to alumin(i)um ?

Or just the secondaries' 'branches' ??

Or, at least some nonmagnetic material (certain stainless steels?). It was presumably done with with WB5, and the original machine.

Aluminum is fine for a vacuum vessel, though I suspect it could not handle as high of temperatures as stainless steels. I heard (from M. Simon) that stainless steels were limited to ~550 degrees C. due to creep (weakening/ saging?). This is a concern for steam generation in conventional powerplants as it limits the thermal differential that effects the efficiency of power production. I don't know how close to this some aluminum alloys could approach. I understand there are some super alloys that can exceed this, but apparently the cost and/ or difficulty of working these alloys limits their use.

Dan Tibbets

[Nik]

I've a vague recollection from Laithwaite's linear motor era that aluminium is often *better* than copper, soft iron or steel for magnetic stuff...

In his case, it was because of the 'magnetic echo' eddy currents, as conductivity vs mass ratio favours the cheaper, lighter aluminium.

In this case, I'd suggest that working with 'fussy' steels might raise issues that an aluminium enclosure may avoid. At a pinch, you may need a replaceable lining...

Uh, IIRC, casting, welding and machining appropriate Al alloys is rather easier than for stainless steel of any flavour. Certainly, the work would be within the remit of a local light-alloy foundry's CNC rather than requiring s/steel specialists' careful jigging and heat treatment...

Designing in cooling ribs / lugs would be easier, too.

[MSimon]

You have to be very careful in choosing the aluminum alloy. Some of them (most of them?) are prone to serious outgassing.

[DeltaV]

If it was going to be aluminum, I'd use BorAl (Boron Aluminum) alloy, for its neutron blocking properties. Might not be at the best position for a layered radiation shield though, if it produces secondary radiation. Might outgas too much also, don't know.

[MSimon]

If it was going to be aluminum, I'd use BorAl (Boron Aluminum) alloy, for its neutron blocking properties. Might not be at the best position for a layered radiation shield though, if it produces secondary radiation. Might outgas too much also, don't know.

B10 is real good with thermal (< .1 eV) neutrons not so hot above 10 eV. In fact the colder the neutrons the higher the cross section.

And then you have to deal with the defects created in the structure and the He and T(?) left behind.

I wouldn't use anything borated inside the device. Unless it was not structural.