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.
Wilfried Heil
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil »

The ions are supposed to remain inside of the magnetic "grid", in an area with high electron concentration, i.e. a potential well.

Tom Ligon gives a short description of the Polywell here:
>viewtopic.php?f=14&t=6726#p45985

Attempts to use magnetic fields to aid in the confinement of ions have been made a number of times. A rather impressive machine was build by Wilson Greatbatch, otherwise inventor of the cardiac pacemaker. The Greatbatch machine could work with permanent magnets, mounted outside of the vacuum chamber.

>viewtopic.php?f=14&t=6681#p42364

Of course, none of these experiments come anywhere near the point of possible energetic breakeven. The machines from Greatbatch, Nebel's POPS and Bussard's Polywell are all studies of technical possibilities, and maybe all are fatally flawed. Considering that they cost very little, at least relative to the politically more ambitious projects, it would be it very unwise not to follow up on these ideas. Be it for the sake of learning what can't be done.

It's quite possible that a successful solution may be found in the future, by someone with an open mind and working in a field completely different from fusion. Probably not by potluck alone, since it takes an high amount of perseverance to reach such a goal.

The missing component is not new physics, it's intuition.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by stob »

Dave,

The magnetic field only serves to confine the electrons.
It isn't supposed to confine the ions, the electrical field produced by the electrons and the grid will to do that.
If the fuel is ionised inside of the grid at an electrical potential below grid potential, the ions simply won't have the kinetic energy to leave.
(Also the electrons knocked out of the fuel won't have the energy to produce a real potential well until they get heated by the electron beams from the e-guns.)


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

Post by Richard Hull »

I hope all who are talking about apples are not in conflict through verbage with those who seem to be talking oranges.

What is the magnetic grid? Are these the coils? if so, they are not a grid at all they are the outside shell effectively of the machine. Within the coils in the potential well, a much smaller knoted region of electrons (theoretically) that are to attract and not trap ions. All the deuterons (ions) are genrated outside the potential well either by high field emission, ion guns or filaments.

The ions infall to hopefully fuse. Those that don't will zip thorugh as in a normal grided fusor and supposedly go for another pass. They are trapped by the electrostatic field within the fusor itself and not the potential well.

I don't see how deuterons trapped in the potential well would ever fuse, unless we are talking a target machine that you could as easily make with a linear accelerator and deuterium target.

The only thing I see different in the polywell device and the common fusor is zero grid loss and supposedly zero electron loss and I seriously doubt the latter. Otherwise, this is just a farnsworth fusor with half the losses removed (in theory), but with no effective gain in fusion.

Any deuterons trapped in the polywell would not be energetic! Would not fuse and would ultimately neutralize.

I saw the various iterations of this thing and the grids were external on the spherical chamber. Once they left a spherical chamber and had a giant tank, the outer shell would still have to be a grid of sorts just inside the coils.

The coils will certainly not trap the ions as Dave has already noted.

Someone needs to define where the ions are created and how and where. Where is the ion trapping electrostatic field established? Between what and what. The assumption is the negative limit is the potential well or electron knot of high density. where is the positive shell or origin of the ions to establish a fixed positive point, which would be at some zero or ground reference to the electron knot. This knot mimes the inner grid in our machines..

Richard Hull
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Fusion is the energy of the future....and it always will be
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by stob »

Sorry about this fruit salad.

Yes the magnetic grid refers to the coils, I prefer the term grid because I'm not sure whether some other geometries that might be used, could still be called coils.
Anyway one can look at them as the shell of the actual machine.

With the potential well I was refering to most/all of the space inside the coils, basically everywhere were the potential gets smaller when moving towards the center. So when you were speaking of recirculating ions and I of ions trapped in the well we meant the same thing.

Pardon my ignorance, but what are the other 50% losses besides grid and electron? I was under the impression in a polywell electron loss would dominate, unless ion density was low compared to neutral density.
Did I overlook a loss channel?

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

Post by Derek »

OMG, I meant to provoke a mild discussion ... Oh well, all discussion is good!

I don't wish to enter discussion with Richard on what constitutes 'the machine' ... some might look at the core and others at the overall effect.

As I understand it the position is as follows:

Farnsworth notes that it might be a bright idea if ions (of whatever fuel) were encouraged to the centre of an electrostatic device to collide with each other (probability = small). The big problem with a simple two electrode device (albeit spherical) is that the ions have other ideas and like to whack into the cathode instead of each other. Recirculation of ions within the machine is thus severely limited.

Elmore, Tuck & Watson observe that it is possible to create a virtual cathode with increased electron density in the centre of a reversed polarity two electrode machine (with an outer cathode and an inner anode) thus creating a three electrode machine (with a virtual cathode). This means that ions contained within the anode cannot strike an actual cathode but only (possibly) an electron which is part of the virtual cathode. Unfortunately the electrons which create the virtual cathode have a nasty tendency to impact on the anode grid which attracted them initially (which is quite understandable given the relative charges/potentials).

Bussard notes that electrons are very susceptible to magnetic fields and will tend to shear away from them. Bussard suggests 'magnetic shielding' of the anode in the ELT machine configuration to prevent electron losses to high potentials. For some reason Bussard suggests that the magnetic shielding can also be used to confine the electrons in the virtual cathode region (apologies Carl W.)

The original question remains: is it a requirement that the electrons are magnetically confined or is it sufficient that they are discouraged from impacting with the anode grid?

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

Post by stob »

To the original question, confinement seems to be a requirement to me.
First there is always some unshielded surface, if the electrons are confined to the center there are less electron losses.
Second for meaningful power incredible ion and electron densitys are required. If the electrons aren't confined they will pull the potential on the coil faces far enough down to let the ions go outside. Once there the ions will be attracted to the vacuum chamber wall and the electron guns and since their density is incredible so will be the loss.

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

Post by Richard Hull »

We have to clearly define an anode in this device. A place where the OTHER power lead goes to. The cathode is being called the electron knot in the center which replaces the grid wire structure in the simple fusor. Fine. No problem here.

Where is the anode? What is the anode structure? To what do we connect the other power lead. In the simple fusor it is classically the SS shell or body of the device.

In a giant cylindrical tank, one would assume the anode would be a wire mesh grid at least! The magnetic coils would be just outside this large grid. If a sphere, the coils would be just outside the metal sphere's body.

However, if we are to inject electrons via a gun how would they get to the cathode potential well as this gun would have to reside out near the anode???

This is a mechanical thing. How do you impliment this in a real world? The norm would be as I noted above a regular fusor with and anode shell, external coils and normal high field ionization where ions and electrons are created all over the device but are mag focused or herded into the center magnetically to form the well.

Ion guns could be used to supply directed ions out near the anode perfectly with a mild bias.

We have to consider the ion current. For any ion current there is an equivalent electron current. No way to get around that one. Do we just squirt in x amount of ions and x amount of electrons and just let the thing run? Not even! What are the new realistic losses. Where do they come from and where do they go? I leave this as an exercise to the student. (Didn't you just hate that in college - Yeah, it forced you to think for once)

I worry that many in the theoretical discussion may not pack th' gear to have physically implimented an ion-electron circuit which is demanded of real world devices.

I have no theoretical issues with the elimination of electron losses within the polywell. It is more with the physical implimentation that I am concerned with, based on some of these discussions. Some seem to think there are ions present and there are electrons present, as if by magic.

Such free, charged particles are all part of an electrical circuit with a source and sink. Beyond the realization that there is a source and sink and that there is a perpetual circuit and current, there is a question as to how to implement the mechanical embodiment so that theory can be made reality.

The source and sink are just a must have mindset and part of any theoretical embodiment.

The physical embodiment of the wheelwork are where the fly is located in all such theoretical ointments.

I do believe that good ole' Carl Willis, Dave Cooper and myself have already voiced many of these concerns earlier in other polywell related posts.

This latter item is what stops perpetual motion machines and apparently what has always kicked thermal machines in the groin.

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Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by DaveC »

Perhaps I've missed something in the construction of Bussard's poywell device. The pictures show a polyhedral assembly of solenoidal coils that actually are more like thick rings, than solenoids. They have been called "toroids", but the windings are all oriented around an axis perpendicular to the plane of coils... which makes the field somewhat solenoidal as opposed to toroidal (or around the perpendicular axis).

The array of these coils (how many, I can't recall) is claimed to produce a closed magentic surface than will trap electrons, once they enter through one of the larger openings. It is part of the inner assembly, we are used to calling the "inner grid".

This is claimed through arm waving and some simulations to create a potential well of many kV.

One has to sit down and walk through the trajectories of some incoming electrons to see how this form of magnetic containment functions. It does NOT create a microscopic point in the center of high electron density and consequent high potential. That sort of concept requires stationary electrons. The concept of this device requires an electron trajectory reversal, so that the change in velocity creates a dynamic electron concentration. This would be the place, that would have a coulombic attraction to an inbound positive ion.

Depending on the exact electron flow within the polywell zone, there will be some sort of effective "concentration" of negative charge - hence the "potential well". Since the electrons will have position dependent velocities, dynamic charge densities will vary all around the interior. Only if a majority of the electron orbits pass through the center will the center be the high negative potential zone.

If you look carefully at Bussard's data and simulations you will realize this "well" is rather broad. Some simple calculations will indicate the magnitude of charge it must contain to have the potential depth needed.

Bussard does some circulating current estimations to indicate how much charge be in motion. I think he was talking about 100's of amperes..

As such the potential well structure resembles a simple electrodeless capacitor (or is it an inductor?) , of probably some fraction of a uF (or Hy) . The equivalent inductor idea runs into difficulties since the electron paths are not constrained to any one trajectory. The net current in some direction could well be close to zero... so.. an equivalent capacitor is the most likely component representation.

This is what is claimed to be the attractor or cathode for the positive deuterium ions.

To repeat my point above...a magnetic field sufficient to create the cathode condition is vastly insufficient to also contain the ions. A field strong enough to also produce closed ion orbits, would effectively isolate the two charges, creating two counter orbiting clouds of opposite polarity. Interesting, but not particularly useful for fusion.

What some do not seem to realize, is that in the simple Farnsworth IEC fusor, the inner grid emits electrons first by secondary emission from ion bombardment, and only after it has reached temperatures above about 2500K - very white heat-will it become a significant thermionic emitter . The original ions are created far out toward the fusor shell by the usual methods of gas ionization, at these pressures.

The ions thus created, travel inward. Many hit the grids, and cause additional... upwards of 2 or more electrons for every ions impact - while the rest pass on through the grid and out the other side.

Somewhere on this route, an occasional deuteron collides with an deuterium/or deuteron and produces fusion products. Since this does not happen very often, the yield as a percentage of total ions flown is very low

If the Bussard configuration were 100% effective in creating a lossless electron well, the only current it would draw, once the well was established, would the current of ion neutralization and fusion.

Predicting how big this current would be depends on your view on ion-electron probabilities inside the inner grid. Ignoring the magnet power, (since they could be replaced by permanent magnet assemblies), the device then resembles a simple capacitor with a bit of leakage, from a strictly electrical standpoint. The neutron & proton flux would account for some fraction of this presumably small leakage current.

Clearly, the polywell concept presumes a number of processes, which while feasible, may not perform the assumed functions in the device.

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

Post by Richard Hull »

As Dave points out, in the end, 'herein lay the rub'

Don't look for a smallish polywell machine at all and don't look to any successful prototype producing much more fusion per watt spent than a simple fusor. The size of even a medium sized successful prototype obviates this.

Fusion's issues are strictly 'failure to fuse' due to rotten probablistic collisions in a low density environment. Increase the density, coupled with increased fusion, and you are back to all the issues with a thermal device!

The way I look at fusion is that it is promised, but non-extant potential energy on the other side of the reaction. It is not making use of real, extant potential energy, but instead, the process of fusion might be termed, the promise of extant potential for potential energy.

It is like robbing Peter to pay Paul. Sort of a balloon credit scheme.

Not at all like fission or burning wood or other such true potential energy releases where the potential energy is real and extant just waiting for a trigger to release it.

The fusion we see done in stars is pretty much reliant on the potential energy exchanges between colombic and gravitational forces within matter and not due to the good offices of any external forces. We, on the other hand, are trying to make fusion happen using only external forces in all out schemes. Sort of backwards, if you will. We can certainly do this, but not to a net power level yet noted.

Stellar fusion is an exchange process we can't initiate or mechanize on the small.

I have always felt that Jupiter was fusing at some subliminal level to pour out more energy than it receives.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by stob »

The coils are the anode, cathodes are the electron guns, the shell of the device and (in a way) the electron cloud formed inside of the coils by the electrons.

Apart from the 'virtual cathode' in the center these are sinks respectively sources.

A big high voltage DC power supply is hooked up between the coils and the electron guns. The device shell is grounded and the electron guns are either grounded too or ideally biased to a potential slightly above ground.


Electrons starting from the e-guns should very likely go straight into the magnetic trap.
This is because the e-gun are placed on the axis, near them the electrical field points directly towards the center of the nearest coil. When the electrons get closer to the coil where the electrical field pulls stronger away from the axis they already have a substantial velocity towards the center and are in a strong magnetic field also pointing to the center. They should have a very good chance of not hitting the coils but entering the trap.
However electrons escaping the trapping are not likely to come out so nicely focused. If the device is good engineered most of them should return into the trap anyway, the coils are shielded by the magnetic fields and they won't have the energy to reach the shell unless they were upscattered. Still some will hit the coils and cause a big loss current for the power supply to struggle with.

Now to the fuel. In the simplest case it is just injected behind the coils and ionised by the fast electrons confined there.
The electrons knocked away from the fuel get confined by the magnetic field and heated by the other electrons via collision.
Eventually they manage to leave the trapping and hit the coils, they then need to be replaced by electrons from the e-guns. They also could recombine with ions so they wouldn't directly produce a loss current but still carry energy away, energy which was introduced to the system by the electron guns.
The ions could leave the confinement via upscattering and would thus (together with the electrons with which they were entered into the machine and which went to the coils) cause a loss current from the device wall and the e-guns to the coils.
Ideally the ions will stay confined until they fuse, the positive charged fusion products would have enough energy to leave the confinement. They would either hit the device shell or the electron guns, also producing a loss current or the coils in which case they cause no current.

In summary:
There is a big electron current from the electron guns into the magnetic trap heating the confined electrons inside it.
This electron current then goes from the inside of the magnetic trap to the coils.
An ion current proportional to the number of ions escaping or fusing goes from where the fuel is ionised to wherever the ions end up (mostly the shell). An aquivalent electron current goes from where the fuel is ionised to the coils.

Now as a side note, I don't think the electrons would form a small knot in the center. Since we want to have as many ions as possible there would also be as many electrons as possible, which means adding fuel until the magnetic trap is about to blow out. At that point electrons would be all over the space inside of the coils.

Of course the physical implementation is the problem, even if everything goes according to theory the engineering might not be feasible or feasible but totally uneconomical.
However I don't see the same fundamental limits as in the common fusor, where part of the losses are (it seems) proportional to the ion density.
I know a lot of loss channels weren't mentioned in this thread, but I think the most important ones in respect to scaling the machine up were considered and I can't see why a polywell shouldn't be able to get a better gain than twice that of a common fusor.

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

Post by jam »

Hello ,

I am back!
This is my first post since Sep/07 , but i did follow this site regularly. I can see that the Bussard device is being investigated again. This is just a reminder that if you look at my simulation done in mid 2007
----,The Bussard device: a 3D simulation : Part 2 ------
you will see what general parameters are required to get the famous well in place. If you remember, the maximum electron density i could get was around 1e10 / cm^3. This was done with 50,000 macro particles in the simulation.
Recently, i did a few more test where i could get the density up to 1e13 /cm^3. To get to fusion power level, the required density is around 1e16 to 1e17 / cm^3. It seems that in order to simulate this, at least 5,000,000 to 50,000,000 particles are required in the simulation to prevent well destruction. ------I don't have enough computer power to do this yet-----
-Alain
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil »

>The original question remains: is it a requirement that the electrons are magnetically confined or is it sufficient that they are discouraged from impacting with the anode grid?

Derek

I also wonder if this question has been answered in full or not at all in the heated discussion. Tom Ligon has actually operated the device and has given many descriptions of details here, from which I draw my understanding. I hope that I understand it correctly.


No, the purpose of the magnetic field is not to shield the anode against electron bombardment. Instead, the magnets guide electrons on closed magnetic field lines, which confine the electrons within the magnetic field. This is not a grid like in a Fusor, but an open assembly of electromagnetic coils.

The electrons can move on circular paths both inside and outside of the magnet assembly "MaGrid". The electrons move through and around the coils and then can return to the center cavity. The ions, however, are confined by electrostatic means inside the "MaGrid". If they leave this space, e.g. by scattering, then they are no longer confined.

The field of the "Magrid" is thought to excert a magnetic pressure on the electrons, which will cause a high concentration of electrons inside the "MaGrid". To my knowledge, whether this potential well actually forms has neither been shown in simulations nor measured in the actual devices. It does appear plausible however, it is just a question of actually measuring it.

Since the electrons need room to circulate around the the magnets, the vacuum chamber needs to be considerably larger than the "MaGrid". Permanent magnets can't be used here, because their field lines move through the magnet and would guide the electrons to a collision with the shell of the magnet, rather than around it.


>A magnetic field sufficient to create the cathode condition is vastly insufficient to also contain the ions. A field strong enough to also produce closed ion orbits, would effectively isolate the two charges, creating two counter orbiting clouds of opposite polarity.

This is Bussard's strike of genius here, or of whatever, that the ions are NOT intended to be confined by the magnetic field. They are confined by the electrostatic field of the electrons which are orbiting around the magnets. Most importantly, there is no grid in the way of the ions.

The area which can contain ions, the "whiffle ball", is fairly large. The way I see it, ions will be attracted into this area and quickly reach a Maxwellian thermal distribution. The temperature of this cloud will be defined by an equilibrium between electron heating and the energy loss by evaporation of fast ions from the well.

In effect, what we have here is a small star. It is held together by electrostatic rather than gravitational forces. If there is any chance that it can be sustained, with a net energy gain against all losses, remains to be seen.


MaGrid drawing from Tom Ligon:
>showimg.php?url=getfile.php%3Fbn%3Dfuso ... rating.jpg
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Derek »

Wilfried,

Thanks for this. I also wonder whether the original question has actually been answered (or even addressed).

My understanding from the various papers (including Ligon's) is that a principle objective was reduction of electron losses to the anode grid (co-axial to the magnetic field - as you point out later, not possible with permanent magnets). There appears to have been a suggestion/decision, somewhere along the way, that magnetic confinement of the electrons in the 'virtual' cathode could be enhanced by the same magnetic field and lead to additional efficiency gains: these potential efficiency gains are those which I originally questioned.

I agree that the electrons should be able to move on (substantially) parabolic paths both inside and outside the 'MaGrid' and further that the ions are confined by electrostatic forces. As you point out ion scattering may result in ions successfully leaving the electrostatic confinement area ... a loss to the system.

I still question whether the magnetic confinement of electrons is required, although I concur that such an effect may occur (if the magnetic fields are chosen carefully). Too effective a magnetic confinement of electrons will also lead to magnetic exclusion of electrons thus leading to problems in the creation of the virtual cathode ... this may be one of the effects concerning Richard H. i.e. how does one get a significant charge into the centre of the polywell anode?

I share your view that there is a requirement for 'true' real space around the anode ('MaGrid'): this is intuitive but I haven't formulated any understanding of exactly how large this space needs to be.

I think we should all be able to agree that electrostatic confinement of ions is seriously more effective (joule for joule) than magnetic confinement ... well it just is isn't it? (or have I lost my marbles entirely and forgotten something about mass charge relationships somewhere?)

Ummm ... well, if we rapidly reach a Maxwellian distribution then we're in deep poop because that is the central assumption in the Rider analysis. I'm not entirely sure that I can agree with Rider since his conclusions seem to be closely dependent on his initial assumptions (one of which is that the plasma will rapidly reach a Maxwellian distribution). If we agree that a Maxwellian distribution will rapidly occur then Rider's conclusions follow and we should all give up forthwith ... ! (well perhaps)

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

Post by Brett »

Hi there! Been lurking mostly, trying to wrap my head around the polywell concept. Here's my tentative understanding of it's evolution:

The original concept was based on currents around the faces of a truncated cube, producing a confinement field for electrons which would be very effective, having only point cusps. Thus you could create a virtual cathode deep enough to electrostatically confine the ions entirely within the polygon. No circulation of ions, no loss, and you've solved the fusion problem.

Spent some time attempting to visualize the field lines on my cad station, and I think I see why Bussard abandoned this to go to coils that had space between them, and thus line cusps: The original polywell produces only point cusps if you're looking at the field vector, but the field *strength* goes to zero along lines from the center to the vertices. Hence bad electron leakage to the surface of the coils.

So, we have the wiffle ball instead, with point cusps at the centers of the coils, and line cusps between them, and a bit more difficulty confining the electrons. So you can't confine the electrons well enough to make your virtual cathode deep enough by itself to confine the ions to entirely within the coils, they're going to circulate, and some fraction of them WILL hit the coils, the field not being as effective at deflecting them as with the electrons.

Problem with this is, the probability of fusion on each go around is quite low, so you can tolerate virtually no loss to the circulation. I don't think it will work if you can't get the electrostatic confinement of the ion cloud to be entirely inside the coils, without circulation. If nothing else, the losses on the lines supplying current to the coils will kill you.

But, here's my thought: Why not confine the electrons with a toroid? Use a ring shaped virtual cathode instead of a spherical one?

Well, because you're injecting the electrons through the cusps, of course, and a toroid doesn't have cusps. But there might be ways around that; For instance, you could inject *negative* ions, at an energy where they'd essentially come to a halt at the virtual cathode, and contribute net negative charge when the collisions there stripped them to deuterons.

Or alternatively you could try to set up some kind of resonance in the plasma, where it was average net neutral, but alternated between having a virtual cathode, and a virtual anode. You'd only be getting fusion half the time, of course.

Or, use a pinched solenoid geometry, which gives you two point cusps you can fire your electrons in through.

Anyway, my tentative conclusion is that the polywell won't work unless you can get a deep enough virtual cathode that the ions are confined inside the coils, and don't circulate. So we ought to be looking for geometries that are better for *confinement*, not circulation, because we don't really want circulation outside the coils.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon »

Richard Hull wrote:

> Someone needs to define where the ions are created and how and where. Where is the ion trapping electrostatic field established? Between what and what. The assumption is the negative limit is the potential well or electron knot of high density. where is the positive shell or origin of the ions to establish a fixed positive point, which would be at some zero or ground reference to the electron knot. This knot mimes the inner grid in our machines..

The ions are accelerated between the field created by the electrons at the center and the positively charged grid.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon »

If you inject the D-D gas inside the positive grid the gas ionizes. The ions are attracted to the virtual cathode. Electrons are stripped off in the process.

With sufficient fusions alphas leaving the system will leave their electrons behind maintaining a net negative charge in the reaction area.

Electron guns may be needed for start up. If they are needed for running the device will not generate net power - in my estimation.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon »

Look up double layer.

It has been known in electron tubes since the 20s.

You can't understand this device without a deep understanding of vacuum tube technology. Which is generally a lost art.

BTW the Japanese IEC folks proved the double layer (well formation) in 1999 with laser probes. Although Langmuir probes had been used since the 20s to map out charge vs distance in tubes. The problem with Langmuir probes is that they disturb the field so that the results are not definitive.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon »

True. You need a significant size to produce net energy. Unless POPS gives you enough of a boost - sadly POPS is easy and yet table top experimenters seem uninterested. A very sad state of affairs IMO. In any case the POPS boys - Nebel and Park - are continuing Dr. B's work. There is hope.

The key is raising the density inside the reaction space without everything thermalizing. Bussard thought he had that figured out. We shall see.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon »

Thermalization of ions happens near the grids where the energy is low.

Thermalization of electrons happens in the center where their energy is low.

Thus the energies are continuously renormalized.

The plasma so created tends to naturally form bunched beams. Those that have tried can listen to it on a HF receiver. With a little help from POPS it should be possible to add energy coherently to those beams increasing the collision density.

So add RF engineering to the talents required.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil »

>I still question whether the magnetic confinement of electrons is required, although I concur that such an effect may occur .,.

Your question, if confinement is needed or just magnetic shielding of the grid, refers to the same thing.

The electrons are not confined forever, they will slow down and all of them will hit the "MaGrid" eventually. Confining the electrons in the magnetic field for some time has the effect of reducing the current which flows to the metal shell of the magnet structure AND increases the e-beam current which flows around the magnets, possibly many thousands of times.

The "MaGrid" is a magnetic storage trap for electrons, like Dave has pointed out. If the magnetic field is strong enough to hold the electrons for 10000 orbits, then the current flowing in the "MaGrid" assembly will be 10000 times stronger than the current delivered by the electron beam sources. This reduces the power needed to set up the electrostatic field to confine ions.

Tom Ligon has observed that after a while, the e-beam current suddenly drops, presumably when the "MaGrid"s electron trap is full. "All hell broke lose" when he switched the magnets off in this state.

Without the magnets, we have Farnsworth's "Multipactor" design, with crossing e-beams which form a potential well and also no need for a grid. Such beams are capable of melting and evaporating the hardest materials, but were not enough for fusion.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull »

From the foregoing and as no one posting above has ever worked a polywell device, there seems to be a lot of ideas about how it might really be implemented.

If the grid structure, (the coil body), is the positive return then it will have to be made proof against heating which will occur from not only its own power input, but electron leakage, up converted ions and neutral bombardment. This magnetic structure demands a lot of power just to establish the field and a lot of cooling. It doesn't need parasitic leakage heating. (engineering and mechanical issues).

As Stefan mentioned above in his analysis, there are a lot of leak/loss paths. Some are common to even a simple fusor while others are generated by this polywell design and perhaps peculiar to it. They will drift out of the woodwork if the polywell is persued to any real degree.

Doubling the energy output per watt input over a fusor is a pyrrhic victory to say the least.

It looks like more ever insidious losses as in all fusion schemes. Do we just just keep making it bigger like the tokomaks and stellartors with the latest fixes in place on this newer device until we create a new billion dollar boon-doggle?

Real watts created in any device per unit viable volume would certainly thermalize this dream. Sometimes I think thermal is, indeed, the way to go, even if it is just to show it can't be done! (At some future point and after more big bucks are tossed into the fusion rat hole.)

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Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil »

So many here discussing the emperor's new clothes and with Richard, as always, firmly convinced that the guy is naked.

Apparently everyone has a different idea of what the "Polywell" is and how it might work. Part of the blame goes to Bussard who could have described it concisely. Instead of chasing a spectre I would much prefer to build such a device and discuss it in the process.

Richard, why do you think that the "Polywell" will be twice as efficient as the fusor?

The ions can fuse as long as they remain captured and if they are thermalized, then the energy of non-fusing collisions will not be lost. However, the fastest ions can escape from the well and take their energy with them.

There may be many paths to a successful fusion reactor. If Bussard's concept increases efficiency by 10000x compared to a Fusor, then we are half there, on a log scale at least. Scaling the thing up might do the rest. If nothing else works, it would still be a hell of a neutron source.

At present, unfortunately, there is no evidence that it works at all, just like Nebel's POPS, the Sandia Z-machine abused for fusion, and so on. All show minor effects which are then extrapolated to bombastic performance. The Z-machine at least sets all kinds of records unrelated to fusion.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull »

.....Richard, why do you think that the "Polywell" will be twice as efficient as the fusor?

I do not look at the polywell as increasing fusion over the stock fusor though some might hope that this is the case.

What is claimed, but not proven, is that the polywell will virtually elimenate the electron loses suffered in a common fusor.

These losses were about half of the energy sucked up by a fusor. If these go away, you are now at a point where energy in to energy out is up by a factor of two. (Doubled the efficiency)

OOPS! We sorta', kinda, forgot that high current coil, magnetic field bill on the energy drag down, didn't we? Apparently we dropped the soap in the shower without watching out for the other guys in there with us. There is always another new loss jockeying for position that tends to screw th' pooch in the fusion reality chain. These are created in a virtual defacto manner with each new brainstorm that supposedly will plug the leak in the dike used to contain fusion.

Man is a creature of endless habituation once on the trail of something that looks like gold. The degree of repeated torture and loss of fortune willing to be suffered in getting at the golden substance separates the interested prospectors into strata that range from the true believers, 'no matter what', to those who claim to see only 'fools gold'.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by stob »

That's not quiet what is claimed.
The claim is that ion losses are virtually eliminated and electron losses remain constant with increasing magnetic field and go up with the square of the device size for a given geometry and drive voltage.

In a contest between a fusor and a polywell, both the size of an average fusor I doubt the polywell would stand a chance in terms of gain.
However the question is how it scales to higher fusion power.

Since for net power the ion density has to be increased by orders of magnetitude it's important to see how ion losses scale and because the reactor has to be quasi neutral the same goes for electrons losses. If these two don't scale very favorably (like claimed for the polywell and unlike the common fusor) there's no chance of net power, the reactor will prefer evaporating.
Losses which don't directly depend on plasma density probably won't increase as strongly as the ion density when scaling up, so they aren't quiet as interesting, but still have to be looked into of course.

Now I'm not sure what this other half of the losses consists of. Will these scale up dramatically with size and plasma density or are they more along the lines of vacuum pumps, measuring equipment and loss in power supplies?

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

Post by SJSVOB »

>We sorta', kinda, forgot that high current coil, magnetic field bill >on the energy drag down, didn't we?

Wasn't this the reason they wanted to use superconducting coils?
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