Making Electricity with the p-B Polywell

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

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ravingdave
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Post by ravingdave »

93143 wrote:
ravingdave wrote:Perhaps I am mistaken, but what becomes of the electrons originally stripped off the fuel when it is ionized ?

I think the current is between the collector grid and the ionizing guns for the fuel, which I think are at MagGrid potential, but the current flow is from the point at which the electrons are stripped to where they are recombined at the collector.
I'm just lumping all that in as the "magrid". The potential differences within the magrid/fueling assembly system should be small. The assumption was that the fuel was ionized by ECR slightly inside the magrid, but there can be other arrangements.

The upshot is that that system - however it is configured - has to lose electrons through a wire at exactly twice the rate at which it loses alphas, or else fueling (ions+electrons in, vs. just ions out) will cause a negative charge buildup.

If I understand you correctly, I think that is right. An Alpha is a helium atom without electrons. Helium has a +2 charge. It requires 2 electrons to neutralize the charge. The Alpha has to combine with 2 electrons to become a "neutral."

I think the term "lose" is misleading. I think the electrons which combine with the alphas are the same electrons stripped off of the hydrogen and boron atoms before fusion occured. These electrons ought to be distinctly different from the electrons emitted by the electron gun for purposes of charging the wiffleball.

In any case, 1 electron is stripped off of the hydrogen fuel atom, and 5 electrons are stripped off the boron fuel atom. Fuse the hydrogen and boron and you create 3 helium ions which need 6 electrons.


In effect, the reactor temporarily strips electrons from fuel atoms, the process of fusion converts them to helium then blows them apart at high velocity, and the then kinetic energy of the ions allows them to force a high positive charge against a highly repelling force in order to pull electrons through a resistive load to reach that highly charged collector grid. The 6 original electrons, having to go somewhere push their way through the wiring to get at that very highly charged source of protons.

The same 6 electrons stripped off originally satisfy your requirement that each alpha particle must aquire 2 electrons to become neutral.

Seems reasonable to me. Did someone claim otherwise ? I must say I sometimes get "brain strain" trying to keep up with the current thread.


David

93143
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Post by 93143 »

ravingdave wrote:Did someone claim otherwise ?
It sure sounded like it to me...

But no, that's right. Just a particle accelerator in reverse.

The intermediate grid doesn't participate in the current exchange; it's just there to shape the potential well in order to allow recirculation.

TheRadicalModerate
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Post by TheRadicalModerate »

93143 wrote:All I'm arguing is that the current flow for the output power is between the magrid and the collector, not between the magrid and the decelerator or the collector and the decelerator.
Would I be correct if I said that you think that power can only be generated through the neutralization current?

TheRadicalModerate
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Post by TheRadicalModerate »

ravingdave wrote: You can get a volage increase without particles recombining !
This just makes the pull between them stronger. It means that they want to recombine more forcefully. The current is caused by recombination.

The decellerator grid thing creates a higher voltage because as they approach the collector grid, the pull on the electrons in the system gets stronger and stronger, even with no current flowing.

David
OK, another vote (for whatever votes are worth) for the power current being the same as the neutralization current.

Simon thinks that's wrong, I think. He claims that we can get a current merely from the induced potential difference. I can't see how without violating KCL.

tombo
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Post by tombo »

Wow, I thought this part was was simple.

It only gets hard when we want to extract the energy efficiently from the 2 (or is it 3?) different populations of alphas.
Each of which has a spread out energy distribution.
(That was why I mentioned mass spectrometers & electron microscopes.)

How we handle the charge imbalance left in the well by the departing alphas depends on the electron current lost to the Magrid.
If it is small (as we hope) then we will need to create a way to extract them without losing their energy. (assuming the B & H are supplied as neutrals)
This will be one of the interesting control handles for us to twiddle.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

MSimon
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Post by MSimon »

TheRadicalModerate wrote:
ravingdave wrote: You can get a volage increase without particles recombining !
This just makes the pull between them stronger. It means that they want to recombine more forcefully. The current is caused by recombination.

The decellerator grid thing creates a higher voltage because as they approach the collector grid, the pull on the electrons in the system gets stronger and stronger, even with no current flowing.

David
OK, another vote (for whatever votes are worth) for the power current being the same as the neutralization current.

Simon thinks that's wrong, I think. He claims that we can get a current merely from the induced potential difference. I can't see how without violating KCL.
Correct. If you can induce a voltage (charge a capacitor) you can extract power. It is a DC accelerator in reverse.

If the particle does not induce a voltage where does the energy go (in a decelerator)?

Where does the energy come from in an DC accelerator? Certainly not from the initial ionization of the particles. It must come from the DC grids. If so then operating an electrostatic accelerator in reverse will supply current (assuming constant voltage) to the DC grids.

What is KCL?
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TheRadicalModerate
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Post by TheRadicalModerate »

MSimon wrote:Correct. If you can induce a voltage (charge a capacitor) you can extract power. It is a DC accelerator in reverse.

If the particle does not induce a voltage where does the energy go (in a decelerator)?

Where does the energy come from in an DC accelerator? Certainly not from the initial ionization of the particles. It must come from the DC grids. If so then operating an electrostatic accelerator in reverse will supply current (assuming constant voltage) to the DC grids.

What is KCL?
Here's why I don't think the "particle accelerator in reverse" argument holds water. In the particle accelerator, when you charge the electrode and push the particles away from it, the voltage on the electrode drops and conservation of energy is satisfied. The voltage drop causes a current to flow into or out of the electrode. However, the event is now over; you've got plenty of time to balance the books, because the particles, like Elvis, have left the building.

In the polywell, two things are different:

1) The voltage on the electrode is increasing due to the electrostatic induction, not decreasiing.

2) That increase is continuous, rather than the transient event in the accelerator.

So, you've got a greater and greater positive voltage building up on the electrode, which is, indeed, inducing current (electrons) to flow from ground through the load, generating power. But, at some point, the capacitave limit of the electrode is reached and no more electrons can flow into it. At this point, Kirchoff's Current Law (KCL) says that the sum of the currents at any node in the circuit sum to zero, so, since no electrons are flowing out (it's a big honkin' positive voltage wrt ground, after all), no electrons can flow in.

Of course, what really happens is that the eventually electrode arcs somewhere. Now current can again flow (into the smoking ruins).

However, there is one way for the electrons to flow out of the electrode: They can combine with the alphas and effectively stop being free electrons. That's why I continue to think that, in steady state, the neutralization current is the only current you have.

Please tell me where the electrons go.

ravingdave
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Post by ravingdave »

tombo wrote:
How we handle the charge imbalance left in the well by the departing alphas depends on the electron current lost to the Magrid.
If it is small (as we hope) then we will need to create a way to extract them without losing their energy. (assuming the B & H are supplied as neutrals)
This will be one of the interesting control handles for us to twiddle.
Why would there be a charge imbalance in the well ? The fuel ions dropped into the well didn't add electrons when they entered, nor take any away when they left. Their electrons were stripped off by the ionizing process in the fuel emitters.

Maybe I misunderstand this, but doesn't the hydrogen and boron atoms part with their electrons just before they fall into the well ?

If that's true, the recombination current will be that of the alpha particles (which used to be hydrogen and boron) recombining with their fomer electrons.

Won't the electron gun-MagGrid current be a separate system ? If I am misunderstanding this, help me get it straight.


David

ravingdave
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Post by ravingdave »

TheRadicalModerate wrote:

Here's why I don't think the "particle accelerator in reverse" argument holds water. In the particle accelerator, when you charge the electrode and push the particles away from it, the voltage on the electrode drops and conservation of energy is satisfied. The voltage drop causes a current to flow into or out of the electrode. However, the event is now over; you've got plenty of time to balance the books, because the particles, like Elvis, have left the building.

In the polywell, two things are different:

1) The voltage on the electrode is increasing due to the electrostatic induction, not decreasiing.

2) That increase is continuous, rather than the transient event in the accelerator.

So, you've got a greater and greater positive voltage building up on the electrode, which is, indeed, inducing current (electrons) to flow from ground through the load, generating power. But, at some point, the capacitave limit of the electrode is reached and no more electrons can flow into it. At this point, Kirchoff's Current Law (KCL) says that the sum of the currents at any node in the circuit sum to zero, so, since no electrons are flowing out (it's a big honkin' positive voltage wrt ground, after all), no electrons can flow in.

Of course, what really happens is that the eventually electrode arcs somewhere. Now current can again flow (into the smoking ruins).

However, there is one way for the electrons to flow out of the electrode: They can combine with the alphas and effectively stop being free electrons. That's why I continue to think that, in steady state, the neutralization current is the only current you have.

Please tell me where the electrons go.

Sorry to interject once again, but if the alphas get to the collector grid and DON'T get an electron to neutralize them you have in effect a capacitor.


The collector becomes one plate of a capacitor and the rest of the machine becomes the other plate of the capacitor, and all the space between becomes a dielectric.

Energy can only be extracted when you create a current flow by putting a load between the collector and the fuel ionizing emitters.


Two opposite charges separated without a current flow between them is a capacitor. Period.


I'm saying the same thing you are, just in a different way.



David

93143
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Post by 93143 »

ravingdave wrote:Maybe I misunderstand this, but doesn't the hydrogen and boron atoms part with their electrons just before they fall into the well?
Yes. I'm still not completely sure where all the electrons in the magrid part of the system come from, but here's my current theory:

With fuel ionization by ECR, the result is a cold population of electrons stuck at the top of the well just inside the magrid. However, most of the electrons in the well have corresponding ions (quasi-neutral plasma). It wouldn' be much of a wiffleball if most of the electrons were cold, and the energy from the hot ones isn't enough to draw all the fuel electrons up to magrid energy, even if that could be done without thermalizing them.

Therefore the vast majority of the wiffleball electrons have to be gunned electrons, not fuel electrons. This means there must be some loss mechanism, whether engineered or accidental, that preferentially sucks out the cold fuel electrons as they try to build up (or doesn't let them enter in the first place, but that requires ion guns and then ion confinement becomes dubious).

It also means that the startup current (and power) for a wiffleball would have to be enormous, since you have to supply ALL of the electrons for the plasma, not just the differential, at high energy.

Apparently Dr. Bussard thought two-color electron effects would be important for something or other. This may be where the two colors of electrons come from.

@TheRadicalModerate: I wouldn't say the neutralization current is the only current in the system - it's just the only non-transient non-parasitic current in the system. It's induced over a high voltage by the operation of the direct conversion system, and coincidentally when you multiply the neutralization current (69 amps for 100 MW worth of p-11B fusion products, if my calculations are correct) by the voltage it's hauled across by the high-energy fusion products (a bit less than 1.5 MV on average, given multiple collectors in an optimal arrangement), you get the fusion power. (Losses to the magrid will reduce it, of course.) So yes, I agree that the neutralization current is the power current.

Also, it's perfectly possible to build a continuously operating particle accelerator. It would work a lot like a direct-conversion Polywell in reverse...

classicpenny
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Polywell electric webpage

Post by classicpenny »

Concerning your many comments with regard to the basic details of “How the pB11 polywell makes electricity” at

http://www.polywellnuclearfusion.com/Cl ... ctric.html

To TheRadicalModerate: I have changed the collector to one solid shell, so the alphas won’t miss. Thank you!

To 93143: I have moved the trap grad further away from the magrid, to avoid impairing electron recirculation. Thank you!

To charliem: I have attempted to use “Trap” and “Collector” according to your proposal for standardizing the naming. Thank you!

To ravingdave: Agreed that decelerator and collector should be one and the same, and I also agree completely that we should think of the electrons as flowing from the ion sources (gun?) to the collector, but why did you suggest “Repeller” grid instead of Trap grid? – you said yourself that it does more than just repel; and most everyone here seems to be pretty consistent now on “trap” grid as charliem defines it. In the interest of good communication – which we definitely need more of, I believe we should stick with trap grid.

I also have two questions:

One- There seems to be a lot of ongoing confusion (in terms of “conservation of charge”) about where the electrons that neutralize the incoming MeV alphas are coming from. I am wondering why so many people are still ignoring the ION SOURCES, and are instead continuing to suggest that the electrons might somehow come from the magrid or the trap grid or both? Isn’t it true that “rugged and survivable ion guns adequate for the needs of large machines” were at the number 2 position in the “To Do” list in the Valencia paper? Also, just a few paragraphs further down, Dr Bussard discusses the need for “a team of 3 people working for 4 years” to develop ion guns, etc. It seems to me that once these working ion sources are in place, the origin of the electrons becomes obvious: the electrons that neutralize the incoming alphas are the electrons that are stripped from the boron 11 and the hydrogen in the ion guns. Is there some obvious fallacy to this that that ravingdave and I am missing here?

Two- I believe that I understand what the Trap grid does: it puts a Faraday cage around the magrid so the re-circulating electrons will not be distracted by the Collector grids; and the Trap sets up an electric field between the Trap and the Collector for decelerating the alphas. But why are a separate deceleration grid and collector shell being proposed? I do not understand why the collector shell can’t also be the deceleration grid. Indeed, I believe that much of the confusion these past few days is related to this idea of having separate collector and decelerator grids.

Suggestion – if it IS necessary to have separate collector and decelerator grids, would it be possible to prepare a diagram that graphically illustrates all this business of the +999,999V decelerator and the 0V collector plate inside the cylindrical grid – I’m afraid I am completely bamboozled by it all – and I DID grow up with vacuum tubes! I took high school electronics in 1958-59 – we used Elements of Radio by Marcus and Marcus. We did all kinds of breadboarding with vacuum tubes, so I think I can think like an electron – but that doesn’t mean I haven’t been more than a little confused lately. Speaking for myself, I believe a good diagram would help a lot.

Also, to aero: Thank you for the NASA HV Alpha Cell piece – it looks promising.

93143
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Re: Polywell electric webpage

Post by 93143 »

classicpenny wrote:One- There seems to be a lot of ongoing confusion (in terms of “conservation of charge”) about where the electrons that neutralize the incoming MeV alphas are coming from. I am wondering why so many people are still ignoring the ION SOURCES, and are instead continuing to suggest that the electrons might somehow come from the magrid or the trap grid or both? Isn’t it true that “rugged and survivable ion guns adequate for the needs of large machines” were at the number 2 position in the “To Do” list in the Valencia paper? Also, just a few paragraphs further down, Dr Bussard discusses the need for “a team of 3 people working for 4 years” to develop ion guns, etc. It seems to me that once these working ion sources are in place, the origin of the electrons becomes obvious: the electrons that neutralize the incoming alphas are the electrons that are stripped from the boron 11 and the hydrogen in the ion guns. Is there some obvious fallacy to this that that ravingdave and I am missing here?
If there are ion guns, the neutralization current will come from the ion guns. I don't know what kind of ion guns Bussard was thinking of, since the ions have to be insufficiently energetic to leave the magrid, which implies that the ion guns are INSIDE the magrid...

But this is a minor detail - the i-guns, e-guns, magrid, and anything else within the trap grid are all at about the same potential, and electrons dumped to ground from there will be at -2 MV (very roughly) with respect to the electrons arriving at the collector.

One thing that WON'T happen is fuel electrons leaving via the trap grid as you've pictured in your document. I don't see how that could occur, unless some weird mechanism exists for injecting ions from there without killing confinement...
Two- I believe that I understand what the Trap grid does: it puts a Faraday cage around the magrid so the re-circulating electrons will not be distracted by the Collector grids; and the Trap sets up an electric field between the Trap and the Collector for decelerating the alphas.
Those are sort of the same thing. If the trap grid weren't there, the alphas would still decelerate fine, provided the potential difference between the collector and the magrid/fueling assembly was maintained. But for that to happen, the magrid would have to acquire a net negative charge, and the electrons would not recirculate, as you have noted. So we need to enforce a potential surface slightly lower than the magrid potential somewhere between it and the collector, so the magrid can stay positively charged.

You've basically got it, I think.
But why are a separate deceleration grid and collector shell being proposed? I do not understand why the collector shell can’t also be the deceleration grid. Indeed, I believe that much of the confusion these past few days is related to this idea of having separate collector and decelerator grids.
How would you do that? The alphas are at (slightly more than) full speed when they reach the trap grid. There has to be another metal surface a couple of MV away from it (necessitating either insulation or empty space to prevent arcing) to do the collecting.

Hang on, are you using the terms the same? The decelerator grid is the same thing as the trap grid. Does that help?

classicpenny
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Re: Polywell electric webpage

Post by classicpenny »

Hang on, are you using the terms the same? The decelerator grid is the same thing as the trap grid. Does that help?
This is why it is so important for us all to standardize the language. My suggestion would be to drop the use of "decelerator grid" entirely because I have seen it used as a synonym for both the Trap grid and the Collector grid; and doing so causes a LOT of confusion. For similar reasons, I would suggest that we also drop all the other words that some of us have been using as synonyms for "Trap" grid, and use trap grid only.

If it turns out that we really need to have a "decelerator" grid that serves a completely different purpose from either the trap or the collector grids -as I said before- I would like to understand it; and I believe a good diagram would help a lot.

classicpenny
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Re: Polywell electric webpage

Post by classicpenny »

One thing that WON'T happen is fuel electrons leaving via the trap grid as you've pictured in your document. I don't see how that could occur, unless some weird mechanism exists for injecting ions from there without killing confinement...
I have a diagram next to the "Third" step that shows "batteries" pumping the stripped "fuel" electrons from the (green) ion sources into the ground. Is that what you mean? (I don't see the ion sources as having anything to do with the trap grid.)

The only connection to the Trap grid that I show is a battery that puts a -20kV bias on the Trap; and (I hope) that has nothing to do with the fuel ions. Truth be told, I have no idea why the Trap bias should be -20kV; I just have a vague memory of someone proposing that somewhere in Talk-Polywell.

MSimon
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Post by MSimon »

TheRadicalModerate wrote:
93143 wrote:All I'm arguing is that the current flow for the output power is between the magrid and the collector, not between the magrid and the decelerator or the collector and the decelerator.
Would I be correct if I said that you think that power can only be generated through the neutralization current?
No.
Engineering is the art of making what you want from what you can get at a profit.

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