Where do the electrons come from?

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

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tonybarry
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Where do the electrons come from?

Post by tonybarry »

Hello All,
I am attempting to understand the polywell as best I can, and have encountered a difficulty that I cannot get around as yet.
In an operating polywell, we have a magnetic field confining a cloud of electrons. The electrons are supplied from "outside", pushed into the cavity by around 20kV (maybe more).
Into this cloud, we drop ions (i.e. atoms which have lost an electron) and they fall to the centre and move around till they fuse with something. In the D-T reaction, the species are deuterium nuclei and tritium nuclei. In the p-B11 reaction, the species are protons (hydrogen nuclei) and boron ions.
So far, so good. Now the fusion reaction produces helium nuclei which zoom off, out of the polywell, and into a collector grid on the outside which is charged to around 2MV (a substantial charge indeed). I assume this is a positive charge. i.e. it has an absence of electrons which slows the helium nuclei down as they approach, before the nuclei interact with the grid, pull electrons from the already positive grid, neutralise the net 2+ charge on each helium nucleus, and leave us with helium gas which we scavenge off out of the chamber.
But where is the return circuit? There's a net positive. This thing just eats electrons and becomes more positive as time goes by. We make positive ions in the b11 and the proton (two, per reaction), but we get three helium nuclei out of that reaction (i.e. six positives), hence a net four positive charges per reaction p + B11.
Where do the balancing electrons come from? In conventional electric operation, we don't create electrons, we just persuade them to move by chemical or magnetic trickery. We *can* produce such things as net positives ... but they are static charges and I don't see how we neutralise them. If we run this thing for a while, we'll eventually build up a huge static charge proportional to how much fusing we've done.

Note:- the following page:-http://powerandcontrol.blogspot.com/200 ... usion.html mentions the following:-

" ... Which is how the current is generated: you basically create an electron "vacuum" as the nuclei pull electrons out of the biased grids, which is then replaced by the circuit's ground."

It's been my experience that the circuit ground is not an infinite source of anything. Things will gradually take on a static charge, and this will make all kinds of weird things happen.

Any thoughts?

Regards,
Tony Barry
Last edited by tonybarry on Sat Jul 14, 2007 1:32 pm, edited 1 time in total.

JoeStrout
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Re: Where do the electrons come from?

Post by JoeStrout »

Dr. Bussard has said that a polywell reactor (using a collector grid) will appear as a giant battery to the outside world. By this I assume he means that it generates a steady DC current. So, the electrons come from the rest of the circuit, i.e. whatever this giant battery is plugged into. If it weren't connected to anything, then I think we would have the problem you describe, just as a battery stops making current when it's not in a circuit.

But I'm not an EE, so maybe I'm all wet here. Does this seem to help?
Joe Strout
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Zixinus
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Post by Zixinus »

My only understanding is that the electrons come from a cathode ray-like tube, and the trick to not make the cathode ray a interfere with the field lines is to quickly "close" it down. This has to be done regularly because some electrons are always lost due to losses (hitting the cusps I recall?).

tonybarry
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Post by tonybarry »

Static charges are common in this world - think lightning, "zaps" from car door handles, etc. They aren't really used in regular power supply because they're temperamental. They create mischief, all kinds of weird effects, corona discharges, etc. In small doses, they're a nuisance (e.g. the door handl zap). In large doses, (lightning) they are lethal. The polywell would make large doses of positive charge (2MV, well above lightning which runs around 300kV http://science.nasa.gov/newhome/headlin ... un99_1.htm) and if this is not a closed circuit, then it's an open circuit - a static charge. The ground will bleed electrons into the circuit, easily at first, then gradually less easily as the static charge builds up and the surrounding positive field increases. Even if we build the device on the seashore, and use the sea as the electron source, it will still be a problem.

Again, the net positive charge comes from the fusion reaction - we get two electrons from ionising the hydrogen atom to a proton, and the boron atom to an ion ... but we must supply six electrons for each fusion product (3 x He nucleus = 6). Net loss is four electrons per fusion reaction.

Now what I don't know about this sort of stuff is considerable. There may be some way to create electrons in a separate chamber, which supplies the shortfall. A nuclear process, that is. Or the polywell may create the electrons in some other manner which is too obvious for Bussard et al to discuss - some nuclear seconday reaction which is accepted by all but unknown to me. I hope this is the case.

Regards,
Tony Barry

tonybarry
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Post by tonybarry »

Zixinus, thank you for your thoughts. The electrons that get forced into the polywell by the 20kV accelerator are also "losses" but as far as I understand they do not get consumed by the reaction all that much - the helium nuclei when they are made are going too fast (?comment?) to grab them, except perhaps if they run into them directly - a collision - which will produce radiation.

However, the alpha particles represent the major energy output of the polywell, and by a neat setup are caught electrostatically on the collecting grid. If we let them smash into things, we'd get all kinds of radiation (I don't know what, it depends on what they run into) and that might include electrons which would serve to balance out the static charge. Or maybe not.

Again, this is my intuition, and what I don't know is simply astounding.

Regards,
Tony Barry

drmike
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Post by drmike »

Howdy Tony,

The idea of the Bussard fusor is to use the magnetic field to hold electrons so you get a negative potential in the center. That entices the positive nuclei to accelerate into the center. By holding the magnet rings positive, you reflect any fast moving ions back towards the center, and the design is supposed to ensure you don't thermalize.

For fusion, all the electrons from an atom need to be stripped off. For D and T it's only one electron, but for the Boron atom you've got 5 to strip off. If you can get that to fuse, you get the helium nuclei (alpha particles) coming off at high energy. Eventually they have to neutralize and get back down to local temperature (the walls of the vessel are cold!)

Since like charges repel, the ideal situation is a matched number of electrons and charged particles. Even a slight imballance can produce large forces, and by creating a slight negative charge in the center the ions can slam into each other and fuse. Stripping them first down to nuclei helps get higher charged particles to accelerate toward a negative center (but when they get close to each other they repel, so Boron - Boron reactions won't happen.)

pstudier
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Post by pstudier »

drmike wrote: The idea of the Bussard fusor is to use the magnetic field to hold electrons so you get a negative potential in the center. That entices the positive nuclei to accelerate into the center. By holding the magnet rings positive, you reflect any fast moving ions back towards the center, and the design is supposed to ensure you don't thermalize.
This can't possibly work. The magnet rings form a Faraday cage (http://en.wikipedia.org/wiki/Faraday_cage ), so there is no electric field on the inside from any charge on the magnets.
Fusion is easy, but break even is horrendous.

tonybarry
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Post by tonybarry »

Hello drmike,
Thank you for the post. If I understand you correctly, the boron ions need to be taken down to a net charge of 5+ before being dropped into the polywell. That gives five electrons from boron, plus one from the ionisation of the proton, equals six electrons (6-).

We have six electrons to return to the positive collection plate, and the reaction product is three helium nuclei (alpha particles) each net charge 2+, giving us six repositories for those six electrons. Nicely balanced. End of story. No static charge building up over the course of the fusion run.

I understand (hopefully correctly) the helium nuclei are slowed down by the +2MV collection grid, bringing their temperature down to something reasonable (i.e. able to retain electrons) and then scavenged off.

I also suspect (hopefully correctly again!) that the collection grid is located outside the magnet assembly. The magnet casings are shielded from the ion and electron traffic by the B field, so they are unlikely to benefit from being a collection point. The wiffleball will leak at the cusps, and that is where the alpha particles will predominantly emerge, being very hot and energetic. I imagine they will emerge from the cusps in all directions though, like a light shining out of a hole ... generally in the straight out direction, but some will emerge at odd angles. If we make the collection grid a goodly distance away from the magnet assembly, we give the grid a reasonable distance for insulation purposes.

However, I wonder if the alphas will just shoot off from the point of fusion and perhaps bump into anything in their path, magnet assemblies included. This will abrade the coil assemblies quite severely, and would make it worthwhile to charge them up to some high positive voltage to reduce the impact energy. But having a large positive voltage adjacent to the electron well will only serve to flatten it out and reduce the electron confinement which makes the polywell.

I guess I need to study some more ...

Regards,
Tony Barry

Schneibster
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Post by Schneibster »

They appear to be figuring on taking ground at a grid near or inside the electron plasma; this ground would be an electron source, as DC grounds always are (from the conventional current perspective). The positive fusion products would exit the plasma, being of much higher energy, and strike a grid well outside the electron plasma; there, their positive charge would attract electrons. Having an electron source and an electron sink, one would then generate a DC current. This is grossly oversimplified, but it gives you the flavor of the concept.

And I am an EE, so ask away. ;)

tonybarry
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Post by tonybarry »

Thank you Schneibster for your post. My main training is also in EE, but more from control than power. Hence I am eager to learn but sadly aware of numerous holes in my knowledge base.

My initial question (that began this thread) regarding electron imbalance has been answered, and that is good.

I thought to describe what I know, and please feel free to correct my understanding if you think I am incorrect.

The system ground I'd describe as a place to reference all measurements of voltage with respect to. It's the place where the operators are at electrically speaking. I presume the magnetic coil assembly is at ground.

The collection grid for the helium nuclei (alpha particles) is outside the magnet assembly, and is raised to +2MV. The sign indicates a dearth of electrons (in conventional current flow, this is Vcc ... but I'd prefer to stick with electrons here and indicate by sign i.e. + indicates electrons missing, - indicates electrons in overabundance).

The injector for the electrons that form the polywell are injected at about -20kV, by some filament (?don't know if the polywell uses a filament to produce electrons?) positioned at a cusp in the polywell, probably about level with the dodecahedral sphere on which the polywell magnets lie. I do not know what reference these electrons use ... I suspect the coil assembly is the return for them, and the filament as a whole is lowered to -20kV, and emits the electrons by thermionic emission. Figure 5 on page 3 of John Santarius's article is what I am using as a guide here.

The polywell electrons (at -20kV) do not migrate towards the magnet assembly at 0V because the magnetic field prevents this. They remain in the interior space of the polywell, more of them at the core, with a lower density of electrons the further one goes from the core.

Into this cloud of electrons, boron ions are dropped, with a charge of +5 on each ion. I don't know what this translates to in volt terms, but they must be hot to be gaseous, and highly positive to get them stripped to this level. That's a lot of electrons to remove. The ions zoom towards the centre of the core, because that's where the electron density is greatest and the positive ions are attracted to the largest density of electrons. They don't recombine because they are too hot, but they are kept in the centre while protons are dropped into the polywell as well.

That's where the fusion occurs, between the protons and the boron ions. The electrons are just there to provide electrostatic incentive for the protons and the boron ions to stay close to each other.

Once the fusion occurs, there appears three helium nuclei, each charged to +2, which are possessed of enormous kinetic energy, and which zoom away from the core as they are created. They are also deflected to some extent (?) by the magnet assemblies but in this case they are not confined because of their velocity. They emerge from the core and are gradually braked by a large positive charge (+2MV) held on a collection grid maintained outside the magnet assembly. When they reach this grid, they obtain two electrons from the grid, and are converted to helium atoms, and are then scavenged from the chamber by a vacuum pump.

The conversion of the alpha particle's kinetic energy to positive potential is what drives the process into net positive electrical energy production. The electrons liberated by the ionisation process of the protons and the boron ions are returned to the helium nuclei, completing the electron path ... but the 20kV we require to ionise is paid back with 2MV from the neutralisation of the alpha particles..

I hope this explanation is sufficiently close to correct to stand inspection by knowledgeable folk. Please advise me if you see any errors.

Regards,
Tony Barry

cuddihy
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Post by cuddihy »

pstudier wrote:
drmike wrote: The idea of the Bussard fusor is to use the magnetic field to hold electrons so you get a negative potential in the center. That entices the positive nuclei to accelerate into the center. By holding the magnet rings positive, you reflect any fast moving ions back towards the center, and the design is supposed to ensure you don't thermalize.
This can't possibly work. The magnet rings form a Faraday cage (http://en.wikipedia.org/wiki/Faraday_cage ), so there is no electric field on the inside from any charge on the magnets.
huh? Well, i would say it is more accurate to say that the only reason the magnet rings are positively charged is because they are intended to act as the cathode for the electrons (the e- emitter is the anode). However, because the magnetic field on the rings is so powerful, it keeps the electrons long lived, away from the magrid, to form a "virtual anode", or a high negative charge, at the center of the device. Thus the fuel ions are kept in the device by the fact that they are attracted to the virtual anode.
Tom.Cuddihy

~~~~~~~~~~~~~~~~~~~~~
Faith is the foundation of reason.

drmike
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Post by drmike »

@tony

Check out the paper "The Advent of Clean Nuclear Fusion: Super-performance Space Power and Propulsion" on Bussard's web page.
Page 11 describes how the wiffle ball is held at high voltage,

The graphics suck, but it gives a lot of interesting info.

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Post by MSimon »

pstudier wrote:
drmike wrote: The idea of the Bussard fusor is to use the magnetic field to hold electrons so you get a negative potential in the center. That entices the positive nuclei to accelerate into the center. By holding the magnet rings positive, you reflect any fast moving ions back towards the center, and the design is supposed to ensure you don't thermalize.
This can't possibly work. The magnet rings form a Faraday cage (http://en.wikipedia.org/wiki/Faraday_cage ), so there is no electric field on the inside from any charge on the magnets.
Well formation was my sticking point for a long time in terms of my reservations about the machine. (I just assumed it and went on designing)

First. I have a lot of good links on the sidebar here:

http://iecfusiontech.blogspot.com/

Second the definitive paper on well formation is there:

http://wwwsoc.nii.ac.jp/aesj/division/f ... hikawa.pdf

Third an understanding of vacuum tubes is essential. I have links to a page full of vacuum tube books (pdf - off copyright) here:

http://iecfusiontech.blogspot.com/2007/07/tubes.html

Start with Chaffee.

drmike
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Post by drmike »

Thanks! The Yoshikawa et.al. looks like fun reading.

tonybarry
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Post by tonybarry »

Hello drmike and MSimon,
Thanks for the references. I am working my way through them.
Regards,
Tony Barry

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