Electron Importance

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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x87330
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Electron Importance

Post by x87330 » Sun Feb 24, 2013 5:44 am

I fail to understand the importance of the electrons in the fusion process. If the inner grid is positively charged to a sufficient degree, and the fuel is already ionized as it enters, can't the electrostatic potential deliver enough force on the ions to produce fusion? If so, you could replace the grids with solid spheres, add a thin dielectric between them, essential making it a spherical capacitor, and pump plasma fuel straight into the inner sphere.

The only hang up I see is that some of the fuel might just pile up and sit in the center, but new fuel sprayed into the chamber, could break that up. Pulse discharging and recharging the spherical capacitor could be another method of breaking up the compressed fuel.

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Carl Willis
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Re: Electron Importance

Post by Carl Willis » Sun Feb 24, 2013 6:39 am

The ordinary Farnsworth Fusor is a kind of glow discharge ion source. If you Google "glow discharge", you'll find a lot of resources that explain the roles of electrons and other particles in any glow discharge, including the fusor. Basically, electrons are liberated from neutral gas molecules and then accelerated by the voltage applied to the electrode to energies where they can ionize other gas molecules. This chain reaction of electrons colliding and liberating more electrons rapidly attains some steady state where a constant current is flowing in the gas. Some of the current is carried by electrons moving toward the positive electrode, and the rest of the current is carried by positive ions heading toward the negative electrode (which in a fusor is the inner grid). The ions--specifically deuterium ions--are used for fusion in the fusor, but the electrons are vital in sustaining the glow discharge that produces the ions.

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Re: Electron Importance

Post by John Futter » Sun Feb 24, 2013 7:54 am

Derek
Carl has given a good reply but you have to have some understanding on how /why this happens
hope the following helps
it is too short to do it justice but here goes

the electron or lack of it is why this works
an ion does not exist in the natural way of things
it is all started by by a cosmic batting off an electron so as to produce an ion read (+)
when this ion hits some neutral atom it may dislodge an electron or more.

now you have many electrons whacking around causing more secondary electrons all of which can whack an atom and dislodge an electron or two.

the secret is that you have to contain where the electrons end up as free electrons will kill an ion to return to a stable state.

very short but if you can understand this you are well on the way
google is your friend at this point

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Dennis P Brown
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Re: Electron Importance

Post by Dennis P Brown » Sun Feb 24, 2013 11:34 am

While the electron does not 'help' fusion in the plasma directly, the electrons are what get the processing going in the fusor. That is, one applies an electron-based current through the neutral gas to heat up that gas (that is the gas, which consists of molecules of deuterium.) The energetic electrons which are accelerated by the potential in the fusor/electrodes enables these electrons to acquire kinetic energy, and these in turn, hit deuterium molecules and cause them to break up and become ionized. Once ionized, the deuterium is a 'naked' nucleus (which consist of a proton/neutron’. This nucleus no longer has the electron ‘bound’ to it.)

Note that this ‘naked’ nucleus is now fully charged (no longer neutral like before with an electron bound in a 'cloud' around it or in more simple terms: in 'orbit' around it.) This nucleus can only now feel the electric field within the fusor and in this manner obtains kinetic energy by acceleration in the potential 'well' that the fusor electrodes provide. Once the nucleus (proton/neutron bound state) achieves enough kinetic energy it will, very rarely, collide with other protons in a manner that permits the two deuterons to approach one another close enough so that the 'strong nuclear' force can take over – i.e. gets with in the range of this 'force' and the two nuclei are pulled together into a bound state. Then quantum effects takes over, energy is released (some extra mass is converted into energy), and a neutron ejected.

Just a side note: the elctrons can never approch the proton/neutron pair close enough to ever directly interact with this nucleus. Also, much of the time, many (but far from all) nuclei remained unbound with the free electrons. From time to time some rebounding of the ionized deuterons occurs with free electrons in the plasma. Significantly, ionized deuterons will bound with the electrons contained in atoms that make up the walls and electrodes (and why these heat up when the KE is passed to them from the deuterons. These process 'rob' the plasma of ionized deuterons and can slow many of the ionized nucli.)

Without the electrons it would be hard to get the deuterium gas to ionize in order to start the process (however, in 'cold' fusion, this does occur without any significant amount of KE or the requirement that the deuterium becomes ionized. But in any real cold fusion to date, only incredibly tiny amounts of fusion has been observed.)

One reason the 'free' electrons in the plasma are very important is due to the fact that without 'charge shielding' by these electrons with the protons in the plasma, the separation of charge (repulsion between like charges) would prevent more than only a minuscule number of deuterium molecules from breaking into free nuclei and ever approaching another nuclei.

A lot more complex but that is the basic process. Really no way to separate any significant number of electrons from fully ionized deuterium nor would that be a desirable thing since far, far fewer deuterons would be able to fuse due to lack of shielding by the electrons.

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Re: Electron Importance

Post by x87330 » Sun Feb 24, 2013 4:32 pm

Right, all of that makes sense. I read both of the introductory papers posted on the site. So after the gas is ionized, we need the electrons to mitigate the effects of the electric force (aka Coulomb barrier, in this case) between the nuclei. It just seems like a lot of effort is being put into maximizing electron cloud density (95-98% transparent grids, polywell magnetized electrodes, etc).

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Re: Electron Importance

Post by Rich Feldman » Sun Feb 24, 2013 4:58 pm

Derek Mitchell wrote:
> ... If the inner grid is positively charged to a sufficient degree, and the fuel is already ionized as it enters, can't the electrostatic potential deliver enough force on the ions to produce fusion? If so, you could replace the grids with solid spheres, add a thin dielectric between them, essential making it a spherical capacitor, and pump plasma fuel straight into the inner sphere.

Derek, the applied high voltage does not create any electric field inside your inner charged sphere, or inside the inner grid of a traditional fusor. Within that space, the E-field is zero (except for any field from the space charge, if electron and D+ ion densities don't match). D+ ions will just carry on with whatever energy they had when they entered.
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Re: Electron Importance

Post by Carl Willis » Sun Feb 24, 2013 6:38 pm

In the conventional Farnsworth-Hirsch fusor--the kind that we hobbyists actually build--electrons have a role in sustaining the glow discharge that produces ions. That can be said with certainty.

"Virtual electrodes" within the grid, caused by space charge from both ions and electrons, are possible in theory. However, their influence in the simple fusor is speculative, and they are not necessary to explain operation and performance.

Space charge is necessary to the theory of the Polywell IEC device. There is a single amateur project seriously devoted to exploring this concept, and so far the only demonstrated examples have been built by Robert Bussard's company.

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Re: Electron Importance

Post by x87330 » Sun Feb 24, 2013 8:21 pm

Yeah, I guess the electric field is only between the electrodes, isn't it? I can still expect the positive electrode to repel the ions at very short distances though, right?

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Re: Electron Importance

Post by Dan Tibbets » Sun Feb 24, 2013 9:25 pm

You are ignoring Gauss's Law. One reply hinted at this. Basically any ion inside a positively (or negatively charged) grid electrode completely ignores (under ideal conditions- there may be some leakage due to hole size and plasma frequency) the charge on the grid. Any momentum the ion has was obtained while it was outside the grid (at a greater radius from the center compared to the grid).

You cannot 'squeeze' positive ions inside a positive grid. You can accelerate positive ions past a negative grid towards the center, but once inside the radius of the grid the ion no longer sees the charge on the grid. It's speed is the residual momentum that it obtained while being accelerated. You cannot accelerate ions in one direction without accelerating electrons in the opposite direction unless you can somehow separate the populations (to a limited extent limited by coulomb charge buildup). Manipulation of magnetic fields and grid placement allows for this. The Polywell is an example, and of course it derives from the Elmore Tuck and Watson (ETW) version of the Fusor.

Simply keep in mind that a structure that creates a space charge only effects the charged particles when they are at a greater radius than the grid, or defined shell of free charged particles. There is a net zero space charge effect at a lesser radius test particle because all of the peripheral charges cancel each other out.

Considering the Fusor with the cathode, the electrons boil off of the electrode and are quickly accelerated outwards if they are released on the outward facing surface. Those electrons released on the inside surface have almost no accelerated voltage, again due to Gauss Law. The ions sitting outside the grid are accelerated towards the grid and then drift inside the grid due to their momentum, until they pass through the center and out the other side of the grid where they are then decelerated to zero radial velocity, and subsequently are re accelerated towards the center. With typical glow discharge fusors this may repeat 10- 20 times before the ion actually hits a grid wire where the KE is lost to heating the wire. Effectively, one electron accellerated to the chamber wall from the grid completes only one pass, there is nothing to recover it's KE, there is no electron recirculation like with the ions. But during it's lifetime the electron contributes in other ways (ionization of neutrals and perhaps the a tiny amount of the space charge (dominated by the electrode charge in this situation I believe)). Basically one electron loss drives ~ 10-20 ions to high KE. This amplification is the root of Fusor efficiency. Now, if you can somehow figure out how to recover the electrons KE by efficiently shielding the walls with magnetic fields while also eliminating the wire grid in the way of the ions, you can increase efficiency so that profitable fusion might be obtained. Both aspects- electron recirculating, and grid transparency has to be improved tremendously before positive Q's are even conceptually possible.

The ETW Fusor idea improved electron recirculation, just as the conventional cathode fusosr recirculates ions, and the recirculated electrons establish a virtual cathode inside the grid that accelerates and traps the ions- the ions do not see the positive grid used to accelerate the electrons inward because the ions are ideally never outside the radius of the grid. But grid transparency to electrons in this case was still a fatal deficiency. The Polywell is an attempt to address both of these issues at the same time.

All of this ignores local Coulomb collisional effects (ions and electrons 'hitting' each other) which greatly complicates the picture.

There are videos of the Gauss Law effects that can be enlightening.

Dan Tibbets

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Re: Electron Importance

Post by Richard Hull » Mon Feb 25, 2013 6:44 pm

Everyone helped in the general understanding of fields and electrostatic acceleration. However, a few also noted that other processes occur other than the ideal we seek and that is why no simple concept will improve fusor operation by an order of magnitude.

There is just too much going on in the system. All the extra processes foul or foil the net goal which we want to think is the main process, when it is not. It is just one of many processes taking place in the system.

I have elaborated on this in many past posts. The fusor and most any such electrostatic/electromagnetic device is all about a multiplicity of losses and loss mechanisms and not about net fusion gains.

Electrons are the sole fusion implimenters here and drive the fusor's fusion process. They are also its number one loss mechanism. Electrons, themselves, are in no way involved in the actual fusion process! It is only colliding deuterons or deuterons and fast deuterium neutrals that do fusion.


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