New Species of Fusor?

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

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D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: New Species of Fusor?

Post by D Tibbets »

ohiovr wrote:Wouldn't the electrons be blow away from the cathode, and sucked into the anode in the fusor? Forget about polywell we are talking about the classic fusor.
Indeed, the electrons are are blown away from the cathode (the virtual cathode in this case. They would ground on the anode,or wall at high energy. This is whathappens in a conventional fusor also. The elmore Tuck and Watson varient, uses a anode grid to accelerate the electrons towards the center. In this case it is the ions that are blown away. if they reach regions outside the radius of the anode.

What makes the Polywell different is that more electrons are forced into the machine- either accelerated by the anode or by having high energy electron guns and a grounded magnet grid (anode of 0 Volts if you wish) This forms a virtual cathode. This accelerates the ions towards the center and contains them. Of course the electrons are repulsed by the virtual cathode- other electrons. As such they are accelerated to the grounded or anode grid located on the outside of the machine. This is where the magnetic fields come into play, they turn the electrons before they reach the anode. The electrons are turned ~ 180 degrees each time they slam into the magnetic field, then fly towards the center again at high speed. The mutual electron repulsion (1 ppm greater than the ions present) again slows them till they reverse/ deflect from the center and again fly/ accelerate towards the magrid, where the magnetic field ....
The electrons are contained by the magnetic field. The ions are contained by the virtual cathode, just like in a normal fusor, except there is no wire for the ions to hit and lose energy to. This serves as separate mechanisms for containing the two contrary species, and benefits over just magnetic containment of both species because ions are contained relatively poorly by magnetic fields, electrons are contained well by magnetic fields. It is the best of both worlds.

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: New Species of Fusor?

Post by D Tibbets »

ohiovr wrote:
ohiovr wrote:Wouldn't the electrons be blow away from the cathode, and sucked into the anode in the fusor? Forget about polywell we are talking about the classic fusor.
http://tommccarthyprojects.com/how-the-fusor-works/
The link is mostly correct, but there are some errors. Though it is irrelevent, the electron is much smaller than either protons or neutrons. The important consideration is that electrons are much less massive and thus have much smaller gyroradii when turning in a magnetic field.

The central grid may be confusing when "hollow sphere" is used
It is actually a wire grid with as much open space between wires as possible so that the ions accelerating past it are least likely to hit it. There are all sorts of variations, but basically this is the picture. If neutral gas molecules are injected, they are mostly ionized initially by the high speed electrons in the system, which come from thermionic emission from the cathode wire in the fusor. Secondary ionization then takes over The nuclei and electrons disassociate from each other. It is no longer a neutral atom or molecule, but separate oppositely charged particles in equal numbers that interact oppositely in an electric field. The electrons are not attracted to the shell anode/ wall so much (depending on how well Gauss Law is operating) but repelled towards the peripheral wall by the more centrally placed cathode wire (or virtual cathode).

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
Posts: 2775
Joined: Thu Jun 26, 2008 6:52 am

Re: New Species of Fusor?

Post by D Tibbets »

This talk may be confusing. Simple logic might suggest that if the ions are contained by a cathode wire and the electrons are quickly lost, then the plasma would be mostly ions. But, remember the Coulomb force contribution. As the electrons leave, the remaining plasma becomes more positive and repells itself. In very short order, the ions are lost as fast as the electrons. Essentially, the energy input to create the cathode bias is lost as electrons streaming from the system. The resultant relatively large excess of ions then form a virtual anode which also repells any ions from the system. The containment of one species must be very close to the containment of the other. The except is when you input one species more quickly, this compensates for the more rapid loss. This can maintain the potential wells, but the question then becomes how much losses of that faster injected species can you tolorate. This is why electron losses are said to dominate the losses in the Polywell. Since they are lost faster, you have to replace them faster to maintain that very narrow population variance that can be tolerated and is nessisary for operation.

Dan Tibbets
To error is human... and I'm very human.

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