non-uniformly charged magrid?

[Aero]

In WB-6 didn't Dr. Bussard use headlight filaments as his electron source. That source couldn't have provided much of a beam. It seems to me it would have been more omnidirectional than beam like. Maybe that works better.

[93143]

As far as having e-guns at high voltage, and the grid grounded;that is reasonable. That was one of the options explored by Bussard. I think WB4 was tested in both modes.

Which end of the circuit is grounded should have absolutely zero effect on how the system works. If that's not what you meant, link please.

[happyjack27]

As far as having e-guns at high voltage, and the grid grounded;that is reasonable. That was one of the options explored by Bussard. I think WB4 was tested in both modes.

Which end of the circuit is grounded should have absolutely zero effect on how the system works. If that's not what you meant, link please.

i believe he means having the grid at 0 charge, and having a high negative charge on the eguns to "fire" the electrons off from it via repulsion, vs having the eguns at low charge and the grid at high positive charge to attract the electrons to it.

the difference lies in the spatial distribution of voltage gradients. with charged guns, you have a negative point charge at each gun which creates an e-field that diminishes radially out from them at 1/r^2. with a charge magrid, on the other hand, you have 1 positive point charge at the center that diminishes in e-field radially at 1/r^2.

this introduces a number of differences in how the particles will move. for example, with charged eguns, the electron acceleration (on its entry path) will be greatest when it is closest to the egun, where as with charged magrid it will be greatest when it is closest to the magrid. the same holds true for electrons that are trying to escape. hence, one might argue, for instance, that a charged magrid would be better at keeping electrons from escaping than charged eguns.

[93143]

EDIT: deleted due to overreaching and saying stuff that wasn't true.

[happyjack27]

You've got to stop thinking in terms of just charges and start thinking in terms of potentials.

charges create electrostatic fields.

at a distance of 0 from a point charge, the potential is infinite.

since i'm talking about something that creates an electrostatic field, and is at a distance of zero from it, not only is charge the proper term, but I CANNOT speak in terms of potential, for potential would be infinite.

that and you got your spatial reasoning wrong.

[D Tibbets]

As stated, low potential e-gun with high potential magrid, is the same as high potential on the E-gun and low or grounded potential on the magrid. At least it is till I start thinking about it. Then I become more confused. Because of Gauss law the outer wall is invisible to the electrons (till they hit it) so a -10,000 eV electron should be attracted to a 0 volt magrid the same as a (~) 0 eV electron is attracted to a +10,000n volt magrid. Where I become confused is the high energy e-gun- if an electron is emitted towards the wall it could end up with about 0 eV before it hit the wall, but it's distribution would be more dispersed from the cusp axis. This would result in less favorable angles for the electron to pass through the cusp before being mirrored back (?). In essesence, I think that this means with + charged magrid, the e-guns can be sloppy )headlight bulbs), while with a high voltage e-gun and a grounded grid the e-gun needs to aim at least a fairly collimated electron beam straight at the cusp.

The recirculation difference is that an escaping electron with ~ average energy would be climbing a potential well of ~ 10,000 volts (electron speed plus potential on magrid - zero or grounded in this case). It would recirculate, but a mildly upscattered electron would not. With an escaping electron with an average speed equivalent to 10,000 colts would become exposed to a positive 10,000 volt potential on the magrid. The reversal of the particle would be the same (reentry speed would be the same), but the distance where the electron reverses would be further out and thus more vulnerability to reaching the wall, or being deflected by other structure (like e-guns) before reaching the turnaround point. Again, I may be confused in how Gauss law works in this situation. Part of the law states that a charge will accelerate towards a charged plane the same amount irregardless of the starting distance. But, what if something perturbs the electron in this region further from the magrid?

Dan Tibbets

[93143]

...okay, that's embarrassing. Yes, my physical reasoning was wrong; the emitters are too sparse to constitute a spherical shell. Thanks for pushing back on that; it would be bad if I misled you.

However, your comments on charge vs. potential require a response.

This system is not driven by adding charge to the components. It is driven by using power electronics to maintain a potential difference between the components, and the charges then distribute themselves as they see fit. Which end of the circuit is grounded is entirely immaterial to what the system actually does, since absolute potential can be considered an entirely artificial theoretical construct in a case like this. In other words, grounded != uncharged.

In the case of charged emitters and uncharged magrid (however you plan to pull that off in an experiment), confinement would be extremely bad, with a nearly flat potential around the magrid and an outward gradient in the wide spaces between the emitters. But it wouldn't be quite as bad as I claimed; while the magrid and the space inside are not at the potential of the surroundings (the Faraday cage, the vacuum chamber, whatever), they are closer to it than to the potential of the emitters.

And yes, in a case like this the emitters would spray electrons everywhere, with a slight outward preference...