Another, possibly relavent example of high current circulation with minimal continued current input would be superconducter magnets. Once loaded, there is considerable current flow within the superconducting wire with ideally no additional current input. The hoped for high electron confinement time and recirculation in the Polywell is similar in principle. The internal current can be maintained with some minimal replacement input current up to some limit - arcing or cusp blowout, or general transport losses.
Dan Tibbets
Discharge plasmas versus ExB ion sources.
Don't forget the accelerator current from ions. It is not just the electron guns.
I guess I always thought of that as fuel and not a current.
But I'm confused as to where this ion current comes from. I thought the ions got all their energy from the fact they started at the top of the well. I guess I don't see where the input goes.
TallDave wrote:Don't forget the accelerator current from ions. It is not just the electron guns.
I guess I always thought of that as fuel and not a current.
But I'm confused as to where this ion current comes from. I thought the ions got all their energy from the fact they started at the top of the well. I guess I don't see where the input goes.
I believe that concidering the ions as a fuel as opposed to an energy input is appropiate. But, like in a car, a fuel pump is needed. If ions are created outside the magrid, they need enough speed to overcome the positive charge on the magrids (minus the smaller and more distant negative charge from the virtual cathode). eg: +12,000 volt on magrids plus (- 10,000 volts potential well * some inverse square law adjustment because the potential well (virtual cathode) is further away). Or, perhaps the distance correction is minimal due to some Gauss law type conciderations, in which case ~ 2000 volts would have to be applied to the ion.
For that matter, depending on the size of the spiky Wiffle Ball contained electron cloud in comparison to the magrid size, ions injected immediatly outside of a face center cusp may be almost as close to the virtual cathode as it is to the positively charged magrid. Concidering vectors- the positive carges on the magrid would be almost entirely lateral if the ion was injected from only a tiny distance beyond the mid line of the magrid, thus requiring only a tiny voltage for the ion to proceed into the machine. The magnetic field lines in this area could also help by preventing an off center ion from being deviated much towards one side or the other untill the ion had traveled far enough for the potential well to be dominate.
Any energy penalty would be avoided if the ions were created/ released within the magrid and near the Wiffle Ball border. Then, I'm guessing only a small amount, or even no energy (beyond that used to create the ion) would be needed.
How the concentrated ion beam and associated structure located within the magrid and at a vunerable cusp location would effect electron confinement and recirculation at that cusp is unknown (to me).
Do the ion guns need to be located percisely at a cusp? I currently understand that to get the potential well voltage near the electron injection energy, the electrons need to be injected directly into a cusp so that they do not deviate much from a central focus. But, is this required for low energy ions? Could the ion guns be located within the magrid but not percisely in a cusp? Would this distort the local magnetic field to much?. I'm supposing that these low energy ions, if left to themselves would quickly flow along the magnetic field lines in that area, but the potntial well would dominate and yank them away from the magnetic domain and accelerated them towards the center.
Concidering the potential well from the injected electrons, Bussard said that they need to be aimed straight down the throat of a cusp to prevent the spread of the electrons (path being curved somewhat by the near cusp magnetic field lines) which would decrease the central density of electrons and coresponding potential well.
With ions this effect might be benificial. Having the ion paths curved somewhat as they enter near (but no exactly in) a cusp would effectively give them more lateral/ transverse energy and less radial energy. This would allow them to be injected further away from the Wiffle Ball border and still have a top of potential well position closer to the Wiffle Ball. This would presumably increase the shielding tolorance for upscattered ions and keep the ion guns further away from the confined electrons. How this would effect the energy balance is unknown. If annealing is real, this initial lateral motion would be damped, or if most of the ions turn in one direction when they are first injected, a spin might be imparted to the plasma. Within limits, would that be good or bad?
Of course, if neutral gas puffers work in a large machine, these arguments are moot.
Dan Tibbets
To error is human... and I'm very human.
An ion fired into the wiffleball (if I'm imagining this correctly) should be very slow by the time it passes the magrid. The initial energy is recovered in the circuitry that keeps the ion guns and magrid at different potentials, similar to the direct conversion idea. The energy to accelerate the ions once they get inside is provided (indirectly) by the electron guns.
Of course, if they've decided to let the ions be hot at the top of the well, that changes things. I don't see how that would be acceptable in terms of annealing, though...
Of course, if they've decided to let the ions be hot at the top of the well, that changes things. I don't see how that would be acceptable in terms of annealing, though...