Okay this is my understanding to date of how Polywell fusion fuelling works. You use an electron gun to inject electrons into the central cathode giving them enough energy to overcome its radially repulsive force.
Then you "drop" in ions from outside the cathode to fuel the device, these autmatically fall towards the centre of the virtual cathode where with luck they fuse, failing that they go back and try again.
In practice I believe this "dropping" of ions is achieved by puffing gas into the outside of the electron cloud where it is ionised by fast electrons at the edge of the magnetic trap. However for every ion that is created from neutralising a neutral atom, you will create a slow electron without enough energy to penetrate to the central cathode, these electrons might nonetheless remain magnetically trapped, and even if they travel a shorter distance before escaping because they will be moving more slowly they might still remain there for a considerable period of time.
What happens to them?
I was thinking one possibility might be that they would cool the fast electrons so that they would no longer have sufficient energy to penetrate into the centre of the device, causing the negative charge distribution to expand radially and degrading the focussing of the ions.
What happens to the cold electrons from the puffed in fuel?
Bussard suggests that the positive MaGrid be the ion source. You'd build your proton/boron gun as part of the field coil and use voltage between the grid and virtual cathode as the projection energy. The advantage of that is being able to control the electrons and inject them as part of the electron gun so they whole system stays neutral.
I do remeber reading some where Bussard suggests not being exactly neutral and stating there was an advantage to that.
You can also ionize gas with microwaves. So some neutral gas can be blasted to be ionized, then fed to the magfield where it drifts into the center and begins to oscillate. I think the advantage of having the gun on the MaGrid is that you inject at high energy to start with, so it's easier to stay there.
I do remeber reading some where Bussard suggests not being exactly neutral and stating there was an advantage to that.
You can also ionize gas with microwaves. So some neutral gas can be blasted to be ionized, then fed to the magfield where it drifts into the center and begins to oscillate. I think the advantage of having the gun on the MaGrid is that you inject at high energy to start with, so it's easier to stay there.