The description of Polywell was that electrons would be trapped in the center, creating a negative charge while the outside grid would be positively charged. The electrons wouldn't be moving around much, nor would they collide with the fusable ions that are moving up and down between the charged zones. I'm imagining that the ions are attracted to the center, zip right through the cloud of electrons without touching them, but might collide with another ion producing nuclear fusion. If they don't collide, they fly out the other side and are repelled by the positively charged outer grid. They then are pulled back into the central electron cloud for another pass. And so on. I assume the fuel ions are not similarly trapped in the center because they have more momentum.

An electron moving around a magnetic field line will shed energy as radiation because it is accelerating in a circular path, right? Is that the bremsstrahlung losses you are referring to or synchrotron radiation? Are they the same thing? Anyway, since the electrons are trapped in the center, they shouldn't radiate much. But I don't see why the fuel ions wouldn't have bremsstrahlung losses. And wouldn't tokamaks have the same problem since they confine charged particles with magnetic field lines ?