As I understand it, one of the techniques used in electron tubes (aka valves) to reduce electrode erosion is to a maintain a negative potential on the “target” electrode. This decelerates the free electrons (that had been accelerated by the grid potential) so that most of the energy has been taken out of them and the electrons impact the plate at low energy. This is a bit like a lunar lander game played out on a very small scale.

If the same situation applies here, then allowing the residual e-beam to contact the +ve anode is the actually making the electrode erosion problem worse, because the electrons are accelerated towards the +ve anode. (Maybe it’s no longer positive after the discharge that formed the plasmoid, but in any case the following should still apply)

Couldn’t we instead have a hole up the middle of the anode and a negative electrode (insulated from the anode) whose task it is to slow the electrons and allow the e-beam to touch with the minimum erosion? The accumulated negative charge would be bled back into the power supply, even if that energy contribution was small.

The unanswered question I’m left with is what is this electrode negative with respect to? The plasmoid is going to be sitting in an electric field at some potential, but I don’t know what that is.