Brian H wrote: I gather, also, that blades and circlets etc. develop exponential irregularities and erosion patterns. It’s actually very difficult to manage filaments on a single structure with a continuous emitting surface/edge.
Cathode erosion tends to be pretty small or more likely, highly uniform. I have encountered situations when the cathode rods developed a structure along the length (z direction in cylindrical coordinates) near the top of the rods. The structure tended to show up in configurations with just a few rods (<10). I tend to use 14 or more rods of small diameter in my PF. I think the issue is related to the current carried in the rods vs the current carried in the plasma between the rods. The plasma focus video is a bit misleading. The filaments or plasma sheet that travels between the anode and the cathode is not solely connected to the cathode rods. A largely vertical plasma exists in many machines between the rods that returns current while by-passing the cathode rods. My personal opinion is that the rods define the return radius more than carry the current. Some folks have experimented with closed cylinders as cathodes. The yields aren't as good but I don't know the reasons. My personal belief is debris build up in the plasma channel and the requirement to carry all the mass between the electrodes instead of pushing it out radially. I know coaxial plasma accelerators, the axial phase of a plasma focus without radial implosion, use a solid cylinder cathode without any signs of a a specific pattern on the cathode.
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