Beam fusion, which what the Farnsworth is, can’t get around the simple fact that your more likely to bounce of other ions rather than fuse. Many many times more likely. This is the so called star mode, and I have not read any credible reports on anything working after power down, that is not even consistent with its claimed working principals.
Non neutral plasma has a well defined potential you need for confinement. Its scales with the amount of charge enclosed and the surface area. Even the size of the moon is not enough for any reasonable fusion rate.
