Can Coulomb repulsion for charged particle beams be overcome?

摘要

Mutual repulsion of discrete charged particles or Coulomb repulsion is widely considered to be an ultimate hard limit in charged particle optics. It prevents the ability to finely focus high current beams into small spots at large distances from the defining apertures, A classic example is the 1970s era "Star Wars" study of an electron beam directed energy weapon as an orbiting antiballistic missile device. After much analysis, it was considered physically impossible to focus a 1000-amp 1-GeV beam into a 1-cm diameter spot 1000-km from the beam generator. The main reason was that a 1-cm diameter beam would spread to 5-m diameter at 1000-km due to Coulomb repulsion. Since this could not be overcome, the idea was abandoned. But is this true? What if the rays were reversed? That is, start with a 5-m beam converging slightly with the same nonuniform angular and energy distribution as the electrons from the original problem were spreading at 1000-km distance. Could Coulomb repulsion be overcome? Looking at the terms hi computational studies, some are reversible while others are not. Since the nonreversible terms should be small, it might be possible to construct an electron beam directed energy weapon.