Plasma formation near the beam collector of a forevacuum-pressure plasma-cathode electron beam source

It was shown that secondary electrons, emitted by the electron beam collector of a forevacuum-pressure plasma-cathode electron source, play an important role in beam plasma generation. Their yield is determined by the secondary electron emission properties of the collector, its negative potential, and the angle of incidence of the electron beam on the collector. Positioning the beam collector surface at an angle to the beam propagation direction results in spatial separation of the two plasma regions formed by the primary electron beam and by secondary electrons generated at the collector. This separation makes it possible to compare the parameters of both plasmas. It was found that the secondary plasma column is always directed perpendicular to the collector surface regardless of the primary beam angle of incidence. The secondary plasma is generated via gas ionization by secondary electrons accelerated by the collector potential. Under certain conditions (high values of secondary electron emission coefficient and collector potential), the contribution of secondary electrons to formation of the near-collector plasma can surpass the contribution from the primary electron beam itself.