Thin electrostatically self-focusing electron streams.

Study of 30 to 380 microampere, 50 to 550 V, 1 to 2 mm, electrostatically self-focusing electron streams (50 cm long) drifting through mercury vapor (at 50 microtorr to 2 millitorr) in a tube with a radius of 6.6 cm. The inside surface of the tube is coated with a transparent layer whose resistivity is 50 ohm-cm per centimeter. In order to determine the charged-particle densities and the potential profile in and around the beam without disturbing the system, a multigrid electrostatic charged particle energy analyzer was used to study separately the energy distributions of both ions and electrons ejected radially from the beam. The results show two energy groupings for electrons. The energy distribution of the high-energy group is produced by ionizing collisions between beam electrons and neutral gas atoms; a group of flow-energy electrons becomes trapped in the potential well within and around the beam, subsequently escaping by collisional mechanisms.