• Theoretical study of particle charging and entrapment in a cylindrical ion beam

      O'Hanlon, John; Brown, Douglas, 1955- (The University of Arizona., 1990)
      A particle within an ion beam is subjected to positive and negative currents. These currents deposit a net charge on the particle which interacts with the potential of the beam. A model is presented which describes this charging, the time required to attain an arbitrary charge, and the resulting coulomb force. Confinement by the beam is investigated through comparison of the electric force to the opposing force of gravity. To quantify this comparison, a normalized force is defined which, when negative, predicts those spatial regions where particle entrapment can occur. Utilizing a specially written VAX-Fortran program, the behavior of this force was characterized as a function of beam parameters. Regions were predicted in which particle confinement can arise and it was found that the magnitude of the trapping force varied significantly with those parameters that affect the beam-ion density. Moreover, calculations of the charging time revealed that the time to attain the minimum trapping charge was sufficiently short so as not to preclude entrapment.