Beam dynamics calculations for the LAMPF optically pumped ion source

The space charge code SCHAR has been used to interpret some of the measurements made with the LAMPF ECR (Los Alamos Meson Physics Facility electron cyclotron resonance) source. Calculations were made for rectangular hole (ribbon beam), single hole, and multihole electrodes. Measured rotation of the plane of the ribbon beam in the constant solenoid field showed that when the polarizer cell was not utilized the beam was essentially not neutralized after it emerged from the extraction electrodes. There is evidence that when the polarizer cell is turned on the beam becomes neutralized from the polarizer back toward the electrode structure. The total measured current from single and multihole electrode with the polarizer cell on is proportional to the area of the electrode apertures. Beam simulation calculations indicate that if the beam extracted from the source is uniform across the multihole structure, then in order for the perimeter holes to provide as much current per area the beam would have to be at least partially neutralized after exiting from the electrode structure. The energy of the ions leaving the (unmodeled) ECR plasma determines the current for a given electrode structure and voltage. Electrode radial fields and beam space charge forces generate most of the transverse velocities observed as the beam exits from the electrodes. Tails present in the measured harp data could be explained by an H₂⁺ component in the beam