Source of low-energy hydrogen ions for measuring electron transfer in surface scattering experiments

We present the design and performance of a beamline which is the source of 5–50-eV protons for surface scattering experiments. The beamline also incorporates a collector for measuring total secondary ion and electron yields. The beam forming optics are built around a commercially available gas discharge ion gun and produce a mass-selected, energy-filtered beam. Results of computer ray tracing are included to illustrate the operation of the beam optics. Tests have produced 50-pA proton beams 3.5-mm wide at 5 eV with an energy spread of about 1 eV.