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.