The design and performance of a simple sputter ion gun is given. It uses a commercial Bayard–Alpert ionization gauge. A two‐stage extraction and acceleration system provides a variable beam profile as well as high currents at low energies (>1 &mgr;A above 200 eV). At a distance of 4 cm from the end of the gun a current density of more than 150 &mgr;A/cm2was obtained at 1.2 keV. A narrow energy distribution may also be obtained (≤1.6 eV FWHM at 1.2 keV).