This paper describes a special designed 8‐cm‐diam broad beam ion source. Special cusp magnetic fields are used to control the beam spot area by magnetic convergence, so that a focusing beam can be extracted from a simple two‐grid accelerator system without using dished grids. A beam current over 350 mA can be extracted from this source for argon gas, and the maximum of beam current density is over 20 mA/cm2at a location 40 cm downstream of the source. The highest energy of the extracted ions is about 10 keV and the maximum of sputter coating rate from high to low sputter yield of target material is 15 A˚/s for aluminum, 7.5 A˚/s for titanium and 2.5 A˚/s for graphite, respectively.