The effects of a magnetic field gradient on the energy profiles of ions extracted from an electron cyclotron resonance (ECR) microwave plasma stream are studied. The mean energy and energy dispersion of the ions strongly depend on the spatial distribution of the magnetic field strength. Ions with an energy dispersion of several eV are extracted from the plasma by the mirror field gradient application. Consequently, the magnetic field gradient, i.e., the magnetic flux profile, is one of the most important parameters in ECR microwave plasma processes.