The Bonn Isochronous Cyclotron accelerates protons from 7-14.5 MeV.

 Unpolarized particles are ionized in a two stage 5 GHz Electron Cyclotron Resonance (ECR) -Ionizer (foreground). The source for polarized protons and deuterons is underneath the cyclotron magnet. During 1988/89 the superconducting Penning-Ionizer was replaced by an 2.5 GHz ECR-Ionizer being as efficient as the Penning-Ionizer but had less magnetic stray field and provided a very stable and quiet beam current.