A proton source employing a 450‐mc/sec. electrodeless discharge in the presence of a magnetic field is described. Ion currents of 400 μa, consisting of over 60 percent protons, are normally obtained, corresponding to a current density due to focused and analyzed protons of 0.03 amp./cm2 at the 1‐mm exit hole. The source requires a hydrogen flow of 30 cc/hr., most of which is prevented from entering the accelerating column by the use of a differential pumping arrangement. The ions diffuse out through the exit hole and are accelerated without the use of a probe, resulting in a well focused, monoenergetic beam accompanied by relatively few stray ions. The experimental results were obtained on a 120‐kv accelerator designed to simulate the initial sections of a typical constant voltage accelerator.