The present invention pertains to an apparatus for generating a charged particle beam comprising a magnetic element for controlling the profile of the beam in a predetermined plane. A cathode can be provided for emitting charged particles and an anode for accelerating the charged particles along an axis of travel. The present invention also pertains to a method for generating a particle beam that has a uniform profile in a predetermined plane comprising inducing emission of charged particles from an emitter, accelerating those particles along and toward an axis of beam travel, generating a magnetic field with a component aligned with the axis of beam travel but different in the predetermined plane than at the emitter, and modifying the beam profile.