an ion source of the electron bombardment type which includes mainly a cathode and an anode confronting the cathode . in order to effect the formation of a magnetic field perpendicular to an electric field established between the cathode and the anode , the anode and / or the cathode is of a particular configuration , more specifically a spiral or helical configuration . a flow of large current is supplied through the anode to establish the magnetic field while application of a given voltage across the cathode produces a multiplicity of electrons . with such an arrangement , movements of charged particles such as electrons or ions are controlled under the influences of the electric and magnetic fields thereby to enhance the production of ions . high temperature operations and simplified implementations become possible because the present ion source itself produces the magnetic field with only a modification of the electrode assembly thereof .