US Patent 7473914 System and method for producing terahertz radiation

An apparatus for producing an annular electron beam comprises a cathode for generating electrons, a cavity having an annular shape and operable to receive the electrons, an energy input coupled to the cavity, where the energy input is operable to supply Radio Frequency (RF) energy at the cavity and an energy output coupled to the cavity and operable to receive accelerated electrons from the cavity and operable to output the accelerated electrons as an annular electron beam.