Continued testing and applications of high power cusp gun

Abstract

Summary form only given. Certain gyro-type devices, including moderately high power, high harmonic gyrotrons and peniotrons, require an axis encircling electron beam. To develop practical and efficient devices of this type, it is necessary to first develop a gun that generates a high quality beam with low velocity spread and ripple. Presented are the development and low voltage testing of a Cusp electron gun designed to operate at 70 kV and 3.5 A beam current, with beam alpha (transverse to axial velocity ratio)=1.5, beam ripple </spl plusmn/10%, and axial velocity spread <5%. The overall gun design concept retains the simplicity of the Northrop Grumman novel gun approach. In which the beam passes through the field reversal while it is still converging, resulting in reduced beam scalloping and less sensitivity to dimensional tolerance. The large transverse velocity spread, due to the spread in cyclotron radius from the inner to the outer beam electrons, is reduced by placing a magnetic ring around the outside of the cathode to divert the magnetic field away from the cathode surface. The magnetics were tested across the full range of gun coil correct. The measured field at the cathode never deviated by more than 6 G from that predicted by the Maxwell code.