High power, low velocity spread, axis encircling beam, electron gun development

Abstract

Summary form only given. Presented is the status of the development of a low velocity spread, 70 kV electron gun for gyro-device research. The design retains the simplicity of the Northrop Grumman (NG) novel gun concept where possible. The main design goals are: beam current =3.5 A, magnetic focusing field =6.5 kG, beam alpha =1.5, beam ripple </spl plusmn/10%, and axial velocity spread less than 5%. Preliminary design candidates were obtained by the code NOVGUN developed at NG. This code calculates the single electron trajectories in the electric and magnetic fields calculated by solving Laplace's equation for the electric and magnetic scalar potentials. The gun electrodes and magnetic pole piece electrodes were varied systematically and automatically through hundreds of iterations until the beam ripple (guiding center spread) and axial velocity spread were minimized. To achieve both low ripple and low velocity spread, it was necessary to incorporate a magnetic ring (floating pole piece) around the cathode to deflect the magnetic field lines away from the cathode. After a preliminary design candidate was found through NOVGUN, the gun was modeled by the Hermannsfeldt code with the magnetics accurately simulated by the MAXWELL code.