A new approach for high power electron beam gun design using scaling rules

Abstract

A method is presented to extrapolate the design of a currently exploited gun into a new family of similar guns with new preferable technological parameters, for example with higher electron beam power, accelerating voltage, electron brightness and so on. The method is based on the scaling theory of electron-optical devices (EOD). According to the theory only EOD with small space charge, i.e., with perveance G < 0.01 μP, can be size and/or voltage scaled. EOD containing relatively big space charge (G ≥ 0,01 μP), such as high energy Pierce type electron guns applied in thermal technological machines, generally cannot be scaled, because of their nonlinear space charge nature. Nevertheless, also in these cases a special procedure of scaling can be applied. The reason is that the electron charge distribution in the gun is not uniform. Near the anode the density of electron charge is much smaller than in the cathode region. The concept of high perveance electron gun designing using scaling rules is based on the idea to apply the scaling rules only to the anode zone of the gun. The procedure for scaling a low power 25 kV and 150 mA electron extract system with a cylindrical electron beam into a high power 75 kV and 150 mA electron extract system is described in this paper. An experimental investigation confirmed the good technological quality of a high voltage, high power gun constructed according to the above concept.