Construction and Characterization of the Diode and Triode Electron Sources for EBM 300 keV/20 mA

Abstract

The technical challenge in constructing the electron source (ES) lies in the joining of metal and ceramic tubes. Furthermore, there is a lack of available technical comparison data for the output performance between the diode and triode ES under the same experimental conditions. The research aim is to describe a simple technique for constructing the diode and triode ES for an electron beam machine (EBM) of 300 keV/20 mA, and to investigate their output characteristics. The method used is to make a flange for mounting the Tungsten filament, Pierce electrodes, and heat shield. Two or three electrodes of the NEC (National Electric Corporation) accelerator tube are removed before the flange is united into the NEC tube, becoming the ES. The ES's are investigated in terms of their electron beam profiles and beam current output for the variation of the extraction electrode voltage as well as the focusing electrode voltage. The experimental results show that for the triode ES, the focusing electrode voltage greatly affects the shape of the electron beam profile up to 3 kV. However, for the diode ES, the shape of the electron beam profile is slightly affected by the extraction electrode voltage. The beam current output increases rapidly with the increase of the extraction electrode voltage up to 2.5 kV. Above this voltage, the beam current slowly increases, and it tends to reach saturation. The diode ES provides a higher electron beam current output than the triode ES output, but the triode ES provides a better shape of the electron beam profile. The constructed ES can provide the electron beam current of 40 mA at the filament current of 18 A.