Simulation Study of Electron Beam Spot Size From Thermionic Electron Gun Using SIMION 8.1 Software

This paper is deal with the result of simulation study of electrons beam spot size from thermionic electron gun
using SIMION 8.1 software. The thermionic electron gun is an important part of electron beam machine (EBM) currently
developed at CAST BATAN Yogyakarta. It produces electrons beam which is dedicated for latex pre-vulcanization
process. The aim of simulation is to analyse the influence of electron gun parameters, such as electron beam intensity,
extraction voltage and acceleration voltage, on electron beam spot size and to predict the optimum size of electron beam spot at titanium window of EBM. The simulation was carried out by varying beam intensity from 2 mA up to 20 mA,
extraction voltage from 2 kV up to 12 kV and accelerating voltage from 150 kV up to 300 kV. From the result of
simulation it is concluded that thermionic electron gun can produce linear divergent electrons beam trajectory. This
trajectory is depend on the equipotential lines which are defined by electron gun parameters comprises electron beam
intensity, extraction voltage and accelerating voltage. Based on the simulation result, the influence of electron gun parameters on electron beam spot diameter can be summarized as follows: the variation of electron beam intensity from 2 mA up to 20 mA at extraction voltage of 12 kV and accelerating voltage of 300 kV yields the variation of electron beam spot diameter from 5.35 cm up to 5.49 cm. The variation of extraction voltage from 2 kV up to 12 kV at accelerating voltage of 300 kV and electron beam intensity of 20 mA yields the decrease of electron beam spot diameter
exponentially. The smallest diameters of electron beam spot are d1 = 5.41 cm and d2 = 5.44 cm at extraction voltage of 10 kV and 12 kV respectively. The variation of accelerating voltage from 150 kV up to 300 kV at extraction voltage of 12
kV and electron beam intensity of 20 mA yields the decrease of electron beam spot diameter significantly. The smallest
diameters of electron beam spot are d1 = 5.41 cm and d2 = 5.42 cm at accelerating voltage of 300 kV and 275 kV
respectively. d1 and d2 are diameter of electron beam spot along y axis and x axis respectively.