Numerical Simulation of Beam Formation and Transport in an Electron Gun for Different Applications

A Pierce-type electron gun with spherical anode has been numerically computer-aided analysed to yield an appropriate beam with suitable properties valid for different applications. It has been proven that, around a certain value of the aspect ratio, 0.75, the resultant beam geometry could be suitably controlled. The gun geometry plays an important role for beam shaping; parallel, converged or diverged. The minimum electric field required to prevent beam expansion due to space charge effect has been estimated and it is found to be proportional to the cubic root of the distance from the anode to the target (Z1/3). Also, it is proved that the minimum beam radius is realized at the minimum beam perveance and the maximum beam convergence angle. As a result, this reveals that, the gun geometry controls the beam emittance. The gun design analysis proposed here helps to choose the better operating conditions suitable for low energy electron beam bombardment and/or injection applications.