Design of Sheet-Beam Electron Gun with Planar Cathode for Terahertz Devices

The design of a sheet-beam electron gun with planar cathode was made with the help of a three-dimensional electrostatic field solver that was capable of forming a sheet-beam of 19 mA at 12 kV. It uses one-dimensional three-fold beam cross-sectional area compression meets the specific requirement of a beam to be formed of height 30 µm and width 600 µm at the beam–waist position with over 100 A/cm2 uniform current density and 0.068 π-mm-mrad emittance, typically, for 0.5 THz devices. A novel beam focusing electrode (BFE) provided with extended-corner rectangular-aperture geometry alleviating the commonly encountered sheet-beam formation problem with a gun that uses a conventional BFE, as well as it reduced beam emittance more than 50%. The practicability of the design was tested by the high-voltage, the thermal and structural analyses. Work has been initiated to test the performance of special high current scandate cathode using anode-aperture mapping.