Development of remote control and monitoring system for the FE gun in HVEM

This paper describes a control and monitoring system for the field emission (FE) gun in the high-voltage electron microscope (HVEM), where the whole FE gun system is located inside a pressure vessel and is floated on a high voltage of 1 MV. The operating condition of the FE gun system is controlled and monitored mainly by a bi-directional communication system between ground and high potential through optical fibres. A mechanical driving system by combination of insulator rods and stepping motors is partially used as a control system for FE gun operation. The monitoring system developed here also functions as a safety circuit that detects abnormal situations, such as an abnormal deterioration of vacuum, and protects the FE tip against fatal damage. The fundamental performance of the microscope has been tested for transmission electron microscope (TEM) and scanning TEM operation modes.