Development of battery charging system for the FE gun system of HVEM

We have developed a reliable and efficient battery-charging system for the field emission (FE) gun system of high voltage electron microscopes, where the operating condition of the whole FE gun system can be controlled and monitored through a bi-directional optical fiber system, and the control and monitoring circuits located on the high potential of 1 MV are driven by rechargeable Ni-Cd batteries. The power transmission from ground to the high potential is performed through filter condenser circuit. Under the condition that the filter condenser current is limited to 0.2 A(rms) (root-mean-square value), it is possible to transmit the maximum power as high as 65 W, which is enough for the daily operation of the FE gun system. The charging circuit has a function of protecting the batteries from over-charging.