PURPOSE: To provide a field emission type electron gun which can radiate a highly bright and stable electron beam by increasing exhaust speed of an ion pump to hydrogen, and reducing pressure of an electron gun chamber.
CONSTITUTION: In a field emission type electron gun to exhaust air from an electron gun chamber 1 by an ion pump 30, the electron gun is provided with a circuit 25 to perform operation on a rate of an AC component to a DC component of an electric field line current, a filament 41, electric power supply 44 for the filament and a control circuit 26 to order to generate chemically active gas by carrying an electric current to the filament 41 when the rate of the AC component of the electric field line current exceeds a specific value.
KOBARI TOSHIAKI
NAKAIZUMI YASUSHI
