Patent ID: 7423390

Claim:
An electron beam generator for multiple columns comprising: a plurality of cathodes, to which a single acceleration voltage supply applies a negative acceleration voltage, and which thus generates thermoelectrons; a grid for each of the plurality of cathodes, the grid converging the thermoelectrons emitted from the cathode to form a beam of electrons; a grid voltage supply for each of the plurality of cathodes, the grid voltage supply giving the grid an electric potential which is negative relative to an electric potential of the cathode; and a control circuit for each of the plurality of cathodes, the control circuit, connected to the acceleration voltage supply, for controlling the electric potential of the grid, wherein the control circuit includes an electric current direction restricting element connected between a positive electrode of the grid voltage supply and the cathode, and wherein the grid electric current supplied from the grid voltage supply is caused to flow to the cathode through the electric current direction restricting element.