Patent ID: 7085354

Claim:
An X-ray tube apparatus comprising: an anode which radiates X-rays; and a cathode electron gun comprising, a cathode main body having a concave portion, at least first, second and third filaments which emit thermoelectrons to collide with the anode, and at least first, second and third respective converging electrodes which converge the respective thermoelectrons emitted by the first, second and third filaments and form respective focuses in a predetermined position of the anode, said at least first, second and third filaments and said at least first, second and third converging electrodes disposed within said concave portion, said first filament being a large focus filament and said second and third filaments being small focus filaments, said first filament and said first converging electrode corresponding to the first filament being provided in a deepest position in a depth direction of said concave portion, and said second and third filaments and said respective second and a third converging electrodes being provided on respective inclined surfaces of the concave portion, wherein the second and third converging electrodes are provided at equal inclination angles on inclined surfaces of the concave portion of the cathode main body, wherein said inclination angles of said inclined surfaces, defined as angles between planes including open end edges of each of the second and third converging electrodes and a plane including surfaces of the cathode main body more projected than all the converging electrodes, fall within a range of 20 to 40°, and wherein the small focus filaments can be simultaneously energized.