DUAL FILAMENT, ELECTROSTATICALLY CONTROLLED FOCAL SPOT FOR X-RAY TUBES

摘要

A dual filament x-ray tube assembly (16) includes an evacuated envelope (52) having an anode (54) disposed at a first end of the evacuated envelope (52) and a cathode assembly (62) disposed at a second end of the evacuated (52). The cathode assembly includes a variable-length filament assembly (72,74; 100) which emits electron beams for impingement on the anode (45) at focal spots having varying lengths. The cathode assembly (62) further includes a cathode cup which is subdivided into a plurality of electrically insulated deflection electrodes (64,66,68; 110, 112). A filament select circuit (80) selectively and individually heats a portion of the variable-length filament assembly (72,74). Electron beams emitted from the filament assembly (72,74) are electrostatically focused and controlled by applying potentials to different ones of the deflection electrodes (64,66,68; 110,112).