| 摘要 |
An X-ray tube is disclosed, which comprises an evacuated envelope having a cathode assembly and an anode assembly provided at the opposite ends of the envelope such that they face each other. The cathode assembly includes a spiral filament for generating an electron beam with a beam axis. One of the terminal ends of the spiral filament is located in the proximity of the center thereof. The anode assembly includes a conical target with a tip corresponding to the beam axis, for radiating X-rays in all directions. When a current flows with the filament of the X-ray tube, the temperature of the filament is reduced for a central portion thereof to reduce the density of electrons emitted from the central portion, thus preventing overheating of the tip of the conical target.
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