| 摘要 |
An x-ray tube having an improved focusing arrangement is provided. The x-ray tube includes an evacuated envelope and an anode disposed within the envelope. A positive electrical potential, with respect to ground, is applied to the anode. A filamentary cathode emits an electron beam toward the anode. A first negative electrical potential, with respect to ground, is coupled to the filament and to an electrically conductive cathode body, which focuses the electron beam onto the anode at a focal spot, the focal spot having a length, corresponding to the length of the filament, and a width. The cathode body has an opening disposed therein and supports the filament in such opening. An electrode is insulatingly disposed in the opening of the body and applied with a negative electrical potential with respect to the first negative potential. With such arrangement, electron emissions from selected portions of the filaments are suppressed by apparatus displaced from the path of the electron beam, thereby reducing the width of the electron beam focal spot, and hence the area of such focal spot, while maintaining the total current of the electron beam substantially unchanged.
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