X-ray tube device
First Claim
1. An X-ray tube device comprising:
- an X-ray tube containing an evacuated envelope;
a cathode structure emitting electron beams within said evacuated envelope, comprising a cathode filament for emitting electrons and an electron beam forming electrode focussing said electrons; and
an anode target having a target surface facing said cathode structure and inclined with respect to an X-ray irradiation axis, and emitting X-rays along said X-ray irradiation axis by bombardment of said electron beams; and
means for applying voltages to said anode target and said electron beam forming electrode with respect to said cathode filament;
wherein said cathode filament has a flat electron emission surface extending longer in a first axis direction than in a second axis direction normal to the first axis direction, the first axis direction being substantially parallel to the direction of the X-ray irradiation axis,a potential flattening electrode separate from said electron beam forming electrode is located on substantially the same plane as said electron emission surface in the vicinity of said electron emission surface of said cathode filament and is substantially at the same potential as said cathode filament;
said electron beam forming electrode has an electron beam transit hole located in the vicinity of said cathode filament and a focussing channel extending toward said anode target from said transit hole having a shape larger than that of said transit hole, a surface of said electron beam transit hole and an opening of focussing channel defining circles or polygonal shapes having at least four sides;
the length in the second axis direction of the surface of said electron beam transit hole is longer than the length in the second axis direction of said electron emission surface of said cathode filament;
the length in the first axis direction of the surface of said electron beam transit hole is substantially equal to the length in the second axis direction; and
the length in the first axis direction of the opening of said focussing channel is substantially equal to the length in the second axis direction.
1 Assignment
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Accused Products
Abstract
An X-ray tube has a cathode assembly for emitting an electron beam and an anode target facing this assembly in an evacuated envelope. The anode target defines a target surface that is slightly inclined to the electron beam axis and the direction in which it is inclined coincides with an X-ray irradiation direction. The cathode assembly comprises a flat cathode with a flat electron emission surface and a focussing electrode which focuses electrons emitted by the cathode. The cathode'"'"'s electron emission surface is elongated and its long axis is coincident with the direction of X-ray irradiation. The focussing electrode possesses an axially symmetric opening with generally the same dimensions lengthways and crosswise. This gives an X-ray tube device in which the shape of the X-ray focal spot seen looking from the X-ray irradiation direction is substantially that of a circle or of a polygon, including a square, and it is possible to vary the size of the X-ray focal spot over a wide range while maintaining its long to short side ratio at 1.4 or less.
47 Citations
8 Claims
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1. An X-ray tube device comprising:
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an X-ray tube containing an evacuated envelope; a cathode structure emitting electron beams within said evacuated envelope, comprising a cathode filament for emitting electrons and an electron beam forming electrode focussing said electrons; and
an anode target having a target surface facing said cathode structure and inclined with respect to an X-ray irradiation axis, and emitting X-rays along said X-ray irradiation axis by bombardment of said electron beams; andmeans for applying voltages to said anode target and said electron beam forming electrode with respect to said cathode filament; wherein said cathode filament has a flat electron emission surface extending longer in a first axis direction than in a second axis direction normal to the first axis direction, the first axis direction being substantially parallel to the direction of the X-ray irradiation axis, a potential flattening electrode separate from said electron beam forming electrode is located on substantially the same plane as said electron emission surface in the vicinity of said electron emission surface of said cathode filament and is substantially at the same potential as said cathode filament; said electron beam forming electrode has an electron beam transit hole located in the vicinity of said cathode filament and a focussing channel extending toward said anode target from said transit hole having a shape larger than that of said transit hole, a surface of said electron beam transit hole and an opening of focussing channel defining circles or polygonal shapes having at least four sides; the length in the second axis direction of the surface of said electron beam transit hole is longer than the length in the second axis direction of said electron emission surface of said cathode filament; the length in the first axis direction of the surface of said electron beam transit hole is substantially equal to the length in the second axis direction; and the length in the first axis direction of the opening of said focussing channel is substantially equal to the length in the second axis direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification