초록 ▼

An improved cathode assembly, including a filament for producing an electron stream having a highly uniform cross sectional density. The cathode assembly comprises a support base, a cathode cup affixed to the support base, and a filament disposed in a slot defined on the bottom face of the cup. In o

An improved cathode assembly, including a filament for producing an electron stream having a highly uniform cross sectional density. The cathode assembly comprises a support base, a cathode cup affixed to the support base, and a filament disposed in a slot defined on the bottom face of the cup. In one embodiment, the side walls of the slot are shaped so as to allow greater electric field penetration about regions of the filament that typically produce relatively low quantities of electrons, thereby increasing electron emission therefrom. Other embodiments are directed to modifying either the filament winding configuration or the wire from which the filament is formed, in order to equalize electron production by the filament. The uniformly dense electron stream is preferably directed toward the anode of an x-ray tube, thereby producing a superior x-ray beam for a variety of applications.

대표청구항 ▼

What is claimed is: 1. An x-ray tube comprising: (a) a vacuum enclosure; (b) a filament and a cathode cup including two walls which cooperate to at least partially define a slot wherein the filament is at least partially disposed, a distance between the filament and the at least one wall varying al

What is claimed is: 1. An x-ray tube comprising: (a) a vacuum enclosure; (b) a filament and a cathode cup including two walls which cooperate to at least partially define a slot wherein the filament is at least partially disposed, a distance between the filament and the at least one wall varying along at least a portion of the longitudinal length of the filament, and the distance between said filament and at least one of the at least two walls being at a minimum proximate a middle portion of the filament; and (c) an anode positioned within the vacuum enclosure so as receive electrons emitted by the filament. 2. The x-ray tube as recited in claim 1, wherein the distance between the filament and at least one of the at least two walls is at a maximum proximate at least one end portion of the filament. 3. The x-ray tube as recited in claim 1, wherein the at least two walls of the slot are of substantially the same shape and are symmetrically disposed with respect to the filament. 4. An x-ray tube as defined in claim 1, wherein the slot further comprises a bottom surface, and wherein the at least two walls are perpendicularly disposed with respect to the bottom surface. 5. The x-ray tube as recited in claim 1, wherein the slot defines a cross-section having a least two different widths. 6. The x-ray tube as recited in claim 1, wherein the filament is configured such that at least one of the properties of the filament varies along at least a portion of a longitudinal length of the filament, wherein the properties of the filament are selected from the group consisting of: filament wire diameter, pitch, filament diameter. 7. The x-ray tube as recited in claim 1, wherein the slot has a cross sectional area that varies along at least a portion of a length of the slot. 8. The x-ray tube as recited in claim 1, wherein an emission profile associated with the filament is such that a density of emitted electrons per unit area is substantially uniform throughout a predefined plane through which a substantial portion of the emitted electrons pass. 9. The x-ray tube as recited in claim 3, wherein the filament defines a plurality of pitches. 10. The x-ray tube as recited in claim 3, wherein the slot has first and second ends, the slot being wider at the first end than at the second end. 11. The x-ray tube as recited in claim 3, wherein the slot has first and second ends, the slot having substantially the same width at the first and second ends. 12. A cathode assembly suitable for use in an x-ray device, the cathode assembly comprising: (a) a base portion; (b) a cathode cup attached to the base portion, the cathode cup including at least two walls which cooperate to at least partially define a slot, wherein the slot defines a cross-section that varies along at least a portion of the length of the slot; and (c) a filament disposed substantially within the slot, the filament taking one of the following forms: a wire wound into successive coils to form a helix configured such that a diameter of the helix varies along a longitudinal axis defined by the filament, the variances in the diameter of the helix being substantially symmetrically arranged with respect to a predetermined location on the longitudinal axis; and a wire wound into successive coils to form a helix, where a diameter of the wire varies along a longitudinal axis defined by the filament, the variances in the diameter of the wire being substantially symmetrically arranged with respect to a predetermined location on the longitudinal axis. 13. The cathode assembly as recited in claim 12, wherein the predetermined location comprises a location proximate a center of the filament. 14. In an x-ray tube having a filament of predetermined longitudinal length, a method for producing an electron stream having a predetermined electron density profile, the method comprising: (a) applying a predetermined electric current to the filament so as to cause emission of electrons by the filament; (b) varying, with respect to the longitudinal length of the filament, the rate at which electrons are emitted by the filament, the varying of the rate at which electrons are emitted by the filament being implemented by performing one of: varying an electrical field strength in selected areas proximate the filament; and heating the filament in such a way that some portions of the filament are at a relatively higher temperature than other portions of the filament; and (c) accelerating at least some of the emitted electrons toward a focal spot located at a predetermined distance from the filament. 15. A filament, comprising: (a) a wire wound into successive coils to form a helix, the helix comprising a middle portion and first and second end portions, wherein at least one of a group of properties varies along at least a portion of a longitudinal length of the filament, the group of properties including: wire diameter, wire pitch, and coil diameter; and wherein the wire diameter is greater in the middle portion of the helix than in the first or second end portions; and (b) first and second electrical leads, the first electrical lead being attached to the first end portion of the helix, and the second electrical lead being attached to the second end portion of the helix. 16. The filament as recited in claim 15, wherein the filament comprises an element of a cathode assembly that includes: a base portion; and a cathode cup attached to the base portion, the cathode cup including two walls which cooperate to at least partially define a slot, the filament being at least partially disposed within the slot. 17. The filament as recited in claim 16, wherein the slot defined by the cathode cup has a cross-section that is substantially constant along a length of the slot. 18. The filament as recited in claim 16, wherein the slot that is defined by the cathode cup has a cross-section that varies along a length of the slot.