X-ray tube cathode with reduced unintended electrical field emission

• US 20070076849A1
• Filed: 09/28/2006
• Published: 04/05/2007
• Est. Priority Date: 09/30/2005
• Status: Active Grant

• Current Assignee: Moxtek Inc (Nippon Kayaku Company Limited)
• Original Assignee: Moxtek Inc (Nippon Kayaku Company Limited)
• Inventors: Liddiard, Steven, Jensen, Charles, Ogden, Shaun, Bard, Erik
• Granted Patent: US 7,382,862 B2
• Time in Patent Office: Days
• US Class Current: 378/121
• CPC Class Codes: H01J 2235/1216 of the vessel
• CPC Class Codes: H01J 35/147 Spot size control
• CPC Class Codes: H01J 35/186 used as targets or X-ray converters

Abstract

An x-ray source has an evacuated tube. An anode is disposed in the tube and includes a material configured to produce x-rays in response to impact of electrons. A cathode is disposed in the tube opposing the anode configured to produce electrons accelerated towards the anode in response to an electric field between the anode and the cathode. A flange extends from the cathode toward the anode, and has a smaller diameter than the evacuated tube. The flange extends closer to the anode than an interface between the cathode and the tube thus forming a reduced-field region between the evacuated tube and the flange.

Claims

1. An x-ray source device, comprising:

a) an evacuated dielectric tube;

b) an anode, disposed at an end of the tube, including a material configured to produce x-rays in response to impact of electrons; and

c) a cathode, disposed at an opposite end of the tube opposing the anode, including a cathode element configured to produce electrons accelerated towards the anode in response to an electric field between the anode and the cathode; and

d) an annular flange, extending from the cathode toward the anode within the tube, having a smaller diameter than an inner diameter of the evacuated tube to form an annular space between the flange and the evacuated tube, and extending closer to the anode than an interface between the cathode and the tube.

2. A device in accordance with claim 1, wherein the interface between the cathode and the evacuated tube is formed by substantially flat opposing faces of the cathode and the evacuated tube, the opposing faces extending between the inner diameter and an outer diameter of the evacuated tube at a substantially orthogonal angle with respect to a longitudinal axis of the evacuated tube.

3. A device in accordance with claim 1, wherein the interface between the cathode and the evacuated tube is formed by substantially flat opposing faces of the cathode and the evacuated tube, the opposing faces extending between the inner diameter and an outer diameter of the evacuated tube at an oblique angle with respect to a longitudinal axis of the evacuated tube to define an annular beveled interface between the cathode and the evacuated tube.

4. A device in accordance with claim 1, wherein the interface between the cathode and the evacuated tube is formed by opposing faces of the cathode and the evacuated tube, the opposing faces including two surfaces forming an approximate right angle and defining a corner in the interface.

5. A device in accordance with claim 1, further including a joining material disposed in an interface between the cathode and the evacuated tube to join the evacuated tube to the cathode element.

6. A device in accordance with claim 5, wherein the cathode includes an annular groove disposed in the cathode adjacent an outer diameter of the annular flange, the annular groove configured to contain excess joining material from the interface between the cathode and the evacuated tube.

7. A device in accordance with claim 1, wherein the flange shields the interface between the cathode and the evacuated tube from the electrons accelerated from the cathode element towards the anode to prevent unintended field emissions.

8. A device in accordance with claim 1, wherein the flange forms a well between the flange and the evacuated tube to contain overfill of a joining or braze material used to join the tube to the cathode element.

9. A device in accordance with claim 1, further comprising:

a field-free region, positioned between the flange and the tube, configured to resist arcing and field emission between the cathode and adjacent materials.

10. A device in accordance with claim 4, wherein the flange focuses the electrons accelerated from the cathode element to the anode element.

11. A device in accordance with claim 1, wherein the tube has a length less than approximately 3 inches, and a diameter or width less than approximately 1 inch.

12. A device in accordance with claim 1, wherein the cathode is a low-power consumption cathode, and wherein the cathode element has a low power consumption less than approximately 1 watt.

13. A device in accordance with claim 1, further comprising a battery power source.

14. A mobile, minature x-ray source device, comprising:

a) an evacuated dielectric tube having a length less than approximately 3 inches, and a diameter or width less than approximately 1 inch;

b) an anode, disposed at an end of the tube, including a material configured to produce x-rays in response to impact of electrons; and

c) a low-power consumption cathode, disposed at an opposite end of the tube opposing the anode, including a cathode element configured to produce electrons accelerated towards the anode in response to an electric field between the anode and the cathode, the cathode element having a low power consumption less than approximately 1 watt; and

d) an annular flange, extending from the cathode toward the anode within the tube, having a smaller diameter than an inner diameter of the evacuated tube to form an annular space between the flange and the evacuated tube, and extending closer to the anode than an interface between the cathode and the tube.

15. A device in accordance with claim 14, wherein the interface between the cathode and the evacuated tube is formed by substantially flat opposing faces of the cathode and the evacuated tube, the opposing faces extending between the inner diameter and an outer diameter of the evacuated tube at a substantially orthogonal angle with respect to a longitudinal axis of the evacuated tube.

16. A device in accordance with claim 14, wherein the interface between the cathode and the evacuated tube is formed by substantially flat opposing faces of the cathode and the evacuated tube, the opposing faces extending between the inner diameter and an outer diameter of the evacuated tube at an oblique angle with respect to a longitudinal axis of the evacuated tube to define an annular beveled interface between the cathode and the evacuated tube.

17. A device in accordance with claim 14, wherein the interface between the cathode and the evacuated tube is formed by opposing faces of the cathode and the evacuated tube, the opposing faces including two surfaces forming an approximate right angle and defining a corner in the interface.

18. A device in accordance with claim 14, further including a joining material disposed in an interface between the cathode and the evacuated tube to join the evacuated tube to the cathode element.

19. A device in accordance with claim 18, wherein the cathode includes an annular groove disposed in the cathode adjacent an outer diameter of the annular flange, the annular groove configured to contain excess joining material from the interface between the cathode and the evacuated tube.

20. A method for making an x-ray source device, comprising:

a) joining an anode to an end of an evacuated tube, the anode including a material configured to produce x-rays in response to impact of electrons;

b) positioning a cathode at an opposite end of the evacuated tube from the anode, the cathode having an annular flange, extending from the cathode into the tube toward the anode, the annular flange having a smaller diameter than an inner diameter of the evacuated tube to form a space between the flange and the evacuated tube, and extending closer to the anode than an interface between the cathode and the tube, and including a cathode element configured to produce electrons accelerated towards the anode in response to an electric field between the anode and the cathode; and

c) joining the cathode to the evacuated tube with the annular flange shielding the interface.