Electron gun device

Abstract

An electron gun device, in particular for an X-ray tube, includes a metallic first electrode having a first electrode contact surface; a metallic second electrode having a second electrode contact surface; and a ring-shaped ceramic insulator having a first insulator contact surface on a first side with respect to an axial direction of the insulator and a second insulator contact surface on an opposite second side with respect to the axial direction. In an assembled state, the first insulator contact surface faces the first electrode contact surface and is connected to the first electrode contact surface via a first brazing joint, and the second insulator contact surface faces the second electrode contact surface and is connected to the second electrode contact surface via a second brazing joint.

Claims

1. An electron gun device, in particular for an X-ray tube, comprising: a metallic first electrode having a first electrode contact surface; a metallic second electrode having a second electrode contact surface; and a ring-shaped ceramic insulator having a first insulator contact surface on a first side with respect to an axial direction of the insulator and a second insulator contact surface on an opposite second side with respect to the axial direction, wherein, in an assembled state, the first insulator contact surface faces the first electrode contact surface and is connected to the first electrode contact surface via a first brazing joint, and the second insulator contact surface faces the second electrode contact surface and is connected to the second electrode contact surface via a second brazing joint.

2. The electron gun device according to claim 1, wherein the first brazing joint and/or the second brazing joint is an active brazing joint.

3. The electron gun device according to claim 1, wherein the first insulator contact surface and/or the second insulator contact surface contains unmetallized portions and is preferably essentially completely unmetallized before brazing.

4. The electron gun device according to claim 1, wherein the first brazing joint is done using a first brazing foil between the first electrode contact surface and the first insulator contact surface and/or the second brazing joint is done using a second brazing foil between the second electrode contact surface and the second insulator contact surface.

5. The electron gun device according to claim 1, wherein the first electrode and/or the second electrode contains and is preferably made from molybdenum or an alloy thereof.

6. The electron gun device according to claim 1, wherein the insulator contains and is preferably made from aluminum oxide or aluminum nitride.

7. The electron gun device according to claim 1, wherein the insulator comprises at least one holding feature for delimiting a flow of a brazing filler metal during brazing.

8. The electron gun device according to claim 7, wherein the holding feature is further intended for positioning a brazing foil prior to brazing.

9. The electron gun device according to claim 7, wherein the holding feature comprises a first collar at least partly and preferably completely encircling the first insulator contact surface and/or a second collar at least partly and preferably completely encircling the second insulator contact surface.

10. The electron gun device according to claim 7, wherein the holding feature at least partly overlaps the first electrode and/or the second electrode preferably at least with respect to the axial direction.

11. The electron gun device according to claim 1, wherein the holding feature is intended to act as a dielectric barrier against spurious electron emission in the vicinity of the electrode-insulator interface.

12. An X-ray tube comprising an electron gun device according to claim 1.

13. A method for assembling of an electron gun device, in particular according to claim 1, in particular for an X-ray tube, the electron gun device comprising: a metallic first electrode having a first electrode contact surface; a metallic second electrode having a second electrode contact surface; and a ring-shaped ceramic insulator having a first insulator contact surface on a first side with respect to an axial direction of the insulator and a second insulator contact surface on an opposite second side with respect to the axial direction, wherein the first insulator contact surface is mounted facing the first electrode contact surface and is connected to the first electrode contact surface via a first brazing, and the second insulator contact surface is mounted facing the second electrode contact surface and is connected to the second electrode contact surface via a second brazing, preferably conducted simultaneously to the first brazing.

14. The method according to claim 13, wherein brazing is done using an active brazing filler metal on unmetallized insulator contact surfaces.

15. The method according to claim 13, wherein the first brazing is made using a first brazing foil between the first electrode contact surface and the first insulator contact surface and/or the second brazing is made using a second brazing foil between the second electrode contact surface and the second insulator contact surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Preferred embodiments of the invention are explained in greater detail below with reference to the appended schematic drawings, which show the following:

[0041] FIG. 1 an X-ray tube comprising an electron gun device;

[0042] FIG. 2 the electron gun device in an assembled state;

[0043] FIG. 3 the electron gun device in a disassembled state before brazing;

[0044] FIG. 4 a ring-shaped ceramic insulator of the electron gun device;

[0045] FIG. 5 a brazing foil of the electron gun device; and

[0046] FIG. 6 a flow diagram of a method for assembling the electron gun device.

DETAILED DESCRIPTION

[0047] FIG. 1 shows an X-ray tube 12, whose geometry and mode of operation is principally known. The X-ray tube 12 comprises an electron gun device 10. The X-ray tube 12 further comprises an electron tube 50, in which the electron gun device 10 is at least partly located. At least during operation, the electron tube 50 is evacuated. The X-ray tube 12 comprises a high voltage supply 48 for supplying a high voltage to the electron gun device 10 via a voltage supply connection 60 of the X-ray tube 12. The electron gun device 10 is intended to generate and eject free electrons 56 along an electron beam direction 62 into the electron tube 50. The electrons 56 are accelerated via a high voltage provided by the high voltage supply 48 toward a target head 52 of the X-ray tube 12. The target head 52 comprises a target 46, whereupon the electrons 56 are directed. Upon hitting the target 46, X-rays 58 are generated and allowed to exit the target head 52 via a window 54 of the target head 52. The target 46 could be made from any suitable material, for example tungsten.

[0048] The invention is directed to the electron gun device 10, which is shown in FIG. 2 in its assembled state. The electron gun device 10 comprises an electron emitter 64 for generating the free electrons 56. The electrode emitter 64 is an oxide-coated dispenser-cathode, which is made from a block of porous tungsten infiltrated by chemicals, most importantly BaO (Barium oxide), and whose actual emitter surface is indirectly heated by a heating filament which is potted into alumina (not shown). However, any other type of electron emitter would also be conceivable.

[0049] The freed electrons 56 are then accelerated and ejected via a stack of three metallic electrodes 14, 18, 44, namely a metallic first electrode 14, a metallic second electrode 18 and a metallic third electrode 44. In alternative embodiments a different number of metallic electrodes 14, 18, 44 could be chosen, for example 2 or at least 4.

[0050] The electron emitter 64 is electrically connected to the third electrode 44. During operation, the third electrode 44 and the electrode emitter 64 together constitute a cathode at an electric potential of typically 3 kV to 0.5 kV. However, a different electric potential could also be conceivable. The third electrode 44 is in the shape of a circular disk with recesses and/or cutouts for the electron emitter 64 and/or for electrical leads to the electron emitter 64 and/or for electrical leads for high voltage supply of the electrodes 14, 18, 44.

[0051] The first electrode 14 is located between the third electrode 44 and the second electrode 18. The first electrode 14 is a grid electrode, intended for controlling an electron flux. The electric potential of the first electrode 14 is changeable and could be set to a potential that is more negative than the cathode potential. The first electrode 14 is in the shape of a circular ring disk with a first passage 66 for letting the electrons 56 pass. The first electrode 14 has a thickness between 0.1 mm and 0.5 mm.

[0052] The second electrode 18 is a focus electrode. During operation, the second electrode 18 is at a more positive potential than the first electrode 14 and the third electrode 44. The second electrode 18 is at ground potential during operation. The second electrode 18 is in the shape of a circular ring disk with a second passage 68 for letting the electrons 56 pass and exit the electron gun device 10 along the electron beam direction 62. Thus, the second passage 68 defines an aperture opening of the electron gun device 10. The second electrode 18 has a thickness between 0.1 mm and 0.5 mm.

[0053] The electron gun device 10 comprises a circular ring-shaped ceramic insulator 22 and a circular ring-shaped ceramic further insulator 23. The electrodes 14, 18, 44 are separated and electrically insulated against each other by the insulator 22 and the further insulator 23. FIG. 4 shows a top view of the insulator 22. The further insulator 23 is identical to the insulator 22 in the present embodiment. However, the further insulator 23 could also have a different geometry and/or material composition than the insulator 22. The insulator 22 has an open interior 70. The further insulator 23 has a further open interior 72. The open interiors 70, 72, the passages 66, 68 and the electron emitter 64 are all aligned along an axial direction 26 of the insulator 22 in order to allow the electrons 56 to pass. The open interiors 70, 72, the passages 66, 68 and the electron emitter 64 are all aligned along the electron beam direction 62.

[0054] The electrodes 14, 18, 44 and the insulators 22, 23 are alternatingly stacked one on top of the other. The electrodes 14, 18, 44 and the insulators 22, 23 are alternatingly stacked face on. Starting from the electron emitter 64, the ordering is as follows: third electrode 44, further insulator 23, first electrode 14, insulator 22, and finally second electrode 18. A distance along the axial direction 26 between the first electrode 14 and the second electrode 18 is between 0.05 mm and 0.5 mm, in particular 0.25 mm. A distance along the axial direction 26 between the electron emitter 64 and the first electrode 14 is between 0.05 mm and 0.5 mm, in particular 0.1 mm.

[0055] The first electrode 14 comprises a first electrode contact surface 16. The second electrode 18 has a second electrode contact surface 20. The insulator 22 comprises first insulator contact surface 24 on a first side with respect to the axial direction 26, the axial direction 26 being parallel to the electron beam direction 62, and a second insulator contact surface 28 on an opposite second side with respect to the axial direction 26. In an assembled state, the first insulator contact surface 24 faces the first electrode contact surface 16 and is connected to the first electrode contact surface 16 via a first brazing joint 30. Likewise, the second insulator contact surface 28 faces the second electrode contact surface 20 and is connected to the second electrode contact surface 20 via a second brazing joint 32.

[0056] The electrode 14, 18, 44 are made from molybdenum. The insulators 22, 23 are made from any typical technical ceramic, such as aluminum oxide or aluminum nitride, the latter being preferred since it has a similar thermal expansion coefficient like molybdenum. Each of the insulators 22, 23 is connected to two of the electrodes 14, 18, 44 by active metal brazing in a high temperature vacuum furnace (not shown). The first insulator contact surface 24 and the second insulator contact surface 28 are essentially completely unmetallized before brazing. The first brazing joint 30 and the second brazing joint 32 are active brazing joints.

[0057] FIG. 3 shows an exploded view of the electron gun device 10 prior to brazing. The first brazing joint 30 is done using a first brazing foil 34 between the first electrode contact surface 16 and the first insulator contact surface 24 and the second brazing joint 32 is done using a second brazing foil 36 between the second electrode contact surface 20 and the second insulator contact surface 28. The brazing foils 34, 36 are made from active metal brazing material. FIG. 5 shows a top view of the first brazing foil 34. The second brazing foil 36 is identical to the first bracing foil 34 in the present embodiment. However, the second brazing foil 36 could also have a different geometry and/or material composition than the first bracing foil 34.

[0058] The insulator 22 comprises a holding feature 38 for delimiting a flow of a brazing filler metal during brazing. The holding feature 38 is further intended for positioning the first brazing foil 34 and the second brazing foil 36 prior to brazing. The holding feature 38 comprises a first collar 40 completely encircling the first insulator contact surface 24 and a second collar 74 completely encircling the second insulator contact surface 28. The brazing foils 34, 36 snugly fit into the respective collar 40, 74 and are dimensioned to not reach into the open interior 70 of the insulator 22. The cross sectional area of the insulators 22, 23 is that of a vertically flattened letter T with the collars 40, 74 at least partly forming the crossbar.

[0059] In the assembled state the holding feature 38 and the collars 40, 74, at least partly overlap the first electrode 14 and the second electrode 18 with respect to the axial direction 26. During operation, the holding feature 38 is intended to act as a dielectric barrier against spurious electron emission in the vicinity of the electrode-insulator interface 42.

[0060] The above descriptions regarding the connection of the insulator 22 to the first electrode 14 and the second electrode 18 apply likewise to the connection of the further insulator 23 to the first electrode 14 and the third electrode 44.

[0061] FIG. 6 depicts a flow diagram of a method for assembling the electron gun device. In a step 100 the electrodes 14, 18, 44, the insulators 22, 23 and the brazing foils 34, 36 are stacked as shown in FIG. 3. In the following step 110 this assembly is brazed by active metal brazing in a high temperature vacuum furnace (not shown). In a following step 120 the assembly is allowed to cool down or is actively cooled down. In a step 130 the electrode emitter 64 is mounted to the third electrode 44. In a step 140 all remaining electrical connections for connecting the first electrode 14 and the second electrode 18 are finalized. In alternative embodiments, the step 130 and/or the step 140 could also be done at the beginning.

REFERENCE NUMERALS

[0062] 10 electron gun device [0063] 12 X-ray tube [0064] 14 first electrode [0065] 16 first electrode contact surface [0066] 18 second electrode [0067] 20 second electrode contact surface [0068] 22 insulator [0069] 23 further insulator [0070] 24 first insulator contact surface [0071] 26 axial direction [0072] 28 second insulator contact surface [0073] 30 first brazing joint [0074] 32 second brazing joint [0075] 34 first brazing foil [0076] 36 second brazing foil [0077] 38 holding feature [0078] 40 first collar [0079] 42 electrode-insulator interface [0080] 44 third electrode [0081] 46 target [0082] 48 high voltage supply [0083] 50 electron tube [0084] 52 target head [0085] 54 window [0086] 56 electrons [0087] 58 X-rays [0088] 60 voltage supply connection [0089] 62 electron beam direction [0090] 64 electron emitter [0091] 66 first passage [0092] 68 second passage [0093] 70 open interior [0094] 72 further open interior [0095] 74 second collar [0096] 100 Step [0097] 110 Step [0098] 120 Step [0099] 130 Step [0100] 140 Step