Two-part high voltage vacuum feed through for an electron tube

Abstract

A high voltage vacuum feed through (23) for an electron tube (25) has an anode (28) and an insulating body (1) of ceramic material, the insulating body (1) having a continuous hollow space (10). The anode (28) has a rear part (2) and a front part (3) mounted thereto. The rear part (2) consists of a first metallic material, having a thermal expansion coefficient corresponding to a thermal expansion coefficient of the ceramic material. The rear part (2) is arranged in the hollow space (10) of the insulating body (1) and is soldered into the insulating body (1) in a vacuum-tight fashion. The front part (3) has a second metallic material whose heat conductivity is larger than that of the first metallic material. The high voltage vacuum feed through reliably remains vacuum-tight during operation and can be easily provided with different target materials.

Claims

1. A solid anode X-ray tube, the tube having a voltage vacuum feed through, wherein the feed through comprises: an insulating body made of ceramic material, said insulating body having a continuous hollow space; and an anode, said anode having a two-part design with a rear part and a front part, said front part having a target to produce X-rays, said rear part being made from a first metallic material having a thermal expansion coefficient α.sub.ht which differs by at most 50% from a thermal expansion coefficient α.sub.ker of said ceramic material, wherein said rear part is arranged in said hollow space of said insulating body and is soldered into said insulating body to seal said hollow space in a vacuum-tight fashion, said front part comprising a second metallic material having a heat conductivity λ.sub.vt which is larger than a heat conductivity λ.sub.ht of said first metallic material of said rear part, wherein said front part is mounted to said rear part, wherein said insulating body has a wall thickness WSv in a front area which is larger than a wall thickness WSm in a central area and said rear part extends at least partially in said central area, wherein WSm≦⅔*WSv and at least ⅔ of a length of said rear part extends in said central area and further comprising a cooling device seated on an outside of said insulating body in said central area.

2. The solid anode X-ray tube of claim 1, wherein said rear part and said front part are inserted into each other.

3. The solid anode X-ray tube of claim 2, wherein said rear part comprises a receiving section having a recess at a front end thereof and said front part has a plug-in section at a rear end thereof, wherein said plug-in section is inserted into said receiving section.

4. The solid anode X-ray tube of claim 3, wherein said front part has a longitudinal bore extending to a bottom of said recess of said receiving section, said front part also having a transverse bore which is connected to said longitudinal bore, wherein said transverse bore terminates outside of said receiving section.

5. The solid anode X-ray tube of claim 2, wherein said rear part and the front part are connected to each other through shrinking.

6. The solid anode X-ray tube of claim 1, wherein said ceramic material of said insulating body is aluminum oxide (Al.sub.2O.sub.3) and said first metallic material of said rear part is made of an iron nickel cobalt alloy.

7. The solid anode X-ray tube of claim 6, wherein said iron nickel cobalt alloy has weight portions of Fe=53-54%, Ni=28-29% and Co=17-18%.

8. The solid anode X-ray tube of claim 1, wherein said second metallic material is Cu.

9. The solid anode X-ray tube of claim 1, wherein a front end of said front part has a coating, a top part or an insert of molybdenum, tungsten, rhodium, silver, cobalt or chromium.

10. The solid anode X-ray tube of claim 1, wherein a rear end of said rear part comprises a connector section having a recess for receiving a high voltage plug.

11. The solid anode X-ray tube of claim 1, wherein said cooling device comprises a metallic sheathing on said insulating body.

12. The solid anode X-ray tube of claim 1, wherein said rear part is soldered into said insulating body with a solder containing Ag or Au, said insulating body having a nickel-plated molybdenum manganese (MoMn) coating, at least in a soldered area thereof.

13. A method for producing the vacuum feed through of the solid anode X-ray tube of claim 1, the method comprising the steps of: a) producing the insulating body; b) inserting the rear part of the anode into the hollow space of the insulating body and vacuum-tight soldering of the rear part into the insulating body; and c) mounting the front part of the anode to the rear part.

14. The method of claim 13, wherein said front part is mounted to said rear part in step c) through placing on top and shrinking.

15. The method of claim 13, wherein steps a) and b) are initially performed for a plurality of vacuum feed throughs and partly finished vacuum feed throughs are subsequently provided with front parts, either individually or in groups in accordance with step c), wherein various different types of front parts are used.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a schematic longitudinal section through a ceramic insulating body in the form of a dumbbell for a high voltage vacuum feed through in accordance with the invention;

(2) FIG. 2 shows a schematic longitudinal section through a partly finished high voltage vacuum feed through in accordance with the invention with an insulating body in the form of a dumbbell in accordance with FIG. 1;

(3) FIG. 3 shows a schematic longitudinal section through a high voltage vacuum feed through in accordance with the invention with an insulating body in the form of a dumbbell and a rear part of an anode in accordance with FIG. 2;

(4) FIG. 4 shows a schematic exterior view of the inventive high voltage vacuum feed through of FIG. 3 with cooling device which has not yet been outwardly seated;

(5) FIG. 5 shows the high voltage vacuum feed through of FIG. 4 in longitudinal section with seated cooling device;

(6) FIG. 6 shows a schematic exterior view of a front part of an anode for an inventive high voltage vacuum feed through which is completely produced of copper;

(7) FIG. 7 shows a schematic exterior view of a front part of an anode for an inventive high voltage vacuum feed through with an insert of tungsten at the front end;

(8) FIG. 8 shows a schematic longitudinal section of an inventive high voltage vacuum feed through with a ceramic insulating body having a substantially uniform wall thickness; and

(9) FIG. 9 shows a schematic longitudinal section of an inventive electron tube with an inventive high voltage vacuum feed through in accordance with FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(10) FIGS. 1 through 3 show the production of an inventive high voltage vacuum feed through in different chronologically successive stages.

(11) A ceramic insulating body 1 is initially produced or provided, cf. FIG. 1. In the present case, the insulating body 1 is produced from aluminium oxide ceramic material, e.g. through slip casting or other conventional forming technologies, followed by sintering. If desired or required, the Al.sub.2O.sub.3 ceramic material may contain sintering aids or other additives for optimizing the production process or the quality of the sintered ceramic material in a manner known per se.

(12) The insulating body 1 is substantially configured to be tubular and has, in particular, a continuous hollow space 10 that extends in a longitudinal direction (cf. longitudinal axis LA) similar to a bore. The insulating body 1 is rotationally symmetrical with respect to the longitudinal axis LA in this case. The hollow space 10 has a step 11 that serves as a stop for a rear part of an anode to be inserted from the front (in the present case right-hand) end 12 (cf. FIG. 2). A high voltage line can be guided to the anode (not shown) from a rear (in the present case left-hand) end 13.

(13) In a front area VB, the insulating body 1 additionally has an (average) wall thickness WSv that is larger than the (average) wall thickness WSm in a central area MB. The (average) wall thickness WSh is moreover again larger in a rear area HB than in the central area MB. For this reason, the insulating body has the shape of a dumbbell. The front area VB, the central area MB and the rear area HB extend together over the overall axial length of the insulating body 1.

(14) A rear part 2 of an anode is then inserted into the insulating body 1 or its hollow space 10, cf. FIG. 2 and is soldered on its outside along its circumference to the inner wall of the hollow space 10. Towards this end, the insulating body 1 may initially be provided on the inside with a MoMn coating at least in an area bordering step 11 on the right hand side, e.g. via a CVD method and be soldered with a solder containing Ag or Au. Soldering is performed in a vacuum-tight fashion, which is easy to realize when the gap between the rear part 2 and the inner wall of the insulating body 1 is sufficiently small. In the present case, the rear part 2 is produced from a Fernico alloy, the thermal expansion coefficient of which corresponds to the thermal expansion coefficient of the insulating body 1 (both with respect to the radial direction and also axial longitudinal direction).

(15) The rear part 2 and the joint seal the hollow space 10 close to the front end 12 in a vacuum-tight fashion, i.e. gas exchange between the front end 12 and the rear end 13 via the hollow space 10 is no longer possible.

(16) The rear end of the rear part 2 is provided with a connector section 14 having a recess 15 for receiving a high voltage plug (the latter is not shown in detail). The front end of the rear part 2 is provided with a receiving section 16 with a recess 17 for receiving a plug-in section of a front part of the anode (cf. FIG. 3 in this connection).

(17) The insulating body 1 with soldered rear part 2 of the anode, however without installed front part, is also called partly produced vacuum feed through 34.

(18) A front part 3 of the anode is then mounted, cf. FIG. 3, for completing the vacuum feed through 23. The rear end of the front part 3 is provided with a plug-in section 18 that is inserted into the recess 17 of the rear part 2.

(19) Towards this end, the front part 3 is initially significantly cooled down, typically to the temperature of liquid nitrogen (approximately 77K), through insertion into the liquid nitrogen such that the plug-in section 18 is radially contracted. The rear part 2 is additionally heated together with the insulating body 1, e.g. in an oven, to 200° C. such that the recess 17 radially widens. With these temperature conditions, the plug-in section 18 may be just about inserted into the recess 17. As soon as the temperature conditions normalize, i.e. the front and rear parts 3, 2 have the same temperature, the recess 17 has been radially contracted and the plug-in section 18 has been radially widened to such an extent that the front and rear parts 3, 2 are radially clamped and can no longer be removed from each other.

(20) In order to prevent air occlusions between the recess 17 and the plug-in section 18, in particular at the bottom 33 of the recess 17, during fitting, the front part 3 has a longitudinal bore 19 and a transverse bore 20 that intersects the longitudinal bore 19. Air can then escape from the bottom 33 of the recess 17 through the bores 19, 20 in case the gap between the side wall 21 of the receiving section 16 and the outer wall of the plug-in section 18 is too small for gas to escape.

(21) In the present case, the front part 3 is completely produced of copper in order to ensure quick and efficient heat transport from the area of the target 22 at the front end of the front part 3 of the anode into the insulating body 1 during operation. The heat thereby flows mainly through the front part 3 to the plug-in section 18, through the side wall 21 of the receiving section 16 of the rear part 2 and partially also through the further rear part 2, into the Insulating body 1.

(22) If desired, the front end of the front part 3 may be provided with a coating, a top part or an insert made from another material than copper in order to generate characteristic X-ray radiation in correspondence with this other material on the target 22 (cf. FIG. 7 in this case).

(23) The front end of the front part 3 projects out of the insulating body 1. The vacuum feed through 23 is integrated in an electron tube or X-ray tube as intended (cf. FIG. 9 in this case).

(24) As is shown in FIG. 4, the vacuum feed through 23 may be provided with a cooling device 4 which consists in the present case of a metallic sheathing, preferably of copper or aluminium. In the illustrated embodiment, the sheathing comprises two semi-shells 4a, 4b which are disposed around the insulating body 1 and surround it through a large area over practically the entire circumference and length of the central area MB. In order to be able to compensate for temperature-related length changes with sufficiently small mechanical stress, each semi-shell 4a, 4b is provided at its rear end with an area 4c having a plurality of slits.

(25) FIG. 5 shows a longitudinal section through the vacuum feed through 23 with installed semi-shells 4a, 4b disposed on the insulating body 1. The thermal flow coming from the target 22 via the rear part 2 of the anode reaches the semi-shells 4a, 4b through short paths, namely through the reduced wall thickness WSm of the insulating body 1 in the central area MB (compared with the larger wall thickness WSv in the front area VB).

(26) In the present case, 9/10 of the rear part 2 extend in the longitudinal direction in the central area MB and the (average) wall thickness WSm in the central area MB is approximately ½ times the (average) wall thickness WSv in the front area VB. The heat may be dissipated in the semi-shells 4a, 4b of the cooling device 4 through the overall length and be discharged/radiated, thereby preventing local overheating of the anode, in particular, of the rear part 2 that is connected to a high voltage plug.

(27) It is generally preferred for the rear part 2 to axially extend at least by ⅔ in an area of the insulating body 1 in which the local radial wall thickness (cf. WSm in the central area MB) of the insulating body 1 is maximally ⅔ of the largest radial wall thickness (cf. WSv in the front area VB) of the insulating body 1.

(28) FIG. 6 shows a front part 3 of an anode for the invention. The part 3 is completely produced of copper. The rear end of the part is provided with a plug-in section 18 and the front end forms the target 22. The flat surface of the target 22 is slightly inclined with respect to the longitudinal axis LA in order to obtain a useful radiation dependence (angular distribution) of the characteristic X-ray radiation excited in the copper by the impinging electrons.

(29) In case the characteristic X-ray radiation of a different material than copper is desired, the front end of the front part 3 may be provided with an insert 24 (dashed lines) made of the other material (“target material”), in the present case tungsten, as target 22, cf. FIG. 7. The insert 24 is arranged in a depression 24a in the front part 3 and is fixed (e.g. soldered) normally prior to fixing the front part 3 to the rear part 2. The flat surface of the insert 24 is also inclined with respect to the longitudinal axis LA.

(30) FIG. 8 shows an alternative embodiment of an inventive high voltage vacuum feed through 23, in which the ceramic insulating body 1 has a substantially uniform wall thickness WS. This configuration is particularly simple and can be effectively used for electron tubes or X-ray tubes with little power or little development of heat on the target 22.

(31) FIG. 9 shows a schematic longitudinal section through an electron tube 25 (in the present case a solid anode X-ray tube) with an inventive vacuum feed through 23 as disclosed in FIG. 5.

(32) A vacuum-tight housing 30 is arranged around the front part 3 of the anode 28 and bordering the insulating body 1, the housing comprising an evacuated space 31. The housing 30 also has a cathode 27 with an electron emitter 26, in the present case an electrically heated coil of tungsten wire.

(33) Electrons are discharged by the electron emitter 26 during operation due to thermionic emission and are accelerated by a high voltage between the cathode 27 and the anode 28 of typically 5 kV to 30 kV through the evacuated space 31 to the anode 28, to be more precise to the target 22 on the front part 3. At this location, in addition to bremsstrahlung, characteristic X-ray radiation 29 is excited which can be discharged through a beryllium window 32 and can be used e.g. for instrumental analysis or medical diagnosis.

(34) Even if the joint between the metallic rear part 2 of the anode 28 and the ceramic insulating body 1 should become hot during operation, the joint will not be subjected to any mechanical stress due to expansion, since the thermal expansion coefficients α.sub.ht and α.sub.ker of the rear part 2 of Fernico and of the ceramic material Al.sub.2O.sub.3 of the insulating body 1 are approximately equal. At the same time, heat is efficiently discharged from the target 22 through the copper material of the front part 3 to the rear (in FIG. 9 towards the left-hand side).