JPH04248233A - Cathode body structure for x-ray tube - Google Patents

Abstract

PURPOSE:To provide a cathode body structure for a X-ray tube, which prevents its cathode filament from being dislocated in position, and also from being deformed, in which its cathode body structure is short in the axial direction, and is easy to be assembled. CONSTITUTION:A ceramic insulator is fixed onto a focusing electrode directly or via other members. A filament support body which is extended in the direction normal to the axis of electron beams, is fixed onto the ceramic insulator. The leg section of a cathode filament is joined to the filament support, and filament voltage feed wires are connected to the filament support body electrically.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a cathode structure for an X-ray tube.

0002

[Prior Art] For example, a rotating anode X-ray tube for mammography is
It is constructed as shown in FIG. 7, and a cathode assembly 2 and an anode target 3 are disposed in a vacuum envelope 1 facing each other. Then, a high voltage is applied to the cathode structure 2 and the anode target 3, and the electron beam emitted from the cathode structure 2 is accelerated and collides with the anode target 3 to emit X-rays, which causes the electron beam to emit X-rays through the X-ray emission window. It radiates from 4a. It is desirable that such a mammography X-ray tube 4 has a dimension L in the tube axis Z direction from the X-ray emission window 4a to the cathode side end as short as possible due to its intended use. Therefore, the axial dimension of the cathode assembly 2 must also be made as short as possible. Note that this X-ray tube is normally housed in a container 5 called a Haube as shown in FIG. 8, and the container 5 is further filled with an insulating/cooling medium 6 such as insulating oil or insulating gas. , an X-ray tube device is constructed.

Conventionally, in the cathode structure of an X-ray tube, a cathode filament is provided in a focusing groove formed in a focusing electrode, and this cathode filament is fixed to a support rod. The support rod is fixed to the focusing groove via the cylindrical body and the insulating spacer.

[0004] Further, a cathode structure for an X-ray tube having a cathode filament in the form of a flat plate or ribbon for the purpose of high resolution, high contrast, etc. is disclosed in Japanese Patent Application Laid-Open No. 15728/1983, which is shown in FIGS. It is configured as shown in FIG. That is, both bent ends 7a and 7b of the ribbon-shaped cathode filament 7 are fixed to a notch 8a, which is one end of the support rod 8, by welding. A box-shaped holding member 10 having a through hole 9 is provided outside the welded portion of the cathode filament 7.
It is fixed by laser welding, etc., including the periphery.

[0005]

[Problem to be solved by the invention] The conventional X as described above
In all cathode assemblies for wire tubes, current is supplied to the cathode filament via a rod-shaped support rod, and further improvements are desired for the following reasons.

(1) The structure for attaching the cathode filament is complicated, and the work tends to be complicated.

(2) By using a rod-shaped support rod,
The dimension of the cathode structure in the electron beam axis direction becomes long, which is particularly disadvantageous for applications such as mammographic X-ray imaging devices.

(3) The cathode filament is likely to be misaligned due to thermal expansion of the support rod.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cathode assembly for an X-ray tube that can shorten the axial dimension of the cathode assembly and is easy to assemble.

0010

[Means for Solving the Problems] In the present invention, a ceramic insulator is fixed to the focusing electrode directly or through another member, and a filament support extending substantially perpendicular to the electron beam axis is fixed to the ceramic insulator. This is a cathode structure for an X-ray tube, in which the legs of a cathode filament are joined to the filament support, and a filament voltage supply lead is electrically connected to the filament support.

[0011]

[Operation] According to the present invention, the dimension of the cathode structure in the electron beam axis direction can be made as short as possible, assembly is relatively easy, and even if an external force is applied to the lead, it is difficult to reach the cathode filament. deformation is unlikely to occur. Therefore, it is particularly suitable for mammography.

0012

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The embodiment shown in FIGS. 1(a), 1(b) to 4 has the following configuration. That is, the electron beam focusing electrode 11 has a focusing groove 12 and an electron beam passage hole 11a. This focusing electrode 11 is fixed to a metal plate 13 made of Kovar or the like having an opening 13a at the bottom, and is fixed with screws 14. Below the focusing electrode 11, a rectangular plate-shaped ceramic insulator 15 having a central hole 15a is connected to the metal plate 1.
3 is fixed by gold brazing. The ceramic insulator 15 is made of alumina-based ceramics. On both sides of this ceramic insulator 15, single-layer metal layers 16 and 17 of, for example, Mo--Mn are formed by a metallization method. In this case, the metal layer 17 is not formed entirely on one surface of the ceramic insulator 15, but as shown in FIG. It is formed only where 20 and 21 are joined. The left and right small metal layers 17b in FIG. 4 correspond to both legs of the cathode filament, and the upper and lower large metal layers 17a correspond to the joining position of the filament supports 20 and 21 made of a pair of metal plates. A ribbon-shaped cathode filament 18 made of tungsten or an alloy containing tungsten as a main component is disposed so as to correspond to the focusing groove 12 and to be located in the central hole 15a of the ceramic insulator 15, and has both legs 18a, 18b. is surface-bonded to the aforementioned small metal layer 17b of the ceramic insulator 15 by laser welding.

Furthermore, the center hole 1 of the ceramic insulator 15
A shield 19 for uniformizing electric field distribution and heat shielding is disposed between the inner periphery of the cathode filament 18 and the inner circumference of the shield 19, and its peripheral edge is fixed to the metal layer 17a of the ceramic insulator 15 by gold soldering. It has the same potential as the cathode filament 18. This shield 19 is connected to the cathode filament 1
This is provided for the purpose of preventing contamination of the ceramic insulator 15 due to metal evaporation from the insulator 8 and preventing insulation failure.

Furthermore, both legs 18a of the cathode filament 18
, 18b are each bent into a U-shape and extended perpendicularly or substantially perpendicularly to the electron beam axis, and furthermore, the tip portions 18c and 18d are bent at right angles. Furthermore, as is clear from FIG. 3, on the lower surface of the ceramic insulator 15, filament supports 20 and 21 made of a pair of metal plates are spaced parallel to each other on both sides of the cathode filament 18 and joined by brazing. has been done. In this case, each filament support 20, 21 is joined to the corresponding large metal layer 17a described above in FIG. 4 and is not electrically shorted to each other. Each of the filament supports 20 and 21 has a bent portion 20a and 21a that is not joined to the ceramic insulator 15, and each bent portion 20a and 21a is connected to a metal holding plate 22 and 23 to hold the cathode filament 18. The bent ends 18c and 18d are welded and joined so as to be sandwiched therebetween. A filament voltage supply lead (not shown) is electrically connected to these.

Normally, resistance welding between the thin cathode filament 18 and the thick bent ends 20a and 21a of the filament supports 20 and 21 is difficult, so resistance welding is performed using metal holding plates 22 and 23. Although this makes it easier, the metal presser plates 22 and 23 are not necessarily essential. For convenience, the bent ends 18c and 18d of the cathode filament 18 and the metal press plates 22 and 23 are not shown in FIG. 3. Further, the shielding body 19 is joined to either of the metal plates 20 and 21 for supplying filament voltage.

Furthermore, in forming the metal layers 16 and 17, in addition to the metallization method, methods such as metal plating, high-temperature diffusion bonding, etc. can also be used. As for the method of fixing the cathode filament 18, in addition to laser welding, electron beam welding, T
Welding methods such as IG welding and plasma welding may be used.

Furthermore, in this embodiment, the case was described in which the metal layers 16 and 17 were mainly composed of Mo--Mn; however,
As the components of the metal layers 16 and 17, metal layers made of Mo, W, Au, Rh, Pt, and Ta that do not contain dopants such as Mn can also be used.

It is also possible to join the cathode filament 18 directly to the ceramic insulator 15 by using the above-mentioned electron beam welding method as a welding method.

Since the cathode structure of the X-ray tube of the present invention is constructed as described above, the leads can be connected without affecting the joint between the cathode filament 18 and the ceramic insulator 15. . That is, the leads may be connected anywhere on the filament supports 20 and 21 made of metal plates. Furthermore, since the filament supports 20 and 21 are brazed and fixed to the ceramic insulator 15, stress during lead connection does not cause any deformation in the cathode filament 18 or the joint between the filament 18 and the ceramic insulator 15. It's not as powerful as it could be.

In the embodiment shown in FIGS. 5 and 6, a first ceramic insulator 15 is soldered to a metal layer 16 via an intermediate thermal expansion metal (not shown), and a metal layer 17 is further soldered to a focusing electrode 11 through an intermediate thermal expansion metal (not shown). The shielding electrode 19 is similarly fixed at some portions by soldering via an intermediate thermal expansion metal (not shown). Through holes are formed on both sides of the shield electrode 19, respectively. A second ceramic insulator 31 is fixed to one of the through holes, and a metal sleeve 32 is fixed to this. This sleeve has a rod-shaped filament support 2.
0 is joined by laser welding. A metal sleeve 33 is directly fixed to the other through hole, and the other rod-shaped filament support 21 is joined to this sleeve by laser welding, and is directly electrically short-circuited. At the inner tip portions of these filament supports 20 and 21, bent extension ends 18 of the ribbon-shaped cathode filaments 18 in the lateral direction are provided.
a and 18b are joined by laser welding. Arrow B
indicates the laser welding location.

According to this embodiment, assembly is easy and the axial dimension of the cathode structure can be shortened.

[0023]

[Effects of the Invention] As explained above, according to the present invention,
The axial dimension of the cathode structure can be shortened. In addition, since the stress applied to the leads does not reach the cathode filament, the cathode filament and the joint between the filament and the ceramic insulator will not be deformed, making the X-ray tube relatively easy to assemble and highly reliable. can get. this is,
It is particularly suitable for mammography X-ray tubes in which it is desirable that the cathode structure has a short axial dimension.

[Brief explanation of the drawing]

FIGS. 1A and 1B are cross-sectional views showing a cathode structure of an X-ray tube according to an embodiment of the present invention, cut from two directions.

FIG. 2 is an enlarged sectional view showing a main part of the cathode structure of the X-ray tube of the present invention.

FIG. 3 is a plan view of the cathode structure of the present invention viewed from above, excluding the focusing electrode.

FIG. 4 is a plan view showing a metal layer on the back surface of the ceramic insulator in the cathode structure of the present invention.

FIG. 5 is a longitudinal sectional view showing another embodiment of the invention.

FIG. 6 is an enlarged view of the main part of FIG. 5.

FIG. 7 is a front view including a partial cross section showing a general X-ray tube.

FIG. 8 is a sectional view showing an X-ray tube device in which an X-ray tube is housed in a container.

FIG. 9 is an exploded perspective view showing the main parts of a cathode assembly in a conventional X-ray tube.

10 is a perspective view showing the manufacturing process of the cathode assembly shown in FIG. 9. FIG.

FIG. 11 is a cross-sectional view showing essential parts of the cathode structure shown in FIG. 10;

[Explanation of symbols]

11... Focusing electrode, 15, 31... Ceramic insulator, 1
7... Metal layer, 18... Cathode filament, 18a, 18b
...Cathode filament leg, 20, 21...Filament support.

Claims (1)

[Claims] 1. A ribbon-shaped cathode filament whose electron emitting surface is substantially flat; a shielding electrode provided to surround the electron emitting surface of the cathode filament; and a shielding electrode provided to surround the electron emitting surface of the cathode filament; In the cathode assembly of an X-ray tube, which is equipped with a focusing electrode provided with a beam focusing groove, a ceramic insulator is fixed to the focusing electrode directly or through another member, and the ceramic insulator is provided with a shape approximately parallel to the electron beam axis. A vertically extending filament support is secured;
A cathode structure for an X-ray tube, characterized in that a leg of the cathode filament is joined to the filament support, and a filament voltage supply lead is electrically connected to the filament support.