JPH0570897B2 - - Google Patents

Abstract

In order to increase the dielectrical resistance without resorting to internal shielding, the ring plate shaped ceramic insulators (13, 23) which carry the cathode (15) and the anode (25) at the axial inside end surfaces (16, 26) of the X-ray tube are stepped down in radial directions by a step (17, 27) in order to permit the forming of an axial hollow (18, 28) running in the form of a ring. On the ceramic insulator (13) which carries the cathode (15), the hollow (18) borders on the external periphery of the ceramic insulator. Conversely, the hollow (28) on the ceramic insulator (23) carrying the anode (25) borders on the inside periphery of the ceramic insulator. Each of the hollows is entirely filled with an insulation material (19, 29), the dielectric constant of which is less than that of the ceramic material. This insulation material (19, 29) is functionally part of a rubber-elastic ring plate (20, 30) which is pressed onto the outer axial end surface of the respective ceramic insulator (13, 23).

Description

Claim 1: An X-ray tube having a cylindrical metal member surrounding an anode and a cathode, wherein at least one of the anode and the cathode is surrounded by a disk-shaped ceramic insulator provided at an axial end of the metal member. Disc-shaped ceramic insulating materials 13, 23, 113, 12 in electrically insulated types with respect to metal members
3,213,223, the axial end face 16, 26, 116, 1 on the side opposite to the internal space of the X-ray tube
26, 216, 226 are annular axial recesses 1
8, 28, 118, 128, 218, 228 are formed in a step or ramp shape in the radial direction, and the recesses are filled with an insulating material whose dielectric constant is smaller than that of the ceramic material. 19,29
The anode 25 is filled with the metal member 11.
Ceramic insulators 13, 113, 2 that insulate
In the case of No. 13, the recess is placed radially inward,
In the case of the ceramic insulators 23, 123, 223 that insulate the cathode 15 from the metal member 11, the recesses are arranged on the outside in the radial direction.
wire tube.

2 Ceramic insulator 13, 23, 113, 12
3,213,223 dents 18,28,118,
The insulating material filled in 128, 218, 228 is
Stepped or ramped end face of ceramic insulator 1
Rubber elastic disks 20, 30 pressed in the axial direction by 6, 26, 116, 126, 216, 226
The X-ray tube according to claim 1, characterized in that the portions 19, 29 are the parts 19, 29.

3. When the rubber elastic disks 20, 30 are under no load, there are no steps and the ceramic insulators 13, 23, 1
3. The X-ray tube according to claim 2, wherein the X-ray tube has an axial end face having substantially the same dimensions as the X-ray tube.

4 Recesses 18, 28, 118, 128, 218,
Claim 1, characterized in that the insulating material 19, 20 filled in the insulating material 228 is silicone rubber having preferably a shore hardness of about 28 and a dielectric constant of about 3.2.
An X-ray tube according to one of clauses 1 to 3.

5. An X-ray tube according to any one of claims 1 to 4, in which the anode and the cathode are electrically insulated from the cylindrical metal member by disk-shaped ceramic insulators, respectively. In each disk-shaped ceramic insulator 13, 23, 113, 1
23, 213, 223, the axial end surface 16, 26, 116 on the side opposite to the internal space of the X-ray tube;
126, 216, 226 are stepped or ramped in the radial direction so as to form an annular axial recess 18, 28, 118, 128, 218, 228, in which the dielectric Insulating material 19,2 whose dielectric constant is smaller than the dielectric constant of the ceramic material.
The recesses 28, 12 of the ceramic insulators 23, 123, 223 are filled with 9 and carry the anodes 25.
8,228 are arranged radially inwardly and carry the cathode 15.
An X-ray tube characterized in that 3,213 recesses 18, 118, 218 are arranged radially outward.

Technical Field The present invention relates to an X-ray tube having a cylindrical metal member surrounding an anode and a cathode, wherein at least one of the anode and the cathode is The present invention relates to a type in which one of the metal members is electrically insulated from the metal member.

BACKGROUND OF THE INVENTION Known X-ray tubes of this type are constructed and arranged in the interior space of a cylindrical metal member in such a way that the electric field generated on the inner surface of the ceramic insulator is directed away from the plane of the insulator and into the interior space of the X-ray tube. It has a shield. In this way, the inner surface of the ceramic insulator with which the unavoidable field-emitted electrons collide is charged due to the secondary electron emission, and therefore a reduction in the insulation strength of the X-ray tube is sufficiently prevented.

DISCLOSURE OF THE INVENTION It is an object of the invention that, despite the absence of the above-mentioned shielding, the electric field on the inner surface of one or each ceramic insulator is directed away from the plane of the insulator and into the interior of the X-rays. The object of the present invention is to create an X-ray tube of the type described in .

This object is achieved according to the invention by configuring the axial end face of the disc-shaped ceramic insulator opposite to the internal space of the X-ray tube in the form of a radial step or ramp to form an annular axial recess. form,
In the case of a ceramic insulator that insulates the anode from the metal member by filling the recess with an insulating material whose dielectric constant is smaller than that of the ceramic material, the recess is placed radially inward and In the case of ceramic insulators which insulate the cathode, this is achieved by placing the recesses radially outward.

With the above configuration of the X-ray tube, it is extremely easy to
The electric field on the inside surface of the insulator can be directed away from the plane of the insulator and into the interior of the x-ray tube. Furthermore, the advantageous effect is that the electric field strength at the point where field emission begins (the so-called triple point) is reduced. On the cathode side, the triple point is located at the brazed joint between the ceramic insulator and the high voltage bushing in the center of the insulator. On the other hand, on the anode side, the triple point is located at the brazed joint between the outer periphery of the ceramic insulator and the cylindrical metal member. Both effects achieved by the arrangement according to the invention contribute to a significant increase in the dielectric strength of the X-ray tube.

In accordance with an expedient design of the X-ray tube according to the invention, the insulating material filling the recesses of the ceramic insulator consists of rubber-elastic discs which are pressed in the axial direction onto the stepped or ramp-shaped end faces of the ceramic insulator. It may be a part.

Other details and advantages will be apparent from the following description of an embodiment of an X-ray tube according to the invention and from the associated drawings illustrated by way of explanation.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an X-ray tube according to the present invention including the connection member, and FIGS. 2 and 3 are axial sectional views of two embodiments of the ceramic insulator on the cathode side. Figures 4 and 5 respectively show similar cross-sectional views of two embodiments of the ceramic insulator on the anode side.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The X-ray tube shown in FIG. 1 has a cylindrical metal member 11 with a hermetically fitted window 12 for extracting the X-ray beam. In FIG. 1, a ring disk-shaped ceramic insulator 13 is provided at the upper end of the metal member 11 in the axial direction, the outer periphery of which is hermetically bonded to the metal member 11. In the central opening of the ceramic insulator 13, a high-voltage bushing 14 carrying the cathode 15 of the X-ray tube is also arranged in a gas-tight manner. The axial end face 16 of the ceramic insulator 13 facing away from the interior space of the metal part 11 is drawn down radially outwards by a circumferentially extending step 17, so that the ceramic insulator 13 An annular recess 18 in the axial direction is formed following the outer circumference thereof. This recess 18 is filled by a portion 19 of a rubber-elastic annular disc 20 which is pressed against the ceramic insulator 13 by means of a connecting member 21. Rubber elastic annular disk 20 has a lower dielectric constant than ceramic insulator 13. It is expedient to provide a layer of insulating grease (not shown) at the joint between the ceramic insulator 13 and the rubber-elastic annular disk 20 and between the connecting member 21 and the rubber-elastic annular disk 20. .

In FIG. 1, at the lower end in the axial direction of the cylindrical metal member 11, there is also a ring-disk shaped ceramic insulator 2 whose outer periphery is hermetically connected to the metal member 11.
3 is provided. In the central opening of the ceramic insulator 23, a high-voltage bushing 24 carrying the anode 25 of the X-ray tube is also arranged in a gas-tight manner. The axial end face 26 of the ceramic insulator 23 facing away from the internal space of the metal part 11 is drawn down radially inwardly by a circumferentially extending step 27, so that the ceramic insulator 23 An annular recess 28 in the axial direction is formed next to the inner circumference thereof. This recess 28 is formed by a rubber elastic annular disk 30.
It is completely filled in by part 29 of . The rubber-elastic annular disc 30 is pressed against the ceramic insulator 23 in a known manner by means of a connecting member 31. Rubber elastic annular disk 30 has a lower dielectric constant than ceramic insulator 23. It is expedient to install an insulating grease layer (not shown) at the joint between the ceramic insulator 23 and the rubber elastic annular disk 30 and between the connecting member 31 and the rubber elastic annular ring 30, respectively. It is true.

When operating the above-mentioned X-ray tube, the metal member 11 is placed at ground potential, while a negative voltage with respect to the ground potential is applied to the cathode 15 via the connecting member 21, and the anode is placed at ground potential. Apply a positive voltage to the potential. In this case, potential lines such as those shown by broken lines 32 and 33 in FIG. 1 are generated in the interior space of the X-ray tube. Due to the recesses 18 of the ceramic insulator 13 filled with an insulating material 19 with a low dielectric constant, the potential lines 32 are diffused away from the direction parallel to the axis in the area of the ceramic insulator 13, so that the potential lines are always An electric field vector 35 perpendicular to ceramic insulator 13 at a flat inner end surface 34 of ceramic insulator 13
Take the direction away from 3 and towards the internal space of the x-ray tube. Similarly, due to the recess 28 of the further ceramic insulator 23 filled with an insulating material 29 of low dielectric constant, the potential lines 33 converge in the area of the ceramic insulator 23 and therefore the electric field vector 36
is the flat inner end surface 37 of the ceramic insulator 23.
oriented away from the ceramic insulator and toward the interior space of the x-ray tube. Electric field vector 35
or 36 and the inner end surface 34 or 37 of the ceramic insulator 13 or 23, the difference between the permittivity of the ceramic material and the permittivity of the rubber-elastic insulating material, the radial width of the recess 18 or 28 and the axial direction depth and ceramic insulator 13 or 2
Depends on the dimensions of 3. The electric field strength on the cathode side and anode side is determined by the ceramic insulator 13 or 2.
3 and toward the inside of the X-ray tube, charging of the ceramic insulators 13 and 23 and the associated increase in electric field strength can be effectively avoided.
Compared to similar known X-ray tubes in which the outer end faces of the ceramic insulation are flat without steps 17, 27, the X-ray tube of FIG. 1 has a significantly greater joint insulation strength.

The above-mentioned advantages have been checked and confirmed for the experimental X-ray tube. The experimental X-ray tube having the structure shown in FIG. 1 has ceramic insulators 13 and 23 with an outer diameter of 107 mm and an inner diameter of 45 mm. The axial thickness of the ceramic insulator is 10 mm, which is reduced to 7 mm at the location of recess 18 or 28, so that step 1
The height of 7 or 27 is 3 mm. The rubber elastic annular disks 20, 30 are made of silicone rubber having a dielectric constant of 3.2 and a shore hardness of 28. In the unloaded state, both axial end faces of each rubber elastic annular disk 20, 30 are flat and parallel, and the outer diameter is 100 mm.
mm, the inner diameter is 45mm, and the axial thickness is 10
mm. This X-ray tube can be operated without problems by applying a maximum voltage of 340KV between the anode and cathode.

Substantially the same good results are obtained when ceramic insulators are formed according to the embodiments of FIGS. 2-5.

Ceramic insulator 11 on the cathode side shown in FIG.
The outwardly facing axial end face 116 of 3 is provided with two steps 117 extending in the circumferential direction and forming an axial recess 118 following the outer circumference of the ceramic insulator.

Ceramic insulator 21 on the anode side shown in FIG.
The outwardly facing axial end face 216 of the ceramic insulator 213 has an axial recess 21 that follows the outer periphery of the ceramic insulator 213.
A ramp-like draw-down portion 217 is provided, which forms an 8 .

Ceramic insulator 12 on the cathode side shown in FIG.
The outwardly facing axial end face 126 of 3 is provided with two steps 117 extending in the circumferential direction and forming an axial recess 128 which follows the inner circumference of the ceramic insulator.

Based on FIG. 5, it is also possible to provide the outwardly facing axial end face of the ceramic insulator 223 on the cathode side with a ramp-like draw-down portion 227, in which case an axial recess continues on the inner circumference of the ceramic insulator. 228
is formed.

Ceramic insulators 113, 21 in Figures 2-5
3, 123, 223 dents 118, 218, 12
8,228, when assembling or installing an X-ray tube,
It is completely filled with a rubber-elastic insulation material whose dielectric constant is less than that of the ceramic insulator.

X-ray tubes having a cathode or anode conductively coupled to a cylindrical metal member are known. In such cases, only the other electrode (ie, anode or cathode) is insulated from the cylindrical metal member by the ceramic insulator. The present invention can also be applied to such an X-ray tube. That is,
In this case, as described above, a recess is provided in the axial end face of the only ceramic insulating material on the side opposite to the inside of the X-ray tube, and an insulating material whose dielectric constant is smaller than that of the ceramic insulator is Fill the cavity completely.