JPH0521028A - X-ray tube - Google Patents

Abstract

(57) [Summary] [Object] To provide an X-ray tube in which a small electric power is sufficient to deflect an electron beam by a deflection coil, and the deflection coil is small and can be implemented cost-effectively. To do. [Constitution] An anode 1 and a cathode 2 are arranged in a container 3 which is exhausted and surrounded by a cooling medium, and an electron beam 10 emitted from the cathode 1 is exhausted in a path leading to the anode 2. Wall 18 in contact with the cooling medium of
It passes through an aperture opening 27 defined by a and 18c.
The walls 18a, 18c having the diaphragm opening 27 are given a potential that is more positive than the cathode potential. A deflection coil 31 for deflecting the electron beam 10 is provided in the region of the aperture opening 27.
And the deflection coil is at least partially surrounded by a cooling medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray tube provided with a cathode and an anode, which are arranged in a container which is evacuated and surrounded by a cooling medium.

[0002]

In an X-ray tube of this kind, some of the electrons that emerge from the cathode and strike the anode at the so-called focal point disperse and return from the anode and then back to the anode again under the influence of the electric field. There is the problem of going back out of focus. This causes so-called out-of-focus radiation,
This out-of-focus radiation is not desired in X-ray diagnostics.
This out-of-focus radiation deteriorates the quality of the X-ray image produced by the X-ray tube.

In order to reduce the out-of-focus radiation, the electron beam emitted from the cathode is made to pass through the opening of a diaphragm arranged near the anode inside the container in the path leading to the anode. It has already been proposed to apply a potential that is also positive. By taking such measures, some of the backscattered electrons (electrons scattered back from the anode) fall into the diaphragm, which reduces the out-of-focus radiation accordingly. By the way, the amount of the backscattered electrons falling to the diaphragm increases as the diaphragm potential approaches the anode potential. Normally, the diaphragm is given a ground potential.
That is, the diaphragm is located between the anode potential and the cathode potential. However, particularly in a high-power X-ray tube, there is a problem in that the diaphragm is strongly heated by the collision of electrons, and the diaphragm material is thermally overloaded by this heating, and the diaphragm is deformed undesirably.

In the X-ray tube described in European Patent Application Publication No. 0009946, such a problem is solved by the X-ray tube wall in contact with the cooling medium surrounding the X-ray tube in the path of the electron beam to the anode. The solution is achieved by passing through the formed aperture opening, the wall being provided with a potential which is more positive than the cathode potential.

In X-ray tubes of the type mentioned at the outset, it is more often desirable to be able to control the position of the focal spot on the anode. To this end, it is known to provide a deflection coil configured to deflect the electron beam in response to a current flowing through the deflection coil.
Placing the deflection coil inside the evacuated container (which can have a negative effect on the vacuum accuracy in the container) is generally undesirable, so the deflection coil is usually placed outside the evacuated container. As a result, the deflection coil will be very far away from the electron beam. Therefore, a relatively large hower is required to deflect the electron beam. Moreover, the deflection coils are very large and are correspondingly expensive.

[0006]

Therefore, the present invention requires only a small electric power for deflecting the electron beam by the deflection coil, and the deflection coil is small and can be implemented cost-effectively. Thus, the task is to form an X-ray tube of the kind mentioned at the outset. Furthermore, it should at least be provided for this purpose, in which the out-of-focus radiation is clearly reduced, possibly without being damaged by the high thermal strain of the components of the X-ray tube.

[0007]

According to the invention, according to the first solution principle of the invention, such an object is provided with a cathode and an anode, which are evacuated and surrounded by a cooling medium. In the X-ray tube arranged inside, the electron beam emitted from the cathode travels in the tubular wall of the exhausted container in the path leading to the anode, and the tubular wall is provided for deflecting the electron beam. The solution is to be surrounded by at least one deflection coil.

According to the present invention, according to the second solution principle of the present invention, the above-mentioned problem is solved by an X-ray tube provided with a cathode and an anode, which are evacuated and surrounded by a cooling medium. In, the electron beam emerging from the cathode passes through a throttle opening defined by at least one wall of which at least a part is in contact with the cooling medium, of the container evacuated in the path leading to the anode, the wall having the throttle opening at this time. Is given a potential that is more positive than the cathode potential,
At least one deflection coil is arranged in the region of the diaphragm opening for deflecting the electron beam, the deflection coil being solved by having at least a portion surrounded by a cooling medium.

[0009]

According to the X-ray tube according to the first solution principle of the present invention, the deflection coil comes to exist in close proximity to the electron beam to be deflected, and as a result, it is necessary to deflect the electron beam. Power is negligible, the deflection coil is compact and cost effective. Particularly good properties are obtained when the cross-section of the tubular wall is not significantly exceeded by the particularly preferred embodiment of the invention so that it does not impede the passage of the electron beam.

According to a likewise preferred embodiment of the invention, the tubular wall is provided with a potential which is more positive than the cathode potential. In this case, the tubular wall traps the electrons that scatter back from the anode, thereby reducing out-of-focus radiation. By forming the wall forming the diaphragm opening in a cylindrical shape in cross section, the number of electrons that enter the diaphragm opening and return from the diaphragm opening while scattering to the anode is small. This is because most of the electrons that have entered the diaphragm opening are trapped by the cylindrical wall. In that case, it is advantageous that no additional components are required to realize the diaphragm function. Advantageous embodiments of the invention ensure that the tubular wall, when at least partly brought into contact with the cooling medium, does not heat the tubular wall unacceptably strongly by electron impact. Increased thermal strain is thereby avoided.

According to another advantageous embodiment of the invention, the deflection coil is at least partly surrounded by a cooling medium. As a result, the power loss of the coil is discharged without any problem.

According to another embodiment of the invention, the tubular wall is coupled to the wall of the evacuated container having the throttle opening, and is provided with a potential which is more positive than the cathode potential and is at least partially Are brought into contact with the cooling medium. For example, if the tubular wall is improperly charged or formed as an insulator and the tubular wall is unable to trap electrons in an amount sufficient to reduce off-focus radiation as desired. In particular, this makes it possible to reduce the out-of-focus radiation to the required amount. This is because the backscattered electrons are trapped by the wall with the diaphragm opening. Overheating of the wall cannot occur because it at least partially contacts the cooling medium.

According to the X-ray tube according to the second solution principle of the present invention, since the wall of the X-ray tube container in contact with the cooling medium forms an aperture, the out-of-focus radiation is effective without causing a thermal problem. It becomes possible to reduce to. Moreover, no additional throttling is required, but rather the advantage is that existing components perform this function. The throttle opening may be defined by a number of walls of the container, in particular all of which are provided with the above-mentioned potential and at least partly in contact with the cooling medium. The deflection coil is arranged in the region of the aperture opening and is surrounded at least in part by the cooling medium, so that the deflection coil is in close proximity to the electron beam and therefore for deflecting the electron beam. Requires very little power. On the other hand, the power loss of the coil is passed to the cooling medium without problems. Furthermore, since the coil is in close proximity to the electron beam, the coil is compact and accordingly constructed cost-effectively.

According to a particularly advantageous embodiment of the invention, the electron beam is of the evacuated container in the path leading to the anode,
It travels in a tubular wall surrounded by deflection coils.
This allows the deflection coil to be placed particularly close to the electron beam, so that the power required for deflection is particularly small and the deflection coil is particularly compact. Is obtained. According to a particularly advantageous embodiment of the invention, the tubular wall defines a diaphragm opening. As a result, the number of return scattered electrons that enter the diaphragm opening and return from the diaphragm opening while scattering back to the anode is reduced. This is because most of the electrons that enter the diaphragm opening are trapped by the cylindrical wall.

According to an embodiment of the invention, the reduction of out-of-focus radiation is maximized if the size of the diaphragm opening does not significantly exceed the size required to not obstruct the passage of the electron beam. . This is because in that case the amount of backscattered electrons falling on the wall of the container with the aperture opening is maximal.

According to a preferred embodiment of the invention, the wall with the diaphragm opening is provided with an anodic potential. By taking such measures, the occurrence of out-of-focus radiation is almost completely avoided, provided that the size of the diaphragm opening is not too large. In fact, all backscattered electrons are trapped by the wall, which acts as a diaphragm of the container, and only a very small amount of electrons can drop onto the anode. In the case of a monopolar X-ray tube in which the cathode and the container are given a common potential, no special measures need to be taken to ensure that the wall with the diaphragm opening is given the anodic potential. In any case, in the case of a monopolar X-ray tube, the insulator provided between the cathode and the container must insulate the entire tube voltage. In a two-pole X-ray tube in which a part of the container has an electric potential located between the cathode potential and the anode potential, the aperture opening is provided so that the wall having the aperture opening can be provided with the anode potential. It is necessary to insulate the walls it has from other areas of the container.

For an X-ray tube having a deflection coil for magnetically deflecting the electron beam, according to one embodiment of the invention, the deflection coil is arranged in the region of the diaphragm opening and is at least partially. Are surrounded by a cooling medium. This, on the one hand, causes the deflection coil to lie very close to the electron beam and thus requires only a small amount of power to deflect the electron beam. On the other hand, the loss power of the coil can be passed on to the cooling medium without problems.

[0018]

Embodiments of the present invention will now be described with reference to the drawings. 1 to 3 are schematic vertical sectional views of different embodiments of the X-ray tube according to the present invention.

The X-ray tube shown in FIG. 1 has a fixedly arranged cathode 1 and a rotating anode generally designated by 2, which are arranged in an evacuated container 3. . The container 3 is housed in a protective container 4 filled with an electrically insulating liquid cooling medium such as insulating oil. 1 for rotating anode 2
One shaft 5 and two rolling bearings 6 and 7 are rotatably supported in the container 3.

The rotary anode 2 formed in rotational symmetry has a central axis M which coincides with the axis of the shaft body 5, and the truncated cone-shaped member 8
have. This truncated cone member 8 is made of tungsten-
A coating 9 made of a rhenium alloy is provided, and an electron beam 10 emitted from the cathode 1 collides with the coating 9 to generate X-rays. The corresponding effective beam bundle, which is shown in FIG. 1 by the central beam Z, exits through the beam exit windows 11, 12 provided in the container 3 and the protective container 4 and collinear with each other.

To drive the rotary anode 2 there is provided an electric motor, generally designated 13 and formed as a squirrel-cage induction motor, which comprises a stator 15 mounted on the container 3 and a container. 3 and a rotor 16 fixedly coupled to the shaft body 5.

The container 3 communicating with the earth potential 17 is hermetically connected to the container member 18a and two substantially plate-shaped container members 18a and 18b whose ends are airtightly connected to the tubular container member 19. It has a cylindrical container member 18c that is open. At least the container members 18a and 18c are made of a metal material. The cathode 1 is attached to the cylindrical container member 18c by an insulator 20, which is the container member 1c.
It is hermetically coupled to 8c. In this way, the cathode 1 is provided in a special chamber of the container 3, which is connected to the container 3 via the cylindrical container member 18c. Container member 1
8a is provided with a recess 21 projecting into the inner chamber of the container in the region of the focus F, and in the region of the focus F, the shape of the recess 21 is substantially matched with the surface of the rotary anode 2 on the container 18a side. The container member 18a has a center hole, and the pot-shaped insulator 22 is inserted in the center hole. The outer ring of the rolling bearing 6 is housed in the recess of the insulator 22 existing inside the container 3. Similarly, the container member 18b has a central hole located on the same straight line as the central hole of the container member 18a, and another tubular container member 23 is hermetically inserted in the central hole. The tubular container member 23 houses the rotor 16 therein, and the stator 15 is attached to the outer surface thereof. An insulator 24 is airtightly inserted into the tubular container member 23 from its free end, and the insulator 24 has an end face inside the container 3 for accommodating the outer ring of the rolling bearing 7. The tubular protrusion used is provided.

The supply of the positive high voltage + U to the rotary anode 2 is effected by a contact 26 which elastically abuts the shaft 5 in a known manner, which is not shown in detail. The contact 26 is housed in the insulator 22 in an airtight manner.

As is apparent from the schematic view of FIG. 1, the cathode 1
A negative high voltage −U is applied to one of the terminals. A heating voltage U _H is applied between both terminals of the cathode 1. The lead wires led to the cathode 1, the contact 26, the container 3 and the stator 15 are connected by a known method to a voltage source (not shown) existing outside the protective container 4, which is an X-ray tube. Supply the necessary voltage to drive the. From the embodiment described above, it is clear that the X-ray tube in FIG. 1 is constructed with two poles.

As is apparent from FIG. 1, the electron beam 10 emitted from the cathode 1 is located in the same path as the cylindrical container member 18c and the hole of the cylindrical container member 18c in the path leading to the rotating anode 2 and is depressed. It passes through the opening provided in the area 21. Opening of container member 18a and cylindrical container member 18
The holes of c together form a diaphragm opening 27, the size of which is selected so as not to significantly exceed the size required to prevent the passage of the electron beam 10. Container member 1
Since 8a and 18c are given a ground potential, and thus are given a more positive potential than the cathode, most of the electrons returning while scattering from the rotating anode 2 are trapped by the container members 18a and 18c. The container members 18a and 18c are the container 3
Besides fulfilling its mission as a wall, it also acts as an aperture used to reduce out-of-focus radiation. A container member 18a which defines or has a diaphragm opening 27,
Since 18c is in direct contact with the cooling medium present in the protective container 4, good cooling is guaranteed and therefore no thermal problems can occur.

In any case, the container member 18c does not come into contact with the cooling medium over its entire length. The insulator 20 is a flange 3 that is oriented outward in the radial direction of the tubular container member 18c.
It is attached to 2. The tubular container member 18c and the container member 18a thus define an annular space which opens outward in the radial direction, in which the deflection coil 31 shown schematically is arranged. Generate a magnetic field which deflects the electron beam 10 in a direction perpendicular to the plane of the drawing of FIG. The deflection coil is connected at its terminal Us to a deflection circuit (not shown), which allows the deflection coil 31 to be supplied with a current which depends on the desired deflection of the electron beam 10 each time. This is especially important in computer tomography. An improvement in image quality can be achieved by taking this known measure of doubling the data used to calculate the body tomographic image. Deflection coil 31
The arrangement described above makes it possible, on the one hand, to place the deflection coil 31 very close to the electron beam 10, so that little power is required to deflect the electron beam. On the other hand, the loss power of the deflection coil can be passed to the cooling medium present in the protective container 4 without any problem. Furthermore, the deflection coil 31 becomes very compact. Moreover, no special components are required to hold the deflection coil. It will be appreciated that the magnitude of the deflection of the electron beam 10 deflected by the deflection coil 31 is taken into account when designing the tubular container member 18c and the aperture opening 27.

The size of the opening provided in the container member 18a and the size of the tubular container member 18c do not necessarily have to match. The cylindrical container member 18c is replaced with the container member 18a.
It is also possible that the opening of the container member 18a is mainly effective as a diaphragm opening and only the container member 18a is effective as a diaphragm as the size difference increases. In this case, in any case, the heat load on the container member 18a becomes large. This is because the container member 18a is no longer in direct contact with the cooling medium in the vicinity of the throttle opening 27. Figure 1
Alternatively, the tubular container member 18c may have its ends similarly inserted into corresponding holes in the container member 18a, so that the aperture opening 27 is cylindrical. It is defined only by the container member 18c. Nevertheless, also in this case, similarly, the container member 18a
Traps some of the backscattered electrons.

The X-ray tube shown in FIG. 2 is substantially identical to the X-ray tube described above and therefore the same or similar parts are provided with the same reference numerals. The main difference from the X-ray tube of FIG. 1 is that the X-ray tube of FIG. 2 uses a monopolar X-ray tube. Therefore, the same potential, for example the ground potential, is introduced into the container 3 and the rotary anode 2. A negative high voltage −U is applied to the cathode 1. Instead of the insulators 22, 24, bearing shields 28, 29 made of an electrically conductive material are provided on the container members 18a, 23 in order to ensure that both the rotating anode 2 and the container 3 are applied with a ground potential.
Airtightly installed therein, the contact 26 is hermetically housed in a bearing shield 28. Since the same potential is introduced to the rotating anode 2 and the container members 18a and 18c, the generation of out-of-focus radiation can be almost completely avoided. This is because practically all the electrons returning from the rotating anode 2 while being scattered are trapped by the container members 18a and 18c. In order to obtain the above-mentioned advantages, the insulator 20 must in any case insulate the whole tube voltage existing between the cathode 1 and the rotating anode 2.

FIG. 3 shows another embodiment of the X-ray tube according to the present invention. This embodiment also substantially corresponds to the embodiment shown in FIG. 1 and therefore the same parts are provided with the same reference numerals. In the case of the X-ray tube shown in FIG. 3, a two-pole X-ray tube is used in the same manner as the X-ray tube shown in FIG. It is insulated from the other three members. Due to such circumstances, it is possible to apply the same potential + U as that of the rotating anode 2 to the container member 18a. This is
A bearing shield 28 made of a conductive material is provided instead of the insulator 22, and the contactor 2 is provided in the bearing shield 28.
This is achieved by housing 6 in a gastight manner. Since no kind of insulation is provided between the container member 18a and the rotating anode 2, the container member 1 with the throttle opening 27 is provided.
8a is applied with the same potential as the rotary anode 2, that is, + U. This reduces out-of-focus radiation,
The advantages mentioned in the description of the X-ray tube shown in FIG. 2 are obtained. Nevertheless, the X-ray tube shown in FIG. 3 can be driven with a conventional bipolar voltage supply. This is especially important if the existing bipolar X-ray tube according to the prior art is to be replaced by the X-ray tube according to the invention and the existing voltage supply system is to be maintained. In the case of the embodiment shown in FIG. 3, the insulator 33 carrying the cathode 1 has a ground potential of 17
Is connected to another cylindrical insulator 35 via a substantially tubular metal member 34 provided with a metal. This tubular insulator 35
Has its other end joined to the container member 18a. Each of the above components is hermetically coupled to one another. The two insulators 33, 35 must each insulate only half of the tube voltage. The insulator 35 can, of course, capture very little backscattered electrons, so that in the case of FIG. 3 only the container member 18a actually has a throttling function.

Although the invention has been described exclusively on the basis of an X-ray tube with a rotating anode, the invention can also be used in an X-ray tube with a fixedly arranged anode.

Cylindrical container member 18c or cylindrical insulator 35
It is also possible to arrange a large number of deflection coils on the top and to deflect the electron beam 10 in different directions in particular.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing a first embodiment of an X-ray tube according to the present invention.

FIG. 2 is a schematic vertical sectional view showing a second embodiment of the X-ray tube according to the present invention.

FIG. 3 is a schematic longitudinal sectional view showing a third embodiment of the X-ray tube according to the present invention.

[Explanation of symbols]

1 cathode 2 rotating anode 3 containers 4 protective containers 5 axis 6,7 Rolling bearing 8 Frustum member 9 film 10 electron beam 11, 12 Electron beam exit window 13 Electric motor 15 Stator 16 rotor 17 Earth potential 18a, 18b container member 18c tubular container member 19 Container member 20 insulator 21 hollow 22 Insulator 23 Container member 24 insulator 26 Contact 27 Aperture opening 28, 29 Bearing shield 30 insulator 31 deflection coil 32 flange 33 insulator 34 Metal member 35 insulator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Klaus Harbor Letzker             Federal Republic of Germany 8526 Bubenreuth               Damashi Yukishutrace 51 (72) Inventor Ernst Neumeier             Germany 8521 Miyunhiora             Tsuha Margaree Tenshiyu Trase 4

Claims (13)

[Claims] 1. A cathode (1) and an anode (2) are arranged in a container (3) which is evacuated and surrounded by a cooling medium, the electron beam (10) emerging from said cathode (1). ) Travels inside the cylindrical wall (18c; 35) of the exhausted container (3) in the path leading to the anode (2), and the cylindrical wall (18c; 35) transmits the electron beam (10). X-ray tube characterized in that it is surrounded by at least one deflection coil (31) provided for deflecting. 2. X-ray according to claim 1, characterized in that the cross section of the cylindrical wall (18c; 35) does not significantly exceed the size required to prevent the passage of the electron beam (10). tube. 3. The X-ray tube according to claim 1, wherein the cylindrical wall (18c) is given a potential that is more positive than the cathode potential. 4. The tubular wall at least partially contacts the cooling medium.
The X-ray tube according to any one of 1. 5. X-ray tube according to claim 1, wherein the deflection coil (31) is at least partially surrounded by the cooling medium. 6. The cylindrical wall (18c; 35) is connected to the wall of the evacuated container (3) having a throttle opening (27) and is given a potential which is more positive than the cathode potential. ,
X-ray tube according to one of the preceding claims, characterized in that at least a part contacts the cooling medium. 7. A cathode (1) and an anode (2), which are arranged in a container (3) which is evacuated and surrounded by a cooling medium, the electron beam (10) emerging from said cathode (1). ) Is a throttle opening (27) defined in the path to the anode (2) by at least one wall (18a, 18c) of the evacuated container (3), at least a portion of which is in contact with the cooling medium. The walls (18a, 18c) with the aperture opening (27) are then given a potential that is more positive than the cathode potential, and the electron beam (10) is applied in the region of the aperture opening (27). X-ray tube, characterized in that at least one deflection coil (31) for deflecting is arranged, the deflection coil being at least partly surrounded by the cooling medium. 8. The evacuated container (3) in the path of the electron beam (10) to the anode (2).
8. An X-ray tube according to claim 7, characterized in that it runs in a cylindrical wall (18c) surrounded by the deflection coil (31). 9. The tubular wall (18c) defines the aperture opening (27).
The X-ray tube described. 10. The size of the aperture opening (27) does not significantly exceed the minimum size required to prevent the passage of the electron beam (10).
X-ray tube according to any one of 1 to 9. 11. An X-ray tube as claimed in claim 1, wherein the walls (18a, 18c) with the aperture opening (27) are provided with an anodic potential. 12. X according to one of claims 1 to 10, characterized in that the wall (18a) with the throttle opening (27) is electrically insulated from the other components of the container. Line tube. 13. An X-ray tube as claimed in claim 1, wherein the walls (18a, 18c) with the aperture opening (27) are provided with a ground potential.