JPH0329125B2 - - Google Patents

Abstract

PURPOSE:To increase the cooling ratio and to make the use of a neutral ground type power source possible by supporting a target on an insulator in which a fluid refrigerant can pass through the inside, and constituting to give a voltage to the target through a contact. CONSTITUTION:An anode target 4 on which electron from a cathode 2 impinge is supported on the supporting portion 118-a of a rotating shaft 118, consisting of an insulator with large heat conductivity, in which a fluid refreigerant passage 134 is opened in the inside, and the shaft 118 is vacum-sealed by a housing 110, a magnet 111, pole pieces 112, 113 and a magnetic fluid 116 to make the rotation of the shaft possible. Further, a contact 123 is contacted with the center portion of the rotation in the target 4 to give a voltage, and to make the use of a neutral ground type high-tension power source possible, using the target 4 as a positive voltage, the cathode 2 as a negative voltage and a case 1 as an earth voltage. Accordingly, it is possible to extremely improve the cooling ratio of the target 4 to increase X-ray output volume.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a rotating anode X-ray tube.

[Technical background of the invention]

Generally, X-ray tubes are used for medical purposes, such as X-ray diagnosis, but in cases such as stomach examinations,
Conventionally, an X-ray tube as shown in FIG. 3 has been used. This X-ray tube is of a so-called rotating anode type, and a cathode 2 is disposed on one side of an envelope 1.
An electron mirror 3 containing a cathode filament that emits thermoelectrons and a focusing electrode is provided eccentrically.
Further, near the center of the envelope 1, a substantially umbrella-shaped anode target 4 is arranged opposite to the cathode 2 . This anode target 4 creates a high potential difference between it and the cathode 2 , accelerates electrons emitted from the cathode filament, causes them to collide, and generates X-rays by bremsstrahlung radiation. It is designed to store and dissipate heat, and is designed to rotate at high speeds to effectively expand the heat generation area. Such an anode target 4
is connected to a covered cylindrical rotor 6 via a support column 5. The rotor 6 generates rotational force by receiving a rotating magnetic field generated by a stator 7 disposed outside the envelope 1, and together with the stator 7 forms an induction motor. In addition, the support column 5 and the rotor 6
are united. A rotating shaft 8 is disposed inside the rotor 6 along the axis, and one end of the rotating shaft 8 is fixed to the rotor 6 with a screw or the like (not shown). A bottomed cylindrical stator 9 is coaxially disposed between the rotating shaft 8 and the rotor 6, and one end thereof is fixed to the envelope 1 via sealing rings 10 and 11. . A portion of the stator 9 is exposed outside the tube, and also serves to support and fix the entire X-ray tube to the outside. Bearings 12 and 13 are provided between the stator 9 and the rotating shaft 8.
is interposed so that the rotating shaft 8 can freely rotate. Now, during operation, when the electrons emitted from the cathode filament reach the target 4, the power reaches 1KW when the anode voltage is 50KV and the current is 20mA. Since more than 99% of this power is exchanged into heat, the target 4 is heated to a high temperature with heat radiation to the outside and heat conduction to other parts. Thermal radiation increases in proportion to the fourth power of temperature, so as the temperature rises, heat radiation increases significantly and thermal equilibrium is reached in a short time. For example, under the above conditions, the temperature reaches equilibrium at 1100°C after 5 minutes. On the other hand, when heat is transferred by thermal conduction, if the other end of the conductive medium is thermally free, the end gradually becomes hotter over a long period of time. The heat of the target 4 is then transferred to the rotor 6 and rotating shaft 8, making them hot. When the rotor 6 becomes high in temperature, thermal radiation increases and thermal equilibrium is reached as described above. Under the above conditions, supporting column 5
The upper point reaches 800°C approximately 15 minutes after the start of energization, the point at rotor 6 reaches 550°C 30 minutes after energization starts, and the point near bearing 12 reaches 400°C approximately 50 minutes after energization starts.
Thermal equilibrium is reached at °C. If the heat conduction of the bearing 12 deteriorates, the temperature at the point will be the same as that at the point,
The temperature will reach 550℃. bearing 12,
Depending on the rotational conditions of the balls in 13, thermal expansion may cause poor clearance between the outer ring and the inner ring, resulting in the above-mentioned problems. Furthermore, if the temperature of the bearings 12 and 13 exceeds 500° C., the hardness of the balls will decrease, causing damage to the bulbs such as stopping rotation.

Also, during heat input, the temperature of the anode target 4 is
Since the temperature is maintained between 800 and 1200℃, the anode target 4
The radiant heat from the anode target 4 varies depending on the surface area, surface emissivity, and shape factor of the anode target 4, but is usually 2 to 4 KW. However, when the temperature of the anode target 4 decreases, the radiant heat decreases significantly in proportion to the fourth power of the absolute temperature, so it takes an extremely long time to cool it sufficiently.

On the other hand, as a method to solve this problem, a rotating anode X-ray tube that employs a method of lowering the temperature of the anode target by flowing a fluid coolant (for example, water) through the anode target is known, for example, from U.S. Pat. No. 2,926,269. It is. In these structures, a coolant flows directly into the metal anode target, and the anode target is maintained at the same arm potential as the housing.

[Problems with background technology]

However, the conventional X-ray tube as described above has the following drawbacks. That is, as mentioned above, the inner rings of the bearings 12 and 13 tend to reach high temperatures, but the outer rings are at a low temperature, and the temperature at this point ranges from 60°C to 60°C.
The temperature varies between 550°C depending on the rotational conditions of the balls in the bearings 12 and 13. When the temperature of the balls increases, not only will there be insufficient clearance between the balls and the inner and outer rings, but the lubricant existing between them will evaporate, causing damage to the bearings 12 and 13.
may be damaged. For these reasons, there is a drawback that rotation stoppage accidents tend to occur frequently. To prevent this, the degree of blackening of the target 4 is increased, the degree of blackening of the surface of the rotor 6 is increased, and the degree of blackening of the target 4 and the rotor 6 is increased.
Although it has been considered to install a heat shield plate between the two, the effect of these is relatively small, and the reality is that the input power to the target 4 is too small.

Furthermore, at the time of input, the allowable temperature of the part where thermionic electrons emitted from the electron gun 3 are accelerated by high voltage and enter the anode target 4 (hereinafter referred to as the electron incidence surface) is such that the anode target 4 is made of tungsten. 2800 to suppress recrystallization.
Must be kept below ℃. As described above,
Since the overall temperature of the anode target 4 rises to 800 to 1200°C, the temperature of the ring-shaped part of the anode target 4 heated by the above electrons (hereinafter referred to as the electron incident orbital plane) increases to 1200 to 1500°C. It is normal to reach ℃. Therefore, the maximum temperature rise ΔT of the electron incidence surface that is allowed due to the incidence of electrons is
The limit is 1,300 to 1,600 degrees, and the possible input electron beam power, and hence the X-ray output amount, is proportional to ΔT and is therefore limited to a small value. In particular, the electron incidence surface,
Therefore, this is noticeable when the X-ray focus is small.

Furthermore, as mentioned above, when the target temperature decreases, the radiation power from the anode target 4 decreases in proportion to the fourth power of the absolute temperature. In order to reach a sufficiently low temperature, it is necessary to leave it for a very long time.

On the other hand, in the case of the known example of US Patent No. 2,926,269, the anode target is at the same ground potential as the housing, so in order to use it for medical purposes, it is necessary to set the cathode potential to 0 to -150 KV. This not only made the high-voltage power supply large and expensive, but also made the cable thick, making it unusable for X-ray equipment using this X-ray tube.

[Purpose of the invention]

An object of this invention is to introduce a liquid coolant flowing in and out through a shaft that rotatably supports an anode target into the anode target, and to efficiently remove heat from the anode target to the outside, thereby increasing the cooling rate of the anode target. In addition to keeping the anode target temperature at a high level, the anode target temperature is kept low at all times to increase the possible input electron beam power and therefore the amount of A positive high voltage is supplied and a negative high voltage is supplied to the cathode to provide a so-called neutral point grounded rotating anode X-ray tube.

[Summary of the invention]

In this invention, a tube container is separated into a vacuum inner part and a vacuum outer part by a vacuum seal bearing using a magnetic fluid, and a cylindrical shaft penetrating through the vacuum seal bearing is provided. Fluid refrigerant is allowed to flow in and out from one end of the vacuum exterior portion, and the other end of the shaft inside the vacuum is terminated with an insulator;
A metallic anode target is attached to the end of the insulator, and the anode target is cooled by a coolant passing through the insulator, and the anode target is electrically insulated from the housing and the coolant, and the tip of the insulator is This is a rotating anode type X-ray tube in which the anode target potential is determined through a thin conductor provided on the outer surface of the tube and a rotating contact provided on the central axis of rotation.

[Embodiments of the invention]

The rotating anode type X-ray tube of the present invention is constructed as shown in FIG. 1, and the same parts as in the conventional example (FIG. 3) are given the same reference numerals.

That is, the housing 1 is made of metal and kept at ground potential, and constitutes a vacuum container 101. A cathode 2 is disposed within the vacuum container 101 and fixed to the housing 1 via an insulator 102. The housing 1 is a central structure 10.
3, a voltage supply section 104, and a bearing section 105, which are connected to O-rings 106 and 107.
They are each connected in a vacuum via. A shaft housing 110 is attached to the bearing portion 105 via bearings 108 and 109. Moreover, a magnet 111 magnetized in the axial direction is attached inside the bearing part 105, and magnetic poles 112 and 113 are attached to O-rings 114 and 11 at both ends thereof.
5 to the bearing portion 105. The above magnetic poles 112, 113 and the shaft housing 11
A magnetic fluid 116 is applied between the shaft housing 110 and the magnetic poles 112 and 113 so that the shaft housing 110 and the magnetic poles 112 and 113 are rotatable in a vacuum-sealed state. The shaft housing 110 is fixed to the shaft 118 via a hollow part 117, and the hollow part 117 is in a vacuum state, making it difficult for the heat of the shaft to be transmitted to the magnetic fluid 116. The inner cylinder of the shaft housing 110 has a notch at its tip, and is adapted to be tightened with a nut 119. An O-ring 119a is tightly attached to the rear end of the shaft housing 110 with a tightening nut 120, and serves as a vacuum seal between the shaft housing 110 and the shaft 118.

The shaft 118 is made of an insulator with high thermal conductivity, and one end on the atmospheric pressure side is opened in a cylindrical shape, and one end on the vacuum side, that is, the target support part 118
-a is closed. The target 4 is coaxially attached to this target support portion 118-a. A refrigerant reservoir 118-a is located inside the target support portion 118-a of the shaft 118.
b, and the refrigerant in this refrigerant reservoir 118-b causes the target support portion 118-a of the shaft 118 to
and thus the target 4. Even when a conductive material such as water is used as the refrigerant, the refrigerant and the target 4 are electrically insulated, and the target 4 can be maintained at an arbitrary potential different from that of the refrigerant. The target 4 and the target support part 118-a may be crimped with a nut 121 via a suitable elastic packing (not shown), or may be fixed by hot pressing or the like. Target support part 118 made of insulator
A conductor 122 is fixed to the surface of -a,
A protrusion made of a hard metal such as SKH9 is provided at the center of rotation, and a part of the contact 123 is brought into contact with this protrusion to apply an electric potential to the target 4. The contactor 123 is fixed to the voltage supply section 104 of the housing 1 via an insulating cylinder 124.

Between the bearing portion of the shaft 118 and the vacuum side end, that is, the target support portion 118-a, there is a pleat portion 118-c for increasing the surface distance, and a ring 125 is arranged around the pleat portion 118-c.
Since it is installed coaxially with the target 4, it is possible to prevent the withstand voltage from deteriorating due to adhesion of secondary electrons coming from the electron incident surface of the target 4.

The housing 1 includes an X-ray emission window 12 made of a material with high X-ray transmittance, such as beryllium.
6 is installed. Further, a vacuum pump 127 such as a small ion pump is attached to the voltage supply section 104 of the housing 1 . This vacuum pump 12
In order to prevent the magnetic field 7 from having an adverse effect on the trajectory of electrons from the electron gun 3 to the target 4, a magnetic shield (not shown) is provided using a material with high magnetic permeability, such as permalloy.

The shaft 118 has the rotor 1 of the induction motor.
28 is fixed, and the stator 7 around it
Rotates at high speed due to the rotating magnetic field generated by the At this time, if a fan (not shown) is attached to the rotor or shaft 118, self-cooling can be achieved. Atmospheric side open end 118- of shaft 118
d, the ring 130 is inserted through the O-ring 129.
is fixed. A cylinder 131 is attached coaxially around the ring 130, and a bushing 132 made of resin plastic, for example, is installed between the ring 130 and the cylinder 131. Furthermore, a refrigerant seal 133 is attached coaxially with the ring 130 to prevent refrigerant from leaking to the outside.

A circular pipe 134 is coaxially attached to the inside of the shaft 118, and refrigerant is supplied from the outside to the refrigerant reservoir 118-b through this circular pipe 134.

The bearing portion 105 includes refrigerant passages 135 and 136.
is provided to cool the magnetic fluid 116. There are also refrigerant passages 137, 1 around the housing 1 .
38 and 139 are provided to absorb radiant heat from the target 4. Further, the stator 7 is fixed to the housing 1 by a support cylinder 140.

Note that FIG. 2 is a sectional view taken along line -' in FIG. 1 and viewed in the direction of the arrow, and shows the refrigerant reservoir 118
-b is divided by a partition wall 118-e, and the refrigerant is stored separately in each refrigerant reservoir 118-b.

Now, during operation, the shaft 118 and target 4 are rotated at 10,000 to 20,000 rpm by the rotor 128.
rotated at high speed. At this time, the magnetic fluid 11
6, the target 4 side is maintained at a high vacuum. Then, an appropriate amount of refrigerant is supplied from the circular pipe 134, and this refrigerant is retained in the refrigerant reservoir 118-b.
The overflowing refrigerant is guided to the outside through the inner wall of the shaft 118.

Thermionic electrons emitted from the electron gun 3 are accelerated by a potential of about 150 KV between the electron gun 3 and the target 4 and reach the surface of the target 4. A plate of tungsten or its alloy is bonded to the surface of the target 4, onto which a high-energy electron beam is incident.
The heat generated thereby is quickly transferred to the inside of the target 4 made of heavy metal by thermal conduction. The heat of the target 4 is transferred to the refrigerant in the refrigerant reservoir 118-b through the target support portion 118-a of the shaft 118, which is made of an insulator with high thermal conductivity. This refrigerant is pushed by the partition wall 118-e, rotates at high speed together with the target 4, and is forced with strong pressure against the inner wall of the refrigerant reservoir 118-b by a strong centrifugal force. Therefore, generation of a vapor phase between this refrigerant and the refrigerant reservoir 118-b can be prevented, increasing the heat transfer coefficient. Refrigerant reservoir 118-
When the refrigerant evaporates due to an increase in the temperature of the wall surface b, the generated gas is pushed toward the center of rotation by the strong centrifugal force of the refrigerant, and is guided to the outside through the inner wall of the shaft 118. At this time, the large latent heat of vaporization effectively cools the target support portion 118-a of the shaft 118. The evaporated refrigerant is supplied from the circular pipe 134, and the refrigerant reservoir 118-b is always filled with refrigerant.

If water is used as the refrigerant, refrigerant reservoir 1
While keeping the inner surface of 18-b always below 120℃,
It is easy to remove about 4KW of heat at all times. Target 4 has a certain heat capacity, for example 500KHU.
By having a
By allowing the temperature of the electron incident orbital surface to rise, it is possible to apply large instantaneous input power. For example, if the temperature of the electron incident orbital surface is designed to be 500℃ or less, the peak power that can be input to the target 4 will be 2800-500/2800 compared to the conventional example above at the same rotation speed and focal spot size. -1500≒1.8 times, which is a revolutionary performance improvement. In other words, the size of the X-ray focal point can be reduced by 0.67 while obtaining the same X-ray output.
This means that the size can be doubled, and the resolution of the X-ray diagnostic apparatus can be greatly improved.

Furthermore, the waiting time for the temperature of target 4 to drop below 200°C is reduced to 1/20 times or less compared to the conventional example, so for example, CT (Computer
When used in Tomography (Tomography) equipment, it can significantly improve patient throughput.

Additionally, since the rotating mechanism is always kept at 120°C or below, reliability is improved and lifespan is extended compared to conventional systems. Further, vibration and noise caused by rotation can be suppressed to low values. Furthermore, it allows for higher speed rotation than before.

Also, target 4 is +75KV, housing 1 is
0V, and the electron gun 3 can be maintained at about -75KV, so the rotating anode type X-ray tube of the present invention can be employed without making any changes to the conventional X-ray equipment.

The above-mentioned conventional example (Fig. 3) is used by being installed in an X-ray tube container (not shown), but the rotating anode type X-ray tube of the present invention can be used as shown in Fig. 1. It is smaller and lighter than the conventional one. In the embodiment shown in FIG. 1, the total length is 42 cm and the maximum diameter is 20 cm.

〔Effect of the invention〕

According to this invention, the following remarkable effects can be obtained.

The cooling rate of the anode target 4 is always a large value, and the time it takes for the anode target 4 to be sufficiently cooled is shortened to several tenths, allowing use with extremely high duty. ) device, patient throughput is significantly improved.

Since the anode target 4 is always kept at a low temperature, the instantaneous possible input is improved by a factor of 1.8 (at the same rotation speed, same target size, and under the same focus), and the focus size has to be changed to obtain the same X-ray output. can be made 0.67 times smaller, and the resolution of X-ray diagnostic equipment using this can be significantly improved.

The anode target 4 is kept at a positive high voltage, the housing 1 is kept at a ground potential, and the electron gun 3 is kept at a negative high voltage. It can be used with a grounded high voltage power supply and can be applied to X-ray diagnostic equipment without any modification.

Since the rotating bearing part 105 is kept at a low temperature, it has extremely high reliability, low vibration,
A low-noise, long-life X-ray tube can be provided.

Since the housing 1 also serves as a tube container, it is small and
Becomes lightweight.

The housing 1 has a daymarantable structure, and defective parts can be replaced, reducing the cost.

Since the temperature of the rotary bearing portion 105 is low, high-speed rotation is possible and X-ray output can be further increased.

[Modified example of the invention]

The vacuum-side end 118-a of the shaft 118 and the anode target 4 are connected to each other using an insulating material 11.
It is preferable to metallize the surface of 8-a and braze both of them to improve the heat transfer coefficient.

Bulkhead 1 in side end 118-a of shaft 118
The height of the shaft 18-e is the same as that of the shaft 11 in the above embodiment.
It is the same as the inner diameter of No. 8, but it does not matter if it is lower or higher than this. Moreover, the partition wall 118-e can also be omitted.

In the above embodiment, the circular tube 134 is connected to the shaft 118.
However, the shaft 118 and the circular tube 134 may be made integrally, or the circular tube 134 may be supported by the shaft 118.
The circular tube 134 may be modified to rotate together with the circular tube 18. In this case, it goes without saying that a rotary joint (not shown) is required in a part of the circular tube 134.

Shaft housing 11 of shaft 118
By metallizing the outer surface from 0 to the end on the atmosphere side, the rotor 128 can be maintained at ground potential through the bearings 108 and 109 to stabilize its operation.

When fixing the shaft 118 and the shaft housing 110, one end of the shaft 118 and the shaft housing 110 on the target side is tapered and fitted together, and a vertical groove is provided in a part of the shaft housing 110 near this fitting part. It should have elasticity to eliminate looseness during thermal expansion, and should also have a strong enough force to prevent the shaft from wobbling during rotation. Further, a shaft 118 and a shaft housing 110 are provided at the other end of the shaft housing 110.
If a material (such as a cylindrical spring) that provides a spring action is inserted inside and tightened, the above effect will be further improved.

The rotor 128 and shaft 118 may be attached in the same manner as described above. Of course, a plurality of electron guns 3 may be attached.

It goes without saying that part or all of the surfaces of the anode target 4 and the housing 1 may be blackened to improve the emissivity.

Furthermore, if a heavy metal such as lead is pasted around the housing 1 , leakage of X-rays can be reduced.

Keeping the refrigerant at a temperature higher than the air temperature, for example 40°C, will prevent condensation and improve reliability. The refrigerant may flow in a closed loop circuit with a heat exchanger, which may be cooled by water cooling or forced air cooling.

Further, in the above embodiment, the high voltage supply sections 141 , 1
42 is provided in a direction parallel to the tube axis, but it is effective to provide both or a part of these in a direction perpendicular to the tube axis because the overall length can be further shortened.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a rotating anode type X-ray tube according to an embodiment of the present invention, and FIG.
FIG. 3 is a cross-sectional view taken along the line and viewed in the direction of the arrow. FIG. 3 is a cross-sectional view showing a conventional rotating anode type X-ray tube. 2 ...Cathode, 4...Target, 105...Bearing section, 110...Shaft housing, 118...
...Shaft, 118-a...Target support part,
116...Magnetic fluid, 118-b...Refrigerant reservoir,
123...Contact, 118-c...Fold, 11
8-e... Bulkhead, 125... Ring.

Claims (1)

[Scope of Claims] 1. A cathode for emitting electron beams disposed in a vacuum container, a rotatable anode target for emitting X-rays disposed opposite to this cathode, and a thermally conductive a target support part made of an insulator joined to the target support part to hold the target and into which a fluid refrigerant is introduced; a rotating shaft; a bearing section provided on the outer periphery of the rotating shaft and having a vacuum sealing mechanism for keeping the vacuum container and the interior space of the container in a vacuum; and a refrigerant passage provided on the rotating shaft leading to the target support section. and potential supply means for applying an operating potential to the anode target from outside the vacuum vessel. 2. The rotating anode X-ray tube according to claim 1, wherein the bearing portion is provided with a vacuum seal mechanism using a magnetic fluid. 3. A disk-shaped anode target is fixed to the outer periphery of a target support made of an insulating material, and a conductive layer is coated on the surface of the target support opposite to the refrigerant passage, and the conductive layer is electrically connected to the anode target. 2. The rotating anode X-ray tube according to claim 1, wherein the conductor layer is coupled to the conductor layer and an operating potential is externally supplied to the conductor layer.