JPH0334183B2 - - Google Patents

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. 4 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 gun 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 provides 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. and stator 9
Bearings 12, 1 are provided between the rotating shaft 8 and the rotating shaft 8.
3 is interposed so that the rotating shaft 8 can rotate freely. Now, during operation, the power when the electrons emitted from the cathode filament reach the target 4 is anode voltage 50KV and current 20mA.
, it reaches 1KW. Since more than 99% of this power is converted 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.
Thermal equilibrium is reached in a short time. For example, under the above conditions, equilibration occurs 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 high temperature. When the rotor 6 becomes high in temperature, thermal radiation increases and thermal equilibrium is reached as described above. Under the above conditions, the point on the support column 5 reaches 800 degrees Celsius approximately 15 minutes after the start of energization, the point on the rotor 6 reaches 550 degrees Celsius 30 minutes after the start of energization, and the point near the bearing 12 reaches about 50 minutes after the start of energization. Thermal equilibrium is reached at 400℃. If the heat conduction of the bearing 12 deteriorates, the temperature at the point will be the same as that at the point, reaching 550°C. bearing 1
Depending on the rotational conditions of the balls 2 and 13, thermal expansion may result in poor clearance between the outer ring and the inner ring, resulting in the above-mentioned problem. 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 ground 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 determined by the temperature when 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 surface) 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 for medical use, the cathode potential must be set to 0 to -150 KV. Not only is the high-voltage power supply large and expensive, but the cable is also thick, making it unusable in an X-ray device using this X-ray tube.

[Purpose of the invention]

The purpose of this invention is to cool the anode target by passing through a shaft that rotatably supports the anode target, guiding a fluid coolant flowing in and out into the anode target, and removing the heat of the anode target to the outside at a good exchange rate. In addition to keeping the anode target temperature high, the anode target temperature is always kept low to increase the possible input electron beam power and thus the amount of X-ray output, and the anode target is isolated from the housing and the coolant and the voltage supply terminal is kept low. A positive high voltage is supplied to the cathode, 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]

This invention separates a tube container into a vacuum inner part and a vacuum outer part by a vacuum seal bearing using magnetic fluid, and provides a cylindrical metal shaft penetrating inside the vacuum seal bearing. A fluid refrigerant flows in and out from one end of the shaft outside the vacuum, and a target support made of an insulator is coaxially attached to the other end of the shaft inside the vacuum, and a metal anode is connected to the target support. The target is mounted and the anode target is cooled by a refrigerant through the target support made of the insulating material, the anode target is electrically insulated from the housing, the refrigerant and the shaft, and the anode target is cooled by the target support made of the insulating material. Rotary anode type
It is a wire tube.

[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. 4) 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. 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 portion 117, and the hollow portion 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 metal such as stainless steel, 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 1
18-a is closed. The target 4 is coaxially attached to this target support portion 118-a. A refrigerant reservoir 11 is located inside the target support portion 118-1 of the shaft 118.
8-1-a, and this refrigerant reservoir 118-1-a
The target support portion 118-1 of the shaft 118 and therefore the target 4 are cooled by the refrigerant. 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 118-1 are connected to the nut 121 through a suitable elastic packing (not shown).
It may be crimped or fixed using a hot press or the like. Since the above-mentioned cooling effect is large and the temperature of the joint between the anode target 4 and the target support part 118-1 is maintained below 600 DEG C., a structure in which both are brazed is preferably used. Target support part 118-1 made of insulator
A conductor 122 is fixed to the surface of the target 4, and 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. Above contact 1
23 is fixed to the voltage supply section 104 of the housing 1 via an insulating cylinder 124.

A ring 1 is placed around the target support part 118-1.
25 is attached coaxially with the target support portion 118-1, deterioration of the withstand voltage due to adhesion of secondary voltage coming from the electron incident surface of the target 4 is prevented.

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, the rotor 128 or the shaft 11
If a fan (not shown) is attached to 8, self-cooling can be achieved. Atmospheric side open end 1 of shaft 118
A ring 130 is fixed to 18-d via an O-ring 129. 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, the refrigerant seal 133 is attached to the ring 1.
It is installed coaxially with 30 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 118-1-a through the cylinder 134.

The shaft 118 and the circular tube 134 are integrally formed with a plurality of substantially parallel through holes, and another rotary seal is provided outside the rotary seal 133 and around the hole in the center, so that the shaft 118 itself is free of refrigerant. It can also be used as a round trip passage.

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 7171 is fixed to the housing 1 by the support cylinder 140.

Moreover, on the inner wall of the target support section 118-1,
As is clear from FIG. 2, a metal layer 141 is attached, and its surface is made corrugated to increase thermal conductivity. Furthermore, since the metal layer 141 and the metal shaft 118 are easily bonded, accidents such as airtight leakage can be prevented. Alternatively, the tip of the circular tube 134 may be covered with a lid, and small holes may be opened radially near the refrigerant reservoir 118-1-a to spray the refrigerant in a mist.

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, this refrigerant is retained in the refrigerant reservoir 118-1-a, and 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 passes through the target support part 118-1 of the shaft 118 made of an insulator with high thermal conductivity and is transferred to the refrigerant reservoir 118-1-a.
is transmitted to the refrigerant inside. This refrigerant is the metal layer 141
The refrigerant rotates at high speed together with the target support part 118-1 due to the friction between the refrigerant and the refrigerant, and is pushed with strong pressure against the inner wall of the refrigerant reservoir 118-1-a by the strong centrifugal force. Therefore, this refrigerant and refrigerant reservoir 118-1-a
It can prevent the formation of a vapor layer between the layers and increase the thermal conductivity. When the refrigerant evaporates due to an increase in the temperature of the wall surface of the refrigerant reservoir 118-1-a, the generated gas is pushed toward the center of rotation by the strong centrifugal force of the refrigerant, and passes through the inner wall of the shaft 118 to the outside. be guided. At this time, due to the large latent heat of vaporization, the target support portion 118- of the shaft 118
1 to effectively cool it. The evaporated refrigerant flows into the circular pipe 134
The refrigerant reservoir 118-1-a is always filled with refrigerant.

If water is used as the refrigerant, refrigerant reservoir 1
It is easy to constantly remove about 4KW of heat from the inner wall of 18-1-a while keeping the temperature below 120°C.
Target 4 has a certain heat capacity, e.g.
By providing 500 KHU, it is possible to apply a large instantaneous input power by allowing the temperature of the electron incident orbital surface to rise while keeping the joint surface with the target support part 118-1 made of an insulator at a low temperature. do. 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
This can be doubled, resulting in a revolutionary performance improvement. In other words, the size of the X-ray focal point can be reduced by 0.67 times while obtaining the same X-ray output, and the resolution of the X-ray diagnostic apparatus can be significantly improved.

Furthermore, the waiting time for the temperature of target 4 to drop below 200°C is reduced to less than 1/10 times that of the conventional example.
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 conventional example (Fig. 4) 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 it is 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 required 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 (same rotation speed, same target size, under the same focus), and the size of the focus needs to be changed to obtain the same x-ray output. It 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 ground potential, and the electron gun 3 is kept at a negative high voltage. It can be used with a 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.

Housing 1 has a daymaran tumble structure, allowing defective parts to be replaced.
Prices are reduced.

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 by a 118 made of an insulating material.
The surface of -a may be metallized and both may be brazed, or the metal layer 141 may be replaced with a thick metal cup and made integral with the end 118-a of the shaft 118 in advance or brazed. A target support portion 118-1 made of an insulator may be attached thereon while maintaining airtightness. In this case, the space between the target support part 118-1 and the shaft 118 does not need to be airtight. As shown in FIG.
It is preferable to provide radial partition walls 141-1 to improve the efficiency of heat transfer between the target support portion 118-1 and the refrigerant.

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.

By metallizing the outer surface of the shaft 118 from the shaft housing 110 to the end on the atmosphere side, the rotor 128 is attached to the bearing 10.
If the ground potential is maintained through the terminals 8 and 109, the operation will be stable.

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 section 141,1
42 is provided in a direction parallel to the tube axis, but it is effective to provide both or part of these in a direction perpendicular to the range, since the overall length can be shortened. It goes without saying that another bearing may be provided on the opposite side of the shaft housing 110 to the anode target 4, and the refrigerant may be passed through the anode target 4.

Next, another modification will be described with reference to FIG. 3, but this modification also provides the same effects as the above embodiment. In addition, the same parts will be given the same reference numerals.

That is, the shaft 118 and the target support section 11
8-1 is mechanically and tightly fixed with a bolt 142, and an O-ring 143 is provided between them to seal the refrigerant. Target support part 1
There is a protrusion 118-1-b at the tip of 18-1, a conductive object 122 is attached to the surface of the protrusion 118-1, and a ball bearing 144 is attached in contact with the conductive object 122. This bearing 144 uses a solid lubricant to reduce friction in a vacuum.
Further, this bearing 144 is supported by a support tube 145, and this support tube 145 is fixed to the voltage supply section 104 of the housing via the insulating tube 124 shown in FIG. The anode target 4 includes the conductor 122, the bearing 144, and the support tube 145.
High voltage is supplied from the outside through.

Furthermore, Si ₃ N ₄ is used as the target support part 118-1.
When used, good results can be obtained because it has a high thermal emissivity, good mechanical strength, and is easy to bond with metal. Also, as the target support part 118-1
Using AlN has good thermal conductivity and a large cooling effect.

Alternatively, the anode target 4 may be cooled by providing a heat pipe structure inside the shaft 118 and cooling the portion of the shaft 118 outside the vacuum.

[Brief explanation of the drawing]

1 is a sectional view showing a rotating anode X-ray tube according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line I-I' in FIG. 1 and viewed in the direction of the arrow; FIG. 3 is a sectional view showing a modification of the present invention, and FIG. 4 is a sectional view showing a conventional rotating anode type X-ray tube. 2... Cathode, 4... Target, 105... Bearing part,
110...Shaft housing, 118...Shaft, 118-1...Target support part, 118-1
-a... Refrigerant reservoir, 123... Contact, 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 metal rotary shaft to be rotated; a bearing section provided on the outer periphery of the rotary shaft and having a vacuum seal mechanism that keeps the vacuum container and the interior space of the container in a vacuum; a rotation drive section attached to the rotary shaft; The rotary shaft is provided with a refrigerant passage leading to the target support portion, and a potential supply means provided to apply an operating potential to the anode target from outside the vacuum vessel, and the rotary shaft is connected to the vacuum vessel. Rotating anode type X characterized by being electrically at the same potential
wire tube. 2. The rotating anode X-ray tube according to claim 1, wherein a metal layer is adhered to the inner surface of the target support made of an insulator, and the metal layer is hermetically sealed to the end of the metal shaft.