JPH01151141A - X-ray tube device - Google Patents

Abstract

PURPOSE:To realize the uniformity of electron intensity distribution, sufficient X-ray intensity and the precise positioning of a flat cathode by supporting the flat cathode with the first leg section and the second leg section having different thermal expansion coefficients and thermal conductivities respectively. CONSTITUTION:A cathode filament 301 is formed with a flat thermoelectron emitting section 301a and the first leg sections 301b and the second leg sections 301c supporting them. The first leg sections 301b are vertical to the thermoelectron emitting section 301a, the second leg sections 301c are fixed and supported by support stanchions 302 while one end of each is put in contact with the first leg section 301b and the other end is extended in the direction of the thermoelectron emitting section 301a. The second leg section uses a material having a larger thermal expansion coefficient and a smaller thermal conductivity than those of the material of the first leg section. The thermal deformation during the operation of the filament 301 is thereby absorbed by both leg sections, the thermoelectron emitting section 301a has little relative displacement, thus the desired objective is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an X-ray tube device, and particularly to an improvement of its cathode structure.

(Prior Art) X-ray tube devices are generally used for medical purposes by being attached to, for example, an X-ray diagnostic device. equipment is used.

This X-ray tube device is of the so-called rotating anode type, with a vacuum envelope 3
A cathode structure and an umbrella-shaped anode target 33 are disposed in the tube 1 so as to be eccentric from the tube axis and facing each other.

The anode target 33 is rotated by a rotor 35 that is rotationally driven by a stator 34 by electromagnetic induction.

Now, the cathode structure 3 of the conventionally used X-ray tube device
2 is constructed as shown in FIG. 6, and a cathode filament 101 is disposed within a focusing groove 106 of a focusing electrode 102. The cathode filament] 01 is made of a tungsten coil for emitting thermoelectrons, and the thermoelectrons are focused by a focusing electrode 102. For this reason, the cathode filament 101 and the focusing electrode 102 are set to approximately the same potential.

In the figure, a broken line 103 represents an equipotential curve near the focusing electrode 102, a symbol 104 represents the trajectory of electrons emitted from approximately the center of the cathode filament 101, and a symbol 1
05 represents the trajectory of electrons emitted from a location close to the side surface of the cathode filament 101.

(Problems to be Solved by the Invention) In the above conventional cathode structure, the cathode filament 1
Since 01 is used in a substantially temperature-limited region, a part of the cathode filament 101 is made to protrude into the focusing electrode 102 in order to strengthen the electric field near the cathode filament 101. Therefore, the equipotential curve near the cathode filament 101 has a swollen shape at the center of the cathode filament 101, as shown by the broken line 103, and the cathode filament 1
Electrons 105 emitted from substantially the sidewalls of 01 are directed to the side. This electron 105 and cathode filament 101
The electrons 104 emitted from approximately the center of the
Unable to focus in the same direction, these trajectories intersect on the axis as shown. Therefore, at a position where approximately all the electrons are focused to some extent, a bimodal electron intensity distribution 107 is shown as shown.

However, as described above, since the electrons emitted from the cathode filament 101 cannot be focused sufficiently by the focusing electrode 102, it is necessary to use a small cathode to obtain a small focus at the position of the anode target 33. Therefore, unless the cathode temperature is raised, sufficient high density electrons cannot be obtained, which poses a problem in the reliability of the cathode filament 101.

Further, since the traveling directions of the electrons at the position of the anode target 33 are not aligned, a minute focus cannot be obtained, and furthermore, the electron distribution lacks sharpness, making it impossible to obtain the desired electron distribution. For this reason, it is not possible to simultaneously obtain a sufficiently high resolution and reduce the maximum temperature rise due to electron incidence on the anode target 33 to increase the amount of incident electrons. When a projection image is created using X-rays generated from the anode target 33, these interfere with the increase in resolution and the reduction in photon noise, making it impossible to obtain a sufficiently clear image.

One possible method for eliminating this drawback is to use a flat cathode filament, and an example of this is a proposal disclosed in Japanese Patent Laid-Open No. 55-68056.

The conventional example having this flat cathode filament is constructed as shown in FIGS. 7 and 8, and the reference numeral 201 in the figure is a cathode filament made of a belt-like flat plate and formed in the shape of a mouth. Filament support column 215.215
It is fixed to the surface and is directly heated by electricity, emitting thermoelectrons. In this case, the cathode filament 201 during operation of the X-ray tube device
Due to the thermal expansion, the central portion, that is, the electron emitting portion, is curved and shifted significantly upward, as shown by the broken line 201a. Both legs also deform outward. In particular, when the position of the electron emitting part changes with changes in filament temperature, the relative positional relationship with the focusing groove 206 of the focusing electrode 202 changes,
The shape of the focal point on the anode target 208 changes.

This also appears as a large change in not only the focal point shape but also the focal width W, which hinders the realization of a fine focal point.

In FIG. 7, a broken line 203 represents the equipotential curve near the focusing electrode 202, and a reference numeral 204 represents the equipotential curve near the focusing electrode 202.
1, reference numeral 205 represents the trajectory of electrons emitted from near the side of the cathode filament 201, and reference numeral 207 represents the electron intensity distribution.

This invention was made in view of the above circumstances, and by improving the shape of the cathode filament, it is possible to obtain an X-ray focus with a uniform electron intensity distribution and sufficient X-ray intensity, and to improve the position of the filament. It is an object of the present invention to provide an X-ray tube device that can be made with high accuracy and does not cause positional shift or deformation even when exposed to high temperatures, so that the size and position of the X-ray focal point can be accurately determined.

[Structure of the Invention] (Means for Solving the Problems) This invention provides a flat cathode filament that includes a thermionic emission section that is formed perpendicularly to the electron beam axis and becomes hot, and both ends of this thermionic emission section. The first leg portions were bent perpendicularly from each other, and one end portion was fixed to the end of the first leg portion, and the other end portion was extended in the direction of the thermionic emission portion and was fixed to the filament support column. This is an X-ray tube device consisting of a flat second leg.

(Function) According to this invention, since the thermionic emission part is flat,
Thermionic emission directions coincide, electron focusing is good, and an X-ray focus having a uniform electron intensity distribution can be obtained.

Furthermore, when installing the flat cathode filament, its position can be finely adjusted, and the installation can be performed with high precision with extremely little variation in position.

Furthermore, even if the temperature of the thermionic emission part reaches a high temperature, for example, 2300° C., the thermal expansion of the legs is absorbed, and the change in position becomes extremely small. Therefore, the range of focal spots previously accepted in the art can be narrowed, increasing the allowable input power and increasing the x-ray output for the same nominal focal spot size.

Furthermore, since the material and thickness of the second leg can be made different from those of the first leg, the temperature of the filament support column can be lowered sufficiently, and the resonance frequency of the cathode filament can be increased. Vibrations caused by the rotation of the anode target during operation do not cause damage due to contact with surrounding metal or instability of the tube current due to relative positional deviation with the electrode.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Note that the same parts are represented by the same symbols.

This invention can be used, for example, for mammography with an anode voltage of 30 KV.
, maximum anode current 300 mA, XN8 focal power 50 μm
An example of application to an X-ray tube device that can be changed in the range of 0.5 mm to 0.5 mm will be shown.

That is, the main parts of the X-ray tube device according to the present invention are constructed as shown in FIGS. 1 to 4, and as shown in FIGS. A cathode assembly 300 is provided opposite to this. This cathode structure 300 includes a directly heated cathode filament 301 supported by a pair of filament support columns 302 and 302 made of molybdenum or the like, a heat shield plate 318, and a heat transfer body 316.
, a heat shield cylinder 317 and a focusing electrode 303.

In this case, the cathode filament 301 is shaped like a flat plate, as is not clear from FIGS. 1 and 2, and has a width of about 2 m, for example.
m, and the thickness is set to about 0.012 mm. A thermionic emission part 301a for emitting thermoelectrons when heated to a high temperature, and a first leg part 30 that is vertically bent at both ends of the thermionic emission part 301a.
1b.

301b and 1. :, (7) First leg portions 301b, 301
A flat plate-shaped second leg portion 3 has one end fixed to each end of b, the other end extended in the direction of the thermionic emission part 301a, and fixed to the filament support column 302.302.
01c and 301c. And the first
leg portion 301b.

301b and the second leg portions 301c, :301c
It is formed in a letter shape or a letter 7 shape. Second leg 301c
, 301c are welded and electrically connected to filament support columns 302 and 302 at a height close to the thermionic emission section 301a.

In the above case, the thermionic emission section 301a and the first leg section 3
In addition to pure tungsten, 01b and 301b are made of a high melting point alloy material such as tungsten containing about 1 to 5% rhenium or lanthanum molybdenum.

Further, the second leg portions 301c, 301c are similar to the first leg portion 30.
1b1301b is made of a material with a larger thermal expansion coefficient and lower thermal conductivity than the first leg parts 301b and 301b, for example stainless steel, and the temperature is lower than that of the first leg parts 301b and 301b. It's the same.

FIG. 2 shows the first leg portions 301b, 301b and the second leg portion 3.
It is an exploded perspective view of 01c and 301c, and shows the state before joining. When assembling, the second leg 301c,
301c is a pair of filament support columns 302.30
It is joined to 2.

Between this pair of second legs 301c, 301c are first legs 301b, 3 which are integrated with the electron emitting part 301a.
01b in the direction of the arrow and adjust the height and position, then insert the second leg 301C.

301c is bent to form the first leg portions 301b, 3.
01b is fixed. After that, it is fixed by laser beam welding or the like.

Furthermore, as shown in FIGS. 3 and 4, a heat shield plate 318 is provided below the thermionic emission portion 301a of the cathode filament 301, and is joined to the heat transfer body 316.

A heat shield tube 317 is joined to this heat transfer body 316, and this heat shield tube 317 is positioned so as to surround the first legs 301b, 301b.

A focusing electrode 303 is formed into a circular cup shape and focuses an electron beam so as to surround the cathode filament 301.
is provided, and at least one of filament support columns 302, 302 is fixed to this focusing electrode 303 via an insulating support column (not shown). Furthermore, the focusing electrode 303
, the thermionic emission part 301a of the cathode filament 301
An electron beam limiting hole 304 is formed opposite to the electron beam limiting hole 304 .

This electron beam limiting hole 304 is located in the thermionic emission section 301a.
For example, it has a rectangular shape with an area smaller than the area of is parallel to. A focusing groove 305 is formed in the focusing electrode 303 continuously and in front of the electron beam limiting hole 304 . This focusing groove 305 has a diameter larger than that of the electron beam limiting hole 304, for example, a rectangle, and
It is formed coaxially with la and has a sufficiently deep depth (d2).

The bottom surface of the focusing groove 305 is formed by the electron beam limiting hole 30.
4 and is tapered. The dimension of this Taber surface along the direction of the central axis (C) is formed to be a small dimension that is less than a fraction of the depth (d2).

The reference numeral 306 in FIG. 3 is an AC power supply, and 307 and 308 are DC power supplies.

Incidentally, since the configuration other than the above is the same as that of the conventional X-ray tube device (FIG. 5), detailed explanation will be omitted.

During use of the X-ray tube device of the present invention having the cathode assembly 300 as described above, the thermionic emission portion 301a of the cathode filament 301 is heated to a high temperature of about 2300°C. First leg 301b, 3 of cathode filament 301
01b, due to heat conduction to the second leg portions 301c, 301c, the temperature at the end portion becomes as low as about 1000° C. with a rapid temperature gradient. Furthermore, a second leg portion 301c.

Since one end of 301C is fixed to the filament support column 302.302 having a large heat capacity, the temperature at the tip of the filament support column 302.302 is even lower at about 600°C. In this way, the filament support column 302.
The temperature of the first leg 302 is lower than the temperature of the first leg 301b, 301b.

Furthermore, the thermionic emission section 301a is connected to the filament support column 30.
2.The position is higher than the tip of 302. However, the second leg 301c.

301C is the first leg 301b so as to cancel out the difference in thermal expansion.
, 301b, the relative displacement of the thermionic emission part 301a is extremely small under any conditions.

Note that the width and thickness of the cathode filament 301 are selected so that the temperature distribution satisfies the above conditions. Furthermore,
The second leg 301c is adjusted such that the resonance frequency is sufficiently high.
, 301c are set to a sufficient value. Thermal expansion in the length direction of the thermionic emission part 301a is caused by the second leg part 301
c, 301c and the first legs 301b, 301b, the U-shaped or V-shaped structure is completely absorbed and will not be deformed in any way.

Since the position of the thermionic emission section 301a does not change in this way, an X-ray tube using this not only has an extremely stable X-ray output, but also has less variation in the X-ray focal point size, so that This allows for large inputs.

Furthermore, by appropriately selecting the electrical resistance of the second leg portions 301c, 301c, the heat generating portion can be substantially changed from the first leg portion 30],
b, 301b, and the power required for heating the cathode filament can be reduced.

(Modification) In the above embodiment, the entire cathode filament 301 has the same width, but the width is changed in the middle, especially at the first leg portion 301b.
, 301b and the second leg 301C% 301C, a convenient temperature distribution can be obtained. Furthermore, the thickness of the cathode filament 301 may be varied. In particular, part or all of the thermionic emission section 301a is connected to the first and second leg sections 301b.

30 l b , 301 c , 30 ], if the thickness is made thinner than c, an even better temperature distribution can be obtained. or,
The width and thickness of the second legs 301c, 301c may be different from those of the thermionic emission section 301a and the first legs 301b, 301b.

Moreover, the second leg portion 301C1301C in the above embodiment
A third leg may be provided between the filament support column 302.302 and the filament support column 302.302.

[Effect of the invention] According to this invention, the following excellent effects can be obtained.

(2) An X-ray focus with a uniform electron intensity distribution is obtained, improving the resolution of X-ray images.

■The variation in the size of the X-ray focal point is reduced, allowing highly accurate X-ray intensity control.

(2) The heating power for the cathode filament is reduced, and in particular, the heating current is required to be small, and an X-ray imaging apparatus using a conventional X-ray tube device can be used without major modification.

■Deformation of the cathode filament due to thermal expansion can be prevented, and an X-ray tube device with sufficient reliability can be provided.

■The resonant frequency of the cathode filament is increased, and even at high temperatures, the cathode filament does not shift its position and does not become out of focus or come into contact with the surroundings.

[Brief explanation of the drawing]

1 and 2 are a perspective view and an exploded perspective view showing the main parts (near the cathode filament) of an X-ray tube device according to an embodiment of the present invention, and FIGS. 3 and 4 are an embodiment of the present invention. 5 is a cross-sectional view showing the cathode structure of the X-ray tube device according to the embodiment; FIG. 5 is a schematic configuration diagram showing the entire conventional X-ray tube device; FIGS. 6 and 7 are
The figures are cross-sectional views showing cathode assemblies (two examples) of conventional X-ray tube devices, and cross-sectional views showing main parts (near the cathode filament) of FIGS. 8C to 7. 31... Vacuum envelope, 33... Anode target, 300... Cathode structure, 30
DESCRIPTION OF SYMBOLS 1... Cathode filament, 301a... Thermionic emission part, = 17-301b... First leg part, 301C... Second leg part,
302...Filament support column. Applicant's agent Patent attorney Takehiko Suzue-18= Figure 3 Figure 7

Claims (4)

[Claims] (1) A cathode structure and an anode target are disposed facing each other in a vacuum envelope, and the cathode structure includes a flat cathode filament supported by a filament support column and a focusing electrode provided in front of the cathode filament. In the X-ray tube device, the flat cathode filament has a thermionic emission part that becomes high temperature and is formed perpendicular to the electron beam axis, and a first part that is bent perpendicularly from both ends of this thermionic emission part. The legs and
One end is fixed to the first leg end, and the other end is extended in the direction of the thermionic emission section, and further includes a flat second leg fixed to the filament support column. Characteristic X-ray tube device. (2) The X-ray tube device according to claim 1, wherein the flat cathode filament is made of tungsten or an alloy thereof. (3) The second leg has a coefficient of thermal expansion larger than that of the first leg.
X-ray tube device as described in . (4) The X-ray tube device according to claim 1, 2, or 3, wherein the second leg has a thermal conductivity lower than that of the first leg.