JPS61128451A - X ray tube device - Google Patents

Abstract

PURPOSE:To restrain the variation of the form of focus, by forming a flat plate filament so as to fold both ends of it from a flat electron emitting part toward the opposite direction of an anode target in U-shape, and connecting these both ends of the filament to a pair of supporting poles. CONSTITUTION:A revolving anode type X ray tube is formed as arranging a cathode structural body 300 in opposition to an anode target 33, in a vacuum enclosing receptacle. Here, a flat plate filament 301 is formed of a flat electron emitting part 301a, the legs which are shaped so as to fold both ends of this flat electron emitting part 301a at right angles, and folded parts 301b which are shaped so as to fold these legs in U-shape. Said folded parts 301b are welded to supporting poles 302, a ratio of the distance L1 from the flat electron emitting part 301a to the lower ends of the U-shaped folded parts 301b, to the distance L2 from the points of contact with the supporting poles 302 to the lower ends of the folded parts 301b, is set 0.5-1.5, and this unit is combined with an electron beam shaping electrode 303. Accordingly, a microfocus can be got as the relative position of the electron emitting part 301a to a beam restriction orifice 304 or a focusing groove 305 is not varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an X-ray tube device, and in particular to an X-ray tube that improves the filament to suppress changes in the shape of a focal point over time and that can realize a minute focal point. Regarding equipment.

[Technical background of the invention and its problems]

In general, X-ray tube devices are used for medical purposes, for example, for X-ray diagnosis, and in cases such as gastric examination, an X-ray tube as shown in FIG. 16 has been conventionally used.

This X-ray tube is of the so-called rotating anode type, and has a vacuum envelope 01).
The cathode structure and the umbrella-shaped anode target are arranged opposite to each other, eccentric from the tube axis. (to) rotates.

The cathode assembly of a conventional general X-ray tube is constructed as shown in FIG. 17, in which a cathode filament (101) is disposed within a focusing groove (106) of a focusing electrode (102).

This cathode filament (101) is made of a tungsten coil to emit thermionic electrons, and the focusing electrode (101) emits thermionic electrons.
102) Focus from c. For this reason, filamen)
(101) and the focusing electrode (102) are at the same potential.

In the figure, the dotted line (108) represents the equipotential curve near the focusing electrode (102), and the symbol (104) represents the trajectory of electrons emitted from approximately the center of the cathode filament (101). 105) is the cathode filament (10
1) represents the trajectory of electrons emitted from a location close to the side.

By the way, in the above-mentioned conventional cathode assembly, since the cathode filament is used almost in a temperature-limited region, a part of this filament is inserted into the focusing electrode (102) in order to strengthen the electric field near the cathode filament (101). It stands out. Therefore, the equipotential surface near the cathode filament (101) becomes bulged at the center of the cathode filament (101), as shown by the dotted line (108), and the energy is emitted from approximately the side wall of the cathode filament (101). The electrons (105) will face to the side. This electron (105
) and the electrons (104) emitted from approximately the center of the cathode filament (101) and facing forward cannot be focused in the same direction, and their 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 mentioned above, the cathode filament) (101)
Since the electrons emitted from the focusing electrode (102) cannot be focused sufficiently small by the focusing electrode (102), it is necessary to use a small cathode in order to obtain a small focus at the position of the anode target (c). 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.

Furthermore, since the traveling directions of the electrons at the position of the anode target are not aligned, a minute focus cannot be obtained, and electron distribution C: lacks sharpness, making it impossible to obtain a desired electron distribution.

For this reason, it is not possible to simultaneously obtain a sufficiently high resolution and increase the amount of incident electrons by reducing the maximum temperature rise due to electron incidence on the anode target. When creating a projection image using X-rays generated from the rays, it is necessary to increase the resolution and reduce photorenoise.

One way to eliminate this drawback is to use a flat cathode filament.

As an example of this, there is a proposal disclosed in Japanese Patent Laid-Open No. 55-68056.

A conventional example shown in FIG. 18 having a cathode filament made of such a strip-like flat plate will be described. The code (20
1) is a cathode filament made of a strip-shaped flat plate and formed in a rectangular shape. It is attached to a filament support (not shown), and is directly heated by electricity and emits thermoelectrons.
202) is a focusing electrode in which the depth of the focusing groove is shallow and 6) is shallow;
The electrons coming out of the cathode filament (201) are focused. The symbol (208) is the equipotential curve in the vicinity of the focusing electrode (202). The anode target indicated by (208) is kept at a high positive potential with respect to the cathode filament (201) and the focusing electrode (202);
) is equal to the focal length (f) of the electron lens.

However, this conventional example has the following drawbacks. The first is that there is a limit to the focusing of electrons.

That is, it is known that the spread width W of the electron beam on the anode (208) is given by w=zr-VL (1). Here, vo is the initial velocity energy (eV) of electrons, and V is the anode potential. However, considering the actual value of t: f = 15 ””
% Vo = O-2e V % Va -80ke
Substituting V into the above equation (1), w=o, oam,
Sufficient microfocus cannot be obtained.

The second drawback is that the electrons emitted from the sides of the cathode filament have very different trajectories from the electrons emitted from the center, and the electron distribution on the anode target has a subfocus.

In addition, when the focusing electrode is made to have the same potential as the filament and the depth of the focusing electrode is increased (f) to make (f) smaller, in order to have an even greater focusing effect, it is necessary to The electric field becomes weaker, the space charge becomes limited, and the current value changes depending on the anode potential. Further, when the anode voltage V is 80 kV@degree, the current value may not be greater than 10 mA.

In some cases, a positive bias voltage is applied to the cathode filament by placing a focusing electrode or an electrode with a shallow focusing groove slightly in front of it, but in this case, it is necessary to It is conceivable that the convergence of the electron beam in the perpendicular direction) becomes poor. However, the technique disclosed in the above-mentioned publication does not disclose any measures for achieving a similar change in focal point shape.

By the way, as shown in Fig. 19, a thin flat plate of filament is bent into a mouth shape, and both ends are connected to a pair of filament support columns (
215), (215), due to thermal expansion of the filament during operation of the X-ray tube device, the
As shown in 01a), the central part, that is, the electron emitting part is curved! It shifts significantly upwards. Both legs also deform outward. When the position of the electron emitting section changes with changes in filament temperature, the relative positional relationship with the focusing groove of the beam shaping electrode, that is, the focusing electrode changes, and the shape of the focal point on the target changes. This also appears as a large change in not only the shape of the focal point but also the focal point, which hinders the realization of a fine focal point.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and by improving the shape of the filament, the positional relationship between the electron emitting part and the electron beam shaping electrode can be adjusted over time and with respect to the temperature change C of the electron emitting part. An object of the present invention is to provide an X-ray tube device that can suppress changes in the shape of a beam focus on a target with almost no change, and can therefore realize a fine focus.

[Summary of the invention]

The present invention has a shape of a flat filament disposed adjacent to and corresponding to the beam limiting hole ζ of an electron beam shaping electrode having a focusing groove. It is characterized by being bent in the opposite direction to the target and then folded back into a substantially U-shape, with both ends being bent perpendicularly≦:lateral force direction:; and joined to a pair of filament support columns. The X-ray tube apparatus is an X-ray tube apparatus, and preferably includes a filament supporting column (; The ratio of the axial dimension (L2) up to the position (
L2/Ll) is set in a range of 0.5 or more and 1.5 or less.

As a result, even if the filament temperature changes during operation of the X-ray tube device, the relative positional relationship between the electron emitting section and the beam limiting hole and focusing groove of the beam shaping electrode hardly changes, and the focus on the anode target remains unchanged. Changes in shape are suppressed. Therefore, it is also extremely advantageous for forming a minute focus.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Identical parts are designated by the same reference numerals.

For example, this invention can be used for mammography with an anode voltage of 80 kT/
, maximum anode current 29mA% X-ray focus is 50μm to 11
An example of application to an X-ray tube in which the range of 1111 can be changed will be shown. This is constructed as shown in Figs. 1 to 7, and an anode target (
) and this: : The anode structure of the cathode structure, which is provided with a cathode structure smoke decoy opposite to it, is made of a directly heated phoenix pole filament (101
) is a pair of filament support columns (802), (802
) is double-sided. In this case, the cathode filament (301) is a strip-like flat plate, for example, the width (D, ) is uniform throughout and about 21111, and the thickness is o, o a
It is made of a thin tungsten plate with a degree of m b, and is formed flat so that the central part becomes the electron emitting part (301a), and both sides are bent at right angles to form the legs, which are further bent into a U-shape to form the folded parts. a filament support column (802), each end extending outwardly at right angles, at a height close to the electron emitting section (101a);
(802) Two welded and electrically connected.

In addition to pure tungsten, a high melting point alloy material such as lanthanum molybdenum can also be used as the material for the filament (801).

A circular cup-shaped electron beam shaping electrode (801) is arranged so as to surround such a cathode filament (801), and the filament support columns (802), (802) are connected to this electron beam shaping electrode (808). ) are fixed via insulating support columns (not shown). The electron beam shaping electrode (801)-2 is connected to the cathode filament (80
An electron beam limiting hole (804) is formed opposite to the electron emitting part (8ota) of 1). This electron beam limiting hole (804) is located in front of the electron emitting part (801a) by approximately 0.71 al (dimension dt), for example, in a rectangular shape having an area smaller than the area of the electron emitting part (10, la). The aperture surface of the electron emitting part (801a) is substantially parallel to the electron emitting part (101a).Two such electron beam limiting holes (fl104) are successively provided with a focusing groove in front of them. (305) is bored in the electron beam shaping electrode.This focusing groove (805) is the electron beam limiting hole (
304) A larger diameter, for example, a rectangle, is formed coaxially with the electron beam limiting hole (804) and the electron emitting part (801a), and the depth d is formed to be sufficiently deep. The bottom of the focusing groove (105) has a restriction hole (80).
4) It is formed in a tapered shape over l2. The dimension along the central axis (C) direction of this taper is formed to be a small dimension, less than a fraction of the depth d.

There is.

Now, when an X-ray tube is in use, the cathode filament (801) whose legs are folded back into a U-shape is relatively cold near the end where it is welded to the support column, but the electron emitting part (801) is relatively low temperature.
1a) and this 1: The nearby U-shaped portions rise to approximately the same temperature and can emit electrons. Therefore, the thermoelectrons trying to exit from the part of the filament other than the electron emitting part (801a) are connected to the electron beam to which a positive potential is applied, and the straight-shaped electrode (308).
In order to prevent heat radiation from flowing into the inner wall surface of the filament and heat radiation from the filament, a shield member (816) is interposed between the filament and the filament as shown. This shield member (3
16) is a substantially bottomed cylindrical shape (;
A rectangular hole (820) is formed in the part from which the electron emitting part (801a) of the filament protrudes.A rectangular cylinder part (917) surrounding the filament leg is formed on the peripheral wall of this rectangular hole (820). Also, there is an auxiliary shield plate (818) immediately below the flat electron emitting part (801m) of the filament that suppresses electron emission from the back side of the filament flat part and also has a heat reflecting effect.
is attached to the rectangular hole in the form of a bridge.

In this way, as can be understood from FIG.
Only 01a) stands out. This shield member ((1
6) may be constructed so that it can be electrically insulated to the filament and, for example, can be given a negative potential, but as shown in the figure (2) one filament support column (802) r: welded and are at the same potential, and are mechanically fixed to the other support column via an insulating spacer (321).

A preferred example of the joint structure between the filament leg end and the support column is the support column C802' as shown in FIG.
The end of the filament is sandwiched between the filament and a Mo metal piece (819) formed into a 5-shape, and welded by applying an electron beam or a laser beam to the metal piece from above as shown by the arrow CP). This prevents the filament itself from becoming brittle due to local melting, and allows welding over a wide area.

Next (;, the configuration for obtaining a minute focus will be explained.

Let the target (to) be the angle β where the center of the electron beam (,) (coinciding with tube axis C in this example) and the target plane intersect, and the target plane and the X-ray emission axis in the direction in which the X-rays are taken out. Let θ be the angle at which it intersects with X.

Further, it is assumed that the short side of the electron beam cross-sectional shape e0 on the target surface is 13xr. Then, the focal point shape X0 viewed from the X-ray radiation axis direction is set so that the ratio of the long side to the short side is kept at 1.4 or less, as is widely accepted in the field.
: Consider the case. When this ratio is 1.0, the focal point shape is square, which is the most preferable state. In order to achieve this, the shape of the electron beam projection surface on the target surface is set so as to satisfy the following conditions.

1.81nθ As mentioned above, the focal shape seen from the X-ray radiation axis direction is allowed with a short to long side ratio of approximately 1.41, so the length and short side ratio of the beam focal point e0 is within the following range. It is sufficient if

Then, at a given beam current C: the minimum focal point (for example -
When obtaining a side of 50 μm, the beam waist, that is, the position where the cross-sectional dimension of the electron beam e is the smallest, is formed so that it exactly coincides with the target plane. Due to mutual repulsion, the beam gradually spreads and the cross-sectional dimension increases.The longitudinal direction of the beam focal shape is made to coincide with the X-ray emission axis X.

Therefore, in order to make the current density distribution at the beam focal point e6 on the target uniform, the shape of the beam focal point 66 and the beam limiting hole (304) of the beam shaping electrode (308) are
The planar shapes of are assumed to be approximately similar. The electron beam exiting the elongated restriction hole (so4) under the shaping electrode bias potential that obtains the minimum focus is placed on the target surface (C: so that the two beam waist positions match) in both the widthwise direction X and the lengthwise direction y. (
I have to do it. In order to satisfy this requirement, the dimensions of each part are set as follows.

First, the depth dimension d of the focusing groove (805) is equal in both the 1 to be in the range of 1/4 to 1 for d;
Configure. That is, 1.0≦□≦4.0 d.

I am trying to satisfy you.

Further, the planar shape and dimensional relationship between the beam limiting hole (804) and the focusing groove (805) are determined as follows. The long side of the restriction hole opening is D, and the short side is D! Also, the long side of the rectangular focusing groove is 8, and the short side is S! As, S A/D.

P,8. /D, is set to a range of 0.4<22<2.0. In other words, in contrast to the rectangular shape of the limiting hole (804), the focusing groove has a relatively short long side dimension (2).The thickness of the side wall of the beam limiting hole (804) is ) is 1/10 or less of the depth d!, preferably about 1/20.

Preferred dimensions of each part under the above-mentioned operating conditions are as follows.

D, =1.21111 D =3.01111
s, = s, 2 ma 8. = 6.010
1a = 4. laa a, = 8.0 + s side wall thickness of limiting opening d, = 0.2 β = 70”, θ
= 20° and filament (801) l: Apply heating power from filament power source (806) and heat directly. Also, a beam shaping electrode (303) CO is connected to the filament.
A bias potential is applied from the Iasumi source (307) that can vary the range of ~-t-tooov, and a positive anode voltage of about 13 QkV is applied to the anode target (to) from the power supply (8
08) and operate it. As a result, the beam waist of the electron beam C coincides with the target plane ζ when the bias potential is around 200V.

The size of the electron beam focus e0 on the target surface is approximately 60 μm on the short side and 4 on the long side. is approximately 126P,
The effective focal point X0 viewed from the direction of the X-ray radiation axis X has a side of approximately 5
A substantially square shape of 0 μm was obtained, and a uniform electron density distribution was obtained.

In addition, by changing the bias potential in the range from Ov to +1000 V, it was possible to make the focus shape almost similar and change the size from about 50 μm on a side to about 1 dew.

Moreover, by making the above-mentioned dimensional relationship ranges, it can be applied to an X-ray tube device that uses an anode voltage of up to 150 kV and anode current of up to 600 mA, and the effective focal point can be made longer and longer.
The short side ratio could be kept at about 1.4 or less. Bias potential and the short side of the electron beam focus! .

The electron beam focusing state of the above embodiment will be explained by showing the results of a simulation using an electronic computer (FIG. 9C).

That is, FIG. 9 is a sectional view corresponding to FIG. 1. As mentioned above, the cathode filament (101) is made of a thin tungsten plate with a width of about 2 mm and a thickness of 0 and 100 mm, and is heated by being energized through the filament support column (802). Ru. cathode filament) (801)
Thermionic electrons emitted from the surface of the electron beam confining hole (8
Accelerated by the electric field created by the bias voltage applied between 04) and the cathode (801),
Electron beam restriction hole (804) <; reaches.

At this time, since the narrow surface of the cathode filament (801) and the surface of the electron beam limiting hole (804) are approximately parallel, the equipotential curves (810) therebetween are approximately parallel, and the electron beam limiting hole (804) ) does not disturb the electron trajectory passing through the edge too much. Further, the electrons (112) emitted from the end and side surface of the cathode filament (801) enter the electron beam limiting hole (a0
4) Absorbed by the wall, focusing groove (805) l There are no two people.

Therefore, the electron emitting part (301
Only the electron beam without fringing effect emitted from a) reaches the anode target (42) C33. The distance d1 between the electron beam limiting hole and the cathode filament is determined so that the electrons emitted from the surface of the cathode filament operate in the temperature limited region by the bias voltage.Therefore, they pass through the electron beam limiting hole (804). The amount of electrons is
It is determined only by the temperature of the cathode filament, and the size of the electron density distribution on the anode target can be varied independently of the current value by changing the bias voltage.

The electrons (812) restricted by the electron beam restriction hole heat the inner wall (818), but the inner wall (818) is tapered in the radiation direction of the electron beam shaping electrode (80B) and is thick enough to conduct heat sufficiently. At best, local overheating will not occur. The electrons that have passed through the electron beam restriction hole (804) are diffused by the concave lens action (=) while passing through the distance d1, but the electron beam density is extremely uniform. Focusing groove (805) +'' that is sufficiently deep and has a strong convex lens effect: Therefore, it is strongly focused, and the beam waist of both the short axis and long axis is located on the surface of the anode target.

In addition, the focusing groove (805) has an equipotential line (814) inside it.
However, almost no aberration occurs in the electron trajectory (815) at the center and the electron trajectory (111) at the end.

Above, I have described the short side shown in Figure 1.
Figure C: A similar focusing effect can be obtained along the long side shown.

According to this X-ray tube device≦2, the following excellent effects can be obtained.

■ Because only the electrons from the center of the cathode filament are accelerated, it is possible to obtain a fine focus with a sharp edge with little aberration. Further, since the electron beam emitted from the side surface of the cathode filament is cut by the electron beam restriction hole, no subfocus is generated.

■ The size of the X-ray focus can be controlled by controlling the bias voltage while keeping the shape of the X-ray focus almost constant. Even if the anode current is increased, the focal spot shape and electron density distribution do not deteriorate.

And, there is little change in the position of the cathode filament,
Since the temperature of the thermionic emission part (801g) is uniform, stable operation can be obtained. That is, as shown in FIG. 10, the thermal expansion of the legs of the cathode filament (801) is almost canceled out by the U-shaped folded parts (801b), (801b), and as shown by the broken line, thermal expansion Child radiant part (aria)
) moves less. Further, the expansion of the thermionic emission part (film) is absorbed by the folded parts (aolb) and (sotb) of the leg parts, so that it does not curve. Second, the legs have sufficient strength and the weight of the filament itself is small, so there is little vibration due to external vibrations. Like this (d)
Electron focusing characteristics can be kept constant and good.

[Modified example of the invention]

In the above embodiment, both the electron beam limiting hole and the focusing groove were formed in a rectangular shape along the longitudinal direction of the filament.
4) and focusing @ (805) may both be formed into an elongated oval shape in the longitudinal direction of the filament. And their short axis D118X m, long axis Da, and Sa are configured so as to satisfy the range of the above-mentioned relational expression. As a result, the same effects as in the above embodiment can be obtained. In this case, the electron beam focus on the anode target becomes an ellipse in which the major axis is 1A111a, the minor axis. Therefore, the X-ray focal point X seen from the X-ray emission port of the X-ray tube is approximately a perfect circle. Also, when changing the bias voltage, the X-ray focus always maintains a substantially circular shape while changing its size. In the above embodiments and modifications, cathode filament) (801)
The width of the leg or the thickness of the electron emitting part (801i)
may be larger than those of

Furthermore, the electron beam limiting hole and the focusing groove do not necessarily have to be of an integral structure.

Moreover, even if the width of the electron emitting part (8011k) of the cathode filament is narrower than the width of the electron beam restriction hole (304),
The same effect as above can be achieved.

In addition, when the tube current becomes open, by changing the bias voltage accordingly, it is possible to
A desired focal spot size can be obtained.

In the embodiment shown in FIG. 12, a beam shaping electrode (808) is formed by press-molding a thin plate, and a beam limiting hole (J104) and a focusing groove (805) are integrally formed. And its bottom space (880) C, fiwomen) (801)
The joint between both ends of the leg (301c) and the support column (802) is extended. Both ends (aolc) of the leg of the filament (801) extend above the position of the electron emitting part (801a). and filamen) (801)
A shield member (116) is provided surrounding the outside portion of the electron emitting portion (301a)'a, that is, the U-shaped bent portion (801b) and both support columns (802). According to this embodiment, both ends of the filament are lengthened and welded to the support column, and this welded portion is connected to the bottom space (88
0), the displacement of the electron emitting part can be more reliably suppressed, and the space inside the press cup-shaped shaping electrode can be effectively used, so that it can be configured compactly.

Next, according to FIGS. 13 and 14, the filament (8
The preferable dimensional relationship ( ; ) of the U-shaped bent shape of 01) will be explained. As already mentioned, in order to make the temperature distribution of the electron emitting part uniform ( ; ), the width of the U-shaped bent leg part, Or, it is not preferable to significantly increase the plate thickness dimension for the electron emitting part C.If the width of the image part and the plate thickness are the same, the first
As shown in Figure 3, the axial dimension (L) from the electron emitting part (801a) to the lower end of the U-shaped folded part (aolb)
1) Ratio of the axial dimension (L2) from the lower end of this U-shaped folded end to the joining position of the 7' width end (801c) to the filament support column to C (L2/1.1
) is set to %io, 5 or more, the displacement of the electron emitting part (801 m) can be kept to about 0.04111 or less≦2. A filament having such a shape is suitable for compaction of a cathode structure used in combination with a beam shaping electrode having a shape as shown in FIG.

On the other hand, as shown in FIG.
By forming the filament to be longer than that, the difference in thermal expansion between the filament legs on both sides of the U-shaped portion can be made zero or extremely small. Practical ratio (L2/Ll) is suitably about 1.5 or less. If C(L2) is made longer than that, the fluctuation of the electron emitting part becomes large, and it becomes unstable and easily vibrates. Therefore, the size ratio (L 2 /L 1 ) is 0.
A range of 5 or more and 1.5 or less is practical.

As mentioned above, the width or thickness of the filament is the same as that of the electron emitting part (even if one or both of the dimensions of the U-shaped leg are made equal or slightly smaller) Good things are natural.

Based on these relationships, the size ratio (L2/Ll) may be set within the above range.

Note that when increasing the area/width dimension of the electron emitting part for the purpose of increasing the obtained anode current, the filament current will increase, so the voltage of the high voltage supply cape (not shown) which also serves as the filament current supply cape will be increased. The descent becomes relatively difficult for two people.

In order to prevent this, it is desirable to provide a filament transformer inside the X-ray tube storage container (1) or near it, and configure the transformer to step down the voltage and supply power to the filament. As shown in Fig. 15, the beam shaping electrode (
At the inner bottom part of the focusing groove (805) of 808), a lamellar filament (801) according to the invention may be placed.

In this case as well, the position of the electron emitting section hardly changes, so that changes in the shape of the focal point can be suppressed.

〔Effect of the invention〕

As explained above, according to the present invention, the shape of the flat filament that corresponds to and is disposed close to the beam-limiting hole of the electron beam shaping electrode provided with the focusing groove is the shape of the beam-limiting hole (; Both sides of the electron emitting part are bent in the opposite direction to the anode target and then folded back into a substantially U-shape, and both ends are joined to a pair of filament support columns, and preferably a flat filament. The axial dimension (Ll) from the lower end of this U-shaped fold to the position where it is joined to the filament support column is
Since the ratio (L2/Ll) of L2) is set in the range of 0.5 or more and 1.5 or less, even if the filament temperature changes during operation of the X-ray tube device, the electrons The relative positional relationship between the radiation section and the beam-limiting hole and the focusing groove of the beam-shaping electrode hardly changes, and the change in the focal point shape on the anode target is suppressed. Therefore, even when the anode current is varied by controlling the filament heating current, the shape of the focal spot hardly changes, and it is extremely advantageous for forming a minute focal spot.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the main part showing one embodiment of the present invention, Fig. 2 is a vertical cross-sectional view in the right angle direction, Fig. 8 is an enlarged view of the main part, and Figs. 6 is a top view of the shaping electrode, FIG. 7 is a perspective view thereof, FIG. 8 is a characteristic diagram showing the relationship between the bias potential of the beam shaping electrode and the beam focal size, and FIG. Fig. 9 is a schematic diagram showing the results of a simulation of the focusing effect by an electronic computer of the device of the present invention, Fig. 10 is an explanatory diagram of the operation of the filament of the present invention, and Fig. 11 is a plan view of main parts showing another embodiment of the present invention. , FIG. 14 is a longitudinal cross-sectional view of the main part showing another embodiment of the present invention, FIG. 13 and FIG. 14 are side views showing the dimensional relationship in the embodiment of the present invention, and FIG. 15 is a further 16 is a schematic diagram of an X-ray tube device, 1
Figure 17 is a schematic diagram of beam focusing using a conventional cathode structure, the first
FIG. 8 is a schematic diagram showing the state of beam focusing in the same conventional example, and FIG. 19 is a longitudinal sectional view showing the state of thermal deformation due to the conventional filament structure. C(1)...Vacuum envelope, (300)...Cathode assembly, (To)...Anode target, (801)...Cathode filament, (801m)...Electron emission part, ( 80
1b)...U-shaped bent portion, (802)...filament support column, (808)...electron beam shaping electrode,
(f304)...Electron beam restriction hole, (105)...
・Focusing groove, (a16)...Shield member, Ll...Axial dimension from the electron emitting part to the U-shaped folded part, L2...Position joined to the filament support column from the U-shaped folded part Axial dimension up to. Figure 1 r Figure 8 Figure 4 Figure 5 Figure 6 Figure 8 I<'I7st → Figure 9 Figure 10 Figure 11 Figure 12 Figure 18 Figure 14 Figure 15 Figure 01v Figure 16 Figure 17 Figure 18 Figure 19

Claims (8)

[Claims] (1) An anode target and a cathode assembly are provided facing each other in a vacuum envelope, and the cathode assembly is provided with a flat filament and an electron beam shaping electrode located in front of the filament. In the X-ray tube device, the filament is bent from a flat electron emitting part facing the beam restriction hole at both sides in the opposite direction to the target, and then folded back into a substantially U-shape. An X-ray tube device characterized in that: is connected to a filament support column. (2) The filament has an axial dimension (L1) from the flat electron emitting part to the lower end of the U-shaped fold, and an axial direction from the lower end of the U-shaped fold to the position where it is joined to the filament support column. Ratio of dimensions (L2) (L2/L1)
The X-ray tube device according to claim 1, wherein is set to a range of 0.5 or more and 1.5 or less. (3) Claims in which the width of the filament near the U-shaped part or the joint to the filament support column is equal to or slightly larger than the width of the flat electron emitting part. The X-ray tube device according to item 2. (4) A patent claim in which the filament is formed so that the plate thickness near the U-shaped portion or the joint to the filament support column is equal to or slightly thicker than the plate thickness of the flat electron emitting portion. The X-ray tube device according to item 2. (5) The X-ray tube device according to claim 1, wherein a shield member is disposed between the U-shaped portion of the filament and the inner wall surface of the electron beam shaping electrode. (6) The X-ray tube device according to claim 5, wherein the shield member is electrically connected to one filament support column. (7) The X-ray tube device according to claim 1, wherein the electron beam shaping electrode has a positive potential applied to the filament by an external bias power source. (8) An electron beam limiting hole is provided at a position between the focusing groove of the electron beam shaping electrode and the flat filament, and the planar shape of the electron beam limiting hole is an elongated rectangle or a thin rectangle corresponding to the longitudinal direction of the filament. The X-ray tube device according to claim 1, which has an elliptical shape.