JP5625965B2 - X-ray tube - Google Patents

Description

The present invention relates to an X-ray tube used in the industrial field, the medical field, and the like, and more particularly to a technique for withstanding voltage of an electrode.

  In X-ray tubes and electron guns, a high voltage exceeding 10 kV is applied between the Wehnelt electrode (also called “focus cup electrode” in the X-ray tube) surrounding the electron source (emitter) and the anode. There is a need to. In general, a technique (conditioning) for improving the withstand voltage between the electrodes by intentionally inducing a discharge while gradually increasing the voltage between the electrodes is performed.

  FIG. 5 shows the conventional conditioning of a microfocus X-ray tube. The horizontal axis in FIG. 5 represents time, the vertical axis in the upper part of FIG. 5 represents the conditioning voltage (tube voltage), and the vertical axis in the lower part of FIG. 5 represents the discharge current (tube current) due to discharge. During conditioning, the voltage drops each time due to the occurrence of discharge until the voltage is gradually raised to the conditioning threshold (insulation voltage). In particular, it is usually programmed so that the voltage application is interrupted when the discharge current exceeds the threshold of the protection circuit of the high voltage power supply. As shown in FIG. 5, the withstand voltage is gradually improved by causing the discharge many times while raising the voltage. When the voltage reaches the conditioning threshold value (insulation voltage), a series of conditioning ends.

  This is because field emission (FE) occurs from minute protrusions on the electron source and strikes the anode, and the electron beam heats the anode or degass the adsorbed residual gas. It is thought to be done. And since the microprotrusions are crushed one after another by the energy of discharge, the withstand voltage characteristic (withstand voltage characteristic) between the electrodes is improved.

  In general, in an electron tube (an electron gun, an X-ray tube using the same) that applies a high voltage, it is necessary to repeat a conditioning operation (for example, every morning). This is because the withstand voltage (withstand voltage) is lowered if the voltage between the electrodes is turned off for a while after being turned off.

  The conditioning operation is regarded as an essential process in an electron tube (X-ray tube or electron gun) that applies a high voltage. However, especially in the conditioning after evacuation after being released to the atmosphere (that is, evacuation is performed by reducing the pressure from the atmospheric pressure), it takes time to reach a desired voltage between the electrodes (insulation voltage) with much discharge. As a result, damage to the high-voltage power supply often occurs. If possible, it is desirable that a desired insulation voltage can be obtained without conditioning or by a short-time conditioning operation. It is also strongly desired to increase the reachable insulation voltage.

  One of the long-known methods for these purposes (no conditioning, short-time conditioning operation or improvement of insulation voltage) is to form an insulating film on the surface of the electrode (for example, non-patent Reference 1). It has been confirmed that when an epoxy film is formed on an electrode made of aluminum, the pressure resistance of the electrode made only of aluminum is almost doubled. Also, the discharge current is reduced when an epoxy film is formed as compared with an aluminum-only electrode.

  It is considered that the formation of the insulating film on the electrode is effective because the minute protrusions and attached fine particles formed on the electrode that induces FE are flattened and so-called “embedded”. Since electron emission due to FE is suppressed by covering with an insulating film of several μm or more, it is presumed that the withstand voltage is quickly improved in conditioning.

  However, the above-described formation of the insulating film on the electrode has not been put into practical use so far because the effect does not last long. This is because a great effect is recognized at the beginning of the film formation, but if the film is broken by several discharges, the insulating characteristics deteriorate and cannot be recovered. This is presumably because the adhesion of the insulating film to the electrode is insufficient, the film is broken by the electrostatic force, and the film is peeled off.

For this reason, instead of forming an insulating film on the electrode, an attempt has been made to form the electrode itself with a ceramic having semiconductivity (volume resistivity ρ = 10 ⁶ to 10 ¹⁰ Ωcm) (for example, Patent Document 1). When a ceramic is used for an electron tube to which a high voltage is applied, a ceramic having a high resistivity such as alumina (Al ₂ O ₃ ) is charged up, so that a certain degree of conductivity is required.

JP 2002-33066 A (page 1-3, FIGS. 1 and 2)

[1] L. Jedynak, Vacuum Insulation of High Voltages Utilizing Dielectric Coated Electrodes, J. Appl. Phys. 35, 1727 (1964);

  However, such a material is expensive and has poor workability, and is inferior in productivity to a method for forming an insulating film on a metal electrode.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an X-ray tube that has excellent adhesion to an electrode and can easily improve the withstand voltage of the electrode.

In order to achieve such an object, the present invention has the following configuration .

That is, the X-ray tube according to the present invention is an X-ray tube for generating X-rays, an electron source for generating an electron beam, a Wehnelt electrode for controlling extraction of the electron beam from the electron source, and the Wehnelt An anode for accelerating the electron beam from the electrode, a target for generating X-rays by collision of the electron beam from the anode, a container for accommodating the electron source, the Wehnelt electrode, the anode and the target, Is formed on the anode-side surface of the Wehnelt electrode and is not formed on the back surface facing the electron source .

[Operation / Effect] According to the X-ray tube of the present invention, focusing on DLC (diamond like carbon) used for applications such as hardness and wear resistance, the DLC is used as the anode side surface of the Wehnelt electrode. the deposited, by not deposited on the rear surface facing the electron source, covers the Wehnelt electrode in the adhesion excellent insulating film capable of withstanding discharge energy. Thereby, it becomes possible to use the technique for improving the insulating property between the electrodes by the insulating film practically by DLC. As described above, when the DLC film is formed on the Wehnelt electrode, the insulation characteristics between the electrodes can be improved and the withstand voltage can be easily improved. The preparation time before using the apparatus can be shortened. In addition, if the discharge is reduced, damage to the high-voltage power supply is reduced, so that a damage accident can be prevented. As a result, the adhesion to the electrodes is excellent, and the withstand voltage between the anode and Wehnelt electrodes can be easily improved. If the same performance as the conventional withstand voltage is achieved, even if the size of the container containing the electron source, Wehnelt electrode, anode, and target is reduced, the discharge hardly occurs and the X-ray tube can be made compact. . In addition, if the same size (same shape) as that of the conventional container is used, the withstand voltage can be improved, so that a high-performance X-ray tube can be realized.

In the present invention ( X-ray tube ), the DLC film is preferably formed by plasma ion implantation. In the case of plasma ion implantation, carbon ions are diffused by plasma throughout the processing chamber (vacuum chamber), so that the DLC film can be formed over the entire surface of the Wehnelt electrode. It should be noted that a portion where the film is not desired to be deposited (for example, the surface of the Wehnelt electrode facing the electron source) is covered with a metal or the like so as to cover the portion, so that DLC is deposited only on the portion desired to be deposited. A film can be formed on the entire surface of the electrode.

  In general, a Wehnelt electrode is constructed by assembling a plurality of parts. Therefore, it is preferable to form a DLC film by plasma ion implantation with these parts assembled in advance. If each component is assembled after the DLC film is formed by plasma ion implantation, the DLC film may be formed up to the assembly location, which may make it difficult to assemble. In addition, after assembling these components, a DLC film is formed by plasma ion implantation, and an electron source is accommodated in the Wehnelt electrode when an electron gun or an X-ray tube is assembled. It has been confirmed that the DLC after film formation can be decomposed without being peeled off by the decomposition even if it is decomposed into the respective parts.

According to the X-ray tube of the present invention, the DLC film is formed on the anode side surface of the Wehnelt electrode and not formed on the back surface facing the electron source. The voltage can be improved easily.

It is a schematic sectional drawing which shows the structure of the micro focus X-ray tube which concerns on an Example. It is a schematic sectional drawing of the focus cup electrode (Wernert electrode) in which DLC was formed into a film on the surface. It is the schematic of the film-forming to the focus cup electrode (Wernert electrode) of DLC by plasma ion implantation. It is a state of conditioning of the micro focus X-ray tube which formed DLC into a film. It is the state of the conventional conditioning of a micro focus X-ray tube.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic cross-sectional view illustrating a configuration of a microfocus X-ray tube according to an embodiment.

  A (microfocus) X-ray tube 1 shown in FIG. 1 includes an electron gun 10, a deflection coil 20, a focus coil 30, and a target 40, and a container 50 that accommodates them. The electron gun 10 includes a support 11, an electron source (emitter) 12, a focus cup electrode 13, and an anode 14. At the position of the electron gun 10, the container 50 is a vacuum container and is structured to be evacuated. The X-ray tube 1 corresponds to the X-ray tube in the present invention, the electron gun 10 corresponds to the electron gun in the present invention, the electron source 12 corresponds to the electron source in the present invention, and the focus cup electrode 13 The anode 14 corresponds to the anode in the present invention, the target 40 corresponds to the target in the present invention, and the container 50 corresponds to the container in the present invention.

  The electron gun 10 has a structure for emitting an electron beam B. Specifically, the support 11 is supported by the container 50 and supports the electron source 12. In this embodiment, the support 11 is made of glass. However, the support 11 is a structure that supports the electron source 12 and is not particularly limited as long as it is an insulator.

The electron source 12 generates an electron beam B. In this embodiment, an electron beam B is generated by heating a single crystal or sintered chip formed of lanthanum hexaboride (LaB ₆ ) or cerium hexaboride (CeB ₆ ) as the electron source 12. Thermionic emission type is adopted. Alternatively, a field emission type in which an electron beam B is generated by applying a strong electric field to a single crystal thin tungsten wire coated with zirconium oxide (ZrO) as the electron source 12 may be employed.

  The focus cup electrode 13 has a shape surrounding the electron source 12 and has a function of controlling extraction of the electron beam B from the electron source 12. A high voltage exceeding 10 kV is applied between the focus cup electrode 13 and the anode 14. The electron beam B is accelerated toward the anode 14. That is, the focus cup electrode 13 has the function of a Wehnelt electrode in the electron gun 10. When used in the X-ray tube 1 as in this embodiment, the Wehnelt electrode is called a “focus cup electrode”. A DLC film is formed on the surface of the focus cup electrode 13. The film formation of DLC will be described later.

  There are two deflection coils 20 in the X direction (horizontal direction in the horizontal plane) and Y direction (vertical direction in the horizontal plane), with two coils as one set. And it has the structure which sandwiched the electron beam B with two coils facing each other in the X direction, and similarly has the structure which sandwiched the electron beam B with two coils facing each other also in the Y direction (FIG. 1 shows only one set). The focus coil 30 is formed in an annular shape. The deflection coil 20 deflects the electron beam B, and the focus coil 30 focuses the electron beam B. A magnetic field is generated by passing an electric current through these coils 20 and 30, and the electron beam B is deflected and focused in the same manner as the lens of the optical system.

  The target 40 generates X-rays R by the collision of the electron beam B from the anode 14 via the coils 20 and 30. In this embodiment, tungsten is used as the target 40. Of course, the target 40 may be formed of an X-ray generating material other than tungsten. The container 50 is made of metal and is grounded.

  Next, DLC film formation will be described with reference to FIGS. FIG. 2 is a schematic cross-sectional view of a focus cup electrode (Wernert electrode) on which DLC is formed, and FIG. 3 is an outline of film formation on the focus cup electrode (Welnert electrode) of DLC by plasma ion implantation. FIG.

  As shown in FIG. 2, the DLC film F is formed on the surface of the focus cup electrode 13 including the back surface. In FIG. 2, the DLC film F formed over the front and back surfaces is illustrated. However, the DLC film F is not formed in a portion where the film is not desired to be formed (for example, the back surface of the focus cup electrode 13 facing the electron source 12). No film is formed.

  In recent years, DLC surface treatment has been performed to improve characteristics (hardness, wear resistance, etc.) of various tools. For this purpose, it is necessary to form the DLC film F on a substrate such as a metal with good adhesion, and a film forming method with excellent adhesion has been developed. With respect to the thickness t of the film, the film formation of t ≧ 1 μm necessary for embedding the minute protrusions is realized.

  For example, when the DLC film F is formed on the surface of the focus cup electrode 13 by plasma ion implantation, the sample S of the focus cup electrode 13 is placed in a grounded processing chamber (vacuum chamber) C as shown in FIG. To accommodate. Depending on the size of the vacuum chamber C, it is possible to accommodate a plurality of samples S and simultaneously produce a plurality of focus cup electrodes 13 having a DLC film F formed on the surface.

  The vacuum chamber C is evacuated by the vacuum pump P, and a gas containing carbon such as hydrocarbon is introduced from the gas supply line L into the vacuum chamber C in a state where the sample S is accommodated in the vacuum chamber C. . Then, the plasma generator G generates plasma PM in the vacuum chamber C by an RF radio frequency (RF) (not shown). Thereafter, a negative high voltage pulse is applied to the sample S to accelerate the carbon ions in the surrounding plasma PM, and the sample S is drawn into the sample S for implantation and film formation.

  As shown in FIGS. 1 to 3, it is possible to perform DLC film formation without difficulty even for a complicated shape with unevenness with respect to the focus cup electrode 13. Further, by forming a film in a state where a plurality of parts are assembled, it is possible to form the DLC film F over the entire surface where the insulation characteristics need to be improved.

  Next, conditioning after DLC film formation will be described with reference to FIG. FIG. 4 shows the conditioning of the microfocus X-ray tube on which DLC is formed. 4, the horizontal axis in FIG. 4 represents time, the vertical axis in the upper part of FIG. 4 represents the conditioning voltage (tube voltage), and the vertical axis in the lower part of FIG. 4 represents the discharge current (tube current) due to discharge. Each is shown. In FIG. 5 of the related art, the discharge current exceeds the threshold value of the protection circuit of the high voltage power supply, and the voltage application is interrupted several times. However, as shown in FIG. It has been confirmed that the desired insulation voltage is reached quickly without any occurrence. Moreover, even if discharge occurs, the damage to the DLC film is such that a hole of several tens of μm is formed, and the deterioration of the insulating characteristics is hardly observed.

  Focusing on DLC (diamond like carbon) used for applications such as hardness and wear resistance, in this embodiment, this DLC is applied to film formation on a Wehnelt electrode (focus cup electrode 13 in this embodiment). . That is, according to the focus cup electrode 13 configured as described above, the adhesion that can withstand the discharge energy by forming the DLC (the DLC film F in FIG. 2) on the surface of the focus cup electrode 13. The focus cup electrode 13 is covered with an excellent insulating film. Thereby, it becomes possible to use the technique for improving the insulating property between the electrodes by the insulating film practically by DLC. Thus, when the DLC film is formed on the focus cup electrode 13, the insulation characteristics between the electrodes can be improved and the withstand voltage can be easily improved. For example, the discharge during conditioning is reduced and the conditioning can be completed in a short time. And the preparation time before using the device can be shortened. In addition, if the discharge is reduced, damage to the high-voltage power supply is reduced, so that a damage accident can be prevented.

  According to the electron gun 10 configured as described above, the DLC (the DLC film F in FIG. 2) is formed on the surface of the Wehnelt electrode (the focus cup electrode 13 in this embodiment), so that As described with respect to the focus cup electrode 13, the adhesion to the electrode is excellent, and the withstand voltage between the anode 14 and the Wehnelt electrode (the focus cup electrode 13 in this embodiment) can be easily improved.

  According to the X-ray tube 1 configured as described above, the DLC (the DLC film F in FIG. 2) is formed on the surface of the Wehnelt electrode (the focus cup electrode 13 in this embodiment). As described with respect to the focus cup electrode 13 and the electron gun 10, the adhesion to the electrode is excellent, and the withstand voltage between the electrodes of the anode 14 and the Wehnelt electrode (in this embodiment, the focus cup electrode 13) can be easily improved. Can do. If the performance is the same as the conventional withstand voltage, even if the size of the container 50 that accommodates the electron source 12, the focus cup electrode 13, the anode 14, and the target 40 is reduced, the discharge hardly occurs, and the X-ray tube 1 Can be made compact. Further, if the same size (same shape) as that of the conventional container 50 is used, the withstand voltage can be improved, so that the high-performance X-ray tube 1 can be realized.

  In this embodiment, it is preferable that a DLC film is formed by plasma ion implantation in the Wehnelt electrode (the focus cup electrode 13 in this embodiment), the electron gun 10 and the X-ray tube 1 according to this embodiment. In the case of plasma ion implantation, carbon ions are diffused by plasma in the processing chamber (vacuum chamber) C, so that the DLC film can be formed over the entire surface of the focus cup electrode 13. Note that a portion where film formation is not desired (for example, the surface of the Wehnelt electrode facing the electron source 12: the back surface of the focus cup electrode 13 in this embodiment) is covered with a metal or the like so as to cover the portion. The DLC can be formed on the entire surface of the focus cup electrode 13 only at the location where the film is desired.

  In general, since the focus cup electrode 13 is constructed by assembling a plurality of components, it is preferable to form a DLC film by plasma ion implantation with these components assembled in advance. If each component is assembled after the DLC film is formed by plasma ion implantation, the DLC film may be formed up to the assembly location, which may make it difficult to assemble. In addition, when these parts are assembled in advance, a DLC film is formed by plasma ion implantation, and when the electron gun 10 or the X-ray tube 1 is assembled, the electron source 12 is a Wehnelt electrode (in this embodiment, a focus cup). It has been confirmed that the DLC after film formation can be decomposed without being peeled off by decomposition even if it is decomposed into each component after film formation for accommodating in the electrode 13).

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) Although the electron gun 10 is used in the X-ray tube 1 in the above-described embodiment, the electron gun 10 may be an electron gun including an electron source, a Wehnelt electrode, and an anode, and a DLC film formed on the surface of the Wehnelt electrode. For example, the electron gun may be applied to apparatuses other than the X-ray tube (for example, a scanning electron microscope, an electron beam microanalyzer, a transmission electron microscope, electron beam lithography, an inspection device, etc.). Moreover, you may use for an electron gun single-piece | unit.

  (2) In the embodiment described above, the Wehnelt electrode (in the embodiment, the focus cup electrode 13) is used in the electron gun 10. However, if the DLC is formed on the surface of the Wehnelt electrode, the Wehnelt electrode alone is used. May be used for

  (3) In the above-described embodiment, DLC is formed on the surface of the Wehnelt electrode (the focus cup electrode 13 in the embodiment) by plasma ion implantation. However, the present invention is not limited to plasma ion implantation. As exemplified by the sputtering method, any film forming method that is normally used may be used. In the case of sputtering, since the surface on which the film can be formed is limited, the surface on which the film can be formed by rotating or moving the Wehnelt electrode becomes the entire surface so that the surface can be formed during the film formation. Rotation and movement control.

  (4) In the above-described embodiment, the X-ray tube 1 includes the deflection coil 20 and the focus coil 30, but it is not always necessary to include these coils when the coils are unnecessary.

DESCRIPTION OF SYMBOLS 1 ... X-ray tube 10 ... Electron gun 12 ... Electron source (emitter)
DESCRIPTION OF SYMBOLS 13 ... Focus cup electrode 14 ... Anode 40 ... Target 50 ... Container B ... Electron beam F ... DLC film R ... X-ray

Claims (2)

An X-ray tube for generating X-rays,
An electron source for generating an electron beam;
A Wehnelt electrode that controls extraction of the electron beam from the electron source;
An anode for accelerating the electron beam from the Wehnelt electrode;
A target that generates X-rays by collision of an electron beam from the anode;
A container for accommodating the electron source, the Wehnelt electrode, the anode, and the target;
An X-ray tube characterized in that DLC is deposited on the anode-side surface of the Wehnelt electrode and not on the back surface facing the electron source . The X-ray tube according to claim 1 ,
An X-ray tube, wherein the DLC film is formed by plasma ion implantation.

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