X-ray generation device

Abstract

The X-ray generating device comprises an electron gun that generates an electron beam, a target that generates X-rays by colliding with the electron beam, an X-ray tube having a vacuum housing that accommodates the electron gun and the target, and a control unit that controls the operation of the X-ray tube. The control unit executes an actual use mode in which the irradiation range of the electron beam to the target becomes a desired irradiation range, and a preheating mode executed prior to the actual use mode, and the density of electrons colliding with the target increases from the start time of the preheating mode to the start time of the actual use mode.

Description

Technology Field

[0001] The present disclosure relates to an X-ray generating device. Background Technology

[0002] Japanese Patent Publication No. 2007-149601 discloses an X-ray generating device comprising two electron guns and two targets, forming a microfocus with the electron guns and targets, and heating an anode with the electron guns and targets. The problem to be solved

[0003] In this context, microfocus X-ray sources require X-rays to be emitted with a small focus, causing the area near the focal point of the target to become locally high. Thermal stress is generated in the target due to the thermal cycle of heating and cooling caused by the electron beam, which can lead to damage such as cracking. If target cracking causes detachment or changes in surface shape, it becomes impossible to properly emit X-rays.

[0004] The present disclosure is made to solve the above problem and aims to provide an X-ray generating device capable of suppressing target cracks. means of solving the problem

[0005] The gist of the present disclosure is as follows.

[0006] [1] An X-ray generating device comprising an electron gun that generates an electron beam, a target that generates X-rays by colliding with the electron beam, an X-ray tube having a vacuum housing that accommodates the electron gun and the target, and a control unit that controls the operation of the X-ray tube, wherein the control unit executes an actual use mode in which the irradiation range of the electron beam to the target is a desired irradiation range, and a preheating mode executed prior to the actual use mode, wherein the density of electrons colliding with the target increases from the start time of the preheating mode to the start time of the actual use mode.

[0007] In this X-ray generator, the density of electrons colliding with the target increases from the start of the preheating mode to the start of the actual operation mode. That is, in this X-ray generator, the electron density in the preheating mode is lower than the electron density in the actual operation mode. According to this configuration, compared to the case where the actual operation mode is executed from the beginning without executing the preheating mode, the rapid rise in temperature near the irradiation range of the target in the actual operation mode can be suppressed. Therefore, stress accumulation caused by the temperature difference between the irradiation range and its edges in the actual operation mode can be reduced. From the above, this X-ray generator can suppress target cracking.

[0008] [2] An X-ray generator according to [1], further comprising an electron gun feeder that supplies power to the electron gun, a target supporter that supports the target, and a high-voltage feeder that supplies high voltage to the target supporter, wherein the control unit controls the electron gun feeder so that a crossover point, which is a point where the electron beam converges, is located between the electron gun and the target, and controls the high-voltage feeder so that the tube current of the X-ray tube in the preheating mode and the tube current of the X-ray tube in the actual use mode are equal. In the X-ray generator, the portion of energy of the electron beam irradiated onto the target that was not converted into X-rays is converted into heat, and the target and the target supporter expand due to the heat. In a configuration where the crossover point is located between the electron gun and the target, the irradiation range of the electron beam onto the target is narrowed from the start of the preheating mode to the start of the actual use mode due to the expansion of the target and the target supporter described above. As a result, compared to running the actual operation mode from the start without running the preheating mode, the temperature difference between the irradiation range and its surroundings in the actual operation mode can be reduced. Therefore, stress accumulation caused by the temperature difference between the irradiation range and its edges in the actual operation mode can be significantly reduced. Furthermore, since the tube current of the X-ray tube is the same in both the preheating mode and the actual operation mode, the execution of the preheating mode and the actual operation mode can be performed simply and easily.

[0009] [3] An X-ray generator according to [2], wherein the above control unit controls the electron gun feed unit so that the convergence angle of the electron beam is 0.1° or more and 120° or less. In this case, the difference between the electron beam irradiation range at the start of the preheating mode and the electron beam irradiation range at the start of the actual use mode can be increased. Therefore, stress accumulation caused by the temperature difference between the irradiation range in the actual use mode and its edges can be reduced more effectively.

[0010] [4] An X-ray generating device [2] or [3], wherein the dimensions of the irradiation range at the start of the above preheating mode are 1.1 times or more and 2.0 times or less than the dimensions of the irradiation range at the start of the above actual use mode. In this case, stress accumulation caused by the temperature difference between the irradiation range and its edges in the actual use mode can be reduced more effectively.

[0011] [5] An X-ray generating device described in any one of [2] to [4], wherein the dimensions of the irradiation range at the start of the above-mentioned actual use mode are 5 μm or more and 500 μm or less. In this case, X-rays can be generated appropriately.

[0012] [6] The control unit controls the high-voltage feed unit so that the tube current of the X-ray tube in the preheating mode and the tube current of the X-ray tube in the actual use mode are equal to 50 μA or more and 1 mA or less. This is an X-ray generating device according to any one of [2] to [5]. In this case, X-rays can be generated appropriately.

[0013] [7] An X-ray generating device according to [1], further comprising an electron gun feeder that supplies power to the electron gun, a target supporter that supports the target, and a high-voltage feeder that supplies high voltage to the target supporter, wherein the control unit controls the electron gun feeder so that the crossover point, which is the point where the electron beam converges, is located on the inner side of the target in the direction of irradiation of the electron beam, and controls the high-voltage feeder so that the tube current of the X-ray tube in the preheating mode is smaller than the tube current of the X-ray tube in the actual use mode. In the configuration where the crossover point is located on the inner side of the target in the direction of irradiation of the electron beam, the irradiation range of the electron beam is expanded from the start of the preheating mode to the start of the actual use mode due to the expansion of the target and the target supporter described above. In addition, since the tube current in the preheating mode is smaller than the tube current in the actual use mode, it is possible to reliably realize a configuration in which the density of electrons colliding with the target increases from the start of the preheating mode to the start of the actual use mode while suppressing the rapid rise in temperature near the target's irradiation range.

[0014] [8] The dimensions of the irradiation range at the start of the above preheating mode are 0.5 times or more and 0.9 times or less than the dimensions of the irradiation range at the start of the above actual use mode, [7] of the X-ray generator. In this case, stress accumulation caused by the temperature difference between the irradiation range and its edges in the actual use mode can be reduced more effectively.

[0015] [9] The dimensions of the irradiation range at the start of the above-mentioned actual use mode are 5 μm or more and 500 μm or less, as described in [7] or [8] X-ray generating device. In this case, X-rays can be generated appropriately.

[0016] According to the present disclosure, target cracks can be suppressed. Brief explanation of the drawing

[0017] FIG. 1 is a cross-sectional view of an X-ray generating device according to one embodiment of the present disclosure. Figure 2 is a figure illustrating the task in the comparative example. Figure 3 is a figure illustrating the task in the comparative example. Figure 4 is a figure illustrating the task in the comparative example. Figure 5 is a figure illustrating the task in the comparative example. Figure 6 is a schematic diagram showing an example of the relationship between the position of the crossover point and the irradiation range of the electron beam. FIG. 7(a) is a schematic diagram showing an example of the electron beam irradiation range at the start of the preheating mode, and FIG. 7(b) is a schematic diagram showing an example of the electron beam irradiation range at the start of the actual use mode. FIG. 8(a) is a figure showing an example of a change in the dimensions of the electron beam irradiation range in a preheating mode and an actual use mode, FIG. 8(b) is a figure showing an example of a change in the tube current in a preheating mode and an actual use mode, and FIG. 8(c) is a figure showing an example of a change in the power density, which is the density of electrons colliding with the target. Figure 9 is a schematic diagram showing another example of the relationship between the position of the crossover point and the irradiation range of the electron beam. FIG. 10(a) is a schematic diagram showing another example of the electron beam irradiation range at the start of the preheating mode, and FIG. 10(b) is a schematic diagram showing another example of the electron beam irradiation range at the start of the actual use mode. FIG. 11(a) is a figure showing another example of a change in the dimensions of the electron beam irradiation range in a preheating mode and an actual use mode, FIG. 11(b) is a figure showing another example of a change in the tube current in a preheating mode and an actual use mode, and FIG. 11(c) is a figure showing another example of a change in power density, which is the density of electrons colliding with a target. Specific details for implementing the invention

[0018] Hereinafter, a preferred embodiment of an X-ray generating device according to one aspect of the present disclosure will be described in detail with reference to the drawings. In addition, terms indicating a specific direction, such as "up" and "down," are based on the state shown in the drawings and are for convenience.

[0019] FIG. 1 is a cross-sectional view of an X-ray generating device according to one embodiment of the present disclosure. The X-ray generating device (1) shown in FIG. 1 comprises an X-ray tube (2), a receiving part (3), a first insulating part (4), a power supply part (5), a conductive member (6), and a conductive paint (8). The X-ray generating device (1) is, for example, a microfocus X-ray source used for X-ray non-destructive inspection.

[0020] The X-ray tube (2) is a vacuum tube for generating X-rays. The X-ray tube (2) is equipped with a housing (21) (vacuum housing), an electron gun (22), a target (23), and an anode (24). The housing (21) accommodates the electron gun (22), the target (23), and the anode (24). The space within the housing (21) is a space where vacuum suction is performed. The housing (21) has a head (211), a valve (212), and a flange (213). The head (211) is formed in a bottom tube shape using a metal material, for example, stainless steel. The valve (212) is formed in a bottom tube shape using an insulating material, for example, glass. The head (211) is hermetically joined to the valve (212) so that the interior of the head (211) communicates with the interior of the valve (212). The flange (213) is formed in a ring shape along the outer frame of the head (211) by a metal material, such as stainless steel. Here, the direction along the central axis (pipe axis) (A1) of the valve (212) is called the Z-axis direction, the direction perpendicular to the Z-axis direction is called the X-axis direction, and the direction perpendicular to both the Z-axis direction and the X-axis direction is called the Y-axis direction.

[0021] The electron gun (22) generates an electron beam within the housing (21) and emits the electron beam toward the target (23). The shape of the electron beam may be, for example, approximately circular, elliptical, or polygonal. Here, the shape of the electron beam refers to the shape represented by the irradiation range of the electron beam toward the target (23) (for example, the irradiation range at half width). The electron gun (22) is composed of a thermionic cathode that emits thermionic electrons, an anode that accelerates electrons, and an electron lens that adjusts the convergence of the electron beam (all omitted from illustration). The electron gun (22) is fixed to the head (211) such that the central axis (A2) of the electron gun (22) is perpendicular to the central axis (A1) of the valve (212). The central axis (A2) of the electron gun (22) follows the X-axis direction.

[0022] The target (23) generates X-rays by colliding with an electron beam emitted from an electron gun (22) within the housing (21). The target (23) is formed in a plate shape using a high melting point metal material, such as tungsten. The target (23) is supported by an anode (24) within the housing (21) so as to face the electron gun (22) in the X-axis direction.

[0023] The positive electrode (24) applies the voltage generated in the power supply unit (5) to the target (23). Because of this, the positive electrode (24) is conductive to the target (23). The positive electrode (24) is formed in a rod shape that extends along the Z-axis direction using a metal material such as copper. The positive electrode (24) extends from outside the housing (21) to inside the housing (21) so that the central axis of the positive electrode (24) coincides with the central axis (A1) of the valve (212). The positive electrode (24) is fixed to the bottom of the valve (212). The front end surface of the positive electrode (24) inside the housing (21) is an inclined surface that is inclined with respect to both the central axis (A1) and the central axis (A2). The target (23) is embedded in the front end (24a) of the positive electrode (24) so ​​that it is in contact with the front end surface of the positive electrode (24).

[0024] The receiving portion (3) accommodates a portion of the X-ray tube (2). In the X-ray generating device (1) of the first embodiment, the receiving portion (3) accommodates a valve (212). The receiving portion (3) is formed in a bottom tube shape using a metal material, such as aluminum. The receiving portion (3) has an upper portion (31) and a side portion (32). The side portion (32) is formed in a tube shape with the Z-axis direction as the height direction. The upper portion (31) blocks one end (in this embodiment, the upper end) of the side portion (32) in the Z-axis direction. An opening (31a) is installed in the upper portion (31). The X-ray tube (2) is located inside the opening (31a). A flange (213) is fixed to the upper portion (31) while the valve (212) is located inside the receiving portion (3). The other end of the side (32) in the Z-axis direction (in this embodiment, the lower end) is fixed to the upper end of the power supply unit (5) (the upper surface (51b) of the second insulating unit (51)). The first insulating unit (4) is enclosed inside the receiving unit (3).

[0025] The first insulating part (4) electrically insulates the X-ray tube (2) and other components. The first insulating part (4) is a liquid insulating part. The first insulating part (4) is an insulating oil, for example, having mineral oil or ester oil as its main component. The first insulating part (4) covers the parts of the valve (212) and the anode (24) exposed outside the housing (21), and the parts of the conductive member (6) exposed outside the second insulating part (51), within the receiving part (3). In this embodiment, the interior of the receiving part (3) is filled with the first insulating part (4).

[0026] The power supply unit (5) generates a voltage to be applied to the target (23) through the conductive member (6) and the anode (24). The power supply unit (5) is positioned on one side (the lower side of the housing (21)) in the Z-axis direction relative to the housing (21). The power supply unit (5) is arranged parallel to the X-ray tube (2) along the Z-axis direction. The power supply unit (5) has a second insulating unit (51) and a circuit unit (52) (high-voltage power supply unit).

[0027] The second insulating part (51) is a solid insulating part that electrically insulates the circuit part (52) and other components. The second insulating part (51) is formed in a rectangular shape using a resin material, such as epoxy resin. The surface (51a) of the second insulating part (51) is composed of an upper surface (51b) which is the side facing the housing (21), a lower surface (51c) opposite to the upper surface (51b), and a side surface (51d) connecting the upper surface (51b) and the lower surface (51c). A portion of the upper surface (51b) is formed to bulge. This portion is in contact with the first insulating part (4) within the receiving part (3). A conductive paint (8) is applied to the side surface (51d) of the second insulating part (51), and the potential of the side surface (51d) is set to the ground potential.

[0028] The circuit section (52) has a substrate (521) which is a rectangular printed circuit board. The surface of the substrate (521) is orthogonal to the Y-axis direction. On the surface of the substrate (521), a first voltage section (52a), a boost section (52b), and a second voltage section (52c) are mounted. The first voltage section (52a) is an input terminal into which a first voltage is input from the outside and is electrically connected to the boost section (52b). The boost section (52b) boosts the first voltage to a second voltage. The boost section (52b) is, for example, a Cockcroft-Walton circuit. The second voltage section (52c) is an output terminal that outputs a second voltage to a target (23) through a conductive member (6) and an anode (24) and is electrically connected to the boost section (52b).

[0029] The booster section (52b) is located in the central part of the surface of the substrate (521). The first voltage section (52a) is located on one side (the lower surface (51c) side) in the Z-axis direction relative to the booster section (52b). The second voltage section (52c) is located on the other side (the upper surface (51b) side) in the Z-axis direction relative to the booster section (52b).

[0030] The circuit section (52) is embedded in the second insulating section (51) such that the entire circuit section (52) is located in the second insulating section (51). The circuit section (52) is embedded in the second insulating section (51) such that the substrate (521) extends straight along the Z-axis direction.

[0031] The conductive member (6) electrically connects the second voltage section (52c) and the target (23) through the positive electrode (24). Because of this, the conductive member (6) has conductivity. The conductive member (6) and the positive electrode (24) form a target support section (60) that supports the target (23) at one end. In the following description, the conductive member (6) and the positive electrode (24) may be collectively referred to as the target support section (60). The circuit section (52) (high voltage power supply section) is connected to the other end of the target support section (60) formed by the conductive member (6) and the positive electrode (24), and supplies high voltage to the target support section (60).

[0032] The conductive member (6) is formed in a rod shape using a metal material such as aluminum, for example. One end of the conductive member (6) (the other end) is electrically connected to the second voltage section (52c), and the other end of the conductive member (6) is electrically connected to the base section (24b) of the anode (24) (the part of the anode (24) located outside the housing (21)). The conductive member (6) is embedded in the second insulating section (51) so that a part of the conductive member (6) is located within the second insulating section (51). The other part of the conductive member (6) is exposed outside the second insulating section (51). The part of the conductive member (6) exposed outside the second insulating section (51) is electrically connected to the base section (24b) of the anode (24) inside the receiving section (3).

[0033] The X-ray generating device (1) further comprises an electron gun feed section (116) and a control section (117).

[0034] The electron gun power supply unit (116) is a voltage generating circuit that generates a voltage applied to the electron gun (22) and is configured to supply power to the electron gun (22). The electron gun power supply unit (116) is controlled by a control unit (117). The electron gun power supply unit (116) may be mounted within the second insulation unit (51) together with the circuit unit (52), or may be mounted on a circuit board outside the second insulation unit (51). The control unit (117) controls the driving of the X-ray tube (2). In this embodiment, the control unit (117) controls the driving of the X-ray tube (2) by controlling the electron gun power supply unit (116) and the circuit unit (52). The control unit (117) is mounted on a circuit board outside the second insulation unit (51).

[0035] The control unit (117) is physically configured to include a processor such as a CPU, a memory medium such as RAM, and a ROM. The control unit (117) may be a smartphone or tablet terminal that has a display unit or an input unit integrated, and may be configured as a microcomputer or an FPGA (Field-Programmable Gate Array).

[0036] Next, regarding the change in power density (d), which is the density of electrons colliding with the target (23) in the X-ray generating device (1) according to the present embodiment, it will be explained in comparison with a comparative example. When the shape of the electron beam is approximately circular, the power density (d) is the value obtained by dividing the X-ray output, i.e., the power input to the target (23), by the focal diameter (diameter) of the electron beam. When the shape of the electron beam is elliptical, the power density (d) is the value obtained by dividing the X-ray output by the square root of the product of the major axis and the minor axis of the ellipse. When the shape of the electron beam is polygonal, the power density (d) is the value obtained by dividing the X-ray output by the average of the diameter of the circumscribed circle and the diameter of the inscribed circle of the polygon.

[0037] In the comparative example, from the start of electron beam irradiation, the electron beam is controlled so that the irradiation range (focal dimension) of the electron beam relative to the target (23) becomes the desired irradiation range. Also, when X-ray emission begins, the power density (d) of the electrons colliding with the target (23) is constant. The power density (d) is, for example, about 1.0 W / μm, and the power density (d) is in a constant high state. Also, the "tube voltage-tube current" of the X-ray tube is, for example, about "200 kV-800 μA," and the "focal diameter (diameter) of the electron beam" is, for example, "100 μm." Here, the X-ray output is expressed by the product of the tube voltage (kV) and the tube current (mA), and in this case, the X-ray output is 160 W, and when the X-ray output is divided by the focal diameter of the electron beam, it becomes 1.6 W / μm, and the X-ray is in a constant high output. In this way, in the comparative example, the electron beam is irradiated so that the irradiation range of the electron beam on the target (23) becomes the desired irradiation range immediately after the start of X-ray emission, and the power density (d) becomes constant at a relatively high state, while the X-ray output becomes constant at a relatively high output. In addition, the higher the tube voltage, the higher the energy of the electron beam irradiated on the target (23), and the greater the tube current, the greater the total amount of electron beam irradiated on the target (23).

[0038] FIGS. 2 to 5 are drawings illustrating the problem in the comparative example. FIG. 2(a) shows the state of electron beam irradiation on a target (23) in an X-ray tube (2), FIG. 2(b) shows an enlarged view of a part (target (23)) in FIG. 2(a), and FIG. 2(c) shows an enlarged view of a part (the electron beam irradiation range on the target (23)) in FIG. 2(b). As shown in FIG. 2(b), a damaged area (DA) is created on the target (23) by electron beam irradiation on the target (23). More specifically, as shown in FIG. 2(c), a crack (C) that causes target cracking is created around the damaged area (DA). When a relatively high-output electron beam is irradiated onto a target (23) from the start of electron beam irradiation with a constant power density (d), the irradiation range of the target (23) becomes locally high, and stress accumulation occurs due to the temperature difference between the irradiation range and its surroundings. The higher the X-ray output, the greater the amount of heat received by the target (23) and the target support (60) due to electron beam irradiation. The greater the amount of heat received, the more likely it is that a change in the surface shape of the target (23) will occur unevenly due to the simultaneous occurrence of thermal expansion of the target (23) and the target support (60) until thermal equilibrium is reached and evaporation of the target (23) caused by heat concentration on the target (23). The stress accumulation described above proceeds through the thermal cycle of heating and cooling by the electron beam, and a crack (C) that causes target cracking occurs. Also, as shown in FIG. 2(c), the damaged area (DA) has a vertical shape, and the surface shape of the target (23) in the electron beam irradiation range changes, which is also a problem.

[0039] Referring to FIGS. 3 to 5, the cause of the damage area (DA) having a vertical shape in the comparative example is explained. As shown in FIG. 3, when a relatively high-power electron beam is irradiated onto the target (23), the target (23) evaporates within the electron beam irradiation range, causing surface roughness on the surface of the target (23) accompanied by gouging and depressions. Furthermore, among the energy of the electron beam irradiated onto the target (23), the portion that was not converted into X-rays is converted into heat, and since the target (23) and the target support (60) are heated, the target support (60) expands and elongates due to the heat. As the elongated portion (T1) is created, the irradiation range gradually moves from the initial position (IP) to the stable position (SP). The stable position (SP) is the electron beam irradiation range on the target (23) when the target support (60) is in thermal equilibrium. As the target support (60) expands due to thermal expansion, the surface of the target (23) is damaged within the electron beam irradiation range. As shown in FIG. 4, as the irradiation range changes continuously from the initial position (IP) to the stable position (SP), a damaged area (DA) having a longitudinal shape of depression is formed. When an electron beam is irradiated into the area containing the damaged area (DA), the electrons scatter within the concave portion of the damaged area (DA) to generate X-rays, so X-rays are generated from a wider range than the electron beam irradiation range. That is, even though the focal diameter of the electron beam (electron beam irradiation condition) is not changed, the surface shape of the target (23) within the electron beam irradiation range changes, and thus the X-ray generation area in the target (23) becomes larger. That is, the focal dimension of the X-rays emitted from the X-ray generating device (1) becomes larger. As shown in FIG. 5(a), the focal dimension of the X-ray emitted from the X-ray generator (1), which is originally approximately circular, changes into a vertical shape as shown in FIG. 5(b).In this way, it is thought that the X-ray image may become blurred due to the apparent increase in the focal size of the X-ray unintentionally.

[0040] As explained above, in the configuration according to the comparative example, when the electron beam is irradiated so that the irradiation range becomes the desired irradiation range immediately after the start of X-ray emission and the power density (d) is kept constant at a relatively high state, there is a problem called a change in the X-ray focal dimension (change in the X-ray focal shape) which causes cracks (C) that cause target cracks and blurring of the X-ray image.

[0041] As a configuration for solving these problems, in the X-ray generating device (1) according to the present embodiment, an actual use mode and a preheating mode executed prior to the actual use mode are set, and the power density (d) is configured to increase from time t0, which is the start time of the preheating mode, to time t1, which is the start time of the actual use mode. Here, for example, time t0 is the time when the emission of X-rays begins, and time t1 is the time when the target (23) and the target support (60) reach thermal equilibrium.

[0042] In this embodiment, in order to increase the power density (d) from time point t0 to time point t1, control of the crossover point (CP), which is the point where the electron beam converges, and control of the tube current are performed. Hereinafter, with reference to FIGS. 6, 7, and 8, the control of the crossover point (CP) and the control of the tube current in this embodiment will be explained in more detail.

[0043] First, the control of the crossover point (CP) will be explained. FIG. 6 is a schematic diagram showing an example of the relationship between the position of the crossover point and the irradiation range of the electron beam. In this embodiment, as shown in FIG. 6, the control unit (117) controls the electron gun feed unit (116) so that the crossover point (CP) is located between the electron gun (22) and the target (23). This manner in which the crossover point (CP) is located ahead of the target (23) that is the target of the electron beam irradiation is also called overfocus. That is, in this embodiment, it can be said that the control unit (117) controls the electron gun feed unit (116) so that the electron beam is overfocused with respect to the target (23). In this case, the focal diameter of the electron beam may be the same in the preheating mode and the actual use mode. That is, in the present embodiment, control of the focal diameter of the electron beam is not required after the irradiation of the electron beam has started. In one example, in the preheating mode and the actual use mode, the focal diameter of the electron beam may be the same focal diameter between 5 μm and 500 μm.

[0044] In the case of overfocus, the electron beam irradiation range changes as the target support (60) extends to form a portion (T1). This change in the electron beam irradiation range is shown in FIGS. 6 and 7. FIG. 7(a) is a schematic diagram showing the electron beam irradiation range at the start of the preheating mode. FIG. 7(b) is a schematic diagram showing the electron beam irradiation range at the start of the actual use mode. In the example shown in FIGS. 6 and 7, the electron beam irradiation range at time t0, which is the start of the preheating mode, is shown as the irradiation range (101), and the electron beam irradiation range at time t1, which is the start of the actual use mode, is shown as the irradiation range (201). As shown in FIG. 7, the irradiation range (101) and the irradiation range (201) have a circular shape, for example. In this case, the dimensions of the inspection range (101) are indicated by the dimension Rs1, which is the diameter of a circle, and the dimensions of the inspection range (201) are indicated by the dimension Rf1. In this embodiment, the dimension Rf1 is the diameter of a circle.

[0045] In the case of overfocus, the irradiation range (101) at time t0 is the widest, and from there the irradiation range of the electron beam narrows. Then, at time t1, the reduction of the irradiation range of the electron beam stops, and from there the irradiation range of the electron beam becomes approximately constant with the irradiation range (201). In other words, the diameter of the electron beam becomes constant with dimension Rf1. Thus, in the case of overfocus, as the part (T1) expands, the irradiation range of the electron beam narrows from the irradiation range (101) to the irradiation range (201).

[0046] In this embodiment, the irradiation range (201) may be a desired irradiation range in the X-ray generator (1). As described above, since the irradiation range of the electron beam decreases between time point t0 and time point t1, if the irradiation range (201) is a desired irradiation range, the irradiation range (101) becomes a range larger than the desired irradiation range. Therefore, in the case of overfocus, the control unit (117) may control the electron gun feed unit (116) so that the irradiation range of the electron beam at the start of the preheating mode becomes larger than the desired irradiation range.

[0047] Along with changes in the irradiation range of the electron beam, the dimensions of the irradiation range also change. Such changes in the dimensions of the electron beam irradiation range are also shown in FIGS. 6 and 7. Similar to the electron beam irradiation range, in the case of overfocus, the dimension Rs1 is largest at time t0, which is the start time of the preheating mode, and from there the dimensions of the irradiation range decrease. Then, at time t1, which is the time when the target (23) and the target support (60) reach thermal equilibrium, the decrease in the dimensions stops, and from there the dimensions become approximately constant with dimension Rf1. As described above, in this embodiment, the irradiation range (201) is the desired irradiation range of the X-ray generator (1), so the dimension Rf1 is the dimension of the desired irradiation range.

[0048] In one example, the dimension Rs1 may be 5 μm or more and 1000 μm or less. The dimension Rf1 may be 5 μm or more and 500 μm or less. The dimension Rs1 may be 1.1 times or more and 2.0 times or less of the dimension Rf1. In this embodiment, the dimension Rs1 is 130 μm and the dimension Rf1 is 100 μm, so the dimension Rs1 is 1.3 times the dimension Rf1.

[0049] Returning to Fig. 6. In this embodiment, the control unit (117) may control the electron gun feed unit (116) such that the convergence angle (θ) of the electron beam is 0.1° or greater and 120° or less. The convergence angle (θ) is, for example, an angle representing the expansion of the orbit (BT) when the electron beam orbit (BT) converges toward the crossover point (CP). The convergence angle (θ) is also an indicator representing the amount of change in the dimension of the electron beam irradiation range between time point t0 and time point t1. For example, as the convergence angle (θ) increases, the amount of change in the dimension of the electron beam irradiation range, that is, the difference between dimension Rs1 and dimension Rf1, increases. In the X-ray generating device (1), by keeping the convergence angle (θ) within the above range, it becomes possible to clearly distinguish the difference between dimension Rs1 and dimension Rf1.

[0050] Next, the control of the tube current is explained. In this embodiment, the control unit (117) controls the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode and the tube current of the X-ray tube (2) in the actual use mode are equal. Here, "equal" does not necessarily mean that the values ​​match. It is acceptable to say that the tube current of the X-ray tube (2) in the preheating mode and the tube current of the X-ray tube (2) in the actual use mode are equal even if the values ​​include a slight difference within a preset range. In one example, the control unit (117) may control the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode and the tube current of the X-ray tube (2) in the actual use mode are equal to the tube current E1. The tube current E1 may be, for example, 50 μA or more and 1 mA or less.

[0051] The relationship between the electron beam irradiation range and tube current described above and the power density (d) is shown in FIG. 8. FIG. 8(a) is a figure showing an example of a change in the dimensions of the electron beam irradiation range in a preheating mode and an actual use mode. FIG. 8(b) is a figure showing an example of a change in the tube current in a preheating mode and an actual use mode. FIG. 8(c) is a figure showing an example of a change in the power density (d), which is the density of electrons colliding with the target. The vertical axis of FIG. 8(a) represents the dimensions of the electron beam irradiation range [μm]. The vertical axis of FIG. 8(b) represents the tube current [μA]. The vertical axis of FIG. 8(c) represents the power density (d) [W / μm]. The horizontal axes of FIG. 8(a), (b), and (c) each represent time [min].

[0052] In this embodiment, as shown in FIGS. 8(a) and (b), the dimension of the electron beam irradiation range decreases from the dimension Rs1 at time t0 to the dimension Rf1 at time t1, and the tube current becomes the same as the tube current E1 after time t0. That is, in this embodiment, while the electron beam irradiation range for the target (23) narrows, the total amount of electrons colliding with the target (23) does not change. For this reason, as shown in FIG. 8(c), the power density (d) increases from time t0 to time t1. In the example shown in FIG. 8(c), the power density (d) represents the power density ds1 at time t0 and increases from there to time t1. Then, the power density (d) represents the power density df1 at time t1 and becomes approximately constant thereafter.

[0053] In one example, the power density ds1 may be 0.5 W / μm or higher and 2 W / μm or lower. The power density df1 may be 1 W / μm or higher and 3 W / μm or lower. In this example, the control unit (117) may control the electron gun feed unit (116) and the circuit unit (52) so that the power density ds1 is 0.5 W / μm or higher and 2 W / μm or lower. The control unit (117) may control the electron gun feed unit (116) and the circuit unit (52) so that the power density df1 is 1 W / μm or higher and 3 W / μm or lower.

[0054] As explained above, the X-ray generator (1) increases the power density (d), which is the density of electrons colliding with the target (23), from time t0, the start time of the preheating mode, to time t1, the start time of the actual use mode. That is, in the X-ray generator, the power density (d) in the preheating mode is lower than the power density (d) in the actual use mode. According to this configuration, compared to the case where the actual use mode is executed from the beginning without executing the preheating mode, the rapid rise in temperature near the irradiation range of the target in the actual use mode can be suppressed. Therefore, stress accumulation caused by the temperature difference between the irradiation range and its edge in the actual use mode can be reduced. From the above, the X-ray generator can suppress target cracking.

[0055] In addition, the X-ray generator (1) controls the electron beam so that at time t1, the irradiation range (201) of the electron beam for the target (23) becomes a desired irradiation range. By doing so, the change in the X-ray focal dimension caused by focal shift (shift in the irradiation range caused by the expansion of the target (23) and the target support (60) due to thermal expansion), which is a problem when the electron beam is irradiated on the target (23) from the beginning in a desired irradiation range, is suppressed.

[0056] In the X-ray generating device (1), the control unit (117) controls the electron gun feed unit (116) so that the crossover point (CP) is located between the electron gun (22) and the target (23), and controls the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode and the tube current of the X-ray tube (2) in the actual use mode are equal. In this case, due to the expansion of the target (23) and the target support unit (60) described above, the irradiation range of the electron beam for the target (23) narrows from time point t0 to time point t1. As a result, compared to the case where the actual use mode is executed from the beginning without executing the preheating mode, the temperature difference between the irradiation range in the actual use mode and its surroundings can be reduced. Therefore, stress accumulation caused by the temperature difference between the irradiation range in the actual use mode and its edges can be reliably reduced. In addition, since the tube current of the X-ray tube (2) is the same in the preheating mode and the actual use mode, the preheating mode and the actual use mode can be executed simply and easily.

[0057] In the X-ray generating device (1), the control unit (117) controls the electron gun feed unit (116) so that the convergence angle (θ) of the electron beam is 0.1° or more and 120° or less. In this case, the difference between the electron beam irradiation range (101) at time point t0 and the electron beam irradiation range (201) at time point t1 can be increased. Therefore, stress accumulation caused by the temperature difference between the irradiation range and its edge in the actual use mode can be reduced more effectively.

[0058] In the X-ray generating device (1), the dimension Rs1 of the irradiation range (101) at time t0 is 1.1 times or more and 2.0 times or less of the dimension Rf1 of the irradiation range (201) at time t1. In this case, stress accumulation caused by the temperature difference between the irradiation range and its edge in the actual use mode can be reduced more effectively.

[0059] In the X-ray generating device (1), the dimension Rf1 of the irradiation range (201) at time t1 is 5 μm or more and 500 μm or less. In this case, X-rays can be generated appropriately.

[0060] In the X-ray generating device (1), the control unit (117) controls the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode and the tube current of the X-ray tube (2) in the actual use mode are equal to 50 μA or more and 1 mA or less. In this case, X-rays can be generated appropriately.

[0061] Although embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the embodiments described above, and various modifications are possible within the scope of not departing from the gist thereof.

[0062] In this modified example as well, control of the crossover point (CP) and control of the tube current are performed to increase the power density (d) from time point t0 to time point t1. Hereinafter, with reference to FIGS. 9, 10, and 11, the control of the crossover point (CP) and the control of the tube current in this modified example will be explained in more detail.

[0063] First, the control of the crossover point (CP) will be explained. FIG. 9 is a schematic diagram showing another example of the relationship between the position of the crossover point and the irradiation range of the electron beam. In this modified example, as shown in FIG. 9, the control unit (117) controls the electron gun feed unit (116) so that the crossover point (CP) is located on the inner side of the target (23) in the direction of electron beam irradiation. This manner in which the crossover point (CP) is located on the inner side of the target (23) that is the target of electron beam irradiation is also called underfocus. That is, in this embodiment, it can be said that the control unit (117) controls the electron gun feed unit (116) so that the electron beam is underfocused with respect to the target (23). Even in this case, the focal diameter of the electron beam may be the same focal diameter in the preheating mode and the actual use mode. That is, in this modified example as well, control over the focal diameter of the electron beam is not required after the electron beam irradiation has started.

[0064] Even in the case of underfocus, the electron beam irradiation range changes as the target support (60) extends to form a portion (T1). This change in the electron beam irradiation range is shown in FIGS. 9 and FIGS. 10. FIGS. 10(a) is a schematic diagram showing another example of the electron beam irradiation range at the start of the preheating mode. FIGS. 10(b) is a schematic diagram showing another example of the electron beam irradiation range at the start of the actual use mode. In the examples shown in FIGS. 9 and FIGS. 10, the electron beam irradiation range at time t0, which is the start of the preheating mode, is shown as the irradiation range (102), and the electron beam irradiation range at time t1, which is the start of the actual use mode, is shown as the irradiation range (202). As shown in FIG. 10, the irradiation range (102) and the irradiation range (202) have a circular shape, for example. In this case, the dimensions Rs2 of the investigation range (102) and Rf2 of the investigation range (202) are represented, for example, by the diameter of the corresponding circle.

[0065] In the case of underfocus, the irradiation range (102) at time t0 is the narrowest, and from there the irradiation range of the electron beam widens. Then, at time t1, the expansion of the irradiation range of the electron beam stops, and from there the irradiation range of the electron beam becomes approximately constant at the irradiation range (202). In this way, in the case of underfocus, as the part (T1) expands, the irradiation range of the electron beam widens from the irradiation range (102) to the irradiation range (202).

[0066] In this modified example, the irradiation range (202) is a desired irradiation range in the X-ray generating device (1). As described above, between time point t0 and time point t1, the irradiation range of the electron beam widens, so when the irradiation range (202) is the desired irradiation range, the irradiation range (102) becomes a range smaller than the desired irradiation range. Therefore, in the case of underfocus, the control unit (117) may control the electron gun feed unit (116) so that the irradiation range (102) of the electron beam at time point t0 becomes smaller than the desired irradiation range.

[0067] In this modified example as well, the dimensions of the irradiation range change along with the change in the irradiation range of the electron beam. Such changes in the dimensions of the irradiation range of the electron beam are also shown in FIGS. 9 and FIGS. 10. Similar to the irradiation range of the electron beam, in the case of underfocus, the dimension Rs2 at time t0 is the smallest, and from there the dimensions of the irradiation range increase. Then, at time t1, the expansion of the dimensions stops, and from there the dimensions become approximately constant at dimension Rf2. As described above, in this modified example, since the irradiation range (202) is the desired irradiation range of the X-ray generator (1), the dimension Rf2 is the dimension of the desired irradiation range.

[0068] In one example, the dimension Rs2 may be 5 μm or more and 300 μm or less. The dimension Rf2 may be 5 μm or more and 500 μm or less. The dimension Rs2 may be 0.5 times or more and 0.9 times or less of the dimension Rf2. In this modified example, the dimension Rs2 is 70 μm and the dimension Rf2 is 100 μm, so the dimension Rs2 is 0.7 times the dimension Rf2.

[0069] Next, the control of the tube current is described. In this modified example, the control unit (117) controls the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode becomes smaller than the tube current of the X-ray tube (2) in the actual use mode. In one example, the control unit (117) may control the circuit unit (52) so that the tube current of the X-ray tube (2) increases from time point t0 to time point t1. In this case, the tube current Es2, which is the tube current of the X-ray tube (2) at time point t0, may be, for example, 0μA or more and 100μA or less. The tube current Ef2, which is the tube current of the X-ray tube (2) at time point t1, may be, for example, 100μA or more and 1 mA or less.

[0070] The relationship between the electron beam irradiation range, tube current, and power density (d) described above is shown in FIG. 11. FIG. 11(a) is a figure showing another example of a change in the dimensions of the electron beam irradiation range in preheating mode and actual use mode. FIG. 11(b) is a figure showing another example of a change in the tube current in preheating mode and actual use mode. FIG. 11(c) is a figure showing another example of a change in power density (d), which is the density of electrons colliding with the target. The vertical axis of FIG. 11(a) represents the dimensions of the electron beam irradiation range [μm]. The vertical axis of FIG. 11(b) represents the tube current [μA]. The vertical axis of FIG. 11(c) represents the power density (d) [W / μm]. The horizontal axes of FIG. 11(a), (b), and (c) each represent time [min].

[0071] In this modified example, as shown in FIGS. 11(a) and (b), the dimension of the electron beam irradiation range increases from the dimension Rs2 at time t0 to the dimension Rf2 at time t1, and the tube current also increases from the tube current Es2 at time t0 to the tube current Ef2 at time t1. That is, in this embodiment, as the electron beam irradiation range for the target (23) widens, the total amount of electrons colliding with the target (23) increases. For this reason, as shown in FIG. 11(c), the power density (d) increases from time t0 to time t1. In the example shown in FIG. 11(c), the power density (d) shows a power density ds2 at time t0 and increases from there to time t1. Then, the power density (d) shows a power density df2 at time t1 and becomes approximately constant thereafter. The range of power density ds2 may be the same as the range of power density ds1, and the range of power density df2 may be the same as the range of power density df1.

[0072] In this modified example, the control unit (117) controls the electron gun feed unit (116) so that the crossover point (CP) is located on the inner side of the target (23) in the direction of electron beam irradiation, and controls the circuit unit (52) so that the tube current of the X-ray tube (2) in the preheating mode becomes smaller than the tube current of the X-ray tube (2) in the actual use mode. In this modified example, due to the expansion of the target (23) and the target support unit (60), the irradiation range of the electron beam widens from time point t0 to time point t1. Also, since the tube current in the preheating mode is smaller than the tube current in the actual use mode, it is possible to reliably realize a configuration in which the power density (d) increases from time point t0 to time point t1 while suppressing the rapid rise in temperature near the irradiation range of the target.

[0073] In this modified example, the dimension Rs2 of the irradiation range (102) at time t0 is 0.5 times or more and 0.9 times or less the dimension Rf2 of the irradiation range (202) at time t1. In this case, stress accumulation caused by the temperature difference between the irradiation range and its edge in the actual use mode can be reduced more effectively.

[0074] In this modified example, the dimension Rf2 of the irradiation range (202) at time t1 is 5 μm or more and 500 μm or less. In this case, X-rays can be generated appropriately.

Claims

Claim 1 An X-ray generating device comprising an electron gun that generates an electron beam, a target that generates X-rays by colliding with the electron beam, an X-ray tube having a vacuum housing that accommodates the electron gun and the target, and a control unit that controls the operation of the X-ray tube, wherein the control unit executes an actual use mode in which the irradiation range of the electron beam to the target becomes a desired irradiation range, and a preheating mode executed prior to the actual use mode, wherein the density of electrons colliding with the target increases from the start time of the preheating mode to the start time of the actual use mode. Claim 2 An X-ray generating device according to claim 1, further comprising an electron gun feed unit that supplies power to the electron gun, a target support unit that supports the target, and a high-voltage feed unit that supplies high voltage to the target support unit, wherein the control unit controls the electron gun feed unit so that a crossover point, which is a point where the electron beam converges, is located between the electron gun and the target, and controls the high-voltage feed unit so that the tube current of the X-ray tube in the preheating mode and the tube current of the X-ray tube in the actual use mode are equal. Claim 3 An X-ray generating device according to paragraph 2, wherein the control unit controls the electron gun feed unit so that the convergence angle of the electron beam is 0.1° or more and 120° or less. Claim 4 An X-ray generating device according to claim 2 or 3, wherein the dimension of the irradiation range at the start time of the preheating mode is 1.1 times or more and 2.0 times or less the dimension of the irradiation range at the start time of the actual use mode. Claim 5 An X-ray generating device according to any one of paragraphs 2 to 4, wherein the dimension of the irradiation range at the start time of the actual use mode is 5 μm or more and 500 μm or less. Claim 6 An X-ray generating device according to any one of claims 2 to 5, wherein the control unit controls the high-voltage feed unit such that the tube current of the X-ray tube in the preheating mode and the tube current of the X-ray tube in the actual use mode are equal to the range of 50 μA or more and 1 mA or less. Claim 7 An X-ray generating device according to claim 1, further comprising an electron gun feed unit that supplies power to the electron gun, a target support unit that supports the target, and a high-voltage feed unit that supplies high voltage to the target support unit, wherein the control unit controls the electron gun feed unit so that a crossover point, which is a point where the electron beam converges, is located on the inner side of the target in the direction of irradiation of the electron beam, and controls the high-voltage feed unit so that the tube current of the X-ray tube in the preheating mode becomes smaller than the tube current of the X-ray tube in the actual use mode. Claim 8 An X-ray generating device according to claim 7, wherein the dimension of the irradiation range at the start time of the preheating mode is 0.5 times or more and 0.9 times or less the dimension of the irradiation range at the start time of the actual use mode. Claim 9 An X-ray generating device according to claim 7 or 8, wherein the dimension of the irradiation range at the start time of the actual use mode is 5 μm or more and 500 μm or less.

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