X-ray generation device

Abstract

This X-ray generation device comprises: an X-ray tube having an electron gun which generates an electron beam, a target which generates X-rays by collision of the electron beam therewith, and a vacuum housing which houses the electron gun and the target; an electron gun power supply part which supplies electric power to the electron gun; and a control part which, by controlling the electron gun power supply part, adjusts the focal spot diameter of the electron beam output from the electron gun. The control part controls the electron gun power supply part such that the focal spot diameter of the electron beam is made different between an actual use mode and a preliminary heating mode executed prior to the actual use mode, with the focal spot diameter of the electron beam in the preliminary heating mode being larger than the focal spot diameter of the electron beam in the actual use mode.

Description

X-ray generator

[0001] One aspect of the present disclosure relates to an X-ray generating device.

[0002] Patent Document 1 discloses an X-ray generating device that is composed of two electron guns and two targets, forms a microfocus with the electron guns and targets, and heats an anode with the electron guns and targets.

[0003] Japanese Patent Application Laid-Open No. 2007-149601

[0004] Here, a microfocus X-ray source needs to output X-rays with a small focal spot, and the target can become locally hot near the focal spot. Thermal stress can occur in the target due to the thermal cycle of heating and cooling by the electron beam, which can lead to cracks. If the target cracks and falls off, it will no longer be able to output X-rays properly.

[0005] One aspect of the present disclosure has been made in consideration of the above-described circumstances, and relates to an X-ray generating device that can suppress cracking of a target.

[0006] (1) An X-ray generating device according to one aspect of the present disclosure includes an X-ray tube having an electron gun that generates an electron beam, a target that generates X-rays when hit by the electron beam, and a vacuum housing that houses the electron gun and the target; an electron gun power supply unit that supplies power to the electron gun; and a control unit that adjusts the focal diameter of the electron beam output from the electron gun by controlling the electron gun power supply unit, wherein the control unit controls the electron gun power supply unit to make the focal diameter of the electron beam different between an actual use mode and a preheating mode that is executed prior to the actual use mode, and controls the electron gun power supply unit so that the focal diameter of the electron beam in the preheating mode is larger than the focal diameter of the electron beam in the actual use mode.

[0007] In an X-ray generator according to one aspect of the present disclosure, two modes (an actual use mode and a preheating mode) are set, each having a different electron beam focal diameter. The electron gun power supply is controlled so that the electron beam focal diameter in the preheating mode, which is executed prior to the actual use mode, is larger than the electron beam focal diameter in the actual use mode. With this configuration, the electron beam is irradiated over a wide area in the preheating mode, and then the focal diameter is reduced and the electron beam is irradiated to the focal point in the actual use mode. This reduces the temperature difference between the focal point and its surroundings in the actual use mode compared to when the electron beam is irradiated with the focal diameter in the actual use mode from the beginning. This reduces stress accumulation due to the temperature difference between the focal point and its surroundings in the actual use mode, and suppresses target cracking due to thermal stress. Furthermore, the electron beam is irradiated over a wide area in the preheating mode, preventing heat concentration. This allows the electron beam to be irradiated with a small focal diameter in the actual use mode after thermal equilibrium is reached. This suppresses the expansion of the X-ray focal spot size due to thermal expansion of the target and target support, which is a problem when the electron beam is irradiated with the focal diameter in the actual use mode from the beginning. As described above, according to the X-ray generating device according to one aspect of the present disclosure, it is possible to suppress cracking of the target and an increase in the X-ray focal spot size.

[0008] (2) In the X-ray generator described in (1) above, the control unit may control the electron gun power supply unit so that a first irradiation range, which is an irradiation range of the electron beam on the target in the preheating mode, includes a second irradiation range, which is an irradiation range of the electron beam on the target in the actual use mode. This allows the periphery of the focal point in the actual use mode to be preheated, reduces the temperature difference between the focal point and its periphery in the actual use mode, and effectively reduces stress accumulation due to the temperature difference.

[0009] (3) In the X-ray generator described in (2) above, the control unit may control the electron gun power supply unit so that the center of the first irradiation range coincides with the center of the second irradiation range. This appropriately preheats the periphery of the focal spot in the actual use mode to reduce stress accumulation, and enables switching between modes simply by changing the focal spot diameter (without changing the center of the irradiation range).

[0010] (4) In the X-ray generator described in (2) or (3) above, the control unit may control the electron gun power supply unit so that at least a part of the first irradiation range and at least a part of the second irradiation range are positioned at the center of the target. By setting the irradiation range to include the center of the target in this way, it is possible to properly irradiate the target even if the irradiation range is shifted for some reason, for example.

[0011] (5) The X-ray generator according to any one of (1) to (4) above may further include a target support unit that supports the target at one end thereof, and a high-voltage power supply unit that is connected to the other end of the target support unit and supplies high voltage to the target support unit, and the control unit may control the high-voltage power supply unit so that the output of X-rays emitted from the X-ray tube is the same in the actual use mode and the preheating mode. By keeping the output constant, the amount of elongation of the target and the target support due to thermal expansion can be stabilized.

[0012] (6) In the X-ray generator according to any one of (1) to (5), the control unit may control the electron gun power supply unit so that the focal diameter of the electron beam in the actual use mode is 300 μm or less. This allows X-rays to be generated appropriately.

[0013] (7) In the X-ray generator described in (6) above, the control unit may control the high-voltage power supply unit and the electron gun power supply unit in the actual use mode so as to satisfy the following relationship: X-ray output (W) emitted from the X-ray tube / focal diameter (μm) of the electron beam ≥ 1. This allows X-rays to be generated appropriately.

[0014] According to an X-ray generating device according to an aspect of the present disclosure, cracking of the target can be suppressed.

[0015] FIG. 1 is a cross-sectional view of an X-ray generator according to an embodiment; FIG. 2 is a diagram illustrating a focal diameter of an electron beam according to a comparative example; FIG. 3 is a diagram illustrating a problem in the comparative example; FIG. 4 is a diagram illustrating a problem in the comparative example; FIG. 5 is a diagram illustrating a problem in the comparative example; FIG. 6 is a diagram illustrating a focal diameter of an electron beam in two modes according to the present embodiment; FIG. 7 is a diagram illustrating a focal diameter of an electron beam in two modes according to the present embodiment.

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, identical or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, terms indicating specific directions, such as "upper" and "lower," are based on the state shown in the drawings and are for convenience only.

[0017] 1, the X-ray generator 1 of the first embodiment includes an X-ray tube 2, a housing 3, a first insulating part 4, a power supply 5, a conductive member 6, and a conductive paint 8. The X-ray generator 1 is a microfocus X-ray source used, for example, in X-ray nondestructive testing.

[0018] The X-ray tube 2 is a vacuum tube for generating X-rays. The X-ray tube 2 includes a housing 21 (vacuum housing), an electron gun 22, a target 23, and an anode 24. The housing 21 houses the electron gun 22, the target 23, and the anode 24. The space inside the housing 21 is a vacuum-drawn space. The housing 21 includes a head 211, a bulb 212, and a flange 213. The head 211 is formed into a cylindrical shape with a bottom from a metal material such as stainless steel. The bulb 212 is formed into a cylindrical shape with a bottom from an insulating material such as glass. The head 211 is airtightly joined to the bulb 212 so that the interior of the head 211 is in communication with the interior of the bulb 212. The flange 213 is formed into a ring shape along the outer edge of the head 211 from a metal material such as stainless steel. Here, the direction along the central axis (tube axis) A1 of the bulb 212 is referred to as the Z-axis direction, the direction perpendicular to the Z-axis direction is referred to as the X-axis direction, and the direction perpendicular to both the Z-axis direction and the X-axis direction is referred to as the Y-axis direction.

[0019] The electron gun 22 generates an electron beam within the housing 21 and emits the electron beam toward the target 23. The electron gun 22 is composed of a hot cathode that emits thermal electrons, an anode that accelerates the electrons, and an electron lens that adjusts the convergence of the electron beam (all of which are not shown). The electron gun 22 is fixed to the head 211 so that the central axis A2 of the electron gun 22 is perpendicular to the central axis A1 of the bulb 212. The central axis A2 of the electron gun 22 is aligned along the X-axis direction.

[0020] The target 23 generates X-rays when the electron beam emitted from the electron gun 22 collides with the target 23 within the housing 21. The target 23 is formed into a plate shape from 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.

[0021] The anode 24 applies a voltage generated in the power supply unit 5 to the target 23. Therefore, the anode 24 is electrically connected to the target 23. The anode 24 is formed of a metal material such as copper in a rod shape extending along the Z-axis direction. The anode 24 extends from outside the housing 21 to inside the housing 21 so that the central axis of the anode 24 coincides with the central axis A1 of the bulb 212. The anode 24 is fixed to the bottom of the bulb 212. The tip surface of the anode 24 within the housing 21 is an inclined surface inclined with respect to both the central axis A1 and the central axis A2. The target 23 is embedded in a tip portion 24a of the anode 24 so as to be flush with the tip surface of the anode 24.

[0022] The housing unit 3 houses a part of the X-ray tube 2. In the X-ray generator 1 of the first embodiment, the housing unit 3 houses the bulb 212. The housing unit 3 is formed into a cylindrical shape with a bottom and made of a metal material such as aluminum. The housing unit 3 has an upper portion 31 and a side portion 32. The side portion 32 is formed into a cylindrical shape with its height direction in the Z-axis direction. The upper portion 31 closes one end (the upper end in this embodiment) of the side portion 32 in the Z-axis direction. An opening 31a is provided in the upper portion 31. The X-ray tube 2 is located inside the opening 31a. The flange 213 is fixed to the upper portion 31 with the bulb 212 located inside the housing unit 3. The other end (the lower end in this embodiment) of the side portion 32 in the Z-axis direction is fixed to the upper end of the power supply unit 5 (the upper surface 51b of the second insulating portion 51). The first insulating portion 4 is sealed inside the housing unit 3.

[0023] The first insulating part 4 electrically insulates the X-ray tube 2 from other components. The first insulating part 4 is a liquid insulating part. The first insulating part 4 is, for example, insulating oil whose main component is mineral oil or ester oil. Inside the accommodation part 3, the first insulating part 4 covers the bulb 212, the part of the anode 24 that is exposed to the outside of the housing 21, and the part of the conductive member 6 that is exposed to the outside of the second insulating part 51. In the X-ray generator 1 of the first embodiment, the inside of the accommodation part 3 is filled with the first insulating part 4.

[0024] The power supply unit 5 generates a voltage to be applied to the target 23 via the conductive member 6 and the anode 24. The power supply unit 5 is disposed on one side of the housing 21 in the Z-axis direction (below the housing 21). The power supply unit 5 is aligned with 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).

[0025] The second insulating portion 51 is a solid insulating portion that electrically insulates the circuit portion 52 from other components. The second insulating portion 51 is formed in a rectangular parallelepiped shape using a resin material such as epoxy resin. The surface 51a of the second insulating portion 51 is composed of an upper surface 51b that faces the housing 21, a lower surface 51c that is opposite the upper surface 51b, and a side surface 51d that connects the upper surface 51b and the lower surface 51c to each other. A portion of the upper surface 51b is formed to be raised. This portion is in contact with the first insulating portion 4 within the housing portion 3. The conductive paint 8 is applied to the side surface 51d of the second insulating portion 51, and the potential of the side surface 51d is set to ground potential.

[0026] The circuit unit 52 has a substrate 521, which is a rectangular printed circuit board. The surface of the substrate 521 is perpendicular to the Y-axis direction. A first voltage unit 52a, a boost unit 52b, and a second voltage unit 52c are mounted on the surface of the substrate 521. The first voltage unit 52a is an input terminal to which a first voltage is input from outside and is electrically connected to the boost unit 52b. The boost unit 52b boosts the first voltage to a second voltage. The boost unit 52b is, for example, a Cockcroft-Walton circuit. The second voltage unit 52c is an output terminal that outputs a second voltage to the target 23 via the conductive member 6 and the anode 24 and is electrically connected to the boost unit 52b.

[0027] The booster 52b is located in the center of the surface of the substrate 521. The first voltage unit 52a is located on one side of the booster 52b in the Z-axis direction (the lower surface 51c side), and the second voltage unit 52c is located on the other side of the booster 52b in the Z-axis direction (the upper surface 51b side).

[0028] The circuit portion 52 is embedded in the second insulating portion 51 so that the entire circuit portion 52 is located in the second insulating portion 51. The circuit portion 52 is embedded in the second insulating portion 51 so that the substrate 521 extends straight along the Z-axis direction.

[0029] The conductive member 6 electrically connects the second voltage unit 52c and the target 23 via the anode 24. Therefore, the conductive member 6 is conductive. The conductive member 6 and the anode 24 constitute a target support unit 60 that supports the target 23 at one end. Hereinafter, the conductive member 6 and the anode 24 may be collectively referred to as the target support unit 60. The circuit unit 52 (high-voltage power supply unit) is connected to the other end of the target support unit 60 that is constituted by the conductive member 6 and the anode 24, and supplies a high voltage to the target support unit 60.

[0030] The conductive member 6 is formed in a rod shape from a metal material such as aluminum. One end (the other end) of the conductive member 6 is electrically connected to the second voltage section 52c, and the other end of the conductive member 6 is electrically connected to the base end 24b of the anode 24 (the portion of the anode 24 located outside the housing 21). The conductive member 6 is embedded in the second insulating section 51 so that a portion of the conductive member 6 is located within the second insulating section 51. The other portion of the conductive member 6 is exposed outside the second insulating section 51. The portion of the conductive member 6 exposed outside the second insulating section 51 is electrically connected to the base end 24b of the anode 24 inside the housing 3.

[0031] The X-ray generator 1 further includes an electron gun power supply unit 116 and a control unit 117 .

[0032] The electron gun power supply unit 116 is a voltage generation circuit that generates a voltage to be 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 the control unit 117. The electron gun power supply unit 116 may be mounted within the second insulating unit 51 together with the circuit unit 52, or may be mounted on a circuit board outside the second insulating unit 51. The control unit 117 is configured to adjust the focal diameter of the electron beam output from the electron gun 22 by controlling the electron gun power supply unit 116 (details will be described later). The control unit 117 is mounted on a circuit board outside the second insulating unit 51.

[0033] Next, the adjustment of the focal diameter of the electron beam in the X-ray generating device 1 according to this embodiment will be described in comparison with a comparative example.

[0034] FIG. 2 is a diagram illustrating the focal diameter of an electron beam according to a comparative example. In FIG. 2(a), the horizontal axis represents time and the vertical axis represents the focal diameter of the electron beam. In the comparative example shown in FIG. 2(a), once X-ray emission begins ("XON" in FIG. 2(a)), the focal diameter of the electron beam is maintained constant. The focal diameter is, for example, approximately 100 μm. The "tube voltage-tube current" of the X-ray tube is, for example, approximately 200 kV-800 μA. Here, the X-ray output is expressed as the product of the tube voltage (kV) and the tube current (mA). In this case, the X-ray output is 160 W, which translates to an X-ray output per unit area (diameter) of 1.6 W / μm, resulting in a constant high output of X-rays. In this way, in the comparative example, the focal diameter is maintained constant at a relatively small size, and the X-ray output is maintained constant at a relatively high output. The higher the tube voltage, the higher the energy of the electron beam irradiated onto the target 23, and the higher the tube current, the greater the total amount of the electron beam irradiated onto the target 23.

[0035] 2B, the irradiation range (electron beam focal diameter) 500 of the electron beam on the target 23 is always constant (constant when the focal diameter is small). In the example shown in FIG. 2B, the electron beam is irradiated onto the target 23 so that the center of the irradiation range 500 is located at the center of the target 23.

[0036] Figures 3 to 6 illustrate the problems encountered in the comparative example. Figure 3(a) shows the state of irradiation of the target 23 in the X-ray tube 2 with an electron beam. Figure 3(b) shows an enlarged view of a portion of Figure 3(a) (the target 23). Figure 3(c) shows an enlarged view of a portion of Figure 3(b) (the area irradiated by the electron beam on the target 23). As shown in Figure 3(b), a damaged area DA is generated in the target 23 due to the irradiation of the electron beam. More specifically, as shown in Figure 3(c), cracks C, which may cause target cracking, are generated around the damaged area DA. When a relatively high-power electron beam is irradiated on the target 23 with a small focal diameter, the irradiated area of ​​the target 23 becomes locally hot, resulting in stress accumulation due to the temperature difference between the irradiated area 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 the irradiation of the electron beam. The greater the amount of heat received, the more likely it is that non-uniform changes in the surface shape of the target 23 will occur due to the simultaneous thermal expansion of the target 23 and the target support part 60 until thermal equilibrium is reached and evaporation of the target 23 due to heat concentration on the target 23. The thermal cycle of heating and cooling by the electron beam accelerates the accumulation of stress described above, resulting in the formation of cracks C that can cause the target to break. Another problem is that the damaged area DA becomes elongated, as shown in Figure 3(c), and the surface shape of the target 23 in the area irradiated by the electron beam changes.

[0037] The reason why the damage area DA in the comparative example has a vertically elongated shape will be explained with reference to Figures 4 to 6. As shown in Figure 4, when a relatively high-power electron beam is irradiated onto the target 23, the target 23 evaporates within the irradiation range of the electron beam, causing the surface of the target 23 to become rough and concave. Furthermore, the energy of the electron beam irradiated onto the target 23 that is not converted into X-rays is converted into heat, which heats the target 23 and the target support 60. The heat causes the target support 60 to expand and elongate. The elongated portion T1 causes the irradiation range to gradually move from the initial position IP to a stable position SP. The stable position SP is the irradiation range of the electron beam on the target 23 when the target support 60 is in thermal equilibrium. While the target support 60 expands due to thermal expansion, the surface of the target 23 is dug in the irradiation range of the electron beam. As shown in FIG. 5 , the irradiation range continuously changes from the initial position IP to the stable position SP, forming a vertically elongated recessed damaged area DA. When the electron beam is irradiated onto a region including the damaged area DA, the electrons scatter within the recessed portion of the damaged area DA and generate X-rays, resulting in X-rays being generated from a wider area than the irradiation range of the electron beam. In other words, even though the electron beam focal spot diameter (electron beam irradiation conditions) remains unchanged, the surface shape of the target 23 in the irradiation range of the electron beam changes, enlarging the X-ray generation region on the target 23. In other words, the focal spot size of the X-rays extracted from the X-ray generator 1 increases. The focal spot size of the X-rays emitted from the X-ray generator 1, which was initially approximately circular as shown in FIG. 6( a), changes to a vertically elongated shape as shown in FIG. 6( b). This unintentional increase in the apparent X-ray focal spot size may result in blurred X-ray images.

[0038] As described above, when the focal diameter of the electron beam is constant as in the configuration according to the comparative example, there are problems such as the occurrence of cracks C that cause breakage of the target and an increase in the size of the X-ray focal point (change in the shape of the X-ray focal point) that causes blurring of the X-ray image.

[0039] To solve this problem, in the X-ray generator 1 according to this embodiment, the control unit 117 controls the electron gun power supply 116 to change the focal diameter of the electron beam between the actual use mode and the preheating mode executed prior to the actual use mode. Specifically, the control unit 117 controls the electron gun power supply 116 so that the focal diameter of the electron beam in the preheating mode is larger than the focal diameter of the electron beam in the actual use mode. With this configuration, the electron beam is irradiated over a wide area in the preheating mode, and then the focal diameter is reduced and the electron beam is irradiated to the focal point in the actual use mode. This reduces the temperature difference between the focal point and its surroundings in the actual use mode compared to when the electron beam is irradiated with the focal diameter in the actual use mode from the beginning. This reduces stress accumulation due to the temperature difference between the focal point and its surroundings in the actual use mode, thereby suppressing target cracking due to thermal stress. Furthermore, in the pre-heating mode, the electron beam is irradiated over a wide area, preventing heat from concentrating, and it becomes possible to irradiate the electron beam with a small focal spot diameter in the actual use mode after thermal equilibrium is reached. This suppresses the expansion of the X-ray focal spot size due to focal spot movement accompanied by digging of the target 23 (movement of the irradiation range caused by expansion of the target 23 and target support part 60 due to thermal expansion), which is a problem when the electron beam is irradiated with the focal spot diameter in the actual use mode from the beginning.

[0040] FIG. 7 is a diagram illustrating focal spot diameters in two modes (preheating mode and actual use mode) according to this embodiment. In FIG. 7A, the horizontal axis represents time, and the vertical axis represents the focal spot diameter of the electron beam. As shown in FIG. 7A, when X-ray emission starts ("XON" in FIG. 7A), the preheating mode is executed first. In the preheating mode, the focal spot diameter of the electron beam is adjusted to be larger than that of the actual use mode executed later. For example, the focal spot diameter is set to approximately 300 μm. After a predetermined time (for example, 15 minutes) has elapsed since the preheating mode was executed, the preheating mode is switched to the actual use mode. In the actual use mode, the focal spot diameter of the electron beam is adjusted to be smaller than that of the preheating mode. For example, the focal spot diameter is set to approximately 100 μm. In this embodiment, the X-ray output is controlled to be the same in the preheating mode and the actual use mode. That is, the "tube voltage-tube current" of the X-ray tube 2 is, for example, about "200 kV-800 μA," and the X-rays are set to a constant high output. In this manner, the control unit 117 may control the electron gun power supply unit 116 and the circuit unit 52 (high-voltage power supply unit) so that the output of X-rays emitted from the X-ray tube 2 is the same in the actual use mode and the preheating mode. In this case, the X-ray output per unit area in each mode is 0.53 W / μm in the preheating mode and 1.6 W / μm in the actual use mode. In this manner, the total amount of energy input to the target 23 (the total amount of heat received by the target) is the same in the preheating mode and the actual use mode, so that changes in the amount of elongation of the target 23 and the target support unit 60 can be suppressed when switching from a state of thermal equilibrium achieved in the preheating mode to the actual use mode. Therefore, the target 23 and the target support part 60 can maintain a state of thermal equilibrium before and after switching between the preheating mode and the actual use mode, which further suppresses changes in the focal spot size of the X-rays.

[0041] In this case, as shown in FIG. 7(b), the irradiation range of the electron beam on the target 23 is initially set to the irradiation range of the preheating mode (first irradiation range 100), and after a predetermined time has elapsed, it is set to the irradiation range of the actual use mode (second irradiation range 200), which is smaller than the first irradiation range 100.

[0042] 7( b), control unit 117 may control electron gun power supply unit 116 so that first irradiation range 100, which is the irradiation range of the electron beam on target 23 in the preheating mode, includes second irradiation range 200, which is the irradiation range of the electron beam on target 23 in the actual use mode. Control unit 117 may control electron gun power supply unit 116 so that second irradiation range 200 is completely included in first irradiation range 100, or may control electron gun power supply unit 116 so that first irradiation range 100 includes at least a part of second irradiation range 200.

[0043] 7B, the control unit 117 may control the electron gun power supply unit 116 so that the center of the first irradiation area 100 and the center of the second irradiation area 200 coincide with each other. "Coinciding" does not only mean a complete coincidence, but also a close enough proximity that they can be regarded as coinciding with each other. The control unit 117 may control the electron gun power supply unit 116 so that the center of the first irradiation area 100 and at least a part of the second irradiation area 200 coincide with each other.

[0044] 7B, the control unit 117 may control the electron gun power supply unit 116 so that at least a portion of the first irradiation range 100 and at least a portion of the second irradiation range 200 are located at the center of the target 23. The control unit 117 may control the electron gun power supply unit 116 so that the center of the first irradiation range 100 and the center of the second irradiation range 200 are located at the center of the target 23.

[0045] The control unit 117 may control the electron gun power supply unit 116 so that the focal diameter of the electron beam in the preheating mode is about two to three times the focal diameter of the electron beam in the actual use mode. The control unit 117 may control the electron gun power supply unit 116 so that the focal diameter of the electron beam in the actual use mode is about 5 μm to 500 μm. The control unit 117 may control the electron gun power supply unit 116 so that the focal diameter of the electron beam in the actual use mode is 300 μm or less.

[0046] The control unit 117 may control the circuit unit 52 (high-voltage power supply unit) of the power supply unit 5 so that the output of X-rays emitted from the X-ray tube 2 is the same in the actual use mode and the preheating mode. In this case, the control unit 117 may control the circuit unit 52 (high-voltage power supply unit) and the electron gun power supply unit 116 so that the output of X-rays is approximately 0.1 W to 500 W. The control unit 117 may also control the circuit unit 52 (high-voltage power supply unit) and the electron gun power supply unit 116 so that the output of X-rays emitted from the X-ray tube 2 is different in the actual use mode and the preheating mode. In this case, the control unit 117 may control the circuit unit 52 (high-voltage power supply unit) and the electron gun power supply unit 116 so that the output of X-rays in the actual use mode is approximately 0.1 W to 500 W and the output of X-rays in the preheating mode does not exceed the output of X-rays in the actual use mode.

[0047] In the actual use mode, the control unit 117 may control the circuit unit 52 (high-voltage power supply unit) and the electron gun power supply unit 116 so as to satisfy the following relationship: X-ray output (W) from the X-ray tube 2 / electron beam focal diameter (μm) ≧ 1.

[0048] Next, the effects of the X-ray generating device 1 according to this embodiment will be described.

[0049] The X-ray generator 1 comprises an X-ray tube 2 having an electron gun 22 that generates an electron beam, a target 23 that generates X-rays when the electron beam collides with it, and a housing 21 that houses the electron gun 22 and the target 23, an electron gun power supply unit 116 that supplies power to the electron gun 22, and a control unit 117 that adjusts the focal diameter of the electron beam output from the electron gun 22 by controlling the electron gun power supply unit 116, and the control unit 117 makes the focal diameter of the electron beam different between an actual use mode and a preheating mode that is executed prior to the actual use mode, and controls the electron gun power supply unit 116 so that the focal diameter of the electron beam in the preheating mode is larger than the focal diameter of the electron beam in the actual use mode.

[0050] The X-ray generator 1 according to this embodiment has two modes (an actual use mode and a preheating mode) in which the electron beam focal spot diameter differs from each other. The electron gun power supply 116 is controlled so that the electron beam focal spot diameter in the preheating mode, which is executed prior to the actual use mode, is larger than the electron beam focal spot diameter in the actual use mode. With this configuration, the electron beam is irradiated over a wide area in the preheating mode, and then the focal spot diameter is reduced and the electron beam is irradiated to the focal spot in the actual use mode. This reduces the temperature difference between the focal spot and its surroundings in the actual use mode compared to when the electron beam is irradiated with the focal spot diameter in the actual use mode from the beginning. This reduces stress accumulation due to the temperature difference between the focal spot and its surroundings in the actual use mode, thereby suppressing target cracking due to thermal stress. Furthermore, in the preheating mode, the electron beam is irradiated over a wide area, preventing heat concentration. This allows for the electron beam to be irradiated with a small focal diameter in the actual use mode after thermal equilibrium is reached. This suppresses the expansion of the X-ray focal spot size due to thermal expansion of the target 23 and the target support 60, which would be a problem if the electron beam were irradiated with the focal spot diameter in the actual use mode from the beginning. More specifically, the expansion of the X-ray focal spot size, which is caused by the thermal expansion of the target 23 and the target support 60 until thermal equilibrium is reached and the simultaneous evaporation of the target 23 due to heat concentration on the target 23, is likely to cause non-uniform changes in the surface shape of the target 23. That is, the X-ray focal spot shape, which is approximately circular at the start of use as shown in FIG. 8( a) , can be maintained in the same state as at the start of use as shown in FIG. 8( b) even after a long period of use, thereby suppressing the expansion and change of the X-ray focal spot size. As described above, the X-ray generator 1 according to this embodiment can suppress target cracking and expansion of the X-ray focal spot size.

[0051] In the X-ray generator 1, the control unit 117 may control the electron gun power supply unit 116 so that the first irradiation range, which is the irradiation range of the electron beam on the target 23 in the preheating mode, includes the second irradiation range, which is the irradiation range of the electron beam on the target 23 in the actual use mode. This makes it possible to preheat the area around the focal point in the actual use mode, reduce the temperature difference between the focal point and its periphery in the actual use mode, and effectively reduce stress accumulation caused by the temperature difference.

[0052] In the X-ray generator 1, the control unit 117 may control the electron gun power supply unit 116 so that the center of the first irradiation range coincides with the center of the second irradiation range. This allows the periphery of the focal spot in the actual use mode to be appropriately preheated to reduce stress accumulation, and also allows the mode to be switched simply by changing the focal spot diameter (without changing the center of the irradiation range).

[0053] In the X-ray generator 1, the control unit 117 may control the electron gun power supply unit 116 so that at least a part of the first irradiation range and at least a part of the second irradiation range are positioned at the center of the target 23. By setting the irradiation range so as to include the center of the target 23 in this way, it is possible to appropriately irradiate the target 23 even if the irradiation range is shifted for some reason, for example.

[0054] The X-ray generator 1 further includes a target support unit 60 that supports the target 23 at one end, and a circuit unit 52 (high-voltage power supply unit) that is connected to the other end of the target support unit 60 and supplies high voltage to the target support unit 60, and the control unit 117 may control the electron gun power supply unit 116 and the circuit unit 52 (high-voltage power supply unit) so that the output of X-rays emitted from the X-ray tube 2 is the same in the actual use mode and the preheating mode. By making the output the same, the amount of heat (energy) input to the target 23 is the same, and therefore the amount of elongation due to thermal expansion of the target 23 and the target support unit 60 can be stabilized.

[0055] In the X-ray generator 1, the control unit 117 may control the electron gun power supply unit 116 so that the focal diameter of the electron beam in the actual use mode is 300 μm or less. This allows X-rays to be generated appropriately.

[0056] In the X-ray generator 1, the control unit 117 may control the circuit unit 52 (high voltage power supply unit) and the electron gun power supply unit 116 in the actual use mode so as to satisfy the following relationship: X-ray output (W) from the X-ray tube 2 / electron beam focal spot diameter (μm) ≥ 1. This allows X-rays to be generated appropriately.

[0057] 1...X-ray generator, 2...X-ray tube, 21...housing (vacuum housing), 22...electron gun, 23...target, 52...circuit section (high voltage power supply section), 60...target support section, 116...electron gun power supply section, 117...control section.

Claims

1. An X-ray generating device comprising: an X-ray tube having an electron gun that generates an electron beam, a target that generates X-rays when the electron beam collides with it, and a vacuum housing that houses the electron gun and the target; an electron gun power supply unit that supplies power to the electron gun; and a control unit that adjusts the focal diameter of the electron beam output from the electron gun by controlling the electron gun power supply unit, wherein the control unit makes the focal diameter of the electron beam different between an actual use mode and a preheating mode that is executed prior to the actual use mode, and controls the electron gun power supply unit so that the focal diameter of the electron beam in the preheating mode is larger than the focal diameter of the electron beam in the actual use mode.

2. An X-ray generating device as described in claim 1, wherein the control unit controls the electron gun power supply unit so that a first irradiation range, which is the irradiation range of the electron beam on the target in the preheating mode, includes a second irradiation range, which is the irradiation range of the electron beam on the target in the actual use mode.

3. An X-ray generating apparatus according to claim 2, wherein said control unit controls said electron gun power supply unit so that the center of said first irradiation range coincides with the center of said second irradiation range.

4. An X-ray generating device as described in claim 2 or 3, wherein the control unit controls the electron gun power supply unit so that at least a portion of the first irradiation range and at least a portion of the second irradiation range are positioned at the center of the target.

5. An X-ray generating device according to any one of claims 1 to 4, further comprising: a target support unit that supports the target at one end; and a high-voltage power supply unit that is connected to the other end of the target support unit and supplies high voltage to the target support unit, wherein the control unit controls the high-voltage power supply unit so that the output of X-rays emitted from the X-ray tube is the same in the actual use mode and the preheating mode.

6. An X-ray generating apparatus according to claim 5, wherein said control unit controls said electron gun power supply unit so that the focal diameter of said electron beam in said actual use mode is 300 μm or less.

7. An X-ray generating device according to claim 6, wherein the control unit controls the high-voltage power supply unit and the electron gun power supply unit so as to satisfy the following relationship in the actual use mode: output (W) of X-rays emitted from the X-ray tube / focal diameter (μm) of the electron beam ≧1.

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