X-ray generating device

Abstract

This X-ray generation device (1) is provided with: an X-ray tube (2) comprising an electron gun (3) having a cathode (C) for emitting an electron beam (EB), and a target (11) on which the electron beam (EB) emitted from the electron gun (3) is incident; and a control unit (51) that controls the driving of the X-ray tube (2). The control unit (51) executes: a first operation mode in which the temperature of the cathode (C) is estimated on the basis of the power consumption of the cathode (C), and the current supplied to the cathode (C) is controlled so as to maintain the estimated temperature of the cathode (C) within a prescribed range for normal operation; and a second operation mode in which the cathode is heated at a cleaning temperature higher than a predetermined range after the first operation mode is implemented for a predetermined time.

Description

Technical Field

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

[0002] Conventionally, an X-ray generating device including an X-ray tube has been known. The X-ray tube includes an electron gun having a cathode that emits an electron beam, and a target to which the electron beam emitted from the electron gun is incident. In the X-ray generating device of Patent Document 1, for example, a configuration in which a part of the electron beam incident on the target is emitted from the target as reflected electrons has been disclosed.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 11-144653

[0006] Patent Document 2: Japanese Patent Laid-Open No. 2012-49122 Summary of the Invention

[0007] [Problems to be Solved by the Invention]

[0008] During the operation of the X-ray generating device as described above, in order to maintain the characteristics of the electron beam, such as the focus size and focus shape of the electron beam, within a desired range, the temperature of the cathode must be maintained within a given range. In conventional X-ray generating devices, in order to obtain a desired output, the temperature of the cathode during operation is maintained at a temperature equal to or higher than a given temperature (for example, 1800 K). However, there is a problem that it is difficult to obtain a long life of the cathode due to the high temperature.

[0009] Regarding this problem, a method of achieving a balance with the output and maintaining the temperature of the cathode during operation at a temperature lower than a given temperature is considered. In this method, by reducing the temperature of the cathode during operation, the life of the cathode is extended. On the other hand, since the temperature of the cathode during operation is reduced, attachment of foreign substances to the cathode surface occurs, and new problems such as deterioration of the emission characteristics of the electron beam may occur.

[0010] Regarding this new problem, for example, the X-ray tube described in Patent Document 2 has a heater that heats the cathode to 1000°C or higher, and the cathode surface is cleaned by performing a flushing process with this heater. In the X-ray tube of Patent Document 2, the cleaning process is appropriately performed as needed. However, since the actual temperature of the cathode is not known from Patent Document 2, it is difficult to confirm whether the desired cleaning process has been actually performed. In addition, since the cathode temperature during normal operation is not known from Patent Document 2, it is difficult to grasp the operating state of the cathode, and it is difficult to perform the cleaning process at an appropriate timing.

[0011] The present disclosure has been made in view of the above problems, and an object thereof is to provide an X-ray generating apparatus capable of surely cleaning the surface of a cathode at an appropriate timing.

[0012] [Technical means for solving the problem]

[0013] The gist of an X-ray generating apparatus according to one aspect of the present disclosure is as follows [1] to [6].

[0014] [1] An X-ray generating apparatus comprising: an X-ray tube including an electron gun having a cathode that emits an electron beam and a target onto which the electron beam emitted from the electron gun is incident; and a control unit that controls the driving of the X-ray tube; and the control unit executes: a first operation mode that estimates the temperature of the cathode based on the power consumption of the cathode and controls the supply current to the cathode to maintain the estimated temperature of the cathode within a given range for normal operation; and a second operation mode that, after the first operation mode has been implemented for a given time, heats the cathode to a cleaning temperature higher than the given range.

[0015] In this X-ray generating apparatus, in the first operation mode, the temperature of the cathode is estimated based on the power consumption of the cathode, and the supply current to the cathode is controlled to maintain the estimated temperature of the cathode within a given range for normal operation. Thus, the temperature of the cathode during normal operation can be appropriately maintained, and therefore the emission characteristics of the electron beam (e.g., focal size and size shape) can be stably maintained within a desired range. Further, in this X-ray generating apparatus, it is considered that foreign matter adheres to the surface of the cathode when the first operation mode is implemented, and the second operation mode for cleaning the surface of the cathode is implemented. In the second operation mode, foreign matter is removed from the surface of the cathode by heating the cathode to a cleaning temperature higher than the given range of the first operation mode, and the emission characteristics of the electron beam can be kept good. In this X-ray generating apparatus, by implementing the first operation mode that maintains the cathode at an appropriate temperature, the second operation mode is implemented after a given time of implementing a given operating condition of the cathode (a condition that maintains an appropriate operating state and can estimate a state change based on the operating time). Thus, the surface of the cathode can be cleaned at an appropriate timing (a timing at which the adhesion of foreign matter to the surface of the cathode continuously progresses), and the second operation mode can be implemented while performing temperature control, and therefore the surface of the cathode can be surely cleaned at an appropriate timing.

[0016] [2] The X-ray generating apparatus according to [1], wherein the cathode includes an electron emission portion made of a single crystal material. In this case, a cathode having desired electron emission characteristics is obtained.

[0017] [3] The X-ray generating device according to [2], wherein the single crystal material contains cerium or lanthanum. In this case, it is easy to obtain a cathode having the desired electron emission characteristics.

[0018] [4] The X-ray generating device according to [2] or [3], wherein the single crystal material contains cerium, and the given range for normal operation in the first operation mode is set to 1720K to 1780K. In this case, by lowering the temperature of the cathode during normal operation compared to the past, the focus size of the electron beam is maintained, and the long life of the film cathode is achieved. Since the temperature of the cathode during normal operation is lowered, it is easy for foreign substances to adhere to the cathode surface, but by the above treatment, the cleaning of the cathode surface can be surely and at an appropriate timing.

[0019] [5] The X-ray generating device according to any one of [1] to [4], wherein when the control unit has controlled the supply current to the cathode in the first operation mode and still has not maintained the estimated temperature of the cathode within the given range, it generates a notification signal indicating this. According to this configuration, during the implementation of the first operation mode, when the estimated temperature of the cathode is not maintained within the given range under the control of the supply current to the cathode, the abnormality of the cathode can be quickly notified to the outside.

[0020] [6] The X-ray generating device according to any one of [1] to [5], which includes an electron beam measurement unit that measures the focus size and / or focus shape of the electron beam emitted from the cathode; and when the focus size and / or focus shape of the electron beam do not satisfy the desired size and / or shape after the implementation of the second operation mode, the control unit generates a notification signal indicating this. According to this configuration, when the emission characteristics of the electron beam are not improved even after the implementation of the second operation mode, the abnormality of the cathode can be quickly notified to the outside.

[0021] [Advantages of the Invention]

[0022] According to the present disclosure, the cleaning of the cathode surface can be surely and at an appropriate timing. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic cross-sectional view showing the configuration of an X-ray generating device according to an embodiment of the present disclosure.

[0024] Figure 2 For showing Figure 1 It is a block diagram showing the configuration of the exhaust part of the X-ray generating device shown.

[0025] Figure 3 For Figure 1 It is a chart related to X-ray irradiation of the X-ray generating device shown.

[0026] Figure 4 A block diagram showing the configuration of a control unit related to the first operation mode and the second operation mode.

[0027] Figure 5 A flowchart of the control unit in each operation mode.

[0028] Figure 6 A diagram showing an example of reference data for estimating the temperature of a cathode. Detailed implementation mode

[0029] Hereinafter, with reference to the drawings, a preferred implementation mode of an X-ray generating apparatus according to one aspect of the present disclosure will be described in detail.

[0030] Figure 1 A schematic cross-sectional view showing the configuration of an X-ray generating apparatus according to an embodiment of the present disclosure. As Figure 1 shown, the X-ray generating apparatus 1 includes an X-ray tube 2, and the X-ray tube 2 includes: an electron gun 3, a rotating anode unit U, a magnetic lens 4, an exhaust unit 5, a housing 6 that houses the electron gun 3, and a housing 7 that houses the rotating anode unit U. In addition, the X-ray generating apparatus 1 includes a control unit 51 that controls the operation of the X-ray tube 2 (see Figure 4 ). The housing 6 and the housing 7 of the X-ray tube 2 may be integrally formed or separately formed. If they are separate, the housing 6 and the housing 7 can be detached from each other or integrally joined in a non-detachable form.

[0031] The electron gun 3 is a part that emits an electron beam EB. The electron gun 3 has a cathode C that emits the electron beam EB. The cathode C is, for example, a circular planar cathode. The electron emission portion Ca of the cathode C is made of, for example, a single crystal material (CeB6 or LaB6) containing cerium or lanthanum. In the present embodiment, CeB6 is used as the single crystal material. The electron emission surface of the cathode C forms a circular shape when viewed from above the cathode C. The cathode C emits an electron beam EB having a circular cross-sectional shape through a supply current from a power supply device 56 (see Figure 4 ).

[0032] The rotating anode unit U has a target 11, a rotating support 12, and a drive unit 13. As the constituent material of the target 11, for example, heavy metals such as tungsten, silver, rhodium, molybdenum, and alloys thereof are cited. The rotating support 12 is configured to be rotatable about a rotation axis A. In the present embodiment, the rotation axis A coincides with the incident direction of the electron beam on the target 11. The rotation axis A can be inclined with respect to the incident direction of the electron beam on the target 11.

[0033] As the constituent material of the rotary support 12, metals such as copper and copper alloys are cited, for example. The rotary support 12 has a flat truncated conical pedestal 12a with the rotary axis A as the central axis. The target 11 is arranged along the peripheral portion of the pedestal 12a. The drive unit 13 is a part for rotationally driving the rotary support 12 around the rotary axis A. The drive unit 13 has a drive source such as a motor, for example.

[0034] One surface of the target 11 arranged on the pedestal 12a rotates while receiving the electron beam EB as the rotary support 12 rotates, and generates X-rays XR. In the present embodiment, the target 11 is a reflection type target, and generates X-rays XR in a direction intersecting (orthogonal) to the incident direction of the electron beam to the target 11. The X-rays XR generated at the target 11 are emitted to the outside of the housing 6 from the emission window 14 formed in the side wall portion of the housing 6. The emission window 14 is hermetically sealed by the window member 15. As the constituent material of the window member 15, light elements such as beryllium, aluminum, and carbon are cited, for example.

[0035] The magnetic lens 4 is a part for controlling the electron beam EB from the cathode C to the target 11. In the present embodiment, the magnetic lens 4 is composed of a deflection coil 21, a focusing lens 22, and a quadrupole lens 23. The deflection coil 21, the focusing lens 22, and the quadrupole lens 23 are all housed in the housing 24. A passage 24a for the electron beam EB to pass through is formed in the housing 24. The deflection coil 21, the focusing lens 22, and the quadrupole lens 23 are sequentially arranged from the cathode C to the target 11 in the housing 24 so as to surround the passage 24a.

[0036] The deflection coil 21 corrects the angular deviation between the emission axis of the electron beam EB from the cathode C and the central axis of the focusing lens and the quadrupole lens 23. The focusing lens 22 is composed of, for example, a coil, a pole piece, a yoke, etc. The focusing lens 22 focuses the electron beam EB while rotating the electron beam EB around the axis. The electron beam EB passing through the arrangement region of the focusing lens 22 rotates in a spiral shape while being focused, for example. The quadrupole lens 23 is composed of, for example, a yoke and a coil. The quadrupole lens 23 changes the cross-sectional shape of the electron beam EB from a circular shape to an elliptical shape.

[0037] The X-ray generating device 1 is as Figure 1As shown, it is equipped with a cooler unit 31 and a temperature sensor 32. The cooler unit 31 and the temperature sensor 32 are connected to each other in a manner capable of information communication. The cooler unit 31 and the temperature sensor 32 can be mutually connected to a control unit such as a CPU unit. In the X-ray generating apparatus 1 having a rotating anode unit U, when the temperature changes by, for example, 0.1 °C, the focal position of the electron beam EB changes by about 1 μm. Therefore, when improving the stability of the X-ray XR, the temperature management of the X-ray tube 2 is an important factor. In the X-ray generating apparatus 1, by performing feedback control on the cooler unit 31 based on the temperature of the X-ray tube 2 detected by the temperature sensor 32, the temperature change of the X-ray tube 2 is suppressed, and an improvement in the stability of the X-ray XR is sought. The feedback control method of the cooler unit 31 can be either proportional control or integral control.

[0038] The cooler unit 31 is a part that supplies a refrigerant adjusted to a given temperature to the X-ray tube 2. As the refrigerant, for example, liquid refrigerants such as water and antifreeze can be used. The cooler unit 31 maintains the temperature of the X-ray tube 2 within a given range by circulating the refrigerant in a flow path formed around a heat source (such as an electron gun, a target, etc.) inside the X-ray tube 2.

[0039] Due to the device configuration of the X-ray generating apparatus 1 in which the cooler unit 31 is assembled, or the arrangement of a lead box for X-ray shielding, etc., for example, the cooler unit 31 may be arranged separately at a considerable distance (such as about 20 m) from the X-ray tube 2. Therefore, in the temperature control using the temperature sensor built in the cooler unit 31, since the distance between the temperature sensor and the X-ray tube 2 is too far, it may be a problem that the accuracy of the temperature control of the X-ray tube 2 cannot be guaranteed. Therefore, in the X-ray generating apparatus 1, as Figure 1 shown, a temperature sensor 32 that is separate from the cooler unit 31 is arranged near the X-ray tube 2.

[0040] The temperature sensor 32 is arranged near the X-ray tube 2 at a position that is not affected by the X-ray XR in order to avoid deterioration caused by the X-ray XR generated by the X-ray tube 2. In the present embodiment, the temperature sensor 32 is arranged in contact with or close to an end portion 6a of the housing 6 on the side opposite to the direction in which the electron beam EB is emitted from the cathode C. Further, the temperature sensor 32 can be arranged in the housing 6 on the side opposite to the emission direction of the X-ray XR. The temperature sensor 32 can be arranged on a refrigerant pipe arranged between the cooler unit 31 and the X-ray tube 2, or can be arranged directly below the X-ray tube 2 so as not to receive the irradiation of the X-ray XR generated by the target 11.

[0041] Figure 2 To show Figure 1 a block diagram showing the configuration of the exhaust portion of the X-ray generating apparatus shown. As Figure 2As shown, the exhaust section 5 includes vacuum pumps 41A and 41B, a buffer tank 42, and a backing pump 43. The vacuum pumps 41A and 41B and the buffer tank 42 are connected to each other through metal bellows or the like. The buffer tank 42 and the backing pump 43 are connected to each other through a foreline valve 44 and metal bellows or the like.

[0042] The vacuum pump 41A is a pump that evacuates the internal space S1 of the housing 6 through an exhaust flow path E1 (see Figure 1 ). The vacuum pump 41B is a pump that evacuates the internal space S2 of the housing 7 through an exhaust flow path E2 (see Figure 1 ). By the vacuum pumps 41A and 41B, the gases generated in the electron gun 3 and the target 11 are removed, and the internal spaces S1 and S2 are maintained in a vacuum state or a partial vacuum state. The internal space S1 is maintained, for example, at 10 -4 Pa or less, preferably 10 -5 Pa or less in a vacuum state or a partial vacuum state. The internal space S2 is maintained, for example, in a vacuum state or a partial vacuum state between 10 -6 Pa and 10 -3 Pa.

[0043] The buffer tank 42 is a large-capacity vacuum chamber disposed between the vacuum pumps 41A and 41B and the backing pump 43. By disposing the buffer tank 42, the discharge pressure of the vacuum pumps 41A and 41B can be ensured even when the backing pump 43 is stopped. In addition, the vibration during the operation of the backing pump 43 is prevented from being directly transmitted to the X-ray tube 2, and in the X-ray tube 2, the change of the focus position of the electron beam EB due to external vibration can be suppressed.

[0044] A vacuum gauge 45 is provided in the buffer tank 42. The vacuum gauge 45 is a part for detecting the internal pressure of the buffer tank 42. By monitoring the internal pressure of the buffer tank 42 with the vacuum gauge 45, the performance degradation of the backing pump 43 can be detected. In addition, by providing the vacuum gauge 45 and connecting the buffer tank 42 and the backing pump 43 with the foreline valve 44, the intermittent operation of the backing pump 43 can be performed. Therefore, the exhaust section 5 can operate with low vibration and low power consumption.

[0045] An outlet pressure sensor 46 is connected to the vacuum pump 41A. The outlet pressure sensor 46 is a part for detecting the internal pressure of the internal spaces S1 and S2 during gas discharge. By monitoring the internal pressure of the internal spaces S1 and S2 during gas discharge with the outlet pressure sensor 46, it can be determined whether the internal pressure of the internal spaces S1 and S2 has risen to an abnormal value.

[0046] In the above exhaust section 5, after evacuating the internal spaces S1 and S2 of the X-ray tube 2 to a given vacuum level or below during initial vacuum evacuation, the foreline pipe valve 44 is closed and the forepump 43 is stopped. Thereafter, the power consumption of the vacuum pumps 41A and 41B is monitored, and the evacuation of the internal spaces S1 and S2 continues. When the power consumption of the vacuum pumps 41A and 41B exceeds a specified value, the foreline pipe valve 44 is opened and the forepump 43 is started. After the power consumption of the vacuum pumps 41A and 41B returns below the specified value, the foreline pipe valve 44 is closed and the forepump 43 is stopped. The operation time of the forepump 43 except for initial vacuum evacuation can be, for example, less than about 0.5 hours in 100 hours.

[0047] The control unit 51 (see Figure 4 ) is a part that controls the operation of the X-ray tube 2. The control unit 51 is a computer system physically composed of a memory such as a RAM and a ROM, a processor (arithmetic circuit) such as a CPU, a communication interface, a storage unit such as a hard disk, and a display unit such as a display. Examples of the computer system include a personal computer, a cloud server, and an intelligent device (such as a smartphone and a tablet terminal). The control unit 51 can be composed of a PLC (programmable logic controller) or an integrated circuit such as an FPGA (Field-programmable gate array).

[0048] Figure 3 is related to Figure 1 a chart related to the X-ray irradiation of the X-ray generating device shown. Figure 3 The chart of Figure 3 is a chart of the first operation mode described later. As Figure 3 shown, when the X-ray generating device 1 outputs the X-ray XR, the exhaust section 5, the drive unit 13 (motor) of the rotary support 12, the magnetic lens 4, the filament are energized (heating of the cathode C), and the power supply device 56 (see Figure 4 ) are driven in the following time sequence. First, at time t0, the vacuum pumps 41A and 41B are driven, and the vacuum level of the X-ray tube 2 rises. In addition, the cold unit 31 is driven, and the temperature control of the X-ray tube 2 is started. Next, the drive unit 13 is driven, and the rotational speed of the motor rises from 0 rpm to about 12,000 rpm. In addition, the supply of current to the focusing lens 22 and the quadrupole lens 23 is started.

[0049] After the vacuum level of the X-ray tube 2 reaches a specified value, the supply of current to the filament is started, and the cathode C is heated. In the present embodiment, the temperature range of the cathode C during heating is set to 1720K to 1780K (details will be described later). In Figure 3In the example, the increase in the supply current to the filament is carried out in two stages. The increase in the supply current to the filament in the first stage is carried out for the stabilization of the thermal expansion of the cathode C and the electron gun 3. When a command signal indicating the start of X-ray XR irradiation is input to the control unit 51 at time t1, the second-stage increase in the supply current to the filament starts, and the tube voltage increases. At time t2 when the increase in the current to the filament and the rise in the tube voltage stop, the tube current increases. As an example, the tube voltage is 120 kV and the tube current is 10 mA.

[0050] With the increase in the tube current, at time t2, X-ray XR starts to be emitted. After the emission of X-ray XR, the supply current to the focusing lens 22 and the quadrupole lens 23 is further increased by one stage, and the focal position and focal shape of the electron beam EB are adjusted to be the desired position and size. After the supply current to the focusing lens 22 and the quadrupole lens 23 is further increased by one stage, at time t3, a command signal indicating the stop of X-ray XR irradiation is input to the control unit 51. During the period ([ Figure 3 period T) until the start of the decrease in the supply current to the focusing lens 22 is the period for obtaining the output of X-ray XR with the desired diameter.

[0051] When a command signal indicating the stop of X-ray XR irradiation is input to the control unit 51 at time t3, the supply current to the focusing lens 22 decreases by one stage. After that, the tube current and the tube voltage decrease. After the decrease in the tube current and the tube voltage, the supply current to the filament decreases and the cathode C cools down. In Figure 3 the example, the decrease in the supply current to the filament is carried out in two stages in the same way as when increasing. The period from time t4 when the supply current to the cathode C stops to time t5 when the driving of the vacuum pumps 41A and 41B stops is the cooling period of the cathode C.

[0052] During the cooling period of the cathode C, the supply current to the focusing lens 22 and the quadrupole lens 23 is stopped, and the driving unit 13 is also stopped. After the driving unit 13 stops, the cooler unit 31 is stopped, and the temperature control of the X-ray tube 2 ends. After the cooling period of the cathode C ends, the vacuum pumps 41A and 41B are stopped. Thus, the vacuum degree of the X-ray tube 2 decreases and the process ends.

[0053] Generally, during the operation of an X-ray generating device, in order to maintain the focus size of the electron beam within a desired range, the temperature of the cathode must be kept within a given range. In conventional X-ray generating devices, for example, the temperature of the cathode during operation is maintained at 1800 K or higher, but there is a problem that it is difficult to obtain a long life of the cathode due to the high temperature. In view of this, in the X-ray generating device 1, as described above, the temperature range of the cathode C made of single crystal material CeB6 is set to 1720 K to 1780 K during operation. In the X-ray generating device 1, by reducing the temperature range of the cathode C compared to the past, the focus size of the electron beam EB is maintained, and the long life of the cathode C is achieved. According to the above temperature range, the focus size of the electron beam EB can be maintained constant for approximately half a year.

[0054] On the other hand, it is considered that when the temperature of the cathode C during operation is reduced, foreign matter is likely to adhere to the surface of the cathode C. If foreign matter adheres to the surface of the cathode C, the emission characteristics of the electron beam EB deteriorate, and there is a concern that the output characteristics of the X-ray XR emitted from the X-ray tube 2 will not be sufficiently obtained. For this reason, in the X-ray generating device 1, in order to clean the surface of the cathode C at an appropriate timing, the control unit 51 executes: the first operation mode related to the output (normal operation) of the X-ray XR shown in Figure 3 and the second operation mode related to the cleaning of the surface of the cathode C.

[0055] Figure 4 FIG. is a block diagram showing the configuration of the control unit related to the first operation mode and the second operation mode. As shown in Figure 4 the control unit 51 includes a power supply control unit 52, a power consumption detection unit 53, a timing unit 54, and a notification unit 55 as components related to the first operation mode and the second operation mode. The power supply control unit 52 is a part that controls the power supply device 56 that supplies current to the cathode C.

[0056] The power supply control unit 52 and the power supply device 56 are communicably connected to each other. The power consumption detection unit 53 is a part that detects the power consumption of the cathode C in the power supply device 56. The power consumption detection unit 53 and the power supply device 56 are communicably connected to each other. The timing unit 54 is a counter that measures time. The notification unit 55 is composed of, for example, a monitor, a speaker, etc.

[0057] In the present embodiment, in addition to the first operation mode and the second operation mode, the control unit 51 also executes a confirmation mode after the execution of the second operation mode. As a component related to the confirmation mode, the X-ray generating apparatus 1 includes an X-ray focus measurement unit 57. The X-ray focus measurement unit 57 corresponds to the electron beam measurement unit of the present disclosure. The X-ray focus measurement unit 57 indirectly measures the state of the electron beam EB based on, for example, the state of the focus of the X-ray XR generated by the electron beam EB emitted from the cathode C. Specifically, the X-ray focus measurement unit 57 includes a pinhole disposed on the axis of the X-ray XR and a camera that captures an image of the focus of the X-ray XR. The X-ray focus measurement unit 57 is communicably connected to the control unit 51.

[0058] Figure 5 It is a flowchart of the control unit in each operation mode. As Figure 5 shown, in the first operation mode, first, the electron beam EB is emitted by supplying current to the cathode C (step S01). After the electron beam EB is emitted, the control unit 51 estimates the temperature of the cathode C based on the power consumption of the cathode C, and controls the supply current to the cathode C to maintain the estimated temperature of the cathode C within a given range for normal operation. Specifically, in the first operation mode, the power consumption detection unit 53 monitors the cathode current and the cathode voltage supplied from the power supply device 56 to the cathode C, and detects the power consumption of the cathode C (step S02). The power consumption detection unit 53 outputs result information indicating the detection result of the power consumption of the cathode C to the power supply control unit 52.

[0059] The power supply control unit 52 estimates the temperature of the cathode C based on the result information received from the power consumption detection unit 53 (step S03). When estimating the temperature of the cathode C, the power supply control unit 52 stores reference data D as shown, for example, Figure 6 shown. This reference data D is data based on the understanding that there is a correlation between the temperature of the cathode C and the power consumption. The reference data D is pre-produced by actually measuring the change in the temperature of the cathode C when the power consumption of the cathode C is changed, and is stored in the power supply control unit 52.

[0060] In Figure 6In the example of [], the estimated temperature of the cathode C has a proportional relationship with the power consumption. That is, the smaller the power consumption of the cathode C, the lower the estimated temperature of the cathode C, and the larger the power consumption of the cathode C, the higher the estimated temperature of the cathode C. The power supply control unit 52 estimates the temperature of the cathode C by referring to the reference data D based on the power consumption of the cathode C, and determines whether the estimated temperature is lower than the given range (here, 1720K to 1780K) for normal operation (step S04). When the estimated temperature is maintained within the given range, the power supply control unit 52 maintains the current power consumption and determines whether a given time has elapsed since the start of the first operation mode (step S05). When the given time has not elapsed, the process returns to step S02, and the subsequent processing is executed again.

[0061] When the estimated temperature is lower than the given range, the power supply control unit 52 controls the power supply device 56 so as to increase the supply current to the cathode C (step S06). After this control, the power supply control unit 52 continues to receive the result information from the power consumption detection unit 53 and determines whether the estimated temperature of the cathode C has returned to the given range (step S07). When it is determined that the estimated temperature of the cathode C has returned to the given range, the process returns to step S02, and the subsequent processing is executed again. When it is determined that the estimated temperature of the cathode C has not returned to the given range, the power supply control unit 52 generates a notification signal indicating this and outputs it to the notification unit 55. The notification unit 55 notifies the outside of the abnormality of the cathode C based on the notification signal, such as by an alarm sound or a warning display (step S08). After this notification, the process ends.

[0062] The second operation mode is implemented after the first operation mode has been implemented for a given time. That is, in step S05 described above, when it is determined that a given time has elapsed since the start of the first operation mode, the second operation mode is implemented. The timing unit 54 measures the time during which the control unit 51 operates in the first operation mode, and at the timing when the measured time reaches the given time, outputs timing information indicating that the first operation mode has been implemented for the given time to the power supply control unit 52. The given time is set to be about 24 hours to 72 hours, for example.

[0063] In the second operation mode, first, the emission of the electron beam EB is stopped (step S09). Next, the cathode C is heated at a cleaning temperature higher than the given range used in the first operation mode. Specifically, in the second operation mode, when the power supply control unit 52 receives the timing information from the timing unit 54, it controls the power supply device 56 so that the estimated temperature of the cathode C is higher than the given range used in the first operation mode (step S10). The cleaning temperature used in the second operation mode is set to, for example, a temperature about 100 K higher than the given range for normal operation used in the first operation mode. In the present embodiment, the cleaning temperature is set in the range of 1820 K to 1880 K. The heating time of the cathode C at the cleaning temperature is set to, for example, 1 minute or more.

[0064] The average residence time τ of gas molecules adsorbed on the solid surface is represented by the following formula (1). In formula (1), τ0 is a constant, E is the adsorption energy, k is the Boltzmann constant, and T is the absolute temperature. According to formula (1), when assuming the adsorption of, for example, water molecules and setting E to 1.0 eV, in the case of increasing the temperature by 100 K from 1720 K, the desorption rate represented by the reciprocal of τ is about 1.5 times. From this, it can be seen that the cleaning temperature used in the second mode is set to a temperature about 100 K higher than the given range for normal operation used in the first operation mode.

[0065] τ = τ0 × exp(E / kT) …(1)

[0066] On the other hand, according to experiments, the cathode evaporation rate at 1820 K is about 2 to 5 times that at 1720 K. Therefore, by making the temperature for normal operation used in the first operation mode 100 K lower than the cleaning temperature used in the second mode, the cathode life can be increased to 2 to 5 times.

[0067] The confirmation mode is implemented after the second operation mode. The confirmation mode is implemented, for example, in parallel with the first operation mode. In the confirmation mode, first, the X-ray focus measurement unit 57 measures the focus size and / or focus shape of the X-ray XR, and based on the measurement results of the focus size and / or focus shape of the X-ray XR, measures the focus size and / or focus shape of the electron beam EB emitted from the cathode C (step S11). The X-ray focus measurement unit 57 outputs the result information indicating the measurement results to the power supply control unit 52. The power supply control unit 52 determines whether the focus size and focus shape of the electron beam EB satisfy the desired size and shape based on the result information from the X-ray focus measurement unit 57 (step S12). When it is determined that the focus size and focus shape of the electron beam EB satisfy the desired size and shape, it is regarded that the cleaning of the surface of the cathode C has been normally completed, and the process is ended (or the implementation of the first operation mode is continued).

[0068] When the power control unit 52 determines that the focus size and / or focus shape of the electron beam EB do not satisfy the desired size and / or shape, it generates an instruction signal for adjusting the electron beam EB. Based on the generated instruction signal, the control unit 51 adjusts the focus size and / or focus shape of the electron beam EB (step S13). The adjustment of the electron beam EB is implemented, for example, by controlling the supply current to the magnetic lens 4 or the like.

[0069] Next, it is determined whether the number of adjustments of the electron beam EB exceeds a given number (step S14). When it is determined that the number of adjustments of the electron beam EB does not exceed the given number, the process returns to step S11 and the subsequent processing is executed again. When it is determined that the number of adjustments of the electron beam EB exceeds the given number, it is regarded that there is an abnormality on the surface of the cathode C, and a notification signal indicating this is generated and output to the notification unit 55. Based on the notification signal, the notification unit 55 notifies the outside of the abnormality of the cathode C by an alarm sound or a warning display or the like (step S15).

[0070] As described above, in the X-ray generating apparatus 1, in the first operation mode, the temperature of the cathode C is estimated based on the power consumption of the cathode C, and the supply current to the cathode C is controlled to maintain the estimated temperature of the cathode C within a given range for normal operation. Thus, the temperature of the cathode C during normal operation can be appropriately maintained, and therefore the emission characteristics (such as the focus size and size shape) of the electron beam EB can be stably maintained within the desired range.

[0071] In addition, in the X-ray generating apparatus 1, considering that foreign matter may adhere to the surface of the cathode C when the first operation mode is implemented, the second operation mode for cleaning the surface of the cathode C is implemented. In the second operation mode, the cathode C is heated to a cleaning temperature higher than the given range of the first operation mode to remove foreign matter from the surface of the cathode C. Thus, the emission characteristics of the electron beam EB can be maintained in good condition. In the X-ray generating apparatus 1, after implementing the first operation mode of maintaining the cathode C at an appropriate temperature for a given time in a given operating condition of the cathode C (a condition in which an appropriate operating state is maintained and a state change based on the operating time can be estimated), the second operation mode is implemented. Thus, the cleaning of the surface of the cathode C can be implemented at an appropriate timing (a timing at which the adhesion of foreign matter to the surface of the cathode C continues), and the second operation mode can be implemented while performing temperature control. Therefore, the cleaning of the surface of the cathode C can be surely and at an appropriate timing.

[0072] In the present embodiment, the cathode C includes an electron emission portion Ca made of a single crystal material. Further, the single crystal material contains cerium or lanthanum. Thus, it is easy to obtain the cathode C having desired electron emission characteristics. Further, in the present embodiment, the single crystal material is CeBe6 containing cerium, and the given range for normal operation in the first operation mode is set to 1720 K to 1780 K. By reducing the temperature of the cathode C during normal operation as compared with the past, the focus size of the electron beam EB is maintained, and the long life of the cathode C is achieved. Since the temperature of the cathode C during operation is reduced, foreign matter is likely to adhere to the surface of the cathode C, but by the above treatment, the surface of the cathode C can be surely cleaned at an appropriate timing.

[0073] In the present embodiment, when the control unit 51 does not maintain the estimated temperature of the cathode C within the given range in the first operation mode even though the supply current to the cathode C has been controlled, the control unit 51 generates a notification signal indicating this. According to this configuration, when the first operation mode is being implemented and the estimated temperature of the cathode C is not maintained within the given range under the control of the supply current to the cathode C, an abnormality of the cathode C can be quickly notified to the outside.

[0074] In the present embodiment, an X-ray focus measurement unit 57 is provided. The X-ray focus measurement unit 57 measures the focus size and / or focus shape of the electron beam EB emitted from the cathode C. When the focus size and / or focus shape of the electron beam EB do not satisfy the desired size and shape after the implementation of the second operation mode, the control unit 51 generates a notification signal indicating this. According to this configuration, when the emission characteristics of the electron beam EB are not improved even after the implementation of the second operation mode, an abnormality of the cathode C can be quickly notified to the outside.

[0075] The present disclosure is not limited to the above embodiment. For example, in the above embodiment, in the confirmation mode following the second operation mode, based on the measurement result of the X-ray focus measurement unit 57, it is indirectly determined whether the focus size and / or focus shape of the electron beam EB satisfy the desired size and / or shape. However, it may also be a form in which an electron beam measurement unit indirectly measures the focus size and focus shape of the electron beam EB.

[0076] The X-ray focus measurement unit 57 can use the focus size and / or focus shape of the X-ray XR as an object for determining whether to generate a notification signal. Since the change in the focus size and / or focus shape of the X-ray XR is caused by the change in the focus size and / or focus shape of the electron beam EB, the measurement of the focus size and / or focus shape of the X-ray XR has the same meaning as the measurement of the focus size and / or focus shape of the electron beam EB.

[0077] In the above-described embodiment, in the confirmation mode subsequent to the second operation mode, based on the measurement result of the X-ray focus measurement unit 57, it is determined whether the focus size and / or focus shape of the electron beam EB satisfy the desired size and / or shape. However, the measurement and determination of the focus size and / or focus shape of the electron beam EB may be in a form manually operated by the user of the X-ray generating apparatus 1. The measurement of the focus size and focus shape of the electron beam EB may be only either one. The confirmation mode may not necessarily be implemented, and after the implementation of the second operation mode, the implementation of the confirmation mode may be omitted and the first operation mode may be implemented.

[0078] Reference Signs

[0079] 1: X-ray generating apparatus

[0080] 2: X-ray tube

[0081] 3: Electron gun

[0082] 11: Target

[0083] 51: Control unit

[0084] 57: X-ray focus measurement unit (electron beam measurement unit)

[0085] C: Cathode

[0086] Ca: Electron emission part

[0087] EB: Electron beam.

Claims

1. An X-ray generating device, comprising: An X-ray tube, which comprises an electron gun having a cathode that emits an electron beam, and a target onto which the electron beam emitted from the electron gun is incident; and A control unit that controls the driving of the X-ray tube, The control unit performs: A first operation mode, which estimates the temperature of the cathode based on the power consumption of the cathode, and controls the supply current to the cathode to maintain the estimated temperature of the cathode within a given range for normal operation; and A second operation mode, which heats the cathode at a cleaning temperature higher than the given range after the first operation mode has been implemented for a given time.

2. The X-ray generating device according to claim 1, wherein The cathode comprises an electron-emitting portion made of a single-crystal material.

3. The X-ray generating device according to claim 2, wherein The single-crystal material comprises cerium or lanthanum.

4. The X-ray generating device according to claim 2 or 3, wherein The single-crystal material comprises cerium, The given range for normal operation in the first operation mode is set to 1720K to 1780K.

5. The X-ray generating device according to any one of claims 1 to 4, wherein When the control unit fails to maintain the estimated temperature of the cathode within the given range even after controlling the supply current to the cathode in the first operation mode, it generates a notification signal indicating this.

6. The X-ray generating device according to any one of claims 1 to 5, wherein Comprises: An electron beam measurement unit that measures the focus size and / or focus shape of the electron beam emitted from the cathode, When the focus size and / or focus shape of the electron beam do not meet the desired size and / or shape after the second operation mode is implemented, the control unit generates a notification signal indicating this.

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