X-ray generator

Abstract

To provide an X-ray generator capable of avoiding damage to a target even when discharge occurs between a cathode electrode and an adjustment electrode.SOLUTION: An X-ray generator 1 includes a cathode electrode 5 that emits electrons E, an adjustment electrode 7 that adjusts an emission amount of the electrons E from the cathode electrode 5, an extraction electrode 8 that extracts the electrons E from the cathode electrode 5, a target 9 that generates an X-ray R by incidence of the electrons E, a discharge detection unit 15 that detects discharge between the cathode electrode 5 and the adjustment electrode 7, and a potential switching unit 16 that sets a potential of the extraction electrode 8 to be higher than a potential of the cathode electrode 5 during a normal operation and sets the potential of the extraction electrode 8 to be equal to or lower than the potential of the cathode electrode 5 during discharge detection.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to x-ray generating devices. [Background technology]

[0002] An example of a conventional X-ray generating device is a radiation generating unit described in Patent Document 1. This conventional radiation generating unit includes a cathode electrode heated by a heater, an extraction electrode that extracts electrons from the heated cathode electrode, a heater power supply connected to the heater, an electrode power supply connected to the extraction electrode, and a target that receives electrons from the cathode electrode and generates radiation.

[0003] In the X-ray generators described above, discharges caused by various factors can be a problem. For example, the X-ray generator described in Patent Document 2 focuses on discharges that occur within the casing. When a discharge occurs within the casing, the voltage (tube voltage) applied between the cathode electrode and the target drops instantaneously. If the bias voltage applied from the Wehnelt is maintained at a constant value at this time, the focal area of ​​the X-rays formed on the target will be excessively narrowed, damaging the target. The X-ray generator described in Patent Document 2 is equipped with a means for detecting discharges that occur within the casing, and when a discharge is detected, the bias voltage applied from the Wehnelt is controlled to prevent the X-ray focal point from becoming smaller than the allowable limit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-130732 [Patent Document 2] Japanese Patent Application Publication No. 8-94546 Summary of the Invention [Problem to be solved by the invention]

[0005] Discharges in X-ray tubes can also occur at specific locations within the casing. For example, if an adjustment electrode for adjusting the amount of electrons emitted from a cathode electrode is disposed within the X-ray tube, it is possible that some of the material constituting the cathode electrode may fly from the cathode electrode heated by a heater and adhere to the adjustment electrode. When deposits accumulate on the adjustment electrode, the gap between the cathode electrode and the adjustment electrode narrows, reducing the inherent voltage resistance characteristics and making discharges more likely to occur. If a discharge occurs between the cathode electrode and the adjustment electrode, the cathode electrode and the adjustment electrode will be at the same potential during the discharge, making it impossible to control the amount of electrons emitted from the cathode electrode, which was previously controlled by the potential difference between the cathode electrode and the adjustment electrode. In this case, there is a risk of excessive electrons being emitted from the cathode electrode. If excessive electrons are emitted from the cathode electrode, excessive electrons will be incident on the target, potentially damaging the target.

[0006] An object of the present disclosure is to provide an X-ray generating device that can avoid damage to the target even when a discharge occurs between the cathode electrode and the adjustment electrode. [Means for solving the problem]

[0007] An X-ray generating device according to one aspect of the present disclosure includes a cathode electrode that emits electrons, an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode, an extraction electrode that extracts electrons from the cathode electrode, a target that generates X-rays when electrons are incident on it, a discharge detection unit that detects discharge between the cathode electrode and the adjustment electrode, and a potential switching unit that makes the potential of the extraction electrode higher than the potential of the cathode electrode during normal operation and makes the potential of the extraction electrode the same as or lower than the potential of the cathode electrode when a discharge is detected.

[0008] In this X-ray generator, when a discharge between the cathode electrode and the adjustment electrode is detected, the potential switching unit changes the potential of the extraction electrode to the same potential as or lower than the potential of the cathode electrode. This reduces or eliminates the initial velocity of electrons emitted from the cathode electrode, thereby suppressing the amount of electrons irradiated onto the target. This makes it possible to avoid damage to the target even if a discharge occurs between the cathode electrode and the adjustment electrode.

[0009] The potential switching unit may include a semiconductor switch. In this case, the high-speed response of the semiconductor switch allows the potential switching unit to quickly switch the potential of the cathode electrode between normal operation and discharge detection. When a discharge occurs between the cathode electrode and the adjustment electrode, the amount of electrons irradiated onto the target can be quickly reduced, thereby more reliably avoiding damage to the target.

[0010] The semiconductor switch may be made up of a plurality of transistors connected in series and parallel to each other, in which case the withstand voltage of the semiconductor switch constituting the potential switching unit is improved, and the potential of the cathode electrode can be switched more safely.

[0011] The potential switching unit may further include a diode connected in series to the plurality of transistors and a damping resistor connected in series to the diode. In this case, the diode and damping resistor connected in series can suppress ringing that occurs when the potential of the cathode electrode switches between normal operation and discharge detection. Therefore, the potential of the cathode electrode can be switched more quickly.

[0012] The potential switching unit may be configured by a gas arrester, in which case a sufficient withstand voltage can be applied to the potential switching unit with a relatively simple circuit configuration.

[0013] The X-ray generator may further include a reverse bias voltage source connected between the cathode electrode and the extraction electrode, and the potential switching unit may apply a voltage from the reverse bias voltage source to make the potential of the extraction electrode lower than the potential of the cathode electrode when detecting a discharge. In this case, the reverse bias voltage source can more reliably and quickly suppress the amount of electrons irradiated onto the target.

[0014] The discharge detector may include at least one of a current detection resistor and a current transformer, in which case the large current generated when a discharge occurs can be appropriately detected as an electrical signal by the current detection resistor and / or the current transformer.

[0015] The discharge detection unit may detect the presence or absence of a discharge based on the magnitude of at least one of the current flowing through the cathode electrode, the current flowing through the adjustment electrode, and the current flowing through the target during discharge detection. By detecting the current at these positions, the occurrence of a discharge can be suitably detected. [Effects of the Invention]

[0016] According to the present disclosure, even if a discharge occurs between the cathode electrode and the adjusting electrode, damage to the target can be avoided. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a configuration of an X-ray generating device according to an embodiment of the present disclosure. [Figure 2] Fig. 2(a) is a diagram showing a current detection signal, Fig. 2(b) is a diagram showing a switching signal, Fig. 2(c) is a diagram showing the potential of a cathode electrode, and Fig. 2(d) is a diagram showing the potential of a cathode electrode in a potential switching unit according to a comparative example. [Figure 3] FIG. 2 is a diagram showing a circuit configuration of a potential switching unit. [Figure 4] 10 is a diagram illustrating the configuration of a potential switching section 16A according to the second embodiment. FIG. [Figure 5] FIG. 10 is a schematic diagram showing the configuration of an X-ray generating device according to a first modified example. [Figure 6] FIG. 10 is a schematic diagram showing the configuration of an X-ray generating device according to a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, a preferred embodiment of an X-ray generator according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0019] [First embodiment] 1 is a schematic diagram showing the configuration of an X-ray generator according to an embodiment of the present disclosure. As shown in the figure, the X-ray generator 1 includes an X-ray tube 2 and a drive circuit 3. The X-ray tube 2 is a transmission type X-ray tube, and includes a cathode electrode 5, a heater 6, an adjustment electrode 7, an extraction electrode 8, and a target 9 within a vacuum housing 4. The cathode electrode 5, the heater 6, the adjustment electrode 7, and the extraction electrode 8 constitute an electron gun EG.

[0020] The vacuum housing 4 is formed into a hollow cylindrical shape by airtightly joining a head portion made of, for example, a metal material and a bulb portion made of an insulating material. Examples of metal materials that make up the head portion include stainless steel, copper, copper alloys, iron alloys, and nickel alloys. Examples of insulating materials that make up the bulb portion include glass and ceramics. A window member 10 is provided at the tip of the head portion. The window member 10 is made of an X-ray transparent material such as beryllium, aluminum, or diamond and is formed into a plate shape with the tube axis as its center line.

[0021] The cathode electrode 5 is an electrode that emits electrons E. The cathode electrode 5 is, for example, an indirectly heated cathode that emits electrons E when heated by a heater 6 in an energized state. The heater 6 is a part that heats the cathode electrode 5. The heater 6 is composed of a filament that generates heat when energized. The electrons E emitted from the cathode electrode 5 pass through the electron passing hole 7a of the adjustment electrode 7 and the electron passing hole 8a of the extraction electrode 8 and proceed toward the target 9.

[0022] The adjustment electrode 7 is a first grid electrode that adjusts the amount of electrons emitted from the cathode electrode 5. The adjustment electrode 7 controls the amount of electrons emitted from the cathode electrode 5 based on the voltage applied to the adjustment electrode 7. Here, the electron emission amount refers to the amount of electrons E that pass through the adjustment electrode 7 and proceed toward the target 9, out of the electrons E emitted from the cathode electrode 5 by heating with the heater 6. The adjustment electrode 7 has electron passing holes 7a that have, for example, a circular cross section. The adjustment electrode 7 limits the amount of electrons E that pass through the electron passing holes 7a and proceed toward the extraction electrode 8. The electron passing holes 7a allow the electrons E emitted from the cathode electrode 5 to pass toward the extraction electrode 8.

[0023] The extraction electrode 8 is a second grid electrode that controls the trajectory of the electrons E from the cathode electrode 5 by forming an electrostatic lens. The extraction electrode 8 functions as an electrode that forms an electric field to extract electrons from the cathode electrode 5. The extraction electrode 8 also functions as a focusing electrode that focuses the electrons E that have been emitted from the cathode electrode 5 and passed through the adjustment electrode 7 onto the target 9 as an electron beam. The extraction electrode 8 has an electron passing hole 8a that has, for example, a circular cross section. The electron passing hole 8a is arranged coaxially with the electron passing hole 7a of the adjustment electrode 7, and allows the electrons E that have passed through the electron passing hole 7a to pass towards the target 9.

[0024] The target 9 is a part that generates X-rays R when electrons E are incident on it. The target 9 is provided on the inner (vacuum side) surface of the window member 10 on the tube axis of the vacuum housing 4. The target 9 is, for example, a film formed on the inner surface of the window member 10. Examples of materials that can be used for the target 9 include tungsten, molybdenum, and copper. The target 9 is electrically connected to the head of the vacuum housing 4, and is at ground potential GND, for example.

[0025] 1, the drive circuit 3 includes a heater power supply 11, a cathode electrode power supply 12, an adjustment electrode power supply 13, and an extraction electrode power supply 14. The heater power supply 11 is electrically connected to the heater 6 and supplies a voltage to the heater 6. The cathode electrode power supply 12 is electrically connected to the cathode electrode 5 and supplies a voltage to the cathode electrode 5. The adjustment electrode power supply 13 is electrically connected to the adjustment electrode 7 and supplies a voltage to the adjustment electrode 7. The extraction electrode power supply 14 is electrically connected to the extraction electrode 8 and supplies a voltage to the extraction electrode 8.

[0026] In the X-ray generator 1 configured as described above, during normal operation in which X-rays R are output from the target 9, a negative high voltage is applied to the X-ray tube 2, for example, with the potential of the target 9 as a reference (ground potential GND). The X-ray tube 2 of this embodiment is a so-called triode X-ray tube, which has, in addition to the cathode electrode 5 and target 9 described above, electrodes such as the adjustment electrode 7 and extraction electrode 8 that control the electrons E emitted from the cathode electrode 5 and directed toward the target 9, and the parameters of the electrons E emitted from the cathode electrode 5 and the X-rays R generated from the target 9 are controlled by the cathode electrode 5, the adjustment electrode 7, and the extraction electrode 8.

[0027] The extraction electrode power supply 14 supplies a negative high voltage, for example, between −130 V and 0 V, to the extraction electrode 8. The cathode electrode power supply 12 supplies a negative high voltage, for example, between −2 kV and 0 V, to the cathode electrode 5, using the voltage generated by the extraction electrode power supply 14 as an offset. The adjustment electrode power supply 13 supplies a negative high voltage, for example, between −500 V and 0 V, to the adjustment electrode 7, using the voltage generated by the cathode electrode power supply 12 as an offset. As a result, during normal operation, the potential of the extraction electrode 8 is higher than the potential of the cathode electrode 5. The potential of the cathode electrode 5 is also higher than the potential of the adjustment electrode 7.

[0028] In the X-ray generator 1, electrons E are emitted from the cathode electrode 5 by application of heat from the heater 6. The amount of electrons emitted from the cathode electrode 5 is controlled by the potential difference between the cathode electrode 5 and an adjustment electrode 7. The initial velocity of the electrons E is controlled by the potential difference between the cathode electrode 5 and an extraction electrode 8. The electrons E that reach the extraction electrode 8 are accelerated by the potential difference between the extraction electrode 8 and a target 9 (here, ground potential GND), and collide with the target 9 while being focused.

[0029] X-rays R generated by the collision of electrons E on the target 9 are emitted to the outside of the X-ray tube 2 through the window member 10. The brightness of the X-rays R is controlled by the potential difference between the cathode electrode 5 and the adjustment electrode 7. The energy of the X-rays R is controlled by the potential (acceleration voltage) of the extraction electrode 8.

[0030] In the X-ray generator 1 described above, a discharge can occur inside the X-ray tube 2. In the X-ray generator 1 in which an adjustment electrode 7 for adjusting the amount of electrons emitted from the cathode electrode 5 is disposed within the X-ray tube 2, for example, when the heater 6 is used to raise the temperature, some of the material constituting the cathode electrode 5 may fly and adhere to the adjustment electrode 7. Furthermore, not only the material constituting the cathode electrode 5 but also various other foreign matter, such as the material constituting the heater 6 and foreign matter mixed into the X-ray tube, may adhere to the adjustment electrode 7. When deposits accumulate on the adjustment electrode 7, the gap between the cathode electrode 5 and the adjustment electrode 7 narrows, reducing the inherent voltage resistance characteristics and making discharge more likely to occur. When a discharge occurs between the cathode electrode 5 and the adjustment electrode 7, the cathode electrode 5 and the adjustment electrode 7 are at the same potential during the discharge, and therefore, the amount of electrons emitted from the cathode electrode 5, which was previously controlled by the potential difference between the cathode electrode 5 and the adjustment electrode 7, cannot be controlled temporarily. In this case, electrons from the cathode electrode 5 are emitted without being controlled according to the potential difference between the cathode electrode 5 and the target 9, which may result in excessive electron emission from the cathode electrode 5. If excessive electrons are emitted from the cathode electrode 5, excessive electrons will be incident on the target 9, which may damage the target 9.

[0031] Therefore, in the X-ray generator 1, the drive circuit 3 is provided with a discharge detection unit 15 that detects discharge between the cathode electrode 5 and the adjustment electrode 7, a potential switching unit 16 that switches the potential of the cathode electrode 5 when a discharge is detected, and a control unit 17. In this embodiment, the discharge detection unit 15 is configured to include at least one of a current detection resistor and a current transformer, and functions as an ammeter provided between the cathode electrode 5 and the cathode electrode power supply 12 (on the negative terminal side of the cathode electrode power supply 12).

[0032] When a discharge occurs between the cathode electrode 5 and the adjustment electrode 7, a current due to the discharge (discharge current) flows from the cathode electrode 5 to the discharge detection unit 15. The discharge current can be approximately 10 times larger than the current due to normal operation (normal current). When the discharge detection unit 15 is a current detection resistor, the discharge detection unit 15 converts the discharge current into a current detection signal Idet in the current detection resistor. When the discharge detection unit 15 is a current transformer, the current transformer may include a primary winding and a secondary winding. The discharge detection unit 15 reduces or increases the magnitude of the current flowing in the primary winding depending on the turns ratio between the primary winding and the secondary winding, and converts the current into a current detection signal Idet in the current detection resistor connected as a load to the secondary winding.

[0033] The discharge detection unit 15 constantly measures the magnitude of the current during normal operation. The discharge detection unit 15 transmits the measured value as a current detection signal Idet to the control unit 17. When the control unit 17 recognizes based on the current detection signal Idet that the discharge detection unit 15 has detected a discharge current (that is, the magnitude of the current has increased significantly), it transmits a switching signal Sc1 to the potential switching unit 16.

[0034] The control unit 17 is physically configured to include a processor such as a CPU, and storage media such as a RAM, a ROM, etc. The control unit 17 may be a smartphone or tablet terminal that is integrally equipped with a display unit and an input unit, or may be configured with a microcomputer, an FPGA (Field-Programmable Gate Array), etc.

[0035] 2(a) and 2(b), for example, the control unit 17 detects that the current detection signal Idet has exceeded the threshold value Ith, and transmits a switching signal Sc1, which is a pulse signal, to the potential switching unit 16. There is a predetermined time difference between the timing at which it detects that the current detection signal Idet has exceeded the threshold value Ith and the timing at which it transmits the switching signal Sc1 to the potential switching unit 16, and the time T1 from when a discharge occurs (from when the current detection signal Idet rises) to when the switching signal Sc1 is transmitted is, for example, 150 ns.

[0036] 1, the potential switching unit 16 includes a first contact terminal P1, a second contact terminal P2, and a third contact terminal P3. During normal operation, the potential switching unit 16 connects the first contact terminal P1 and the third contact terminal P3. This connects the cathode electrode 5 and the cathode electrode power supply 12. Therefore, during normal operation, the potential of the extraction electrode 8 is higher than the potential of the cathode electrode 5. Under normal conditions, a current flows from the first contact terminal P1 to the third contact terminal P3.

[0037] When the switching signal Sc1 is input, the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2. This connects the cathode electrode 5 and the extraction electrode power supply 14. That is, during discharge detection, a voltage is supplied to the cathode electrode 5 from the extraction electrode power supply 14, not from the cathode electrode power supply 12. When the first contact terminal P1 and the second contact terminal P2 are connected, the potential of the extraction electrode 8 is higher than the potential of the cathode electrode 5, so a discharge-time current flows from the second contact terminal P2 to the first contact terminal P1. As a result, the potential Vk of the cathode electrode becomes the same as the potential Vg of the extraction electrode 8, as shown in FIG. 2(c).

[0038] The time T2 from when a discharge occurs (when the current detection signal Idet rises) until the potential Vk of the cathode electrode becomes the same as the potential Vg of the extraction electrode 8 is, for example, 400 ns. The potential switching unit 16 switches the connection relationship of the first contact terminal P1, the second contact terminal P2, and the third contact terminal P3, thereby making the potential Vg of the extraction electrode 8 higher than the potential Vk of the cathode electrode 5 during normal operation and making the potential Vg of the extraction electrode 8 the same as the potential Vk of the cathode electrode 5 when a discharge is detected.

[0039] 2(b), after a stabilization time T3 has elapsed since the control unit 17 transmitted the switching signal Sc1 to the potential switching unit 16, the control unit 17 transmits the switching signal Sc2 to the potential switching unit 16. Here, the stabilization time T3 is, for example, the time required for a discharge to converge after it occurs between the cathode electrode 5 and the adjustment electrode 7.

[0040] When the switching signal Sc2 is input, the potential switching unit 16 connects the first contact terminal P1 and the third contact terminal P3. This connects the cathode electrode 5 and the cathode electrode power supply 12, and normal current again flows from the first contact terminal P1 to the third contact terminal P3. As a result, as shown in FIG. 2(c), the potential Vk of the cathode electrode becomes lower than the potential Vg of the extraction electrode 8.

[0041] Next, a detailed configuration of the above-mentioned potential switching unit 16 will be described. FIG. 3 is a diagram showing a circuit configuration of the potential switching unit. The potential switching unit 16 includes a semiconductor switch. In this embodiment, the semiconductor switch is configured of a plurality of transistors (e.g., MOSFETs) connected in series and parallel to each other. In this embodiment, the semiconductor switch will be described as a semiconductor switch configured of a plurality of FETs 161 to 164. The FETs 161 and 162 connected in cascade to each other between the first contact terminal P1 and the third contact terminal P3 are arranged symmetrically with respect to the FETs 163 and 164 connected in cascade to each other between the first contact terminal P1 and the second contact terminal P2. The FETs 162 and 163 are connected in cascade to each other at the first contact terminal P1. Each of the plurality of FETs 161 to 164 is a FET capable of high withstand voltage and high switching performance. Each of the plurality of FETs 161 to 164 is, for example, a silicon carbide (SiC) FET or a gallium nitride (GaN) FET. In this embodiment, the state in which the plurality of FETs 161 to 164 having such characteristics are connected in cascade is referred to as a plurality of series-parallel connected FETs 161 to 164. The potential switching unit 16 further includes diodes 165 and 166 connected in series to the plurality of FETs 161 to 164, and damping resistors 167 and 168 connected in series to the diodes.

[0042] The specific configuration of the potential switching section 16 is as follows. Of the multiple FETs 161 to 164, the drain terminal of FET 162 is connected to the first contact terminal P1. The source terminal of FET 162 is connected to the drain terminal of FET 161. The source terminal of FET 161 is connected to the anode terminal of diode 165. The cathode terminal of diode 165 is connected to one end of damping resistor 167. The other end of damping resistor 167 is connected to the third contact terminal P3.

[0043] Of the multiple FETs 161 to 164, the source terminal of FET 163 is connected to the first contact terminal P1. The drain terminal of FET 163 is connected to the source terminal of FET 164. The drain terminal of FET 164 is connected to the cathode terminal of a diode 166. The anode terminal of the diode 166 is connected to one end of a damping resistor 168. The other end of the damping resistor 168 is connected to the second contact terminal P2.

[0044] In the potential switching unit 16, during normal operation, a switching signal Sc2 is input from the control unit 17 to the gate terminals of FET 161 and FET 162, turning on FET 161 and FET 162. On the other hand, FET 163 and FET 164 are turned off. As a result, the potential Vk of the cathode electrode 5 drops to a potential lower than the potential Vg of the extraction electrode 8. When a discharge is detected, a switching signal Sc1 is input from the control unit 17 to the gate terminals of FET 163 and FET 164, turning on FET 163 and FET 164. On the other hand, FET 161 and FET 162 are turned off. As a result, the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg of the extraction electrode 8.

[0045] In this embodiment, the number of FETs (FETs 161 and 162) that contribute to a drop in the potential Vk of the cathode electrode 5 is the same as the number of FETs (FETs 163 and 164) that contribute to an increase in the potential Vk of the cathode electrode 5. This is because, when the FETs 161 to 164 are all the same type of FET, the withstand voltage value of the FET that contributes to a drop in the potential Vk of the cathode electrode 5 is the same as the withstand voltage value of the FET that contributes to an increase in the potential Vk of the cathode electrode 5. If the FETs 161 to 164 are not all the same type of FET and have different withstand voltage values, the numbers do not necessarily need to be the same.

[0046] The diode 166 and the damping resistor 168 suppress ringing that occurs when the potential Vk of the cathode electrode rises to the same potential as the potential Vg of the extraction electrode 8. Similarly, the diode 165 and the damping resistor 167 suppress ringing that occurs when the potential Vk of the cathode electrode drops to a potential lower than the potential Vg of the extraction electrode 8. FIG. 2(d) is a diagram showing the potential Vk of the cathode electrode 5 when the potential switching unit 16 does not include the diodes 165 and 166 and the damping resistors 167 and 168. In the example of FIG. 2(d), ringing occurs when the potential Vk of the cathode electrode 5 rises and falls, compared to the potential Vk of the cathode electrode 5 in FIG. 2(c). Such ringing is a phenomenon that should be suppressed from the viewpoint of not supplying an excessive voltage to the cathode electrode 5 and from the viewpoint of allowing the potential switching unit 16 to stably and quickly switch the potential Vk of the cathode electrode 5. As shown in FIG. 2(d), the time ΔT1 required for the ringing to reach its maximum positive amplitude when the potential Vk rises is equal to the time ΔT2 required for the ringing to reach its maximum negative amplitude when the potential Vk falls.

[0047] Next, the operations of the diodes 165 and 166 and the damping resistors 167 and 168 will be described. A parasitic capacitance Cds exists between the drain terminal and source terminal of each FET. The parasitic capacitance of the diodes 165 and 166 is smaller than the parasitic capacitance Cds. For example, during normal operation, when the FETs 163 and 164 are off, the parasitic capacitances Cds of the FETs 163 and 164 and the inductance component of the wiring pattern may form a resonance component. In this state, when the FETs 163 and 164 are on during discharge detection, the resonance component is formed, and ringing occurs when the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg of the extraction electrode 8.

[0048] In contrast, in the potential switching unit 16, the diode 166 is connected in series with the FETs 163 and 164, and thus the parasitic capacitance in the diode 166 and the parasitic capacitance Cds are combined. Because the parasitic capacitance of the diode 166 is smaller than the parasitic capacitance Cds, the combined capacitance is smaller than the parasitic capacitance Cds of the FETs 163 and 164. In addition, by connecting a damping resistor 168 that suppresses ringing in series with the diode 166, it is possible to suppress ringing that occurs when the potential Vk of the cathode electrode rises. Similarly, in the potential switching unit 16, the diode 165 is connected in series with the FETs 161 and 162, and thus the parasitic capacitance in the diode 165 and the parasitic capacitance Cds are combined. Because the parasitic capacitance of the diode 165 is smaller than the parasitic capacitance Cds, the combined capacitance is smaller than the parasitic capacitance Cds of the FETs 161 and 162. In addition, by connecting a damping resistor 167 for suppressing ringing in series with the diode 165, it is possible to suppress ringing that occurs when the potential Vk of the cathode electrode drops.

[0049] Even if only the damping resistors 167 and 168 are provided without the diodes 165 and 166, the ringing suppression effect can be achieved. However, in this case, the resistance values ​​of the damping resistors 167 and 168 become large, which may delay the response of the potential Vk of the cathode electrode 5. Therefore, in this embodiment, it is preferable to provide the diodes 165 and 166.

[0050] The potential switching unit 16 further includes decoupling capacitors 169 and 170 connected in series with each other, a resistor 173 connected in parallel with the decoupling capacitor 169, and a resistor 174 connected in parallel with the decoupling capacitor 170. The terminal of the decoupling capacitor 169 that is not connected to the decoupling capacitor 170 is connected to a node between the third contact terminal P3 and the damping resistor 167. The terminal of the decoupling capacitor 170 that is not connected to the decoupling capacitor 169 is connected to a node between the second contact terminal P2 and the damping resistor 168.

[0051] The decoupling capacitors 169, 170 supply electric charge to the cathode electrode 5 when the potential switching unit 16 switches the potential of the cathode electrode Vk. This prevents the potential Vk of the cathode electrode 5 from fluctuating when the potential Vk of the cathode electrode is switched. The decoupling capacitors 169, 170 are preferably arranged near the cathode electrode 5 to minimize the influence of inductance due to wiring.

[0052] Resistors 173 and 174 determine the potentials of decoupling capacitors 169 and 170. Without resistors 173 and 174, the potentials of decoupling capacitors 169 and 170 may not be stable and may fluctuate excessively when the potential Vk of the cathode electrode is switched. In such a case, by connecting resistors 173 and 174 in parallel with the capacitors, the potentials of decoupling capacitors 169 and 170 are always equally divided, thereby suppressing fluctuations in the voltage applied to the capacitors. This prevents the capacitors 169 and 170 from being subjected to a voltage higher than their designed withstand voltage.

[0053] In the X-ray generator 1 described above, when a discharge between the cathode electrode 5 and the adjustment electrode 7 is detected, the potential switching unit 16 makes the potential Vg of the extraction electrode 8 equal to or lower than the potential Vk of the cathode electrode 5. This reduces or eliminates the initial velocity of the electrons E emitted from the cathode electrode 5, thereby suppressing the amount of electrons irradiated onto the target 9. This makes it possible to avoid damage to the target even when a discharge occurs between the cathode electrode 5 and the adjustment electrode 7.

[0054] The potential switching unit 16 includes a semiconductor switch. In this case, the high-speed response of the semiconductor switch allows the potential switching unit 16 to quickly switch the potential Vk of the cathode electrode 5 between normal operation and discharge detection. When a discharge occurs between the cathode electrode 5 and the adjustment electrode 7, it becomes possible to quickly suppress the amount of electrons irradiated onto the target 9, thereby more reliably avoiding damage to the target 9.

[0055] The semiconductor switch is composed of a plurality of transistors (MOSFETs, hereinafter referred to as FETs) 161 to 164 connected in series and parallel to one another. In this case, the parasitic capacitance components of the semiconductor switches constituting the potential switching unit 16 are reduced, and the withstand voltage is improved, so that the potential Vk of the cathode electrode 5 can be switched more safely.

[0056] The potential switching unit 16 further includes diodes 165, 166 connected in series to the plurality of FETs 161 to 164, and damping resistors 167, 168 connected in series to the diodes 165, 166. In this case, the diodes 165, 166 and the damping resistors 167, 168 connected in series with each other can suppress ringing that occurs when the potential Vk of the cathode electrode 5 switches between normal operation and discharge detection. Therefore, the potential Vk of the cathode electrode 5 can be switched at higher speed.

[0057] The discharge detector 15 includes at least one of a current detection resistor and a current transformer. In this case, the current detection resistor and / or the current transformer can appropriately detect a large current generated when a discharge occurs as a current detection signal Idet.

[0058] [Second embodiment] 4 is a diagram illustrating the configuration of a potential switching unit 16A according to the second embodiment. The potential switching unit 16A differs from the potential switching unit 16 according to the first embodiment in that it includes a gas arrester 171 and a gas arrester driving circuit 172 instead of a semiconductor switch. The gas arrester 171 includes a pair of electrodes 171a and 171b facing each other. One electrode 171a is connected to a first contact terminal P1 via a diode 172h included in the gas arrester driving circuit 172. The other electrode 171b is connected to a second contact terminal P2.

[0059] The gas arrester driving circuit 172 is a circuit that generates a high voltage to be supplied between a pair of electrodes 171a, 171b of the gas arrester 171. The gas arrester driving circuit 172 includes a transistor 172a and a transformer 172b including a primary winding and a secondary winding. When the control unit 17 recognizes, based on the current detection signal Idet, that a discharge current has been detected in the discharge detection unit 15, the control unit 17 generates a driving signal Sc1A and transmits the driving signal Sc1A to a control terminal of the transistor 172a. The driving signal Sc1A may be, for example, a pulse wave oscillating at a predetermined frequency or a PWM wave. In the example of FIG. 4, a clamp resistor 172c is provided between the control terminal of the transistor 172a and the other electrode 171b.

[0060] The transistor 172a switches the voltage generated by the power supply Vcc based on the drive signal Sc1A and supplies it to the primary winding of the transformer 172b. As illustrated in FIG. 4, a resistor 172d and a diode 172e may be provided between the power supply Vcc and the primary winding. A capacitor 172f may also be provided in parallel with the primary winding of the transformer 172b and the transistor 172a. The transformer 172b amplifies the switched voltage in accordance with the turns ratio between the primary winding and the secondary winding.

[0061] The capacitor 172g functions, for example, as a coupling capacitor. When a discharge is detected, the capacitor 172g switches the transformer 172b and instantaneously generates a negative high-voltage pulse, thereby making the gas arrester 171 conductive. The diode 172h functions, for example, as a blocking diode. When a discharge is detected, the diode 172h prevents current from flowing to the cathode electrode power supply 12 and generates a high voltage between 171a and 171b that is sufficient to discharge the gas arrester 171.

[0062] When a high voltage is supplied between the pair of electrodes 171a, 171b, the pair of electrodes 171a, 171b is short-circuited, and as a result, the first contact terminal P1 and the second contact terminal P2 are connected, and the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg of the extraction electrode 8.

[0063] In the potential switching unit 16A, the first contact terminal P1 and the third contact terminal P3 are always connected, so when the first contact terminal P1 and the second contact terminal P2 are connected, the cathode electrode power supply 12 may be short-circuited and damaged. Therefore, when detecting a discharge, the control unit 17 drives the gas arrester drive circuit 172 for a stabilization time T3 and stops the cathode electrode power supply 12. Then, after the stabilization time T3 has elapsed, the control unit 17 stops the gas arrester drive circuit 172 and drives the cathode electrode power supply 12.

[0064] The potential switching unit 16A has the gas arrester 171, so that a sufficient withstand voltage can be applied to the potential switching unit with a relatively simple circuit configuration.

[0065] [Variations] Although the embodiments of the present disclosure have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

[0066] 5 is a schematic diagram showing the configuration of an X-ray generator according to a first modification. The X-ray generator 1A according to the first modification differs from the X-ray generator 1 according to the embodiment in that it includes a reverse bias voltage source 18 between the cathode electrode 5 and the extraction electrode 8. When detecting a discharge, the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2, thereby connecting the positive terminal of the reverse bias voltage source 18 to the cathode electrode 5 and the negative terminal of the reverse bias voltage source 18 to the extraction electrode 8. As a result, the potential switching unit 16 controls the reverse bias voltage source 18 to make the potential Vg of the extraction electrode 8 lower than the potential Vk of the cathode electrode 5 when detecting a discharge. In this case, the reverse bias voltage source 18 can more reliably and quickly reduce the amount of electrons irradiated onto the target.

[0067] In the above-described embodiment and modified examples, the position at which the discharge detection unit 15 is provided is not limited to between the cathode electrode 5 and the cathode electrode power supply 12 (on the negative terminal side of the cathode electrode power supply 12). The discharge detection unit 15 may be provided between the adjusting electrode 7 and the negative terminal of the adjusting electrode power supply 13. In this case, the discharge detection unit 15 detects the current flowing from the adjusting electrode 7 to the negative terminal of the adjusting electrode power supply 13 (the current flowing through the adjusting electrode 7) as the discharge current. The discharge detection unit 15 may be provided between the positive terminal of the adjusting electrode power supply 13 and the cathode electrode 5. In this case, the discharge detection unit 15 detects the current flowing from the positive terminal of the adjusting electrode power supply 13 to the cathode electrode 5 as the discharge current. The discharge detection unit 15 may be provided between the target 9 and ground potential GND. In this case, the discharge detection unit 15 detects the current flowing through the target 9 as the discharge current.

[0068] The discharge detection unit 15 may be provided between the third contact terminal P3 and the negative terminal of the cathode electrode power supply 12. In this case, the discharge detection unit 15 detects the current flowing between the third contact terminal P3 and the negative terminal of the cathode electrode power supply 12 as the discharge current. The discharge detection unit 15 may be provided between a node N, to which the extraction electrode 8 is connected between the positive terminal of the cathode electrode power supply 12 and the negative terminal of the extraction electrode power supply 14, and the positive terminal of the cathode electrode power supply 12. In this case, the discharge detection unit 15 detects the current flowing between the node N and the positive terminal of the cathode electrode power supply 12 as the discharge current. The discharge detection unit 15 may also function as a voltmeter. In this case, the discharge detection unit 15 is provided, for example, in parallel with the adjustment electrode power supply 13 and detects fluctuations in the magnitude of the voltage supplied to the adjustment electrode 7 during discharge detection.

[0069] As described above, when detecting a discharge, the discharge detection unit 15 may detect the presence or absence of a discharge based on the magnitude of at least one of the current flowing through the cathode electrode 5, the current flowing through the adjustment electrode 7, and the current flowing through the target 9. By detecting the current at these positions, the occurrence of a discharge can be suitably detected.

[0070] Fig. 6 is a schematic diagram showing the configuration of an X-ray generator according to a second modified example. As shown in Fig. 6, the X-ray generator 1B differs from the X-ray generator 1 in that the adjusting electrode power supply 13 is electrically connected to the adjusting electrode 7 and also to the extraction electrode 8. In this case, the adjusting electrode power supply 13 supplies a negative high voltage of, for example, -2.5 kV or more and -2 kV or less to the adjusting electrode 7, using the voltage generated by the extraction electrode power supply 14 as an offset.

[0071] In the above-described embodiment and modified examples, the potential of the extraction electrode 8 may be used as the reference (ground potential GND). In this case, the target 9 may be grounded via the extraction electrode power supply .

[0072] In the above-described embodiment and modified examples, when the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2 during discharge detection, the potential switching unit 16 may maintain the first contact terminal P1 and the second contact terminal P2 in a connected state. In this case, the control unit 17 does not need to control the potential switching unit 16 to change from the connected state during discharge detection (the state in which the first contact terminal P1 and the second contact terminal P2 are connected) to the connected state during normal operation (the state in which the first contact terminal P1 and the third contact terminal P3 are connected). For example, the control unit 17 does not need to transmit the switching signal Sc2 to the potential switching unit 16 after the stabilization time T3 has elapsed since transmitting the switching signal Sc1 to the potential switching unit 16.

[0073] For example, in the above embodiment, a transmission type X-ray tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may be a reflection type X-ray tube. Also, in the above embodiment, a sealed tube structure in which the vacuum housing 4 is sealed as a vacuum tube is exemplified as the X-ray tube 2, but the X-ray tube 2 may be an open tube structure equipped with an exhaust pump or the like. Also, in the above embodiment, a hot cathode structure equipped with a heater 6 is exemplified as the electron gun EG, but the electron gun EG may be a cold cathode structure. The relationship of the potentials applied to the electron gun EG and the target 9 only needs to be such that electrons E are directed toward the target when X-rays are generated, and an electrode other than the target 9 may be at a reference potential (ground potential).

[0074] The gist of this disclosure is as follows [1] to [8]. [1] An X-ray generating device comprising: a cathode electrode that emits electrons; an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode; an extraction electrode that extracts the electrons from the cathode electrode; a target that generates X-rays when the electrons are incident on it; a discharge detection unit that detects discharge between the cathode electrode and the adjustment electrode; and a potential switching unit that makes the potential of the extraction electrode higher than the potential of the cathode electrode during normal operation, and makes the potential of the extraction electrode the same as or lower than the potential of the cathode electrode when a discharge is detected. [2] The X-ray generating device according to [1], wherein the potential switching unit includes a semiconductor switch. [3] The X-ray generating device according to [2], wherein the semiconductor switch is composed of a plurality of transistors connected in series and parallel to each other. [4] The X-ray generating device according to [3], wherein the potential switching unit further includes a diode connected in series to the plurality of transistors, and a damping resistor connected in series to the diode. [5] The X-ray generating device according to [1], wherein the potential switching unit is constituted by a gas arrester. [6] An X-ray generating device according to any one of [1] to [5], further comprising a reverse bias voltage source connected between the cathode electrode and the extraction electrode, wherein the potential switching unit, when detecting the discharge, applies a voltage from the reverse bias voltage source to make the potential of the extraction electrode lower than the potential of the cathode electrode. [7] The X-ray generator according to any one of [1] to [6], wherein the discharge detection unit includes at least one of a current detection resistor and a current transformer. [8] An X-ray generating device according to any one of [1] to [7], wherein the discharge detection unit detects the presence or absence of the discharge based on the magnitude of at least one of the current flowing through the cathode electrode, the current flowing through the adjustment electrode, and the current flowing through the target during the discharge detection. [Explanation of symbols]

[0075] 1, 1A, 1B...X-ray generator, 5...cathode electrode, 7...adjusting electrode, 8...extraction electrode, 9...target, 15...discharge detection unit, 16, 16A...potential switching unit, 18...reverse bias voltage source, 161, 162, 163, 164...FET, 165, 166...diode, 167, 168...damping resistor, 171...gas arrester, E...electrons, R...X-rays, Vg...potential of extraction electrode, Vk...potential of cathode electrode.

Claims

1. a cathode electrode that emits electrons; an adjusting electrode that adjusts the amount of electrons emitted from the cathode electrode; an extraction electrode that extracts the electrons from the cathode electrode; a target that generates X-rays when the electrons are incident on it; a discharge detection unit that detects a discharge between the cathode electrode and the adjustment electrode; a potential switching unit that sets the potential of the extraction electrode higher than the potential of the cathode electrode during normal operation, and sets the potential of the extraction electrode to the same potential as or lower than the potential of the cathode electrode when a discharge is detected.

2. 2. The X-ray generating apparatus according to claim 1, wherein said potential switching unit includes a semiconductor switch.

3. 3. The X-ray generating apparatus according to claim 2, wherein said semiconductor switch is composed of a plurality of transistors connected in series and parallel to each other.

4. The potential switching unit is a diode connected in series to the plurality of transistors; 4. The X-ray generating device of claim 3, further comprising a damping resistor connected in series with said diode.

5. 2. The X-ray generating apparatus according to claim 1, wherein the potential switching unit is configured by a gas arrester.

6. a reverse bias voltage source connected between the cathode electrode and the extraction electrode; 6. The X-ray generating device according to claim 1, wherein the potential switching unit applies a voltage from the reverse bias voltage source to make the potential of the extraction electrode lower than the potential of the cathode electrode when the discharge is detected.

7. 6. The X-ray generating device according to claim 1, wherein the discharge detecting section includes at least one of a current detecting resistor and a current transformer.

8. The X-ray generating device according to any one of claims 1 to 5, wherein the discharge detection unit detects the presence or absence of the discharge based on the magnitude of at least one of the current flowing through the cathode electrode, the current flowing through the adjustment electrode, and the current flowing through the target during the discharge detection.

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