Electron gun drive power supply

Abstract

An electron gun drive power supply 30 drives an electron gun including a cathode electrode 5 that emits electrons E, an adjustment electrode 7 that adjusts the amount of the electrons E to be emitted from the cathode electrode 5, and an extraction electrode 8 that extracts the electrons E from the cathode electrode 5. The electron gun drive power supply comprises a potential switching unit 16 that switches between a state in which the potential of the cathode electrode 5 is lower than the potential of the extraction electrode 8 and a state in which the potential of the cathode electrode 5 is higher than or equal to the potential of the extraction electrode 8. The electron gun drive power supply 30 can rapidly switch between an ON state in which a target is irradiated with the electrons and an OFF state in which the target is not irradiated with the electrons.

Description

Electron gun drive power supply

[0001] The present disclosure relates to an electron gun drive power supply.

[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. Of the above-mentioned components, the components excluding the target can be considered to constitute an electron gun drive power supply for generating radiation.

[0003] In the electron gun drive power supply included in the radiation generating unit described in Patent Document 1, radiation irradiation is turned off by making the potential of the extraction electrode smaller than the potential of the cathode electrode, and radiation irradiation is turned on by making the potential of the extraction electrode larger than the potential of the cathode electrode.

[0004] In order to control the amount of electrons emitted from the cathode electrode with higher precision, the electron gun driving power supply may further include an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode, in addition to the configuration of the electron gun driving power supply included in the radiation generating unit described in Patent Document 1.

[0005] JP 2014-130732 A

[0006] When the radiation on / off technique of the power supply of Patent Document 1 is applied to an electron gun drive power supply equipped with an adjusting electrode, it is expected that X-ray irradiation will be turned off by making the potential of the adjusting electrode smaller than the potential of the cathode electrode, so that electrons do not reach the target. On the other hand, when X-ray irradiation is turned on, it is expected that electrons will be sufficiently irradiated onto the target and X-rays of the desired brightness will be output by setting the potential of the adjusting electrode to a desired value larger than the potential of the cathode electrode.

[0007] However, since the adjustment electrode has a relatively high impedance, the potential may not be quickly switched to a desired value, which poses a problem that simply adjusting the potential of the adjustment electrode in an analog manner makes it difficult to quickly switch between an ON state in which electrons are irradiated onto the target and an OFF state in which electrons are not irradiated onto the target.

[0008] The present disclosure provides an electron gun drive power supply that can quickly switch between electron on and off states.

[0009] An electron gun driving power supply according to one aspect of the present disclosure is an electron gun driving power supply that drives an electron gun that includes a cathode electrode that emits electrons, an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode, and an extraction electrode that extracts electrons from the cathode electrode, and includes a potential switching unit that switches between a state in which the potential of the cathode electrode is lower than the potential of the extraction electrode and a state in which the potential of the cathode electrode is the same as or higher than the potential of the extraction electrode.

[0010] In this electron gun drive power supply, when the potential of the cathode electrode becomes lower than the potential of the extraction electrode, the power supply enters an ON state in which electrons are irradiated onto the target. In the ON state, electrons emitted from the cathode electrode are given an initial velocity corresponding to the potential difference between the potential of the cathode electrode and the potential of the extraction electrode, and the electrons are irradiated onto the target. On the other hand, in this electron gun drive power supply, when the potential of the cathode electrode becomes the same as or higher than the potential of the extraction electrode, the power supply enters an OFF state in which electrons are not irradiated onto the target. In the OFF state, the electrons from the cathode electrode are not given an initial velocity, and the electrons are no longer irradiated onto the target. In this electron gun drive power supply, the ON and OFF states of the electrons are switched by switching the potential of the cathode electrode, regardless of the potential of the adjustment electrode. This allows for rapid switching between the ON state in which electrons are irradiated onto the target and the OFF state in which electrons are not irradiated onto the target.

[0011] When the potential of the cathode electrode is equal to or higher than the potential of the extraction electrode, the potential of the adjustment electrode may be higher than the cutoff voltage. In this case, when the potential of the cathode electrode is equal to or higher than the potential of the extraction electrode, the potential of the adjustment electrode can be made higher than the cutoff voltage. This makes it possible to reduce the increase in the potential of the adjustment electrode for generating X-rays when electrons are turned on.

[0012] The electron gun drive power supply may further include a detector that generates a detection signal indicating the magnitude of the voltage of the adjustment electrode when the potential of the cathode electrode switches from a state in which the potential of the cathode electrode is equal to or higher than the potential of the extraction electrode to a state in which the potential of the cathode electrode is lower than the potential of the extraction electrode, a driver connected to the detector that generates an instruction signal based on a difference between the detection signal and a target value, and a waveform stabilization circuit that has one end connected to the cathode electrode and the other end connected to the adjustment electrode and that flows a current between the one end and the other end corresponding to the magnitude of the voltage of the adjustment electrode indicated by the instruction signal. In this case, the waveform stabilization circuit flows a current from the cathode electrode side to the adjustment electrode side in accordance with the potential difference, thereby discharging charge accumulated in the electrostatic capacitance within the electron gun drive power supply. This makes it possible to stably reduce overshoot that occurs in the adjustment electrode potential when, for example, the potential of the cathode electrode switches to a state in which the potential of the extraction electrode is lower than the potential of the extraction electrode.

[0013] The potential switching unit may be configured to 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 an electron on state and an electron off state.

[0014] The semiconductor switch may be composed of a plurality of FETs connected in series and parallel to each other, in which case the parasitic capacitance of the semiconductor switch constituting the potential switching unit is reduced and the withstand voltage is improved, allowing the potential of the cathode electrode to be switched more safely.

[0015] The potential switching unit may further include a diode connected in series to the plurality of FETs and a resistor connected in series to the diode. In this case, the diode and resistor connected in series can suppress ringing that occurs when the potential of the cathode electrode switches between the electron on state and the electron off state. Therefore, the potential of the cathode electrode can be switched at a higher speed.

[0016] According to the present disclosure, electrons can be rapidly switched between ON and OFF states.

[0017] FIG. 1 is a schematic diagram showing the configuration of an X-ray generator including an electron gun power supply according to an embodiment of the present disclosure. FIG. 2(a) is a diagram showing a switching signal for switching the potential of a cathode electrode. FIG. 2(b) is a diagram showing the potential of a cathode electrode. FIG. 2(c) is a diagram showing the potential of an adjustment electrode. FIG. 3 is a diagram for explaining a cutoff voltage. FIG. 4 is a diagram showing the circuit configuration of a potential switching unit. FIG. 5 is a diagram for explaining the configuration of an X-ray generator including an electron gun power supply according to a second embodiment. FIG. 6 is a diagram showing a circuit diagram of the waveform stabilization circuit and its peripheral circuits shown in FIG. 5. FIG. 7(a) is a diagram showing the potential of an adjustment electrode. FIG. 7(b) is a diagram showing the potential of an adjustment electrode according to a comparative example. FIG. 8 is a diagram for explaining the configuration of an X-ray generator including an electron gun power supply according to a third embodiment. FIG. 9(a) is a diagram showing a current detection signal. FIG. 9(b) is a diagram showing a switching signal. FIG. 9(c) is a diagram showing the potential of a cathode electrode. FIG. 9(d) is a diagram showing the potential of a cathode electrode in a potential switching unit according to a comparative example. Fig. 10 is a diagram for explaining the configuration of an X-ray generator including an electron gun drive power supply according to a first modified example. Fig. 11 is a diagram for explaining the configuration of an X-ray generator including an electron gun drive power supply according to a second modified example. Fig. 12 is a circuit diagram showing the internal configuration of an adjustment electrode power supply according to the second modified example. Fig. 13 is a circuit diagram showing specific configuration examples of a first charging circuit and a second charging circuit. Fig. 14 is a diagram for explaining the configuration of a potential switching unit according to a third modified example. Fig. 15 is a circuit diagram showing an example of a waveform stabilization circuit in an X-ray generator according to a fourth modified example.

[0018] Hereinafter, preferred embodiments of an electron gun driving power supply according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0019] 1 is a schematic diagram showing the configuration of an X-ray generator including an electron gun drive power supply 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 housed within a vacuum housing 4. The drive circuit 3, the cathode electrode 5, the heater 6, the adjustment electrode 7, and the extraction electrode 8 constitute an electron gun drive power supply 30. 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 a current-carrying 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 current is applied. The electrons E emitted from the cathode electrode 5 pass through the electron passing holes 7 a in the adjustment electrode 7 and the electron passing holes 8 a in the extraction electrode 8 and proceed toward the target 9.

[0022] The adjustment electrode 7 is an 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, for example, electron passing holes 7a that are circular in 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 an 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 for extracting 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 having the above configuration, during normal operation in which X-rays R are output from the target 9, for example, a negative high voltage is applied to the X-ray tube 2, with the potential of the target 9 as the 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 these cathode electrode 5, adjustment electrode 7, and extraction electrode 8.

[0027] The extraction electrode power supply 14 supplies a negative high voltage, for example, of not less than −130 kV and not more than 0 V, to the extraction electrode 8. The cathode electrode power supply 12 supplies a negative high voltage, for example, of not less than −2 kV and not more than 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, of not less than −500 V and not more than 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, at ground potential), and collide with the target 9 while being focused.

[0029] X-rays R generated by the target 9 due to the collision of electrons E 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 , the drive circuit 3 is provided with a potential switching unit 16 that switches the potential of the cathode electrode 5 , and a control unit 17 .

[0031] 1, the potential switching unit 16 includes a first contact terminal P1, a second contact terminal P2, and a third contact terminal P3. The control unit 17 is physically configured to include a processor such as a CPU, and storage media such as a RAM and a ROM. The control unit 17 may be a smartphone or tablet terminal that has an integrated display unit and input unit, or may be configured by a microcomputer or a field-programmable gate array (FPGA).

[0032] The control unit 17 transmits a switching signal Sc to the potential switching unit 16 to switch the potential of the cathode electrode 5. As shown in Fig. 2(a), the switching signal Sc is a pulse wave that alternates between a high level and a low level. The period of the pulse wave is, for example, several tens of milliseconds.

[0033] When the switching signal Sc rises from low level to high level, the potential switching unit 16 connects the first contact terminal P1 and the third contact terminal P3, thereby connecting the cathode electrode 5 to the cathode electrode power supply 12. As a result, as shown in FIG. 2B, the potential Vk of the cathode electrode 5 becomes lower than the potential Vg1 of the extraction electrode 8.

[0034] When the potential Vk of the cathode electrode 5 is lower than the potential Vg1 of the extraction electrode 8, the electrons E emitted from the cathode electrode 5 are irradiated onto the target 9 with an initial velocity corresponding to the potential difference between the potential Vk of the cathode electrode 5 and the potential Vg1 of the extraction electrode 8. Then, the target 9 emits X-rays R with a brightness corresponding to the magnitude of the voltage applied to the adjustment electrode 7. Therefore, while the switching signal Sc is at a high level, the electrons E are irradiated onto the target 9, and X-rays R are emitted from the target 9. A current (irradiation current) when the electrons E are irradiated onto the target 9 (electrons E are in an on state) flows from the first contact terminal P1 to the third contact terminal P3.

[0035] When the switching signal Sc drops from high level to low level, the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2. This connects the cathode electrode 5 to the extraction electrode power supply 14. In other words, the cathode electrode 5 is supplied with voltage from the extraction electrode power supply 14, not from the cathode electrode power supply 12. As a result, as shown in FIG. 2B, the potential Vk of the cathode electrode becomes the same potential as the potential Vg1 of the extraction electrode 8.

[0036] When the potential Vk of the cathode electrode is the same as the potential Vg1 of the extraction electrode 8, the electrons E emitted from the cathode electrode 5 are not given an initial velocity and are not irradiated to the target 9. As a result, X-rays R are not emitted from the target. Therefore, while the switching signal Sc is at a low level, the electrons E are not irradiated to the target 9 and X-rays are not emitted from the target 9. When the first contact terminal P1 and the second contact terminal P2 are connected, the potential Vg1 of the extraction electrode 8 is higher than the potential Vk of the cathode electrode 5, so a current (current during non-irradiation) in a state in which the electrons E are not irradiated to the target 9 (electron E off state) flows from the second contact terminal P2 to the first contact terminal P1.

[0037] Next, the potential Vg2 of the adjustment electrode 7 will be described. When the switching signal Sc rises from a low level to a high level, the potential Vg2 of the adjustment electrode 7 rises from a potential Vg21 to a potential Vg22, as shown in FIG. 2C. The magnitude of the potential Vg22 may be changed as appropriate to adjust the brightness of the X-rays R. When the switching signal Sc falls from a high level to a low level, the potential Vg2 of the adjustment electrode 7 falls from the potential Vg22 to a potential Vg21. A potential greater than a cutoff voltage Vcf, which will be described later, is applied to the potential Vg21 in order to irradiate the target 9 with electrons E (to emit X-rays R from the target 9).

[0038] If the state in which X-rays R are emitted is switched to a state in which X-rays R are not emitted solely by the potential Vg2 of the adjustment electrode 7, it is assumed that X-ray irradiation is turned off by setting the potential Vg2 to a potential at which electrons E do not reach the target 9. The cutoff voltage Vcf is the upper limit (critical value) of the potential that the adjustment electrode 7 can assume so that electrons E emitted from the cathode electrode 5 do not pass through the electron passing holes 7a of the adjustment electrode 7. In other words, it corresponds to a potential at which electrons E do not reach the target 9.

[0039] FIG. 3 is a graph illustrating the cutoff voltage Vcf. In FIG. 3, the horizontal axis represents the potential Vg2 of the adjustment electrode 7, and the vertical axis represents the magnitude of the cathode current (current flowing from the cathode electrode 5 toward the cathode electrode power supply 12). Here, the cathode current is proportional to the current flowing from the target 9 and proportional to the brightness value of the X-rays R. FIG. 3 illustrates the relationship between the potential Vg2 of the adjustment electrode 7 and the cathode current when the potential Vk of the cathode electrode 5 is set to one of potentials Vka, Vkb, and Vkc. The potentials Vka, Vkb, and Vkc increase in this order. At each of potentials Vka, Vkb, and Vkc, the magnitude of the cathode current decreases as the potential Vg2 of the adjustment electrode 7 decreases. The potential Vg2 when the magnitude of the cathode current becomes 0 A corresponds to the cutoff voltage Vcf. The cutoff voltage of the potential Vka, the cutoff voltage of the potential Vkb, and the cutoff voltage of the potential Vkc are all different voltage values.

[0040] Next, the detailed configuration of the potential switching unit 16 will be described. FIG. 4 is a diagram showing the circuit configuration of the potential switching unit. The potential switching unit 16 includes a semiconductor switch. In this embodiment, the semiconductor switch is configured from 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 from a plurality of FETs 161 to 164. The FETs 161 and 162, which are connected in cascade between the first contact terminal P1 and the third contact terminal P3, are arranged symmetrically with respect to the FETs 163 and 164, which are connected in cascade 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 an 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 multiple FETs 161 to 164 having such characteristics are connected in cascade is referred to as multiple series-parallel connected FETs 161 to 164. The potential switching unit 16 further includes diodes 165 and 166 connected in series to the multiple FETs 161 to 164, and damping resistors 167 and 168 connected in series to the diodes.

[0041] The specific configuration of the potential switching unit 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 a diode 165. The cathode terminal of the diode 165 is connected to one end of a damping resistor 167. The other end of the damping resistor 167 is connected to the third contact terminal P3.

[0042] 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 diode 166 is connected to one end of a damping resistor 168. The other end of damping resistor 168 is connected to the second contact terminal P2.

[0043] In the potential switching unit 16, when the target 9 is irradiated with electrons E (hereinafter referred to as "irradiation"), a control signal generated based on the switching signal Sc rising to a high level from the control unit 17 is input to the gate terminals of the FETs 161 and 162, turning on the FETs 161 and 162. On the other hand, the FETs 163 and 164 are turned off. As a result, the potential Vk of the cathode electrode 5 drops to a potential lower than the potential Vg1 of the extraction electrode 8. When the target 9 is not irradiated with electrons E (hereinafter referred to as "non-irradiation"), a control signal generated based on the switching signal Sc falling to a low level from the control unit 17 is input to the gate terminals of the FETs 163 and 164, turning on the FETs 163 and 164. On the other hand, the FETs 161 and 162 are turned off. As a result, the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg1 of the extraction electrode 8.

[0044] 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 FETs 161 to 164 are all the same type of FET, the withstand voltage values ​​of the FETs that contribute to a drop in the potential Vk of the cathode electrode 5 are the same as the withstand voltage values ​​of the FETs that contribute to an increase in the potential Vk of the cathode electrode 5. If FETs 161 to 164 are not all the same type of FET and each FET has a different withstand voltage value, the numbers do not necessarily need to be the same.

[0045] 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 Vg1 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 Vg1 of the extraction electrode 8.

[0046] Next, the operation 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, when the FETs 163 and 164 are off during irradiation, 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 non-irradiation, the resonance component is formed, causing ringing when the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg1 of the extraction electrode 8.

[0047] 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 within 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, ringing that occurs when the potential Vk of the cathode electrode rises can be suppressed. 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 within 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.

[0048] 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.

[0049] The potential switching unit 16 further includes decoupling capacitors 169 and 170 connected in series, a resistor 173 connected in parallel to the decoupling capacitor 169, and a resistor 174 connected in parallel to the decoupling capacitor 170. The terminal of the decoupling capacitor 169 that is not connected to the decoupling capacitor 170 is connected to the 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 the node between the second contact terminal P2 and the damping resistor 168.

[0050] The decoupling capacitors 169, 170 supply electric charge to the cathode electrode 5 when the potential switching unit 16 switches the potential Vk of the cathode electrode 5. This prevents the potential Vk of the cathode electrode 5 from fluctuating when the potential Vk of the cathode electrode 5 is switched. The decoupling capacitors 169, 170 are preferably disposed near the cathode electrode 5 to minimize the influence of inductance due to wiring.

[0051] 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 voltages exceeding the designed withstand voltage of decoupling capacitors 169 and 170 from being applied.

[0052] In the electron gun drive power supply 30 described above, when the potential Vk of the cathode electrode 5 is lower than the potential Vg1 of the extraction electrode 8, the power supply is in an ON state in which electrons E are irradiated onto the target 9. In the ON state, the electrons E emitted from the cathode electrode 5 are given an initial velocity corresponding to the potential difference between the potential Vk of the cathode electrode 5 and the potential Vg1 of the extraction electrode 8, and the electrons E are irradiated onto the target 9. On the other hand, in this electron gun drive power supply 30, when the potential Vk of the cathode electrode 5 is equal to the potential Vg1 of the extraction electrode 8, the power supply is in an OFF state in which the electrons E are not irradiated onto the target 9. In the OFF state, the electrons E of the cathode electrode 5 are not given an initial velocity, and the electrons E are no longer irradiated onto the target 9. In this electron gun drive power supply 30, the ON state and OFF state of the electrons E are switched by switching the potential Vk of the cathode electrode 5, regardless of the potential Vg2 of the adjustment electrode 7. This allows high-speed switching between an ON state in which the electrons E are irradiated onto the target 9 and an OFF state in which the electrons E are not irradiated onto the target 9 .

[0053] In a state in which the potential Vk of the cathode electrode 5 is the same as the potential Vg1 of the extraction electrode 8, the potential Vg2 of the adjustment electrode 7 is greater than the cutoff voltage Vcf, which is the lower limit for irradiating the electrons E onto the target 9. In this case, in a state in which the potential Vk of the cathode electrode 5 is the same as the potential Vg1 of the extraction electrode 8, the potential Vg2 of the adjustment electrode 7 can be made greater than the cutoff voltage Vcf. This makes it possible to reduce the increase in the potential Vg2 of the adjustment electrode 7 for generating X-rays R when the electrons E are turned on.

[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 irradiation (electrons E in an ON state) and non-irradiation (electrons E in an OFF state).

[0055] The semiconductor switch is composed of a plurality of 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, making it possible to switch the potential Vk of the cathode electrode 5 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 irradiation and non-irradiation. Therefore, the potential Vk of the cathode electrode 5 can be switched at a higher speed.

[0057] Second Embodiment Fig. 5 is a diagram illustrating the configuration of an X-ray generator 1A including an electron gun drive power supply 30A according to a second embodiment. In addition to the configuration of the X-ray generator 1 according to the first embodiment, the X-ray generator 1A includes a waveform stabilization circuit 21 and its peripheral circuitry between the positive and negative poles of the adjustment electrode power supply 13 for stabilizing the behavior when the potential Vg2 of the adjustment electrode 7 rises to potential Vg22. The peripheral circuitry includes a detection unit 18, a drive unit 19, and a transmission unit 20. The drive circuit 3, cathode electrode 5, heater 6, adjustment electrode 7, extraction electrode 8, waveform stabilization circuit 21, and its peripheral circuitry constitute the electron gun drive power supply 30A. The cathode electrode 5, heater 6, adjustment electrode 7, and extraction electrode 8 constitute the electron gun EG.

[0058] The detector 18 generates a detection voltage Vdet that indicates the magnitude of the potential Vg22 (the potential during irradiation) when the potential Vg2 of the adjustment electrode 7 rises to the potential Vg22. The input terminal of the detector 18 is connected to the adjustment electrode 7 and the negative electrode of the adjustment electrode power supply 13. The detector 18 outputs the detection voltage Vdet to the driver 19.

[0059] The driver 19 generates a command voltage Vdrc based on the detection voltage Vdet. The driver 19 has a first input terminal 19a and a second input terminal 19b. A set voltage Vset for setting the magnitude of the potential Vg22 during irradiation is input to the first input terminal 19a. The set voltage Vset is a target value for the potential Vg22 during irradiation. The first input terminal 19a is connected to, for example, an external control element, and the set voltage Vset may be input to the first input terminal 19a from the external control element. The detection voltage Vdet is input to the second input terminal 19b. The second input terminal 19b is connected to the output terminal of the detector 18.

[0060] The driver 19 generates the instruction voltage Vdrc based on the difference between the detection voltage Vdet and the target value. In this embodiment, the driver 19 generates the instruction voltage Vdrc based on the difference between the set voltage Vset and the detection voltage Vdet. The driver 19 outputs the instruction voltage Vdrc to the transmitter 20. The set voltage Vset is an example of a setting signal. The detection voltage Vdet is an example of a detection signal. The instruction voltage Vdrc is an example of an instruction signal. In this embodiment, the setting signal, the detection signal, and the instruction signal will be described as voltage signals.

[0061] The transmission unit 20 transmits the command voltage Vdrc to the waveform stabilization circuit 21. The input terminal of the transmission unit 20 is connected to the output terminal of the drive unit 19. The output terminal of the transmission unit 20 is connected to the waveform stabilization circuit 21.

[0062] The waveform stabilization circuit 21 flows a current corresponding to the magnitude of the command voltage Vdrc from a node N2 between the positive electrode of the adjusting electrode power supply 13 and the potential Vg22 toward a node N1 between the negative electrode of the adjusting electrode power supply 13 and the potential Vg22. The waveform stabilization circuit 21 functions to stably converge the potential Vg22 to a voltage corresponding to the set voltage Vset. A predetermined dielectric strength voltage is ensured between the waveform stabilization circuit 21 and the transmission unit 20. The waveform stabilization circuit 21 includes a first input terminal 21a, a second input terminal 21b, and an output terminal 21c. The first input terminal 21a is connected to the node N2. The second input terminal 21b is connected to the output terminal of the transmission unit 20. The output terminal 21c is connected to the node N1.

[0063] The drive unit 19, the transmission unit 20, and the waveform stabilization circuit 21 operate when the potential Vg2 of the adjustment electrode 7 rises to the potential Vg22, and stop after the potential Vg22 has been reached. Specifically, they operate when a difference occurs between the detection voltage Vdet and the target value (when the detection voltage Vdet exceeds the set voltage Vset), and stop when the difference disappears.

[0064] FIG. 6 is a circuit diagram showing an example of the driver 19, transmitter 20, and waveform stabilization circuit 21. In the example of FIG. 6, the driver 19 is configured as an error amplifier. The driver 19 includes a first input terminal 19a, a second input terminal 19b, and an output terminal 19c. A set voltage Vset for setting the magnitude of the potential Vg22 during irradiation is input to the first input terminal 19a. The first input terminal 19a may be connected to, for example, an external control element, and the set voltage Vset may be input from the external control element. A detection voltage Vdet is input to the second input terminal 19b. The second input terminal 19b is connected to the output terminal of the detector 18. An instruction voltage Vdrc is output from the output terminal 19c. The output terminal 19c is connected to the transmitter 20.

[0065] The driver 19 generates the command voltage Vdrc based on the difference between the set voltage Vset and the detected voltage Vdet. The set voltage Vset is a fixed value unless, for example, the user changes the setting. The driver 19 generates the command voltage Vdrc when the magnitude of the detected voltage Vdet is greater than the set voltage Vset. The magnitude of the command voltage Vdrc increases in proportion to the magnitude of the difference between the set voltage Vset and the detected voltage Vdet. In other words, when the magnitude of the detected voltage Vdet is greater than the set voltage Vset, the magnitude of the command voltage Vdrc increases in proportion to the magnitude of the detected voltage Vdet, and therefore the magnitude of the potential Vg22 during irradiation.

[0066] In the example of FIG. 6 , the transmission unit 20 is composed of a light-emitting element. The anode terminal of the transmission unit 20 is connected to the output terminal 19c of the driver 19, which is an error amplifier. The cathode terminal of the transmission unit 20 is connected to the ground potential GND. The transmission unit 20 converts the command voltage Vdrc into light energy. At this time, as the magnitude of the command voltage Vdrc increases, the amount of current flowing through the transmission unit 20 increases, and the light emission intensity of the transmission unit 20 increases. The transmission unit 20 is, for example, an LED or a laser diode.

[0067] The waveform stabilization circuit 21 includes a phototransistor 210, a plurality of transistors 211 to 213, and a plurality of resistors 214 to 217. The phototransistor 210 includes an input terminal 210a, a first current terminal 210b, and a second current terminal 210c. The input terminal 210a is optically connected to the transmission unit 20, which is a light-emitting element. The input terminal 210a is the second input terminal 21b of the waveform stabilization circuit 21. The first current terminal 210b is connected to the transistor 213. The second current terminal 210c is connected to a node N1. The second current terminal 210c is the output terminal 21c of the waveform stabilization circuit 21. The light-emitting element and the phototransistor 210 that constitute the transmission unit 20 may constitute a photocoupler. In this case, the withstand voltage between the transmission unit 20 and the phototransistor is, for example, 1 kV.

[0068] When an optical signal having an intensity corresponding to the command voltage Vdrc is input from the transmission unit 20 to the input terminal 210a of the phototransistor 210, the phototransistor 210 causes a discharge current Ichg corresponding to the intensity of the optical signal to flow from the first current terminal 210b to the second current terminal 210c. In other words, the phototransistor 210 causes the discharge current Ichg to flow from the transistor 213 side to the node N1 side.

[0069] The plurality of transistors 211 to 213 are connected in series and parallel to one another between the first input terminal 21a (one end) and the output terminal 21c (the other end). The plurality of resistors 214 to 217 are connected in series to one another between the first input terminal 21a (one end) and the output terminal 21c (the other end). Furthermore, the input terminals 211a to 213a of the plurality of transistors 211 to 213 are connected between adjacent resistors of the plurality of resistors 214 to 217. The specific configuration is as follows:

[0070] The first current terminal 211b of the top-stage transistor 211 also serves as the first input terminal 21a and is connected to node N2. The second current terminal 211c of the top-stage transistor 211 is connected to the first current terminal 212b of the second-stage transistor 212. One end of the top-stage resistor 214 also serves as the first input terminal 21a and is connected to node N2. The input terminal 211a of the top-stage transistor 211 is connected to a node between the other end of the top-stage resistor 214 and one end of the second-stage resistor 215. The above configuration is repeated up to the third-stage transistor 213. The second current terminal 213c of the third-stage transistor 213 is connected to the first current terminal 210b of the phototransistor 210. The other end of the fourth-stage resistor 217 is connected to the second current terminal 210c of the phototransistor 210.

[0071] 6, the plurality of transistors are configured in three stages, but may be configured in any other stages as long as there are M stages (M is an integer equal to or greater than 2).Furthermore, the plurality of resistors are configured in four stages, but may be configured in any other stages as long as there are (M+1) stages.

[0072] A voltage obtained by dividing the potential Vg22 of the adjustment electrode 7 during irradiation by the plurality of resistors 214-217 is input to the input terminals 211a-213a. In other words, a bias voltage is applied to the plurality of transistors 211-213. As a result, each of the plurality of transistors 211-213 is driven in the saturation region. In the saturation region, the magnitude of the current that each of the plurality of transistors 211-213 can pass from the first current terminals T211b-213b to the second current terminals T211c-213c is constant (saturated state). In other words, by driving each of the plurality of transistors 211-213 in the saturation region, the waveform stabilization circuit 21 is able to pass a sufficient amount of current.

[0073] In this state, when an optical signal corresponding to the command voltage Vdrc is input to the input terminal 210a of the phototransistor 210, a discharge current Ichg having a magnitude proportional to the magnitude of the command voltage Vdrc flows through the waveform stabilization circuit 21. The discharge current Ichg flows from the first input terminal 21a (one end) of the waveform stabilization circuit 21 toward the second current terminal 210c of the phototransistor 210.

[0074] In other words, the discharge current Ichg flows from the node N2 side toward the node N1 side. In other words, the discharge current Ichg flows from the cathode electrode 5 (positive electrode of the adjusting electrode power supply 13) side toward the adjusting electrode 7 (negative electrode of the adjusting electrode power supply 13) side. Since the magnitude of the command voltage Vdrc increases in proportion to the difference between the potential Vg22 when the adjusting electrode 7 is irradiated and the target value, the waveform stabilization circuit 21 can flow a current based on the difference between the potential Vg22 and the target value. In other words, the waveform stabilization circuit 21 can variably control the amount of the discharge current Ichg based on the magnitude of the potential Vg22.

[0075] Next, the effect of providing the waveform stabilization circuit 21 will be described with reference to FIG. 7 . FIG. 7( a) shows the same waveform as FIG. 2( c). That is, FIG. 7( a) shows the potential Vg2 of the adjustment electrode 7 in the X-ray generator 1 that does not include the waveform stabilization circuit 21. FIG. 7( b) shows the potential Vg2 of the adjustment electrode 7 in the X-ray generator 1A that includes the waveform stabilization circuit 21. As shown in FIGS. 7( a) and 7(b), in the X-ray generator 1A, the rate at which the potential Vg2 rises to the potential Vg22 during irradiation is faster than that in the X-ray generator 1. As a result, in the X-ray generator 1A, the rise time Tr2 required for the potential Vg2 to rise from the potential Vg21 to the potential Vg22 is shorter than the rise time Tr1 in the X-ray generator 1.

[0076] The waveform stabilization circuit 21 discharges the charge accumulated in the capacitance of the electron gun drive power supply 30 of the X-ray generator 1A by flowing a discharge current Ichg from the cathode electrode 5 toward the adjustment electrode 7 in accordance with the potential difference based on the difference between the potential Vg22 and the target value. This stably reduces waveform disturbances such as overshoot that may occur in the adjustment electrode 7 when the potential Vg2 rises to the potential Vg22 during irradiation. This improves the rate of rise Tr when the potential Vg2 rises to the potential Vg22, making it easier for the potential switching unit 16 to achieve even faster switching. Furthermore, since the rate of change of the potential Vg2 of the adjustment electrode 7 per unit time is improved, image quality can be improved, for example, when the X-rays R emitted from the target 9 are used for diagnostic imaging.

[0077] In the X-ray generator 1A, after the potential Vg2 of the adjusting electrode 7 rises to the potential Vg22 (after the difference between the potential Vg22 and the target value is eliminated), when the waveform stabilization circuit 21 is stopped, the superimposition of a ripple voltage on the potential Vg22 is suppressed. For example, in order to improve the rate of rise when the potential Vg22 rises, it is conceivable to provide a dummy resistor between the positive and negative electrodes of the adjusting electrode power supply 13 instead of the waveform stabilization circuit 21. However, in this case, a certain load of the dummy resistor exists even during irradiation, which may cause a ripple voltage to be superimposed on the potential Vg22 during irradiation. In contrast, when the waveform stabilization circuit 21 is stopped, a state close to no load is achieved, which makes it possible to suppress the superimposition of a ripple voltage on the potential Vg22 during irradiation.

[0078] 8 is a diagram for explaining the configuration of an X-ray generator 1B according to a third embodiment. In addition to the configuration of the X-ray generator 1 according to the first embodiment, the X-ray generator 1B includes a discharge detector 15 that detects discharge between the cathode electrode 5 and the adjustment electrode 7. The drive circuit 3, the cathode electrode 5, the heater 6, the adjustment electrode 7, the extraction electrode 8, and the discharge detector 15 constitute an electron gun drive power supply 30B. The cathode electrode 5, the heater 6, the adjustment electrode 7, and the extraction electrode 8 constitute an electron gun EG.

[0079] In the X-ray generator 1B, a discharge may 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, it is conceivable that a portion of the material of the cathode electrode 5 heated by the heater 6 may fly and adhere to the adjustment electrode 7. Furthermore, not only the material of the cathode electrode 5 but also various foreign matters, such as the material of the heater 6 and foreign matters 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, it becomes temporarily impossible to control the amount of electrons emitted from the cathode electrode 5 using the potential difference between the cathode electrode 5 and the adjustment electrode 7. 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.

[0080] Therefore, in the X-ray generator 1B, 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. Furthermore, in the X-ray generator 1B, the potential switching unit 16 switches the potential of the cathode electrode 5 when a discharge is detected. 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).

[0081] 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.

[0082] 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 (i.e., the magnitude of the current has increased significantly), it transmits a switching signal Sc1 to the potential switching unit 16.

[0083] 9(a) and 9(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 the control unit 17 detects that the current detection signal Idet has exceeded the threshold value Ith and the timing at which the control unit 17 transmits the switching signal Sc1 to the potential switching unit 16. 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.

[0084] During normal operation, the potential switching unit 16 connects the first contact terminal P1 and the third contact terminal P3, thereby connecting the cathode electrode 5 and the cathode electrode power supply 12. Therefore, during normal operation, the potential Vg1 of the extraction electrode 8 is higher than the potential Vk of the cathode electrode 5. Under normal conditions, a current flows from the first contact terminal P1 to the third contact terminal P3.

[0085] 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, the cathode electrode 5 is supplied with voltage 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 Vg1 of the extraction electrode 8 is higher than the potential Vk of the cathode electrode 5, so that a discharge 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 Vg1 of the extraction electrode 8, as shown in FIG. 9C.

[0086] The time T2 from when a discharge occurs (from when the current detection signal Idet rises) until the potential Vk of the cathode electrode becomes the same as the potential Vg1 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 Vg1 of the extraction electrode 8 higher than the potential Vk of the cathode electrode 5 during normal operation and making the potential Vg1 of the extraction electrode 8 the same as the potential Vk of the cathode electrode 5 when a discharge is detected.

[0087] 9B, 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 the discharge occurs between the cathode electrode 5 and the adjustment electrode 7.

[0088] 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 Figure 9(c), the potential Vk of the cathode electrode becomes lower than the potential Vg1 of the extraction electrode 8.

[0089] In the X-ray generator 1B, 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. 9D 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. 9D, 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. 9C. 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. 9D, 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.

[0090] In the X-ray generator 1B described above, when a discharge between the cathode electrode 5 and the adjustment electrode 7 is detected, the potential switching unit 16 sets the potential Vg1 of the extraction electrode 8 to the same potential as 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 9 even when a discharge occurs between the cathode electrode 5 and the adjustment electrode 7.

[0091] In the above-described X-ray generator 1B, the position where the discharge detector 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 detector 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 detector 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 detector 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 detector 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 detector 15 may be provided between the target 9 and ground potential GND. In this case, the discharge detector 15 detects the current flowing through the target 9 as the discharge current.

[0092] 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 N3, 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 N3 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.

[0093] As described above, in the X-ray generator 1B, the discharge detector 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 during discharge detection. By detecting the current at these positions, the occurrence of a discharge can be suitably detected.

[0094] [First Modification] 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.

[0095] 10 is a diagram for explaining the configuration of an X-ray generator 1C including an electron gun drive power supply 30C according to the first modification. The X-ray generator 1C and the electron gun drive power supply 30C differ from the X-ray generator 1 and the electron gun drive power supply 30 according to the embodiment in that a reverse bias voltage source 22 is provided between the cathode electrode 5 and the extraction electrode 8.

[0096] The operation of the X-ray generator 1C differs from that of the X-ray generator 1 in that the potential Vk of the cathode electrode 5 may become higher than the potential Vg1 of the extraction electrode 8. When the switching signal Sc drops from a high level to a low level, the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2. This connects the cathode electrode 5 to the positive terminal of the reverse bias voltage source 22, and connects the negative terminal of the reverse bias voltage source 22 to the extraction electrode 8. As a result, the potential Vk of the cathode electrode becomes higher than the potential Vg1 of the extraction electrode 8.

[0097] When the potential Vk of the cathode electrode is higher than the potential Vg1 of the extraction electrode 8, the electrons E emitted from the cathode electrode 5 are not given an initial velocity and are not irradiated to the target 9. As a result, X-rays R are not emitted from the target. In this electron gun drive power supply 30C, the on and off states of the electrons E are switched by switching the potential Vk of the cathode electrode 5, regardless of the potential Vg2 of the adjustment electrode 7. This makes it possible to quickly switch between the on state in which the electrons E irradiate the target 9 and the off state in which the electrons E do not irradiate the target 9.

[0098] In the X-ray generator 1A and the X-ray generator 1B, a reverse bias voltage source 22 may also be provided between the cathode electrode 5 and the extraction electrode 8. Even when the reverse bias voltage source 22 is applied to the X-ray generator 1A, the X-ray generator 1A can stably reduce waveform disturbances such as overshoot that may occur in the adjustment electrode 7 when the potential Vg2 rises to the potential Vg22 during irradiation.

[0099] When the reverse bias voltage source 22 is applied to the X-ray generator 1B, during discharge detection, 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 22 to the cathode electrode 5 and the negative terminal of the reverse bias voltage source 22 to the extraction electrode 8. As a result, the potential switching unit 16, using the reverse bias voltage source 22, makes the potential Vg of the extraction electrode 8 lower than the potential Vk of the cathode electrode 5 during discharge detection. In this case, the reverse bias voltage source 22 can more reliably and quickly suppress the amount of electrons irradiated onto the target.

[0100] 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. Furthermore, 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. Furthermore, 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).

[0101] [Second Modification] The X-ray generator 1B according to the third embodiment may function so that, when a discharge occurs between the cathode electrode 5 and the adjusting electrode 7, the potential of the adjusting electrode 7 can be quickly restored to the potential before the discharge. Fig. 11 is a diagram for explaining the configuration of the X-ray generator 1D including an electron gun driving power supply 30D according to the second modification. The driving circuit 3A, the cathode electrode 5, the heater 6, the adjusting electrode 7, the extraction electrode 8, and the discharge detection unit 15 constitute the electron gun driving power supply 30D. The driving circuit 3A differs from the driving circuit 3 in the X-ray generator 1B in that it includes an adjusting electrode power supply 13A instead of the adjusting electrode power supply 13.

[0102] In the drive circuit 3A, the adjusting electrode power supply 13A has a first terminal on the high potential side electrically connected to the second terminal of the cathode electrode power supply 12 via a line L1, and a second terminal on the low potential side electrically connected to the adjusting electrode 7 via a line L2. The adjusting electrode power supply 13 supplies a voltage Vad to the adjusting electrode 7 to create a potential difference between the cathode electrode 5 and the adjusting electrode 7.

[0103] 12 is a circuit diagram showing the internal configuration of the adjusting electrode power supply 13A. The adjusting electrode power supply 13A has a power supply 130, a first charging circuit 131, a second charging circuit 132, and a control unit 137. The power supply 130 has a first terminal on the high potential side and a second terminal on the low potential side. The power supply 130 generates a voltage Vad between the first terminal and the second terminal to apply a potential difference between the cathode electrode 5 and the adjusting electrode 7. The first terminal of the power supply 130 is electrically connected to the wiring L1.

[0104] The first charging circuit 131 and the second charging circuit 132 are connected in parallel with each other between the power supply 130 and the adjusting electrode 7, specifically between the second terminal of the power supply 130 and the line L2. The first charging circuit 131 and the second charging circuit 132 store electric charges and maintain the voltage Vad. The second charging circuit 132 has the same configuration as the first charging circuit 131. Each of the first charging circuit 131 and the second charging circuit 132 includes a resistor 133, a charging capacitor 134, a switch 135 (first switch), and a current source 136. The switch 135 and the current source 136 may both form a current source switch 138.

[0105] In each of the first charging circuit 131 and the second charging circuit 132, one end of the resistor 133 is electrically connected to the second terminal of the power supply 130. The other end of the resistor 133 is electrically connected to one electrode of the capacitor 134 through a node N1. The other electrode of the capacitor 134 is electrically connected to the first terminal of the power supply 130. This makes the potential of the other electrode of the capacitor 134 the same as the potential of the first terminal of the power supply 130. The capacitor 134 accumulates a predetermined amount of charge and generates a voltage between one electrode and the other electrode according to the amount of accumulated charge. The capacitance of the capacitor 134 is, for example, 1 nF to 100 nF. The capacitance of the capacitor 134 of the first charging circuit 131 is, for example, equal to the capacitance of the capacitor 134 of the second charging circuit 132. The type of the capacitor 134 is, for example, a multilayer ceramic capacitor (MLCC) primarily made of barium titanate. Current source 136 is provided on the current path between one end of capacitor 134 (i.e., node N10) and adjustment electrode 7. Current source 136 limits the amount of current between node N10 and adjustment electrode 7. Switch 135 is connected in series with current source 136 on the current path. Switch 135 enables the state between one end of capacitor 134 and adjustment electrode 7 (specifically, between node N10 and line L2) to be switched between a connected state and a disconnected state.

[0106] The control unit 137 receives a current detection signal Idet from the discharge detection unit 15 and controls the operation of the switch 135 based on the current detection signal Idet. During normal operation when the discharge detection unit 15 is not detecting a discharge, both the first charging circuit 131 and the second charging circuit 132 maintain the voltage Vad. During normal operation, the control unit 137 controls the first charging circuit 131 and the second charging circuit 132 so that mainly one of the first charging circuit 131 and the second charging circuit 132 (or only one of the charging circuits) applies the voltage Vad to the adjusting electrode 7. When the discharge detection unit 15 detects a discharge, the control unit 137 switches control based on the detection of the discharge so that mainly one of the first charging circuit 131 and the second charging circuit 132, other than either of the charging circuits (or only one of the charging circuits) applies the voltage Vad to the adjusting electrode 7.

[0107] Specifically, the control terminals of the switches 135 of the first charging circuit 131 and the second charging circuit 132 are electrically connected to the control unit 137. The control unit 137 controls the switch 135 of the first charging circuit 131 with a control signal Sa1 and controls the switch 135 of the second charging circuit 132 with a control signal Sa2. During normal operation, the control unit 137 controls the switch 135 of either the first charging circuit 131 or the second charging circuit 132 so that one end of the capacitor 134 of that charging circuit is connected to the adjusting electrode 7. In addition, during normal operation, the control unit 137 controls the switch 135 of a different charging circuit from either of the first charging circuit 131 and the second charging circuit 132 so that one end of the capacitor 134 of that charging circuit is disconnected from the adjusting electrode 7. Then, when discharge detection unit 15 detects a discharge, control unit 137 controls switch 135 of any one of the charging circuits so that one end of capacitor 134 of that one of the charging circuits is disconnected from adjustment electrode 7. In addition, when discharge detection unit 15 detects a discharge, control unit 137 controls switch 135 of a different charging circuit so that one end of capacitor 134 of that different charging circuit is connected to adjustment electrode 7.

[0108] The control unit 137 physically includes a processor such as a CPU, and storage media such as a RAM, a ROM, etc. The control unit 137 may be a smartphone or tablet terminal that is integrated with a display unit and an input unit, or may be configured with a microcomputer, an FPGA (Field-Programmable Gate Array), or the like.

[0109] 13 is a circuit diagram showing a specific configuration example of each of the first charging circuit 131 and the second charging circuit 132. As shown in FIG. 13, in this configuration example, a resistor 13a is connected in parallel with the capacitor 134, and a resistor 13b is connected between the node N10 and one end 135a of the switch 135. The switch 135 constituting the current source switch 138 is composed of, for example, a photocoupler and a MOSFET. The switch 135 may also be composed of only the photocoupler. A power supply 13d is connected to the photocoupler via a resistor 13c, and the photocoupler is driven by the power supply 13d. The photocoupler receives a control signal Sa1 (or a control signal Sa2) from the control unit 137 and switches the state between one end 135a and the other end 135b between a connected state and a disconnected state in response to the control signal Sa1 (or a control signal Sa2).

[0110] The current source 136 includes a transistor 1361 and a resistor 1364. The transistor 1361 is, for example, an N-channel MOSFET. The transistor 1361 is, for example, a depletion-type MOSFET and is always on. The diagram clearly shows a parasitic diode 1362 and a junction capacitance 1363 between the current terminals of the transistor 1361. One current terminal (e.g., the source terminal) of the transistor 1361 is connected to the other end 135b of the switch 135. The other current terminal (e.g., the drain terminal) of the transistor 1361 is connected to the wiring L2 via a diode 13e for preventing backflow. The diagram clearly shows a parasitic capacitance 13f of the diode 13e. The control terminal (gate terminal) of the transistor 1361 is connected to the other end of the switch 135 and to a node N10 via a resistor 13b. The resistor 1364 is connected between one end and the other end of the switch 135.

[0111] In this exemplary configuration, charge from the power supply 130 is stored in the capacitor 134. The accumulation of charge generates a voltage Vad across the capacitor 134, and this voltage Vad is applied to one end 135a of the switch 135. When the switch 135 is in the off state, one end 135a of the switch 135 is not connected to the other end 135b, so almost no current flows through the transistor 1361. In other words, the voltage Vad is not output to the wiring L2. When the switch 135 is in the on state, one end 135a of the switch 135 is connected to the other end 135b, so a current flows through the transistor 1361 and the voltage Vad is output to the wiring L2.

[0112] In the drive circuit 3A according to the second modification, mainly one of the first charging circuit 131 and the second charging circuit 132 (for example, the first charging circuit 131) applies a voltage to the adjusting electrode 7. When the discharge detection unit 15 detects a discharge, a charging circuit different from the first charging circuit (for example, the second charging circuit 132) applies a voltage to the adjusting electrode 7.

[0113] The moment a discharge occurs between the cathode electrode 5 and the adjusting electrode 7, the charge in the charging circuit that is applying a voltage to the adjusting electrode 7 decreases due to the discharge, and the output voltage from that charging circuit drops. However, the charge in a charging circuit different from that charging circuit (which was not applying a voltage to the adjusting electrode 7) does not decrease, or decreases only slightly, so the drop in the output voltage from that different charging circuit is suppressed. Therefore, by switching control so that the different charging circuit mainly applies voltage Vad to the adjusting electrode 7 based on the detection of a discharge by the discharge detection unit 15, the potential of the adjusting electrode 7 can be quickly restored to the potential before the discharge, without waiting for the charge in the charging circuit that has lost charge to be recharged.

[0114] Referring again to Fig. 11, the potential switching unit 16 switches the potential of the cathode electrode 5 when a discharge is detected. When the control unit 17 recognizes that a discharge current has been detected (the magnitude of the current has increased significantly) based on the current detection signal Idet from the discharge detection unit 15, the control unit 17 transmits a switching signal Sc1 to the potential switching unit 16. Details of the operation of the control unit 17 are the same as those described in Figs. 9(a) and 9(b) in the third embodiment.

[0115] During normal operation, the potential switching unit 16 connects the first contact terminal P1 to the third contact terminal P3. This connects the cathode electrode 5 to 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, current flows from the first contact terminal P1 to the third contact terminal P3. In addition, in the adjusting electrode power supply 13, both the first charging circuit 131 and the second charging circuit 132 hold the voltage Vad, and the control unit 137 performs control so that mainly either the first charging circuit 131 or the second charging circuit 132 applies the voltage Vad to the adjusting electrode 7.

[0116] When the switching signal Sc1 is input, the potential switching unit 16 connects the first contact terminal P1 and the second contact terminal P2, thereby connecting the cathode electrode 5 and the extraction electrode power supply 14. When the first contact terminal P1 and the second contact terminal P2 are connected, the potential Vg1 of the extraction electrode 8 is higher than the potential Vk of the cathode electrode 5, so that a discharge current flows from the second contact terminal P2 to the first contact terminal P1.

[0117] Also, at this time, in the adjusting electrode power supply 13, the control unit 137 switches control so that neither the first charging circuit 131 nor the second charging circuit 132 applies a voltage to the adjusting electrode 7. That is, in both the first charging circuit 131 and the second charging circuit 132 shown in Fig. 12, the switch 135 is set to a non-connected state. Thereafter, at a timing after the discharge state is resolved, the control unit 137 switches control so that the voltage Vad is output from one of the first charging circuit 131 and the second charging circuit 132 that is different from the charging circuit that output the voltage Vad when the discharge occurred.

[0118] After the control unit 137 switches control so that the voltage Vad is output from the different charging circuits, the control unit 17 transmits a switching signal Sc2 to the potential switching unit 16. When the switching signal Sc2 is input, the potential switching unit 16 connects the first contact terminal P1 to the third contact terminal P3. This connects the cathode electrode 5 to the cathode electrode power supply 12, and normal current again flows from the first contact terminal P1 to the third contact terminal P3. This makes the potential of the cathode electrode 5 lower than the potential of the extraction electrode 8, and emission of electrons E from the cathode electrode 5 resumes.

[0119] In the X-ray generator 1D, when a discharge between the cathode electrode 5 and the adjustment electrode 7 is detected, the potential switching unit 16 makes the potential of the extraction electrode 8 the same as or lower than the potential 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 9 even if a discharge occurs between the cathode electrode 5 and the adjustment electrode 7.

[0120] In the above example, the control unit 17 sends the first switching signal to the potential switching unit 16 each time it detects that the current detection signal Idet has exceeded a certain threshold. The present invention is not limited to this configuration. The control unit 17 may send the switching signal Sc1 to the potential switching unit 16 only when an event in which the current detection signal Idet exceeds the certain threshold occurs frequently (occurs multiple times within a predetermined time). Even in this case, the control unit 137 switches the charging circuit that outputs the voltage Vad to the adjusting electrode 7 between the first charging circuit 131 and the second charging circuit 132 each time a discharge occurs. Even in this configuration, as in the above embodiment, the potential of the adjusting electrode 7 can be quickly restored to the potential before discharge without waiting for the charging circuit whose charge has decreased to be recharged.

[0121] [Third Modification] As described above, the X-ray generators 1B and 1D include the cathode electrode 5 that emits electrons E, the adjustment electrode 7 that adjusts the amount of electrons E emitted from the cathode electrode 5, the extraction electrode 8 that extracts the electrons E from the cathode electrode 5, the target 9 that generates X-rays R when the electrons E are incident on it, the discharge detection unit 15 that detects discharge between the cathode electrode 5 and the adjustment electrode 7, and the potential switching unit 16 that makes the potential of the extraction electrode 8 higher than the potential of the cathode electrode 5 during normal operation and makes the potential of the extraction electrode 8 the same as or lower than the potential of the cathode electrode 5 during discharge detection. The potential switching unit 16 may be configured by a gas arrester instead of a semiconductor switch.

[0122] 14 is a diagram illustrating the configuration of a potential switching unit 16A according to the third modification. The potential switching unit 16A differs from the potential switching units 16 according to the embodiment, the first modification, and the second modification in that it includes a gas arrester 171 and a gas arrester drive 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 drive circuit 172. The other electrode 171b is connected to a second contact terminal P2.

[0123] The gas arrester drive circuit 172 generates a high voltage to be supplied between the pair of electrodes 171a, 171b of the gas arrester 171. The gas arrester drive 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 the discharge detection unit 15 has detected a discharge current, the control unit 17 generates a drive signal Sc1A and transmits the drive signal Sc1A to a control terminal of the transistor 172a. The drive signal Sc1A may be, for example, a pulse wave oscillating at a predetermined frequency or a PWM wave. In the example of FIG. 14 , a clamp resistor 172c is provided between the control terminal of the transistor 172a and the other electrode 171b.

[0124] 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. 14, a resistor 172d and a diode 172e may be provided between the power supply Vcc and the primary winding. Furthermore, a capacitor 172f may 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.

[0125] 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 the diodes 171a and 171b that is sufficient to discharge the gas arrester 171.

[0126] When a high voltage is supplied between the pair of electrodes 171 a and 171 b, the pair of electrodes 171 a and 171 b are short-circuited, so that the first contact terminal P1 and the second contact terminal P2 are connected to each other, and the potential Vk of the cathode electrode 5 rises to the same potential as the potential Vg of the extraction electrode 8.

[0127] In potential switching unit 16A, first contact terminal P1 and third contact terminal P3 are always connected, so when first contact terminal P1 and second contact terminal P2 are connected, cathode electrode power supply 12 may be short-circuited and damaged. Therefore, when detecting a discharge, control unit 17 drives gas arrester drive circuit 172 for stabilization time T3 and stops cathode electrode power supply 12. Then, after stabilization time T3 has elapsed, control unit 17 stops gas arrester drive circuit 172 and drives cathode electrode power supply 12.

[0128] 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.

[0129] [Fifth Modification] The waveform stabilization circuit 21 in the X-ray generator 1A according to the second embodiment is not limited to the circuit configuration shown in Fig. 6. Fig. 15 is a circuit diagram showing an example of a waveform stabilization circuit 21A in an X-ray generator according to the fifth modification. The waveform stabilization circuit 21A differs from the waveform stabilization circuit 21 according to the embodiment in the following points.

[0130] The first input terminal 21a is connected to a constant potential line 220, not to node N2. The first input terminal 21a is connected to the constant potential line 220 via a resistor 221. The constant potential line 220 applies a positive bias to the plurality of transistors 211 to 213. The potential of the constant potential line 220 is, for example, +15 V with respect to node N2. However, the potential of the constant potential line 21d is not limited to this, as long as it is a positive potential with respect to node N2. In the waveform stabilization circuit 21 shown in FIG. 6, when the potential Vg22 from the adjustment electrode 7 decreases, it becomes difficult for the plurality of MOSFET transistors 211 to 213 to operate in the active region. Furthermore, the bias voltage between the second input terminal 21b and the potential of node N1 alone is insufficient to pass a sufficient amount of current through the phototransistor 210, and the operating speed of the phototransistor 210 decreases. In the waveform stabilization circuit 21A of this modification, a constant voltage bias is applied to the first input terminal 21a from the constant potential line 220 in order to operate the plurality of transistors 211 to 213 in the active region even when the potential Vg22 from the adjustment electrode 7 drops. This allows the plurality of transistors 211 to 213 and the phototransistor 210 to continue operating in the active region regardless of the magnitude of the potential at the node N2, thereby improving the transient response and DC static characteristics of the waveform stabilization circuit.

[0131] In addition, the output terminal 21c is connected to the node N1 via the diode 222. In a configuration in which the first input terminal 21a is connected to the constant potential line 220 as in this modified example, even if the potential Vg22 from the adjustment electrode 7 is set to 0 V, the actual potential is at the same level as the bias voltage of the constant potential line 220 and does not become 0 V. To prevent this, the output terminal 21c is connected to the node N1 via the forward diode 222, thereby clamping the potential of the node N1, i.e., the potential Vg22. This makes it possible to suppress the potential Vg22 to a magnitude equivalent to the forward voltage of the diode 222 at most.

[0132] Additionally, in this modification, the plurality of transistors 211 to 213 are all depletion-type MOSFETs, which allows the gate-source voltage Vgs of each of the plurality of transistors 211 to 213 to be biased uniformly, thereby maintaining the linearity of the potential Vg22 over an extremely low voltage range.

[0133] The gist of the present disclosure is as follows: [1] to [6]. [1] An electron gun drive power supply for driving an electron gun including a cathode electrode that emits electrons, an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode, and an extraction electrode that extracts the electrons from the cathode electrode, the electron gun drive power supply including a potential switching unit that switches between a state in which the potential of the cathode electrode is lower than the potential of the extraction electrode and a state in which the potential of the cathode electrode is the same as or higher than the potential of the extraction electrode. [2] The electron gun drive power supply according to [1], wherein when the potential of the cathode electrode is the same as or higher than the potential of the extraction electrode, the potential of the adjustment electrode is higher than a cutoff voltage. [3] The electron gun drive power supply according to [1] or [2], further comprising: a detector that generates a detection signal indicating the magnitude of the voltage of the adjustment electrode when the potential of the cathode electrode switches from a state in which it is the same as or higher than the potential of the extraction electrode to a state in which the potential of the cathode electrode is lower than the potential of the extraction electrode; a driver connected to the detector and that generates an instruction signal based on a difference between the detection signal and a target value; and a waveform stabilization circuit having one end connected to the cathode electrode and the other end connected to the adjustment electrode, and flowing a current between the one end and the other end according to the magnitude of the voltage of the adjustment electrode indicated by the instruction signal. [4] The electron gun drive power supply according to any one of [1] to [3], wherein the potential switching unit is configured to include a semiconductor switch. [5] The electron gun drive power supply according to [4], wherein the semiconductor switch is configured from a plurality of FETs connected in series and parallel to each other. [6] The electron gun drive power supply according to [5], wherein the potential switching unit further includes a diode connected in series to the plurality of FETs and a resistor connected in series to the diode.

[0134] 5...cathode electrode, 7...adjusting electrode, 8...extraction electrode, 9...target, 16...potential switching unit, 18...detection unit, 19...driver, 21...waveform stabilization circuit, 21a...first input terminal (one terminal), 21c...output terminal (other terminal), 30...electron gun drive power supply, 161, 162, 163, 164...FET, 165, 166...diode, 167, 168...damping resistor, E...electron, Vcf...cutoff voltage, Vg1...potential of extraction electrode, Vg2...potential of adjustment electrode, Vk...potential of cathode electrode.

Claims

1. An electron gun drive power supply that drives an electron gun comprising: a cathode electrode that emits electrons; an adjustment electrode that adjusts the amount of electrons emitted from the cathode electrode; and an extraction electrode that extracts the electrons from the cathode electrode, the electron gun drive power supply comprising: a potential switching unit that switches between a state in which the potential of the cathode electrode is lower than the potential of the extraction electrode and a state in which the potential of the cathode electrode is the same as or higher than the potential of the extraction electrode.

2. An electron gun drive power supply according to claim 1, wherein the potential of said adjustment electrode is higher than the cut-off voltage when the potential of said cathode electrode is the same as or higher than the potential of said extraction electrode.

3. An electron gun drive power supply as claimed in claim 1 or 2, further comprising: a detection unit that generates a detection signal indicating the magnitude of the voltage of said adjustment electrode when the potential of said cathode electrode switches from a state in which it is the same as or higher than the potential of said extraction electrode to a state in which the potential of said cathode electrode is lower than the potential of said extraction electrode; a drive unit that is connected to said detection unit and generates an instruction signal based on the difference between the detection signal and a target value; and a waveform stabilization circuit that has one end connected to said cathode electrode and the other end connected to said adjustment electrode, and that flows a current between said one end and said other end according to the magnitude of the voltage of said adjustment electrode indicated by the instruction signal.

4. An electron gun drive power supply according to any one of claims 1 to 3, wherein the potential switching section includes a semiconductor switch.

5. An electron gun drive power supply according to claim 4, wherein said semiconductor switch is composed of a plurality of FETs connected in series and parallel to each other.

6. An electron gun drive power supply according to claim 5, wherein said potential switching section further includes: a diode connected in series to said plurality of FETs; and a resistor connected in series to said diode.

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