Electron gun

Abstract

This electron gun is provided with: a vacuum container; electrodes that are accommodated in the vacuum container and that include at least a cathode for emitting thermionic electrons from an electron emission surface and an anode for extracting the thermionic electrons; and a gas supply unit that supplies a cleaning gas for cleaning the cathode to the inside of the vacuum container.

Description

electron gun

[0001] The present disclosure relates to electron guns.

[0002] The electron gun includes a cathode, an anode, and a vacuum vessel that houses the cathode and anode. The electron gun heats the cathode in a vacuum and applies a high voltage between the cathode and anode, causing thermions to be emitted from the surface of the cathode, forming an electron beam (see, for example, Patent Document 1).

[0003] Patent No. 2964284

[0004] In an electron gun such as that described in Patent Document 1, the surface of the cathode may react with a portion of the residual gas in the vacuum chamber, forming a contaminant layer on the surface of the cathode. The formation of the contaminant layer reduces the amount of electron beam generated by thermoelectrons emitted from the surface of the cathode, causing problems such as loss of beam amount stability and cathode failure. Therefore, it is necessary to properly clean the surface of the cathode.

[0005] The present disclosure has been made in view of the above, and has an object to provide an electron gun that is capable of appropriately cleaning the surface of the cathode.

[0006] The electron gun according to the present disclosure includes a vacuum vessel, an electrode housed in the vacuum vessel and including at least a cathode that emits thermoelectrons from an electron emission surface and an anode for extracting the thermoelectrons, and a gas supply unit that supplies a cleaning gas into the vacuum vessel to clean the cathode.

[0007] According to the present disclosure, it is possible to properly clean the surface of the cathode.

[0008] Fig. 1 is a diagram schematically showing an example of an electron gun according to this embodiment. Fig. 2 is a diagram schematically showing another example of an electron gun. Fig. 3 is a diagram showing another example of a gas supply unit. Fig. 4 is a diagram schematically showing another example of an electron gun. Fig. 5 is a diagram schematically showing another example of an electron gun.

[0009] Hereinafter, embodiments of an electron gun according to the present disclosure will be described with reference to the drawings. Note that the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially identical.

[0010] Fig. 1 is a schematic diagram showing an example of an electron gun 100 according to this embodiment. The electron gun 100 shown in Fig. 1 supplies an electron beam to various devices such as a research electron beam accelerator, an ion source, an X-ray generator, etc. As shown in Fig. 1, the electron gun 100 includes a vacuum vessel 10, an electrode 20, a gas supply unit 30, and a control unit 40.

[0011] The vacuum vessel 10 is a vessel having an internal space K. The vacuum vessel 10 is provided with a pressure reduction mechanism 11 such as a pump that reduces the pressure in the space K. By reducing the pressure in the space K (a vacuum state) in the vacuum vessel 10, molecules such as gases in the space K are discharged, and collisions between thermions emitted from the cathode 21 and other molecules are suppressed.

[0012] The electrode 20 has a cathode 21 and an anode 22. A high voltage is applied between the cathode 21 and the anode 22 by a power supply 23. The cathode 21 is heated by power supplied from a heating power supply, and when heated, it emits thermoelectrons from the electron emission surface 21a, forming an electron beam EB. The anode 22 extracts the thermoelectrons emitted from the cathode 21 and accelerates the thermoelectrons. In this embodiment, the anode 22 is electrically grounded. Note that the anode 22 does not have to be electrically grounded, and the cathode 21 may be electrically grounded.

[0013] The gas supply unit 30 supplies cleaning gas G for purifying the cathode 21 to the space K inside the vacuum vessel 10 from the surfaces of the vacuum vessel 10 and the electrode 20 at a portion different from the cathode 21. Hereinafter, the portion of the vacuum vessel 10 and the electrode 20 different from the cathode 21 and from which the cleaning gas G is supplied from the surface will be referred to as the "supply portion." In this embodiment, the supply portion is the anode 22. That is, in this embodiment, the gas supply unit 30 supplies cleaning gas G to the space K from the surface of the anode 22.

[0014] In the electron gun 100, the electron emission surface 21a of the cathode 21 may react with part of the residual gas remaining in the space K inside the vacuum vessel 10, forming a contaminant layer 21b on the electron emission surface 21a. The formation of the contaminant layer 21b reduces the amount of electron beam EB generated by thermoelectrons emitted from the electron emission surface 21a, causing problems such as loss of beam amount stability and failure of the cathode 21. Therefore, it is necessary to properly clean the electron emission surface 21a.

[0015] In this embodiment, the gas supply unit 30 supplies a cleaning gas G capable of removing the contaminant layer 21b formed on the electron emission surface 21a of the cathode 21 to the space K inside the vacuum vessel 10. The gas supply unit 30 has a gas supply source 31, a gas flow path 32, and an outlet 33.

[0016] The gas supply source 31 is provided, for example, outside the vacuum vessel 10. As the gas supply source 31, for example, a gas cylinder can be used.

[0017] The gas flow path 32 is connected to the gas supply source 31 and is provided so as to penetrate from the outside to the inside of the vacuum vessel 10. A part of the gas flow path 32 is provided inside the anode 22, which is the supply part. Hereinafter, the part of the gas flow path 32 that is provided inside the anode 22 will be referred to as an internal flow path 32a. The gas flow path 32 is also provided with a valve 34. The valve 34 can adjust the flow rate of the cleaning gas G in the gas flow path 32 by adjusting the opening degree. The opening degree of the valve 34 can be configured to be automatically controlled by the control unit 40, for example, but may also be configured to be manually adjustable by an operator. In this embodiment, the gas supply unit 30 is provided with a valve 34. －７ Pa to 10 －６ The cleaning gas G is supplied to the space K so as to maintain a pressure of about Pa. When supplying such a small amount of gas, a variable leak valve, for example, can be used as the valve 34. In addition, an orifice 32f may be provided in the internal flow path 32a to adjust the flow rate of the cleaning gas G. Note that the orifice 32f does not necessarily have to be provided. The orifice 32f may be provided in the gas flow path 32.

[0018] The jet nozzle 33 is provided on the surface 22a of the anode 22 facing the space K. In the present embodiment, the jet nozzle 33 is arranged on the surface of the anode 22 facing the beam axis, but this configuration is not limiting. The jet nozzle 33 may be arranged on the surface of the anode 22 facing the cathode 21, for example. The jet nozzle 33 jets the cleaning gas G into the space K inside the vacuum vessel 10. The shape of the jet nozzle 33 may be, for example, a circle, an ellipse, or the like. The shape of the jet nozzle 33 may be any shape other than the above.

[0019] In the gas supply unit 30, an internal flow path 32a and an ejection port 33 are formed so as to promote the reaction between the beam and the cleaning gas G and to eject the cleaning gas G toward the cathode 21. For example, inside the anode 22, the tip side of the internal flow path 32a is provided in a curved or bent state toward the cathode 21. In the example shown in FIG. 1 , a bent portion 32c bent toward the cathode 21 is provided at the tip side of the internal flow path 32a. In addition, the ejection port 33 is provided on a surface of the anode 22 facing the beam axis. With this configuration, the angle between the ejected cleaning gas flow and the beam axis is reduced, the cross-sectional area of ​​the reaction between the beam and the cleaning gas is increased, and the cleaning gas G can be efficiently delivered to the cathode 21.

[0020] The control unit 40 controls the operation of each unit of the electron gun 100. The control unit 40 can control the operation of the power supply unit 23. The control unit 40 can control the opening degree of the valve 34 in the gas supply unit 30 and the timing of adjusting the opening degree. The control unit 40 can cause the gas supply unit 30 to supply a cleaning gas G, for example, during a period when thermions are being emitted from the cathode 21. In this case, the cleaning gas G supplied from the gas supply unit 30 can be a gas that removes the contaminant layer 21b on the electron emission surface 21a of the cathode 21 by interacting with the electron beam EB.

[0021] Alternatively, the apparatus may have a detector 50 that detects the beam amount of the electron beam EB and supplies the detection results to the control unit 40. For example, the beam amount can be measured based on the measurement results of a separately provided current transmitter and the value of the current flowing through the power supply unit 23, but the configuration for measuring the beam amount is not limited to the above. In this case, the control unit 40 can control the supply of the cleaning gas G by the gas supply unit 30 based on the detection results of the beam amount.

[0022] Next, the operation of the electron gun 100 configured as described above will be described. First, the space K inside the vacuum vessel 10 is evacuated. In this state, the cathode 21 is heated by power supplied from a heating power supply. When the cathode 21 is heated, electrons present in the cathode 21 become thermions and are emitted from the cathode 21.

[0023] As described above, when the electron emission surface 21a of the cathode 21 reacts with part of the residual gas remaining in the space K inside the vacuum vessel 10, a contaminant layer 21b is formed on the electron emission surface 21a. When the contaminant layer 21b is formed, the amount of the electron beam EB caused by the thermoelectrons emitted from the electron emission surface 21a decreases, so the electron emission surface 21a is cleaned.

[0024] When cleaning the electron emission surface 21 a, cleaning gas G is supplied from the gas supply unit 30 to the space K inside the vacuum vessel 10. When the detected beam amount is equal to or less than a predetermined threshold, the control unit 40 causes the gas supply unit 30 to supply cleaning gas G. By performing the above control by the control unit 40, cleaning gas G is automatically supplied when the beam amount is equal to or less than the predetermined threshold, so that the contaminant layer 21 b on the electron emission surface 21 a can be properly removed.

[0025] In this embodiment, a gas capable of removing the contaminant layer 21b through interaction with the electron beam EB is used as the cleaning gas G. Therefore, the control unit 40 controls the gas supply unit 30 to supply the cleaning gas G, for example, during a period in which thermions are emitted from the cathode 21. This allows the contaminant layer 21b to be efficiently removed through interaction between the cleaning gas G and the electron beam EB. The gas supply unit 30 is also configured to eject the cleaning gas G toward the cathode 21. Therefore, the gas supply unit 30 can efficiently supply the cleaning gas G toward the cathode 21.

[0026] When cleaning gas G is supplied from the gas supply unit 30, a portion of the supplied cleaning gas G interacts with the electron beam EB and is ionized. In this case, the ions Ga collide with the contaminant layer 21b of the cathode 21, and the impact physically removes a portion of the contaminant layer 21b. Furthermore, molecules Gb of the supplied cleaning gas G chemically react with the contaminant layer 21b. This chemical reaction chemically removes the contaminant layer 21b from the cathode 21. The composition of the cleaning gas G can be selected from one that is easily removed by the heat generated by the cathode and one that has a cleaning effect on a specific contaminant layer in a very small amount. The molecules Gb of the cleaning gas G can be selected from, for example, lanthanum hexaboride (LaB ６ ) carbon dioxide (CO ) in a situation where the cathode is contaminated with hydrocarbons. ２ ) can be selected, but compositions other than those exemplified above may also be used. By removing the contaminant layer 21b from the cathode 21, the electron emission surface 21a is cleaned, and a predetermined beam amount can be obtained as the beam amount of the electron beam EB.

[0027] The electron gun 100 according to this embodiment comprises a vacuum vessel 10, an electrode 20 housed in the vacuum vessel 10 and including at least a cathode 21 that emits thermoelectrons and an anode 22 for extracting the thermoelectrons, and a gas supply unit 30 that supplies cleaning gas G for purifying the cathode 21 into the interior of the vacuum vessel 10 from the surfaces of the vacuum vessel 10 and the electrode 20 at a supply portion different from that of the cathode 21.

[0028] According to this configuration, the gas supply unit 30 supplies cleaning gas G that cleans the cathode 21 from the surface of the supply portion into the inside of the vacuum vessel 10, so that the cathode 21 can be properly cleaned by the cleaning gas G.

[0029] Fig. 2 is a diagram schematically illustrating another example of an electron gun. The electron gun 200 shown in Fig. 2 has a configuration in which, in addition to the components of the electron gun 100 shown in Fig. 1, a Wehnelt electrode 25 is provided on the electrode 20. A negative voltage is applied to the Wehnelt electrode 25 with respect to the cathode 21 by the power supply unit 23. The Wehnelt electrode 25 may also be set to the same potential as the cathode 21 by the power supply unit 23. As a result, the traveling direction of thermions emitted from the cathode 21 and passing through the Wehnelt electrode 25 is narrowed toward the central axis AX.

[0030] In the electron gun 200, the gas supply unit 130, like the gas supply unit 30 of the electron gun 100, supplies cleaning gas G to the space K inside the vacuum vessel 10 from the surfaces of the vacuum vessel 10 and the supply portion of the electrode 20 that is different from the cathode 21. On the other hand, in this embodiment, the supply portion is the Wehnelt electrode 25. That is, in this embodiment, the gas supply unit 130 supplies cleaning gas G to the space K from the surface of the Wehnelt electrode 25. Like the gas supply unit 30 of the electron gun 100, the gas supply unit 130 has a gas supply source 131 such as a gas cylinder, a gas flow path 132 through which the cleaning gas G flows, and an ejection port 133 from which the cleaning gas G is ejected.

[0031] The gas flow path 132 penetrates from the outside to the inside of the vacuum vessel 10. A portion of the gas flow path 132 is provided inside the Wehnelt electrode 25, which is the supply portion. Hereinafter, the portion of the gas flow path 132 that is provided inside the Wehnelt electrode 25 will be referred to as an internal flow path 132a. A valve 134 is provided in the gas flow path 132. The opening of the valve 134 may be adjusted manually by an operator or may be automatically controlled by the control unit 40. An orifice may be provided in the gas flow path 132 to adjust the flow rate of the cleaning gas G.

[0032] The ejection port 133 is provided on the surface 25a of the Wehnelt electrode 25. The ejection port 133 is provided at the tip of the internal flow path 132a. The ejection port 133 ejects the cleaning gas G into the space K inside the vacuum vessel 10. The shape of the ejection port 133 may be, for example, a circle, an ellipse, or the like, but may also be any other shape.

[0033] In the gas supply unit 130, an internal flow path 132a and an ejection port 133 are formed so that the cleaned gas G is ejected toward the cathode 21. For example, inside the Wehnelt electrode 25, the tip side of the internal flow path 132a is provided in a curved or bent state toward the cathode 21. In the example shown in FIG. 2 , a bent portion 132c bent toward the cathode 21 is provided at the tip side of the internal flow path 132a. This configuration allows the cleaned gas G to efficiently reach the cathode 21.

[0034] 2 also uses a cleaning gas G that can remove the contaminant layer 21b through interaction with the electron beam EB. For this reason, the control unit 40 controls the gas supply unit 130 to supply the cleaning gas G, for example, during a period in which thermoelectrons are emitted from the cathode 21. This allows the contaminant layer 21b to be efficiently removed through interaction between the cleaning gas G and the electron beam EB.

[0035] The electron gun 200 according to this embodiment comprises a vacuum vessel 10, an electrode 20 housed in the vacuum vessel 10 and including at least a cathode 21 that emits thermoelectrons and an anode 22 for extracting the thermoelectrons, and a gas supply unit 130 that supplies cleaning gas G for purifying the cathode 21 to the inside of the vacuum vessel 10 from the surfaces of the vacuum vessel 10 and a supply portion of the electrode 20 that is different from the cathode 21, and the electrode 20 further includes a Wehnelt electrode 25 that confines the thermoelectrons emitted from the cathode 21, and the supply portion is provided on the Wehnelt electrode 25.

[0036] According to this configuration, the supply portion for supplying the cleaning gas G from the gas supply unit 130 is provided on the Wehnelt electrode 25, so that the cleaning gas G can be appropriately supplied to the cathode 21. Furthermore, by using a gas that removes the contaminant layer 21b by interacting with the electron beam EB as the cleaning gas G, it is possible to efficiently generate an interaction with the electron beam EB.

[0037] Fig. 3 is a diagram showing another example of a gas supply unit. The gas supply unit 230 shown in Fig. 3 can be used in place of the gas supply unit 30 of the electron gun 100 and the gas supply unit 130 of the electron gun 200 described above. Fig. 3 will be described taking an electron gun 300 equipped with the gas supply unit 230 as an example. As shown in Fig. 3, the gas supply unit 230 has a gas supply source 231, a gas flow path 232, a gas outlet 233, a gas adsorbent 234, a first valve 235, and a second valve 236.

[0038] The gas supply source 231 is provided, for example, outside the vacuum vessel 10. As the gas supply source 231, for example, a gas cylinder can be used.

[0039] The gas flow path 232 is connected to the gas supply source 231 and penetrates from the outside to the inside of the vacuum vessel 10. A portion of the gas flow path 232 is provided inside the supply portion 220 (e.g., the vacuum vessel 10, the anode 22, the Wehnelt electrode 25, etc.). Hereinafter, the portion of the gas flow path 232 provided inside the supply portion 220 will be referred to as an internal flow path 232a. An orifice 232f may be provided in the internal flow path 232a to adjust the flow rate of the cleaning gas G. However, the orifice 232f does not necessarily have to be provided. The gas flow path 232 also has a branch flow path 232b upstream of the internal flow path 232a. The branch flow path 232b is connected to a storage chamber 237 that stores the gas adsorbent 234.

[0040] The ejection port 233 is provided on the surface 220a of the supply portion 220. The ejection port 233 is provided at the tip of the internal flow path 232a. The ejection port 233 ejects the cleaning gas G into the space K inside the vacuum vessel 10.

[0041] The gas adsorbent 234 is capable of adsorbing the cleaning gas G supplied from the gas supply source 231. An example of the gas adsorbent 234 is a Ti getter. The gas adsorbent 234 is heated using, for example, a heating mechanism 238, thereby releasing the adsorbed cleaning gas G.

[0042] The first valve 235 and the second valve 236 can adjust the flow rate of the cleaned gas G in the gas flow path 232 by adjusting their opening degrees. The first valve 235 and the second valve 236 can be, for example, variable leak valves. The first valve 235 is provided in the gas flow path 232 upstream of the branch flow path 232b. The second valve 236 is provided in a portion of the gas flow path 232 between the branch flow path 232b and the internal flow path 232a. The opening degrees of the first valve 235 and the second valve 236 can be configured to be automatically controlled by, for example, the control unit 40, or may be configured to be manually adjustable by an operator.

[0043] The control unit 40 controls the opening degree and the timing of the opening degree adjustment of the first valve 235 in the gas supply unit 230. The control unit 40 can cause the cleaned gas G from the gas supply source 231 to be adsorbed by the gas adsorbent 234, for example, by opening the first valve 235 and closing the second valve 236.

[0044] After the clean gas G has been adsorbed into the gas adsorbent 234, the control unit 40 closes the first valve 235, opens the second valve 236, and causes the gas adsorbent 234 to generate heat, thereby releasing the adsorbed clean gas G from the gas adsorbent 234. The released clean gas G passes through the open second valve 236, reaches the internal flow path 232 a, and is released from the internal flow path 232 a through the outlet 233 into the space K inside the vacuum vessel 10.

[0045] When all of the purified gas G has been released from the gas adsorbent 234, the first valve 235 can be opened again and the second valve 236 can be closed, thereby allowing the purified gas G from the gas supply source 231 to be adsorbed by the gas adsorbent 234.

[0046] In this way, after the cleaning gas G is adsorbed into the gas adsorbent 234, the adsorbed cleaning gas G is released from the gas adsorbent 234, thereby supplying an appropriate amount of cleaning gas G to the space K inside the vacuum vessel 10.

[0047] Fig. 4 is a diagram schematically illustrating another example of an electron gun. The electron gun 400 shown in Fig. 4 has a configuration in which, in addition to the components of the electron gun 100 shown in Fig. 1, a Wehnelt electrode 25 is provided on the electrode 20. The configuration of the Wehnelt electrode 25 is the same as that described in Fig. 2.

[0048] In the electron gun 400, the gas supply unit 330 supplies the cleaning gas G to the space K inside the vacuum vessel 10 via the vacuum vessel 10. The gas supply unit 330 supplies the cleaning gas G to the space K via the bottom 12 of the vacuum vessel 10. In other words, the supply portion is the bottom 12 of the vacuum vessel 10. Similar to the gas supply unit 30 of the electron gun 100, the gas supply unit 330 has a gas supply source 331 such as a gas cylinder, a gas flow path 332 through which the cleaning gas G flows, and an ejection port 333 from which the cleaning gas G is ejected.

[0049] The gas flow path 332 penetrates the bottom 12 of the vacuum vessel 10 from the outside to the inside. The arrangement of the gas flow path 332 shown in FIG. 4 is an example. The gas flow path 332 may be provided at another position on the bottom 12 of the vacuum vessel 10. A valve 334 is provided in the gas flow path 332. The opening of the valve 334 may be adjusted manually by an operator, or may be automatically controlled by the control unit 40. An orifice may be provided in the gas flow path 332 to adjust the flow rate of the cleaning gas G.

[0050] The ejection port 333 is provided at a position protruding upward from the bottom 12 of the vacuum vessel 10. The ejection port 333 is provided at the tip of the gas flow path 332. The ejection port 333 ejects the cleaning gas G into the space K inside the vacuum vessel 10. The shape of the ejection port 333 may be, for example, a circle, an ellipse, or the like, but may also be any other shape.

[0051] In the gas supply unit 330, a gas flow path 332 and an ejection port 333 are formed so that the cleaned gas G is ejected toward the cathode 21. For example, the tip side of the gas flow path 332 is provided in a curved or bent state toward the cathode 21. In the example shown in Fig. 4, the tip side of the gas flow path 332 is provided with a bent portion 332c that is bent toward the cathode 21. This configuration allows the cleaned gas G to efficiently reach the cathode 21.

[0052] Fig. 5 is a diagram schematically illustrating another example of an electron gun. The electron gun 500 shown in Fig. 5 is different from the electron gun 400 shown in Fig. 4 in the arrangement of the gas supply unit, but is otherwise similar in configuration to the electron gun 400.

[0053] In the electron gun 500, the gas supply unit 430 supplies the cleaning gas G to the space K inside the vacuum vessel 10 via the vacuum vessel 10. The gas supply unit 430 supplies the cleaning gas G to the space K via the side portion 13 of the vacuum vessel 10. In other words, the supply portion is the side portion 13 of the vacuum vessel 10. Like the gas supply unit 330 of the electron gun 400, the gas supply unit 430 has a gas supply source 431 such as a gas cylinder, a gas flow path 432 through which the cleaning gas G flows, and an ejection port 433 from which the cleaning gas G is ejected.

[0054] The gas flow path 432 is provided so as to penetrate the side portion 13 of the vacuum vessel 10 from the outside to the inside. The arrangement of the gas flow path 432 shown in FIG. 5 is one example. The gas flow path 432 may be provided at another position on the side portion 13 of the vacuum vessel 10. A valve 434 is provided in the gas flow path 432. The opening of the valve 434 may be adjusted manually by an operator, or may be automatically controlled by the control unit 40. An orifice may be provided in the gas flow path 432 to adjust the flow rate of the cleaning gas G.

[0055] The ejection port 433 is provided at a position protruding horizontally from the side portion 13 of the vacuum vessel 10. The ejection port 433 is provided at the tip of the gas flow path 432. The ejection port 433 ejects the cleaning gas G into the space K inside the vacuum vessel 10. The shape of the ejection port 433 may be, for example, a circle, an ellipse, or the like, but may also be any other shape.

[0056] In the gas supply unit 430, a gas flow path 432 and an ejection port 433 are formed so that the cleaned gas G is ejected toward the cathode 21. For example, the tip side of the gas flow path 432 is provided in a curved or bent state toward the cathode 21. In the example shown in Fig. 5, the tip side of the gas flow path 432 is provided with a bent portion 432c that is bent downward toward the cathode 21. This configuration allows the cleaned gas G to efficiently reach the cathode 21.

[0057] 4 and 5 also use a cleaning gas G that can remove the contaminant layer 21b through interaction with the electron beam EB. For this reason, the control unit 40 controls the gas supply unit 330 to supply the cleaning gas G, for example, during the period when thermions are being emitted from the cathode 21. This allows the contaminant layer 21b to be efficiently removed through interaction between the cleaning gas G and the electron beam EB.

[0058] The electron guns 400 and 500 according to this embodiment comprise a vacuum vessel 10, an electrode 20 housed in the vacuum vessel 10 and including at least a cathode 21 that emits thermoelectrons and an anode 22 for extracting thermoelectrons, and a gas supply unit 330, 430 that supplies cleaning gas G from the vacuum vessel 10 to the inside of the vacuum vessel 10 to clean the cathode 21.

[0059] According to this configuration, the cleaning gas G can be supplied from the vacuum vessel 10 by the gas supply units 330, 430, and therefore the installation positions of the gas supply units 330, 430 can be selected with a high degree of freedom from the bottom 12 or the side 13 of the vacuum vessel 10. Furthermore, by using a gas that removes the contaminant layer 21b by interacting with the electron beam EB as the cleaning gas G, it is possible to efficiently generate an interaction with the electron beam EB.

[0060] As described above, according to the first aspect of the present disclosure, there is provided an electron gun comprising: a vacuum vessel 10; an electrode 20 housed in the vacuum vessel 10 and including at least a cathode 21 that emits thermions and an anode 22 for extracting thermions; and a gas supply unit 30 that supplies cleaning gas G for purifying the cathode 21 into the vacuum vessel 10. Specifically, the electron gun comprises the vacuum vessel 10; the electrode 20 housed in the vacuum vessel 10 and including at least a cathode 21 that emits thermions and an anode 22 for extracting thermions; and the gas supply unit 30 that supplies cleaning gas G for purifying the cathode 21 into the vacuum vessel 10 from the surfaces of supply portions of the vacuum vessel 10 and the electrode 20 that are different from those of the cathode 21.

[0061] According to this configuration, the gas supply unit 30 supplies cleaning gas G that cleans the cathode 21 from the surface of the supply portion into the inside of the vacuum vessel 10, so that the cathode 21 can be properly cleaned by the cleaning gas G.

[0062] According to a second aspect of the present disclosure, in the electron gun according to the first aspect, the gas supply unit 30 is provided to eject the cleaning gas G toward the cathode 21 .

[0063] According to this configuration, the cleaning gas G can be efficiently supplied from the gas supply unit 30 toward the cathode 21 .

[0064] According to a third aspect of the present disclosure, in the electron guns according to the first and second aspects, the gas supply unit 30 has an internal flow path 32a for the cleaning gas G inside the supply portion and has a jet 33 connected to the internal flow path 32a on the surface of the supply portion. Specifically, the gas supply unit 30 has a flow path 32a for the cleaning gas G inside the anode 22 and has a jet 33 connected to the flow path 32a on the surface of the anode 22. The gas supply unit 30 also has a flow path 132a for the cleaning gas G inside the Wehnelt electrode 25 and has a jet 133 connected to the flow path 132a on the surface of the Wehnelt electrode 25.

[0065] According to this configuration, the cleaned gas G can be efficiently supplied by circulating the cleaned gas G through the internal flow paths 32a, 132a of the supply section and ejecting the cleaned gas G from the nozzles 33, 133 on the surface of the supply section.

[0066] According to a fourth aspect of the present disclosure, in the electron gun according to any one of the first to third aspects, the supply portion is provided on the anode 22. Specifically, the anode 22 is electrically grounded, and the gas supply unit 30 supplies the cleaning gas from the surface of the anode 22.

[0067] According to this configuration, the cleaning gas is supplied from the surface of the anode 22, so that discharge at the anode 22 can be avoided.

[0068] According to a fifth aspect of the present disclosure, in the electron gun according to any one of the first to fourth aspects, the electrode 20 further includes a Wehnelt electrode 25 that confines thermions emitted from the cathode 21, and the supply portion is provided in the Wehnelt electrode 25. Specifically, the gas supply unit 30 supplies the cleaning gas from the surface of the Wehnelt electrode 25.

[0069] According to this configuration, by supplying the cleaning gas G to the cathode 21 from the surface of the Wehnelt electrode 25, it is possible to efficiently generate an interaction between the cleaning gas G and the electron beam EB.

[0070] According to a sixth aspect of the present disclosure, the electron gun according to any one of the first to fifth aspects further comprises a control unit 40 that controls the supply of cleaning gas G by the gas supply unit 30 .

[0071] According to this configuration, the supply of the cleaning gas G by the gas supply unit 30 can be automatically performed under the control of the control unit 40.

[0072] According to a seventh aspect of the present disclosure, in the electron gun of the sixth aspect, the gas supply unit 30 supplies a cleaning gas G that removes the contaminant layer 21 b on the electron emission surface 21 a of the cathode 21 by interacting with the electron beam EB, and the control unit 40 causes the gas supply unit 30 to supply the cleaning gas G during the period when the thermoelectrons are emitted.

[0073] According to this configuration, by causing the gas supply unit 30 to supply the cleaning gas G during the period in which the thermoelectrons are emitted, it is possible to efficiently generate an interaction between the electron beam EB and the cleaning gas G.

[0074] According to the eighth aspect of the present disclosure, the electron gun according to the seventh aspect is provided with a detection unit 50 that detects the beam amount of the electron beam EB generated by thermions, and the control unit 40 causes the gas supply unit 30 to supply the cleaning gas G based on the detection result of the beam amount.

[0075] According to this configuration, the control unit 40 can automatically control the supply of the cleaning gas G by the gas supply unit 30 based on the detection result of the beam amount.

[0076] According to a ninth aspect of the present disclosure, in the electron gun according to the eighth aspect, the control unit 40 causes the gas supply unit 30 to supply the cleaning gas G when the detection result of the beam amount is equal to or less than a threshold value.

[0077] According to this configuration, when the detection result of the beam amount becomes equal to or less than the threshold value, the gas supply unit 30 is caused to supply the cleaning gas G, so that the electron emission surface 21 a of the cathode 21 can be properly cleaned.

[0078] 10 Vacuum vessel 11 Pressure reduction mechanism 20 Electrode 21 Cathode 21a Electron emission surface 21b Contamination layer 22 Anode 22a, 25a, 220a Surface 23 Power supply unit 25 Wehnelt electrode 30, 130, 230, 330, 430 Gas supply unit 31, 131, 231, 331, 431 Gas supply source 32, 132, 232, 332, 432 Gas flow path 32a, 132a, 232a Internal flow path 32c, 132c Bent portion 32f, 232f Orifice 33, 133, 233, 333, 433 Jet port 34, 134 Valve 40 Control unit 50 Detection unit 100, 200, 300, 400, 500 Electron gun 220 Supply portion 232b Branch flow path 234 Gas adsorbent 235 First valve 236 Second valve 237 Storage chamber 238 Heating mechanism AX Central axis EB Electron beam G Cleaning gas Ga ion Gb molecule K space

Claims

1. An electron gun comprising: a vacuum vessel; electrodes housed in the vacuum vessel and including at least a cathode that emits thermoelectrons from an electron emission surface and an anode for extracting the thermoelectrons; and a gas supply unit that supplies a cleaning gas into the vacuum vessel to clean the cathode.

2. The electron gun according to claim 1, wherein the gas supply unit is provided so as to jet the cleaning gas toward the cathode.

3. The electron gun according to claim 1, wherein the anode is electrically grounded, and the gas supply unit supplies the cleaning gas from a surface of the anode.

4. The electron gun according to claim 3, wherein the gas supply unit has a flow path for the cleaning gas inside the anode and a nozzle connected to the flow path on the surface of the anode.

5. The electron gun according to claim 1, wherein the electrode further includes a Wehnelt electrode for constricting the thermions emitted from the cathode, and the gas supply unit supplies the cleaning gas from a surface of the Wehnelt electrode.

6. The electron gun according to claim 5, wherein the gas supply unit has a flow path for the cleaning gas inside the Wehnelt electrode and a nozzle connected to the flow path on the surface of the Wehnelt electrode.

7. The electron gun according to claim 1, further comprising a control unit that controls the supply of the cleaning gas by the gas supply unit.

8. The electron gun according to claim 7, wherein the control unit controls the gas supply unit to supply the cleaning gas during the period in which the thermoelectrons are emitted.

9. The electron gun according to claim 7, further comprising a detection unit that detects the amount of the electron beam generated by the thermal electrons, and the control unit controls the gas supply unit to supply the cleaning gas based on the detection result of the beam amount.

10. The electron gun according to claim 9, wherein the control unit causes the gas supply unit to supply the cleaning gas when the detected beam quantity is equal to or less than a threshold value.

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