WO2008068806A1

WO2008068806A1 - Rf electron gun

Info

Publication number: WO2008068806A1
Application number: PCT/JP2006/323978
Authority: WO
Inventors: Hironari Yamada; Daisuke Hasegawa; Norio Toyosugi
Original assignee: Photon Production Laboratory, Ltd.
Priority date: 2006-11-30
Filing date: 2006-11-30
Publication date: 2008-06-12
Also published as: JPWO2008068806A1; JP4900620B2

Abstract

A small and inexpensive RF electron gun capable of outputting an electron beam with high convergence comprises a housing (10), a magnet consisting of a pole piece (13d) and a coil (14d) to generate a magnetostatic field, an emitter (15) arranged in a region generating the magnetostatic field and emitting electrons (e), an acceleration cavity (16) arranged in a region generating the magnetostatic field and generating a high frequency electric field on receiving a microwave (RF), and correction magnets (18d, 19d), wherein the magnet forms a first region having a uniform magnetostatic field and second regions (A1, A2) where the strength of magnetostatic field varies monotonously, and a plurality of electrons emitted from the emitter (15) are moved spirally (S) by the high frequency electric field and the magnetostatic field in the first region and then converged by the magnetostatic field in the second region (A1) and the correction magnets (18d, 19d) before being outputted.

Description

Specification

RF electron gun

Technical field

TECHNICAL FIELD [0001] The present invention relates to an RF electron gun, and more particularly to a small RF electron gun that can output an electron beam with high focusing.

Background art

An RF electron gun is known as an electron beam generating means. As an example, FIG. 8 shows an RF electron gun disclosed in Patent Documents 1 and 2 below.

[0003] The RF electron gun shown in Fig. 8 includes an RF electron gun cavity 101, a force sword 102 that generates thermal electrons, a drift space 103, a vacuum box 105, a slit 106 that determines the energy width of the electron beam 104, and an electron Α electromagnet 107 that deflects beam 104 into α shape, acceleration tube 108 that further accelerates electron beam 104 extracted from α electromagnet 107, beam duct 109, beam extraction window 110 that extracts the electron beam from the vacuum to the atmosphere 110, RF A phase shift attenuator 111 for adjusting the phase and amplitude of the microwave supplied to the electron gun cavity 101, a power distributor 112 for distributing the microwave power, a main oscillator 113, an RF source 114 operated by the main oscillator 113, and A pulse modulator 115 for powering the RF source 114;

[0004] The operation is as follows. When microwaves are supplied to the RF electron gun cavity 101 from the RF source 114 via the power distributor 112 and the phase shift attenuator 111, a microwave electric field is generated in the RF electron gun cavity 101 in the axial direction. Thermoelectrons are drawn from the high-temperature force sword 102 placed in The electron beam 104 extracted from the force sword 102 is further accelerated by the electric field in the RF electron gun cavity 101 and reaches the entrance of the α electromagnetic stone 107 through the drift space 103 which is a vacuum duct. The electron beam 104 at this time has a continuous energy spectrum up to a predetermined maximum value due to the phase of the microwave. When the electron beam 104 with various speeds passes through a uniform magnetic field formed by the α electromagnet 107, momentum dispersion occurs and the beam width widens, so that only electrons in a predetermined energy range can be seen. It can pass between the slits 106 and enters the acceleration tube 108. Reference numerals 104a to 104c denote electron beams that can pass through the slit 106. From RF power supply 114 The high power microwave is generated by amplifying the low power microwave from the main oscillator 113 with an RF amplifier, and the RF source 114 functions as a microwave amplifier. The RF source 114 is normally driven by a pulse and produces a strong peak power.

[0005] The energy spectrum of the electron beam extracted from the RF electron gun cavity 101 is related to the phase of the microwave electric field formed in the RF electron gun cavity 101, and the bunched electron beam on the orbit in the α electromagnet 107 Accelerated by the acceleration tube 108. Further, a quadrupole magnet that forms a quadrupole magnetic field may be arranged behind the α electromagnetic stone 107 to bundle the electron beam 104 ^^ extracted from the α electromagnet 107.

Patent Document 1: Japanese Patent Laid-Open No. 7-235399

Patent Document 2: U.S. Pat.No. 4,641,103

Disclosure of the invention

Problems to be solved by the invention

[0006] As described above, the conventional RF electron gun needs to separately provide means for emitting and accelerating thermionic electrons and means for selecting a specific energy electron (a electromagnet). It was a large and expensive device. In addition, if a means (quadrupole magnet) for focusing the electron beam is provided behind the means (α electromagnet) for selecting electrons of a specific energy, the apparatus becomes larger and more expensive.

Therefore, an object of the present invention is to provide a small and inexpensive RF electron gun that can output an electron beam with high focusing.

Means for solving the problem

The object of the present invention is achieved by the following means.

That is, the RF electron gun according to the present invention includes a magnet that generates a static main magnetic field, an emitter that emits electrons disposed in a region where the main magnetic field is generated, and the main magnetic field. And an acceleration cavity that generates a high-frequency electric field when microwaves are input, and the magnet has a first region where the static magnetic field is uniform, and the static magnetic field strength decreases monotonously in a predetermined direction. The plurality of electrons that form a small second region and also emit the emitter force are moved in a spiral shape around the emitter by the high-frequency electric field and the static magnetic field of the first region. It is characterized by being output after being focused by a static magnetic field of two regions Yes.

[0010] In the RF electron gun, the predetermined direction is a direction in which the Emitter force moves away, and the static magnetic field strength in the second region may monotonously decrease in the static magnetic field strength force in the first region. it can.

[0011] Further, the RF electron gun includes two first correction magnets and two second correction magnets arranged in the vicinity of the second region, and the two first correction magnets are arranged in the second region. Are arranged opposite to each other, generate a static magnetic field parallel to the main magnetic field between them, and the two second correction magnets are arranged opposite to each other with the second region interposed therebetween, A static magnetic field parallel to the main magnetic field is generated between them, and the magnetic pole of the opposing surface of one of the first correction magnets and the magnetic pole of the opposing surface of the other first correction magnet have opposite polarities, The magnetic pole of the opposing surface of the second correction magnet and the magnetic pole of the opposing surface of the other second correction magnet have opposite polarities, and the first correction magnet disposed on the same side with respect to the second region And the magnetic poles of the opposing surfaces of each of the second correction magnets have opposite polarities, and the electrons pass between the first correction magnets. After that, when the first correction magnet passes between the second correction magnets and the electrons pass between the two first correction magnets, the first correction magnet has a longer passing distance as the energy increases. When the electrons pass between the two second correction magnets, the second correction magnet may be arranged such that the smaller the energy, the longer the passing distance.

[0012] In the RF electron gun, the emitter is disposed on a first wall surface of the acceleration cavity, the first wall surface has a slit through which electrons pass, and the electron emitted by the emitter force is After accelerating in the center direction of the acceleration cavity, approach the first wall surface, pass through the slit on the first wall surface, and pass through the second region formed outside the acceleration cavity. It is out.

[0013] In the RF electron gun, the emitter is disposed on a first wall surface of the acceleration cavity, the first wall surface has a slit through which electrons pass, and the electron emitted by the emitter force is After accelerating toward the center of the acceleration cavity, approach the first wall surface, pass through the slit on the first wall surface and exit to the outside of the acceleration cavity, and then pass the slit on the first wall surface again. Pass through and pass through the second region. The invention's effect

According to the present invention, a small and inexpensive RF electron gun can be realized by disposing the means for emitting and accelerating thermionic electrons in the static magnetic field generating means.

[0015] In addition, by forming the distribution of the main magnetic field so that the magnetic field strength decreases monotonously as it moves away from the means for emitting thermal electrons in a part of the spiral orbit of the electron beam, The focusing property of the electron beam can be improved.

[0016] Further, the electron beam can be further focused by disposing the correction magnet in the static magnetic field generating means.

[0017] Further, by focusing the electron beam immediately after exiting the acceleration cavity, the acceleration efficiency of the electrons can be increased, and the current value of the electron beam taken out from the RF electron gun can be increased.

Brief Description of Drawings

FIG. 1 is a perspective view showing an RF electron gun according to an embodiment of the present invention.

FIG. 2 is a horizontal sectional view showing a configuration of an RF electron gun according to an embodiment of the present invention.

FIG. 3 is a vertical sectional view showing a configuration of an RF electron gun according to an embodiment of the present invention.

FIG. 4 is a graph showing a magnetic field distribution generated inside the RF electron gun according to the embodiment of the present invention.

FIG. 5 is a horizontal sectional view showing a part of an RF electron gun according to another embodiment of the present invention.

FIG. 6 is a diagram showing an electron beam trajectory obtained by a simulation in a state where a correction magnet is not provided in the RF electron gun according to the embodiment of the present invention.

FIG. 7 is a diagram showing an electron beam trajectory obtained by simulation in a state in which a correction magnet is provided in the RF electron gun according to the embodiment of the present invention.

FIG. 8 is a plan view showing a configuration of a conventional RF electron gun.

Explanation of symbols

[0019] 1 RF electron gun

10 Enclosure

11 RF guide section

12 Beam extraction section 13u, 13d pole piece

14u, 14d coil

15 Emmit

16 Acceleration cavity

17u, 17d convex

18u, 18d 1st correction magnet

19u, 19d 2nd correction magnet

20 Extraction pipe

S electron beam

A1 ~ A5 Focusing area

e

RF microwave

Ll, L2 Electron beam spread after focusing

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing an RF electron gun according to an embodiment of the present invention. The RF electron gun 1 includes a casing unit 10, an RF guide unit 11, and a beam extraction unit 12. For convenience of explanation, set the XYZ axes that intersect directly as shown in Fig. 1. The XYZ axes are the forces shown in the upper right of FIG. 1 and will be described below assuming that the origin is located at the center of the casing 10.

The RF guide unit 11 is connected to an RF source (not shown) that supplies microwave RF having a predetermined frequency, and functions as a waveguide that transmits the microwave RF. The inside of the RF electron gun 1 is maintained in a vacuum, and the beam extraction unit 12 is connected to an accelerator or an external device according to the purpose, and an electron beam generated inside the casing unit 10 as described later. Supplied to the equipment.

FIG. 2 is a horizontal cross-sectional view through the XY plane of the RF electron gun 1 shown in FIG. Fig. 3 is a vertical cross-sectional view through line III-III shown in Fig. 2. As shown in FIGS. 2 and 3, the casing 10 has two pole pieces 13u and 13d facing each other, coils 14u and 14d wound around the pole pieces 13u and 13d, and an emitter. Accelerating cavity 16 with 15 and first correction magnet Stones 18u and 18d, second correction magnets 19u and 19d, and an extraction pipe 20 are provided. In Figs. 1 to 3, the power supply for supplying current to the coils 14u and 14d is omitted.

[0024] The casing 10 and the pole pieces 13u, 13d are formed of a ferromagnetic material (for example, iron, the same shall apply hereinafter), and constitute a magnetic circuit (magnet) together with the coils 14u, 14d. A direct current of the same value flows in the coils 14u and 14d in the same direction, and a static magnetic field (also referred to as a main magnetic field) in the Z-axis direction is formed between the opposing pole pieces 13u and 13d. As shown in FIGS. 2 and 3, the pole piece 13u is provided with two elongated projections 17u on the surface facing the pole piece 13d, and has a symmetrical shape with respect to the XZ plane. Similarly, the pole piece 13d includes two elongated protrusions 17d on the surface facing the pole piece 13u, and has a symmetrical shape with respect to the XZ plane. The pole pieces 13u and 13d and the coils 14u and 14d are arranged so as to be symmetric with respect to the XY plane. These symmetrical shapes and arrangements, and the convex portions 17u and 17d are for forming a uniform magnetic field distribution (a magnetic field distribution having the same strength and direction) in a predetermined range including the central portion of the casing 10. Is.

[0025] The acceleration cavity 16 is formed in a shape suitable for forming a high-frequency electric field having a predetermined frequency by using a nonmagnetic conductive material. As will be described later, a slit (not shown) is formed on the wall surface of the acceleration cavity 16 to allow the electron e emitted from the emitter 15 to pass therethrough.

[0026] The first correction magnets 18u and 18d are rectangular flat plate-like permanent magnets, which are magnetized almost uniformly in the thickness direction, and are arranged so that the magnetic pole surfaces face each other across the XY plane. Yes. The second correction magnets 19u and 19d are also formed and arranged in the same manner as the first correction magnets 18u and 18d. Regarding the polarities of the magnetic poles of these four opposing surfaces, the magnetic poles of the opposing surface of the first correction magnet 18u and the magnetic poles of the opposing surface of the first correction magnet 18d have opposite polarities. The magnetic pole and the magnetic pole of the opposing surface of the second correction magnet 19d have opposite polarities, and the magnetic pole of the opposing surface of the first correction magnet 18u and the magnetic pole of the opposing surface of the second correction magnet 19u have opposite polarities. Accordingly, the magnetic poles on the opposing surface of the first correction magnet 18d and the magnetic poles on the opposing surface of the second correction magnet 19d have opposite polarities. Although not shown, the first magnet 18u and the second magnet 19u are connected by a yoke made of a ferromagnetic material, and the first magnet 18d and the second magnet 19d are connected by another yoke made of a ferromagnetic material. ing.

[0027] The extraction tube 20 is formed of a ferromagnetic material in a cylindrical shape, and the electron beam from the RF electron gun 1 is Is necessary to stably take out in a predetermined direction. Since the magnetic flux passes through the inside of the cylindrical wall of the extraction tube 20, there is almost no magnetic field inside the extraction tube 20, and the trajectory of the electron beam incident on the extraction tube 20 is along the cylindrical axis of the extraction tube 20. It becomes straight.

Next, the operation of the RF electron gun 1 configured as described above will be described. Here, a uniform static magnetic field is formed in the positive direction of the Z-axis, and the opposing magnetic pole surface forces of the first correction magnets 18u, 18d and the second correction magnets 19u, 19d are N pole, S pole, S pole, It is assumed that there are N poles.

First, a direct current in the same direction is passed through the coils 14u and 14d to generate a main magnetic field in the Z-axis direction that is uniform within a predetermined range including the center between the opposing pole pieces 13u and 13d.

In this state, electrons are generated. That is, the microwave RF from the RF source source is supplied to the acceleration cavity 16 via the RF guide unit 11 and the emitter 15 is heated. As a result, a high-frequency electric field is generated in the acceleration cavity 16, and electrons emitted from the high-temperature emitter 15 are accelerated by this high-frequency electric field. Here, the direction of the high-frequency electric field is designed to be parallel to the Y-axis.

[0031] Electrons emitted from the emitter 15 are subjected to a force by electromagnetic interaction with a high-frequency electric field and a static magnetic field formed between the pole pieces 13u and 13d, and the emitter is centered as shown by a broken line. Draw a spiral orbit (electron beam S). That is, the electrons are initially subjected to a force that moves from the emitter 15 toward the center of the accelerating cavity 16 by the electric field. As the electrons are accelerated, the electrons receive a greater force due to the interaction with the main magnetic field and draw an arc-shaped curve. It approaches the wall surface of the acceleration cavity 16 where is placed, passes through the slit formed in the acceleration cavity 16, and goes out of the acceleration cavity 16. The electrons then approach the acceleration cavity 16 again, pass through the slit formed in the acceleration cavity 16, pass through the slit formed on the wall opposite to the wall where the emitter 15 is disposed, and enter the extraction tube 20. And output from the beam extraction unit 12. Here, it is designed that the distance of each turn of the rotating electron beam S is an integral multiple of the wavelength of the microwave RF.

[0032] At this time, the electrons emitted from the emitter 15 have almost no velocity component in the Z-axis direction and do not spread very much (the spread in the Z-axis direction is less than about 0.1 mm), but the velocity in the XY plane The components are relatively large and their variation is relatively large. Therefore, in the present invention, the electron beam S is focused when passing through the focusing area A1 indicated by the dotted line in FIGS. To that end, it will be described later As described above, the distribution of the main magnetic field formed inside the casing 10 is devised. Further, a correction magnet is preferably arranged inside the housing unit 10.

FIG. 4 is a graph showing changes in the main magnetic field strength Bz (Z component of the magnetic field) on the Y axis. In Fig. 4, the reference A1 is added to the range on the Y axis in the focusing area A1 for reference. In the focusing region A1 through which the electron beam S passes, the magnetic field intensity distribution force in the normal direction of the electron beam S (the direction perpendicular to the electron velocity direction in the electron trajectory plane) becomes uniform as it moves away from the emitter 15. The main magnetic field distribution is formed so as to monotonously decrease from a strong magnetic field strength B0 to a predetermined magnetic field strength B1. Here, since the pole pieces 13u and 13d are elongated in the X-axis direction, they are on a straight line parallel to the Y-axis within a predetermined distance from the Y-axis, that is, a straight line parallel to the Y-axis passing through the region A1 Above, the magnetic field strength changes in the same way as the graph in Figure 4. By forming the magnetic field distribution of the main magnetic field in this way, when the electron beam S with insufficient focusing properties passes through the focusing region A1, the magnetic field strength differs depending on the location where the electrons pass. The force that the electron receives by the action will be different. As a result, the focusing property of the electron beam S can be improved, and a high-quality electron beam S can be obtained. In FIG. 2, a partial region is used for bundling the force electron beam indicating a relatively long focusing region A1 formed by the shape of the casing 10 and the pole pieces 13u and 13d.

Further, in FIGS. 2 and 3, the first correction magnets 18u and 18d and the second correction magnets 19u and 19d are arranged above and below the focusing area A1. The first correction magnets 18u and 18d and the second correction magnets 19u and 19d have a magnetic pole arrangement similar to the quadrupole magnet as described above. Therefore, the electron beam can be further focused by passing through the first correction magnets 18u and 18d and the second correction magnets 19u and 19d. At this time, the passage distance of electrons between the first correction magnets 18 u and 18 d and between the second correction magnets 19 u and 19 d is changed according to the energy of the electrons. That is, although the details will be described later, the first energy is set so that the electron having the higher energy (the electron passing through the orbit having a large curvature of the orbit) passes through the first correction magnets 18u and 18d. Correcting magnets 18u and 18d are arranged. On the contrary, the second correction magnets 19u and 19d are arranged so that the distance that electrons having lower energy pass between the second correction magnets 19u and 19d is longer. As a result, the higher the energy, the larger the trajectory is corrected. Therefore, the electron beam S is more effectively focused. FIGS. 6 and 7 are diagrams showing simulation results regarding the RF electron gun according to the embodiment of the present invention. FIG. 6 shows a simulation result in a state where the correction magnet is not provided, and FIG. 7 shows a simulation result in a state where the correction magnet (first and second correction magnets 18d and 19d) is provided. The simulation sets the initial velocity of the electrons emitted from the emitter 15 to a constant value (equivalent to a magnitude of 10 eV), and the phase of the electron emission position and the change in the high-frequency electromagnetic field (time = 1Z (2.44 46 GHz). X 2) The trajectory was calculated while changing for 2 seconds). In both figures, the spiral solid line starting from Emitter 15 is the boundary of the region through which the electron passes with the final energy between 0.955 and 0.995 MeV (i.e., the innermost and outermost orbits). ). The spiral dotted line starting from Emitter 15 represents the boundary of the region through which electrons pass with a final energy of 0.9 to 1. lMeV.

[0036] From Fig. 6, it can be seen that the electron beam is focused at the portion indicated by reference numeral C1 included in the focusing region A1. After that, the electron beam spreads out and converges again at the part indicated by D1. Therefore, if the extraction tube 20 is arranged so that the tube port is located at the portion indicated by the symbol D1, the electron beam can be extracted with high focusing.

[0037] In FIG. 7, as in FIG. 6, the electron beam is focused at the portion indicated by the reference symbol C2 included in the focusing region A1, and then the electron beam spreads gradually, but again indicated by the reference symbol D2. It can be seen that the light is focused on the part. In FIG. 7, compared with FIG. 6, the spread of the electron beam after being focused at the portion indicated by reference numeral C2 is small (L2 <L1). This indicates that the acceleration efficiency of the electrons is high, and the spread of the electron beam at the portion indicated by the symbol D2 is also smaller than in FIG. Therefore, if the extraction tube is arranged so that the tube port is located at the portion indicated by reference numeral D2, the correction magnet is provided, and in this case, the correction magnet is provided. The electron beam can be extracted.

In FIG. 7, a desirable electron orbit is a portion indicated by a force sign C2 passing between two spiral solid lines, and the inner electron orbit intersects with the outer electron orbit. That is, after being emitted from the emitter 15, the electrons passing through the outermost solid line trajectory pass through the innermost solid line trajectory after passing through the portion indicated by the symbol C2. Conversely, after being emitted from the emitter 15, the electrons passing through the innermost solid line trajectory pass through the outermost solid line trajectory after passing through the portion indicated by the symbol C2. Therefore, as mentioned above, electrons with higher energy ( Before passing through the part indicated by C2, the longer the distance that passes between the first correction magnets 18u and 18d, the smaller the energy (indicated by C2). The distance that passes between the second correction magnets 19u and 19d increases as the electron passes through the outer orbit after passing through the part.

By the above, for example, it is possible to realize a small RF electron gun that can extract an electron beam of about 1 MeV and has an outer dimension of about 250 mm × about 200 mm × about 180 mm. At this time, the uniform main magnetic field strength is 500G, and the correction magnetic field strength generated by the correction magnet is about 150G.

[0040] Although the present invention has been described above using the embodiments, the present invention is not limited to the above-described embodiments, and can be implemented with various modifications. Included in range.

For example, as shown in FIG. 5, in any one of the regions A2 to A5 including a part of the spiral orbit of the electron beam S, the magnetic field strength changes monotonously as shown in FIG. If the magnetic field distribution is formed in the region, the regions A2 to A5 can be used as the focusing region. Here, the area A 2 is an area shorter in length than the correction area A 1 in FIGS.

[0042] Since the region A5 shown in FIG. 5 is located outside the acceleration cavity 16, correction magnets may be disposed above and below the region A5. In terms of electron acceleration efficiency, it is desirable to place correction magnets above and below the region A2 where electrons immediately after exiting the acceleration cavity 16 pass to focus the electron beam, but the correction magnets above and below the region A5 A certain amount of bundling effect can be obtained even when the is placed.

FIGS. 2 and 3 show the case where the accelerating cavity 16 and the casing portion 10 are arranged so that the respective central axes coincide with the X axis. However, the present invention is not limited to this arrangement, and the electron beam S If the accelerating cavity 16 and the housing part 10 are arranged so that the main magnetic field distribution can be formed so that the majority of the spiral orbits are located in the main magnetic field and a part passes through the focusing region. Good.

[0044] In the above description, the case where a static magnetic field is generated inside the casing by an electromagnet using a coil has been described. However, the present invention is not limited to this, and a main magnetic field may be formed using a permanent magnet. . For example, in FIG. 3, a permanent magnet magnetized in the Z-axis direction may be disposed between the pole piece 13u and the casing 10 and between the pole piece 13d and the casing 10. [0045] Further, in the above, the force described in the case of forming the elongated protrusion in one direction (Y-axis direction) on the surface of the rectangular pole piece is not limited to this. Two poles parallel to the X-axis direction and two protrusions parallel to the Y-axis direction may be formed on the surface of one pole piece. A convex portion may be formed on the surface. Furthermore, a convex part may be formed in a circular ring shape using a cylindrical casing part and a circular pole piece.

In addition, in FIGS. 1 to 3, the direction in which the electron beam is extracted is parallel to the incident direction of the microwave RF, but the direction in which the electron beam is extracted can be arbitrarily designed, for example, as illustrated in FIG. A tube 20 may be arranged to extract the electron beam in a direction perpendicular to the direction of microwave RF application.

[0047] Although the case where the shape of the correction magnet is a rectangular parallelepiped has been described, the present invention is not limited to this, and the correction magnet may have a plate shape with an acute angle greater than 90 degrees or a disk shape. In addition, one yoke connecting the correction magnet is arranged to connect the first correction magnets 18u and 18d, and the other yoke is arranged to connect the second correction magnets 19u and 19d. But ヽ.

[0048] The direction of the main magnetic field may be the negative direction of the Z axis. In that case, considering the fact that the spiral trajectory of the electron beam is reversed, the position of the emitter, the shape and position of the slit of the acceleration cavity, the position of the correction magnet and the polarity arrangement should be designed. .

[0049] In the focusing area, the case where the magnetic field distribution is generated so that the value of the main magnetic field with a uniform intensity also decreases monotonically has been described. However, the intensity of the main magnetic field with a uniform intensity increases monotonously. To generate a magnetic field distribution in the focusing region and bundle it with an electron beam.

Industrial applicability

[0050] According to the present invention, it is possible to provide a small and inexpensive RF electron gun that has a high focusing property and can output an electron beam.

Claims

The scope of the claims

[1] a magnet that generates a static main magnetic field;

An emitter disposed in a region where the main magnetic field is generated and emitting electrons; and an accelerating cavity disposed in the region where the main magnetic field is generated and receiving a microwave to generate a high-frequency electric field;

The magnet forms a first region where the static magnetic field is uniform and a second region where the static magnetic field strength monotonously decreases in a predetermined direction,

The plurality of electrons emitted from the emitter are moved in a spiral shape around the emitter by the high-frequency electric field and the static magnetic field in the first region, and are focused by the static magnetic field in the second region. RF electron gun, characterized by output.

[2] The predetermined direction is a direction away from the emitter.

2. The RF electron gun according to claim 1, wherein the static magnetic field strength in the second region monotonously decreases from the static magnetic field strength in the first region.

[3] comprising two first correction magnets and two second correction magnets arranged in the vicinity of the second region,

The two first correction magnets are arranged opposite to each other with the second region interposed therebetween, and generate a static magnetic field parallel to the main magnetic field between them,

The two second correction magnets are arranged opposite to each other with the second region interposed therebetween, and generate a static magnetic field parallel to the main magnetic field between them,

The magnetic pole on the facing surface of one of the first correction magnets and the magnetic pole on the facing surface of the other first correction magnet have opposite polarities,

The magnetic pole of the opposing surface of one of the second correction magnets and the magnetic pole of the opposing surface of the other second correction magnet have opposite polarities,

The magnetic poles of the facing surfaces of each of the first correction magnet and the second correction magnet arranged on the same side with respect to the second region have opposite polarities,

The electrons pass between the first correction magnets and then pass between the second correction magnets,

When the electrons pass between the two first correction magnets, the energy is higher. The first correction magnet is arranged so that the passing distance becomes longer,

When the electrons pass between the two second correction magnets, the second correction magnet is arranged such that the smaller the energy is, the longer the passing distance is. The RF electron gun according to 1 or 2.

[4] The emitter is disposed on the first wall surface of the acceleration cavity,

The first wall has a slit through which electrons pass;

The electrons emitted from the emitter are accelerated toward the center of the acceleration cavity, then approach the first wall surface, pass through the slit on the first wall surface, and are formed outside the acceleration cavity. The RF electron gun according to any one of claims 1 to 3, wherein the RF electron gun passes through the second region.

[5] The emitter is disposed on a first wall surface of the acceleration cavity,

The first wall has a slit through which electrons pass;

After the electrons emitted from the emitter are accelerated toward the center of the acceleration cavity, approach the first wall surface, pass through the slit on the first wall surface, and exit outside the acceleration cavity. The RF electron gun according to any one of claims 1 to 3, wherein the RF electron gun passes through the slit of the first wall surface again and passes through the second region.