JP3412625B2 - Electron gun for hollow electron beam emission - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an electron gun which emits a hollow electron beam in an electron tube such as a gyrotron which generates a high power microwave or a millimeter wave, and particularly, in an electron gun section. The present invention relates to prevention of electric discharge.

[0002]

2. Description of the Related Art The present invention is intended to solve the above-described problem of preventing discharge in the electron gun section from two viewpoints, and here, two examples of conventional technologies corresponding to the respective viewpoints are described. I will give you.

An electron tube utilizing an electron cyclotron resonance maser action represented by a gyrotron is being used as a high frequency and large power source in the microwave band, millimeter wave and submillimeter wave band.

Such a gyrotron is generally shown in FIG.
It is configured as shown in. In the figure, 39 is an electron gun section that generates a hollow electron beam 47, 40 is a beam tunnel section that guides the electron beam to the interaction region, 41 is a cavity resonator section, and 42 is an electron beam that has completed interaction. And the electromagnetic wave 4 generated in the cavity resonator section 41.
A collector portion acting as a waveguide for transmitting 3 is an output window portion, 45 is a waveguide coupling flange, and 46 is a solenoid of the magnetic field device.

The present invention relates to the electron gun unit 39 in FIG. 7, and as a first conventional technique relating to this,
For example, as shown in Japanese Patent Laid-Open No. 61-138430, the electron gun shown in FIG. In this figure, 1 is a cathode, 2 is an electron emission ring band that emits electrons, 3 is a cathode support mechanism, 4 is a hollow cylindrical coaxial anode provided around the cathode 1, 5 is a heater wire, 6 Is a heater support pillar, 7 is an insulator that insulates between the electrodes, 8 is an insulator that insulates between the heater wire and the cathode, 9 is an example of an electron orbit in an electron beam emitted from this electron gun, and 48 is an electron gun A magnet for generating a magnetic field in the section, and 49 is an exhaust port for exhausting the electron gun section.

Next, the operation will be described. The cathode 1 is supported by the cathode support mechanism 3 and is surrounded by the anode 4. An axial magnetic field having a certain strength is applied to the vicinity of the cathode 1 by the magnet 48. A heater for heating the electron emission ring zone 2 is installed inside the cathode 1, and electric power to the heater is supplied through the heater wire 5 and the heater support column 6. The electrodes are insulated from each other by an insulator 7.
The anode 4 is applied with a negative voltage with respect to the gyrotron body including the beam tunnel portion 40, and the cathode 1 is applied with a further negative voltage with respect to the anode 4 through the cathode support mechanism 3. Exhaust of the electron gun is mainly performed through the exhaust port 49.

The electron emission ring zone 2 is heated by a heater,
Emits electrons. The electrons are accelerated by the electric field between the cathode 1 and the anode 4, and proceed while drawing a spiral orbit so as to be wrapped around the axial magnetic field generated in the magnet 48. Further, in FIG. 7, the hollow electron beam extracted from the electron gun portion 39 passes through the beam tunnel portion 40, and the eigenmode and the electron cyclotron resonance maser in the cavity resonator portion 41 which is usually a cylindrical cavity. After interacting with each other and a part of the kinetic energy of the electrons is converted into an electromagnetic wave, it is collected in the collector electrode section.

As an example of the second prior art, for example, Japanese Patent Laid-Open No.
The electron gun shown in FIG. 9 shown in Japanese Patent Laid-Open No. 3-238734 will be cited. This electron gun has an electron emission ring zone 2 for generating electrons,
Adjacent to the electron emission ring zone 2, a front electrode 30 and a rear electrode 31, which have the same potential as the electron emission ring zone 2, a cathode 1 composed of these three electrodes, a potential for extracting electrons from the cathode 1 are formed. 1 is provided with a hollow cylindrical anode 4 coaxially arranged around, an insulator 7 for maintaining insulation between these electrodes, and a heater 5 for heating the electron emission ring zone 2. next,
The operation will be described. The electron beam is extracted from the surface of the electron emission ring zone 2 by the thermoelectron emission action. At that time, the electron beam is desired to have a small energy dispersion due to the electric field distribution formed by the cathode 1 and the anode 4 including the front electrode 30, the rear electrode 31, and the electron emission ring zone 2 and the axial magnetic field applied from the outside. To form a hollow electron beam.

[0009]

First, the problems of the electron gun according to the first prior art will be described. During operation of the electron gun, the cathode 1 is heated to a high temperature, heat conduction and heat radiation also heat various peripheral components, and gas is released from these components. Further, there are many factors that deteriorate the degree of vacuum in the electron gun, such as gas being emitted even when electrons are emitted from the electron emission ring zone 2. Deterioration of the degree of vacuum lowers the current of the obtained electron beam, induces discharge between the electrodes, and causes damage to components.
In particular, the gas that has entered the space around the cathode support mechanism 3 on the left side of the cathode 1 in FIG. 8 is only exhausted through the gap between the cathode 1 and the anode 4. However, this interval is narrow,
Since the exhaust conductance of this portion is small, it is difficult to exhaust the peripheral portion of the cathode support mechanism 3, the degree of vacuum is deteriorated, and there is a problem that discharge between electrodes is induced.

Next, the problem of the electron gun according to the second conventional technique will be described. The front electrode 30 and the rear electrode 31 in the cathode 1 of this electron gun are indispensable electrodes for making the electron beam emitted from the band-shaped electron emission ring zone 2 have a predetermined performance, and form a smooth equipotential surface. In that sense, their outer peripheral surfaces must be joined smoothly.

However, the front electrode 30, the electron emission ring zone 2,
In the configuration in which the rear electrode 31 is integrated and the surfaces are in contact with each other,
While the continuous surface is easily formed, the heat of the heater 5 for heating the electron emission ring zone 2 reaches the front electrode 30 and the rear electrode 31, and the heater power required to heat the electron emission ring zone 2 to a predetermined temperature. Becomes larger, and even these electrodes are heated to a high temperature. The front electrode 30 and the rear electrode 31 are usually made of a refractory metal such as molybdenum, and no electrons are emitted from the surface in the initial stage of operation, but the electron-emission ring zone is associated with long-term operation. There is a possibility that electron-emissive substances such as barium evaporated from No. 2 may adhere to the surfaces of these electrodes and cause unwanted electron emission. Furthermore, in order to prevent undesired electron emission from the surfaces of the front electrode 30 and the rear electrode 31, when these electrodes are thermally separated, the electron emission ring zone 2 operates from the end surface or the edge portion. There is a possibility to emit a large amount of electrons, which is completely inconvenient to. Since these electrons are not formed so as to satisfy the beam focusing condition for efficiently performing the electron cyclotron resonance maser interaction in the cavity resonator portion, not only the interaction is adversely affected but also the anode 4 And the anode current becomes excessive, the anode voltage control is disabled, or the discharge between the cathode 1 and the anode 4 is triggered, which makes the operation of the electron gun itself unstable. It was

The present invention has been made in order to solve the problems of the above two conventional electron guns that the discharge between electrodes is likely to occur and the operation is unstable. An object of the present invention is to provide a hollow electron beam emitting electron gun capable of preventing discharge and performing stable operation by facilitating exhaustion and suppressing a current flowing into an anode.

[0013]

[0014]

[0015]

Means for Solving the Problems] electron gun hollow electron beam emission according to claim 1 is disposed to sandwich the electron emission annulus
A cathode having a front electrode and a rear electrode, and extracting electrons
A hollow cylindrical anode provided around the cathode in order to
A heater for heating the electron emission ring zone is placed in a vacuum atmosphere.
In the hollow electron beam emitting electron gun to be arranged, the electron emitting annulus, the front electrode and the rear electrode are closely fixed to each other through a heat insulating high melting point insulator.

The electron gun hollow electron beam emission according to claim 2, claim 1, the surface of the refractory insulating material covered with conductive thin film
It is the one described.

[0017]

[0018]

[0019]

In the hollow electron beam emitting electron gun according to the first aspect of the present invention, the electron emission ring zone and the front electrode and the rear electrode are closely fixed to each other through the adiabatic high melting point insulator. Therefore, it is possible to prevent unwanted emission of electrons from unnecessary portions, suppress discharge between the anode and the anode, and obtain an electron gun that operates stably.

In the hollow electron beam emitting electron gun according to the second aspect of the invention, since the surface of the high-melting-point insulator is covered with the conductive thin film, the electron emission is achieved in addition to the effect described in the first aspect. It is possible to suppress distortion of the electric field near the edge of the ring zone.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the electron gun according to the present invention is shown in FIG. 1 and will be described below. In the figure, 2 is an electron emission ring zone made of, for example, tungsten that emits a hollow electron beam, and its front electrode 30 and rear electrode 3 are shown.
A plate 32 made of a refractory metal, such as molybdenum, which is hard to emit electrons, is fixed to both end faces facing 1 by brazing or the like. The metal plate 32 is integrally processed with the electron emission ring zone 2 to form a smooth electrode surface. Is forming. This electron emission ring zone is adiabatically fixed to the front electrode 30 and the rear electrode 31 with a gap by the supports 33a and 33b to form the cathode 1. Due to the potential difference applied between the cathode 1 and the hollow cylindrical anode 4 coaxially arranged around the cathode 1 and the axial magnetic field applied in the axial direction, a hollow electron beam is generated. Is drawn above.

Next, the operation will be described. The electron emission ring zone 2 formed in a ring shape is impregnated with an electron emission substance, is heated by a heater 50 provided inside, and emits electrons by a thermoelectron emission action. Front electrode 30,
The electric field distribution formed in the space between the cathode 1 constituted by the electron emission ring zone 2 and the rear electrode 31 and the anode 4 due to the potential difference applied, and the axial magnetic field applied from the outside. Depending on the combination of distributions, electrons are drawn in a predetermined orbit. In particular, the initial velocity and velocity dispersion of electrons are determined by the surface shape of the cathode 1 composed of the front electrode 30, the electron emission ring zone 2, and the rear electrode 31, so that the surface near the electron emission ring zone 2 is Discontinuities that disturb the electric field distribution must be avoided. However, in order to avoid electron emission from electrodes other than the electron emission ring zone 2, there is a contradiction that the front electrode 30, the rear electrode 31 and the electron emission ring zone 2 must be thermally separated. . Therefore, as shown in FIG. 1, a thin high melting point metal plate 32 is fixed to both end faces of the electron emission ring zone 2 by brazing or the like and integrally processed with the electron emission ring zone 2. The turbulence of the electric field near the surface of the emission ring zone 2, especially the turbulence of the electric field at the edge portion of the electron emission ring zone 2, can be reduced. Further, since the adiabatic gap 35 between the electron emission ring zone 2 and the front and rear electrodes 30, 31 is sufficiently smaller than the distance between the electron emission ring zone 2 and the anode 4, the surface of the electron emission ring zone 2 is reduced. The disturbance of the electric field is sufficiently small in other spaces.

FIG. 2 shows how the cathode 1 of FIG. 1 is viewed from the downstream side of the electron beam. Due to the presence of the metal plate 32, the end surface portion 34 of the electron emission ring zone is further
Electron emission in an unnecessary direction from is suppressed. If the plate 32 does not exist, for example, even if 0.3 mm is selected as the adiabatic gap 35, if the angle θ between the surface of the electron emission ring zone 2 and the central axis is about 25 degrees, Electron emission ring zone end face 34 directly visible from the beam downstream side
Has a radial length of about 0.14 mm, and electrons from this portion are accelerated in unnecessary directions, which adversely affects the operation of the electron tube. Although the metal plate 32 is used in the above embodiment, as shown in FIG. 3, a ring 36 having a width such that the end face 34 of the electron emission ring band cannot be seen from the downstream side of the electron beam may be used. It has the same effect.

Next, another embodiment of the electron gun according to the present invention is shown in FIG. 4 and will be described. In the above, the minute gap 35 is adopted as the heat insulating structure between the electron emission ring zone 2 and the front and rear electrodes 30 and 31, but in this example, the ends of the front electrode 30 and the rear electrode 31 on the electron emission ring zone 2 side. The part is processed to be thinner than the other parts so as to maintain the heat insulating property, and the front electrode 30, the electron emission annulus 2 and the rear electrode 31 are fixedly adhered to each other so that the surfaces thereof are smoothly and continuously connected. In the above case, although minute, the surface of the electron emission ring zone 2 and the surfaces of the front and rear electrodes 30, 31 are spatially discontinuous, so that the disturbance of the electric field near the electrode surface is inevitable.
On the other hand, according to this example, although the heat insulating performance is slightly inferior, since there is no discontinuity on the electrode surface, it is possible to prevent the emission of electrons in an undesired direction. Further, since the end surface of the electron emission ring zone 2 is not exposed, it is possible to prevent electron emission from unnecessary portions.

Next, another embodiment of the electron gun according to the present invention is shown in FIG. 5 and will be described. In the above-mentioned embodiment, as a heat insulating structure between the electron emission ring zone 2 and the front and rear electrodes 30, 31, a fine gap or contact with a thin metal is adopted, but in this example, this heat insulating structure is A high melting point insulator having a small thermal conductivity is interposed between the electron emission ring zone 2 and the front and rear electrodes 30 and 31. In the figure, 37a and 37b are high melting point insulators such as ceramics sandwiched to achieve heat insulation between the electron emission ring zone 2 and the front and rear electrodes 30 and 31. As shown in the figure, since the end surface of the electron emission ring zone 2 is covered, electron emission from unnecessary portions can be prevented.

In this embodiment, the high melting point insulator 37 is used.
Discontinuity of the electric field exists at the portions a and 37b, but in order to prevent this discontinuity, the surfaces of the insulators 37a and 37b may be covered with a conductive thin film. FIG. 6 is a partially cutaway perspective view showing an essential part of an embodiment of the present invention. In the figure, 3
Reference numeral 8 is a conductor thin film that covers the surfaces of the high melting point insulators 37a and 37b. By doing so, it is possible to prevent discontinuity of the electric field between the surfaces of the respective electrodes, and to suppress the emission of electrons in an undesired direction or at an unexpected initial velocity.

[0027]

[0028]

[0029]

Effects of the Invention According to the invention described in claim 1, and the electron emission annulus and the front electrode and the rear electrode, since it was tightly fixed through the adiabatic refractory insulation, the unnecessary portion It is possible to prevent the unwanted emission of electrons, suppress the discharge between the anode and the electron gun, and obtain an electron gun that operates stably.

According to the second aspect of the present invention, since the surface of the high melting point insulating material is covered with the conductive thin film, in addition to the effect described in the first aspect , the electric field near the edge of the electron emission ring band is changed. Distortion can be suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an electron gun for hollow electron emission according to the present invention.

FIG. 2 is a plan view of a cathode of the electron gun for hollow electron emission shown in FIG. 1 viewed from a downstream side of an electron beam.

FIG. 3 is an enlarged view of a main part showing a cathode of an electron gun for hollow electron emission according to the present invention.

FIG. 4 is an enlarged view of an essential part showing a cathode of the electron gun for hollow electron emission according to the present invention.

FIG. 5 is an enlarged view of a main part showing a cathode of the electron gun for hollow electron emission according to the present invention.

FIG. 6 is an enlarged view of a main part showing a cathode of the electron gun for hollow electron emission according to the present invention.

FIG. 7 is a cross-sectional view showing a conventional gyrotron.

FIG. 8 is a cross-sectional view showing a configuration of a conventional hollow electron emission electron gun.

FIG. 9 is a cross-sectional view showing the vicinity of a cathode of a conventional electron gun for hollow electron emission.

[Explanation of symbols]

1 cathode 2 Electron emission ring zone 3 Cathode support mechanism 4 anode 5 heater wire 7 insulator 8 Heater support pillar insulator 10 Voltage supply conductor 12 communication paths 14 through holes 15 Exhaust path through the outside of the anode 16 Connection parts 17 Exhaust slit 18 metal net 19 Non-evaporable getter pump 22 heater 23 communication routes 24 Parts that alleviate electric field concentration 25 Titanium getter pump 28 Shield 29 Parts that alleviate electric field concentration 30 front electrode 31 Rear electrode 32 metal plate 33 Support 34 Edge surface of electron emission ring 35 Adiabatic gap 36 ring 37 High melting point insulator 38 Conductor thin film 39 Electron gun 40 beam tunnel 49 Electron gun exhaust port 50 heater 51 metal tube 52 Gas adsorbent

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-351836 (JP, A) JP-A-4-286837 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 23/075

Claims (2)

(57) [Claims] 1. A cathode having a front electrode and a rear electrode disposed with an electron emission ring sandwiched therebetween, a hollow cylindrical anode provided around the cathode for extracting electrons, and the electron emission ring. In a hollow electron beam emitting electron gun in which a heater for heating a band is arranged in a vacuum atmosphere, the electron emitting ring band and the front electrode and the rear electrode are closely fixed via an adiabatic high melting point insulator. An electron gun for emitting a hollow electron beam, which is characterized in that 2. A hollow electron beam emission electron gun according to claim 1, wherein the surface of the refractory insulating material, characterized in that covered by the conductive thin film.