JP2003242898A - Magnetron - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetron in which a cathode part need not be heated. <P>SOLUTION: A cathode substrate 5 is kept at 800 to 900°C, dilution gas of hydrocarbon such as acetylene and methane is reacted with a surface of the cathode substrate 5 by a hot CVD method or a plasma CVD method. An electron emission source with orientation-carbon nano-tubes 6 oriented in the direction perpendicular the surface of the cathode substrate 5 with nickel or iron present in the surface of the cathode substrate 5 grown is held by upper and lower end hats 4 to constitute a cathode part 7 of the magnetron. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a cathode part of a magnetron used in a high frequency heating device such as a microwave oven or a pulse generator such as a radar.

[0002]

2. Description of the Related Art In the currently used magnetron, a hot cathode is used as an electron source. The hot cathode supplies electrons by thermionic emission. Thermionic emission is a mechanism in which by heating a substance to about 1500 to 2700K, conduction band free electrons obtain thermal energy and get over the surface potential barrier to be emitted to the space.

FIG. 5 is an axial sectional view showing an embodiment of a conventional magnetron. In the figure, a hot cathode 2 is arranged in the central portion of a plurality of anode vanes 1. The hot cathode 2 is formed by spirally forming thorium-containing tungsten wire rods 3 at substantially equal intervals, and holding both end portions by end hats 4.

By the way, a hot cathode body is mainly used as an electron source of a magnetron.

The hot cathode body is roughly classified into an indirectly heated type and a direct heated type according to the heating method. In the indirectly heated type, a heater is arranged near the hot cathode to indirectly heat, and a relatively high current density can be obtained, but since it is indirectly heated, the rise of electron emission is slow and the cost is high. The direct heating type heats by applying an electric current to the hot cathode itself, and the direct heating type has a fast rise of electron emission, but cannot obtain a high current density.

In order to solve this problem, a field emission type cathode assembly can be considered.

Field emission is a high electric field (1
09 V / m), the surface potential barrier lowers, and the tunneling phenomenon that occurs causes the free electrons in the conduction band to be emitted. Since field emission requires a high electric field, the primary electrode that emits primary electrons has a structure in which electric field concentration is likely to occur (a needle-like structure having a small tip radius of curvature).

[0008]

However, in the conventional magnetron, since the direct heating type hot cathode is used as described above, not only a high current density cannot be obtained, but also the curvature of the tip such as a needle-like shape. The structure was not such that the electric field concentration was small and the radius was small. Further, in addition to heat loss due to heat generation of the magnetron itself, the hot cathode itself is also operated at a high temperature, so it is necessary to use expensive refractory metal for parts around the cathode.

The present invention provides a magnetron for solving the above problems.

[0010]

The magnetron of the present invention comprises a cathode portion having carbon nanotubes formed on at least a part of the surface of an electron emission source.

With this configuration, electric field concentration occurs at the tip of the carbon nanotube, and it becomes possible to emit primary electrons without heating.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the magnetron of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view in the axial direction showing the structure of the main part of a magnetron having a cathode portion in which carbon nanotubes are formed on the cathode surface, and FIG. 2 uses carbon nanotubes as a primary electron emission source and an oxide film. FIG. 3 is an axial cross-sectional view of a cold cathode magnetron used as a secondary electron emission source. FIG. 3 is an enlarged cross-sectional view of a cathode surface using powdered carbon nanotubes and carbon oxide slurry, and FIG. 4 is an axial cross-sectional view showing a main part configuration of a magnetron including a cathode using carbon nanotubes and thorium tungsten filaments. It is a figure.

In FIG. 1, the cathode substrate 5 is kept at 800 to 900 ° C., and a hydrocarbon-based diluent gas such as acetylene or methane is reacted on the surface of the cathode substrate 5 by a thermal CVD method or a plasma CVD method. 5 A cathode part 7 is formed by sandwiching an electron emission source in which oriented carbon nanotubes 6 grown vertically with respect to the surface of a cathode substrate 5 with nickel or iron existing on the surface as a nucleus are sandwiched by upper and lower end hats 4. This is the first embodiment.

A strong electric field (107 V / c) is applied to the surface of the cathode portion.
By adding m) and thinning the potential barrier on the cathode surface, electrons can be emitted into the space without heating due to the tunnel effect caused by the wave nature of the electrons.

In the cathode part of the magnetron according to the second embodiment shown in FIG. 2, barium carbonate is vapor-deposited on the outer peripheral surface of the cylindrical cathode substrate 8 by the thermal CVD method, and then heated at 800 ° C. for oxidation. The secondary electron emission source decomposed into barium and having the oxide film 9 formed thereon is arranged at both axial ends of the primary electron emission source composed of the cylindrical cathode substrate 10 on which the carbon nanotubes 6 are formed.

The divided anode is an existing magnetron (10 divisions, inner diameter 8 mm), and a voltage of 6.0 kV is applied between the anode and the cathode of the magnetron having the above-mentioned cathode portion,
A DC magnetic field 11 of 0.35 T was generated in the axial direction. The radial electric field 12 generated by the voltage between the positive and negative electrodes caused a field emission current emission phenomenon in the oriented carbon nanotubes 6 of the cathode, and emitted electrons. The electrons were cyclotron-moved by the axial DC magnetic field 11 and re-entered the oxide film 9. The electrons were multiplied by the secondary electron emission, the maximum current of 50 mA was emitted, and the maximum oscillation of 200 W was obtained at 2.45 GHz. It was confirmed.

The cathode part of the magnetron according to the third embodiment shown in FIG. 3 is composed of a slurry and a powder obtained by mixing the surface of the cathode substrate 5 with a carbonate having a particle size of several microns to several tens of microns and a binder. A mixture of carbon nanotubes is applied and heated to form carbonate 13 as an oxide, carbon nanotubes 6 are used as an electron emission source for primary electron emission, and oxide 13 on the cathode surface is used for electron emission for secondary electron emission. It is the source. With this configuration, the number of electrons can be further increased.

The cathode portion of the magnetron according to the fourth embodiment shown in FIG. 4 is configured such that the cathode portion is partially formed by the thorium tungsten filament 14 and the carbon nanotube 6 is formed at the other portion. With such a configuration, the initial operation of the magnetron is performed by the electrons emitted from the carbon nanotubes 6, and then the temperature of the cathode portion 15 rises, the thorium tungsten filament 1
The thermionic emission from 4 makes it possible to supply electrons during the operation of the magnetron.

[0020]

According to the present invention, as described above,
The following effects are achieved.

By using the carbon nanotubes for the cathode part, it is not necessary to heat the cathode part, so that the transformer for the heater is omitted from the operating power source and the structure is simplified.

The power supply current for heating the heater is generally several to several tens of amperes, which requires thick wiring. However, since the heater current is not necessary, only the current flowing between the positive and negative electrodes can be supplied. It was good, and it became possible to use a thin conductor.

Since the operating temperature of the cathode is lower than that of the conventional hot cathode, metals (Ni, Fe, SUS304, etc.) which are cheaper than refractory metals are used for parts around the cathode.

Since the field emission electrons from the cathode portion have a narrow energy band, the thermal agitation is small and the noise during the operation of the magnetron is reduced.

[Brief description of drawings]

FIG. 1 is an axial cross-sectional view showing a main structure of a magnetron including a cathode part in which carbon nanotubes are formed on a cathode surface according to the present invention.

FIG. 2 is an axial cross-sectional view showing the structure of a main part of a magnetron including a cathode part using a carbon nanotube and an oxide film according to the present invention.

FIG. 3 is an enlarged cross-sectional view of a cathode surface using powdered carbon nanotubes and a carbonate slurry according to the present invention.

FIG. 4 is an axial cross-sectional view showing the configuration of a main part of a magnetron including a cathode part using a carbon nanotube and a thorium tungsten filament according to the present invention.

FIG. 5 is an axial cross-sectional view showing the configuration of the main part of a conventional hot cathode magnetron.

[Explanation of symbols]

5,10 cathode substrate 6 carbon nanotubes 7,15 Cathode part 9 Oxide film 11 DC magnetic field 12 Radial electric field 13 oxides 14 Thorium tungsten filament

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshiyuki Tsukada             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5C029 CC01 CC07

Claims (6)

[Claims] 1. A magnetron comprising a cathode part having carbon nanotubes formed on at least a part of a surface of an electron emission source. 2. The magnetron according to claim 1, wherein the electron emission source is formed in a cylindrical shape. 3. The magnetron according to claim 1, wherein the electron emission source is formed in a polygonal column shape. 4. The magnetron according to claim 1, wherein the surface of the electron emission source is provided with a cathode part in which an oxide film having a large secondary electron gain is partially formed. 5. A mixture of a slurry in which a carbonate having a particle size of several to several tens of microns is mixed with a binder and a powder of carbon nanotubes is applied to the surface of the cathode, heated to convert the carbonate into an oxide, and mixed. The magnetron according to any one of claims 1 to 4, wherein the present carbon nanotube is used as an electron emission source. 6. The electron emission source is partially composed of a thorium tungsten filament.
The magnetron according to any one of claims 1 to 5.