JP2009245711A - Magnetron, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve cost reduction by eliminating the necessity of a troublesome removing work of a formed film, and enable to extract a suppressing effect of a dark current to the maximum. <P>SOLUTION: A manufacturing method includes assembling processes 102, 103 wherein to a cathode sleeve on which an electron emitting surface (electron emitting surface forming process 101) is formed, an end shield made of nickel-chromium alloy is bonded and a tube is assembled by connecting a support (electrode) lead to this end shield, and includes a tube evacuation and chromium oxide film forming process 104 in which after these assembling processes, a carbon dioxide gas is filled into the tube and heated and in which a chromium oxide film is formed on the surface of the end shield. In this process 104, in vacuum evacuation, a cathode is activated, the carbon dioxide gas is generated by heat decomposition of its oxide cathode material [for example, (BaSrCa)CO<SB>3</SB>], and by controlling partial pressure of this carbon dioxide gas, the chromium oxide film is formed on the surface of the end shield. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a magnetron and a manufacturing method thereof, and more particularly to a surface treatment method of a magnetron end shield for realizing a high output pulse.

  FIG. 4 shows a schematic configuration of a cathode and an anode in a conventional magnetron, and FIG. 5 shows a configuration of the cathode. In the magnetron, a cathode 2 is arranged inside an anode 1 forming a plurality of resonance circuits. As shown in FIG. 5A, for example, a bell-shaped end shield 4 is joined to both the upper and lower sides of the cathode sleeve 3 by welding or pressure bonding, and an oxide cathode material is formed on the side surface of the cathode 2. The electron emission surface 5 is formed. The cathode 2 is supported by support leads 6a and 6b at the upper and lower end shields 4 and is electrically connected.

  FIG. 5B shows another configuration example of a cathode using a disk-shaped end shield. In this cathode 8, the disk-shaped end shield 10 is welded to both the upper and lower sides of the cathode sleeve 9. Alternatively, the electron emission surface 11 coated with an oxide cathode material is formed on the side surface while being joined by pressure bonding or the like.

  In such a magnetron, the end shields 4 and 10 serve to prevent electrons in the working space between the anode 1 and the cathode 2 from leaking in the axial direction, and are necessary for obtaining a high output pulse. It becomes a member. However, since the end portions of the end shields 4 and 10 are one of the places where the strongest electric field is applied in the tube, when the oxide cathode material of the electron emission surface 11 adheres to the surface, there is a problem called end shield emission. appear. This end shield emission becomes a current (dark current) that does not contribute to the microwave oscillation, and adversely affects the start-up characteristics and operation efficiency of the magnetron. Therefore, conventionally, as a measure for suppressing this dark current, the material, shape and surface treatment of the end shields 4 and 10 have been improved.

  As the material of the end shields 4 and 10, pure nickel is generally used. However, in a high-power magnetron, 599 nickel (silicon-added nickel) or a nickel chromium alloy is adopted, and molybdenum or the like is often used. Further, as shown in FIGS. 5 (A) and 5 (B), the end shields 4 and 10 have a bell-like shape and a disc-like shape, but the bell-shaped end shield 4 is used. The thing has a high effect of dark current suppression.

As the surface treatment of the end shields 4 and 10, an oxide film (high resistance) or an inactive film is formed. For example, the surface is sprayed with α-alumina powder like sandblast. In particular, in 599 nickel or nickel chromium alloy, a silicon oxide film or a chromium oxide film is formed on the surface by high-temperature oxidation in a wet hydrogen stream. Further, when molybdenum is used, a carbonized layer is formed by carburizing in a hydrogen stream while being in contact with carbon.
JP-A-9-69340

  By the way, the end shields 4 and 10 of the conventional magnetron are fixed to the cathode sleeves 3 and 9 by welding or pressure bonding, and the support leads 6a and 6b are welded or pressure bonded to the end shields 4 and 10. In these welding and pressure bonding, if the formed film (for example, an oxide film) is present on the bonding surface with the cathode sleeves 3 and 9 and the support leads 6a and 6b, mechanical and electrical bonding problems occur. In addition, in electric welding, not only the joint surface with the parts necessary for supporting the cathode sleeves 3 and 9 and the support leads 6a and 6b but also the joint failure with the welding electrode occurs.

Therefore, conventionally, on the surface of the end shields 4 and 10, the bonding surface with the cathode sleeves 3 and 9 and the surrounding formation film, and the bonding surface with the support leads 6a and 6b and the surrounding formation film are mechanically formed. Alternatively, chemical removal is performed.
FIG. 6 is a view of the inside of the magnetron as viewed from above. For example, in the upper end shield 4, the formed film on the entire upper surface 4 </ b> S is removed for bonding to the support lead 6 a (the outer surface portion remains as it is). . Therefore, there is a problem that such a removal operation of the formed film becomes complicated and costs are increased because man-hours are required.

  In addition, the film formed around the welding or crimping location is particularly noticeable when electric welding is performed. However, since it is necessary to remove a relatively wide range, the end shields 4 and 10 have a surface without the film formed. There is a problem that it exists widely and suppression of dark current due to end shield emission is not sufficiently effective.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its object is to reduce the cost by eliminating the need for complicated removal of the formed film, and to maximize the dark current suppression effect. And a manufacturing method thereof.

In order to achieve the above object, a magnetron manufacturing method according to the invention of claim 1 includes an electron emission surface forming step of forming an electron emission surface of a cathode material containing an electron emitting material on the surface of the cathode sleeve, and the electron emission. An assembly process of assembling a tube by joining an end shield made of a metal containing at least chromium to the cathode sleeve obtained in the surface forming process and connecting an electrode lead to the end shield, and after the assembly process, An end shield oxide film forming step of oxidizing the chromium exposed on the surface of the end shield by filling the tube with carbon dioxide gas and heating to form a chromium oxide film. Features.
The invention according to claim 2 includes, as the cathode material, an oxide cathode material containing an oxide of an alkaline earth metal mainly composed of barium oxide, and the step of forming the end shield oxide film includes the oxide cathode The tube is filled with carbon dioxide gas generated when the material is thermally decomposed, and the chromium oxide film is formed on the surface of the end shield.

According to a third aspect of the present invention, in the end shield oxide film forming step, the cathode temperature is controlled to 600 to 900 ° C., and the partial pressure of carbon dioxide gas to be filled in the tube is 1.33 × 10 ⁻⁴ to 1. Control within the range of 33 × 10 ⁻² Pa.
According to a fourth aspect of the present invention, there is provided a magnetron comprising an electron emission surface of a cathode material containing an electron emitting substance on a surface of a cathode sleeve, and an end shield made of a metal containing at least chromium on the cathode sleeve on which the electron emission surface is formed. And an electrode lead is connected to this end shield and assembled into a tube, and the end shield surface is covered with a chromium oxide film formed by oxidation of chromium on the end shield surface. Features.

  According to the configuration of the present invention, after assembling the tube by joining the end shield to the cathode sleeve formed with the electron emission surface of the cathode material and connecting the electrode lead to the end shield, the vacuum exhaust process is performed. The tube is filled with carbon dioxide gas, and the carbon dioxide gas partial pressure and cathode temperature are controlled to a predetermined value, so that oxidation using carbon dioxide gas is performed, thereby oxidizing the surface of the end shield. A chromium film is formed.

According to the configuration of claim 2, for example, a carbonate such as (BaSrCa) CO ₃ is used as the cathode material of the cathode sleeve, and the partial pressure of carbon dioxide gas and the cathode temperature are set during the exhaust process. If the value is controlled, a chromium oxide film is formed on the surface of the end shield by the carbon dioxide gas generated by the thermal decomposition of the oxide cathode material.

According to the magnetron and the manufacturing method thereof of the present invention, a chromium oxide film can be formed on the surface of the end shield during the exhaust process after assembling the tube. Therefore, welding or pressure bonding between the end shield, the cathode sleeve, and the cathode support lead This eliminates the need for the conventional complicated oxide film removal step performed before the step, and has the advantage that the cost can be reduced.
In addition, since the chromium oxide film can be formed on the entire end shield other than the joint portion with each member without a gap, the effect of suppressing dark current can be maximized.

  FIG. 1 shows each step of a magnetron manufacturing method according to an embodiment of the present invention, and FIG. 2 shows a configuration at the time of assembling the magnetron. Oxidation is performed using carbon dioxide gas generated by thermal decomposition. In addition, the structure of the cathode of an Example becomes the same as that of the above-mentioned FIG. In the embodiment, a magnetron tube is assembled using an end shield having no oxide film formed on the surface, and this tube assembly is the same as the conventional process.

In FIG. 1, first, in an electron emission surface forming step 101, an electron emission surface is formed on the surface of the cathode sleeve 3 (made of nickel) of the cathode 2 shown in FIG. That is, for example, a nickel structure of about 50 to 100 μm is baked on the cathode sleeve 3 to form a matrix structure, and then an oxide cathode material is applied to the matrix structure to form the electron emission surface 5. Examples of the oxide cathode material for the electron emission surface 5 include carbonates such as (BaSrCa) CO ₃ and (BaSr) CO ₃ .

  In the next cathode assembly step 102, the cathode 2 is assembled. That is, the nickel-chrome alloy end shield 14 without an oxide film is set at the electrode position, and the nickel cathode sleeve 3 and the end shield obtained in the previous step 101 are assembled while incorporating an insulator and a tungsten insulator. 14 are joined by arc welding (TIG). At this time, since the chromium oxide film is not formed on the surface of the end shield 14, good bonding can be easily obtained. In this way, the cathode 2 shown in FIG. 2 or FIG. 5 is formed.

  Subsequently, in the tube assembly step 103, the tube is assembled, the cathode 2 is supported at a predetermined position with respect to the anode 16 shown in FIG. 2, and electrical connection is performed. That is, as shown in FIG. 2, the upper support lead (electrode lead) 6 a is arc welded to the end shield 14, and the lower support lead (electrode lead) 6 b is provided at the center of the lower end shield 14. The cathode 2 is supported and electrically connected by arc welding to the arbor terminal. Also at this time, since the chromium oxide film does not exist on the surface of the end shield 14, the bonding is easily and satisfactorily performed. Thereafter, the inside of the tube is set in a sealed state.

Then, in the next tube exhaust and chromium oxide film forming step 104, an exhaust stand equipped with a vacuum pump is coupled to the sealed tube, and the assembled tube is exhausted to a high vacuum. Oxidation with carbon dioxide gas is performed. In the embodiment, the entire tube is first baked to about 100 ° C. to 400 ° C. while the inside of the tube is evacuated to a vacuum degree of 1.33 × 10 ⁻⁵ Pa or less. Subsequently, a chromium oxide film is formed on the surface of the end shield 14 while activating the cathode 2.

In the example, activation of the cathode 2 causes thermal decomposition of (BaSrCa) CO ₃ , which is an oxide cathode material, as shown in the following chemical formula 1, but the partial pressure of carbon dioxide gas generated at this time is controlled. Thus, the end shield 14 is oxidized at a high temperature, thereby forming a chromium oxide film.
(BaSrCa) CO ₃ → (BaSrCa) O + CO ₂ ↑ (1)

For example, when the temperature of the cathode 2 is set to about 600 ° C. with a tungsten heater, thermal decomposition of the (BaSrCa) CO ₃ starts to occur. Thereafter, the exhaust gas velocity is controlled by valve operation or the like, and the thermal decomposition rate of the oxide cathode material is controlled by adjusting the cathode temperature, so that the carbon dioxide gas partial pressure is 1.33 × 10 ⁻⁴ to 1.33. × 10 ⁻² Pa. When this in-pipe atmosphere is continued for 10 hours or longer, a chromium oxide film (Cr ₂ O ₃ ) is formed on the entire surface of the end shield 14 made of nickel chromium alloy by an oxidation reaction of the following chemical formula 2.
2Cr + 3CO ₂ → Cr ₂ O ₃ + 3CO (2)

In such oxidation, when the carbon dioxide gas partial pressure is lower than 1.33 × 10 ⁻⁴ Pa, a chromium oxide film (1 μm or more) necessary for practical use cannot be obtained, and the carbon dioxide gas partial pressure is If it exceeds 1.33 × 10 ⁻² Pa, a eutectic of carbonate (BaSrCa) CO ₃ before pyrolysis and oxide (BaSrCa) O after pyrolysis is involved, and oxidation occurs in the matrix structure of the cathode 2. The cathode material is practically damaged and the emission characteristics are deteriorated.

  On the other hand, it is preferable to control the cathode temperature in the range of 600 ° C. to 900 ° C. Since the thermal decomposition rate is slow at 599 ° C. or lower, the cathode activation cannot be completed in practical time. Since the decomposition rate is high, not only the carbon dioxide gas partial pressure cannot be controlled, but also the above-described eutectic (eutectic temperature is about 903 ° C.) causes the oxide cathode material in the matrix structure to melt, resulting in deterioration of emission characteristics. Arise.

  Furthermore, the duration of the atmosphere for forming the oxide film described above needs to be at least 10 hours or more practically. In the example, when it was held for 10 hours to 45 hours, a necessary and sufficient chromium oxide film M was obtained on the surface of the end shield 14 of the cathode 2 as shown in FIG. Further, even if the time longer than this was continued, the film thickness hardly changed. This is because as the chromium oxide film M becomes thicker, the oxidation interface is separated from the atmosphere, and film growth does not proceed. Conversely, in a short time of about 3 hours, the presence of the chromium oxide film could not be confirmed visually.

  Thus, in the embodiment, it is possible to efficiently assemble a magnetron without removing the chromium oxide film on the surface of the end shield as in the prior art. Further, there is an advantage that the chromium oxide film M can be formed on the entire surface of the end shield 14 made of nickel chrome alloy without any gap, and the suppression of the end shield emission (dark current) can be ensured.

  In the above embodiment, the thermal decomposition of the oxide cathode material is used as the carbon dioxide gas supply source. However, the carbon dioxide gas cylinder is used as an auxiliary or main component, and the carbon dioxide gas is supplied into the tube. May be. That is, in the above embodiment, carbon dioxide gas is generated by thermal decomposition of the oxide cathode material, and carbon dioxide gas is supplementarily supplied from the gas cylinder into the tube, whereby the carbon dioxide gas partial pressure is predetermined. It may be set to a value.

  In addition, when an oxide cathode material that does not generate carbon dioxide gas, for example, an oxide cathode material such as barium aluminate, is used, the carbon dioxide gas in the gas cylinder is supplied into the tube so that the surface of the end shield 14 A chromium oxide film can be formed. When the supply from the gas cylinder is used, it is easy to maintain a constant atmosphere in the tube, and the carbon dioxide gas partial pressure can be easily controlled.

It is a figure which shows each process of the manufacturing method of the magnetron based on the Example of this invention. It is a partial cross section figure which shows the structure inside the tube of the magnetron which concerns on an Example. It is a figure after the chromium oxide film | membrane formation is shown, showing the structure inside the tube of the magnetron which concerns on an Example. It is a perspective view which shows the internal structure of the conventional magnetron. It is a side view which shows two structural examples of the cathode of the prior art and an Example. It is the figure at the time of the chromium oxide film removal which shows the structure inside the tube of the conventional magnetron using the cathode of FIG. 5 (A).

Explanation of symbols

1,16 ... Anode, 2,8 ... Cathode,
3, 9 ... Cathode sleeve, 4, 10, 14 ... End shield,
5, 11 ... Electron emission surface, 6a, 6b ... Support lead,
M: Chrome oxide film.

Claims (4)

An electron emission surface forming step of forming an electron emission surface of a cathode material containing an electron emitting substance on the surface of the cathode sleeve;
An assembly step of assembling a tube by joining an end shield made of a metal containing at least chromium to the cathode sleeve obtained in the electron emission surface forming step, and connecting an electrode lead to the end shield;
After the assembling process, the tube is filled with carbon dioxide gas and heated to oxidize the chromium exposed on the surface of the end shield, thereby forming an end shield oxide film forming process. A method for producing a magnetron, comprising:   The cathode material includes an oxide cathode material containing an oxide of an alkaline earth metal mainly composed of barium oxide, and the end shield oxide film forming step occurs when the oxide cathode material is thermally decomposed. 2. The method of manufacturing a magnetron according to claim 1, wherein the tube is filled with carbon dioxide gas to form the chromium oxide film on the surface of the end shield. In the end shield oxide film formation step, the cathode temperature is controlled to 600 to 900 ° C., and the partial pressure of carbon dioxide gas to be filled in the tube is 1.33 × 10 ⁻⁴ to 1.33 × 10 ⁻² Pa. 3. The method of manufacturing a magnetron according to claim 2, wherein the control is performed within a range. The cathode sleeve has an electron emission surface of a cathode material containing an electron emitting substance on the surface,
An end shield made of a metal containing at least chromium is joined to the cathode sleeve on which the electron emission surface is formed, and an electrode lead is connected to the end shield and assembled into a tube,
The magnetron formed by coating the end shield surface with a chromium oxide film formed by oxidizing chromium on the end shield surface.

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