JPS6323614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetron, and particularly to improvements in its cathode structure. [Technical Background of the Invention] In general, magnetrons that generate a magnetic field perpendicular to an electric field are now widely used in electronic equipment, such as microwave ovens, but with this, regulations regarding noise leakage have been introduced. It is on track to be strengthened. Internationally, this noise regulation is being implemented or under consideration in each country based on the recommendations of the International Special Committee on Radio Disorders (CISPR). Therefore, measures to reduce the noise generated from the magnetron itself have become even more desirable. By the way, the cause of low frequency noise (e.g. below 100MHz) generated by magnetrons is
I have the following idea. That is, FIG. 1 schematically shows an anode vane 26 and a cathode 25 constituting an anode coaxially arranged in a magnetron. , a high voltage of several thousand V is applied between the anode, and the cathode 2
When thermionic electrons are emitted from 5, in the electron action space 39, due to the space charge near the cathode, the potential has a downward concave portion that is more negative than the cathode potential, as shown by the dotted curve a in the figure. distribution. On the other hand, as shown by arrow B, a DC magnetic field of 1000 to 2000 Gauss is applied to the electron action space 39 in the cathode axial direction, so that the cathode 25
The emitted electrons orbit around the cathode 25 due to the action of the electric and magnetic fields. In particular, due to the orthogonal electromagnetic field, the traveling distance of the electrons is long, so there is a high probability that the electrons will collide with residual gas, and a significantly larger number of positive ions are generated than in other straight tubes. The generated positive ions flow into the valley of the potential distribution shown by curve a, that is, the potential minimum (indicated by the symbol m in the figure), and the electrons in the space charge and positive ions gradually become neutralized, and as a result, this The potential near the valley rises to a potential equal to or slightly higher than that of the cathode 25, as indicated by the symbol n. In this state, the potential distribution in the working space becomes like a solid line curve b. Positive ions flow into the cathode. In the next step, a potential valley m is again formed by space charges. This series of processes is repeated periodically. As a result, a complicated pulsation phenomenon occurs in the current between the cathode and the anode, that is, the anode current, and it can be assumed that this leaks into the external circuit as noise. Such noise mainly appears as so-called line noise that leaks along the input line, causing various radio interference. Therefore, as one measure to reduce such noise, by providing a third electrode near the cathode and applying a negative potential of several tens to several hundreds of volts to the third electrode with respect to the cathode, it is possible to eliminate the valleys in the potential distribution, that is, the potential.・The positive ions that gather to the minimum m are
It is considered that the noise caused by positive ions can be reduced by capturing them with electrodes. This example is constructed as shown in FIG. 2. That is, an end hat 51a and an end tip 52 are fixed to one end of a rod-shaped cathode support 32 arranged on the tube axis, and the other end of this cathode support 32 is connected to a cathode terminal and an exhaust pipe (both not shown). is joined to. The sleeve-shaped cathode support 33 is coaxially arranged with one end insulated by a ceramic spacer 55, and the end hat 5
1b, and the other end is connected to another cathode terminal (not shown). A spirally wound thorium-tungsten directly heated cathode 25 is connected between the end chip 52 and the end hat 51b. Thereby, the cathode 25 is heated by the heating power supplied to the cathode terminal. Now, in the vicinity of the cathode 25, a third electrode 60 is provided. This third electrode 60 is provided with a conductive cylindrical base 61 smaller than the spiral inner diameter of the cathode 25 inside the cathode 25, and a spiral protruding piece protruding from the outer periphery of the base 61 between each spiral of the cathode 25. 62 is integrally provided. The lower end 61a of the base body 61 is left as a free end without intervening an insulator or the like, and is connected to the inner rod-shaped cathode support 3 by a ceramic insulator 63 at a position farther upward in the figure than the end hat 51b.
2, and the other end is tightly fitted into the center hole of a third electrode terminal (not shown) and mechanically held. In this way, the third electrode 60 is held on the cathode support via the insulator at a position sufficiently distant from the cathode 25, and its tip remains free. Further, the third electrode 60 has a protruding piece 62 located between the spirals of the cathode 25 and protruding to a position equivalent to the outer periphery of the cathode 25. Moreover, this third electrode 60 includes W, Mo, Ta,
A single substance or alloy selected from poorly soluble metals such as Ti, formed with a surface condition that does not emit primary or secondary electrons, and as shown in the figure, the flow of electrons near the cathode and from the cathode to the anode. be placed in a position that does not interfere with As an example
A magnetron with an output of approximately 800W in the 2.45GHz band,
The diameter of the cathode coil wire is 0.58 mm, and the pitch spacing of the cathode and third electrode protrusions is 2.0 mm.
The outer diameter of the spiral is 5.0mm, and the inner diameter of the anode vane tip is
It is 10mm. Therefore, the cathode spiral and the third electrode spiral are arranged alternately at 1 mm intervals on the same outer peripheral surface. Note that the anode vane 26 and the anode cylinder constitute a plurality of cavity resonators, and together form an anode.
28 is a strap ring. Next, the operation will be described. The cathode 25 is heated and emits thermoelectrons. A high voltage of several thousand volts is applied between the cathode 25 and the anode vane 26, and a DC magnetic field of approximately 1500 gauss of magnetic flux parallel to the tube axis is applied to the electron action space 39, causing oscillation. do. The microwave energy generated in the cavity resonator is transmitted from the output section to the external load through the antenna conductor. Now, cathode 25
When the third electrode 60 is heated, a potential valley m is formed in the vicinity of several tens of micrometers to several hundreds of micrometers in front of the cathode 25 as shown in FIG. For example, if you set it to a negative potential of about 10 to 100 V with respect to 25,
The positive ions that gather toward the potential valley m are immediately captured by the third electrode 60 because the third electrode 60 has a more negative potential than this. In other words, the positive ions do not stay near the cathode but flow into the third electrode 60 , and the unstable electron-ion neutralization phenomenon near the cathode does not occur. the result,
Noise below 100MHz is significantly reduced. [Problems with the background art] In the magnetron shown in Figure 2 above,
As the magnetic flux density increases and the anode voltage increases,
It was found that the effect on noise weakened as shown in FIG. The assumption is that as the magnetic flux density increases, the flow of electrons in the working space changes from a simple circular motion to a complex cycloidal trajectory, and as a result, a potential minimum is formed even at the intermediate position between the anode and cathode. It is thought that ions are accumulated. To confirm the above speculation, the inventor made an experimental tube in which needles 64 were erected from the cathode support 32 as shown in FIG. 4, and investigated the tendency of the distance l between the needles 64 and noise. The results are shown in FIG. As can be seen from this result, the noise suddenly changes when the distance (diameter) l between the needles 64 reaches around 6.3 mm, and the reason for this is that ions accumulated near this diameter are captured by the needles 64, and the noise increases. It is thought that the situation suddenly changed, and the above speculation was confirmed. [Object of the invention] The object of the invention is to reduce noise and
To provide a magnetron which improves oscillation stability and further captures positive ions accumulated in a potential minimum formed between a cathode and an anode by a third electrode without impeding oscillation stability. That's true. [Summary of the Invention] The present invention has an electron emitting cathode and an anode containing a cavity resonator that are arranged coaxially with each other, and a magnetic field parallel to the cathode axis is generated in the electron action space between the cathode and the anode. a magnetron provided with end hats at both ends of the cathode, a third electrode made of a conductor conductively connected to or electrically insulated from the cathode is disposed near the cathode,
The third electrode is a magnetron that has at least a portion of a gap that serves as a path for electrons to easily move in a direction parallel to the cathode axis direction (magnetic field direction) in the vicinity of the cathode. [Embodiments of the Invention] Generally, in a magnetron, a magnetic field is applied in the axial direction, so the method of trapping ions using a radial electric field is affected by the magnetic field. Therefore, it is easier to create and capture an electric field in the axial direction. Therefore, the main parts (near the cathode) of the magnetron of the present invention are constructed as shown in FIGS. 6 and 7, and the same parts as in FIG. 2 are given the same reference numerals. That is, along the tube axis, e.g. carbonized thorium
A spiral electron emitting cathode 25 made of tungsten or lanthanum-molybdenum is provided, and both ends are fixed to end hats 51a and 51b, respectively. The end hat 51b is supported by a cylindrical outer cathode support 33, and the end hat 51a is supported by a rod-shaped inner cathode support (not shown) passing inside the outer cathode support 33 and cathode 25. Furthermore, a third electrode 73 is arranged near the cathode 25. This third electrode 73 has a conductive cylindrical base 74 smaller than the spiral inner diameter of the cathode 25 disposed inside the cathode 25, and a spiral protrusion protruding from the outer periphery of the base 74 and between each spiral of the cathode 25. A piece 75 is provided integrally. In this case, the protruding piece 75 is formed in a so-called gear shape. In other words, a gap 80 is provided near the cathode 25 as a path for electrons to easily move in the cathode axial direction (magnetic field direction).
Further, as is clear from the figure, the envelope surface formed by the end of the spiral and gear-shaped protruding piece 75 is shaped like a drum. That is, the expansion in the direction perpendicular to the cathode axis (radial direction) is large near the end hats 51a and 51b, and is small at the center of the cathode 25. The third electrode 73 is made of W (tungsten) or Mo (molybdenum), or is made of a metal such as W or Mo treated with a thin film having a low thermal emissivity, such as Pt or Au. Note that the magnetron of this invention has a second structure other than the above.
Since the configuration is similar to that shown in the figure, detailed explanation and illustration will be omitted. Now, during operation, the thermoelectrons emitted from the cathode 25 move around the cathode 25 in a space not covered by the third electrode 73 without being directly affected by the third electrode 73 , and then the microwave Interaction with the electric field forms spokes that move toward the anode. Furthermore, positive ions generated in this space are captured by the potentials of the third electrodes 73 on both sides. Then, the electrons emitted from the cathode 25 in the area covered by the third electrode 73 move in the axial direction, exit into the space not covered by the third electrode 73 , and behave in the same manner as the electrons described above. Furthermore, in the present invention, although positive ions are captured from the end of the third electrode 73 , they do not affect the main part of oscillation at all. Therefore, both oscillation stability and dark current are good. Furthermore, the third
If the slope of the electrode 73 is made too strong, on the contrary, the suppression of electrons becomes too strong, resulting in a state in which positive ions are surrounded by electrons, and the effect of trapping positive ions is reduced. [Effect of the invention] According to this invention, a third
Since the electrode 73 is provided, it is possible to reduce noise and improve the stability of oscillation.
It is possible to capture positive ions accumulated in the potential minimum formed between the electrode and the anode without interfering with the stability of oscillation. That is,
If the drain effect is strengthened by increasing the radial spread in the vicinity of the end hats 51a and 51b, the effect of interfering with the electron movement of the third electrode 73 at the center of the cathode 25, which mainly contributes to fundamental microwave oscillation, will be reduced, thereby improving operation. becomes stable. Moreover, since the third electrode 73 has a macroscopic potential gradient in the direction of the magnetic field, the drain effect is also increased, which is effective in reducing noise in the medium wave to ultrahigh frequency band. Further, in this invention, since the third electrode 73 is provided with the gap 80, there is an advantage that electrons can easily move in the cathode axial direction (magnetic field direction) in the vicinity of the cathode. In the above embodiment, the third electrode 73 is shaped like a drum, but it does not necessarily have to be shaped like a drum. Further, FIGS. 8 to 10 a and b show modified examples of the present invention, which provide the same effects as the above-mentioned embodiments. That is, in the case of FIG. 8, the gear-shaped portion of the protruding piece 82 of the third electrode 73 is only at the center, and the portions near the end hats 51a and 51b are not gear-shaped. In the case of FIG. 9, a plurality of L-shaped needle-like conductor pieces 76 are provided radially protruding from the outer periphery of the cathode support 32.
A third electrode 73 is provided. The third electrode 73 made of these needle-like conductor pieces is made of a high melting point metal such as molybdenum, and is connected to the spiral cathode 2.
5, and its tip is slightly protruded toward the anode vane 26 from the outer peripheral surface of the cathode. In the magnetron of this embodiment, the third electrode made of a needle-shaped conductor is mechanically and electrically connected to the cathode support, and the structure is relatively simple and noise can be reduced.
Although the figure shows an example in which four third electrodes made of needle-shaped conductors are provided at equal intervals on the circumference, the present invention is not limited to this. For example, the same number of third electrodes as the number of vanes may be provided radially around the cathode support. It's okay. Further, as is clear from the figure, the envelope surface connecting each end of the third electrode 73 is shaped like a drum, but it does not necessarily have to be shaped like a drum. In the case of FIGS. 10a and 10b, the third electrode 73 is formed by integrally protruding a plurality of needle-like pieces 85 in a spiral shape from a conductive cylindrical base 84, and each needle-like piece 85 is connected to the cathode 2.
It protrudes between the spirals of No. 5 and protrudes slightly outward from the outer diameter of the cathode 25. In each of the above embodiments, the third electrode may be assembled to have the same potential as the cathode, or it may be assembled electrically insulated from the cathode and then externally connected to the same potential as the cathode. You can also operate it by Alternatively, it may be electrically insulated from the cathode and operated without any other electrical connection so as to have a floating potential. Even in this case, as the third electrode is operated, it receives reverse electron impact and becomes a negative potential, and can capture positive ions.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing the noise generation mechanism in a magnetron, Figure 2 is a cross-sectional view of an example of a magnetron equipped with a third electrode to reduce noise, and Figure 3 is an anode voltage due to changes in magnetic flux density. Figure 4 is a cross-sectional view of an experimental tube used to confirm the mechanism of noise generation. Figure 5 shows the relationship between needle length and noise in the experimental tube shown in Figure 4. A characteristic curve diagram, FIG. 6 is a front view including a partial cross section showing the main parts of a magnetron according to an embodiment of the present invention, and FIG. 7 is a cross-sectional view of the third electrode portion at 7-7 in FIG. , Figure 8, Figure 9,
FIG. 10a is a longitudinal cross-sectional view showing a modification of the present invention, and FIG. 10b is a cross-sectional view of FIG. 10a. 25...Cathode, 26...Anode vane, 32
...Inner cathode support, 33...Outer cathode support, 39...Electron action space, 51a, 51b...End hat, 52...End tip, 73...Third electrode, 74 ...Cylindrical base, 75...Protruding piece, 76...Acicular shape Piece, 80...Gap, 82...Protruding piece, 84...Tylindrical base, 85...Acicular piece.

Claims (1)

[Claims] 1. A radial anode vane 26 constituting a cavity resonator, a spiral cathode 25 for electron emission arranged on the central axis of the anode vane, and a spiral cathode 25 connected to both ends of the cathode, respectively. end hats 51a, 51b, and spiral protrusions 75, 7 disposed in a non-contact manner between the spirals of the cathode.
6 and 85, and a magnetic field parallel to the cathode axis is applied to the electron action space 39 between the cathode and the anode, the third electrode having: The spiral protrusion 75,7
A magnetron characterized in that it has a large number of hollow portions 80 provided at predetermined intervals along the spiral at 6 and 85. 2 The third electrode has its spiral protrusions 75, 76,
2. The magnetron according to claim 1, wherein the magnetron 85 protrudes more toward the anode vane 26 in the vicinity of the end hats 51a, 51b than in the central portion of the cathode 25.