JP5562577B2 - Magnetron - Google Patents

Description

  The present invention relates to a structure for controlling the magnetic flux density distribution in the working space and increasing the frequency stability in a pulse in a magnetron, particularly a high-power pulse magnetron.

  FIG. 11 shows a configuration of a conventional high-power pulse magnetron. This magnetron 1 includes, for example, a cylindrical anode body 3 having an internal space 2 in which a plurality of cavity resonators are formed, and an internal space 2. The cathode body 4 disposed at the center of the disk, the left and right openings of the internal space 2, and disc (disk) -like sealing members (metals) 5a, 5b for sealing the openings at both ends of the cylindrical anode body 3, The disk-shaped sealing members 5a and 5b are formed of disk-shaped magnetic bodies 6a and 6b provided at the center of the outer surface of the disk-shaped sealing members 5a and 5b, and magnets (magnetic poles) 7a and 7b disposed so as to sandwich the internal space 2 from both sides. .

  In such a magnetron 1, since the magnetic flux density distribution in the working space 50 in the portion of the electron emission surface 4E of the cathode body 4 has a strong influence on the oscillation state, the magnetic flux density distribution in the working space 50 is Z-axis in all regions. Ideally, it is parallel to the direction (the axial direction of the cathode body 4) and homogeneous (Z axis symmetry).

  By the way, in the conventional magnetron 1, the magnetic flux spreads between the magnets 7a and 7b, and the uniformity of the magnetic flux density distribution in the Z-axis direction and the radial direction (the radial direction of the anode body 3 and the cathode body 4) decreases. There is. In addition, the magnetic flux density distribution even when the shapes of the pair of magnets 7a and 7b are different from each other due to various reasons such as spatial limitations represented by specifications such as the position of the input / output, or the position of the exhaust pipe. In addition, after the start of magnetron oscillation, the characteristics and fixing positions of the magnets 7a and 7b change as the temperature rises, and the homogeneity of the magnetic flux density distribution may be reduced. Thus, when the homogeneity of the magnetic flux density distribution in the working space 50 is lowered, problems such as unnecessary mode oscillation (moding), generation of noise, and reduction in output power occur.

  Therefore, conventionally, the shape of the magnets 7a and 7b is devised, or the magnetron 1 of FIG. 11 is also provided with the magnetic bodies 6a and 6b as the focusing bodies on the disk-like members 5a and 5b. The magnetic bodies 6a and 6b have a diameter smaller than the diameter of the magnets 7a and 7b. By adjusting the magnetic lines of force between the magnets 7a and 7b toward the center of the Z axis, the spread of the magnetic flux can be increased. It has improved.

  Further, Patent Documents 1 to 5 listed below exist as conventional techniques relating to such improvement of the magnetic flux density distribution. First, Patent Document 1 is an example in which the spread of the magnetic flux between the magnetic poles is improved by devising the shape of the magnetic pole, and by providing a protrusion on the pole piece as the magnetic pole, the Z-axis direction, particularly in the position of the inner end face of the anode vane, is provided. It improves the magnetic field strength distribution and suppresses noise of low frequency components.

  Patent Document 2 is an example in which the spread of magnetic flux is improved by devising a pole piece, which is a magnetic pole piece, into a shape such as a concave surface, and the axial direction in the vicinity of the anode vane as compared with the axial magnetic field strength in the vicinity of the cathode surface. It is configured so that the magnetic field strength is equal or strong, improving the radial stability of the magnetic flux density, and improving the operational stability, such as increasing the upper limit of the anode current that does not cause a modal phenomenon. .

  In Patent Document 3, a magnetic path correcting pole piece having a ring-shaped protrusion protruding in the vane direction is arranged on the surface of one magnet, and the cathode is supported on the surface of the other magnet by protruding in the vane direction. This is an example in which a pole piece provided with a ring-shaped protrusion (the diameter of which is different from the protrusion of the magnetic path correcting magnetic pole piece) is arranged, and the magnetic flux density distribution in the radial direction of the working space is made uniform. This is to prevent bad oscillation from occurring.

Patent Document 4 is an example corresponding to the temperature rise of a magnet, and is caused by the magnet temperature increase by magnetizing the magnetic pole piece with a magnetic pole piece having a protrusion protruding to the vane side. It is intended to obtain a stable output by suppressing fluctuations in the magnetic flux density in the working space.
Finally, Patent Document 5 provides a cut-and-raised portion on the outer peripheral portion of a focusing plate made of a magnetic material, and fits the outer peripheral portion of the annular magnet to the cut-and-raised portion, so that the radial direction between the focusing plate and the annular magnet is increased. It prevents position shift and improves performance.

JP-A-63-91932 Japanese Patent Laid-Open No. 53-38966 JP 51-56172 A JP 51-58859 A JP 2002-163993 A

  However, in the conventional magnetron 1 of FIG. 11, even if the magnetic bodies 6a and 6b are disposed, the spread of the magnetic flux is not sufficiently improved, and further improvement of the homogeneity of the magnetic flux density distribution in the working space 50 is required. Yes.

  FIG. 12 shows the magnetic flux density distribution in the Z-axis direction on the electron emission surface 4E in the magnetron 1 of FIG. 11, and as shown in the figure, the magnetic flux density is low at the center point 0 of the Z-axis, and both end points A And the difference in magnetic flux density between the center and both ends is increased.

  In Patent Documents 1 to 5, the pole piece and the magnetic piece are provided with protrusions and protrusions to make the magnetic flux density distribution uniform. In such a configuration, the magnetic flux density is uniform. There is a limit to making it difficult to make fine adjustments. Moreover, in general, the inner space of a magnetron is narrow, and there is a situation in which a spatial restriction occurs when a magnetic material is arranged.

  Further, the magnetron 1 having a high output pulse has a problem that the rising of the pulse oscillation becomes unstable. That is, the high-power magnetron has an anode voltage of several tens of kV and a peak power of MW class, and is mainly used for a microwave source of a linear accelerator in an X-ray generator or the like. In addition to high output power, high frequency stability within the pulse is required. In particular, if unnecessary oscillation (moding) that occurs in a very short time at the rising edge of pulse oscillation exists at a slight frequency, there is a disadvantage that arcing occurs, and even when arcing does not occur, for example, as jitter of X-ray intensity This adversely affects the characteristics of the X-ray generator.

  FIG. 13 shows the pulse waveforms of the anode voltage and anode current in the magnetron 1 of FIG. 11. As shown in the figure, in the anode voltage pulse waveform 101, an unnecessary oscillation (π-1 mode oscillation) part of the pulse rise is shown. Ka is generated, and jitter is generated in the anode current pulse waveform 201.

  The magnetron 1 with a high output pulse requires a large amount of electron emission from the cathode body 4 in order to operate with a large anode current, and this amount of electron emission is achieved by increasing the area of the electron emission surface 4E. However, in order to increase the area of the electron emission surface 4E, the cathode body 4 has a higher height than the diameter [the length of the cathode body 4 in the working space axis (Z-axis) direction is increased]. Is called. When the height of the cathode body 4 is increased, the distribution range of the magnetic flux density in the working space Z-axis direction becomes wider, so that the magnetic flux density difference on the electron emission surface 4E of the cathode body 4 increases in the Z-axis direction, and the pulse At the rise time, the electron gathering state is different between the central portion (Z-axis 0 point) and both end portions (Z-axis A point) of the cathode body 4, and the oscillation rise becomes unstable.

  In particular, if the frequency of occurrence of unwanted mode oscillation (moding) increases at the start of oscillation, the intra-pulse frequency stability deteriorates. For example, when the high-power pulse magnetron 1 is used as the microwave source of the linear accelerator, the reflection from the linear accelerator. Not only can the power increase and sufficient microwave power cannot be supplied to the linear accelerator, but also the magnetron itself has a disadvantage in that the oscillation frequency changes due to the influence of the reflected power and the operation becomes unstable.

  As described above, a high output pulse magnetron used particularly for a linear accelerator requires a high output and a high frequency stability at the same time. However, the height of the cathode body 4 is increased in design in order to increase the output. Therefore, the intra-pulse frequency stability is reduced, and it is necessary to suppress this decrease in frequency stability. However, the high-power pulse magnetron has a problem that it is difficult to obtain a high intra-pulse frequency stability that satisfies the requirements due to spatial limitations.

  Furthermore, in a high-power magnetron for a linear accelerator, the magnet is often a separate type, and it is almost difficult to change the shape of the magnet (magnetic pole) and adjust the magnetic force in the pole piece attached to the magnet.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is to easily and efficiently further homogenize and adjust the magnetic flux density distribution. The object is to provide a magnetron with extremely high stability.

In order to achieve the above object, a magnetron according to claim 1 of the present application includes a cathode body, an anode body in which the cathode body is disposed in an internal space, a plurality of cavity resonators, and a central axis of the cathode body. A magnetic pole body (for example, a magnet) for forming a magnetic flux coaxially with a certain Z axis, and a disk-shaped first electrode disposed on the opening side of the internal space of the anode body and having a diameter smaller than the diameter of the magnetic pole body in the magnetron having 1 and the magnetic body, a radially outer position of the cathode body Z axis center side and the first magnetic body from the magnetic pole bodies, which are arranged in a Z-axis and coaxially, than the diameter of the pole pieces An annular magnetic body having a large diameter, wherein a second magnetic body having a thickness in the Z-axis direction larger than that of the first magnetic body is disposed.
A second aspect of the present invention is the magnetron according to the first aspect, wherein the magnetron is arranged coaxially with the Z-axis at a position on the cathode Z-axis center side and the second magnetic body in the radial direction from the magnetic pole body, An annular magnetic body disposed radially outside the second magnetic body, wherein a third magnetic body having a thickness in the Z-axis direction larger than that of the second magnetic body is disposed. .

  According to the configuration of the present invention, the annular second magnetic body is disposed in, for example, the annular groove on the outer peripheral wall of the anode body in the outer circumferential direction of the first magnetic body or the sealing member that holds the first magnetic body. By arranging the third magnetic body outside the second magnetic body, it is possible to adjust the magnetic force generated by the magnetic pole body so that the magnetic force spreading in the outer peripheral direction of the anode body is shifted inward. It is possible to reduce the magnetic flux density difference between the center and both ends on the electron emission surface (Z-axis).

  According to the present invention, the magnetic flux density distribution can be further homogenized, the second magnetic body is separate from the first magnetic body, and the third magnetic body is separate from the first magnetic body and the second magnetic body. Thus, the magnetic flux density distribution can be adjusted easily and efficiently because it can be arranged in the groove on the outer wall of the anode body as required.

  In addition, the high power magnetron of the present invention has the effect that the stability of the intra-pulse frequency is extremely high. That is, on the electron emission surface of the cathode body, the difference in magnetic flux density between the central portion and both end portions becomes small, so that at the rising edge of the oscillation pulse, there is an inconvenient difference in the cluster state of electrons between the central portion and both end portions of the cathode body. The frequency of occurrence of unnecessary mode oscillation can be reduced, and the frequency of occurrence of unnecessary mode oscillation can be improved, thereby improving the intra-pulse frequency stability.

It is a partial cross section figure which shows the structure of the magnetron (high power pulse magnetron) which concerns on 1st Example of this invention. It is explanatory drawing which shows the effect | action of the 2nd magnetic body of 1st Example. It is a graph which shows magnetic flux density distribution on the electron emission surface (Z-axis direction) obtained with the magnetron of 1st Example. It is a graph which shows the pulse waveform obtained with the magnetron of 1st Example. It is a partial cross section figure which shows the structure of the magnetron based on 2nd Example. It is a partial cross section figure which shows the structure of the magnetron based on 3rd Example. It is an enlarged view of the attachment part (sealing member attachment part) of the 2nd magnetic body of FIG. It is a partial cross section figure which shows the structure of the magnetron based on 4th Example. It is an enlarged view which shows the attachment part of the 2nd magnetic body of FIG. It is a figure which shows the other structure of the 2nd magnetic body of an Example. It is a partial cross section figure which shows the structure of the conventional magnetron. It is a graph which shows magnetic flux density distribution on the electron emission surface (Z-axis direction) obtained with the conventional magnetron. It is a graph which shows the pulse waveform obtained with the conventional magnetron.

  FIG. 1 shows the configuration of a magnetron according to a first embodiment of the present invention. The first embodiment is configured as a high-power pulse magnetron for a linear accelerator in an X-ray generator. The magnetron 10 of FIG. 1 is, for example, a hole-and-slot type, and includes a cylindrical anode body 3 in which a plurality of cavity resonators are formed in an internal space 2. A cathode body 4 is arranged (coaxially), and the left and right openings of the internal space 2 of the anode body 3 are sealed with disk-like sealing members (metals) 5a and 5b. The outer periphery of the sealing members 5a and 5b is sealed and fixed to the opening end of the anode body 3 by welding or the like.

  In addition, a disc-like (iron material or the like) is formed at the central portion of the outer surface of the sealing members 5a and 5b at a position coaxial with the Z-axis that is the central axis (vertical axis) of the cathode body 4 or anode body 3 (internal space 2) The first magnetic bodies 6a and 6b are provided, and magnets (magnetic pole bodies) 7a (for example, N) and 7b (for example, S) are disposed so as to sandwich the internal space 2 of the anode body 3 from both sides. .

  And the annular groove 12 is formed in the right-and-left end of the outer peripheral wall of the said anode body 3, and this annular groove 12 is cyclic | annular (iron material) coaxially with the Z-axis (center axis) of 1st magnetic body 6a, 6b. Second magnetic bodies 14a and 14b (made of a ferromagnetic metal such as) are provided. The second magnetic bodies 14a and 14b are disposed at positions radially outside the first magnetic bodies 6a and 6b on the Z axis center side from the magnets 7a and 7b, but the first of the sealing members 5a and 5b. It is also possible to arrange the magnetic bodies 6a and 6b outside through a mounting groove or the like.

  The annular second magnetic bodies 14a and 14b have a thickness (height) in the Z-axis direction that is greater than the thickness of the first magnetic bodies 6a and 6b. The thickness of the second magnetic bodies 14a and 14b needs to be adjusted by the magnetic flux density of the magnets 7a and 7b and the distance between the magnetic poles. For example, the distance between the magnetic poles of the magnets 7a and 7b is about 75 mm. When the thickness (wall thickness) of 6b is about 0.7 mm, the thickness of the second magnetic bodies 14a and 14b is preferably set to about 9 mm.

The first embodiment is configured as described above. According to the first embodiment, the magnetic flux density in the working space 50 can be homogenized by the second magnetic bodies 14a and 14b.
That is, in FIG. 2, the magnets 7a, but outside of the magnetic field lines in the space between 7b is shown, the second magnetic bodies 14a, magnetic force lines B ₁ which has passed through the outside case 14b is not, the second magnetic body 14a, by 14b, will be shifted inwardly as the magnetic field lines _{B 2.} As a result, the magnetic flux density in the internal space 2 and the working space 50 is homogenized.

  FIG. 3 shows the magnetic flux density distribution in the Z-axis direction on the electron emission surface obtained in the first embodiment. When FIG. 3 is compared with the conventional FIG. 12, the electron emission surface 4E is compared. The difference in magnetic flux density between the central portion (Z axis: 0 point) and both ends (Z axis: A point) was reduced, resulting in homogenization. For example, in the prior art (FIG. 12), the magnetic flux density difference between the Z-axis 0 point and the A point was about 90 gauss, whereas in the first embodiment (FIG. 3), it was reduced to about 50 gauss.

In addition, according to the first embodiment, the oscillation rising characteristic is stabilized, so that unnecessary oscillation at the oscillation rising does not occur.
FIG. 4 shows the pulse waveforms of the anode voltage and the anode current in the magnetron 10, and in comparison with the conventional FIG. 13, in the first embodiment, as shown by the anode voltage pulse waveform 102, the pulse rising edge is shown. The unnecessary oscillation (π-1 mode oscillation) portion (Ka) disappeared, and as shown in the anode current pulse waveform 202, the presence of jitter disappeared and a good pulse waveform was obtained.

FIG. 5 shows the configuration of the second embodiment. This second embodiment further includes an annular third magnetic body.
In FIG. 5, two annular grooves 12a and 12b having different diameters coaxially with the Z axis and different depths are formed on the left and right of the outer peripheral wall of the anode body 3, and the second groove is formed in the inner groove 12a. The annular third magnetic bodies 14c and 14d are fitted and disposed in the magnetic bodies 14a and 14 and the outer groove 12b. Then, the thickness (length in the Z-axis direction) of the third magnetic bodies 14c and 14d having a large diameter arranged on the outside is made larger than the thickness of the second magnetic bodies 14a and 14b. In addition, it is also possible to arrange three or more (fourth magnetic body, fifth magnetic body...) Of the annular magnetic bodies having different diameters, and the annular magnetic body in this case is arranged on the outside. Try to increase the thickness.

  According to the configuration of the second embodiment, the third magnetic bodies 14c and 14d are further added to the second magnetic bodies 14a and 14b, thereby further homogenizing the magnetic flux density and further adjusting the homogenization. be able to. That is, in the present invention, since the second magnetic bodies 14a and 14b and the third magnetic bodies 14c and 14d are separated from the first magnetic bodies 6a and 6b, the thicknesses of the second and third magnetic bodies 14a to 14d By appropriately selecting the number and the arrangement position, there is an effect that the adjustment of the magnetic flux density homogenization becomes easy and efficient.

FIGS. 6 and 7 show the configuration of the third embodiment. In the third embodiment, the second magnetic body is prevented from falling off by a sealing member.
As shown in the enlarged view of FIG. 7, in the third embodiment, the outer circumferential end of the metal disk-shaped sealing member 5a is stretched to the opening (inlet) of the annular groove 12 of the anode body 3. An annular protrusion (overhang) 16 is formed. The protrusions 16 may be provided on the entire circumferential direction of the sealing member 5a, or may be provided on several portions in the circumferential direction.

  According to the third embodiment, the sealing members 5a and 5b are sealed by arc welding or the like to the attachment portion (stepped portion) of the anode body 3, but at this time, the sealing member The second magnetic bodies 14a and 14b are in a fixed state so that the protruding portions 16 of 5a and 5b block a part (inner peripheral side) of the annular opening of the groove 12, whereby the second magnetic bodies 14a and 14b are fixed. Is prevented from falling off. That is, since the annular second magnetic bodies 14a and 14b always receive an attractive force from the magnets 7a and 7b and receive a force drawn from the groove 12, they are easy to come off. In the third embodiment, it is possible to prevent the magnets 7a and 7b from dropping off due to the attractive force, and a highly reliable magnetron can be obtained.

FIG. 8 and FIG. 9 show the configuration of the fourth embodiment. This fourth embodiment prevents the second magnetic body from falling off at the protrusion on the anode body side.
As shown in the enlarged view of FIG. 9, in the fourth embodiment, an annular protrusion (overhang) 17 is formed to project from the outer peripheral edge of the annular groove 12 of the anode body 3 to its opening. The projecting portion 17 is formed by caulking or deforming the outer peripheral edge, or by welding another member, and the projecting portion 17 may be provided on the entire edge of the annular groove 12 or on the circumference. It may be provided in several places in the direction. Further, the protruding portion 17 may be formed so as to protrude from the inner peripheral edge of the annular groove 12 to the opening.

  According to the fourth embodiment, the second magnetic bodies 14a and 14b are fixed in such a manner that the protruding portion 17 provided in the annular groove 12 closes a part (outer peripheral side) of the opening of the annular groove 12. Thus, the second magnetic bodies 14a and 14b are prevented from falling off. That is, it is prevented from gradually falling off by the attractive force received from the magnets 7a and 7b. The fourth embodiment can also be applied to the case where the third magnetic bodies 14c and 14d shown in FIG. 5 are provided.

  FIG. 10 shows another example of the second and third magnetic bodies 14a to 14d used in each of the above-described embodiments. As shown in the drawing, the annular second and third magnetic bodies 14a to 14d are shown. In 14d, the cutting part 18 is formed in at least one place. The width of the cut portion 18 is preferably 10 mm or less, and if it is 10 mm or less, there is no difference in the substantial effect of the annular second and third magnetic bodies 14a to 14d.

  According to the cutting portions 18 of the second and third magnetic bodies 14a to 14d, the cutting portions 18 can be formed even when the protruding portions 16 and 17 are formed first as in the third and fourth embodiments. The second and third magnetic bodies 14a to 14d can be easily arranged in the annular groove 12 while opening. In addition, since the thin plate can be bent without using a mold or the like, it is advantageous in terms of cost as compared with the case where the thick plate is removed by electric discharge machining or a die.

  In each of the above embodiments, ferromagnetic metal iron is used as the first magnetic bodies 6a and 6b, the second and third magnetic bodies 14a to 14d, but various other alloys and compounds are used instead of the iron. May be used.

1, 10 ... magnetron, 2 ... internal space,
3 ... Anode body, 4 ... Cathode body,
5a, 5b ... sealing member, 6a, 6b ... first magnetic body,
7a, 7b ... magnet (magnetic pole body), 12 ... groove,
14a, 14b ... 2nd magnetic body, 14c, 14d ... 3rd magnetic body,
16, 17 ... projecting part, 18 ... cutting part,
50: Working space.

Claims (2)

A cathode body;
This cathode body is arranged in the internal space, and an anode body having a plurality of cavity resonators,
A magnetic pole body for forming a magnetic flux coaxially with the Z axis, which is the central axis of the cathode body,
In a magnetron having a disk-shaped first magnetic body disposed on the opening side of the internal space of the anode body and having a diameter smaller than the diameter of the magnetic pole body,
An annular magnetic body disposed coaxially with the Z-axis at a position on the center side of the cathode body Z-axis from the magnetic pole body and radially outside the first magnetic body, and having a diameter larger than the diameter of the magnetic pole body A magnetron comprising a second magnetic body having a thickness in the Z-axis direction larger than that of the first magnetic body. 2. The magnetron according to claim 1, wherein the magnetron is disposed coaxially with the Z-axis at a position on the cathode body Z-axis center side and on the radially outer side of the second magnetic body from the magnetic pole body, and in a radial direction of the second magnetic body . A magnetron comprising an annular magnetic body disposed on the outside, wherein a third magnetic body having a thickness in the Z-axis direction larger than that of the second magnetic body is disposed.

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