JP2000059108A - Coaxial waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a high-pass filter which is simple and small by propagating high-frequency electric power to a cylindrical space part partitioned with a partition plate. SOLUTION: This waveguide is equipped with an internal conductor 12 and an external conductor 14 which are arranged coaxially and a partition plate 80 which short-circuits them electrically, and provided with a high-pass filter function by propagating high-frequency electric power to the cylindrical space part 82 partitioned with the partition plate 80. Namely, a rectangular waveguide 20 is rounded having the internal conductor 12 as one long side 24 and the external conductor 14 on the other and the excess from the long side 24 for the internal conductor 12 is used as the partition plate 80 to constitute the coaxial waveguide. This waveguide has a cutoff frequency as well as the rectangular waveguide and its size is determined by the mean length L of the space part 82. The internal diameter of the external conductor 14 and the external diameter of the internal conductor 12 are determined by the found cutoff frequency. Namely, the mean length L of the space part 82 between the internal and external conductors is so selected as to correspond to the length (a) of the rectangular waveguide 20 when the cutoff frequency of the rectangular waveguide 20 is found, but this is a rough estimate and the detailed size is determined by simulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coaxial waveguide, and more particularly, to a coaxial waveguide having a high-pass filter function, which is suitable for use in a high-order mode damper of a high-frequency accelerating cavity in a ring accelerator. About pipes.

[0002]

2. Description of the Related Art In order to transmit high-frequency power, usually,
A waveguide is used. Typical examples of this waveguide include:
There are a coaxial type and a square type.

As shown in FIG. 1 (transverse sectional view) and FIG. 2 (longitudinal sectional view), the coaxial waveguide 10 includes an inner conductor 12 and an outer conductor 14, both of which are electrically separated. ing.
In this, the high-frequency power propagates in the axial direction (Z direction) while creating an electromagnetic field composed of a radial electric field E and a circumferential magnetic field M as shown in the figure. In this coaxial waveguide, high frequency power of an arbitrary frequency can propagate.

On the other hand, as shown in FIG. 3, the rectangular waveguide 20 has a rectangular cross section having, for example, a long side 22 having a length a and a short side 24 having a length b. FIG. 4 shows the electromagnetic field distribution, and FIG. 5 shows the current distribution. In this rectangular waveguide, an electromagnetic wave having a frequency lower than a certain frequency (referred to as a cutoff frequency) cannot propagate, and thus has a high-pass filter function.

The cut-off frequency fc of the rectangular waveguide is determined by the shape of the waveguide (particularly, the length a of the long side 22).
The light velocity is represented by c, and is expressed by the following equation.

Fc = c / 2a (1)

For example, 500 MH often used in accelerators
When transmitting high frequency power of z, a = 300 mm or more is required. On the other hand, in the coaxial waveguide, high frequency power of any frequency can be propagated in principle with any small size. Therefore, using a coaxial waveguide can reduce the size of the transmission system.

[0008]

However, if the spectrum of the high-frequency source is composed of a plurality of frequency components and it is desired to transmit only those having a specific frequency or higher among them,
A coaxial waveguide cannot be used.

An example of such a requirement is a higher mode (Higher Ordr) of a high-frequency accelerating cavity in a ring accelerator.
Mode: abbreviated as HOM).

The high-frequency accelerating cavity 30 generates an electric field in the traveling direction of the electron or charged particle (hereinafter referred to as "electron") beam B by supplying high-frequency power into the cavity main body 32 as shown in FIG. To accelerate the electrons. In the figure, 28 is a beam duct of a ring-shaped accelerator (not shown), 34 is a beam port of a high-frequency acceleration cavity 30 connected to the beam duct 28, 36 is
An antenna port to which the antenna 38 is connected, and a tuner port 40 to which a tuner 42 is connected.

The high frequency used for this acceleration is
It is determined by the perimeter of the ring and the number of bunches of orbiting electrons. The size, structure, and the like of the acceleration cavity 30 are determined so as to resonate at this frequency, but there are many resonance modes and not one. Normally, of these, the lowest frequency fundamental mode is used for acceleration, while the others are called higher order modes (HOM), which do not only provide acceleration but also cause some instability that causes instability. There are even things. Normally, high-frequency power supplied from the outside is of a single frequency, so that no higher-order mode does not occur without an electron beam. However, those that excite the electron beam itself when passing through the cavity 30 are not limited to this. Absent.

The HOM damper is a device for removing higher-order mode electromagnetic waves excited in a cavity by an electron beam. In the example shown in FIG. 7, the loop antenna 52 and the rod antenna 54 are inserted into the cavity 30 from the ports opened on the side walls of the acceleration cavity. In the figure, 56 is a ceramic window having a function of a vacuum partition for holding the loop antenna 52 and the rod antenna 54, and 58 is
An extended coaxial (type waveguide) tube connected to the rear ends of the loop antenna 52 and the rod antenna 54, 60 is a vacuum flange, 62 is a ceramic support for holding a portion connected to the high frequency absorber, 64 is for cooling the antenna Cooling water channel.

FIG. 7 shows two types, one with a loop antenna 52 at the tip and one with a rod antenna 54. Here, the loop antenna type will be described. Note that the loop antenna 52 and the rod antenna 54 have a complementary relationship to each other, and a mode that can be picked up by the loop antenna 52 cannot be picked up by the rod antenna 54, and the rod antenna 54
The mode that can be picked up by the loop antenna 52 cannot be picked up by the loop antenna 52. So to pick up all higher modes,
Both types of antennas are required.

The tip of the loop antenna 52 is coupled to a higher-order mode in the cavity, guided to a subsequent extended coaxial waveguide 58, and finally removed by a high-frequency absorber (not shown).
By the way, the loop antenna 52 at the tip couples not only with the higher-order mode but also with the fundamental mode. Therefore, in this example, the termination is short-circuited at a half of the fundamental wavelength (in this example, the fundamental frequency is 500 MHz) at a branch point so that the fundamental mode does not propagate toward the high frequency absorber. The extended coaxial tube 58 is attached. By doing this,
The fundamental mode is equivalent to a short circuit at the branch position in terms of high frequency, and the fundamental mode is totally reflected at the branch position and returns to the cavity 30. However, for all high frequencies having a frequency that is an integer multiple of the fundamental mode, this holds. Therefore, among the higher-order modes, those having an integral multiple of the frequency of the fundamental mode cannot be removed by the HOM damper 50. In this example, attention is paid only to a specific higher-order mode (the one that causes or may cause instability), and the other higher-order modes are ignored. As described above, in designing the HOM damper 50, it is determined in advance which mode causes instability,
Must be specified.

As another example, FIG. 8 (longitudinal sectional view) and FIG.
(A cross-sectional view along IX-IX in FIG. 8). This HOM damper uses a rectangular waveguide 71 whose dimensions are selected so that the cutoff frequency is higher than that of the fundamental mode and lower than the frequency of the lowest higher-order mode. As a result, the fundamental mode is not propagated and does not affect the acceleration of electrons.
It is removed by the high-frequency absorber at the end of the first. In the figure,
72 is a probe port, 74 is a coupler port, and 76 is a spare port.

However, in the HOM damper of the type shown in FIG. 8, if the fundamental frequency is 200 MHz and the lowest-order mode frequency is 500 MHz, a = 30.
A rectangular waveguide of 0 to 750 mm must be chosen,
This is because the length of the acceleration cavity 30 in the beam traveling direction is 300
Considering that the diameter is about mm, there is a problem that the diameter is clearly too large.

The present invention has been made to solve the above-mentioned conventional problems, and has as its object to constitute a simple and compact high-pass filter.

[0018]

According to the present invention, as shown in FIG. 10, in a coaxial waveguide 11, an inner conductor 12 and an outer conductor 14, which are disposed coaxially, are electrically short-circuited. The above-mentioned problem has been solved by providing a high-pass filter function by transmitting high-frequency power to a substantially cylindrical space 82 divided by the partition plate 80. .

Further, based on the radius ri of the inner conductor 12, the radius ro of the outer conductor 14, and the thickness d of the partition plate 80, the cut-off frequency fc is calculated by the following equation: fc = c / [2 ｛π (ri + Ro) -d}] (2) (where c is the speed of light).

Further, a plurality of the partition plates are provided, and the space is equally divided into a plurality of portions to increase a cutoff frequency.

According to the present invention, as shown in FIG. 11, the rectangular waveguide 20 is rolled up to form one of the long sides 24 as the inner conductor 12, the other as the inner conductor 12, and the short side 24 as the partition plate 80. It can be interpreted as having been. Therefore, also in this case,
As in the case of the rectangular waveguide, it can be seen that there is a cutoff frequency, the magnitude of which is determined by the average length L of the space 82. Actually, FIG. 12 (longitudinal sectional view), FIG.
Cross-section along the line XIII-XIII), FIG. 14 (also XIV
As shown in the cross-sectional view taken along the line -XIV), when a simulation is performed using a model in which a partition plate 80 according to the present invention is inserted in the middle of a normal coaxial waveguide, the outer diameter di of the inner conductor 12 is 88 mm. , Inner diameter do of outer conductor 14 = 152 mm,
When the thickness d of the partition plate 80 is 4 mm, the reflected power is as shown in FIG.
5, and the transmitted power is as shown in FIG. These are a high-frequency power that is reflected and returned to the same port when high-frequency power is sent from one port (FIG. 15) and a high-frequency power that is transmitted and output to the other port (FIG. 16). Are expressed as ratios to the input power from the respective inlets. As the results show, 400-500M
It can be seen that a cutoff frequency of Hz is present. Incidentally, when the parameters used in the simulation are applied to the equation (2), the cut-off frequency fc = 402.2 MHz
And almost agrees with the simulation.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the first embodiment of the present invention, as shown in FIG. 10, an inner conductor 12 and an outer conductor 14 are disposed coaxially.
And a partition plate 80 that electrically shorts them.
A substantially cylindrical space 82 divided by the partition plate 80
The high-frequency power is propagated to provide a high-pass filter function.

The inner diameter of the outer conductor 14 and the outer diameter of the inner conductor 12 are determined by the required cutoff frequency fc.
Specifically, assuming that the radius of the inner conductor 12 is ri, the radius of the outer conductor 14 is ro, and the thickness of the partition plate 80 is d, the equation (2) is roughly set. That is, the average length L of the space 82 between the inner and outer conductors is selected so as to correspond to a in the cutoff frequency in the case of the rectangular waveguide 20 (a). However, this is an approximate value, and the detailed dimensions are desirably determined by, for example, a computer simulation.

FIG. 17 shows a second embodiment of the present invention.
In the present embodiment, two partition plates 80a and 80b are provided, and the space is equally divided into 82a and 82b.

In this embodiment, since the average length L of the space is half that of the first embodiment, the cut-off frequency fc
Is doubled. Similarly, by increasing the number of divisions to three or four times, the cutoff frequency can be increased to three or four times.

In each of the above-described embodiments, the cross-sectional shape of the waveguide is circular, but the cross-sectional shape is not limited to a circle, and may be rectangular as in the third embodiment shown in FIG. It may be.

This embodiment conceptually corresponds to a rectangular waveguide 20 bent in a U-shape.

In each of the above embodiments, the waveguide is used for the HOM damper of the high-frequency accelerating cavity in the ring type accelerator. However, the application of the waveguide is not limited to this. It can be applied to general uses.

[0030]

According to the present invention, a simple and small high-pass filter can be constructed. Thus, for example, HO
In the M damper, a small HOM damper can be configured without previously identifying a higher-order mode that causes instability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a configuration of a conventional coaxial waveguide and an electromagnetic field.

FIG. 2 is a longitudinal sectional view of the same.

FIG. 3 is a perspective view showing a configuration of a conventional rectangular waveguide.

FIG. 4 is a perspective view showing an electromagnetic field distribution.

FIG. 5 is a perspective view similarly showing a current distribution.

FIG. 6 is a longitudinal sectional view showing a configuration of a high-frequency acceleration cavity to which the present invention is applied;

FIG. 7 is a longitudinal sectional view showing the configuration of an example of the HOM damper.

FIG. 8 is a longitudinal sectional view showing an example of a HOM damper using a rectangular waveguide.

9 is a cross-sectional view taken along line IX-IX in FIG.

FIG. 10 is a cross-sectional view showing the configuration of the first embodiment of the present invention.

FIG. 11 is a diagram for explaining the principle of the present invention.

FIG. 12 is a longitudinal sectional view showing a configuration of a simulation model used for confirming the principle of the present invention.

FIG. 13 is a cross-sectional view taken along line XIII-XIII of FIG.

FIG. 14 is a cross-sectional view along the line XIV-XIV.

FIG. 15 is a diagram showing an example of reflected power as a result of a simulation;

FIG. 16 is a diagram showing an example of transmitted power.

FIG. 17 is a cross-sectional view showing the configuration of the second embodiment of the present invention.

FIG. 18 is a transverse sectional view showing the principle and configuration of the third embodiment.

[Explanation of symbols]

 10, 11 ... coaxial waveguide 12 ... inner conductor 14 ... outer conductor 20 ... rectangular waveguide 22 ... long side of rectangular waveguide 24 ... short side of rectangular waveguide 30 ... high frequency accelerating cavity 32 ... cavity body 34 ... beam port 36 ... antenna port 38 ... antenna 40 ... tuner port 42 ... tuner 50 ... HOM damper 52 ... loop antenna 54 ... rod antenna 56 ... ceramic window 58 ... extended coaxial tube 60 ... vacuum flange 62 ... ceramic support 64 ... cooling water channel 71 ... rectangular waveguide 72 ... probe port 74 ... coupler port 76 ... spare port 80, 80a, 80b ... partition plate 82, 82a, 82b ... space

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2G085 AA13 BA05 BB12 BB17 CA03 CA13 5J006 HC12 JA04 JA23 JA31 JB00 LA12 LA21 5J014 AA00 BA01 BA04 DA00 EA01

Claims (3)

[Claims] An inner conductor and an outer conductor disposed coaxially; and a partition plate for electrically short-circuiting the inner conductor and the outer conductor, and transmitting high-frequency power to a substantially cylindrical space defined by the partition plate. A coaxial waveguide having a high-pass filter function. 2. A cut-off frequency f based on a radius ri of the inner conductor, a radius ro of the outer conductor, and a thickness d of the partition plate.
The coaxial waveguide according to claim 1, wherein c is determined based on the following equation: fc = c / [2 {π (ri + ro) -d}] (where c is the speed of light). tube. 3. The coaxial waveguide according to claim 1, wherein a plurality of said partition plates are provided, and said space portion is equally divided into a plurality of portions.