JPH0729698A - High-order mode damper for high frequency accelerating cavity - Google Patents

Abstract

PURPOSE:To satisfactorily keep an acceleration mode without changing filter characteristic by forming the short-circuit part of a concentric resonator by a movable plate, and moving and regulating the movable plate so that the resonance frequency is coincident to an acceleration frequency. CONSTITUTION:A high-order mode damper 1 has a concentric resonator constituted between a middle conductor 3 and an external conductor 5, and filter function is imparted by them. The conductors 3, 5 are short-circuited by a disc movable short-circuit plate 8 having a central hole bored therein. When the short-circuit plate 8 is shifted to the outside, inductance L is increased, and resonance frequency is reduced. When it is shifted to the inside, the inductance L is reduced, and the resonance frequency is increased. When a beam is passed, an incidental resonance mode having a high gap speed frequency is induced in a high frequency accelerating cavity body 22 with the beam as an exciting source. When the gap between the conductors 3, 5 is then regulated to make the acceleration frequency coincident to the resonance frequency, a high frequency power is absorbed by the high-order damper 1. Thus, the performance can be enhanced without changing the filter characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a higher mode damper for a high frequency accelerating cavity used in a particle accelerator for accelerating charged particles.

[0002]

2. Description of the Related Art A particle accelerator is used for accelerating a beam of electrons, protons, ions, etc. to a high energy state. Recently, a synchrotron radiation (S) from an electron beam has been used.
A relatively small type, for example, an accelerator having a diameter of about 10 m has been constructed as an application to a new field such as VLSI microfabrication (lithography) using OR light).

The accelerator is provided with a high frequency accelerating cavity for accelerating particles and replenishing energy lost by synchrotron radiation. In this high-frequency acceleration cavity, a high electric field of high frequency of several hundred megahertz synchronized with the orbit of the particle is generated, and the particle is accelerated by this high electric field.

FIG. 3 shows an example of a conventional high frequency acceleration cavity. As shown in FIG. 3, this high-frequency acceleration cavity has two side plates 20 each having a nose portion and having a substantially disk shape, and a cylindrical outer cylinder 21.
High frequency accelerating cavity body 22 in which and are joined by brazing, etc.
And an antenna 23 for inputting high-frequency power, a high-order mode damper 1a described later, and the like. The high-frequency acceleration cavity is connected to a vacuum duct 24 and is maintained in an ultrahigh vacuum. Then, the beam advances on the central axis of the high-frequency acceleration cavity main body 22 as shown by the arrow in the figure, and is accelerated each time it passes.

Next, the higher mode damper 1a related to the present invention will be described. When the beam passes as shown by an arrow in FIG. 3, this beam becomes an excitation source and induces various parasitic resonance modes having a frequency higher than the acceleration frequency in the high frequency acceleration cavity body 22. This parasitic resonance mode is generically referred to as a higher order mode, and some higher order modes generate a large electromagnetic field in the high frequency accelerating cavity body 22 and have an adverse effect of eliminating the beam. Therefore, the higher-order mode damper 1 for absorbing and attenuating these higher-order modes
a is attached.

An example of this higher order mode damper 1a is shown in FIG. The higher order mode damper 1a has a double coaxial structure, the inner conductor 2 and the intermediate conductor 3 are connected to the resistive load 4, and the absorbed higher order mode is consumed by the resistive load 4.

The inner conductor 2 and the outer conductor 5 are connected via a coupling loop 6, which has a function of coupling with an electromagnetic field of a higher order mode. The outer conductor 5 is bolted to the vacuum port of the high frequency acceleration cavity body 22 via a vacuum seal to form a vacuum boundary with the ceramic vacuum window 7.

Since the coupling loop 6 of the higher-order mode damper 1a is also coupled with the acceleration mode, it also absorbs the input power from the antenna 23. In order to prevent this, a coaxial resonator is formed between the intermediate conductor 3 and the outer conductor 5.

That is, a narrow gap between the conductors 3 and 5 has a function of a capacitor (capacitance C), and a wide gap has a function of a coil (inductance L). The resonance frequency f = 1 / If 2π · (LC) ^1/2 is the same as the acceleration frequency, the filter does not pass the power of this frequency.

In this way, a design is made in which only the higher-order modes are absorbed and attenuated without wasting the power in the acceleration mode. It should be noted that, although there are some which use a rod-shaped antenna instead of the coupling loop 6 of FIG. 4 and those which have different coaxial resonator shapes, the principle is exactly the same as above.

[0011]

By the way, the high-order mode damper 1a, when power is applied to the high-frequency acceleration cavity,
Although having the above-described filter action, some electric power flows between the intermediate conductor 3 and the outer conductor 5 which are filters. The heat load due to this electric power is water-cooled by a cooling structure (not shown), but the temperature rise is unavoidable, and the dimensional relationship between the intermediate conductor 3 and the outer conductor 5 changes, and the resonance frequency of the coaxial resonator changes.

For this reason, the filter characteristic is deteriorated and the temperature rises further, resulting in a vicious circle. Further, the change in the resonance frequency also occurs due to the change in the outside temperature. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-order mode damper for a high-frequency acceleration cavity in which the filter characteristics do not change and the acceleration mode is not adversely affected.

[0013]

In order to solve the above-mentioned problems, a high-order mode damper for a high-frequency acceleration cavity according to the present invention absorbs a higher-order mode having a frequency higher than the acceleration frequency in the high-frequency acceleration cavity. In a high-order mode damper for a high-frequency acceleration cavity having a coaxial resonator, the short-circuited part of the coaxial resonator is used as a movable plate, and the movable plate is moved and adjusted to accelerate the resonance frequency of the coaxial resonator to the above-mentioned value. The frequency is the same as the frequency.

Then, a bellows is attached to an end of the coaxial resonator provided with the movable plate, and a vacuum boundary is formed by the bellows, or a ceramic vacuum window is provided at the center of the coaxial resonator provided with the movable plate. Attached, this vacuum window may be the vacuum boundary.

[0015]

In the present invention having the above structure, the resonance frequency of the coaxial resonator can be changed by using the movable plate as the short-circuited portion of the coaxial resonator. Therefore, even if the resonance frequency deviates from the acceleration frequency due to a temperature change, this deviation can be corrected, so that good filter characteristics can always be maintained. Also, a bellows is attached to the end of the coaxial resonator, or a ceramic vacuum window is attached to the center of the coaxial resonator to form a vacuum boundary.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a high-order mode damper for a high-frequency acceleration cavity according to the present invention. Note that the same or corresponding portions as those of the conventional configuration will be described using the same reference numerals as those in FIGS. 3 and 4.

The high-order mode damper 1 shown in FIG. 1 constitutes a coaxial resonator between the intermediate conductor 3 and the outer conductor 5 similarly to FIG. 4, and these have a filter function. Intermediate conductor 3
A central hole is bored between the outer conductor 5 and the outer conductor 5 to short-circuit them with a disk-shaped movable short-circuit plate 8.

A plurality of drive rods 9 are attached and fixed to one side surface of the movable short-circuit plate 8 at predetermined intervals, and the drive rods 9 are attached to a mounting base 12.
The movable short-circuit plate 8 slides between the intermediate conductor 3 and the outer conductor 5 in the left-right direction in the figure by moving by 1.

In addition, since the contact portion between the movable short-circuit plate 8 and the intermediate conductor 3 and the contact portion between the movable short-circuit plate 8 and the outer conductor 5 cannot hold a vacuum in that state, a plurality of end portions of the outer conductor 5 cannot be held. A bellows 10 is attached and a vacuum is maintained with this as a vacuum boundary.

Next, the operation of this embodiment will be described.
When the movable short-circuit plate 8 shifts to the outside (the direction away from the coupling loop 6), the inductance (L) increases and the resonance frequency f = 1 / 2π · (LC) ^1/2 decreases, and conversely, to the inside (the coupling loop). 6), the inductance (L) decreases and the resonance frequency f increases.

The high-order mode damper 1 moves and adjusts the movable short-circuit plate 8 even if the resonance frequency of the coaxial resonator portion deviates due to the heat load from the high-frequency acceleration cavity body 22 or the temperature change of the outside. The resonance frequency can be matched to the acceleration frequency.

As described above, according to this embodiment, by matching the resonance frequency with the acceleration frequency, the filter effect at the acceleration frequency becomes complete. In other words, the high-order mode damper 1 of high performance, in which the high-order mode damper 1 does not absorb and lose high-frequency power input at the acceleration frequency,
Can be provided.

FIG. 2 is a sectional view showing another embodiment of the high-order mode damper for a high-frequency acceleration cavity according to the present invention. In addition,
The same parts as those in the above-mentioned embodiment will be described with the same reference numerals. In this embodiment, instead of the bellows 10 of the above-mentioned embodiment, an auxiliary ceramic vacuum window 13 is provided between the intermediate conductor 3 and the outer conductor 5 which form the coaxial resonator at the substantially central portion in the axial direction.
Is arranged.

Therefore, this auxiliary ceramic vacuum window 1
By setting 3 as a vacuum boundary, the bellows 10 becomes unnecessary and the structure can be simplified. The other structure and operation are the same as those of the above-mentioned embodiment, and the explanation thereof is omitted.

[0025]

As described above, according to the high-order mode damper for a high-frequency acceleration cavity according to the present invention, the short-circuit portion of the coaxial resonator is used as a movable plate, and the movable plate is moved and adjusted to increase the height. Since the resonance frequency of the coaxial resonator of the next-mode damper can be adjusted to be the same as the acceleration frequency, it is possible to provide a high-performance higher-order mode damper with almost no loss of the input high-frequency power. Further, by attaching this higher-order mode damper to the high-frequency acceleration cavity, it is possible to provide a high-performance particle accelerator with no beam loss.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a high-order mode damper for a high-frequency acceleration cavity according to the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of a high-order mode damper for a high-frequency acceleration cavity according to the present invention.

FIG. 3 is a sectional view showing a general high-frequency acceleration cavity.

FIG. 4 is a sectional view showing an example of a conventional high-order mode damper.

[Explanation of symbols]

 1 Higher Mode Damper 2 Inner Conductor 3 Intermediate Conductor (Coaxial Resonator) 4 Resistive Load 5 Outer Conductor (Coaxial Resonator) 6 Coupling Loop 7 Ceramic Vacuum Window 8 Movable Short-Circuit Board 9 Drive Rod 10 Bellows 11 Drive Unit 12 Mounting Base 13 Auxiliary ceramic vacuum window

Claims (3)

[Claims] 1. A high-order mode damper for a high-frequency acceleration cavity, which has a coaxial resonator and absorbs and attenuates a higher-order mode having a frequency higher than the acceleration frequency in the high-frequency acceleration cavity, and a short-circuit portion of the coaxial resonator. Is a movable plate, and the movable plate is moved and adjusted to make the resonance frequency of the coaxial resonator the same as the acceleration frequency. A high-order mode damper for a high-frequency acceleration cavity. 2. A high-order accelerating cavity for a high-frequency acceleration cavity according to claim 1, wherein a bellows is attached to an end of the coaxial resonator provided with the movable plate, and the bellows serves as a vacuum boundary. Mode damper. 3. The high-frequency acceleration cavity according to claim 1, wherein a ceramic vacuum window is attached to the center of the coaxial resonator provided with the movable plate, and the vacuum window serves as a vacuum boundary. Higher-order mode damper.