JP2002324700A - Control method of charged particle energy and charged particle accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device which can control accelerated charged particle energy simply and surely with high reliability. SOLUTION: A superconducting accelerator 6 having a superconducting accelerating cavity accelerating charged particles 4 maintained in a superconductive condition by high frequency electric field is used as a linear accelerator accelerating the charged particles 4 given from a charged particle source 2. Then, high frequency reflection from the superconducting accelerator 6 is adjusted substantially to zero, and energy E of the charged particle 4 after accelerated at the superconductive accelerator 6 is controlled based on the relation of E=P/i using output P of high frequency power output from a high frequency oscillator 16 and current value i of the charge particles 4 after being accelerated at the superconductive accelerator 6. An energy control device 36 has a function processing above control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency linear accelerator (Linac; also called a linac), which accelerates charged particles such as electrons and ions, and performs crosslinking, modification, and the like by electron beam irradiation. Sterilization, sterilization, insecticide, etc., or ion implantation by ion irradiation, related to charged particle accelerator and charged particle energy control method used for reforming, more specifically, by using a superconducting accelerator as a linear accelerator And means for facilitating control of charged particle energy.

[0002]

2. Description of the Related Art A charged particle source for generating charged particles such as electrons and ions, a linear accelerator for accelerating charged particles provided from the charged particle source by a high-frequency electric field in an acceleration cavity, and a high-frequency A charged particle accelerator including a high-frequency oscillator for supplying electric power is called a high-frequency linac or the like and has already been used in various fields.

[0003]

Unlike an accelerator using a static electric field such as a Cockcroft type, it is very difficult to control the energy of charged particles accelerated by a conventional linear accelerator using a high-frequency electric field as described above.

The conventional linear accelerator uses a normal conduction type accelerating cavity, and most of the input high-frequency power is consumed as Joule heat loss in the accelerating cavity, and this heat causes the acceleration. This is because unevenness and large distortion are generated in the cavity, and unstable operation easily occurs. It is very difficult to suppress the occurrence of instability. Even if the occurrence of instability is suppressed with a certain energy, the occurrence of instability easily occurs with another energy.

[0005] It is not easy to know the energy of charged particles after acceleration. This is because, as described above, most of the input high-frequency power is consumed as Joule heat loss in the accelerating cavity, and it is not exactly known how much of the remaining is converted to charged particle energy. Because. The rate of this energy conversion varies depending on the device configuration, the frequency of high-frequency power, power, input adjustment, and the like, and is not constant.

Conventionally, in order to obtain the energy of charged particles after acceleration, (a) the intensity of a high-frequency electric field generated in an acceleration cavity is measured using an antenna or the like to estimate the acceleration electric field intensity, and the energy is estimated. (B) calculating the energy from the degree of bending by bending a charged particle that has emerged from the linear accelerator by a bending electromagnet, and (c) using an event whose energy is known, such as a nuclear reaction. The necessary parameters are calibrated with energy, and the interval is determined appropriately by interpolation.
And other means.

However, the above-mentioned means (a) repeats guesswork, and lacks reliability. The means (b) requires a deflecting electromagnet and requires a large configuration. Moreover, bending the charged particles requires a large space. In some cases, it is difficult to adopt a device arrangement for bending charged particles using a bending electromagnet. Since the means (c) uses a calibration system such as a calibration graph, it takes time and effort. In addition, it is necessary to periodically check whether the calibration has changed over time.

Accordingly, an object of the present invention is to provide a method and an apparatus capable of controlling the energy of charged particles after acceleration simply and accurately with high reliability.

[0009]

According to the present invention, there is provided a method for controlling charged particle energy, comprising a superconducting accelerating cavity which is maintained in a superconducting state and accelerates the charged particles by a high-frequency electric field. Using an accelerator, the high-frequency reflection from the superconducting accelerating cavity in the superconducting accelerator is adjusted to substantially zero, the output P of the high-frequency power output from the high-frequency oscillator and the charged particles accelerated by the superconducting accelerator. It is characterized in that the energy E of the charged particles after being accelerated by the superconducting accelerator is controlled based on the relationship of E = P / i using the current value i.

[0010] The charged particle accelerator according to the present invention includes, as the linear accelerator, a superconducting accelerator having a superconducting accelerating cavity which is maintained in a superconducting state and accelerates the charged particles by a high-frequency electric field. A reflection adjusting mechanism for adjusting the reflection of high frequency from a superconducting acceleration cavity in the superconducting accelerator to substantially zero, an output measuring device for measuring a high-frequency output P output from the high-frequency oscillator, and the superconducting accelerator A current measuring device for measuring the current value i of the charged particle accelerated by the above, and using the output P measured by the output measuring device and the current value i measured by the current measuring device, after being accelerated by the superconducting accelerator. The energy E of the charged particles of E = P / i
And an energy control device that performs control based on the following relationship.

According to the above configuration, the high-frequency power output from the high-frequency oscillator adjusts the reflection of the high-frequency wave from the superconducting acceleration cavity to substantially zero, and is therefore all supplied to the superconducting acceleration cavity.

In this superconducting accelerating cavity, since it is superconducting, Joule heat loss is substantially zero, that is, there is no loss in the accelerating cavity, and all supplied high frequency power is used to accelerate charged particles. Used and converted to charged particle power.

Therefore, the following relationship is established between the output P of the high-frequency power output from the high-frequency oscillator and the power W of the charged particles accelerated by the superconducting accelerator.

[0014]

## EQU1 ## P = W

On the other hand, the power W of the charged particle after acceleration is the product of the energy E of the charged particle and the current value i of the charged particle, and is expressed by the following equation.

[0016]

## EQU2 ## W = E · i

From the above equations (1) and (2), the following equation is obtained.

[0018]

E = P / i

By using a superconducting accelerating cavity and adjusting a high frequency wave from the superconducting cavity to a non-reflection state, the inventors of the present application have realized the above equation (3) in a charged particle accelerator.
Was found to hold.

The output P of the high-frequency oscillator can be easily and accurately measured by a known technique such as a high-frequency power meter.

The current value i of the charged particles can be easily and accurately measured by a known technique such as a current transformer.

The present invention uses the output P and the current value i which can be measured simply and accurately as described above.
The energy E of the charged particles is controlled based on the relationship of the above Expression 3, whereby the energy of the charged particles after acceleration can be easily and accurately controlled with high reliability.

[0023]

FIG. 1 is a schematic diagram showing an example of a charged particle accelerator for implementing an energy control method according to the present invention. FIG. 2 is a schematic cross-sectional view showing an example around the superconducting accelerator in FIG.

This charged particle accelerator accelerates a charged particle source 2 for generating (ejecting) charged particles 4 and a charged particle 4 supplied from the charged particle source 2 maintained in a superconducting state by a high-frequency electric field. A superconducting accelerator 6 having a superconducting acceleration cavity 14 (see FIG. 2), and a high-frequency power for charged particle acceleration is supplied to the superconducting accelerator 6 (more specifically, to the superconducting acceleration cavity 14 therein). A high-frequency oscillator 16, a reflection adjusting mechanism 30 for adjusting the reflection of high-frequency waves from the superconducting accelerator 6 (more specifically, from the superconducting accelerating cavity 14 therein) to substantially zero, and And an energy control device 36 for controlling the energy E of the charged particles 4 after acceleration.

The charged particles 4 are, for example, electrons or ions.

When the charged particles 4 are electrons, the charged particle source 2
Is, for example, an electron gun. When the charged particles 4 are ions,
The charged particle source 2 is, for example, an ion source.

In this example, the high-frequency oscillator 16 is an output measuring device 1 for measuring the output P of the high-frequency power output therefrom.
8 and a reflection measuring device 20 for measuring a high frequency reflection R from the superconducting accelerator 6 (more specifically, from the superconducting accelerating cavity 14 therein). The output measuring device 18
For example, a high-frequency power meter. The reflection measuring device 20 is, for example, a reflection power meter.

The high-frequency power output from the high-frequency oscillator 16 is supplied to the superconducting acceleration cavity 14 in the superconducting accelerator 6 via the coaxial tube 22 in this example. However, instead of the coaxial waveguide 22, a waveguide or the like may be used. In addition,
In this specification, "high frequency" is used in a broad concept including microwaves.

The superconducting accelerator 6 is a kind of high-frequency linear accelerator, and has a structure as shown in FIG. 2 in this example.

That is, the superconducting accelerator 6 includes a plurality (five in this example) of superconducting acceleration cavities 1 connected in series in a liquid helium container 10 filled with liquid helium 12.
4 and the liquid helium container 10 is further housed in a vacuum container 8. That is, the superconducting acceleration cavity 14 has a five-cell structure.

The liquid helium container 10 contains the liquid helium 12
Is provided, but is not shown here. Further, a nitrogen temperature shield or the like is usually provided between the liquid helium container 10 and the vacuum container 8, but this is also not shown.

In this example, each superconducting acceleration cavity 14 is formed of niobium (Nb), and is kept in a superconducting state at a temperature of 4.2 K of the liquid helium 12. However, a superconducting material other than niobium may be used for the superconducting accelerating cavity 14, and a cooling temperature and a cooling medium for keeping the superconducting state may be determined according to the material.

Each of the superconducting accelerating cavities 14 is supplied with high frequency power for accelerating charged particles from the high frequency oscillator 16 via the coaxial tube 22 and the antenna 26 in this example. As a result, a high-frequency electric field is generated in each superconducting acceleration cavity 14, and the charged particles 4 are generated by the high-frequency electric field.
Can be accelerated.

The maximum acceleration energy of the charged particles 4 is generally determined by the number of superconducting accelerating cavities 14 (the number of cells) and the frequency of the high-frequency power. For example, when accelerating electrons, if 5 cells are used at 500 MHz, a maximum of 10 MeV
Energy can be obtained. According to the present invention, the energy E can be easily adjusted within the range below this range according to the relationship of the above equation (3).

In this example, as shown in FIG. 2, the reflection adjusting mechanism 30 includes an antenna 26 connected to the coaxial tube 22 for supplying high-frequency power to the superconducting accelerating cavity 14, and the antenna 26 is indicated by an arrow B. Driving unit 2 that moves in and out as shown
8 is provided. The drive unit 28 has a motor. The through portion of the antenna 26 is separated from the inner vacuum atmosphere and the outer atmosphere by a partition plate 24 made of ceramics or the like.

The antenna 2 is controlled by the reflection adjusting mechanism 30.
By moving in and out 6, the state of high-frequency coupling with the superconducting accelerating cavity 14 is adjusted to adjust the reflection R from the superconducting accelerating cavity 14 to substantially zero (that is, to the extent that it can be regarded as zero or zero). be able to. In this example, the reflection R can be monitored by the reflection measuring device 20 described above.

Further, in this example, a reflection control device which controls the drive unit 28 in accordance with the reflection R measured by the reflection measuring device 20 and automatically adjusts the reflection R from the superconducting acceleration cavity 14 to substantially zero. 32 are provided. However, the above adjustment of the reflection R may be performed manually while looking at the reflection measuring device 20. In that case, the reflection control device 32 is unnecessary, and the drive unit 28 may be a manual mechanism.

The charged particle accelerator further includes a current measuring device 34 for measuring a current value i of the charged particles 4 accelerated by the superconducting accelerator 6.

In this example, the current measuring device 34 is provided at the outlet of the superconducting accelerator 6, and is a winding for measuring a current flowing when the charged particles 4 after acceleration pass through the inside. Can also be called a current transformer. The current measuring device 34 may be provided at the entrance of the superconducting accelerator 6 to measure the current value i of the charged particle 4 immediately before entering the superconducting accelerator 6, or immediately after leaving the charged particle source 2. Charged particles 4
May be measured. Alternatively, the charged particle source 2
Is an electron gun, the current measuring device 34 described above is used.
Instead, a current measuring device for measuring the cathode current may be used. In this apparatus, it can be considered that the charged particles 4 output from the charged particle source 2 are all accelerated without any loss on the way. Therefore, even if the current value i of the charged particles 4 is measured at any of the above points, good.

The energy control device 36 is provided with the output measuring device 1
Using the output P measured at 8 and the current value i measured at the current measuring device 34, the calculation of the formula 3 is performed to obtain the energy E of the charged particles 4 output from the superconducting accelerator 6, and It has a function of controlling the energy E to a desired (target) value. For example, while maintaining the output P output from the high-frequency oscillator 16 constant, the charged particle source 2 can be controlled so that the target energy E is obtained, and the current value i of the charged particles 4 output therefrom can be controlled. . Alternatively, target energy E and current value i
Is obtained, the output P of the high-frequency power output from the high-frequency oscillator 16 and the current value i of the charged particles 4 output from the charged particle source 2 can be controlled.

The energy control device 36 and the reflection control device 32 may be incorporated in one control device. That is, an integrated control device having the above functions of the two 32 and 36 may be provided.

A scanner (scanning coil in the illustrated example) 38 for scanning charged particles 4 output from the superconducting accelerator 6 and a diverging scanning tube 40 are provided downstream of the superconducting accelerator 6 as in this example. Is provided, and the charged particles 4 scanned through the window foil 42 provided at the distal end of the scanning tube 40 are taken out into an irradiation atmosphere (for example, the atmosphere), and the object 44 to be irradiated is provided.
May be configured to be irradiated. In this case, if the charged particles 4 are electrons, this device becomes a scanning type electron beam irradiation device. As a result, the irradiation target 44 can be subjected to, for example, processing such as crosslinking, modification, sterilization, sterilization, and insecticide.

As described above, the conventional high-frequency linear accelerator uses a normal conduction type acceleration cavity, and most of the input high-frequency power is caused by Joule heat loss. Since it is not constant, it is impossible to obtain the relationship of the above equation (1).

On the other hand, in this superconducting accelerator 6,
As described above, since the superconducting accelerating cavity 14 is used and the Joule heat loss there is substantially zero (ie, zero or negligibly small), all of the input high-frequency power is charged particles. 4 power. In addition, the reflection adjusting mechanism 30 adjusts the state to no reflection. As a result, in the charged particle accelerator, the relationship of the above Equation 3 is established.

Moreover, the output P of the high-frequency oscillator 16 can be easily and accurately measured by the output measuring device 18, for example. The current value i of the charged particles 4 can also be easily and accurately measured by the current measuring device 34, for example.

In this charged particle accelerator, the high-frequency oscillator 16 capable of easily and accurately measuring is provided.
Is used to control the energy E of the charged particles 4 based on the relationship of the above Equation 3 using the output P of the charged particles 4 and the current value i of the charged particles 4, whereby the charged particles after acceleration by the superconducting accelerator 6 Can be easily and accurately controlled to a desired value. The reproducibility of the energy E is also very good.

Further, unlike the case of using the bending electromagnet for the conventional energy measurement, the charged particles 4 do not need to be bent, and the trajectory of the charged particles 4 can be maintained in a straight line. 4 can be used for the intended processing, so that the device configuration is simplified and the space is saved.

Further, as can be seen from the above equation (1), by keeping the output P of the high-frequency oscillator 16 constant, the power W of the charged particles 4 output from the superconducting accelerator 6 can be kept constant. As can be seen from the above equation 3, the energy E of the charged particles 4 can be easily changed by changing the current value i of the charged particles 4 while maintaining the value as described above. For example, the power W of the charged particles 4 output from the superconducting accelerator 6 is set to 100 k
It is easy to output the charged particles 4 with the energy E of 10 MeV and the current value i of 10 mA while maintaining the constant W, or to output the charged particles 4 with the energy E of 5 MeV and the current value i of 20 mA. Can be realized.

This is particularly convenient when the accelerated charged particles 4 are used for processing an object to be irradiated, for example, as in the electron beam irradiation apparatus described above. This is because the power W of the charged particles 4 is directly related to the processing capability of the irradiation object, and there is a case where it is desired to change only the energy E of the charged particles 4 without changing the processing capability. For example, in a case where an irradiation target having different heights is conveyed on the same conveyor and the target is irradiated with an electron beam to perform a sterilization process, the energy E of the electron beam is changed without changing the power of the electron beam. It is preferable to change the penetrating power of the electron beam (that is, the depth of the sterilization treatment) by changing according to the height of the irradiation object, and this can be easily coped with.

In a conventional linear accelerator using a normal conduction type acceleration cavity, it is very difficult to change the acceleration energy as described above, and the reproducibility of the acceleration energy after energy adjustment is poor. In such a case, it is hardly possible to easily change the energy and respond.

In a conventional linear accelerator using a normal conduction type acceleration cavity, since the Joule heat loss in the acceleration cavity is very large and it is difficult to cool the acceleration cavity, the duty ratio is extremely small (for example, 1% or less). In contrast to the pulse operation, only the pulse operation was performed. In the superconducting accelerator 6, since there was almost no problem of heat generation due to Joule heat loss in the superconducting acceleration cavity 14, the continuous operation for continuously extracting the charged particles 4 accelerated was performed. It can be performed. Alternatively, the duty ratio is much larger than the conventional one (for example, 25% or 5%).
Intermittent operation (such as 0%) is of course also possible. Therefore, the utilization efficiency of the charged particles 4 is dramatically improved as compared with the related art. Therefore, for example, by using such charged particles 4 for processing an object to be irradiated, the processing efficiency can be dramatically increased.

[0052]

As described above, according to the present invention, the energy E of the charged particles is converted to E = P / i by utilizing the fact that all the input high frequency power is converted into the power of the charged particles as a feature of superconductivity. The control is performed based on the following relationship, whereby the energy of the charged particles after acceleration can be accurately and simply controlled with high reliability.

Moreover, since the superconducting accelerating cavity is used and there is almost no problem of heat generation due to Joule heat loss, the continuous operation for continuously extracting the charged particles accelerated and the duty ratio is much larger than the conventional one. Intermittent operation is also possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a charged particle accelerator for implementing an energy control method according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example around a superconducting accelerator in FIG.

[Explanation of symbols]

 Reference Signs List 2 charged particle source 4 charged particle 6 superconducting accelerator 14 superconducting accelerating cavity 16 high frequency oscillator 18 output measuring device 20 reflection measuring device 30 reflection adjusting mechanism 32 reflection control device 34 current measuring device 36 energy control device

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Eiji Iwamoto, Inventor F-term (reference) 2G085 AA03 BA05 BA08 BA19 BB17 BE02 BE03 BE05 CA02 CA06 CA12 CA15 CA21 in Nisshin High Voltage Co., Ltd. CA22 CA26 EA02 EA08 4C058 AA01 BB06 DD03 DD07 KK03 KK32 5C034 CC01 CD02

Claims (2)

[Claims] 1. A charged particle source for generating charged particles, a linear accelerator for accelerating and outputting charged particles supplied from the charged particle source by a high-frequency electric field in an acceleration cavity, and an accelerating cavity in the linear accelerator for acceleration. A high-frequency oscillator that supplies high-frequency power of a charged particle accelerator, wherein as the linear accelerator, a superconducting accelerator having a superconducting acceleration cavity that is maintained in a superconducting state and accelerates the charged particles by a high-frequency electric field is used; The reflection of the high frequency from the superconducting acceleration cavity in the superconducting accelerator is adjusted to substantially zero, and the output P of the high-frequency power output from the high-frequency oscillator and the current value i of the charged particles accelerated by the superconducting accelerator are adjusted. And controlling the energy E of the charged particles after being accelerated by the superconducting accelerator based on a relationship of E = P / i. Method of controlling the particle energy. 2. A charged particle source for generating charged particles, a linear accelerator for accelerating and outputting charged particles supplied from the charged particle source by a high-frequency electric field in an acceleration cavity, and an acceleration cavity in the linear accelerator for acceleration. And a high-frequency oscillator that supplies high-frequency power of the charged particle accelerator, comprising, as the linear accelerator, a superconducting accelerator having a superconducting acceleration cavity that is maintained in a superconducting state and accelerates the charged particles by a high-frequency electric field. A reflection adjusting mechanism for adjusting the reflection of high frequency from the superconducting acceleration cavity in the superconducting accelerator to substantially zero; an output measuring device for measuring a high-frequency output P output from the high-frequency oscillator; A current measuring device for measuring a current value i of the charged particles accelerated by the superconducting accelerator; and an output P measured by the output measuring device and a current measured by the current measuring device. With the current value i, the energy E of the charged particles after the accelerated superconducting accelerator E = P
/ I, an energy control device for controlling based on the relationship of / i.