JPH1041099A - Folding orbit high frequency electron accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accelerating method and an accelerating system for VHF frequency which is compact, easily carries out energy conversion, has high electric power efficiency, and is possible to be driven continuously. SOLUTION: A small size irradiating device is so composed as to be driven continuously and easy to convert energy by combining a resonator having an extent of one-dimensional or two-dimensional electric field and a plurality of d.c. magnets 6 which deflect the beam orbit 5 at 180 degrees in order to accelerate electrons to high energy by repeatedly applying the electric field of the VHF frequency resonator for acceleration. More practically, a cylindrical resonator in TE mode or drum-like re-entrant resonator and the magnets 6 are so arranged as to generate an electric field having one-dimensional of two-dimensional distribution, turn back beam by 180 degree deflecting d.c. magnets 6, repeatedly pass the beam through the electric field, and accelerate the beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Electron beams are known to promote cross-linking and polymerization reactions of polymer materials to improve their properties, sterilize medical supplies and preserve foods, and have good energy efficiency. Have been. A high-intensity electron concentrator used for the purpose is mainly a DC voltage accelerator for energy of 5 MeV or less, and acceleration to higher energy is almost always performed by a microwave linear accelerator.

Although gamma rays are also used in the above applications, electron beams have a high processing speed and require less than 1/1000 of the time required for gamma rays. It has the advantage of no waste disposal problems,
Its use is gradually increasing. An object of the present invention is to provide industrial irradiation equipment which is easy to use at several MeV or more.

[0003]

2. Description of the Related Art DC accelerators have good power efficiency.
There is a problem that the structure must be increased together with the accelerating voltage in order to reduce the discharge and secure the operation reliability.
The maximum energy currently obtained is a force of 5 MeV, and the size of the accelerator body reaches 2.8-4.5 m in diameter and 7-7.5 m in height. It is technically possible to further increase the accelerating voltage itself, but it is not practical in terms of magnitude.

[0004] Since the high-frequency accelerator has a relatively higher discharge withstand voltage in the acceleration gap than the DC accelerator, it is possible to obtain a large acceleration energy with a relatively small acceleration structure. For example, a microwave linear accelerator for industrial irradiation is 1 m. 5M in length
An acceleration of 10 MeV at eV and 2 m is common. Many medical low power devices are capable of accelerating high energy with a shorter accelerating tube. Therefore, a microwave linear accelerator has the advantage that it can be smaller than a DC accelerator in order to obtain the same acceleration energy. On the other hand, it requires an expensive high-power microwave generator and integrates AC power into beam power. There is a problem that the conversion efficiency is 20% or less, which is lower than that of the DC unit. In addition, the microwave linear accelerator requires a pulse acceleration operation, and cannot irradiate the sample continuously. But 5M
Since acceleration energy of eV or more cannot be obtained with a commercially available DC accelerator, a microwave linear accelerator is used.

Some attempts have been made to use VHF band frequencies to solve the above-mentioned problems of the industrial irradiation microwave accelerator. FIG. 3 shows a type using one cavity resonator. FIG. 3A shows an outer diameter of about 1.2 m developed in Russia.
And realizes 2 MeV and 15 mA pulse acceleration at a frequency of 110 MHz.
(Auslender: U.S. Pat. No. 4,140,942 / 19)
(Feb. 1979) (b) shows an outer diameter of about 0.7 developed in Japan.
m, pulse operation model with a resonance frequency of 175 MHz (Fujisawa et al .: The 10th Accelerator Science Research Conference, Hitachi Nakashi, 199
(5 Oct., 64 pages), acceleration energy is 300k
The acceleration is eV to 1 MeV, 10 mA. Both are quite different even with the same single cavity structure. Russian devices have sought higher energy, but have not succeeded due to the high frequency discharge in the resonator.

[0006] Fig. 4 shows a device called a French cacitron in which three cavities having a resonance frequency of about 170 MHz and an outer diameter of about 1 m are connected in series to accelerate 8 MeV. However, it is difficult to control the coupling between the three cavities and difficult to operate stably. At present, it has been replaced by a conventional microwave linear accelerator.

FIG. 5 is a graph of the 1987 Sacre Institute in France.
(Potier et al .: French Patent Application 87 07)
378 / May 26, 1987) The manufacturing right was transferred to a company, and a practical machine with 10 MeV and 100 kW was completed in 1994.
The beam power is the largest for a V industrial irradiator. The operating frequency is 110 MHz, and continuous acceleration can be performed using a tetrode. With a single resonant cavity, there is no problem of instability of high-frequency coupling between multiple cavities, such as a castron, and it is easy to extract the beam to the outside and change the energy by setting the magnetic field of the deflecting magnet in the middle to 0. Can be However, the direction of the extracted beam is the position of the magnet,
Therefore, a transport system that guides a beam to a certain irradiation sample position that varies depending on energy becomes complicated. In addition, the distance between magnets is almost equal to the wavelength of the high frequency, and unless a high frequency is used, the distance is large and a convergent lens cannot be placed on the way, so that the beam orbit may be difficult to converge. Recently the beam power is 35 kW,
We are developing a model with a small structure using a frequency of 215 MHz.

Other high-energy electron accelerators include betatrons, microtrons, and electron synchrotrons, all of which have difficulty accelerating large currents and are not suitable for industrial irradiators.

[0009]

The microwave linear accelerator most frequently used for high-energy acceleration of electrons at present is a method of repeatedly accelerating with a high-intensity electric field of microwave to reach high energy. However, there are practically the following problems. A special high-power vacuum tube such as a klystron or a magnetron is required for an electron tube for generating microwaves, which is more expensive than a normal triode or quadrupole vacuum tube. The efficiency of the microwave output tube to convert the power of the power supply into microwaves is low, and considering the efficiency of applying this microwave power to the beam and the power used by cooling and other peripheral devices, the power efficiency is lower than that of DC machines. Low. In order for acceleration to be performed normally, the relationship between the amplitude and the phase of the high-frequency electric field in each part of the accelerating tube must be properly maintained, but first, the temperature change in each part must be sufficiently small. An accelerating tube is a collection of many resonators. If the dimensions change due to a rise in temperature, the resonance frequency changes and normal operation cannot be performed. On the other hand, the linear accelerator can accelerate to high energy in a short distance because high power high frequency is injected to generate a large electric field, and the electric power naturally heats the accelerator tube strongly. In order to reduce the temperature rise, the amount of heat generated must be reduced by a pulse operation with a short operation time. In addition, a high-voltage and large-current switch device called a modulator, which supplies a klystron or the like with a pulse of a DC voltage and supplies a large peak power to the klystron or the like, is necessary. In recent years, the problem that electromagnetic noise emitted from electric devices interferes with the operation of other devices that handle weak electric signals has become more and more serious, and there is a severe demand for suppression of noise in high-power devices. However, it is very difficult to suppress electromagnetic noise by high power pulses. Great care must be taken to use increasingly sophisticated measuring instruments and calculators. To use beam irradiation, it is necessary to ensure the uniformity of the dose. For this purpose, attention must be paid to the relationship between the pulse interval and the moving speed of the sample.

An object of the present invention is to solve these problems and to provide an industrial electron beam irradiation apparatus excellent in reliability and economy.

[0011]

FIGS. 1A and 1B show the principle of the present invention. FIG. 1A is a diagram showing a cross section of an accelerator resonator in a plane including the trajectory of an electron beam, and FIG. It is sectional drawing cut | disconnected perpendicular to the central axis of the resonator by XX of a). 1 is an outer shell of the resonator; 2 'is a ridge-shaped electrode provided to form an acceleration gap 3 inside the resonator. Electrons injected from the electron gun 4 are accelerated through the beam orbit 5 at the gap 3 and exit the outer conductor through the window 9 provided in the outer shell 1 and are turned 180 degrees by the magnetic field of the magnet 6. It is changed and driven again from the window 9 toward the acceleration gap. By repeating this, the electrons are accelerated to high energy, and are finally extracted as the beam 7 whose acceleration has been completed.

In order for repetitive acceleration to be established, the time required for electrons passing through the acceleration gap to reach the next gap must be an odd multiple of a half cycle of the acceleration high frequency. If the energy of the electrons increases and the speed approaches the speed of light, the distance traveled during a half cycle is almost equal to 1/2 wavelength and is constant, so that the distance between the magnets can be set to be approximately constant. But in some early orbitals, the speed of electrons is smaller than light,
It is necessary to change the setting position of the magnet for each orbit.

When different energies are used, a low energy beam can be extracted to the outside by setting the magnetic field of the intermediate magnet to zero. Since the direction of the beam 8 in the figure is the same as 7, it can be guided to the same irradiation position as 7 with a simple magnet system. If it is necessary to use it in a completely different position, it can be pulled out from the opposite side, for example, 8 '. As an example of such use, there is a case where, on the one hand, electron beam irradiation is carried out, and on the other hand, it is converted into X-rays and then its large transmission power is utilized. Since a high-power X-ray generating target requires a large-capacity cooling facility and requires time and effort for installation and removal, it is more convenient to be separated from the electron beam irradiation system.

According to the method of the present invention, electrons can be accelerated to high energy by repeatedly using the voltage generated in the gap of the resonator, and continuous operation can be performed by the VHF high-frequency device. Since it is not necessary to increase the energy by one acceleration as in the example of the Russian device in FIG. 3A, a relatively small voltage can be generated.
There is no need to worry about discharge, and highly reliable operation is possible. Further, since the peak value of the electric power is small, the heat generating power in the resonator is small, and therefore it is not necessary to perform the pulse operation.

Further, since a plurality of resonators are not used as in the case of the cacitron shown in FIG. 4, there is no fear of unstable operation due to weak coupling between the resonators. It does not require a control device to keep the amplitude and relative phase under conditions suitable for acceleration, and is suitable for practical industrial irradiation equipment.

FIG. 1 is a diagram for explaining the principle of the present invention by taking the TE mode of a cylindrical resonator as an example. However, the description does not include the case where the electric field distribution of another type of resonator is used. it is obvious. FIG. 2 (a) is a view of the structure of FIG. 1 as viewed from above, wherein the holes 9 through which the beam enters and exits the outer conductor of the resonator are arranged in a straight line, and are linearly distributed on the central axis of the cylindrical resonator. It can be seen that the electric field of the TE mode is used for acceleration. However, if the outer shell of FIG. 1A is replaced with, for example, a cylinder whose central axis is vertical, and the electrodes 2, 2 'are replaced with two cylinders whose central axes coincide with each other, this is a diagram viewed from above with a reentrant resonator. Is 2 (b). The accelerating electric field has a two-dimensional distribution, and the number of times of repetitive acceleration can be extremely increased. Of course, the loss of the resonator with the large area of the reentrant part is large, but the number of accelerations can be increased, so that the energy of one acceleration can be reduced, and therefore the voltage of the gap can be reduced to reduce the power loss. This is not a significant disadvantage, except that a large number of magnets are required. In addition, various cross-sectional shapes such as a square and a rectangle can be considered for the resonator.

The electric field of a one-dimensional or two-dimensional distribution usually varies in magnitude within the distribution. In FIG. 1, when the ridge electrodes 2, 2 'reach near the end plates at both ends, the electric field at the central portion becomes maximum and decreases toward both ends of the distribution. In the present invention, even if the distribution is not uniform, there is no problem in acceleration, but the distribution can be made nearly flat by deformation of both ends of the electrodes 2 and 2 'and adjustment of the gap interval.
FIG. 6 (a) shows a case where bars having the same width are attached to both ends of the electrode of FIG. 1 and a uniform distribution is obtained by adjusting the length and thickness thereof. The distribution after attachment is conceptually indicated by dotted line 15. FIGS. 7A and 7B are examples in which the same effect is obtained by reducing the gap interval near both ends.

[0018]

In this device, an electron beam having a relatively small gap voltage and high energy can be obtained by repeatedly passing an electron beam through the acceleration gap of a single high-frequency resonator. Unlike conventional high-energy electron accelerators such as betatrons and synchrotrons, there is no need to change the magnetic field over time, so continuous acceleration can be performed instead of pulse operation with less repetition as in those devices. As a result, the average acceleration current can be increased, which is suitable for industrial irradiation equipment. Further, high energy acceleration, which is impossible with a DC machine conventionally used for industrial irradiation, can be easily performed, and the size is gently small.

At present, microwave linear accelerators are used for industrial irradiation of 5 MeV or more, such as for sterilization of medical supplies. However, all of them operate in a pulsed manner. There are many points that need improvement, such as efficiency. The device of the present invention does not require the use of microwaves, uses a VHF waveband oscillation tube having a large power capacity and a low price, and has the advantage that high power efficiency can be obtained by continuous operation.

The loadtron, which appeared on the market around 1994 and whose conceptual diagram is shown in FIG. 5, also used VHF waves and succeeded in accelerating a large output electron beam by continuous operation. Is almost equal to the wavelength of the high frequency wave, and at the same frequency, twice as large as the distance between the magnets of the present invention. Since the direction is completely different for each deflection magnet, there is a problem that the transport system for guiding the beam to the position of the irradiation equipment is more complicated than the present invention.

[0021]

FIG. 1 shows an example in which a TE mode of a cylindrical resonator is used. Since the outer shell 1 also serves as a conductor of the resonator and a vacuum vessel, a mechanically strong material that can withstand the pressure when evacuated to a vacuum is used. It is a structure that is manufactured by using copper plating inside or bonding a copper plate to form an external conductor. The electrodes 2, 2 'are made of a copper plate and the beam 5
Is provided with a hole for passing through. Since the inside of the electrode is also a vacuum, there is no problem of the vacuum pressure, but since the electrode is heated by a high-frequency current, it must be cooled sufficiently. Outer shell 1
The beam is also provided with a through hole 9 and the beam is redirected by the magnet 6 outside the outer shell.

The beam accelerated by the acceleration gap 3 is turned 180 degrees by the magnet 6 and enters the gap 3 again. At this time, the direction of the electric field of the gap needs to be reversed. For that purpose, the time from passing through 3 to reentering 3 must be half of the high frequency cycle or an odd multiple thereof. If the speed of the electron is the speed of light, the length of the orbit from 3 to 3 is 1 of the high-frequency free-space wavelength.
/ 2 or an odd multiple thereof, and the distance between 6 is constant. However, while the energy of the electrons is small, the speed is small and changes with every acceleration, so the position of the magnet 6 must be changed accordingly. . Since the product of the magnetic field strength required to change the direction of the electron beam and the orbital radius is small for electrons of energy used for industrial irradiation, the magnet size and power consumption are small, and There are no major difficulties.

It is desirable that the beam injected from the electron gun 4 is focused on the acceleration phase of the high-frequency electric field by velocity modulation before receiving the first acceleration by the gap 3. Although not shown, a device called a buncher for that purpose can be installed between the electron gun 4 and the acceleration gap 3.

While the acceleration current is relatively small, the loss of current can be reduced by giving the deflecting electromagnet 6 convergence. However, the trajectory of a beam having a large current and a low energy tends to diverge. For the orbit, a lens having a converging action is provided inside the ridge electrode, so that the loss of the large current beam can be reduced. Since the distance between the magnets 6 is short, current can be easily transferred, and a converging lens can be inserted into the track, acceleration of a large current beam is easier than that of the loadtron shown in FIG.

Usually, the acceleration beam 7 is used for irradiation in FIG. 1 (a), but when irradiation with lower energy is required, the magnet magnetic field at the corresponding position 8 or 8 'is set to 0. By doing so, the beam can be used for irradiation. According to this method, a beam of different energy can be used easily and quickly by a simple operation of the magnet power supply. Also, since the direction of the beam 8 is the same as that of 7, the same irradiation equipment can be used by a simple beam transport means, and when it is desired to use irradiation equipment separate from electron beam irradiation such as X-ray irradiation, 8 It is possible to guide the beam to a completely different position by pulling out to '.

The above is an example in which the TE mode of a cylindrical resonator is used. However, it is possible to use another resonator such as a reentrant or rectangular resonator shown in FIG. It is. However, the cylindrical structure has the advantage that it is easy to select either a vertical or horizontal beam extraction direction, and the installation floor area and building height can be reduced.

[0027]

As described above, a DC accelerator for 5 MeV or less and a microwave linear accelerator for 5 MeV or more have been mainly used for industrial electron beam irradiation. The structure of a DC accelerator grows rapidly as the acceleration energy increases,
There is a problem that a large space or a large building with a high ceiling is required for installation.The microwave accelerator is relatively small, but its power efficiency is inferior, it requires pulse operation, and it has special requirements such as magnetron and klystron. It has been pointed out that a vacuum tube for high frequency and large power is required, and that the power supply modulator is expensive and has a short life. The present invention can provide an electron beam accelerator capable of using a VHF wave having a frequency of 300 MHz or less, which is gently lower than that of a microwave, and having a variable energy of several 100 keV to 10 MeV. The building height and the floor space required for installation are small. Triodes and tetraodes, which are already widely used in broadcasting and communication, can be used, can operate continuously, and have better power efficiency than microwave tubes.

Conventionally, in the VHF frequency band, FIG.
Although the single-cavity mold shown in FIG. 4B and the three-cavity mold shown in FIG. 4 were produced, the single-cavity mold has a limited reaching energy. When a plurality of cavities are used, they must be combined and controlled. However, it has not always been easy and has not been widely used for industrial purposes. The present invention has a single cavity, but by using the electric field for acceleration multiple times, it functions as an accelerator with many cavities and realizes an apparatus with no difficulties in controlling many cavities. It is characterized by the easiness of operation required for industrial irradiation equipment and high reliability obtained by using a commercially available vacuum tube as a high frequency source. 300 keV
Above 5 MeV, the high-frequency acceleration method is smaller than the direct-current acceleration method, does not require a high-pressure gas container, and thus has the advantage of requiring less installation space.

[Brief description of the drawings]

FIG. 1 shows an example of a structure using a TE mode of a cylindrical resonator in the present invention. (A) is a sectional view including a central axis and a raceway surface of a cylinder. (B) is sectional drawing cut | disconnected at right angles to the center axis of the cylinder along xx. In addition, the meaning of each number and code is common to all the drawings.

FIG. 2A is a diagram of an apparatus using the cylindrical resonator of FIG. 1 as viewed from above. The beam extraction hole 9 appears on a straight line. FIG. 1B shows a case where the cross section of a portion called a nose cone in the center of a donut-shaped reentrant cavity is large, and a cross section taken along a plane YY and Y′-Y ′ including the central axis is shown in FIG. ), But the beam extraction holes 9 are two-dimensionally distributed.

FIG. 3 (a) shows a single cavity V developed in Russia.
HF electron accelerator conceptual diagram. (B) The figure shows a single-cavity electron beam accelerated irradiation device developed in Japan. The structure of the cavity is clearly different from that of Russia.

FIG. 4 is a conceptual diagram of a VHF electron accelerator named a three-cavity Casitron developed in France.

FIG. 5 is a conceptual diagram of a VHF high-power electron accelerator, which was devised in France and succeeded in practical use by a Belgian manufacturer, and was named Roadtron. (A) Horizontal section, (b) Vertical section

FIG. 6 (a) shows a case where bars having the same width as the electrodes are attached to both ends of the ridge electrodes 2, 2 ′ of FIG. 1 in order to improve the uniformity of the electric field distribution. (B) is a diagram conceptually showing the effect, in which the solid line 14 is the electric field distribution before mounting and the dotted line 15 is the electric field distribution after mounting.

FIG. 7 (a) is a graph for improving the uniformity of the electric field distribution.
The case where the gaps at both ends of the ridge electrodes 2 and 2 ′ in FIG. 1 are locally narrowed. (B) is a diagram conceptually showing the effect, and the meaning of the solid line 14 and the dotted line 15 is the same as in FIG.

[Explanation of symbols]

1: The outer shell of the resonator, usually the inner surface, is made conductive, and also serves as the outer conductor of the resonator. 1 '; an outer conductor separately provided inside the outer shell, divided. 2; accelerating electrode. 2; an acceleration electrode facing 2; 3; acceleration gap 4; electron gun. 5; beam trajectory. 6; 180 ° orbital deflecting magnet. 7: Beam whose acceleration has been completed. 8: A beam taken out halfway to obtain electrons of different energies. 8 '; a beam extracted in the opposite direction to beam 7. 9; a hole provided for taking out the beam from the resonator shell. 10; high frequency source. 11; vacuum pump 12; conductor for improving the electric field distribution attached to both ends of the ridge electrodes 2, 2 '. 13; a conductor added to locally narrow the interval between the ridge electrodes 2, 2 '. 14: Distribution of the gap electric field before adding the conductors 12 and 13. 15: Distribution of the gap electric field after adding the conductor.

Claims (9)

[Claims] An electric field in an acceleration gap uses only one set of high-frequency resonators having a one-dimensional or two-dimensional distribution,
An acceleration method in which the direction of the accelerated electrons is deflected by 180 degrees by a DC magnetic field outside the resonator and accelerated again in the acceleration gap, thereby accelerating the electrons to energy gently higher than the gap voltage. And accelerators. 2. The accelerating device according to claim 1, wherein the length of the beam trajectory from passing through the acceleration gap to being deflected by 180 degrees and reentering the acceleration gap is determined by the time that the electrons travel between them is 1 / the frequency of the high frequency. An acceleration method and an acceleration device in which an electron group is always synchronized with a high-frequency phase and accelerated by having a length corresponding to an odd multiple of two periods. 3. An acceleration method and an acceleration apparatus according to claim 1, wherein the acceleration electric field distribution can be changed by locally changing the size of the acceleration gap or the shape of the electrode of the resonator. 4. An acceleration method and an acceleration apparatus according to claim 1, wherein the linear trajectories after 180-degree deflection are parallel to each other, and the arrangement of the deflection magnet and the setting of the magnetic field intensity are easy. 5. The magnetic field of any bending electromagnet according to claim 4,
And a variable energy acceleration system and an acceleration device capable of easily extracting electron beams having different energies. 6. The beam extraction of claim 5, wherein the directions of the beams extracted to the same side of the acceleration cavity are parallel to each other, and beams with different energies are used for irradiating the same target by a simple beam transport system. An acceleration method and an acceleration device that can be used in completely different applications, for example, X-ray generation and electron beam irradiation at different positions if taken out in the direction opposite to the cavity. 7. The distance between the deflecting magnets is as short as about 波長 wavelength, the divergence of the beam between the magnets can be reduced, and even if a converging lens is mounted in the accelerating electrode, the beam can be irradiated even with a large current. Accelerator capable of low-loss acceleration. 8. An acceleration method and an acceleration device in which the distance between linear orbits is narrowed, and the orbit is folded, so to speak, so that the electric field of one resonator can be used repeatedly for acceleration, and can be made smaller than the energy reached. 9. Unlike a microwave electron linear accelerator which is currently most frequently used for accelerating electrons at 5 MeV or more, a continuous operation VHF wave band device suitable for industrial irradiation purpose is constituted by a normal triode or tetraode. Acceleration method and accelerator.