JPS63274098A - Standing wave linear accelerator - Google Patents

Abstract

PURPOSE:To obtain the continuous energy value over a wide range by resonating side-coupled cavities with the same resonance frequency as accelerating cavities and in the different resonance modes and providing frequency fine tuning tuners on the side-coupled cavities. CONSTITUTION:In a standing wave linear accelerator provided with multiple accelerating cavities 1, 2 and side-coupled cavities 9, 10 coupling the electromagnetic energy between the adjacent accelerating cavities among the multiple accelerating cavities 1, 2, the side-coupled cavities 9, 10 are resonated with the same resonance frequency as the accelerating cavities 1, 2 and in the different resonance modes, and frequency fine tuning tuners 16, 15 are provided on the side-coupled cavities 9, 10. The continuous energy value can be thereby obtained over a wide range from the low energy practically equal to 0 to the maximum energy using the whole length of an accelerating tube as the effective acceleration length.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a standing waveform linear accelerator, and particularly to a standing waveform linear accelerator for generating X-rays with high intensity and variable energy.

(Prior Art) Generally, there is a linear accelerator as a device that accelerates charged particles in a straight line using a high frequency with a constant frequency from several 10M)-1z to several 100100O.

Among this type of linear accelerator, a standing wave linear accelerator is conventionally configured as shown in FIG.
3 is a drift tube that blocks the electric field and allows electron flow to pass through; 4 is a ring-shaped side coupling cavity that couples adjacent acceleration cavities among the plurality of acceleration air conditioners; and 5 is the acceleration cavity 1.2 and the side coupling cavity. A coupling hole connecting the shell 4, 6 an input cavity for entering the particle beam, 7 an output cavity for taking out the particle beam, 8 a particle beam generation section, and 9.10 a hole between adjacent acceleration cavities. It is a side coupling cavity that couples electromagnetic energy.

In operation, accelerated charged particles (generally electrons)
It is converted to xIl by a target such as tungsten, but because the conversion efficiency is low, it is necessary to increase the number of accelerated electrons (current) in applications such as radiation therapy. Furthermore, it is desirable to make the X-ray energy variable depending on the depth of the treatment site. In order to make the X-ray energy variable, it is sufficient to make the electron acceleration energy variable, and this can be achieved by making the high-frequency power that provides the electron acceleration energy variable.

On the other hand, in order to obtain a high-intensity electron beam, the particle beam generating section 8
It is necessary to efficiently aggregate the electrons incident on the accelerating tube from the electron gun, and to synchronize the electron velocity with the accelerating electric field by making the acceleration cavity spacing on the upstream side of the electron flow shorter than on the downstream side. It is necessary to aim for

This synchronization is determined by both the electron velocity and therefore the radio frequency power and the cavity spacing. As mentioned above, when the high frequency power is changed to make the acceleration energy of electrons variable, the synchronization deviates from the optimum condition due to the change in the accelerating electric field, resulting in efficient acceleration, that is, acceleration of large currents. It has the disadvantage that it cannot be carried out.

In recent years, in order to overcome this drawback, a part that accelerates the electron speed to an energy that can be considered to be almost equal to the speed of light due to relativistic effects (hereinafter referred to as the puncher part), and a part located downstream of the electron flow that has the required energy The electric field strength of the puncher section does not change from the optimum value even for different required energies, and by changing the phase or amplitude of the electric field of the subsequent accelerating tube section, the energy can be increased with high intensity. Variable standing waveform linear accelerators have been proposed (for example, described in Japanese Patent Publication No. 56-63800, Japanese Patent Publication No. 57-
55099, JP-A-61-253800, JP-A-61-288400).

(Problems to be Solved by the Invention) In the standing wave linear accelerator described in Japanese Patent Publication No. 56-63800, the resonance modes of the individual coupling cavities are in phase (TMo s tr ) or in opposite phases between the two coupling holes. phase (TEM, or TMn 11), and the resonant frequencies of the two resonant modes are approximately equal to the resonant frequency of the acceleration cavity,
The length of the center conductor of the semi-coaxial individual coupling cavity is changed mechanically.

As a result, the phase of the electric field in the acceleration cavity below this side coupling cavity is changed to increase the electron energy in the acceleration tube section (TMQIO), or conversely to decrease it (TE
M or TMo s t ) can be selected. If the acceleration energy at the puncher section is El and the acceleration energy at the acceleration tube section is E2, the obtained energy is El + E2
, or Et-E2. This scheme has the disadvantage that the energy available is limited to only two ways. In addition, the center conductor of the semi-coaxial individual coupled cavity is located close to the outer wall of the acceleration cavity, and there is a drawback that there is not enough space to install a bellows or drive mechanism for maintaining a vacuum.

Next, the standing wave linear accelerator described in Japanese Patent Publication No. 57-55099 utilizes the fact that the electric field strength of adjacent acceleration cavities changes depending on the degree of coupling of intervening individual coupling cavities, and the electric field strength of the puncher part is This is to change the acceleration energy of electrons by relatively changing the amplitude of the electric field in the accelerating tube while keeping it at an optimum level. In order to change the degree of coupling, the semi-coaxial individual coupling cavity is mechanically deformed, and the resonance frequency in the side coupling cavity is kept approximately equal to the co-(dragon) frequency of the acceleration cavity. Make the electromagnetic field asymmetric.

By changing the energy of the accelerating tube section from O to E2, it is possible to change it almost continuously from El to El + E2.

However, with this method, the above-mentioned
Compared to the standing waveform linear accelerator described in the publication, it has the disadvantage that energy below E1 cannot be selected.

Next, the standing wave linear accelerator described in Japanese Patent Application Laid-open No. 61-253800 uses mechanical deformation to lower the resonance frequency of the individual coupling cavity from the resonance frequency of the accelerating cavity while maintaining the symmetry of the electromagnetic field distribution. By detuning, the relative phase and amplitude between the puncher section and the acceleration tube section are changed.

However, even with this method, the above-mentioned Special Publication No. 57-55099
Similar to the standing wave linear accelerator described in the publication, it is possible to continuously vary the energy, but it has the disadvantage that it is not possible to select energies below E1.

Next, the standing wave linear accelerator described in Japanese Patent Application Laid-Open No. 61-288400 is one in which two adjacent acceleration cavities are coupled by a plurality of individual coupling cavities. Each individual coupling cavity has a coupling hole of a different shape between it and the acceleration cavity, and two states, resonance or complete non-resonance, can be selected by a tuning mechanism.

The energy can be varied depending on the combination of resonance and non-resonance and the shape of the coupling hole.

However, in this method, the energy lq takes only a finite number of discrete values at most. In order to obtain a large number of different energies, a large number of individual coupling cavities are required, which has the drawbacks of difficulty in structural adjustment and high cost. Also, the energy is from El to Fl +E
It takes a value between 2 and cannot have an energy below E1.

The purpose of this invention is to provide a standing waveform linear accelerator that can generate high-intensity X-rays whose energy is continuously variable from near zero energy to maximum energy. shall be.

[Structure of the Invention] The present invention provides a standing wave linear accelerator phase system comprising a plurality of acceleration air conditioners and an individual coupling cavity that couples electromagnetic energy between adjacent acceleration cavities among the plurality of acceleration air conditioners. The individual coupled cavity is made to resonate at the same resonance frequency as the acceleration cavity and at a different resonance seventh, and the individual coupled cavity is further provided with a tuner for frequency fine adjustment to form a standing waveform. It is a linear accelerator.

(Operation) According to the present invention, it is possible to take a continuous energy value over a wide range from a low energy substantially equal to O to a maximum energy where the entire acceleration tube length is the effective acceleration length.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The standing waveform linear accelerator according to the present invention is shown in FIGS.
It is constructed as shown in the figure, and FIG. 2 is an enlarged view of the main part of FIG. 1, and the same parts as in the conventional example (FIG. 4) are given the same reference numerals.

That is, a particle beam generating section 8 is provided at one end of the accelerator main body 11, and at a predetermined interval from the particle beam generating section 8, an entrance cavity 6 into which the particle beam is incident, and a plurality of accelerators are provided in the accelerator main body 11. Medium l111.2, output medium 1j to extract particle beam! 7 are successively formed and connected by a drift tube 3 that blocks the electric field and allows the electron flow to pass. Further, on both sides of the accelerator main body 11, there are individual coupling cavities 4 for coupling adjacent acceleration cavities among the plurality of acceleration cavities, and electromagnetic energy between adjacent acceleration cavities among the plurality of acceleration cavities. A ring-shaped side bonding hole rIA9.10 is provided on both sides so as to connect the
It is connected via a connecting hole 5 to the acceleration cavity 1.2.

Furthermore, in this invention, as is clear from FIG. 2, the frequency fine adjustment tuner 16 is provided in one side coupling air rI49, and the frequency fine adjustment tuner 15 is provided in the other side coupling air 110. There is. Each fine frequency tuner 16.15 is an adjustable tuning mechanism that changes the resonant frequency of the individual coupling cavity 9.10.

In FIG. 2, 12 is the center conductor in the open state in the individual coupling cavity 9, 13 is the center conductor in the open state in the individual coupling cavity 10, and 14 is the center opposite to the center conductor 12.13. Indicates a protrusion.

Now, the above side coupling cavity W49.10 is caused to resonate at the same resonance frequency as the acceleration cavity 1.2, but in a different resonance mode. That is, by adjusting the frequency fine tuning tuner 15, the side coupling cavity 1110 resonates in a TMa 1 a-like mode at the resonant frequency of the acceleration cavity. This coupling induces in the acceleration cavity 1.2 an electric field with a phase that accelerates the electrons.

On the other hand, by adjusting the frequency fine tuning tuner 16, the individual coupling cavities 9 can be tuned to the TM frequency at the same frequency as that of the acceleration cavities.
The dimensions and positions of the central conductor 12, 13 and the central protrusion 14 are set so that they resonate in the a s or TEM-like mode. This coupling causes the acceleration cavity 2 to have rI during acceleration.
An electric field having a phase that decelerates the electrons accelerated by A1 is generated.

Now, operate the frequency fine tuning tuner 16 and tune the side coupling cavity 9.
If the resonant frequency of is shifted from the resonant frequency of the acceleration cavity 1.2, the coupling by the individual coupling cavity 9 will be weakened, and the side coupling cavity #A1
Bonds by 0 become dominant.

The electric field strength distribution in this case is shown in FIG. 3(a).

As is clear from this figure, the energy obtained by the electron is E
It becomes l +E2.

On the other hand, if the resonance frequency of the other individual coupling cavity 10 is shifted and the resonance frequency of the individual coupling cavity 9 is made to substantially match the resonance frequency of the acceleration cavity 1.2, the coupling by the individual coupling cavity 9 becomes dominant. becomes. The electric field strength distribution in this case is shown in FIG. 3(b). Since the electrons are decelerated in the acceleration cavity 2, the energy obtained by the electrons is El-E2. If E! ~E2, it can be set to approximately 0.

Furthermore, if the resonance frequency of one or both of the side coupling cavities 11i9.10 is shifted from the resonance frequency of the acceleration cavity 1.2, the resulting coupling will be in an intermediate state between FIGS. 3(a) and (b), i.e. Take Fig. 3 (C) and (d). That is, during acceleration, the electric field of 1i12 changes continuously from the phase of accelerating the electron to the phase of decelerating it, and the energy of the electron becomes El-
It is continuously variable from E2 (=O) to El +E2. By this operation, the electric field strength in the acceleration cavity 1 can be kept unchanged, so that a high-intensity electron beam can be obtained without deteriorating the acceleration efficiency.

In the above embodiment, the frequency fine tuner 15.
16 to adjust the resonance frequency of the individual coupling cavities 9.10, fine frequency adjustment may be performed by making the center conductor 12.13 or the center protrusion variable.

[Effects of the Invention] According to the present invention, continuous energy values can be taken over a wide range from a low energy substantially equal to 0 to a maximum energy where the entire acceleration tube length is the effective acceleration length.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a standing waveform linear accelerator according to an embodiment of the present invention, FIG. 2 is a sectional view showing the main part of the invention (near the variable energy mechanism), and FIGS. d) is a waveform diagram showing the electric field strength distribution in the standing wave linear accelerator of the present invention, and FIG. 4 is a sectional view showing the conventional standing wave linear accelerator. 1.2... Accelerating cavity, 4.9.10... Individual coupling cavity, 15.16... Tuner for m-frequency tuning. Applicant's agent Patent attorney Hiko Suzue RLC M 1 Figure

Claims (1)

[Claims] A standing wave linear accelerator comprising a plurality of acceleration cavities and a side coupling cavity that couples electromagnetic energy between adjacent acceleration cavities among the plurality of acceleration cavities, The side coupling cavity has a standing waveform characterized in that the side coupling cavity resonates at the same resonance frequency as the acceleration cavity and in a different resonance mode, and the side coupling cavity is further provided with a tuner for frequency fine adjustment. Linear accelerator.