JPH05326198A - Particle accelerator - Google Patents

Abstract

PURPOSE:To efficiently correct the deviation from a closed orbit resulted from the end leaked magnetic field of a deflecting electromagnet. CONSTITUTION:A particle accelerator is provided with a deflecting electromagnet 4 for applying a determined directional magnetic field to an electron beam in a vacuum duct 3 to form a circumferential orbit, and a high frequency accelerating cavity 5 for accelerating the electron beam. The particle accelerator also has an accelerating frequency control device 21 for controlling the accelerating frequency of the high frequency accelerating cavity 5 so that the slippage from the closed orbit of the electron beam is minimized during the acceleration of the electron beam. The accelerating frequency control device 21 increases the accelerating frequency of the high frequency accelerating cavity 5 when the electron beam is shifted on the outside of the designed orbit by the end leaked magnetic field of the deflecting electromagnet 4, and reduces the accelerating frequency when it is shifted on the inside.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle accelerator such as a synchrotron, and more particularly to a particle accelerator for accelerating an electron beam incident from a linear accelerator.

[0002]

2. Description of the Related Art A particle accelerator is a device for accelerating a beam of electrons, protons, etc. to a high energy of several billion electron volts, and recently, in addition to the conventional large particle accelerator for particle physics research. Furthermore, small particle accelerators for utilizing synchrotron radiation have been developed.

Particle accelerators for synchrotron radiation are
It is expected to be used in a wide range of fields such as the semiconductor field, physics field, and medical field. Particularly in the semiconductor field, submicron-order lithography can be performed by using strong X-rays emitted when an electron beam is bent. It can be carried out.

Therefore, such a particle accelerator is required to be small in size, inexpensive, and easy to control the beam.

FIG. 6 shows a conventional particle accelerator by taking an electron synchrotron as an example.

The conventional particle accelerator has a linear accelerator 1 for generating and accelerating electrons, a transport tube 2 for guiding the electron beam emitted from the linear accelerator 1, and an electron beam incident from the transport tube 2 in an ultrahigh vacuum. A vacuum duct 3 held therein; a deflection electromagnet 4 for applying a magnetic field in a predetermined direction to the electron beam to form a circular orbit; a quadrupole electromagnet 9 for focusing the electron beam;
And a high frequency accelerating cavity 5 for further accelerating the incident electron beam.

In FIG. 6, the deflection electromagnet 4 is adapted to apply a magnetic field so that the electron beam draws a clockwise orbit, and under the control of the deflection electromagnet power supply controller 7, a predetermined amount is supplied from the deflection electromagnet power supply 6. It is supposed to be supplied with power.

A high frequency power source 8 supplies a predetermined high frequency power to the high frequency acceleration cavity 5.

The conventional particle accelerator has a COD (close
d orbit distortion, deviation from closed orbit), that is,
A steering electromagnet 10 for correcting the deviation of the electron beam from the designed orbit, a beam position monitor 11 for measuring the deviation value of the beam closed orbit at a predetermined position in the vacuum duct,
A steering electromagnet power supply 12 for supplying a predetermined electric power to the steering electromagnet 10, and a steering electromagnet power supply 12
And a steering electromagnet power supply control device 13 for controlling.

To accelerate an electron beam using a conventional particle accelerator, first, electrons are generated by the linear accelerator 1 and the generated electrons are accelerated to, for example, about 100 million electron volts (100 MeV).

Next, the accelerated electrons are made to enter the vacuum duct 3 as an electron beam.

Then, the electron beam incident on the vacuum duct 3 is accelerated in the high-frequency acceleration cavity 5 to increase the energy of the electron beam to, for example, several GeV.

Since the electrons incident from the linear accelerator 1 have already been accelerated to near the speed of light, the acceleration frequency of the high frequency acceleration cavity 5 is usually kept constant while the electron beam is accelerated.

Further, the deflection electromagnet power supply controller 7 controls the deflection electromagnet power supply 6 so that the magnetic field strength of the deflection electromagnet 4 increases as the beam energy increases, and while the beam energy is being accelerated, the electron beam Keep the circumference constant.

Further, when a deviation from the designed trajectory of the electron beam occurs due to the installation error of the electromagnet, etc.,
Using the signal from the beam position monitor 11, the steering electromagnet power supply controller 13 controls the steering electromagnet power supply 12 to return the electron beam to the designed trajectory.

By such a correction operation, it is possible to prevent the electron beam from colliding with the vacuum duct 3 or the like and lowering the beam energy.

A technique for correcting such a deviation of the closed orbit is disclosed in JP-A-63-307700 and JP-A-3-18.
It is disclosed in Japanese Patent Publication No. 2098.

[0018]

However, the deviation of the electron beam from the designed trajectory is not only due to the installation error of the electromagnet, but also due to the leakage magnetic field from the end of the deflection electromagnet, and the amount of deviation to be corrected. Will grow.

Further, the leakage magnetic field from the end portion of the deflection electromagnet changes in accordance with the change in the magnetic field strength of the deflection electromagnet, and the deviation from the design trajectory also changes accordingly.

Therefore, there is a problem that the operation of adjusting the deviation from the designed trajectory by the steering electromagnet 10 becomes very difficult.

Furthermore, if the deviation of the electron beam is large, the uniform region of the magnetic field of each electromagnet must be increased, so that the deflection electromagnet, the quadrupole electromagnet, and the steering electromagnet have to be large in size, and the entire synchrotron is large in size. There was a drawback that it turned into.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a particle accelerator capable of efficiently correcting a deviation from a closed orbit due to an end leakage magnetic field of a bending electromagnet. To aim.

[0023]

In order to achieve the above object, the particle accelerator according to the present invention has the following features.
In a particle accelerator equipped with a bending electromagnet that applies a magnetic field in a predetermined direction to an electron beam in a vacuum duct to form a circular orbit, and a high-frequency acceleration cavity that accelerates the electron beam, while accelerating the electron beam, An acceleration frequency control device for controlling the acceleration frequency of the high-frequency acceleration cavity so that the deviation from the closed orbit of the electron beam is reduced, wherein the acceleration frequency control device is an electron beam generated by an end leakage magnetic field of the deflection electromagnet. Is shifted to the outside of the design trajectory, the acceleration frequency of the high-frequency acceleration cavity is increased, and when it is shifted to the inside, the acceleration frequency is decreased.

[0024]

When the electron beam is accelerated, the acceleration frequency of the high-frequency accelerating cavity is increased when the electron beam is deviated to the outside of the designed trajectory due to the end leakage magnetic field of the deflection electromagnet, and the acceleration frequency is deviated to the inside. To reduce.

Therefore, the deviation of the electron beam from the closed orbit during the beam acceleration can be reduced and the electron beam can be efficiently accelerated.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the particle accelerator of the present invention is applied to a synchrotron will be described below with reference to the accompanying drawings.

The parts that are substantially the same as those in the prior art are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a plan view showing the synchrotron according to the first embodiment.

As described in the prior art, the synchrotron of the first embodiment has a linear accelerator 1 for generating and accelerating electrons, a transport tube 2 for guiding an electron beam emitted from the linear accelerator 1, and a transport. A vacuum duct 3 for holding the electron beam incident from the tube 2 in an ultrahigh vacuum; a deflection electromagnet 4 for applying a magnetic field in a predetermined direction to the electron beam to form a circular orbit;
A quadrupole electromagnet 9 that focuses the electron beam, a high-frequency acceleration cavity 5 that further accelerates the incident electron beam, a steering electromagnet 10 that corrects the deviation of the electron beam from the designed orbit, and a beam at a predetermined position in the vacuum duct. A beam position monitor 11 for measuring the deviation value of the closed orbit, a steering electromagnet power supply 12 for supplying a predetermined electric power to the steering electromagnet 10, and a steering electromagnet power supply control device 13 for controlling the steering electromagnet power supply 12 are provided.

Further, the synchrotron of this embodiment is provided with an acceleration frequency control device 21 for controlling the acceleration frequency of the high frequency acceleration cavity 5 during the acceleration of the electron beam so that the deviation from the closed orbit of the electron beam becomes small. ..

The accelerating frequency control device 21 controls the high frequency power source 8 using the signal from the beam position monitor 11, and the electron beam is moved to the outside of the designed trajectory due to the end leakage magnetic field of the deflection electromagnet 4. When deviated, the acceleration frequency of the high-frequency acceleration cavity 5 is increased, and when deviated inward, the acceleration frequency is decreased.

FIG. 2 shows how the electron beam deviates from the designed orbit due to the end leakage magnetic field of the deflection electromagnet 4.

The deflection electromagnet 4 is supplied with electric power from the deflection electromagnet power supply 6 under the control of the deflection electromagnet power supply control device 7 so that the magnetic field strength increases as the electron beam is accelerated.

Therefore, in the deflecting electromagnet 4, magnetic saturation in the iron core gradually progresses as the electron beam is accelerated, and the magnetic field leaking from the end becomes smaller as the saturation progresses.

In other words, the electron beam is applied to the linear accelerator 1
At the stage of the incident from, the end leakage magnetic field is large, and as shown in FIG. 2, the effective magnetic length Δ of the deflection electromagnet 4 is increased.
L becomes longer.

ΔL becomes gradually smaller as the electron beam is accelerated, and becomes 0 at the stage of the rated time when the beam energy reaches the rated value.

Because of this magnetic effective length ΔL, the electron beam passes the designed orbit 31 at the time of rating, but tries to pass the orbit 32 at the time of incidence.

During the beam acceleration, if the acceleration frequency f is the rated acceleration frequency f _N , the circumference of the beam orbit is kept constant due to the synchrotron phase stability, and the magnetic effective length ΔL is kept constant. This is because the length of the straight line makes it attempt to pass the track 32 outside the designed track 31 by Δx.

The acceleration frequency controller 21 uses the signal from the beam position monitor, that is, Δx, to evaluate the amount of change Δf from the acceleration frequency f _N at the rated time such that this Δx is as small as possible, and then the high frequency acceleration is performed. The high frequency power source 8 is controlled so that the cavity 5 accelerates the electron beam at the acceleration frequency f = (f _N + Δf).

The acceleration frequency controller 21 evaluates Δf as follows.

Assuming that the circumference of the designed orbit is L, the circumference L'of the orbit at the time of incidence is as follows when Δf is sufficiently small:

## EQU1 ## L ′ = L × f _N / (f _N + Δf) (1), and the difference ΔL between L and L ′ is

[Expression 2] ΔL to −L × Δf / f _N (2)

On the other hand, if ΔL is expressed using Δx,

[Expression 3] ΔL to −2πΔx (3) Therefore, approximately,

[Expression 4] Δf = 2πf _N Δx / L (4)

After evaluating Δf, the acceleration frequency control device 2
1 controls the high-frequency power source 8 so that the high-frequency acceleration cavity 5 accelerates the electron beam at the acceleration frequency (f _N + Δf), so that the electron beam passes through the orbit 33.

Next, the procedure for actually accelerating the electron beam using the synchrotron of the first embodiment will be described.

This procedure is divided into two steps. The first step is a step of preliminarily accelerating the electron beam to the rated value to correct the deviation from the design trajectory due to the installation error of the electromagnet, and the second step. The step is a step of accelerating the electron beam to the rated value again while correcting the deviation from the design trajectory due to the end leakage magnetic field of the deflection electromagnet 4.

In the first step, first, electrons are generated by the linear accelerator 1, and the generated electrons are guided to the vacuum duct 3 via the transport tube 2.

Next, for example, when the light enters the vacuum duct 3,
While keeping the acceleration frequency constant, the electron beam of 100 MeV
The high-frequency acceleration cavity 5 accelerates to, for example, several GeV.

Here, in order to keep the acceleration frequency constant,
As described with reference to FIG. 2, the electron beam passes through the orbit 32, for example, during acceleration.

When the energy of the electron beam reaches the rated value, the deviation from the design trajectory due to the end leakage magnetic field of the deflection electromagnet converges to 0, and the deviation from the design trajectory due to the installation error of the electromagnet remains. ..

The deviation from the designed trajectory is measured by the beam position monitor 11, and the measured value is sent to the steering electromagnet power supply controller 13.

The steering electromagnet power source control device 13 is
The steering electromagnet power supply 12 is arranged so that the deviation value sent from the beam position monitor 11 becomes as small as possible.
To control.

With respect to the deviation from the design trajectory due to the installation error of the electromagnet, after being optimized in this way, the deviation from the design trajectory at each position of the beam position monitor 11 (ideally, all should be 0). ) X ₁ , x ₂ ,
x ₃ ..., X _n are sent to the acceleration frequency control device 21, and the contents of controlling each steering electromagnet power source 12 as described above are stored as control data.

X ₁ , x ₂ , x ₃ , ..., X _n are target values for correcting the deviation from the design trajectory due to the end leakage magnetic field of the deflection electromagnet in the second step.

A trajectory having such a deviation is called a reference trajectory, and ideally, it coincides with the design trajectory.

In the second step, as in the first step, electrons are generated by the linear accelerator 1 and the generated electrons are guided to the vacuum duct 3 via the transport tube 2.

Next, for example, when the light is incident on the vacuum duct 3,
An electron beam of 100 MeV is applied to the high-frequency accelerating cavity 5 for several Ge
Accelerate to V.

While the electron beam is being accelerated, the steering electromagnet power supply controller 13 controls the steering electromagnet power supply 12 according to the stored control data.

Further, the acceleration frequency control device 21 shifts from the design trajectory sent from the beam position monitor 11.
_{x '1, x' 2,} x '3, ··· x' and _n, the target value x ₁ of the above,
x ₂ , x ₃ , ... Differences with x _n Δx ₁ , Δx ₂ , Δ
x ₃ , ... Δx _n is calculated.

Next, these differences Δx ₁ , Δx ₂ , Δx
_3, with a · · · [Delta] x _n, evaluating the deviation [Delta] x from the reference trajectory to be corrected, for example, as their average value.

That is,

## EQU5 ## Δx = ΣΔx _i / n (5) Substituting this into equation (4),

## EQU6 ## Δf = 2πf _N ΣΔx _i / (nL) (6) Δf is obtained.

Using the obtained Δf, the acceleration frequency controller 21 determines that the high frequency acceleration cavity 5 has the acceleration frequency (f _N + Δ
The high-frequency power source 8 is controlled so as to accelerate the electron beam in f), and the electron beam has a reference trajectory (ideally the design trajectory 33).
To pass through.

Further, the acceleration frequency control device 21 sequentially updates the above Δf while accelerating the electron beam so that the electron beam always passes through the design trajectory 33 until the beam energy of the electron beam reaches the rated value. To

As described above, the electron beam is emitted from the linear accelerator 1
Since the beam energy is always incident on the vacuum duct 3 and is accelerated through the orbit 33 until the beam energy reaches the rated value, it does not collide with the vacuum duct 3 or the like.

Therefore, the electron beam can be efficiently accelerated while maintaining the current value at the time of incidence.

Further, since the electron beam almost passes through the designed trajectory, the vacuum duct 3 can be downsized.

Further, since the electron beam almost passes through the designed orbit, the uniform region of the magnetic field of each electromagnet can be small.

Therefore, it becomes possible to reduce the load on the deflection electromagnet, the quadrupole electromagnet, the steering electromagnet, etc., and to miniaturize them, which in turn makes it possible to miniaturize the entire particle accelerator.

Furthermore, since the electron beam can be accelerated to the rated value while maintaining the current value of the electron beam at the time of incidence, the life of the electron beam can be extended.

In this embodiment, the beam position monitor 11 is provided at the entrance / exit of the deflection electromagnet 4, but it is not necessary to provide it at all of them, and it may be provided at a predetermined number of places.

In the present embodiment, the same beam position monitor 11 is connected to the steering electromagnet power supply controller 13 and the acceleration frequency controller 21, but a dedicated beam position monitor may be connected to each.

Further, in this embodiment, all the signals from the beam position monitor 11 are used, but only a predetermined beam position monitor may be used.

Further, in this embodiment, deviation from the design orbit transmitted from the beam position monitors _{11 x '1, x' 2} ,
x _'3, ··· x' and _n, the target value x ₁ of the above, x _2, x _3,
... difference from x _n Δx ₁ , Δx ₂ , Δx ₃ , ... Δx
_Although the deviation Δx from the design trajectory to be corrected is evaluated by averaging _n , the present invention is not limited to such an evaluation method, and for example, a predetermined weighting function may be given to take the average.

Further, in the present embodiment, during the beam acceleration, the optimum acceleration frequency (f _N + Δf) is set to the acceleration frequency controller 21.
The high frequency power source 8 is controlled so as to accelerate the electron beam at this acceleration frequency. However, the acceleration frequency control device 21 determines only whether the deviation Δx from the design trajectory to be corrected is Δx. Is positive, that is, if the electron beam is deviated outside the design orbit, the acceleration frequency Δf is positive, and if Δx is negative, that is, if the electron beam is deviated inside the design orbit, the acceleration frequency Δf is negative and the high frequency The power supply 8 may be controlled.

Next, a second embodiment in which the particle accelerator of the present invention is applied to a synchrotron will be described.

The same parts as those of the prior art or the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

FIG. 3 shows a synchrotron according to the second embodiment.

The synchrotron of the second embodiment is similar to the first embodiment in that the linear accelerator 1 for generating and accelerating electrons is used.
A transport tube 2 for guiding the electron beam emitted from the linear accelerator 1, a vacuum duct 3 for holding the electron beam incident from the transport tube 2 in an ultrahigh vacuum, and applying a magnetic field in a predetermined direction to the electron beam. A deflection electromagnet 4 that forms a circular orbit, a quadrupole electromagnet 9 that focuses the electron beam, a high-frequency acceleration cavity 5 that further accelerates the incident electron beam, and a steering electromagnet 1 that corrects the deviation of the electron beam from the designed orbit.
0, a beam position monitor 11 that measures the deviation value of the beam closed trajectory at a predetermined position in the vacuum duct, a steering electromagnet power supply 12 that supplies predetermined power to the steering electromagnet 10, and a steering electromagnet power supply 12 are controlled. And a steering electromagnet power supply control device 13.

The synchrotron of this embodiment uses the ammeter 31 such as CT for measuring the current value I supplied to the deflection electromagnet 4 and the current value I from the ammeter 31 to close the electron beam. An arithmetic circuit 32 for calculating an acceleration frequency capable of reducing the deviation from the orbit and an acceleration frequency control device 33 for controlling the high frequency power source 8 so that the electron beam is accelerated at the calculated acceleration frequency are provided.

As described in the first embodiment, the electron beam deviates from the designed trajectory due to the end leakage magnetic field of the deflection electromagnet 4, but the magnitude of this deviation depends on the magnetic field strength B formed by the deflection electromagnet 4. To do.

Therefore, if the current value of the current supplied to the deflection electromagnet 4 and the deviation from the design trajectory of the electron beam are known in advance by experiments, etc., the increase / decrease amount Δf of the acceleration frequency can be calculated by the equation (4). Can be evaluated.

The arithmetic circuit 32 preferably stores the relationship between the current value I of the current supplied to the deflection electromagnet 4 and the acceleration frequency f as a table in a memory (not shown).

FIG. 4 is a graph showing the relationship between the current value I of the current supplied to the deflection electromagnet 4 and the acceleration frequency f. The horizontal axis represents the deflection electromagnet excitation current value and the vertical axis represents the acceleration frequency. Has been taken.

[0083] Further, each I _in, I _N, the current value at the time of the incident, represents the value of the current at rated, f _in, f _N are each shows the acceleration frequency, acceleration frequencies at rated at injection.

As can be seen from FIG. 4, the relationship between the current value I of the current supplied to the deflection electromagnet 4 and the acceleration frequency f is expressed as a linear function, and if the excitation current value I of the deflection electromagnet is known, then The acceleration frequency f at this time can be known by the following equation.

[0085]

[Equation 7]

The arithmetic circuit 32 sends the obtained acceleration frequency f to the acceleration frequency controller 33, and the acceleration frequency controller 3
3 controls the high-frequency power source 8 so that the high-frequency accelerating cavity 5 accelerates the electron beam at the accelerating frequency f so that the electron beam passes through the trajectory 33.

The procedure of actually accelerating the electron beam by using the synchrotron of the second embodiment is divided into two procedures as in the case of the first embodiment, and the first step is to prepare the electron beam. The process of correcting the deviation from the design trajectory due to the installation error of the electromagnet by automatically accelerating to the rated value, and the second step is again correcting the deviation from the design trajectory due to the end leakage magnetic field of the deflection electromagnet 4 while again performing the electron beam. Is the process of accelerating the temperature to the rated value.

Here, since the first step is almost the same as that of the first embodiment, detailed description will be omitted.

In the second step, as in the first step, electrons are generated by the linear accelerator 1 and the generated electrons are guided to the vacuum duct 3 via the transport tube 2.

Next, for example, when the light enters the vacuum duct 3,
An electron beam of 100 MeV is applied to the high-frequency accelerating cavity 5, for example, several Ge.
Accelerate to V.

During the acceleration of the electron beam, the steering electromagnet power supply controller 13 controls the steering electromagnet power supply 12 according to the stored control data.

The ammeter 31 also measures the current value I of the current supplied to the deflection electromagnet 4 and sends the measured value to the arithmetic circuit 32.

The arithmetic circuit 32 obtains the acceleration frequency f for the current value I by referring to the built-in table and sends it to the acceleration frequency controller 33.

The acceleration frequency control device 33 includes an arithmetic circuit 32.
The high frequency power source 8 is controlled so that the electron beam is accelerated at the acceleration frequency sent from the electron beam so that the electron beam passes through the orbit 33.

Further, the arithmetic circuit 32 successively updates the above-mentioned f while accelerating the electron beam, and the acceleration frequency control device 33 makes a high frequency so that the electron beam is accelerated at the updated acceleration frequency f. The power source 8 is controlled so that the electron beam always passes through the trajectory 33 until the beam energy of the electron beam reaches the rated value.

Thus, the electron beam is emitted by the linear accelerator 1
Since the beam energy is always incident on the vacuum duct 3 and is accelerated through the orbit 33 until the beam energy reaches the rated value, it does not collide with the vacuum duct 3 or the like.

Therefore, the electron beam can be efficiently accelerated while maintaining the current value at the time of incidence.

Further, since the electron beam almost passes through the designed orbit, the vacuum duct, the bending electromagnet, the quadrupole electromagnet, the steering electromagnet, etc. can be downsized, and the particle accelerator as a whole can be downsized, as in the first embodiment. In addition, the life of the electron beam can be extended.

In the second embodiment, the relation between the current value I of the current supplied to the deflection electromagnet 4 and the acceleration frequency f is approximated by a linear function, but it may be approximated by a higher order function. Store multiple data sets of current value and acceleration frequency,
From the current value I measured by the ammeter 31, the desired acceleration frequency f
The interpolation calculation may be performed using a predetermined data set among the above-mentioned data sets when obtaining

In the second embodiment, the current sent from the deflection electromagnet power supply 6 to the deflection electromagnet 4 is read, but the control signal sent from the deflection electromagnet power supply control device 7 to the deflection electromagnet power supply 6 causes the deflection electromagnet 4 to move. The exciting current may be evaluated.

In the second embodiment, the optimum acceleration frequency f is evaluated by using the exciting current I of the deflection electromagnet 4, but the magnetic field strength B of the deflection electromagnet 4 is directly measured and this magnetic field strength is measured. The acceleration frequency f may be evaluated using B.

In the second embodiment, the current is measured by the ammeter 31 and the optimum acceleration frequency f is evaluated by the arithmetic circuit 32 using this current value. However, as shown in FIG. A clock circuit 41 for generating a time signal t at a predetermined timing, an arithmetic circuit 42 for evaluating an acceleration frequency f corresponding to the time signal t received from the clock circuit 41,
An acceleration frequency control device 43 that controls the high frequency power supply 8 so that the electron beam is accelerated at the acceleration frequency f received from the arithmetic circuit 42 may be provided.

The arithmetic circuit 42 preferably stores the value of the acceleration frequency f corresponding to each time t as a table.

As can be seen from FIG. 5, the clock circuit 41 is preferably used also as a clock circuit which sends a signal to the deflection electromagnet power source control device 7 for a predetermined time.

[0105]

As described above, the particle accelerator of the present invention comprises a deflecting electromagnet for forming a circular orbit by applying a magnetic field in a predetermined direction to an electron beam in a vacuum duct, and a high frequency accelerating cavity for accelerating the electron beam. In the particle accelerator provided with, during the acceleration of the electron beam, by providing an acceleration frequency control device for controlling the acceleration frequency of the high-frequency acceleration cavity so that the deviation from the closed orbit of the electron beam becomes small, When accelerating the electron beam, the acceleration frequency of the high-frequency acceleration cavity is increased when the electron beam shifts to the outside of the designed trajectory due to the end leakage magnetic field of the deflection electromagnet, and the acceleration frequency is decreased when it shifts to the inside. ..

Therefore, the deviation from the closed orbit of the electron beam during the beam acceleration can be reduced, and the electron beam can be efficiently accelerated.

[Brief description of drawings]

FIG. 1 is a plan view of a particle accelerator according to this embodiment.

FIG. 2 is a diagram for explaining a deviation of an electron beam from a designed trajectory due to an end leakage magnetic field of a bending electromagnet 4.

FIG. 3 is a plan view of a particle accelerator according to a second embodiment.

FIG. 4 is a graph showing a relationship between a bending magnet exciting current and an acceleration frequency.

FIG. 5 is a plan view of a particle accelerator according to a modification of the second embodiment.

FIG. 6 is a plan view of a conventional particle accelerator.

[Explanation of symbols]

 1 linear accelerator 2 transportation pipe 3 vacuum duct 4 deflection electromagnet 5 high frequency acceleration cavity 6 deflection electromagnet power supply 7 deflection electromagnet power supply control device 8 high frequency power supply 9 quadrupole electromagnet 10 steering electromagnet 11 beam position monitor 12 steering electromagnet power supply 13 steering electromagnet power supply control device 21 Acceleration frequency controller 31 Ammeter 32 Arithmetic circuit 33 Acceleration frequency controller 41 Clock circuit 42 Arithmetic circuit 43 Acceleration frequency controller

Claims (1)

[Claims] 1. A particle accelerator comprising a deflecting electromagnet for applying a magnetic field in a predetermined direction to an electron beam in a vacuum duct to form a circular orbit, and a high-frequency accelerating cavity for accelerating the electron beam. The acceleration frequency of the high-frequency accelerating cavity is controlled so that the deviation from the design trajectory of the electron beam is reduced, the acceleration frequency controlling device is provided at the end of the deflection electromagnet. A particle accelerator characterized in that, when the electron beam is deviated to the outside of the designed trajectory due to the leakage magnetic field, the acceleration frequency of the high-frequency acceleration cavity is increased, and when it is deviated to the inside, the acceleration frequency is decreased. ..