JP3381577B2 - Accelerator and its operation method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accelerator for orbiting a charged particle beam and a method for operating the accelerator.

[0002]

2. Description of the Related Art When the tune of a charged particle beam orbiting an orbiting type accelerator (frequency of betatron oscillation per orbit of charged particle beam) approaches 0.5 or 0, betatron oscillation of charged particle beam Resonance occurs. Then, the amplitude of the betatron oscillation of the charged particle beam increases, and the charged particle beam collides with the vacuum duct and is lost. The tune is a four-pole electromagnet for focusing and four for diverging.
It is adjusted by controlling the magnetic field gradient generated by the pole electromagnet, that is, by controlling the exciting currents of the focusing quadrupole electromagnet and the diverging quadrupole electromagnet.

Further, when the beam current of the incident charged particle beam becomes large, as shown in FIG. 8, the current density in the beam central region increases, and the repulsive force due to the space charge effect of the charged particle beam itself increases. This repulsive force is for divergence 4
The tune changes because the force acting on the charged particles in the polar electromagnet has a similar effect. The change in tune due to the space charge effect is described in "Monthly Physics Accelerator Physics (3)" (p.12 Kaiyodo Publishing Co., Ltd., 1985).

The larger the current density, the more the tune decreases. As shown in FIG. 9, the tune is greatly reduced in the central region rather than the beam peripheral region.

In the prior art, in order to stably orbit the beam, even if the tune is reduced by the space charge effect of the charged particle beam itself, the fractional part of the tune is 0.5.
The currents of the converging quadrupole electromagnet 5 and the diverging quadrupole electromagnet 6 are set so as not to be 0 and 0.

Further, in Japanese Patent Laid-Open No. 8-148298, even if the tune decreases and resonance occurs, an 8-pole electromagnet is used.
It is described that the charged particles are subjected to a force toward the center of vibration to increase the tune of the charged particles and stop the resonance.

[0007]

SUMMARY OF THE INVENTION In the above prior art,
There were the following problems.

Accelerating a large current charged particle beam with an accelerator
When accumulating, the tune reduction due to space charge effect is very large. At this time, only by controlling the converging quadrupole electromagnet and the diverging quadrupole electromagnet, the fractional part of the tune becomes 0 or 0.5 and resonance occurs. As a result, the amplitude of the betatron oscillation of the charged particle beam increases and the charged particle beam is lost.

Further, in the prior art disclosed in Japanese Unexamined Patent Publication No. 8-148298, if the octupole electromagnet is strengthened in order to increase the tune, instability occurs in the charged particle beam orbiting the accelerator, and the charged particle beam is There was a problem of colliding with the vacuum duct and being lost.

An object of the present invention is to provide an accelerator capable of reducing the beam loss of a circulating charged particle beam and stably injecting, accelerating and accumulating even a large current charged particle beam, and an operating method thereof.

[0011]

Feature of the present invention to achieve the above object, according to an aspect of the time of incidence start of the charged particle beam, in the incident, or during storage acceleration, high-frequency applying device, the charged particles
The channel that does not generate the resonance of the betatron oscillation of the beam
The high-frequency electric field or a high-frequency magnetic field comprises a frequency defined based on the value of tune that is set in advance to a value of Yun, is applied to the charged particle beam orbiting orbit, a plurality included in the charged particle beam Among the charged particles, it is to increase the amplitude of betatron oscillation of the charged particles having a set value of tune.

According to this feature, among the plurality of charged particles included in the charged particle beam, the betato of the charged particle beam is used.
A betatron oscillation of a charged particle having a tune of a value that does not cause resonance of the Ron oscillation and has a preset tune includes a frequency determined based on the preset value. Synchronize with high frequency electric field or high frequency magnetic field. The charged particles are energized by the high frequency electric field or the high frequency magnetic field, and the amplitude of the betatron oscillation is increased. Since the range of vibration of the charged particles having the increased amplitude spreads outward in the radial direction of the beam, the density of the charged particles becomes small in the range where the charged particles having a tune of a preset value were vibrating. Therefore, in the range where the density of the charged particles is reduced, the change of the tune due to the space charge effect can be prevented, so that the occurrence of resonance can be suppressed and the beam loss can be prevented, and the beam can be stably incident, accelerated or accumulated. it can. In particular, if the amplitude of the betatron oscillation of the charged particles gathering in the central portion of the beam is increased, the range of oscillation of these charged particles extends from the central portion of the beam to the outer peripheral portion. The number of charged particles in the central portion of the beam decreases, and the number of charged particles increases in the outer peripheral portion, so that the distribution of the charged particle density becomes flat. Therefore, it is possible to prevent the tune from changing due to the space charge effect in the central portion of the beam, so that it is possible to stably enter, accelerate, or accumulate the beam while suppressing the occurrence of resonance and preventing the beam loss.

Further, if the amplitude of the betatron oscillation of the charged particle having a tune of a preset value is increased from the start of the incident, the tune changes due to the space charge effect even if the beam energy at the incident is low. Therefore, charged particles can be stably injected into the accelerator. Further, since the incident energy can be reduced, the pre-stage accelerator and the injector can be downsized.

[0014]

[0015]

Particularly, if a high frequency electric field or a high frequency magnetic field containing a frequency determined based on the tune value of the charged particles gathering at the center of the beam is applied to the charged particle beam, the beta of these charged particles is obtained. The range of tron oscillation extends from the vicinity of the center of the beam to the outside in the vertical direction. The number of charged particles near the center of the beam decreases, and the number of charged particles increases in the outer peripheral portion, so that the distribution of the charged particle density becomes flat. Therefore,
At the center of the beam, changes in the tune due to the space charge effect can be prevented, so that it is possible to stably enter, accelerate, or accumulate the beam while suppressing the occurrence of resonance and preventing the beam loss.

If a high-frequency electric field or a high-frequency magnetic field containing a frequency determined based on a preset tune value is applied to the charged particle beam from the start of incidence,
Even if the energy of the beam at the time of incidence is low, changes in tune due to the space charge effect can be prevented, and charged particles can be stably incident on the accelerator. Further, since the incident energy can be reduced, the pre-stage accelerator and the injector can be downsized.

Further, the frequency of the high frequency electric field or the high frequency magnetic field applied to the charged particle beam may be determined based on a preset tune value and the orbiting frequency of the charged particle beam.

In addition, a frequency range from a first frequency determined based on the preset first tune value to a second frequency determined based on the preset second tune value is set. A high frequency electric field or a high frequency magnetic field having a width may be applied to the charged particle beam. At this time, among the plurality of charged particles included in the charged particle beam, the betatron vibration of the charged particles having tunes from the first tune to the second tune is synchronized with the high frequency electric field or the high frequency magnetic field. Therefore, in the range where the charged particles having the tune from the first tune to the second tune are in the betatron oscillation, it is possible to prevent the change of the tune due to the space charge effect, so that the occurrence of resonance is suppressed and the beam loss is prevented. However, the beam can be stably incident, accelerated, or accumulated.

In particular, if the range from the first tune to the second tune includes the range of tunes possessed by the charged particles gathering at the center of the beam, the number of charged particles near the center of the beam will decrease. , The distribution of charged particle density becomes flat. Therefore, it is possible to prevent the tune from changing due to the space charge effect in the central portion of the beam, so that it is possible to stably enter, accelerate, or accumulate the beam while suppressing the occurrence of resonance and preventing the beam loss.

Further, in a range from the first frequency determined based on the preset first tune value to the second frequency determined based on the preset second tune value. Alternatively, a high frequency electric field or a high frequency magnetic field having a changed frequency may be applied.

[0022]

DETAILED DESCRIPTION OF THE INVENTION

(Embodiment 1) An orbiting accelerator 111 according to a first embodiment of the present invention will be described with reference to FIG. Accelerator 1 of this embodiment
Reference numeral 11 is for accumulating a charged particle beam (hereinafter, simply referred to as a beam) supplied from the pre-accelerator 16 while orbiting, accelerating, and emitting the same to a laboratory.

The accelerator 111 of this embodiment is the same as the pre-stage accelerator 1.
An injector 15 for injecting the beam supplied from 6 into the vacuum duct 10, a pulse electromagnet 9 for bringing the orbit of the incident beam close to the design orbit 1, a deflection electromagnet 2 for bending the orbit of the beam 2, and a metertron oscillation of the beam are adjusted. Focusing quadrupole electromagnet 5 and divergence quadrupole electromagnet 6, high-frequency acceleration cavity 8 that imparts energy to the beam for acceleration, output pulse electromagnet 20 that separates the trajectory of the beam from design trajectory 1 for extraction, and the beam It has an emitter 4 for emitting light to the laboratory, a beam current measuring device 11 for measuring the amount of current of the beam, and a high frequency applying device 3 for changing the charged particle density of the beam around the designed orbit 1.

FIG. 2 shows the high frequency applying device 3. The high frequency applying device 3 includes a parallel plate electrode 112 installed in the vacuum duct 10 and a high frequency generating device 11 for generating a high frequency signal.
3, an amplifier 114 that amplifies the high frequency signal generated by the high frequency generator 113 and applies it to the parallel plate electrode 112, and a controller 1 that controls the frequency and the amplification factor of the high frequency signal.
Have 15. The controller 115 controls the frequencies fa to fb.
When the high-frequency generator 113 is controlled so as to generate a high-frequency signal having a frequency spectrum ranging from 0 to 1, a vertical electric field having a frequency spectrum ranging from frequencies fa to fb is generated between the parallel plate electrodes 112. The magnitude of the high-frequency electric field is calculated in advance, or is experimentally determined by using the beam current measuring device 11 so that the maximum current can be injected, and the control device 115 controls the amplification factor of the amplifier 114. A high-frequency electric field of appropriate magnitude is generated.

When this electric field is applied to the beam of this embodiment, the distribution of charged particle density and the distribution of tune in the beam change. Changes in the charged particle density distribution and the tune distribution in this embodiment will be described below.

First, the distribution of the current density around the beam center and the distribution of the tune after the beam is incident on the accelerator 111 and before the high-frequency electric field is applied to the beam by the high-frequency applying device 3 will be described.

FIG. 3 shows the distribution of the current density of the beam.
FIG. 3A is a current density distribution in the horizontal direction (direction parallel to the orbiting surface of the beam and perpendicular to the traveling direction of the beam).
(B) is a current density distribution in the vertical direction (direction parallel to the orbiting surface of the beam and perpendicular to the beam traveling direction).

When the orbit of the incident beam is gradually moved in the horizontal direction in order to bring it closer to the design orbit 1, the beam diameter in the horizontal direction becomes larger than the beam diameter in the vertical direction. Current density (charged particle density)
Is flatter than the current density in the vertical direction.

Since the orbit does not move in the vertical direction like in the horizontal direction, charged particles gather at the center of the beam,
The current density in the central part of the beam is larger than that in the peripheral part of the beam.

Change in tune due to space charge effect Δν
Is a negative value, and its absolute value is smaller as the current value is smaller, the beam size is larger, and the particle number distribution is flat. Therefore, the change (absolute value) in the tune of the beam in the vertical direction is relatively larger than the change in the tune in the horizontal direction.

FIG. 4 shows the distribution of ν in the vertical direction. Since the charged particle density varies depending on the position in the beam, the tune value also varies depending on the position in the beam. The larger the current density (the larger the charged particle density), the larger the change Δν in tune, so that the tune is greatly reduced in the central portion of the beam rather than the peripheral portion of the beam.

Further, the lower the energy of the beam, the larger the tune changes, so that the tune decreases greatly especially when the orbiting beam has a low energy. The fractional part of the tune when there is no space charge effect immediately after the start of injection is νns, the minimum value of the tune when the space charge effect appears is νmin, and the maximum value is νmax.

Next, the charged particle density distribution and the tune distribution around the beam center when a high frequency electric field is applied to the beam by the high frequency applying device 3 will be described.

The frequency of the high frequency signal generated by the high frequency generator 113 is determined as follows. ν a to ν min
To a smaller value (but greater than 0 or 0.5), ν b is set to the lowest value of the fractional part of the desired tune ν (less than ν max and well greater than 0 or 0.5). The frequency fb is a frequency obtained by multiplying νb by the orbiting frequency frev of the beam. The frequency fa is a frequency of a value obtained by multiplying νa by the circulation frequency frev.

When a high-frequency electric field in the vertical direction having a frequency spectrum ranging from frequencies fa to fb is applied to the beam by the high-frequency applying device 3, νa to νb in the beam are applied.
The betatron oscillation of a charged particle with a tune of is synchronized with the vertical high frequency electric field. A charged particle with a tune of νa to νb is given energy from a high frequency electric field,
The amplitude of the betatron oscillations in the vertical direction is amplified. That is, the range of betatron oscillation of charged particles having a tune of νa to νb extends from the vicinity of the beam center to the outside in the vertical direction. Therefore, as shown in FIG. 5, the number of charged particles near the center of the beam decreases, and the number of charged particles increases in the outer peripheral portion.
The distribution of charged particle density becomes flat.

FIG. 4 shows the distribution of the tunes at this time. Since the distribution of the charged particle density has become flat, the tune at the center of the beam is increasing. The particles whose tune is larger than ν b are not synchronized with the frequency of the high frequency electric field applied by the high frequency applying device 3, so that the amplitude of the betatron oscillation does not increase.

Further, even if the beam is incident on the accelerator 111 and the charged particle density is increased and the tune becomes νb or less due to the space charge effect, the charged particle density of the charged particle density is increased by the high frequency electric field applied from the high frequency applying device 3. The distribution becomes flat.

Therefore, according to the accelerator 111 of the present embodiment, it is possible to accelerate and accumulate the beam while preventing the tune from changing due to the space charge effect, suppressing the occurrence of resonance, and preventing the beam loss.

In the above description, the case where the distribution of the charged particle density is changed after the beam is incident on the accelerator 111 has been described. However, when the high current beam is rapidly incident on the accelerator 111 and the tune is rapidly reduced. The above-mentioned high-frequency electric field may be applied by the high-frequency applying device 3 from the start of incidence. Even if the amount of current of the beam is increased, the flat charged particle density distribution is maintained, so that the beam loss at the time of incidence can be reduced. High-frequency applying device 3 from the start of injection
By applying the above-mentioned high frequency electric field, even if the energy of the beam at the time of incidence is low, the decrease in tune can be prevented and the charged particles can be stably incident on the accelerator. Further, since the incident energy can be reduced, the pre-stage accelerator and the injector can be downsized.

Even during acceleration, if the high-frequency electric field is applied by the high-frequency applying device 3, it is possible to perform stable acceleration while maintaining a flat distribution of charged particle density.

FIG. 6 shows a method of operating the accelerator 111 of this embodiment in which the high frequency applying device 3 is applied at the time of incidence and acceleration.

Before the start of incidence, the high frequency electric field is applied in advance by the high frequency applying device 3 (1). Front-stage accelerator 1
Beam injection starts from 6 (2). When the beam incidence is completed (3), the beam acceleration is started (4). Energy is applied to the beam from the high-frequency acceleration cavity 8 and the magnetic field strength of the deflection electromagnet 2, the quadrupole electromagnets 5 and 6 is increased. At this time, the frequency fre at which the beam goes around the accelerator
As v increases, the controller 115 is correspondingly increased.
Then, the frequencies fb and fa of the high frequency signal generated by the high frequency generator 113 are also increased. Since the space charge effect decreases with acceleration, when the beam energy reaches a predetermined value, the application of the high frequency electric field by the high frequency applying device 3 is stopped (6). When the energy reaches the target energy, the acceleration is terminated and the beam is emitted (7).

In (5), the frequency of the high-frequency electric field applied by the high-frequency applying device 3 is increased in accordance with the increase of the circulating frequency. However, if the space charge effect sharply decreases when accelerated, the frequency becomes high. It may be constant. In addition, when the orbital frequency rapidly changes with acceleration and the space charge effect decreases, the frequency of the high-frequency electric field applied by the high-frequency applying device 3 may be constant, and the application need not be stopped.

Further, in the above description, the high frequency electric field applied by the high frequency applying device 3 is applied from the frequency fa to fb. However, the high frequency electric field having a single wave number is applied and the single frequency is scanned from fa to fb. You may do it.

In this embodiment, the case where a high frequency electric field in the vertical direction is applied to the beam has been described. However, even if a high frequency magnetic field in the horizontal direction is applied, the same effect as the present embodiment can be obtained.

(Second Embodiment) Next, an accelerator 111 according to a second embodiment of the present invention will be described. Accelerator 11 of this embodiment
1 is the same as that described in the first embodiment and the high frequency applying device 3
Only different.

In the accelerator 111 of the present embodiment, the magnetic field intensity of the pulse electromagnet 9 for injection is changed within the time in which the beam makes one revolution around the accelerator 111, and the beam for one revolution is incident. The incident beam has the same beam size in the horizontal direction and the vertical direction, and the tune changes in the horizontal direction and the vertical direction are almost the same.

The accelerator 111 of this embodiment is intended to suppress a decrease in tune that occurs in the horizontal and vertical directions.

FIG. 7 shows the high frequency applying device 3. The high frequency applying device 3 includes a parallel plate electrode 112h and a high frequency generating device 11 in order to suppress a decrease in the horizontal beam tune.
3h and an amplifier 114h are provided with a parallel plate electrode 112v, a high frequency generator 113v and an amplifier 114v in order to suppress the decrease of the vertical beam tune, and a controller 115 for controlling the frequency and the amplification factor of the high frequency signal. . Both the horizontal high frequency generator 113h and the vertical high frequency generator 113v generate a single frequency.

High-frequency generator 1 as in the first embodiment.
13h generates a high frequency signal of frequency fbh corresponding to the horizontal tune νbh of the beam, and the high frequency generator 113
Similarly, v also generates a high frequency signal of frequency fbv corresponding to the vertical tune νbv of the beam.

If the high frequency power is sufficiently amplified by the amplifiers 114h and 114v, even if a high frequency electric field of a single frequency is applied to the beam, the betatron oscillation can be increased and the distribution of the charged particle density can be made flat. Yes, the tune is νbh,
It does not become smaller than νbv.

Therefore, according to the accelerator 111 of the present embodiment, it is possible to accelerate and store the beam while preventing the tune from changing due to the space charge effect, suppressing the occurrence of resonance, and preventing the beam loss.

The accelerator 111 of the first and second embodiments can be applied to all charged particle beams regardless of whether the beam is electrons, positive ions or negative ions.

[0054]

According to the present invention, the beam of a charged particle beam is
It is a tune with a value that does not generate resonance of tatron oscillation.
In the range where charged particles having a tune of a preset value are vibrating, changes in the tune due to the space charge effect can be prevented, so that resonance is suppressed and beam loss is prevented while stable beam incidence ， Can be accelerated or accumulated.

Further, even if the energy of the beam at the time of incidence is low, the change of the tune due to the space charge effect is prevented,
Charged particles can be stably injected into the accelerator. Further, since the incident energy can be reduced, the pre-stage accelerator and the injector can be downsized.

[Brief description of drawings]

FIG. 1 is a diagram showing an accelerator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a high frequency applying device 3 according to a first embodiment.

FIG. 3 is a diagram showing a current density distribution of a beam that orbits an accelerator 111.

FIG. 4 is a diagram showing changes in the tune distribution of a beam when a high-frequency electric field is applied by the high-frequency applying device 3.

FIG. 5 is a diagram showing changes in distribution of charged particle density of a beam when a high frequency electric field is applied by the high frequency applying device 3.

FIG. 6 is a diagram showing a method of operating the accelerator 111 according to the first embodiment.

FIG. 7 is a diagram showing a high frequency applying device 3 of a second embodiment.

FIG. 8 is a diagram showing a distribution of a current density of a beam in a conventional accelerator.

FIG. 9 is a view showing a distribution of beam tunes in a conventional accelerator.

[Explanation of symbols]

1 ... Design trajectory, 2 ... Bending electromagnet, 3 ... High frequency applying device,
4 ... Ejector, 5 ... Focusing 4-pole electromagnet, 6 ... Divergence 4-pole electromagnet, 8 ... High-frequency acceleration cavity, 9 ... Incident pulse electromagnet,
10 ... Vacuum duct, 11 ... Beam current measuring device, 12 ...
Magnetic pole, 15 ... Injector, 16 ... Pre-accelerator, 17 ... Incident beam transport system, 20 ... Pulse electromagnet for emission, 111 ... Accelerator, 112 ... Parallel plate electrode, 113 ... High frequency generator,
114 ... Amplifier, 115 ... Control device.

Continuation of front page (56) Reference JP-A-3-263800 (JP, A) JP-A-9-115700 (JP, A) JP-A-9-330800 (JP, A) JP-A-11-329799 (JP , A) JP 10-64699 (JP, A) JP 7-263200 (JP, A) JP 7-111199 (JP, A) JP 6-36894 (JP, A) JP 5-198397 (JP, A) JP 63-307700 (JP, A) JP 8-148298 (JP, A) JP 5-258900 (JP, A) JP 9-45499 (JP, A) JP-A-9-35899 (JP, A) JP-A-8-64400 (JP, A) JP-A-8-203700 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) ) H05H 13/04

Claims (9)

(57) [Claims] 1. A ring-type accelerator for a charged particle beam incident from the outside to accelerate or accumulate along the orbit, incident at the start of the charged particle beam, in the incident, or during storage acceleration, the charged Of the betatron oscillation of the particle beam
A high-frequency electric field or a high-frequency magnetic field containing a frequency that is a tune value that does not generate resonance and is determined based on the preset tune value is applied to the charged particle beam that is orbiting the orbit, and the charging is performed. An accelerator comprising: a high-frequency applying device for increasing the amplitude of betatron oscillation of the charged particles having a tune of the set value among a plurality of charged particles included in the particle beam. 2. A high-frequency applying device, comprising a vacuum duct that forms the circular orbit and in which the charged particles circulate.
The accelerator according to claim 1, further comprising a pair of electrodes installed in the vacuum duct to generate an electric field therebetween. 3. The accelerator according to claim 1, wherein the frequency is determined based on a preset tune value and an orbital frequency of the charged particle beam that orbits the orbit. Wherein said high frequency electric field or a high frequency magnetic field, the second of the chew <br/> emissions from the first frequency which is determined based on the value of the first of the tune that is set in advance, is set in advance The accelerator according to claim 1, wherein the accelerator is a high-frequency electric field or a high-frequency magnetic field in a frequency range extending over a second frequency determined based on the value of. Wherein said high frequency electric field or a high frequency magnetic field, the second of the chew <br/> emissions from the first frequency which is determined based on the value of the first of the tune that is set in advance, is set in advance The accelerator according to claim 1, wherein the accelerator is a high frequency electric field or a high frequency magnetic field whose frequency changes in a range over the second frequency determined based on the value of. 6. A method for operating an orbiting accelerator in which a charged particle beam is incident from the outside into an orbiting accelerator and is accelerated or accumulated while orbiting the charged particle beam along an orbit, the injection of the charged particle beam. Of the betatron oscillations of the charged particle beam during initiation, injection, acceleration or accumulation
A high-frequency electric field or a high-frequency magnetic field containing a frequency that is a value of the tune that does not generate resonance and is determined based on a value of the tune that is preset is applied to the charged particle beam that is orbiting the orbit, and the charging is performed. Among the plurality of charged particles included in the particle beam, an amplitude of betatron oscillation of the charged particles having a tune of the set value is increased, and an accelerator operating method. Wherein said frequency claims, characterized in that defined on the basis of the revolution frequency of the charged particle beam circulating values and the orbit preset the Chu <br/> down 6 Accelerator operation method. Wherein said high frequency electric field or a high frequency magnetic field, the second of the chew <br/> emissions from the first frequency which is determined based on the value of the first of the tune that is set in advance, is set in advance 7. The method of operating an accelerator according to claim 6, wherein the high frequency electric field or the high frequency magnetic field is in a frequency range over the second frequency determined based on the value of. Wherein said high frequency electric field or a high frequency magnetic field, the second of the chew <br/> emissions from the first frequency which is determined based on the value of the first of the tune that is set in advance, is set in advance The method of operating an accelerator according to claim 6, wherein the frequency is a high frequency electric field or a high frequency magnetic field in a range over the second frequency determined based on the value of.