JP2892562B2 - Circular accelerator and its operation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charged particle bi - relates to circular acceleration device for orbiting the beam, in particular, suitable circular accelerator to perform a highly accurate experiments with the outgoing beam and regarding the operating method thereof <br />

[0002]

2. Description of the Related Art A conventional circular accelerator accelerates while orbiting a charged particle beam of electrons or ions, emits charged particles from its orbit, transports the charged particles by a transport system, and performs physical experiments. Used for As a method for emitting a charged particle beam from a circular orbit, a resonance emission method using resonance of betatron oscillation, which is a lateral vibration of the beam, is used.

[0003] The resonance of betatron oscillation is the following phenomenon. The charged particles orbit while oscillating betatrons in the horizontal or vertical direction. The betatron frequency per revolution is called a tune. The tune can be controlled by adjusting the amount of excitation of the quadrupole magnet installed on the orbit. Further, when a multipole magnet having six or more poles is provided on the orbit, the tune changes depending on the betatron amplitude (amplitude of betatron oscillation). To avoid confusion here,
A tune of a particle whose betatron amplitude is close to zero is called a basic tune. Hereinafter, the term "tune" simply means a tune of a particle having a certain finite betatron amplitude.

Here, the basic tune is represented by an integer + p / q
(P, q: an irreducible integer) and at the same time, when the above-described multipole magnet is excited, the charged particles having a betatron amplitude greater than or equal to a certain value among a large number of orbiting charged particles are excited. The tune coincides with the resonance point, and the betatron amplitude sharply increases. This phenomenon is called betatron oscillation resonance. The betatron amplitude when the tune coincides with the resonance point is called the stability limit of betatron oscillation. The betatron amplitude at this stability limit becomes smaller as the basic tune is closer to the resonance point.

Therefore, conventionally, while the basic tune is gradually approached to the resonance point, the size of the stability limit is gradually reduced, and particles having a large betatron amplitude are gradually emitted. This is a commonly used resonance emission method. In this resonance emission method, since the emission angle of the beam fluctuates with a change in the stability limit, it is necessary to correct and control the beam trajectory using an auxiliary deflection magnet in order to correct this. .

In order to keep the beam emission angle constant over time, the following powerful methods have recently been proposed. In this method, the stability of the betatron oscillation is kept constant, and the amplitude of the betatron is gradually increased by means of applying electromagnetic noise having a certain frequency width to kick in the lateral direction. In this way, particles exceeding the stability limit are emitted with the emission angle kept constant over time. This conventional method has a great advantage that it is not necessary to correct and control the beam trajectory and can be realized by a simple device. This method is described in p.62 of the 47th Annual Meeting of the Physical Society of Japan (March 1992).

[0007]

In the above-mentioned prior art in which the emission angle can be made constant over time, the charged particle beam accumulated in the accelerator is emitted as it is, so that the energy width of the beam is limited. It is stored as it is in the emission beam. For this reason, depending on the application, the accuracy of the experiment, the processing accuracy, and the like may be reduced due to the spread of the energy of the emission beam, and the device cannot be used as it is in applications requiring high accuracy.

An object of the present invention is to provide a circular accelerator suitable for applications requiring high precision and a method of operating the same.

[0009]

An object of the present invention is to provide a circulating load.
Of the particles immediately before the emission among the particles forming the electron beam
Circular accelerator that emits betatron oscillations in resonance
At the point, particles in the required energy band
Narrow band electromagnetic noise that kicks in the direction
The narrow band electromagnetic noise that kicks in the
Selectively growing only betatron oscillations of band particles
This is achieved by emitting light . The above purpose is further
Betatro by narrow band electromagnetic noise kicking in the direction
By the time the particles that are selectively excited
The narrow band electromagnetic noise that kicks in the orbital direction
So that the energy width of the child group does not increase significantly
Passing the strength of the narrow-band electromagnetic noise that kicks over the entire frequency band
Or partially reduced.

[0010]

[0011]

[0012]

[0013]

[0014]

The charged particles emitted from the circular accelerator of the present invention
Has a narrow energy width and a constant emission angle.
The precision of experiments performed with particle beams has become higher, and
High-precision processing is possible by using this charged particle beam.
It works .

[0015]

An embodiment of the present invention will be described below with reference to the drawings. The circular accelerator according to the present embodiment includes the following units.
Have a slip. (1) supplying particles to a certain energy band, and the energy band
Only the betatron oscillations of the particles
Shoot. (2) While growing the betatron oscillation of the beam,
Reduce the energy width. (3) While growing the betatron oscillation of the beam,
Only the particles present in a certain energy band are selectively emitted. (4) The betatron frequency of the beam gradually approaches the resonance point
To reach a betatron frequency near the resonance point.
The betatron oscillation of the reached particles is selectively grown and output.
Shoot. First, the means (1) will be described as an example. FIG.
1 is a schematic plan view of a circular accelerator according to a first embodiment of the present invention which emits an accelerated beam, and shows a device arrangement of the circular accelerator which emits a charged particle beam. In the circular accelerator, the beam 17 emitted from the pre-stage accelerator 16 is transferred to the beam transport system 1.
The light is incident from the injector 15 through 8. The circular accelerator comprises a deflecting magnet 3 for bending the beam trajectory, quadrupole magnets 5 and 7 for converging the beam trajectory and controlling the tune, and a beam.
A hexapole magnet 9 for exciting resonance at the time of beam emission, a hexapole magnet 10 for adjusting chromaticity, a high frequency applying device 24 for applying an electromagnetic noise A for kicking the beam in the circumferential direction, and a lateral direction. The apparatus comprises a high-frequency application device 25 for applying an electromagnetic noise B for kicking a beam, an emission deflector 13 for emitting particles having an increased betatron amplitude, and the like.

The trajectory of the beam incident from the injector 15 is bent by the deflecting magnet 3 in the course of orbit. In the quadrupole magnet, the orbit gradient can be changed by a force proportional to the deviation from the design orbit 1. The quadrupole magnet 5 changes the orbit gradient in a direction converging the beam in the horizontal direction, and the quadrupole magnet 7 changes the beam gradient in the horizontal direction.
It works to change the orbital gradient in the direction of divergence. In the vertical direction, each quadrupole magnet has the opposite convergence
Has a divergent function. By the action of these quadrupole magnets,
The orbit moves around the design trajectory 1 with betatron oscillation. In order to make the beam circulate stably, the tune (betatron frequency per one revolution of the accelerator) is shifted from the resonance point. In particular, it is shifted from the lower-order resonance point of the third or lower order.

In the coordinate system, as shown in FIG. 1, the beam circling direction is s, the horizontal direction is x, and the vertical direction is y. The beam orbits while vibrating around the design orbit 1 which is an orbit. The betatron amplitude differs for each particle constituting the beam, and particles having a large amplitude to small particles are mixed.

By adjusting the quadrupole electromagnet 5 and the quadrupole electromagnet 7,
When the horizontal tune νx or the vertical tune νy approaches an integer + p / q (p, q: an irreducible integer) and the resonance excitation magnet 9 is excited, particles having a betatron amplitude larger than the stability limit are obtained. Is increased by resonance. The resonance at this time is called a q-order resonance. Hereinafter, a case where the beam is taken out from the horizontal direction will be described by taking a third-order resonance as an example.

By adjusting the quadrupole electromagnet 5 and the quadrupole electromagnet 7,
When the horizontal tune νx or the vertical tune νy approaches an integer ± １ ／ and the resonance excitation magnet 9 is excited,
A tertiary resonance is excited by a particle having a large betatron amplitude. FIG. 2 shows the state of (x, dx / ds) for each round at the installation position of the deflector 13 for emission in FIG.

The broken line shown in FIG. 2 indicates the stability limit in the phase space of (x, dx / ds). Particles exceeding the stability limit have a sharp increase in betatron amplitude every round due to resonance. Numerals 1 to 10 attached to particles exceeding the stability limit in FIG. 2 indicate the number of turns. The stability limit becomes smaller as the deviation of the fundamental tune from the resonance point becomes smaller and as the intensity of the multipole magnetic field for generating resonance becomes larger. Reference numeral 20 in FIG. 2 indicates an electrode of the emission deflector 13 in FIG. 1, and particles entering a region sandwiched between the electrodes 20 are emitted outside the circular accelerator.

FIG. 3 is an explanatory view of the principle in the present embodiment . FIG. 3 shows the energy distortion on the horizontal axis and the betatron amplitude on the vertical axis. The illustrated dozens of curves show contour lines where the horizontal tune is constant. The broken line represents the stability limit of the betatron oscillation, and the horizontal tune is at the resonance point on the broken line. In the case of the third order resonance, the fraction of the horizontal tune on this broken line is 1/3 or 2/3.
It is.

The center energy E0 circulates the ring at a certain circulating frequency, and a narrow band noise A having a certain frequency width including a frequency f0 that is an integral multiple of the circulating frequency is applied. The narrow-band noise A is an electromagnetic noise that kicks the charged particle beam in the orbital direction.
The relationship with the deviation Δf is as follows: Δf / f0 = − (α−γ ~ ² ) ΔE / E0 using the momentum compaction factor α. Here, γ is a relativistic factor of the beam energy. The particle beam spreads in an energy region corresponding to the frequency region of the narrow band noise, and has a substantially flat distribution in the energy region. The rate of change due to the energy of the tune is referred to as chromaticity. If the chromaticity is adjusted to a finite value other than zero by adjusting the excitation amount of the chromaticity adjusting hexapole magnet 10 shown in FIG. Keep the tune different. At this time, the beam having the above-mentioned energy width has a tune width.

Here, a narrow band noise B for kicking the beam in the horizontal direction is further applied to the beam. As shown in FIG. 3, the frequency band of the narrow band noise B includes a resonance frequency (dashed line) forming a stability limit of betatron oscillation, and a part of the betatron frequency band in which particles exist. Overlap. If this electromagnetic noise B has a frequency component of (fraction of tune + integer n) × circulation frequency, the same effect is obtained even if the integer n is different. Only a part of the particle group having a narrow energy width is substantially affected by the narrow band noise B,
This portion is selectively diffused in the lateral direction to excite the betatron oscillation, and the betatron amplitude grows and is emitted beyond the stability limit. As a result, an emission beam with a narrow energy width can be obtained. Therefore, using this beam
This enables highly accurate beam utilization.

FIG. 4 shows an example of an operation method in the emission process.
This will be described with reference to FIG. First, in step 1 of FIG. 4, the application of energy to the beam from the high-frequency acceleration cavity 8 is stopped.
As a result, the beam does not form a bunch and becomes a continuous beam.

Next, in step 2, the electromagnetic noise applying device 24 provided in the circular accelerator of FIG. 1 applies narrow-band electromagnetic noise A that kicks the beam in the orbital direction. In this case, as described above, the narrow-band electromagnetic noise A includes a frequency that is an integral multiple of the circulating frequency. Although the basic tune has a certain width based on the energy width formed by the electromagnetic noise A, it is necessary to narrow the frequency band of the electromagnetic noise so that it does not include the third resonance point. By applying the narrow-band electromagnetic noise A, the beam is diffused in the energy space and has a uniform distribution with an energy width corresponding to the frequency width of the electromagnetic noise A. This electromagnetic noise A is continuously applied until beam emission is completed.

Next, in step 3, the excitation amount of the quadrupole magnets 5 and 7 is adjusted, and the basic tune in the horizontal direction is set near the tertiary resonance point. Then, in step 4, the hexapole magnet 9 for resonance excitation and the hexapole magnet 10 for chromaticity adjustment are excited. The excitation amount of the hexapole magnet 9 is set so that almost all particles including particles having a large betatron amplitude fall within the stability limit. At this time, the trajectory of the beam in the phase space at the position of the output deflector 13 has a triangular shape as shown in FIG.

In the next step 5, a narrow-band electromagnetic noise B for kicking the beam in the horizontal direction is applied by the high-frequency application device 25 provided in the circular accelerator of FIG. in this case,
The narrow-band electromagnetic noise B has a frequency band ranging from a frequency of (integer + fraction of tune F) × circulation frequency to a frequency of (integer + fraction of resonance tune) × circulation frequency. Here, the tune F refers to a tune of a portion close to the resonance point among the basic tunes having a width. By applying the narrow-band electromagnetic noise B to the beam, a part of the beam having a narrow energy width is diffused in the lateral direction, the betatron amplitude grows, and the stability limit of the betatron oscillation is increased. Are emitted from the emission deflector 13. This is as shown in FIG. In this process, the stability limit of betatron oscillation is kept constant over time, so that the exit angle of the exit beam is always kept constant. By the time the narrow band electromagnetic noise A kicks in the lateral direction, the energy width of the particle group is reduced by the narrow band electromagnetic noise A that is kicked in the circulating direction until the particle group whose betatron oscillation is selectively excited by the narrow band electromagnetic noise B is emitted. It is necessary to adjust the intensity of the narrow-band electromagnetic noise A kicking in the circling direction over the entire frequency band or partially so that does not increase significantly.

By the above operation, it is possible to obtain an emission beam having a constant emission angle over time and a narrow energy width. This makes it possible to perform high-precision experiments and
Can be controlled. In the above operation, the order of steps 2, 3, and 4 in FIG. 4 does not necessarily have to be as described above, and the order may be interchanged with each other or may be performed in parallel.

Another embodiment of the operation method in the process of emitting light will be described with reference to FIG. Step 1 to Step 4 in FIG.
Are the same as Steps 1 to 4 in FIG. In step 5 of the present embodiment, the application of the electromagnetic noise A is stopped after the flattening of the energy distribution by the electromagnetic noise A is completed. Then, in the next step 6, a narrow band electromagnetic noise B for kicking the beam in the horizontal direction is applied. In this case, the frequency band of the narrow-band electromagnetic noise B is set so as not to include (fraction of tune + integer) × circulation frequency so as not to affect the beam effectively. At this time, in the embodiment of FIG. 4, the basic tune is kept constant over time, but in this embodiment, the basic amount in the horizontal direction is controlled by controlling the excitation amount of the quadrupole magnets 5, 7. The tune is gradually approached to the third resonance point. Since the frequency band of the narrow-band electromagnetic noise B exists in the vicinity of the resonance point across the third-order resonance point, the beam gradually approaches the frequency band of the narrow-band electromagnetic noise B. Part of the beam entering the frequency band of the narrow band electromagnetic noise B begins to be effectively affected by the narrow band electromagnetic noise B, and is quickly diffused in the lateral direction and emitted. This is as shown in FIG. In this way, the particles enter the frequency band of the narrow-band electromagnetic noise B one after another, and are emitted as if the beam were cut out little by little. Since the stability limit of betatron oscillation is kept substantially constant in time for the emitted beam, the emission angle of the emitted beam is always kept constant in this embodiment as well. The betatron oscillation is caused by the narrow band electromagnetic noise B kicking in the lateral direction. By the operation of bringing the betatron oscillation frequency of the beam closer to the resonance point by the time the selectively excited particles are emitted, It is necessary to adjust the speed at which the betatron frequency of the beam approaches the resonance point so that the energy width of the particle group does not increase significantly.

In this embodiment, in addition to the characteristic that the emission angle is constant in time and the energy width is narrow, an emission beam in which the emission current is constant in time can be obtained. This
High-precision control in experiments and processing using beams
Becomes In the above operation, steps 2 and 5 in FIG.
The order of 3, 4, and 5 is not necessarily required to be as described above, and the order may be interchanged with each other, and those that can be performed in parallel may be performed in parallel.

[0031]

According to the present invention, a beam having a narrow energy width is provided.
It can be emitted beam at the emission angle constant and Do Ri Precision
Of beam processing, that Do not allow such experiments.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a circular accelerator including a beam emitting device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the principle of an embodiment of the present invention.

FIG. 3 is a diagram illustrating the principle of the embodiment of the present invention.

FIG. 4 is a flowchart of an operation procedure at the time of beam emission according to the first embodiment.

FIG. 5 is a flowchart of an operation procedure at the time of beam emission according to the second embodiment.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaji Nishi 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Energy Research Laboratory, Hitachi, Ltd. (56) References JP-A-5-198397 (JP, A) JP-A-5-258900 (JP, A) JP-A-5-62799 (JP, A) JP-A-6-36894 (JP, A) JP-A-7-14699 (JP, A) (58) Fields investigated ( Int.Cl. ⁶ , DB name) H05H 7/00-15/00

Claims (5)

(57) [Claims] 1. A magnet for orbiting a charged particle beam, and an emission deflector for emitting a betatron oscillation of particles just before emission of a group of particles forming the orbiting charged particle beam and emitting the resonance, In a circular accelerator equipped with
Supplying particles to an energy band, and a particle data of the energy band;
Means for selectively growing and emitting only the tron oscillation
And a narrow band that kicks the particle in the transverse direction to the orbital direction
First electromagnetic wave noise applying means and
And second application means for narrow-band electromagnetic noise
A circular accelerator . 2. The method according to claim 1, wherein the particles are laterally kicked.
Betatron oscillation is the frequency band of narrow band electromagnetic noise
Resonance frequency + integer n × circulation frequency (n = 0, ± 1, ±
2, ... )), and contains a frequency component
The frequency band of narrow-band electromagnetic noise that kicks in the clockwise direction is an integer
mx any one of the rounding frequencies (m = 1, 2, ... )
A circular accelerator characterized by including a wave number component . 3. A kick in a lateral direction according to claim 1.
Selective betatron oscillation by narrow band electromagnetic noise
Kick in the circling direction until the excited particles are emitted
Energy band of the particle swarm due to narrow band electromagnetic noise
Band that kicks in the circumferential direction so that does not increase significantly
Reduce the intensity of electromagnetic noise over the entire frequency band or partially
Circular acceleration characterized by comprising means for reducing
Bowl . 4. Particles forming a charged particle beam orbiting.
Betatron oscillation of particles in the group immediately before emission is in resonance
Required energy band in a circular accelerator
Narrow-Band Electromagnetic Kicking Particles Laterally with Orbit
Noise and a narrow band electromagnetic noise that kicks the particle
And the betatron oscillation of the particles in the energy band
Characterized by selectively growing and emitting only
How to operate the circular accelerator . 5. The kick according to claim 4, wherein the kick is performed in a lateral direction.
Selective betatron oscillation by narrow band electromagnetic noise
Kick in the circling direction until the excited particles are emitted
Energy band of the particle swarm due to narrow band electromagnetic noise
Band that kicks in the circumferential direction so that does not increase significantly
Reduce the intensity of electromagnetic noise over the entire frequency band or partially
A method for operating a circular accelerator, characterized in that it is made smaller .