JP2000164400A - Beam incident method to storage ring and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a conventional incident method without caring about the change of the peripheral length at the time of incidence even for a small SR ring just like for a normal large ring. SOLUTION: When a storage beam is fed while the perturbation magnetic field is applied to part of a circulating closed part 10 to displace an incident path 14, frequency modulation is applied to the high frequency for accelerating a circulating beam at the same timing and wave-form as the excitation of the said perturbation magnetic field to prevent the occurrence of a phase drift caused by the peripheral length difference between the closed path 10 and the incident path 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for injecting a beam into a storage ring, and more particularly, to a small-sized device having a perimeter L of 20 m or less, such as an industrial electron storage ring (hereinafter referred to as an SR ring). A beam applied to the storage ring when a beam is incident upon applying a perturbation magnetic field to a part of a closed orbit in which the stored beam orbits, which is suitable for use in an SR ring, is displaced to an incident orbit. Related to the launch and the device.

[0002]

2. Description of the Related Art In a synchrotron, as shown in FIG.
Main magnet 20 for forming orbits of orbiting electrons, quadrupole magnet for preventing divergence of electron beam (referred to as Q magnet)
22 and a closed orbit 1 composed of a high-frequency accelerating cavity (referred to as an RF cavity) 24 for accelerating orbiting electrons
On a closed trajectory called “0”, the beam that has been incident, that is, is being accumulated, orbits as an electron bunch (a group of electrons) 12.

In FIG. 1, reference numeral 26 denotes an RF power supply for supplying high-frequency power to the RF cavity 24, and reference numeral 28 denotes the RF power supply.
A radio frequency (RF) standard signal generator for supplying a standard signal of a frequency corresponding to the frequency of the electrons to the power source 26;
0 is a pertabeta (also called a kicker) for applying a perturbation magnetic field at the time of incidence, and 32 is the pertabeta 30
Is a reference pulse generator for operating the pertabeta power supply 32 only at a required timing, and 40 is a pulse electromagnet for injecting a beam from outside the ring into the ring. Inflector.

In such a synchrotron, when the resonance incidence method for generating an incident trajectory without affecting the electron beam being accumulated is not used, a part of the trajectory is pulsed by the perta beta 30 at the time of incidence. It is necessary to displace the closed trajectory 10 to the incident trajectory 14 by applying a magnetic field. That is, the closed orbit 10 is distorted so as to be in contact with the inflector 40.

[0005] This means that the orbit is changed to the incident orbit 14 so that the accumulated beam that has already entered and is orbiting on the closed orbit 10 passes near the inflector 40. After this displacement at the position of the inflector 40 has turned from a maximum to a decrease, as shown in FIG.
That is, while the incident trajectory 14 is closest to the inflector 40 and is moving away, the next beam is newly incident. FIG. 2 shows the relationship between the beam incidence and the timing of the excitation of the perta beta. Since this perturbation magnetic field is applied in a pulsed manner, the beam returns to its original closed orbit as the perturbation magnetic field decreases. It is important that the perturbation field is dynamically decreasing during the incidence, otherwise the incident beam will collide with the inflector 40 and be lost in a few rounds. Since the distortion of the closed orbit decreases as the perturbation magnetic field decreases, the incident beam moves away from the inflector 40 with each orbit, and continues to orbit without colliding with the inflector 40. Due to the disappearance of the perturbation magnetic field, the newly-entered beam orbits along the closed orbit 10 together with the already-injected accumulated beam. At this time, the size of the newly-injected beam is large in the horizontal direction, and the partition When the 30 is excited, the inflector 40
Will collide with The beam size of the newly incident electron beam decreases with time due to the radiation attenuation effect.
After a certain period of time (referred to as the radiation decay time), it becomes the same size as the stored beam and becomes completely integrated. Thereafter, by repeating the above operation, the incident beam can be accumulated on the closed orbit 10.

In the conventional incidence method, the reference pulse generator 3
4 and the part beta power supply 32 are linked, and the RF cavity 2
4 is independent of the system that supplies RF power.
Power was continuously supplied to the RF cavity 24 and had nothing to do with the timing of the beam incidence. Although not shown, a timing signal is also supplied to the power supply of the inflector 40 in the same manner as the part beta power supply 32.

A conventional SR ring has a circumference L of 1 when it is large.
Km and more than 50m even for small ones.
Even if the closed orbit 10 is displaced to the incident orbit 14 by the perturbation magnetic field of 0, the difference ΔL between the circumference Li of the incident orbit and the circumference Ls of the orbit does not cause any practical problem.

[0008]

However, in the case of a small SR ring, the circumference L is reduced to about 10 m, and this difference ΔL (about several cm per circumference) depends on the condition for synchronizing the beam and the high frequency for acceleration. The impact on the environment is no longer negligible. In other words, there is a problem that even if the difference is slight in one round, errors are accumulated during repeated rounds, resulting in a non-negligible difference.

As one means for avoiding this problem,
There is a method of adjusting the beam rotation condition. In particular,
Change the parameters of the beam convergence system (such as the strength of the Q magnet). The strength of the convergence system determines the operating point (operation point) of the SR ring, and is usually determined in advance at the time of design, and this change is not desirable. However, as a result of controlling the lateral vibration of the beam (later horizontal betatron vibration described later) by adjusting the convergence condition,
In general, even if ΔL is a problem at the operating point of the design value, an operating point at which ΔL does not matter can be found somewhere else. However, it often involves undesired effects such as poor incidence efficiency. Conventionally, the operating point at which the light can be incident has been empirically searched for by trial and error.

The present invention has been made to solve the above-mentioned problems without any limitation as described above, and it is intended that a significant difference be produced in the circumference between the incident orbit and the accumulated orbit. However, it is an object to prevent inconvenience.

[0011]

SUMMARY OF THE INVENTION The present invention provides a method for accelerating a circulating beam when applying a perturbation magnetic field to a part of a closed orbit during which a stored beam is circulating and displacing the beam into an incident trajectory. This problem is solved by applying frequency modulation to a high frequency at least in synchronization with the excitation of the perturbation magnetic field so as to prevent a phase shift due to a difference in circumference between the closed orbit and the incident orbit.

Further, the frequency modulation is applied in synchronization with the excitation and the timing and the waveform of the perturbation magnetic field.

The present invention also comprises a main magnet for forming the orbit of the orbiting beam, a Q magnet for preventing divergence of the beam, and a high-frequency accelerating cavity for accelerating the orbiting beam, A perturbator applies a perturbation magnetic field to a part of the closed orbit during which the accumulated beam is orbiting, and displaces the part of the closed orbit to the incident orbit in contact with the inflector to put the incident beam on the incident orbit and injects the beam. High frequency standard signal generating means for generating a standard signal having a frequency in which frequency modulation is added to a frequency corresponding to the circulating frequency of the beam, and a high frequency standard signal generating means A high-frequency power supply for supplying high-frequency power subjected to frequency modulation at least in time with excitation of a perturbation magnetic field to the high-frequency acceleration cavity according to a standard signal. With the door, so as not to cause a phase shift due to the circumferential length difference of the incident raceway and closed trajectory is also obtained by solving the above problems.

Further, there is provided a waveform generating means for generating a waveform similar to the waveform applied to the part beta, wherein a frequency corresponding to the circulating frequency of the beam is adjusted to an amount corresponding to the similar waveform generated by the waveform generating means. , And frequency modulation that matches the timing and waveform with the excitation of the perturbation magnetic field.

In a synchrotron, the principle of phase stability works as a basic principle of stably circulating a beam.
That is, standard energy (referred to as reference energy) E0
The phase of the RF electric field that a particle (here, an electron) has at the center of the RF cavity 24 is always constant, and this phase is called a synchronous phase φs. The group of electrons is scattered in a certain energy range ± ΔE around the reference energy E0, and these electrons oscillate around the synchronous phase φs as shown in FIG. 3 (synchrotron oscillation). The horizontal axis indicates the phase φ (or time t), and the vertical axis indicates the electron energy ΔE.
/ E, this vibration can be represented by a rotational motion as shown in FIG. The magnitude of this vibration is proportional to ΔE,
As long as it is in a region (referred to as an RF bucket) surrounded by a closed curve (referred to as a separatrix) B shown by a solid line in FIG. 4, it continues to exist stably and is not lost as a beam. Conversely, for some reason (external factors)
If a situation occurs in which electrons jump out of this bucket, the electrons will eventually be lost as the circuit goes around.

The theory of synchrotron oscillation based on the principle of phase stability is established when the circumferential length L is constant. If the orbital length changes by ΔL, the wavelength of the high-frequency wave becomes λ.
The phase (timing) at which the beam encounters the high-frequency electric field is shifted by Δφ = 2π (ΔL / λ). This is because the RF bucket B in FIG.
At a certain moment, as shown by the broken line C, which corresponds to a lateral shift of Δφ, and as can be seen from the figure, at this time, electrons undergoing synchrotron oscillation near the outer periphery of the RF bucket B, that is, energy variation ΔE Electrons jump out of the bucket B. In this way, electrons are continually lost from electrons having large energy variations.

In a small industrial ring, this phenomenon is likely to occur at the time of incidence, and it is often difficult to enter a beam according to a normal incidence method. That is, when the orbital length changes as in the case of beam incidence, the relationship between the electron and the phase of the high frequency shifts with each orbit. In the figure, this corresponds to a shift in the separatrix, and it appears to the electrons that the RF bucket has moved to the left and right.
This shift amount accumulates while the part beta is excited at the time of incidence (in the case of a certain small SR ring, about 150
Degree), and as a result, a part or most of the beam moves outside the RF bucket. This phenomenon is temporary, and the excitation of the part beta is terminated, the incident trajectory returns to the accumulation trajectory, and the relationship between the electrons and the RF bucket becomes stable, but it does not restore the original state. Electrons that have jumped out beyond the boundary of the RF bucket, that is, beyond the separatrix, can no longer continue stable oscillation and are dissipated.

Therefore, in the present invention, in order to overcome the phase shift caused by the change of the circumference, frequency modulation is applied to a high frequency at the time of incidence, for example, the frequency is changed from f → f + Δf,
By changing the wavelength from λ to λ-Δλ, the influence of the change ΔL in the circumference is canceled. Specifically, the phase advance dφ per rotation is adjusted so as to be an integral multiple of 2π.
At this time, dφ = 2π (L−ΔL) / (λ−Δλ) = 2π (L /
λ) = 2nπ, so the high frequency may be adjusted so that Δλ = ΔL / n.

At this time, it is necessary to pay attention to the height of the RF bucket. If the RF bucket is reduced by applying frequency modulation, as can be seen from FIG. 4, of the electrons stably existing in the bucket, ΔE
Spill out sequentially from the one with the largest / E. here,
The height of the RF bucket (defined by the maximum ΔE / E that electrons present in the bucket can have) is an amount determined by the voltage of the RF cavity (V _{RF in} FIG. 3). In general, the RF cavity of an accelerator has a sharp resonance characteristic with respect to frequency, and a small Δf changes the voltage V _RF in the cavity greatly (usually decreases).
I do.

There are two ways to avoid this inconvenience. One is a method in which the RF cavity is previously detuned (detuned) and provided for incidence. The RF cavity that is sensitive to Δf due to the sharp resonance characteristic during tuning has a lower sensitivity to Δf in the detuned state.
The reduction of the F bucket can be reduced to a level that does not cause a problem. The amount of detune needed may be determined on a case-by-case basis. The second method is to use both frequency modulation and amplitude modulation. Now with the RF power constant,
Since the frequency dependence of _VRF near the tuning point can be determined from the resonance characteristics of the RF cavity incorporated in the SR ring, the amount of change in _VRF depending on the frequency shift Δf from the tuning point can be calculated. Thus, the amount of RF power correction required to cause the predetermined amplitude modulation is determined. Note that it is of course possible to apply this amplitude modulation to the former method and more precisely control the height of the RF bucket. This can be an effective means in some cases, such as when trying to maximize the electron beam incidence efficiency.

There are several points to be considered when actually applying amplitude modulation properly. For example, in practical use, the RF amplitude device also has a frequency characteristic, and it is necessary to take this into consideration. Since the RF cavity has a high Q value, a certain time delay occurs with a time constant depending on the Q value before a voltage corresponding to the injected excitation power is generated. Standard R for SR ring
In the F cavity, this time constant is several tens of microseconds, which is much longer than the incident time of 1 microsecond discussed here. Therefore, it is necessary to take measures to anticipate this time delay.

In practice, it is preferable to consider only the frequency modulation, and the amplitude modulation is worth considering in the research and development of accelerators.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In this embodiment, as shown in FIG. 1, a main magnet 20, a Q magnet 22, an RF cavity 24, an RF power source 26, an RF standard signal generator 28, a perta beta 30, a perta beta power source 32, a reference pulse In the small SR ring including the generator 34 and the inflector 40, an arbitrary waveform generator 50 that creates a waveform similar to the waveform applied to the pertabeta 30 is further provided, and a frequency corresponding to the orbital frequency of electrons is provided. The standard signal generator 28 generates a standard signal having a frequency with an amount of frequency modulation corresponding to the similar waveform generated by the arbitrary waveform generator 50, and perturbs the RF cavity 24 from the RF power supply 26. Frequency modulated RF that matches magnetic field excitation with timing signal and waveform
Electric power is supplied so that a phase shift due to a difference in circumference between the closed orbit and the incident orbit does not occur.

The main magnet 20 is also called a deflection magnet,
The path of the electrons is deflected by a dipole magnetic field so that the electrons orbit around a certain orbit. The sum of the deflection angles per rotation is 360 °, and in the case of a small ring as shown in the figure, it is often constituted by two units. In this case, the deflection angle per unit is 180 °. The larger the size, the more magnets are used, and the smaller the deflection angle per unit.

The Q magnet 22 is a quadrupole magnet having a converging action so that the electron beam does not diverge.
Unlike light, it cannot exert a convergence effect in the same horizontal and vertical directions at the same time, but has a divergent effect in either one direction. In the figure, each linear portion between two main magnets 20 is
The Q magnets 22 having a converging action in the horizontal direction are arranged for each table. In this case, the vertical convergence force is
It is created by the internal magnetic field.

The RF cavity 24 resonates at a specific frequency, that is, has a structure capable of generating a high voltage with a small power, and supplies energy to the orbiting electrons. As shown in the figure, one is usually used for a small ring, but usually several are installed for a large ring. The frequency of the high frequency used is an integral multiple (7 times in the figure) of the orbital frequency of the electron.
Electronic bunches 12 corresponding to the number are circling the ring.

The inflector 40 is a pulse electromagnet for placing an incident beam on the incident trajectory 14, and is placed in contact with a straight portion of the ring. Electrons use this inflector 40
After being deflected by, it enters the ring.

The pertabeta 30 is a pulse electromagnet incorporated in a ring and used at the time of incidence. That is, the orbit 10 of the stored beam, which is called a closed orbit, is distorted by applying a pulsed perturbation, and the distorted orbit becomes the incident orbit 14.

Here, the closed trajectory refers to the trajectory around which the already-injected electrons orbit. Electrons circulate while oscillating in the horizontal and vertical directions and the traveling direction in a plane perpendicular to the traveling direction of the beam, and are called betatron oscillation and synchrotron oscillation, respectively. . Closed orbit is the concept for betatron oscillations, and is named because the beam returns to the same point again (with a single stroke) in a few rounds. The problem at the time of incidence is the horizontal movement. Unless the trajectory of the oscillation is discussed, there is no difference from the concept of the accumulated orbit in which the incident beam keeps orbiting stably.

The incident trajectory 14 is a trajectory distorted by applying a perturbation magnetic field to the closed trajectory by the perta beta 30, and corresponds to a course in which a beam enters upon incidence. That is, it is a trajectory that is temporarily generated at the time of incidence. The distortion is performed here in order to make the accumulation trajectory approach the inflector 40 which is a pulse electromagnet for incidence.

In the present embodiment, even if a significant difference occurs in the circumference between the incident trajectory 14 and the storage trajectory 10, the reference pulse generator 34 and the standard signal generator 28
0, and the frequency modulation is applied to the high frequency, so that the phase shift does not matter.

Hereinafter, the operation of the present embodiment will be described with reference to FIG.

First, the reference pulse generator 34 shown in FIG.
As shown in (a), a reference pulse which is a signal for determining the timing of incidence is generated.

Upon receiving the reference signal output from the reference pulse generator 34, the pertabeta power supply 32 excites the pertabeta 30 with a half-sine wave waveform. Accordingly, as shown in FIG. 2B, the perta beta 30 generates a perturbation magnetic field having a half-sine wave shape.

At the same time, the arbitrary waveform generator 50
As shown in (c), a waveform similar to a half sine wave generated by the part beta power supply 32 is created and input to the standard signal generator 28.

In the RF standard signal generator 28, FIG.
As shown in (1), a standard signal of a frequency obtained by adding a frequency modulation Δf of an amount corresponding to a similar waveform generated by the arbitrary waveform generator 50 to a frequency corresponding to the circulating frequency of electrons is transmitted to the RF power supply 26.

The storage orbit is distorted in accordance with the amount of excitation of the part beta 30, and the orbital length of the corresponding electron changes as shown in FIG. 2 (e) (when ΔL <0). Accordingly, the displacement of the trajectory becomes maximum at the peak of the half-sine wave, and the beam can be incident at the trailing edge of the pulse thereafter. In this embodiment, at this time, there is no problem because the phase difference corresponding to the difference in the orbital length is canceled by the RF cavity.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An SR ring is constructed so that a constant relation L = nλ is established between a circumference L and a high frequency f. n (called the harmonic number) is equal to the number of electron bunches. In one example, the circumference is L = 11 m because the design is made with f = 190 MHz (therefore, λ = 1.6 m) and n = 7. According to the simulation,
For L = 11 m, the amount of change in the orbit is maximum ΔL = −
Since it is about 5 cm, the amount of phase change when frequency modulation is not applied is Δφ = 11 °. This means that the electrons lag by 11 ° with respect to the high frequency phase, or that the phase of the RF bucket advances by 11 ° with respect to the electrons. However, this is the maximum amount of phase change per rotation, and in fact, the perturbation magnetic field of the perta beta is excited by a half sine wave having a period of 2 μs (in other words, a half sine wave having a full width of 1 μs, and Since the beam makes around 27 rounds), the amount of this phase change by accumulation is as high as 150 °. In this case, the correction amount of the high frequency is Δλ / λ = Δλ / nλ = −0.0045, that is, the frequency modulation with the peak value of 0.45% (Δf = 0.85)
MHz) may be applied as a half sine wave.

FIGS. 5 to 7 show the SR generated by the electron beam.
Light is observed at the port of the main magnet. Since a streak camera is used for the measurement, the horizontal axis indicates the beam position in the horizontal direction, and the vertical axis indicates the time transition from top to bottom.

FIG. 5 shows a case where frequency modulation is not applied to a high frequency. After the beam is swung to the right and the orbit is displaced at the moment when the part beta is excited, the orbital meander of the orbit due to the synchrotron oscillation also occurs. Is not attenuated, and the beam oscillates right and left while oscillating. Also, since the SR light signal is blurred in the time axis direction from top to bottom,
As time elapses, the electrons are disassembled from the bunch state, change from the bunched state to a discrete state, and fall out of the RF bucket.

FIGS. 6 and 7 show how the behavior of the beam differs depending on the presence or absence of frequency modulation, based on observation results of SR light by a streak camera for a longer time than in FIG. Fig. 6 without applying frequency modulation
(However, when the phase shift is not so severe as to cause most of the electrons to spill out as shown in FIG. 5), during the beta excitation, the electron bunch is swung from the center of the RF bucket to the periphery and the synchrotron oscillation occurs. Is excited, and it can be seen that the oscillation of the beam due to this is maintained. This is because, due to the excitation of the part beta, a difference occurs in the orbital length at the time of beam incidence, and the phase of the beam and the high frequency shift. On the other hand, in FIG. 7 to which the frequency modulation according to the present invention is applied, synchrotron oscillation is hardly observed after the excitation of the part beta, and no beam oscillation occurs.

In the above description, the waveform (excitation curve of the perturbation magnetic field) applied to the part beta is assumed to be a half sine wave, and a similar waveform is generated by the arbitrary waveform generator 50 capable of generating an arbitrary waveform. Although it has been created, the shape of the excitation curve and a method of generating a similar waveform are not limited thereto, and for example, a sine wave generator may be used, or the
It is also possible to generate a similar waveform using the output of No. 2 or to use a non-similar waveform even if there is a slight phase shift.

[0044]

According to the present invention, it is possible to use a conventional incident method in a small SR ring as in the case of an ordinary large ring without worrying about a change in the circumference at the time of incidence. it can.

[Brief description of the drawings]

FIG. 1 is a plan view showing an entire configuration of an embodiment of the present invention, including a partial block diagram.

FIG. 2 is a diagram showing an example of a signal waveform of each part.

FIG. 3 is a diagram showing the relationship between high frequency and synchrotron oscillation for explaining the principle of synchrotron oscillation and phase stability.

FIG. 4 is a diagram showing a relationship between an RF bucket and synchrotron oscillation.

FIG. 5 is a diagram showing a streak waveform in a state where electrons are disassembled from a bunch state and spilled from an RF bucket in the related art.

FIG. 6 is a diagram showing a streak waveform in a state in which beam oscillation due to synchrotron oscillation is sustained in a conventional technique without frequency modulation.

FIG. 7 is a diagram showing a streak waveform in a state where beam fluctuation is eliminated when the frequency modulation according to the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Closed orbit 12 ... Electron bunch 14 ... Injection orbit 20 ... Main magnet 22 ... Q magnet 24 ... High frequency accelerating cavity (RF cavity) 28 ... High frequency (RF) standard signal generator 26 ... High frequency power supply 30 ... Parter beta 32 ... Parter beta power supply 34: Reference pulse generator 40: Inflector 50: Arbitrary waveform generator

Claims (4)

[Claims] 1. A method according to claim 1, wherein a perturbation magnetic field is applied to a part of the closed orbit during which the accumulated beam is orbiting, and when the beam is displaced to the incident orbit and the beam is incident, the perturbation magnetic field is excited to a high frequency to accelerate the orbiting beam. A beam injection method to a storage ring, wherein at least the timing is adjusted to apply frequency modulation so as to prevent a phase shift due to a circumferential length difference between a closed orbit and an incident orbit. 2. A method according to claim 1, wherein said frequency modulation is applied in synchronization with the timing and waveform of excitation of said oscillating magnetic field. 3. A circulating beam is formed by using a main magnet for forming a trajectory of the circulating beam, a Q magnet for preventing divergence of the beam, and a high-frequency accelerating cavity for accelerating the circulating beam. A storage ring for applying a perturbation magnetic field to a part of the inner closed orbit by a pertabeta and displacing a part of the closed orbit to the incident orbit in contact with the inflector to put the incident beam on the incident orbit. A high-frequency standard signal generating means for generating a standard signal having a frequency in which frequency modulation is added to a frequency corresponding to the circulating frequency of the beam; and a standard signal supplied from the high-frequency standard signal generating means. A high-frequency power supply that supplies high-frequency power that has been subjected to frequency modulation at least in timing with excitation of a perturbation magnetic field, to the high-frequency acceleration cavity, Beam injection device to the storage ring, characterized in that so as not to cause a phase shift due to the circumferential length difference of the track and the incident raceway. 4. The apparatus according to claim 3, further comprising a waveform generating means for generating a waveform similar to the waveform applied to said part beta, wherein said waveform generating means generates a waveform corresponding to the circulating frequency of the beam. A beam injection device for a storage ring, characterized in that an amount corresponding to a similar waveform is subjected to frequency modulation that matches the timing and waveform of excitation of a perturbation magnetic field.