JP3302852B2 - Accelerator, beam emission control method thereof, and beam emission control device - 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 such as a synchrotron, and more particularly to a beam emission control system called "slow extraction".

[0002]

2. Description of the Related Art It is important in the operation of an accelerator such as a synchrotron to generate a magnetic field so that particles do not escape from a closed orbit while moving around the orbit. This magnetic field is a combination of magnetic fields generated by a bending electromagnet, a focusing quadrupole electromagnet, and a diverging quadrupole electromagnet, called a main electromagnet.

When a beam accelerated by a synchrotron is emitted, usually, a closed orbit is temporarily changed by exciting an electromagnet called a kicker or a bump in a pulsed manner, and is taken out of the synchrotron at once. Send to accelerator etc.
The pulse width of the output beam at this time is a size measured in microseconds.

On the other hand, for therapeutic use, high-energy physics experiments, biological experiments, and the like, it is necessary to increase the pulse width of the emitted beam from several hundred milliseconds to several seconds or more. This is done by a beam emission control scheme called "slow extraction".

Various beam emission control methods have been tried in the past. A typical method is a method called a resonance emission method, which utilizes the fact that the betatron oscillation period of a beam particle moving around a closed orbit is deeply related to the stable orbit of the beam.

[0006] A thing in which the betatron oscillation period is normalized by one round of the orbit is called a tune. When the tune value is a multiple of a specific resonance value (for example, 1/2 or 1/3), the beam has a small stable area and the beam is likely to be out of orbit. If the tune value is a multiple of another integer ratio (1/4 or 1/5 or less), the beam stability area is larger and overall stable.

The tune value can be adjusted by changing the tracking ratio that the magnetic field (and thus the current) of the focusing quadrupole magnet maintains with the magnetic field (or current) of the bending electromagnet. That is, a stable tune value (for example, a multiple of 1/4) is maintained during the period from the incidence of the beam to the acceleration.
The magnetic field of the focusing quadrupole electromagnet is changed to an unstable tune value (for example, a multiple of 1/3) in the beam emission section. As a result, the unstable region of the beam expands, and the beam in the unstable region is extracted outside the synchrotron via the electrode provided in the beam extraction unit.

Documents describing such a synchrotron beam control method include "Parity Physics Course" Accelerator Science "" by Toru Kamei and Motohiro Kihara (Maruzen Co., Ltd., September 1993).

[0009]

However, in the conventional beam extraction control method called "slow extraction", a small change in the magnetic field of the focusing quadrupole electromagnet controls the unstable region of the beam. Very sensitive to ripple,
As a result, the output beam often becomes an unstable pulse synchronized with the commercial frequency.

For this reason, in a beam irradiation apparatus that takes in the beam emitted from the accelerator and performs a treatment or a test, the operation cycle of scanning the irradiation range is close to the commercial frequency to several times that of the commercial frequency. There is a risk of being biased to a specific location, and there is a problem of safety of the irradiated object (patient) for medical use, and a problem of accuracy for test use.

In order to avoid such a phenomenon, the residual ripple of the exciting current is set to, for example, 10 to ⁷ or less, or feedback control for suppressing the residual ripple of the exciting current by detecting the ripple on the output beam is performed. Measures such as taking measures are conceivable. However, realization is difficult. Even if realization is possible, a significant increase in apparatus cost is unavoidable and cannot be used for general purposes.

An object of the present invention is to solve the above-mentioned problems of the prior art by a simple method and to provide a stable beam emission control method and apparatus which are not affected by a power supply ripple.

An object of the present invention is to provide an accelerator capable of performing a safe beam irradiation without irradiating an irradiation beam taken out of the accelerator to a specific location.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide an accelerator, such as a synchrotron, which includes a bending magnet, a focusing magnet, and a diverging magnet, and which accelerates and emits a low-speed incident beam at high speed. In the beam emission control method referred to as “beam emission control method”, the magnetic field of the focusing electromagnet is alternately perturbed between a stable region where the beam is unlikely to emerge and a stable region where the beam is likely to emerge during the beam extraction period (emission period). Can be achieved.

The perturbation of the magnetic field is performed by superimposing an exciting current of the focusing electromagnet with a high frequency that changes at a firing cycle determined by the number of phases of a converter constituting the electromagnet power supply or a cycle of a multiple thereof during a beam extraction period. It is realized by doing.

Further, the present invention is characterized in that the operation cycle of the beam irradiation apparatus is taken in, and the perturbation cycle is set so as to be asynchronous with the operation cycle.

[0017]

According to the present invention, the exciting current of the focusing quadrupole electromagnet in the beam emitting section is perturbed by the perturbation means at a frequency sufficiently higher than the power supply frequency (normally, commercial frequency) of the exciting current. In response to this, the value of the tune fluctuates, and the unstable region of the beam becomes wider or narrower, so that the output beam becomes a pulse having a frequency significantly higher than the power supply frequency, for example, a thin pulse having a period of about 1 millisecond. As a result, the influence of the ripple of the excitation power supply can be avoided, and the output beam can be stably extracted.

Further, since the excitation current is perturbed by superimposing a high frequency of about 0.01 to 0.1% of the amplitude value of the excitation current, the configuration is easy and there is no obstacle to cost. further,
The ripple content of the power supply can be made higher than before, so that a cheaper power supply can be used.

Further, since the perturbation frequency is set by the perturbation frequency setting means asynchronously with the operating frequency (usually the commercial frequency) of the beam irradiation device, the bias of the irradiation beam distribution can be avoided, and the safety and reliability are high. An irradiation device can be provided.

[0020]

An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a configuration diagram of the entire accelerator to which the present invention is applied. This accelerator is a synchrotron that operates cyclically and includes a main electromagnet that generates a magnetic field for forming a closed orbit, an input electrode and an output electrode (not shown), and the like. The main electromagnet includes a bending electromagnet 1B and a focusing electromagnet 1Q.
f and a divergent electromagnet 1Qd, the latter two being quadrupole electromagnets.

Each electromagnet 1 has a power source 2B, 2Q
f, 2Qd. The firing angle control and feedback control (ACR and AVR) of each power supply 2 are performed by the respective converter control devices 5B, 5Qf, and 5Qd. The converter control device 5 takes in the command value from the control device 6 and the control result of the excitation circuit, and controls the firing angle according to the deviation.

The control devices 6B, 6Qf, and 6Qd determine the control command value of each converter control device 5 and repeatedly control the operation of the synchrotron. Note that the converter controls 5B, 5Q
f, 5Qd have the same basic configuration. Control devices 6B, 6
Qf and 6Qd are the same except for the current pattern processing means 63 added according to the present invention.

FIG. 1 is a configuration diagram of a power supply control device for a focusing electromagnet according to an embodiment of the present invention. A plurality of focusing electromagnets 1Qf are connected in series (hereinafter abbreviated as electromagnets 1Qf),
It is excited by the power supply 2. The power supply 2 is a voltage source such as a thyristor converter or a GTO converter. The output voltage Vf of the power supply 2 is measured by the voltage divider 3 and the output current If is measured by the DCCT 4, and becomes a feedback value to the converter control device 5. AVR for controlling the exciting current I of the electromagnet 1
An automatic phase shifter (APPS) 52 converts an EC command as an output signal into a firing pulse of the thyristor 2.

The control device 6 sends a current command Ir to the ACR 53.
, A voltage pattern memory 63 for giving a voltage command Vr to the AVR 51, and output means 64 and 65, respectively. The current pattern is ACR5
3 (Accurately, the arithmetic unit 56), the voltage pattern is A
The ignition control of the converter of the power supply 2 is performed in accordance with the deviation between the output current If and the feedback value of the output voltage Vf, which are given as command values of the VR 51 (more precisely, the arithmetic unit 54). The reason why two voltage pattern memories 62 are provided in FIG. 1 is to enable the voltage pattern to be changed by the alternate buffer method.

FIG. 3 shows each of the electromagnets 1B, 1Qf and 1Qd.
2 shows the pattern of the exciting current. 14A shows a bending magnet current pattern IBr, FIG. 14B shows a focusing magnet current pattern Ir ′ (Ir), and FIG. 14C shows a diverging magnet current pattern IQ.
d shows the current command value for one cycle of the synchrotron that is repeatedly operated. Each pattern shows a trapezoid, and the timing of each point is the same.

FIG. 4B shows a current pattern Ir (IQf) of the electromagnet 1Qf, in which the low current value section is a period during which low energy particles are incident on the synchrotron, and the current value (and thus the magnetic field) increases. The momentum of the particles increases in proportion to the acceleration, and the section of the acceleration completion where the current value becomes maximum corresponds to the period of emission from the synchrotron to the irradiation device 7 (or another accelerator or the like).

The current pattern Ir is determined by the thyristor converter 2
Is given as time-series data Iri shown in (Equation 1) in order to obtain a command value synchronized with the operation of (1).

[0029]

(Equation 1)

Here, 1 <i <n and k <m <n.
K indicates the start position of the beam extraction section, and m indicates the end position of the beam extraction section.

Further, n indicates the end of one cycle of the synchrotron, and is determined from the number of phases N of the converter of the power supply 2 and the commercial frequency f as shown in (Expression 2).

[0032]

(Equation 2)

Normally, assuming that the number of converter phases of the power supply 2 is N = 12 or 24, the commercial frequency f = 50 Hz, and the period Ts of one cycle of the synchrotron is 2 seconds, n = 1200 or 2400, and Iri is 1.667 or 0.8
The data is updated every 33 milliseconds.

The current pattern Ir is input to the pattern processing device 63, and is processed into a current pattern Ir 'by giving a high-frequency perturbation (zigzag variation in amplitude) to the current value Ir in the extraction section. This processing is performed in the emission section (k <i <k
+ M-1) is controlled as shown in (Equation 3). Note that the incident / acceleration section (i <k-1) and the reset section (k + m <i <k + n) after emission are unchanged,
r = Ir ′.

[0035]

(Equation 3)

Here, A is a high frequency amplitude value, which is approximately 0.01 to 0.1% of the amplitude value Ir of the trapezoidal portion. Note that A
May be changed together with the tune instead of being fixed. M is the period of perturbation Tr (M / N · f) to be given
Is determined to be a multiple of the firing period of the converter 2. When M is other than 1, the control by the current pattern (Equation 3) is performed in M units.

Further, the pattern processing device 63 has a means for setting a perturbation period Tr, and determines M so as to be asynchronous with the operation period T of the irradiating device 7 taken in. The perturbation period T
r is set. The operation cycle T is usually 1/3 to 1/4 times the commercial power supply cycle and 5 to 6.7 milliseconds. Therefore, the perturbation cycle Tr is set to be shorter and not an integral multiple. You. The pattern processing device 63
May be realized as a part of software processing of the control device 6.

The enlarged view of FIG. 3 (b) schematically shows the current pattern thus created. In this example, M = 1, and the current pattern Ir of the electromagnet 1Qf is
Is processed into a zigzag pattern Ir ′. As a result, the current value (therefore, the magnetic field) at the perturbation start point k becomes a stable area where the beam is hard to come out, and at the next k + 1 point, it becomes an unstable area where the beam is easy to come out. Repeat. In this case, the direction in which the perturbation of the current pattern Ir 'starts differs depending on whether k is an even number or an odd number, but it is natural that the starting point k is an even number times the number N of phases of the converter.

The synchrotron repeats the operation mode corresponding to the pattern of Iri = 1 to n at a cycle of Ts = 1 to 2 seconds, and the beam is taken into the irradiation device 7 every beam emission section (extraction section). As shown in FIG. 3, the reason why the current pattern Ir of the focusing electromagnet 1Qf is lowered to the right is that the area inside the separatrix that defines the stable region is the distance from the resonance line of the betatron frequency and the strength of the nonlinear magnetic field. This is to cope with this.

The voltage pattern Vr stored in the voltage pattern memory 62 is calculated from the current pattern Ir and the constant of the excitation circuit of the electromagnet 1 according to (Equation 4) and stored.

[0041]

(Equation 4)

Here, L is the inductance between the electromagnet 1 and the cable, and R is the DC resistance between the electromagnet 1 and the cable.
The directions of the voltage Vr and the current Ir are positive in the direction of the arrow in FIG.

FIG. 4 is an explanatory diagram of the effect of the present embodiment.
FIG. 3 shows an extracted beam waveform (A) according to the present embodiment corresponding to a current pattern (command value) and a conventional extracted beam waveform (B).

In this embodiment, in the beam emission section,
Since the exciting current of the focusing quadrupole electromagnet is perturbed at a high frequency of 0.833 milliseconds or M times the same, high-frequency pulse-like emission as shown in waveform (A) in an unstable region spreading according to the perturbation period. It can be taken out stably as a beam, and the influence of power supply ripple can be eliminated.

On the other hand, in the case of the conventional tracking ratio, since the unstable region changes according to the power supply ripple,
As shown in the waveform (B), the output beam has a pulse shape close to the cycle T synchronized with the commercial frequency, and the amplitude value is unstable due to the influence of the ripple.

FIG. 5 is a schematic diagram for comparing the distribution of irradiation beams. In the case of (A) according to the present embodiment, the pulse cycle of the beam emitted from the synchrotron is sufficiently higher than the operation cycle T of the irradiation device 7 (scanning cycle in which the irradiation beam draws one circle) and is asynchronous, so that irradiation is performed. The beam is evenly distributed over the irradiation area. On the other hand, in the case of the conventional (B), the pulse cycle of the output beam is synchronized with the operation cycle T of the irradiation device 7, so that the irradiation beam is partially biased. Therefore, in the case of a treatment irradiation device, there is a risk that the conventional method concentrates on a part of the irradiation range of the patient. On the other hand, in this embodiment, irradiation can be performed on the irradiation range of the patient on average, and the treatment effect is improved with safety.

[0047]

According to the present invention, the influence of the ripple (commercial frequency) of the electromagnet power supply on the output beam by perturbing the exciting current pattern of the focusing electromagnet at a high frequency in the "slow extraction" of the beam (particle) accelerator. Therefore, there is an effect of stabilizing beam extraction.

Further, since the output beam does not include the power supply ripple, interference with the irradiation device can be eliminated, and the irradiation beam can be uniformly distributed in the irradiation range, so that safe and highly reliable irradiation can be performed. There is an effect.

Furthermore, the perturbation of the amplitude value of the exciting current is as small as 1% or less, which is advantageous in that it can be realized with a simple and inexpensive configuration.

[Brief description of the drawings]

FIG. 1 shows an embodiment of the present invention, and is a block diagram of a control device of an electromagnet power supply in an accelerator.

FIG. 2 is an overall configuration diagram of an accelerator (a synchrotron in this example) to which the present invention is applied.

FIG. 3 is a schematic diagram of an exciting current pattern of each of the deflection, focusing, and diverging electromagnets according to the embodiment.

FIG. 4 is a comparison diagram of an emitted (extracted) beam waveform.

FIG. 5 is a schematic diagram illustrating an irradiation beam distribution by the irradiation device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electromagnet, 1B ... Bending electromagnet, 1Qf ... 4 pole focusing electromagnet, 1Qd ... 4 pole diverging electromagnet, 2 ... Power supply (thyristor converter), 2B ... Power supply for bending electromagnet, 2Qf ... Power supply for focusing 4 pole electromagnet, 2Qd ... Power source for divergent quadrupole electromagnet, 5 ... Control device for converter, 6 ... Control device, 51 ... AVR, 52 ... A
PPS, 53 ACR, 54-56 arithmetic unit, 61 current pattern memory, 62 voltage pattern memory, 63
Pattern processing device, 64, 65 ... output device, 7 ... irradiation device.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-198397 (JP, A) JP-A-6-111998 (JP, A) JP-A-5-258900 (JP, A) JP-A-62-1983 198099 (JP, A) JP-A-8-88972 (JP, A) JP-A-6-342700 (JP, A) JP-A-5-67299 (JP, A) JP-A-4-64991 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05H 13/04

Claims (6)

(57) [Claims] 1. A beam emission control method called a slow extraction, which is provided with a bending electromagnet, a focusing electromagnet, and a diverging electromagnet, and is an accelerator such as a synchrotron which accelerates and emits an incident low-speed beam at a high speed. A beam emission control method for an accelerator, wherein the exciting current of a focusing electromagnet is perturbed during a beam extraction period at a firing cycle determined by the number of phases of a converter constituting an electromagnet power supply or a cycle of a predetermined multiple thereof. . 2. The beam emission control method for an accelerator according to claim 1, wherein a cycle of the perturbation is asynchronous with an operation cycle of a beam irradiation device that takes in a beam emitted from the accelerator. 3. The method according to claim 1, wherein the cycle of the perturbation is a frequency f of a power supply of the focusing electromagnet.
When the number of phases N of the converter and the predetermined multiple M, M / N
A beam emission control method for an accelerator, wherein f is set to f; 4. The perturbation according to claim 1, 2 or 3, wherein the perturbation is a superposition of a high frequency having an amplitude of about 0.01 to 0.1% of an original current value in the extraction period and fluctuating in the perturbation cycle. A beam emission control method for an accelerator. 5. A plurality of sets of a bending electromagnet, a focusing quadrupole electromagnet, and a diverging quadrupole electromagnet, which are alternately arranged along a closed orbit, a power converter for exciting each electromagnet, and each converter. A converter control device comprising a combination of an ACR and an AVR for feedback control; and a command control device for applying a current command to the ACR and a voltage command to the AVR to accelerate a low-speed incident beam at a high speed. In a beam emission control device called slow extraction by an accelerator such as a synchrotron that emits, a command control device corresponding to the focusing quadrupole electromagnet changes a current command pattern stored in advance during a beam extraction period. And beam patterning control of the accelerator, characterized by providing pattern processing means perturbed at a cycle corresponding to a firing cycle determined by the number of phases of the converter. Location. 6. A plurality of sets of a bending electromagnet, a focusing electromagnet, and a diverging electromagnet which are alternately arranged along a trajectory, a power converter for exciting each electromagnet, and an ACR for feedback-controlling each converter. An accelerator comprising: a converter control device comprising a combination of AVRs; and a command control device for applying a current command to the ACR and a voltage command to the AVR so as to control the slow extraction of the beam, corresponding to the focusing electromagnet. The command control device, the pattern of the current command stored in advance, during the beam extraction period, corresponds to the firing cycle determined by the number of phases of the converter, and the operation cycle of the irradiation device using the output beam and Is an accelerator provided with a pattern processing means that perturbs at a predetermined period so as to be asynchronous.