JPH08203700A - Accelerator, and beam emission control method and beam emission control device - Google Patents

Abstract

PURPOSE: To eliminate the influence of power source ripple in the 'late taking' of an accelerator, and provide a stable beam emission control method. CONSTITUTION: The magnetized current command value of a synchrotron is given as the truncated waveform of the same timing as the current pattern IBr of a deflecting electromagnet, the current pattern Ir (IQf) of a focusing electromagnet, and the current pattern IQd of a diffusing electromagnet. A high frequency is superposed and perturbed only in the taking section of the current pattern IR of these patterns. When a commercial frequency is F, the source resultant pulse number of the converter of a power source is N, and the magnification of perturbation to ignition period of the converter is M, the period of the high frequency for perturbation is M/N.f. The amplitude of the high frequency is about 0.01-0.1% of Ir. Thus, the magnetic field of the focusing electromagnet is swung to an unstable area, or an area where the beam is easily emitted every perturbing period, and the emitted beam is stably taken out as a pulse of high density, and never influenced by the power source ripple.

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 extraction control system called "slow extraction".

[0002]

2. Description of the Related Art An important factor in the operation of an accelerator such as a synchrotron is to generate a magnetic field so that a particle does not escape from a closed orbit while it orbits a predetermined closed orbit. This magnetic field is a combination of magnetic fields generated by a deflection electromagnet called a main electromagnet, a focusing quadrupole electromagnet, and a diverging quadrupole electromagnet.

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

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

Various beam extraction control methods have been tried in the past. A typical method is a method called a resonance extraction 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.

A tune is one in which the betatron oscillation period is standardized in one round of the orbit. 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 region, and the beam easily deviates from the orbit. If the tune value is a multiple of another integer ratio (1/4 or 1/5 or less), the stable region of the beam is larger and stable as a whole.

The tune value can be adjusted by changing the tracking ratio maintained by the magnetic field (and hence the current) of the focusing quadrupole electromagnet with respect to the magnetic field (or current) of the deflection electromagnet. That is, a stable tune value (for example, a multiple of 1/4) is maintained from the beam incidence to the acceleration,
The magnetic field of the focusing quadrupole electromagnet is changed to an unstable tune value (eg, a multiple of 1/3) in the beam emission section. As a result, the unstable region of the beam spreads, and the beam in the unstable region is extracted to the outside of the synchrotron through the electrode provided in the beam extraction part.

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

[0009]

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

For this reason, in a beam irradiation apparatus which takes in the emitted beam of the accelerator and performs treatments and tests, the operation period for scanning the irradiation range is close to several times the commercial frequency, and therefore the emitted beam is in the irradiation range. There is a risk of being biased to a specific part, and there was a safety problem of the irradiated body (patient) for medical use, and a precision problem for a 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 is performed by detecting the ripple on the outgoing beam. Measures such as taking measures can be considered. However, it is difficult to realize, and even if it can be realized, a large increase in the device cost is unavoidable, and it 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 extraction control method and apparatus which is not affected by a power supply ripple.

An object of the present invention is to provide an accelerator capable of performing safe beam irradiation in which an irradiation beam taken out from the accelerator is not concentrated on a specific part.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide an accelerator such as a synchrotron which includes a deflection electromagnet, a focusing electromagnet and a diverging electromagnet and accelerates and outputs an incident low-speed beam at a high speed. In a beam extraction control method called a beam extraction control method, the magnetic field of the focusing electromagnet is perturbed alternately between a stable region where the beam is hard to come out and a stable region where the beam is easy to come out during the beam extraction period (exiting section). Can be achieved.

In the perturbation of the magnetic field, the exciting current of the focusing electromagnet is superposed on a high frequency which changes during the beam extraction period at an ignition cycle determined by the number of phases of the converter constituting the electromagnet power source or a cycle thereof. It is realized by doing.

Further, the operation cycle of the beam irradiation device is taken in and the perturbation cycle is set so as to be asynchronous with this.

[0017]

According to the present invention, the exciting current of the focusing quadrupole electromagnet in the beam extraction section is perturbed by the perturbing means at a frequency sufficiently higher than the power supply frequency of the exciting current (usually a commercial frequency). In response to this, the value of the tune fluctuates, and the unstable region of the beam expands or narrows, so that the outgoing beam becomes a pulse having a frequency significantly higher than the power supply frequency, for example, a period of about 1 millisecond. As a result, the influence of the ripple of the excitation power supply can be avoided, and the outgoing beam can be taken out stably.

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

Further, since the perturbation frequency is set asynchronously with the operating frequency (usually, commercial frequency) of the beam irradiation device by the perturbation frequency setting means, deviation of the irradiation beam distribution can be avoided, which is safe and highly reliable. An irradiation device can be provided.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram of the entire accelerator to which the present invention is applied. This accelerator is a synchrotron that periodically operates, and includes a main electromagnet that generates a magnetic field for forming a closed orbit, an incident electrode and an emission electrode (not shown), and the like. The main electromagnet includes a deflection electromagnet 1B and a focusing electromagnet 1Q.
f and a diverging electromagnet 1Qd, and the latter two are quadrupole electromagnets.

Each electromagnet 1 has its own power supply 2B, 2Q.
It is excited from f and 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, 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, 6Qd determine the control command value of each converter control device 5 and repeatedly control the operation of the synchrotron. In addition, converter control 5B, 5Q
The basic configurations of f and 5Qd are the same. Control device 6B, 6
Qf and 6Qd are also the same except for the current pattern processing means 63 added by the present invention.

FIG. 1 is a block diagram of a power supply controller 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 electromagnet 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, which are feedback values to the converter control device 5. AVR for controlling the exciting current I of the electromagnet 1
51 is provided, and an EC command which is an output signal thereof is converted into an ignition pulse of the thyristor 2 by the automatic phase shifter APPS52.

The controller 6 sends a current command Ir to the ACR 53.
And a voltage pattern memory 63 for giving a voltage command Vr to the AVR 51, and respective output means 64, 65. Current pattern is ACR5
The command value and voltage pattern of 3 (to be exact, calculator 56) are A
It is given as a command value of each of the VRs 51 (correctly, the calculator 54), and ignition control of the converter of the power supply 2 is performed according to the deviation between the output current If and the feedback value of the output voltage Vf. Note that the two voltage pattern memories 62 are provided in FIG. 1 in order to enable the change of the voltage pattern by the alternating buffer method.

FIG. 3 shows the electromagnets 1B, 1Qf and 1Qd.
The pattern of the exciting current of is shown. In the figure, (a) is a deflection electromagnet current pattern IBr, (b) is a focusing electromagnet current pattern Ir ′ (Ir), and (c) is a diverging electromagnet current pattern IQ.
FIG. 3d shows the current command value for one cycle of the synchrotron which is repeatedly operated. Each pattern shows a trapezoid, and the timing of each point is the same.

FIG. 3B shows a current pattern Ir (IQf) of the electromagnet 1Qf, in which the low current value is a period in which low-energy particles are injected into the synchrotron and the current value (and therefore the magnetic field) increases. The momentum of particles due to acceleration increases in proportion to each other, and corresponds to the period of emission from the synchrotron to the irradiation device 7 (or another accelerator or the like) in the acceleration completion section in which the current value becomes maximum.

The current pattern Ir is obtained by the thyristor converter 2
In order to make the command value in synchronization with the operation of, the time series data Iri shown in (Equation 1) is given.

[0029]

[Equation 1]

Here, 1 <i <n and k <m <n.
Further, 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 synchroton, and is determined from the number N of phases of the converter of the power source 2 and the commercial frequency f as shown in (Equation 2).

[0032]

[Equation 2]

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

This current pattern Ir is input to the pattern processing device 63, and high-frequency perturbation (zigzag fluctuation of amplitude) is given to the current value Ir in the extraction section to process it into a current pattern Ir '. This processing is performed in the emission section (k <i <k
The current pattern of + m-1) is controlled as shown in (Equation 3). The incident / acceleration section (i <k-1) and the reset section (k + m <i <k + n) after emission are unchanged and I
r = Ir '.

[0035]

(Equation 3)

Here, A is a high frequency amplitude value, which is approximately 0.01 to 0.1% of the trapezoidal amplitude value Ir. Note that A
The value of may not be fixed and may be changed with the tune. M is the perturbation period Tr (M / Nf)
Is a value that determines how many times the firing cycle of the converter 2 is to be set. When M is other than 1, the control of the current pattern by (Equation 3) is performed in M units.

Further, the pattern processing device 63 has means for setting the perturbation period Tr, determines M so as to be asynchronous with the operation period T of the incorporated irradiation device 7, and determines the perturbation period T.
r is set. Since the operation cycle T is normally 1/3 to 1/4 times the commercial power supply cycle and is 5 to 6.7 milliseconds, the perturbation cycle Tr is set shorter than that and not set to an integral multiple. It The pattern processing device 63
May be implemented as part of the software processing of the control device 6.

The enlarged view of FIG. 3B 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 pattern Ir 'which is changed in zigzag. As a result, the current value (and hence the magnetic field) at the perturbation start point k becomes a stable region in which the beam is hard to come out, and becomes an unstable region in which the beam is easy to come out at the next k + 1 point. Is repeating. In this case, the direction in which the perturbation of the current pattern Ir ′ starts is different depending on whether k is an even number or an odd number, but it is natural that the starting point k is an even multiple of the phase number N 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 at every beam extraction section (extraction section). As shown in FIG. 3, the reason why the current pattern Ir of the focusing electromagnet 1Qf is downward-sloping is that the internal area of 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 because it fluctuates depending on the above, and it corresponds to this.

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

[0041]

[Equation 4]

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

FIG. 4 is an explanatory diagram of the effect of this embodiment.
FIG. 3 shows an extraction beam waveform (A) according to the present embodiment corresponding to a current pattern (command value) and a conventional extraction 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 of that, in the unstable region that spreads according to the perturbation period, high-frequency pulsed emission as in waveform (A) It can be stably extracted as a beam, and the effect of power supply ripple can be eliminated.

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

FIG. 5 is a schematic diagram for comparing distributions of irradiation beams. In the case of (A) according to the present embodiment, the pulse period of the beam emitted from the synchrotron is sufficiently higher than the operation period T of the irradiation device 7 (the scanning period in which the irradiation beam draws one circle) and becomes asynchronous, so that the irradiation is performed. The beam is evenly distributed in the irradiation area. On the other hand, in the case of the conventional case (B), since the pulse cycle of the emitted beam is synchronized with the operation cycle T of the irradiation device 7, the irradiation beam is biased to a partial range. Therefore, in the case of a therapeutic 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 the present embodiment, the irradiation range of the patient can be irradiated on average, which is safe and the therapeutic effect is improved.

[0047]

According to the present invention, in the "slow extraction" of the beam (particle) accelerator, by perturbing the exciting current pattern of the focusing electromagnet with a high frequency, the influence of the ripple (commercial frequency) of the electromagnet power source on the outgoing beam is obtained. Since it can be avoided, there is an effect of stabilizing the beam extraction.

Further, since the emitted 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 is possible. There is an effect.

Further, the perturbation of the amplitude value of the exciting current is as small as 1% or less, and there is an effect that it can be realized with a simple and inexpensive structure.

[Brief description of drawings]

FIG. 1 is a block diagram of a control device for an electromagnet power source in an accelerator according to an embodiment of the present invention.

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

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

FIG. 4 is a comparison diagram of outgoing (extracting) beam waveforms.

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electromagnet, 1B ... Deflection electromagnet, 1Qf ... 4-pole focusing electromagnet, 1Qd ... 4-pole diverging electromagnet, 2 ... Power supply (thyristor converter), 2B ... Deflection electromagnet power supply, 2Qf ... Focusing 4-pole electromagnet power supply, 2Qd ... Power source for divergent quadrupole electromagnet, 5 ... Converter control device, 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.

Claims (7)

[Claims] 1. A beam extraction control method called slow extraction, which comprises a deflecting magnet, a focusing electromagnet, and a diverging electromagnet, and is an accelerator such as a synchrotron that accelerates and outputs an incident low-speed beam at a high speed. The magnetic field of the focusing electromagnet is changed during the extraction of the beam.
A method for beam extraction control of an accelerator, characterized in that perturbation is alternately performed between a stable region where a beam is hard to come out and a stable region where a beam is easy to come out. 2. A beam extraction control method called slow extraction, which comprises a deflecting magnet, a focusing electromagnet, and a diverging electromagnet, and is an accelerator such as a synchrotron that accelerates and emits an incident low-speed beam at a high speed. A beam extraction control method for an accelerator, wherein an exciting current of a focusing electromagnet is perturbed during a beam extraction period at an ignition period determined by the number of phases of a converter constituting an electromagnet power source or a period of a predetermined multiple thereof. . 3. The beam extraction control method for an accelerator according to claim 2, wherein the perturbation cycle is asynchronous with an operation cycle of a beam irradiation device that takes in a beam emitted from the accelerator. 4. The cycle of the perturbation according to claim 2 or 3, wherein a frequency (commercial frequency) f of a power source of the focusing electromagnet, a phase number N of the converter, and the predetermined multiple M.
At this time, M / N · f is set, and the beam extraction control method for the accelerator is characterized. 5. The perturbation according to claim 2, 3 or 4, wherein a high frequency having an amplitude of about 0.01 to 0.1% of an original current value of the extraction period and varying in the perturbation cycle is superimposed. A beam extraction control method for an accelerator, comprising: 6. 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, each power supply converter exciting each electromagnet, and each converter. Each converter control device composed of a combination of ACR and AVR for feedback control and each command control device for giving a current command to the ACR and a voltage command to the AVR are provided to accelerate an incident low speed beam at high speed. In a beam emission control device called slow extraction by an accelerator such as a synchrotron that emits light, a command control device corresponding to the focusing quadrupole electromagnet outputs a pattern of the current command stored in advance during a beam extraction section. , Beam extraction control of an accelerator, characterized in that pattern processing means is provided for perturbing in a cycle corresponding to an ignition cycle determined by the number of phases of the converter. Location. 7. A plurality of sets of a bending electromagnet, a focusing electromagnet and a diverging electromagnet, which are alternately arranged along an orbit, converters for each power source for exciting each electromagnet, and an ACR for feedback controlling each converter. An accelerator provided with each converter controller comprising an AVR combination and each command controller for giving 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 sets a pattern of the current command stored in advance as an operation period of an irradiation device that corresponds to an ignition period determined by the number of phases of the converter during a beam extraction section and that uses an emitted beam. Is an accelerator characterized in that it is provided with pattern processing means that perturbs at a cycle determined to be asynchronous.