JP2014053194A - Synchrotron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synchrotron capable of improving extracting accuracy of charged particle beams from a circulation orbit.SOLUTION: The present invention relates to a synchrotron 1 accelerating charged particle beams along a circulation orbit Tr. The synchrotron includes: a pickup 7 provided on the circulation orbit Tr and detecting the distribution of the charged particle beams and positions of the charged particle beams; a kicker electrode 8 and a deflector 9 by which the charged particle beams are extracted from the circulation orbit Tr; and a control section 10 controlling the kicker electrode 8 and the deflector 9 on the basis of the detection result of the pickup 7.

Description

  The present invention relates to a synchrotron that accelerates charged particles.

  Conventionally, for example, Patent Document 1 is known as a technical document related to a synchrotron. Patent Document 1 discloses a synchrotron for accelerating a charged particle beam along a circular orbit, a high-frequency application device for shifting the charged particle beam on the circular orbit from a stable region to an unstable region, and an unstable region A device including a deflector that extracts a charged particle beam that has been transferred to (1) from a circular orbit and a measuring device that measures the extracted charged particle beam is described.

Japanese Patent Laid-Open No. 5-198397

  Incidentally, high stability is required for the output of a charged particle beam by a synchrotron. The stability is greatly affected by the extraction accuracy of the charged particle beam from the orbit, and the conventional synchrotron described above has room for improvement in improving the extraction accuracy.

  Therefore, an object of the present invention is to provide a synchrotron capable of improving the accuracy of extracting a charged particle beam from a circular orbit.

  In order to solve the above-mentioned problems, the present invention is a synchrotron for accelerating a charged particle beam along an orbit, and is provided on the orbit, and detects the distribution of the charged particle beam and the position of the charged particle beam. In-orbit detection means, extraction means for extracting the charged particle beam from the orbit, and control means for controlling the extraction means based on the detection result of the in-orbit detection means.

  According to the synchrotron according to the present invention, the extraction means is controlled based on the detection result of the in-orbit detection means provided on the orbit, so that an appropriate beam according to the state of the charged particle beam on the orbit is obtained. The extraction can be realized, and the extraction accuracy of the charged particle beam can be remarkably improved as compared with the conventional synchrotron that measures only the beam after the extraction. This greatly improves the output stability of the synchrotron.

In the synchrotron according to the present invention, the take-out means has a kicker electrode for taking out the charged particle beam by moving the charged particle beam from the stable region to the unstable region of the orbit. The kicker electrode may be controlled based on the detection result.
According to this synchrotron, by controlling the kicker electrode based on the detection result of the in-orbit detection means and accurately adjusting the increase in the amplitude of the betatron oscillation of the charged particle beam, the synchrotron can be compared with the conventional synchrotron. A delicate beam can be taken out.

The synchrotron according to the present invention further includes an out-of-orbit detection unit that is provided at a position deviated from the orbit, and detects the current value or radiation amount of the charged particle beam extracted from the orbit by the extraction unit, and the control unit includes The take-out means may be controlled based on the detection result of the out-orbit detection means and the detection result of the in-orbit detection means.
According to this synchrotron, the feedback control of the extraction means can be realized by using the detection result of the out-of-orbit detection means for the current value or radiation dose of the beam extracted from the orbit, so that the feedback control can be performed. Compared with the case where it is not performed, the extraction accuracy of the charged particle beam can be further improved.

  ADVANTAGE OF THE INVENTION According to this invention, the synchrotron which can improve the extraction accuracy of the charged particle beam from a circular orbit can be provided.

It is the schematic which shows 1st Embodiment of the synchrotron which concerns on this invention. It is a block diagram for demonstrating the control part of a synchrotron. It is a schematic diagram which shows the locus | trajectory in the phase space of the representative particle of a charged particle beam. It is the schematic which shows 2nd Embodiment of the synchrotron which concerns on this invention. It is a block diagram for demonstrating the control part which concerns on 2nd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
A synchrotron 1 of the first embodiment shown in FIG. 1 is an accelerator that accelerates a charged particle beam along a circular trajectory Tr. Examples of the charged particles include protons, heavy particles (heavy ions), and electrons. Hereinafter, as shown in FIG. 1, description will be made assuming that the circumferential direction of the charged particle beam in the orbit Tr is S, the horizontal direction orthogonal to the circulation direction S is X, and the vertical direction is Y. The orbiting direction S, the horizontal direction X, and the vertical direction Y are directions orthogonal to each other, and SXY is a local coordinate whose direction changes depending on the position on the orbiting track Tr.

  The synchrotron 1 includes a front stage accelerator 2, an injector 3, a quadrupole magnet 4 for horizontal convergence, a quadrupole magnet 5 for vertical convergence, a multipole magnet 6, a pickup (in-orbit detection means) 7, a kicker electrode 8, and a deflector 9. It has.

  The synchrotron 1 includes a control unit (control means) 10 shown in FIG. The control unit 10 is an electronic control unit including a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], and the like, and controls the synchrotron 1. The control unit 10 is connected to the front stage accelerator 2, the injector 3, the horizontal focusing quadrupole magnet 4, the vertical focusing quadrupole magnet 5, the multipolar magnet 6, the pickup 7, the kicker electrode 8, and the deflector 9.

  In the synchrotron 1 shown in FIG. 1, the charged particle beam accelerated by the former accelerator 2 is incident on the orbit Tr through the injector 3. As the front stage accelerator 2, a linear accelerator is mainly used. The charged particle beam incident on the circular orbit Tr is bent in the traveling direction by a deflecting electromagnet (not shown) and circulates on the circular orbit Tr.

  The position of the charged particle beam in the circular orbit Tr is adjusted by the horizontal focusing quadrupole magnet 4 and the vertical focusing quadrupole magnet 5. The horizontal focusing quadrupole magnet 4 is an electromagnet that changes the orbital gradient so that the charged particle beam converges in the horizontal direction X and diverges in the vertical direction Y. The vertical focusing quadrupole magnet 5 is an electromagnet that changes the orbital gradient so that the charged particle beam converges in the vertical direction Y and diverges in the horizontal direction X. A plurality of horizontal convergence quadrupole magnets 4 and vertical convergence quadrupole magnets 5 are arranged (for example, four sets) on the circular trajectory Tr.

  The charged particle beam circulates on the circular trajectory Tr while vibrating in the circular direction (traveling direction) S and in the horizontal direction (horizontal direction X and vertical direction Y). The vibration of the charged particle beam in the lateral direction is called betatron vibration, and the betatron frequency per round in the circular orbit Tr is called tune. In order to circulate the charged particle beam stably, it is necessary to control the tune to a value that does not cause resonance.

  The tuning of the charged particle beam is controlled by the amount of excitation of the horizontal focusing quadrupole magnet 4 and the vertical focusing quadrupole magnet 5. The control unit 10 controls the horizontal focusing quadrupole magnet 4 and the vertical focusing quadrupole magnet 5 so as not to cause a tune that causes particularly low-order resonance. The charged particle beam that circulates on the circular trajectory Tr is given energy from a high-frequency acceleration cavity (not shown), and the charged particle beam gradually accelerates while circling in a controlled state.

  Next, extraction of the charged particle beam accelerated to the target energy from the circular orbit Tr will be described with reference to FIG. FIG. 3 is a schematic diagram showing a locus in a phase space of a representative particle of a charged particle beam (an arbitrary particle included in the charged particle beam).

  The horizontal axis of FIG. 3 indicates the position of the representative particle in the horizontal direction X, and the vertical axis indicates the relationship (horizontal orbital gradient) dx / ds between the horizontal change dx and the rotation direction change ds of the representative particle. ing. That is, FIG. 3 shows the relationship between X and dx / ds (phase space) for each revolution of the representative particle.

  Moreover, the broken lines W1-W3 of FIG. 3 have shown separatrix (stability limit). Separatrix hits the boundary line between the stable region A and the unstable region B. That is, the stable region A is a region surrounded by broken lines W1 to W3 in the phase space shown in FIG. 3, and the charged particle beam in the stable region A is stably orbited without causing resonance of betatron oscillation. Go around Tr. On the other hand, the unstable region B is a region outside the broken lines W1 to W3 in the phase space shown in FIG. 3, and the amplitude of the betatron oscillation increases in the charged particle beam in the unstable region B due to resonance.

  In FIG. 3, the number of circulations is assigned to the representative particles in the unstable region B as numbers. As shown in FIG. 3, the charged particle beam in the unstable region B is in an unstable state, and the amplitude of betatron oscillation increases rapidly.

  The separatrix is formed by the multipolar magnet 6. The multipolar magnet 6 is, for example, a hexapole electromagnet or an octupole electromagnet, and is disposed on the circular trajectory Tr. The stable region A surrounded by the separatrix becomes smaller as the magnetic field strength of the multipolar magnet 6 increases. Further, the stable region A becomes smaller as the deviation from the integer ± 1/3 of the horizontal tune of the charged particle beam becomes smaller.

  As shown in FIG. 1, the charged particle beam that circulates on the circular trajectory Tr is detected by the pickup 7. The pickup 7 is a detector that is provided on the circular orbit Tr and detects the distribution and position (for example, the position of the center of gravity) of the charged particle beam in the circular orbit Tr. The provision on the orbit Tr is not limited to being provided so as to strictly overlap the orbit Tr, but may be provided so as to surround the orbit Tr, or the like. Is an expression that also includes

  Further, the configuration of the pickup 7 is not particularly limited. As the pickup 7, for example, a plurality of pickup electrodes can be used. Further, the pickup 7 may detect the size of the charged particle beam and the position of the center of gravity. Depending on the accuracy of the pickup 7, the trajectory of the charged particles in the phase space shown in FIG. 3 can be obtained from the detection result. The pickup 7 transmits a detection signal corresponding to the detected distribution and position of the charged particle beam to the control unit 10.

  The control unit 10 controls the kicker electrode 8 based on the detection signal (detection result) of the pickup 7. The kicker electrode 8 is an electrode that is provided on the circular trajectory Tr and moves a part of the charged particle beam from the stable region A to the unstable region B.

  The kicker electrode 8 is provided at a position opposite to the deflector 9 on the circular trajectory Tr (a position farthest from the deflector 9 on the circular trajectory Tr). Note that the pickup 7 is provided on a circular trajectory Tr between the kicker electrode 8 and the deflector 9. The kicker electrode 8 shifts a part of the charged particle beam from the stable region A to the unstable region B by increasing the amplitude of the betatron oscillation of the charged particle beam.

  The method for increasing the amplitude of betatron oscillation by the kicker electrode 8 is not particularly limited. Methods for increasing the amplitude of the betatron oscillation include (a) a method of applying a time-varying magnetic field to the charged particle beam, (b) a method of applying a time-varying electric field to the charged particle beam, (c ) A method of causing a particle different from a charged particle beam to collide with the charged particle beam is known.

  The control unit 10 controls the kicker electrode 8 based on the detection signal of the pickup 7 and increases the amplitude of the betatron oscillation of the charged particle beam at an appropriate timing, thereby causing the stable region A to shift to the unstable region B. . The control unit 10 may be configured to process the detection signal of the pickup 7, perform amplification and inversion of polarity with an amplifier, and transmit the amplified signal to the kicker electrode 8.

  In the charged particle beam transferred to the unstable region B by the kicker electrode 8, the amplitude of the betatron oscillation increases rapidly as the number of revolutions increases as in the representative particle shown in FIG. The charged particle beam having an increased amplitude is extracted from the orbit Tr by the deflector 9 (see FIG. 1). The kicker electrode 8 and the deflector 9 constitute extraction means described in the claims.

  The deflector 9 is, for example, an ESD [Electro Static Deflector], and includes a conductive plate 9A and an electrode 9B shown in FIG. A strong electric field is formed between the conductive plate 9A and the electrode 9B, and the charged particle beam (for example, the 58th round of the representative particle in FIG. 3) entering between the conductive plate 9A and the electrode 9B circulates by deflection. It is taken out from the trajectory Tr.

  The charged particle beam taken out from the circular orbit Tr by the deflector 9 is largely deflected by a septum magnet (not shown) and emitted from the synchrotron 1. In order to facilitate extraction, a bump magnet that brings the charged particle beam toward the deflector 9 may be provided in the orbit Tr.

  Further, the smaller the thickness of the conductive plate 9A of the deflector 9, the easier it is for the charged particle beam to get over the conductive plate 9A. On the other hand, the charged particle beam that cannot get over the conductive plate 9A collides with the conductive plate 9A and disappears. For this reason, it is desirable that the deflector 9 is an ESD that can thin the conductive plate 9A. A configuration other than ESD (for example, a configuration using a coil) may be employed as the deflector 9.

  According to the synchrotron 1 according to the first embodiment described above, since the transition to the unstable region B is performed by increasing the amplitude of the betatron oscillation of the charged particle beam in the stable region A, for beam extraction. The extraction efficiency (outgoing efficiency) of the charged particle beam can be improved without changing the separatrix (range of the stable region A). Further, in this synchrotron 1, it is not necessary to change the separatrix, so that the exciting force of the horizontal focusing quadrupole magnet 4, the vertical focusing quadrupole magnet 5, and the multipole magnet 6 can be made substantially constant. Easy to control. Further, in the synchrotron 1, the beam diameter of the charged particle beam incident on the deflector 9 can be made substantially constant by making the separatrix constant, so that the output stability of the charged particle beam can be improved.

  In addition, according to the synchrotron 1, the kicker electrode 8 and the deflector 9 are controlled based on the detection result of the pickup 7 provided on the orbital track Tr. As compared with a conventional synchrotron that measures only the beam after being extracted, the extraction accuracy of the charged particle beam can be remarkably improved. This greatly improves the output stability of the synchrotron 1. It is not always necessary to control the deflector 9 based on the detection result of the pickup 7.

  Further, according to this synchrotron 1, since the kicker electrode 8 can be controlled based on the detection result of the pickup 7 and the amplitude increase of the betatron oscillation of the charged particle beam can be accurately adjusted, Compared with this, a more delicate beam can be extracted.

[Second Embodiment]
As shown in FIGS. 4 and 5, the synchrotron 21 according to the second embodiment includes an extraction beam detector (out-of-orbit detection means) 22 as compared with the synchrotron 1 according to the first embodiment. There is a big difference. 4 and 5, the same components as those of the synchrotron 1 according to the first embodiment are denoted by the same reference numerals, and redundant description is omitted.

  The extracted beam detection unit 22 is a detector that is provided at a position deviated from the circular orbit Tr and detects the current value or radiation dose of the charged particle beam extracted from the circular orbit Tr by the deflector 9. The configuration of the extraction beam detection unit 22 is not particularly limited, but an electrode or the like may be employed.

  The control unit 23 according to the second embodiment controls the kicker electrode 8 and the deflector 9 based on the detection result of the extraction beam detection unit 22 and the detection result of the pickup 7. The control unit 23 performs feedback control of the kicker electrode 8 and the deflector 9 using the detection result of the extraction beam detection unit 22. The control unit 23 may perform feedback control using the detection result of the extraction beam detection unit 22 for the horizontal convergence quadrupole magnet 4, the vertical convergence quadrupole magnet 5, and the multipolar magnet 6.

  According to the synchrotron 21 according to the second embodiment described above, by using the detection result of the extraction beam detection unit 22 for the current value or the radiation amount of the beam extracted from the circular orbit Tr, the kicker electrode 8 and Since feedback control of the deflector 9 can be realized, the charged particle beam extraction accuracy can be further improved as compared with the case where feedback control is not performed.

  The present invention is not limited to the embodiment described above. For example, the positional relationship among a horizontal focusing quadrupole magnet, a vertical focusing quadrupole magnet, a multipolar magnet, a pickup, a kicker electrode, and a deflector is not limited to that shown in FIG. The pickup may be provided not on the side of the injector on the orbit, but on the side opposite to the injector (the lower side of the paper surface of FIG. 1). The kicker electrode is not necessarily provided at the position farthest from the deflector.

  Further, the number of horizontal focusing quadrupole magnets, vertical focusing quadrupole magnets, and multipolar magnets is not limited to that shown in FIG.

  Furthermore, the synchrotron according to the present invention does not necessarily include a multipole magnet. By detecting the charged particle beam with high accuracy by a pickup and kicking the kicker electrode with sufficient strength at an appropriate timing, it is also possible to take out the charged particle beam from the orbit without making a separatrix.

DESCRIPTION OF SYMBOLS 1,21 ... Synchrotron 2 ... Pre-stage accelerator 3 ... Injector 4 ... Horizontal focusing quadrupole magnet 5 ... Vertical focusing quadrupole magnet 6 ... Multipole magnet 7 ... Pickup (in-orbit detection means) 8 ... Kicker electrode (extraction) Means) 9 ... Deflector (extraction means) 9A ... Conductive plate 9B ... Electrode 10, 23 ... Control part (control means) 22 ... Extraction beam detection part (out-orbit detection means) A ... Stable area B ... Unstable area Tr ... Circulation Orbit W1-W3… Separatrix

Claims (3)

A synchrotron for accelerating a charged particle beam along a circular orbit,
An in-orbit detection means provided on the orbit for detecting the distribution of the charged particle beam and the position of the charged particle beam;
Extraction means for extracting the charged particle beam from the orbit,
Control means for controlling the take-out means based on the detection result of the in-orbit detection means;
A synchrotron. The extraction means has a kicker electrode that extracts the charged particle beam by moving the charged particle beam from a stable region of the circular orbit to an unstable region,
The synchrotron according to claim 1, wherein the control unit controls the kicker electrode based on a detection result of the in-orbit detection unit. Further comprising out-of-orbit detection means for detecting a current value or a radiation dose of the charged particle beam provided at a position off the orbit, and taken out from the orbit by the extraction means;
The synchrotron according to claim 1, wherein the control unit controls the extraction unit based on a detection result of the out-of-orbit detection unit and a detection result of the in-orbit detection unit.

Images