Charged-particle beam ejection method and apparatus using the method

Abstract

 The strength of the high-frequency electromagnetic field generated by a high-frequency electromagnetic field applying unit 11 is controlled based on the energy of a charged-particle beam to be ejected from a synchrotron 1, by applying the high-frequency electromagnetic field to the charged-particle beam revolving in the synchrotron 1.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a charged-particle ejection method of ejecting a charged-particle beam from an acceleration, and especially to a charged-particle ejection method capable of ejecting a charged-particle beam with a simple control.

[0002] A synchrotron is generally well-known as an accelerator for ejecting a charged-particle beam (hereafter, referred to as a beam), and a beam ejection method using a synchrotron is disclosed in Japanese Patent Application Laid-Open No. Hei 5-198397 as follows. That is, the stability limit of a beam which revolves along an orbit in a synchrotron is being held by controlling a quadrupole electromagnet. Next, the charged-particle beam staying within the stability limit is moved outside the stability limit by applying a high-frequency electromagnetic field to the charged-particle beam, using a high-frequency electromagnetic field applying device, and the charged-particle beam moved outside the stability limit is ejected from the synchrotron by causing resonance oscillations in the beam.

[0003] Here, it is well known that unless the frequency of the high-frequency electromagnetic field is changed corresponding to the energy of the beam, the beam cannot efficiently be ejected in the above-described method. Japanese Patent Application Laid-Open No. Hei 7-14699 discloses a method in which the central frequency and the band width of the high-frequency electromagnetic field applied to a beam is changed corresponding to the energy of the beam.

[0004] In the above conventional technique, any method of determining the strength of the high-frequency electromagnetic field applied to the beam is described at all. However, it has been newly found that the ejection amount per unit time of a beam changes depending on the strength of the high-frequency electromagnetic field applied to the beam. Therefore, the above conventional techniques which do not disclose any method of determining the strength of the high-frequency electromagnetic field applied to a beam cannot control the ejection amount per unit time of the beam.

SUMMARY OF THE INVENTION

[0005] An object of present invention is to provide a charged-particle beam ejection method and a charged-particle beam ejection apparatus capable of controlling the ejection amount per unit time of a charged-particle beam.

[0006] To attain the above object, the present invention provides a charged-particle beam ejection method of ejecting a charged-particle beam from an accelerator by applying a high-frequency electromagnetic field to the charged-particle beam revolving along an orbit in the accelerator, wherein the strength of the high-frequency electromagnetic field is set based on the energy of the charged-particle beam ejected from the accelerator.

[0007] The number of charged particles ejected per unit time (the ejection amount of a beam) is proportional to the speed in transition of betatron oscillation beyond the stability limit, that is, to the strength of the high-frequency electromagnetic field applied to the charged-particle beam. Therefore, by setting the strength of the high-frequency electromagnetic field based on the energy of the charged-particle beam ejected from the accelerator, it is possible to control the ejection amount per unit time of the charged-particle beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 

Fig. 1 is a diagram showing the composition of an acceleration system of an embodiment according to the present invention.

Fig. 2 is a flow chart of procedures for ejecting a charged-particle beam with the acceleration system.

Fig. 3 is a diagram showing a high-frequency electromagnetic field applying unit 11 and a power source 22 shown in Fig. 1.

Fig. 4 is a diagram showing the composition of an acceleration system of another embodiment according to the present invention.

Fig. 5 is a diagram showing a high-frequency electromagnetic field applying unit 11 and a power source 22 shown in Fig. 4.

Fig. 6 is a conceptual illustration showing a method of irradiating the diseased part with a charged-particle beam in a remedy system of another embodiment according to the present invention.

Fig. 7 is a diagram showing a time chart of operational cycles of the synchrotron according to the present invention.

Fig. 8 is a diagram showing a time chart of operational cycles of a conventional synchrotron.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The first embodiment:

[0009] Hereafter, the embodiments will be explained in detail with reference to the drawings.

[0010] Fig. 1 schematically shows the composition of an acceleration system of an embodiment according to the present invention.

[0011] The acceleration system of this embodiment includes a synchrotron 1 in which a charged-particle beam (hereafter, referred to simply as a beam) of charged particles with energy of about 20 MeV is injected, and is ejected after the beam is accelerated to a predetermined energy level.

[0012] In Fig. 1, a pre-stage accelerator 4 emits a beam with about 20 Mev in accordance with a control signal from a control unit 3. The beam emitted from the pre-stage accelerator 4 is transmitted to an injector 16 via a beam transportation system, and is injected into the synchrotron 1 by the injector 16.

[0013] The synchrotron 1 includes a high-frequency electromagnetic field applying unit 11 for increasing the amplitude of betatron oscillation of the beam by applying a pair of high-frequency electric and magnetic fields (referred to as an electromagnetic field), deflection electromagnets 12 for deflecting the trajectory of the beam, quadrupole electromagnets 13 for controlling the betatron oscillation of the beam, hexapole electromagnets 14 for exciting resonance oscillation of the beam when the beam is ejected, a high-frequency acceleration cavity 15 for adding energy to the beam, that is, accelerating the beam, an injector 16 for injecting a beam into the synchrotron 1, and a beam-ejection deflector 17 for ejecting the beam from the synchrotron 1. In the above devices, the hexapole electromagnets 14, the high-frequency electromagnetic field applying unit 11, and the beam-ejection deflector 17 are used only in the process of ejecting the beam.

[0014] The control unit 3 sends a power source 21 a control signal designating the value of current to be fed from the power source 21 to the deflection electromagnets 12, corresponding to the energy of the beam revolving along its orbit in the synchrotron. The power source 21 then feeds the current of the value designated by the control signal sent from the control unit 3 to the deflection electromagnet 12. Further, each deflection electromagnet 12 generate a magnetic field corresponding to the current fed from the power source 21. Meanwhile, although it is shown in Fig. 1 that the power source 21 feeds current to a single deflection electromagnet 12, the power source 21 feeds current to the other deflection electromagnets 12 also. (Such simplification in showing connections between the power source 21 and the quadrupole and hexapole electromagnets 13 and 14 also is done in Fig. 1.) Furthermore, the trajectory of the beam injected into the synchrotron 1 by the injector 16 is deflected by each defection electromagnet 12 during its revolution in the synchrotron 1.

[0015] In the quadrupole electromagnets 13, some quadrupole electromagnets 13 make the beam converge horizontally, and excite the vertical motion component of the beam. The other ones make the beam converge vertically, and excite the horizontal motion component of the beam. Current is fed to these quadrupole electromagnets 13 from the power source 21 as well as the deflection electromagnets 12, and the value of the fed current is instructed by the control unit 3, corresponding to the energy of the beam revolving in the synchrotron 1. By the above functions of the quadrupole electromagnets 13, the beam revolves in the synchrotron 1 while continuing betatron oscillation, and the oscillation number of the betatron oscillation is controlled by the strength of the magnetic field generated by the quadrupole electromagnets 13. To stably revolve the beam in the processing of injection and acceleration of the beam, it is necessary to set the oscillation number of the betatron oscillation per one revolution (referred to as the tune), such that the resonance oscillation does not occur in the betatron oscillation, and specifically to set the tune with a value far from the tune causing the lower-order resonance oscillation. In this embodiment, the strength of the magnetic field generated by the quadrupole electromagnets 13 is controlled by the control unit 3 and the power source 21 so that the tune νx in the horizontal direction and the tune νy in the vertical direction are 1.75 and 1.25, respectively.

[0016] Under the above conditions, the beam stably revolves in the synchrotron 1, and the beam is further accelerated by applying a high-frequency electric field to the beam to add energy to the beam in the high-frequency acceleration cavity 15. Here, the integer multiple (n multiple) of the frequency of the beam oscillation is set to the frequency of the high-frequency electric field generated in the high-frequency acceleration cavity 15. Also, current with the value designated by the control unit 3 is fed to the high-frequency acceleration cavity 15 from the power source 21. Furthermore, the beam revolves in the synchrotron 1, synchronizing with the frequency of the high-frequency electric field in a n-bunch state.

[0017] When the beam is accelerated in the high-frequency acceleration cavity 15, the strength of each magnetic field is increased while holding the ratio of the strength of the magnetic field generated by each deflection electromagnet 12 to that generated by each quadrupole electromagnet 14 constant. Accordingly, at the deflection electromagnets 12, the increase of the centrifugal force due to the energy increase of the beam balances with the increase of the centripetal force due to the increase of the magnetic field strength of the deflection electromagnets 12, and the beam revolves along the same orbit even if the energy of the beam is increased.

[0018] Further, when the energy of the beam increases to the target energy which is input to the control unit 3 by an operator, the beam is ejected from the synchrotron 1. The procedures performed until the beam is ejected are indicated by the flow chart shown in Fig. 2. At first, in step 21, the addition of energy to the beam, which is performed in the high-frequency acceleration cavity 15, is stopped. By stopping the addition of energy to the beam, the bunch-state beam becomes the continuous beam. Next, in step 22, the tune νx in the horizontal direction is set to 1.676 by controlling the quadrupole electromagnets 13 with the power source 21. Further, in step 23, current is fed to the hexapole electromagnets 14 to cause the resonance oscillation in the beam. The value of the current fed to each hexapole electromagnet 14 is a value such that charged particles with a large amplitude of the betatron oscillation in the beam stay within the stability limit, and the value is obtained by a calculational analysis in advance or while repeating the ejection of the beam. Furthermore, in step 24, the high-frequency electromagnetic field applying unit 11 applies a high-frequency electromagnetic field to the beam. This high-frequency electromagnetic field applying unit 11 will be explained later. By the application of the high-frequency electromagnetic field, the trajectory of the beam is changed, and the amplitude of the betatron oscillation in the beam is increased. The amplitude of the betatron oscillation in the beam, which has exceed the stability limit, rapidly increase due to resonance oscillation. Thus, in step 25, the beam in which the amplitude of the betatron oscillation has rapidly increased is ejected from the synchrotron 1 by the beam-ejection deflector 17.

[0019] Fig. 3 schematically shows the composition of the power source 22 connected to the high-frequency electromagnetic field applying unit 11 and the control unit 3. The control unit 3 shown in Fig. 3 determines the square root V (referred to as the voltage amplitude V) of mean square of the amplitude in the AC voltage fed to the high-frequency electromagnetic field applying unit 11, and the central frequency fc and the band width ΔBW of the AC voltage, based on the energy E of the ejected beam and the time width T of the ejection-start to the ejection-end of the beam. The relationship between sets of the voltage amplitude V, the central frequency fc, and the band width ΔBW (one-side width), and pairs of the energy E and the time width T is stored in the control unit 3, and the control unit 3 obtains the necessary voltage amplitude V, central frequency fc, and band width ΔBW, corresponding to the required energy E and time width T input by the operator. Moreover, the voltage amplitude V is set so as to increase as the time elapses. Also, the strength of the high-frequency electromagnetic field is proportional to the voltage amplitude V.

[0020] In the following, the values of the voltage amplitude V, the central frequency fc, and the band width ΔBW which are stored in the control unit 3 will be explained. If the revolving frequency corresponding to the energy E of the beam is frs, the AC voltage with a frequency spectrum including a band width of about 0.66frs to 0.70frs is fed to the high-frequency electromagnetic field applying unit 11. That is, the AC voltage fed to the high-frequency electromagnetic field applying unit 11 is generated so that the central frequency fc is 0.68frs, and the one-half side width of the band width ΔBW is 0.02frs. The reason why the AC voltage fed to the high-frequency electromagnetic field applying unit 11 is generated as described above is as follows. Meanwhile, the revolution frequency is obtained from the energy E.

[0021] The tune of the beam revolving in the synchrotron 1, which has the very small amplitude of the betatron oscillation, is the value 1.676 set by the quadrupole electromagnets 13, but the tune of the beam with the amplitude of the betatron oscillation near the stability limit for causing resonance oscillation has the value 1.666 due to the operation of the hexapole electromagnets 14. Therefore, the tune values of the beam revolving in the synchrotron 1 continuously distribute within the range of 1.666 to 1.676. On the other hand, to increase the amplitude of the betatron oscillation in the beam, it is required that the frequency of the high-frequency electromagnetic field satisfies the following equation (1) or (2).

[0022] In this embodiment, the frequency f of the high-frequency electromagnetic field is determined by setting the integer as 0. That is, the frequency f required for the beam with the tune value of 1.666 is frs×(0 + 0.666) = 0.666 frs. Also, the frequency f required for the beam with the tune value of 1.676 is frs×(0 + 0.676) = 0.676 frs. As mentioned above, since the AC voltage fed to the high-frequency electromagnetic field applying unit 11 of this embodiment possesses a frequency spectrum including the band width of about 0.66frs to 0.70frs, the AC voltage includes all the frequency components necessary to increase the amplitude of the betatron oscillation in the beam with the tune value of 1.666 to 1.676. That is, it is possible to increase the amplitude of the betatron oscillation in every beam revolving in the synchrotron 1. Here, the frequency components included in the AC voltage fed to the high-frequency electromagnetic field applying unit 11 is equal to those in the high-frequency electromagnetic field generated by the high-frequency electromagnetic field applying unit 11.

[0023] If the second-order resonance is used to cause the resonance of the betatron oscillation, the central frequency fc is set to 0.5frs, and the band width ΔBW is set to 0.02frs as well as the above band width ΔBW.

[0024] On the other hand, representing the time of the ejection-start to the ejection-end of the beam revolving in the synchrotron 1, the energy of the beam, the revolution frequency of the beam, the frequency band width of the high-frequency electromagnetic field, and the distance between the plate electrodes 111 and 112 composing the high-frequency electromagnetic field applying unit 11 as T, E, frs, ΔBW, and d, it has newly been found that the voltage amplitude V of the AC voltage fed to the high-frequency electromagnetic field applying unit 11 can be expressed by the following mathematical expression (3).

[0025] The mark ∝ in the mathematical expression (3) shows that if the value of the right-hand side of this mathematical expression increases, the value of the left-hand side of this mathematical expression also increases. However, the value of the right-hand side is not directly proportional to the value of the left-hand side

[0026] In the mathematical expression (3), by using the measured value of the distance d, the value E input by the operator, the above-described band width ΔBW, the set value of the energy E, the calculated value of the revolution frequency frs obtained based on the energy E, the voltage amplitude V can be obtained. From the mathematical expression (3), it is seen that while the energy E is increased, the voltage amplitude V is increased.

[0027] However, even if the voltage amplitude V obtained based on the mathematical expression (3) continues to be fed to the high-frequency electromagnetic field applying unit 11, the number of charged particles ejected from the synchrotron 1 per unit time (referred to as the ejection amount of a beam) decreases as the time elapses. That is, the mathematical expression (3) is obtained assuming that a sufficient number of charged particles remains within the stability limit. Therefore, if the number of charged particles remaining within the stability limit decreases as the time elapses, the ejection amount of the beam also decreases. In this embodiment, to solve the problem, the voltage amplitude V is increased as the time elapses. Since the ejection amount of a beam is proportional to the product of the number of charged particles staying within the stability limit and the speed in transition of the betatron oscillation beyond the stability limit, even if the number of charged particles within the stability limit decreases as the time elapses, by increasing the strength of the high-frequency electromagnetic field applied to the beam (the voltage amplitude V), it is possible to increase the speed in transition of the betatron oscillation beyond the stability limit, and to maintain the number of charged particles ejected from the synchrotron 1 per unit time constant. Here, a plurality of patterns of increasing the voltage amplitude V are obtained based on results of calculational analysis in advance.

[0028] The plurality of the pattern are arranged corresponding to sets of the voltage amplitude V, the distance d, the energy E, the band width ΔBW, the time T, and the revolution frequency frs, and are stored in the control unit 3.

[0029] The control unit 3 outputs the obtained voltage amplitude V, central frequency fc, and band width ΔBW to an amplifier 224, an oscillator 221, and an oscillator 222, respectively. Further, the oscillator 221 outputs the AC voltage (a sin wave) with a frequency equal to the central frequency fc to a multiplier 223. Furthermore, the oscillator 222 outputs the AC voltage with frequency components of 0 ±ΔBW. Moreover, the multiplier 223 multiplies the input two AC voltage values, and outputs the result of the multiplication to the amplifier 224. The voltage output from the multiplier 223 is the AC voltage with frequency components of fc±ΔBW. The amplifier 224 amplifies the input AC voltage so that the pattern of increasing the amplitude of the AC voltage input from the multiplier 223 is equal to the pattern of increasing the voltage amplitude V, which is input from the control unit 3, and outputs the amplified AC voltage to the plate electrodes 111 and 112 of the high-frequency electromagnetic field applying unit 11. Here, the VC voltage is applied to the plate electrodes 111 and 112 so that the phase of the VC voltage applied to the electrode 111 is reverse to that applied to the electrode 112.

[0030] The plate electrodes 111 and 112 generate the high-frequency electromagnetic fields according to the input AC voltage, and apply the generated electromagnetic fields to the beam revolving in the synchrotron 1. The orientation of the electric field or the magnetic field generated by the plate electrodes 111 and 112 is the orientation such as that shown by arrow marks in Fig. 3. Meanwhile, the strength of the electric and magnetic fields increase in accordance with the amplitude increase of the input AC voltage.

[0031] As described above, by determining frequency components to be included in the AC voltage applied to the plate electrodes 111 and 112 based on the energy E of the beam, it becomes possible to efficiently eject all particles in the beam revolving in the synchrotron 1 even if the energy E is changed. Also, by determining the pattern of increasing the voltage amplitude V in the AC voltage based on the energy E and the time T of ejecting the beam, it becomes possible to eject all particles in the beam in the synchrotron 1 within the time T even if the energy E is changed. Thus, the ejection amount of the beam is held constant even if the energy E is changed. That is, as shown in Fig. 7, all charged particles in the beam revolving in the synchrotron 1 are ejected for the same time T. In Fig. 7, T1 = T2. Accordingly, it is possible to held the period T for ejecting the beam in one operational cycle of the synchrotron 1 constant independent of the energy of the ejected beam, which makes it simple to control the synchrotron 1. On the other hand, if the strength of the high-frequency electromagnetic field is set as constant regardless of the energy of the beam, the time of ejecting the beam in the operational cycles of a synchrotron changes depending on the energy of each beam as shown in Fig. 8. In Fig. 8, T1 < T2.

[0032] Although the required frequency components in the AC voltage is generated using the two oscillators 221 and 222, and the multiplier 223, those frequency components can be obtained by a method of extracting frequency components in the required-band from a voltage signal with a wider-band frequency spectrum, using a filter, a method of integrating a plurality of frequency components, or a method of changing the frequency of a voltage signal with a single frequency.

The second embodiment:

[0033] Fig. 4 shows the composition of a remedy system which uses the acceleration system of the first embodiment, for treating a cancer. In the following, the components newly added to the acceleration system of the first embodiment will be mainly explained.

[0034] In Fig. 4, a rotating irradiation unit 5 irradiates a diseased part with the beam ejected from the synchrotron 1. The trajectory of beam injected into the rotating irradiation unit 5 is adjusted by deflection electromagnets 51 and 52, and quadrupole electromagnets 53, and the beam is transmitted to scanning electromagnets 54 and 55. Here, current is fed to the deflection electromagnets 51 and 52, and the quadrupole electromagnets 53 from a power source 57 in accordance with control signals from the control unit 3.

[0035] A power source 58 feeds current of a sin wave to the scanning electromagnet 54, and also feeds current of a sin wave whose phase is shifted from that of the former sin wave by 90 degrees to the scanning electromagnet 55. Accordingly, the position of the diseased part in a patient is circularly scanned with the beam transmitted to the scanning electromagnets 54 and 55. A dose monitor 56 measures the irradiation dose due to the beam, and outputs the measurement results to the control unit 3. The irradiation dose output from the dose monitor 56 is compared with the preset target irradiation dose by the control unit 3, and the control unit determines whether or not the irradiation dose reaches the target dose.

[0036] Further, the remedy system of this embodiment includes a current monitor 59 provided in the rotating irradiation unit 5. This current monitor 59 measures the current of the beam, and outputs the measured current value to the power source 22. As shown in Fig. 5, the measured current value output from the current monitor 59 is input to a comparator 225 in the power source 22. On the other hand, the preset target current value is also input to the comparator 225, and is compared with the measured current value. If the result of the comparison indicates that the target current value is larger than the measured current value, the amplifying gain of the amplifier 224 is increased, and vice versa.

[0037] In the method of circularly scanning the diseased part with a beam, which is performed by the remedy system of this embodiment, since the beam ejected from the synchrotron 1 of the first embodiment is used, it is possible to hold the scanning speed implemented by the scanning electromagnets 54 and 55 constant. In a conventional synchrotron, since the ejection amount of a beam depends on the energy of the beam as mentioned previously, if the energy of the beam is low, and the ejection amount of the beam is large, the scanning speed of scanning electromagnets needs to be increased. On the other hand, since the synchrotron 1 of this embodiment ejects the constant ejection amount of a beam, independent of the energy of the beam, the scanning speed of the scanning electromagnets 54 and 55 does not need to be increased. Therefore, it is not necessary to change the value of current fed to the scanning electromagnets 54 and 55. Thus, it becomes possible to irradiate the diseased part with a beam, using a simple control method.

[0038] Although the circular scanning of a beam is adopted in this embodiment, a scanning type is not restricted to the circular scanning, and any type of scanning can be applied in the present invention, which brings the same effects as those gained in this embodiment.

The third embodiment:

[0039] The different points between the remedy systems of the second and third embodiments are explained below. As shown in Fig. 6, in this embodiment, the diseased part to be irradiated with a beam is divided into a plurality of layer regions L1 - Ln (referred to as layers L1 - Ln) in the beam proceeding direction, and each layer, for example, the layer L1, is further divided into a plurality of sub-regions A11, A12, ... Every sub-region is separately irradiated with the beam. The composition of the remedy system of this embodiment is the same as that of the remedy system of the second embodiment.

[0040] In this embodiment, each layer is irradiated with the beam with the energy such that a Bragg peak is positioned at this layer. Therefore, while the position of the target layer becomes shallower from the layer L9 to the layer L1, the energy of the beam needs to be lowered. Thus, according to this embodiment, even if the energy of the beam is changed corresponding to the position of the layer to be irradiated, the ejection amount of the beam can be held constant.

[0041] When the target sub-region (A11, A12 ...) to be irradiated is changed, the strength of the high-frequency electromagnetic field applied to the beam by the high-frequency electromagnetic field applying unit 11 is temporarily decreased, for example, to one tenth of the strength during the irradiation operation. By the above temporary decrease of the electromagnetic field, the irradiation dose which the human body receives while the target sub-region is changed can be decreased, and a surplus irradiation dose can be reduced.

[0042] Further, if the applying of the high-frequency electromagnetic field to the beam is stopped while the beam is transferred to the next region, the surplus irradiation dose during the transferring of the target region can be removed.

[0043] In reducing the ejection amount of the beam, or stopping of the beam ejection during the transferring of the beam to the next region, which is performed in this embodiment, the irradiation dose of the beam can be accurately controlled if the ejection amount of the beam is constant independent of the energy of the beam. That is, a definite time is necessary for reducing the ejection amount or stopping the ejection of the beam, and the human body is irradiated with the beam a little for that time. If the ejection amount of a beam depends on the energy of the beam just as it does in a conventional synchrotron, since the irradiation dose for a time of reducing the ejection amount or stopping the beam ejection also differs depending on the energy of the beam, it is necessary to irradiate the human body by taking this point into account. On the other hand, according to the this embodiment, since the ejection amount can be hold constant independent of the energy of the beam, the irradiation dose for a time of reducing the ejection amount or stopping the beam ejection, independent of the energy of the beam, also becomes constant, and the value of that irradiation dose can be estimated in advance, which makes it possible to accurately control the dose of the irradiation on the human body.

[0044] In the above embodiments, the time width T of the ejection-start to the ejection-stop is about 0.5 sec. However, if a lung or a liver which moves synchronizing with breathing is treated, since the ejection of the beam needs to be performed only for a time during which the breathing is stopped, it is desirable to set T as about 0.2 sec. According to the embodiments, the time T can be easily set.

[0045] As described above, in accordance with the present invention, a charged-particle beam can be ejected with a simple control.

Claims

1. A charged-particle beam ejection method of ejecting a charged-particle beam from an accelerator by applying a high-frequency electromagnetic field to said charged-particle beam revolving in said accelerator, wherein the strength of said high-frequency electromagnetic field is set based on the energy of said charged-particle beam to be ejected from said accelerator.

2. A charged-particle beam ejection method of ejecting a charged-particle beam according to claim 1, wherein the higher the energy of said beam is, the higher value the strength of said high-frequency electromagnetic field is set to.

3. A charged-particle beam ejection method of ejecting a charged-particle beam according to claim 1, wherein the lower the energy of said beam is, the lower value the strength of said high-frequency electromagnetic field is set to.

4. A charged-particle beam ejection method of ejecting a charged-particle beam according to claim 1, wherein the strength of said high-frequency electromagnetic field is gradually increased from the start to the end of ejecting said charged-particle beam.

5. A charged-particle beam ejection method of ejecting a charged-particle beam according to claim 1, wherein a frequency of said high-frequency electromagnetic field is controlled based on the energy of said charged-particle beam.

6. A charged-particle beam ejection method of ejecting a charged-particle beam according to claim 1, wherein the strength of said high-frequency electromagnetic field is controlled based on a current value of said charged-particle beam.

7. An charged-particle beam irradiation method of irradiating a diseased part with a charged-particle beam ejected from an accelerator by scanning said diseased part with said charged-particle beam, wherein said charged-particle beam is ejected from said accelerator, using said charged-particle beam ejection method according to claim 1.

8. An charged-particle beam irradiation method of irradiating a diseased part with a charged-particle beam ejected from an accelerator by dividing said diseased part into a plurality of regions and separately irradiating each region with said charged-particle beam and by stopping beam-irradiation while a target region to be irradiated is transferred to a next region, wherein said charged-particle beam is ejected from said accelerator, using said charged-particle beam ejection method according to claim 1.

9. A charged-particle beam ejection apparatus including a high-frequency electromagnetic field applying unit (11) for increasing an amplitude of betatron oscillation in a charged-particle beam revolving in an accelerator by applying a high-frequency electromagnetic field to said beam and an ejection deflector (17) for ejecting said beam in which said amplitude of said betatron oscillation is increased, said charged-particle beam ejection apparatus comprising:

a control unit (3) to control the strength of said high-frequency electromagnetic field based on the energy of charged-particle beam.

10. A charged-particle beam ejection apparatus according to claim 9, wherein a frequency of said high-frequency electromagnetic field is controlled based on the energy of said beam to be ejected.

11. A charged-particle beam ejection apparatus according to claim 9, further including a current monitor to measure a value of current of said charged-particle beam ejected from said ejection deflector, wherein the strength of said high-frequency electromagnetic field is controlled based on said value of said current measured by said current monitor.

Drawing