JP3984918B2 - FFAG betatron - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in emission efficiency of a FFAG (Fixed Field Alternating Gradient) betatron accelerator that generates high energy X-rays or high energy charged particle beams used in the medical field or the like.
[0002]
[Prior art]
In the circular accelerator, as shown in Patent Document 1, particles launched from an electron gun or the like (hereinafter sometimes referred to as a beam) are accelerated while circling on a circular orbit, and when the beam is emitted from the circular orbit, The beam trajectory is bent by an electric field or a magnetic field, guided to the entrance of an exit deflector (hereinafter referred to as an exit septum), and the beam is taken out by the exit septum.
FFAG (Fixed Field Alternating Gradient) accelerators for electron acceleration have been reported only in the prototype of MURA (Midwestern Universities Research Association) (Patent Document 2) (The Review of Scientific Instruments P403 Vol.28 Num. 6 1957).
[0003]
However, in the FFAG betatron, the beam is a continuous beam, and the radius of rotation gradually increases as it is accelerated. Because of this special characteristic, the extraction method is slightly different from the above example, but the integrated value of the acceleration voltage when reaching the exit septum differs depending on the acceleration voltage at the time of incidence. On the other hand, since the orbit radius is determined by the integral value of the acceleration voltage, the orbit is shifted if the integral value of the acceleration voltage is different. As a result, the incident position on the exit septum is shifted and the deflection amount of the beam is changed accordingly, so that the ratio of the beam entering the exit acceptance (the exitable region) changes. For this reason, even if the exit septum is installed at an optimum position for beam emission, the emission efficiency is lowered due to the deviation of the trajectory.
[0004]
[Patent Document 1]
JP-A-5-258900 Circular accelerator and its beam extraction method
[Patent Document 2]
The Review of Scientific Instruments. Volume 28 NUMBER 6. JUNE, 1957
[0005]
[Problems to be solved by the invention]
In the conventional FFAG betatron, the integration value of the acceleration voltage when reaching the exit septum varies depending on the variation of the acceleration voltage. On the other hand, since the orbit radius is determined by the integral value of the acceleration voltage, the orbit is shifted if the integral value of the acceleration voltage is different. As a result, the incident position on the exit septum is shifted and the deflection amount of the beam is changed accordingly, so that the ratio of the beam entering the exit acceptance (the exitable region) changes. For this reason, even if the exit septum is installed at a position optimal for beam emission, there is a problem that the emission efficiency is lowered due to the deviation of the trajectory.
In addition, there is a problem that the acceleration voltage varies depending on the passage of the particles to be accelerated, and it is difficult to keep the acceleration voltage stable.
[0006]
The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an FFAG betatron in which the emission efficiency does not decrease due to fluctuations in acceleration voltage.
[0007]
[Means for Solving the Invention]
The FFAG betatron according to the present invention includes an annular vacuum vessel that forms a passage for charged particles, charged particle incident means for injecting the charged particles into the passage, and the charged particles that are disposed substantially orthogonal to the passage Magnetic field generating means for generating a magnetic field for guiding
An annular central conductor having an acceleration gap in a direction along the passage, an acceleration voltage inducing means arranged to intersect the annular central conductor and inducing an acceleration voltage in the acceleration gap;
An exit for emitting the charged particles to the outside from the passage;
Voltage measuring means for measuring the accelerating voltage, an integrated value of the accelerating voltage measured by the voltage measuring means from the time when the charged particle is incident to an arbitrary time before the time of emission. Integration means to be obtained,
Accelerating voltage correcting means for correcting the output of the accelerating voltage inducing means after the arbitrary time point based on the obtained integral value is provided.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
First, the basic structure of the FFAG betatron may not necessarily be well known to those with ordinary knowledge in the field of this technology. Further, understanding the configuration is indispensable for understanding the present invention, so the outline will be described with reference to the drawings. FIG. 16 is a schematic diagram of the FFAG accelerator, and FIG. 17 is a horizontal sectional view thereof.
Next, the operation will be described. Electrons generated by the electron gun 1 (hereinafter sometimes referred to as particles, charged particles, or particle beams for convenience of explanation) form a ring-shaped vacuum container 3 (charged particle beam passage) by an electrostatic deflector 2. In an annular vacuum vessel). The electron gun 1 and the electrostatic deflector 2 are called charged particle incident means. The electrons are bent by the field magnetic field generated by the electromagnet 4 (magnetic field generating means) and confined on the spiral trajectory 10 (charged particle beam path). Since the field magnetic field is kept constant while the electrons are accelerated, the orbital radius increases as the electron energy increases, and orbits around the orbital radius determined by the energy. Since the strength of the magnetic field is configured to increase as the radius increases, an increase in the radius of the orbit is suppressed.
The ring-shaped vacuum vessel 3 is provided with an acceleration gap 5 (a part of the ring that is electrically cut while maintaining a vacuum) orthogonal to the orbit, and the magnetic flux Φ in the acceleration core 6 changes. At this time, a voltage is induced in the ring-shaped vacuum vessel 3 according to the law of electromagnetic induction, and an electric field is generated in the acceleration gap 5. In this case, the vacuum vessel 3 also serves as an annular central conductor having an acceleration gap in the direction along the passage. The acceleration core 6 is acceleration voltage inducing means. Each time the electric field is circulated, the electrons are accelerated to become a high-energy electron beam 7 and are extracted from the exit septum 11. The exit septum 11 changes charged particles from a circular orbit to an exit orbit. The extracted high-energy electron beam 7 may be used as it is, or may be irradiated to the X-ray conversion target 8 and converted to X-rays 9.
[0009]
This accelerator is a betatron acceleration method, and is high because the circulating particles pass many times during the acceleration phase of the alternating electric field applied to the acceleration gap 5 (period in which the direction of the electric field is the direction of accelerating electrons). Get energy. That is, the period from the incidence to the emission of electrons ends within one cycle of the alternating electromagnetic field. This will be described with reference to FIG. 18 showing the acceleration voltage applied to the acceleration gap 5 and the timing of electron incidence and emission. In FIG. 18, an acceleration time 13 and an incident time 14 enter the acceleration phase 12. Usually, in the acceleration phase 12 of the sine wave used for core driving, the acceleration voltage takes a positive value only for half the time. Next, the relationship between the electron incidence and emission timings, the acceleration time 13 and the incident time 14 will be described. The electrons begin to be introduced into the ring-shaped vacuum vessel 3 at the same time as the acceleration time 13 starts. The introduction continues for the incident time 14.
[0010]
FIG. 19 is a schematic diagram for explaining how electrons are emitted. A deflection magnetic field 15 is provided in a part of the spiral trajectory 10. When the electrons reach the set energy, the corresponding orbit radius is reached. Since the energy corresponds to the integral value of the acceleration voltage received by the electrons during acceleration, when this value reaches a certain value, the trajectory radius suitable for emission (referred to as the emission trajectory radius) is reached. A deflection magnetic field 15 is provided at the exit orbit radius, and the deflection magnetic field 15 causes the electrons to be greatly bent outward, creating a space between the orbits where the exit septum 11 can be disposed. The electrons incident on the exit septum 11 have their trajectories bent by an electric field or a magnetic field, and travel toward an exit (not shown, but near the exit side of the exit septum 11). At this time, if electrons (E0, E2, etc.) whose electron energy is not the predetermined value E1 are included, the amount of deflection due to the magnetic field is different, and therefore, the beam is deviated from the emission acceptance (emergence possible region) of the emission septum 11. The emission efficiency of the is reduced.
[0011]
FIG. 20 shows an example of a core drive circuit that gives an acceleration voltage. In the voltage generated by this circuit, voltage fluctuation of the AC source and voltage drop due to discharge from the capacitors C1 and C2 appear, and therefore voltage fluctuation of about several percent occurs. As a result, the time at which the integral value of the acceleration voltage becomes constant fluctuates by several percent, and the integral value of the acceleration voltage differs between the incident initial electron and the final electron, resulting in a decrease in emission efficiency.
[0012]
Embodiment 1 FIG.
The FFAG betatron according to Embodiment 1 of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic diagram showing a configuration of the FFAG betatron according to the first embodiment, and FIG. 2 is an explanatory diagram of a core voltage for explaining the operation of the FFAG betatron of FIG.
Next, the operation will be described. The acceleration core 6 is driven by the core driving power source 18, whereby an acceleration voltage is induced in the annular central conductor (here, the vacuum vessel 3) wound around the acceleration core 6, and a voltage is generated in the acceleration cap 5. FIG. 2A shows an example of a change in the acceleration voltage applied to the acceleration gap 5 within the acceleration time period 13. If a constant voltage such as the planned value Vc is obtained, the emission efficiency does not change. However, for example, if it is assumed that the output energy is 5 MeV by accelerating 1000 times at 5 kV, if an error of 1% is allowed in the energy level at the time of emission, the acceleration voltage reproducibility with an error of 0.001% or less is Although required, this accuracy is difficult to realize with ordinary electronic circuit technology, and thus varies as indicated by 201 in the figure.
[0013]
Therefore, the acceleration voltage is monitored by the voltmeter 16 (voltage measuring means), and the integrated value of the acceleration voltage corresponding to (proportional to) the energy of the particles is integrated by the integrating circuit 17 (integrating means) from the start of acceleration (time 0). Measurement is performed until a certain time (time t1) during the acceleration period. FIG. 2B shows an integral measurement value of the acceleration voltage. Based on the measured integral measurement value, an energy error of particles estimated to occur at the time of emission is calculated, and the output voltage of the core drive power supply 18 after time t1 is corrected so as to correct this error. This calculation is performed by the acceleration voltage correction circuit 117 (acceleration voltage correction means). This is shown in FIG. 2 (c). By correcting in this way, as shown in FIG. 2D, the acceleration voltage at the time of particle emission (when charged particles pass through the emission septum 11 and exit the emission port) is corrected to the initial predetermined value. I can do it.
[0014]
Next, the effect will be described. If the structure of FIG. 1 is taken, the voltage control precision requested | required of the core drive power supply 18 will be eased. That is, let Ta be the time length required from incidence to emission, Tc be the correction time length, and let ΔVa and ΔVc be the allowable error voltages, respectively. Since the allowable value of the error is the product of these (Ta · ΔVa and Tc · ΔVc), the relationship ΔVc / ΔVa = Ta / Tc holds. For example, when the correction time Tc is 1/10 of the acceleration time Ta, the voltage accuracy of the power supply for obtaining the output energy accuracy obtained when the power supply voltage accuracy is 0.001% is relaxed to 0.01% (however, the acceleration voltage Monitor accuracy is not relaxed).
[0015]
Embodiment 2. FIG.
The configuration of the FFAG betatron according to the second embodiment will be described with reference to FIG. In the configuration of FIG. 3, a second acceleration core 19 (auxiliary core) is provided separately from the acceleration core 6 (referred to as the first acceleration core in FIG. 3) and the first drive power supply 18 that drives the first acceleration core 6. And a second drive power supply 20 that supplies current to the core. The second driving power source 20 does not need to generate a main acceleration voltage and supplies only a magnetic field for generating a correction voltage for correcting the error voltage ΔV, so that the size of the core is smaller. The corrected voltage accuracy is the product of the two power supply accuracy. That is, in order to achieve an accuracy of 0.001%, each needs to have an accuracy of approximately 0.3%.
[0016]
The correction circuit 118 calculates a correction amount based on the signal from the integration circuit 17 and controls the second drive power supply 20.
Although not shown in the drawing, if the correction means described in the first embodiment is further combined with the above, the accuracy required for each power source is 1%, which can be easily realized. However, as in the first embodiment, the monitoring accuracy of the acceleration voltage is not relaxed. When monitoring cannot be performed with sufficient accuracy, it is necessary to perform monitoring with higher accuracy as described in Embodiments 6 and 7 described later.
Further, if a plurality of second acceleration cores 19 having the configuration shown in FIG. 3 are combined, the requirement for accuracy is reduced in terms of a geometric series. When the auxiliary core 19 (second acceleration core) is used separately from the acceleration core 6 (first acceleration core), there is an advantage that interference between power sources that drive each core is reduced. When the same core is excited by a plurality of power sources, an induced voltage generated by magnetic flux excited by another power source is applied to the power source, so a protection circuit is required. However, as shown in FIG. If they are provided separately, the degree of mutual interference between the voltages decreases.
[0017]
Embodiment 3 FIG.
The configuration of the FFAG betatron of the third embodiment is the same as that of FIG. 3 of the second embodiment, and the magnetic permeability of the magnetic material constituting the second acceleration core 19 is set to the magnetic property of the first acceleration core 6. The magnetic permeability material is higher than the magnetic permeability of the material. The first accelerating core 6 is required to increase the fluctuation magnetic flux amount Φ = B · S (B: in-core magnetic flux density, S: core cross-sectional area) in order to keep the acceleration voltage long. When the core cross-sectional area is large, an expensive material is expensive, and therefore, a material such as a silicon steel plate that is inexpensive and has a high saturation magnetic flux density is desirable. On the other hand, the second acceleration core 19 is required to have a high saturation magnetic flux density and good response to the correction signal, that is, one that can be driven at a high frequency. In terms of cost, the core cross-sectional area required for the second accelerating core 19 is within a few percent of the cross-sectional area of the first accelerating core 6, so even if a slightly expensive material is used, the effect on the overall cost is not affected. small.
[0018]
The drive current I = B · L / μ (L: average magnetic path length, μ: magnetic permeability) is smaller as the magnetic permeability of the core is larger. That is, a high saturation magnetic flux density high magnetic permeability material (permalloy, iron-based amorphous, iron-based nanocrystal material, etc.) having a permeability 5 to 30 times larger than that of a silicon steel plate is used as the magnetic material of the second acceleration core 19. By using the auxiliary core, it is possible to obtain an auxiliary core having good responsiveness to the correction signal. In addition, FIG. 4 shows the relationship between the frequency characteristics and power supply capacity of the power semiconductor described on page 38 of Power Electronics (Masao Yano, Ryohei Uchida, published by Maruzen Co., Ltd.). As shown in the figure, the smaller the power source capacity is, the higher the frequency can be driven. In the case of the second accelerating core, the voltage to be corrected is determined. Therefore, if the drive current is reduced and the drive power is reduced, the second acceleration core can be driven at a higher frequency, and the responsiveness can be further improved.
[0019]
Embodiment 4 FIG.
The fourth embodiment relates to a temporal change of the correction voltage described in the first and second embodiments, that is, a correction voltage pattern. As described above, since charged particles are incident continuously for a certain length, it takes a finite time from the start of incidence when the first particle begins to be incident until the last particle is completely incident (referred to as an incident period). . In addition, it takes a finite time from the start of emission when the first particle starts to be emitted until the last particle is emitted (referred to as an emission period).
In Embodiments 1 and 2, the integral value of acceleration voltage (particle energy) is corrected so as to be constant at the end of acceleration (the time when particles pass through the exit port) in order to increase the extraction efficiency. Strictly speaking, the timing at which the acceleration voltage fluctuates is either within the incident period from the start of incidence to the end of incidence and within the exit period from the start of emission to the end of exit, or from the end of incidence to the start of emission. Depending on whether or not, the method of fluctuation of the particle energy is different (details will be described later). For this reason, it is desirable that the correction method also corrects with different voltage patterns depending on the difference in the conditions.
[0020]
This situation will be described with reference to FIG. FIG. 5A shows an example of a change in acceleration voltage from the start of incidence to the end of emission. In the figure, Vc (broken line) is a set voltage, and a solid line 202 indicates an actual acceleration voltage. In this accelerator, a continuous beam having a certain length is incident. The length from the beginning to the end of the beam is appropriately set in the range of several turns to about 100 turns (when the spiral rotation speed is 1000 turns) in the vacuum vessel 3.
For this reason, immediately after the incident, only the tip of the continuous beam is inside the vacuum vessel 3 of the accelerator, and the rest is not incident. This situation corresponds to the section A in FIGS. 5 (a) and 5 (b). When the end of the beam enters the accelerator, it becomes a phase where all the beams exist inside the accelerator. This situation corresponds to section B. Finally, the head of the beam is emitted and the rest is in the phase in the accelerator. This situation corresponds to section C.
[0021]
Next, the integrated value (according to the particle energy) of the acceleration voltage applied to the leading particle ((1) in FIG. 5 (b)), the middle particle ((2)), and the final particle ((3)). Pay attention. Since the leading particles exist in the accelerator between the start of incidence and the start of emission, the acceleration voltage is applied during the interval A + the interval B. Similarly, the final particles are accelerated with an acceleration voltage between the interval B and the interval C. That is, the acceleration voltage in the section B is applied to all particles in common, whereas the acceleration voltage in the sections A and C is applied only to the particles existing in the accelerator. Depending on the position, the influence of fluctuations in the acceleration voltage varies.
[0022]
FIG. 5 (c) shows the energy distribution of particles due to the difference in position in the beam when the acceleration voltage changes as shown in FIG. 5 (a). The fluctuation in the acceleration voltage in the section B affects all particles, so it is related only to the increase or decrease in the average energy. However, if there is a difference in the acceleration voltage between the sections A and C, the position of the position in the continuous beam An energy difference is produced between different particles.
The voltage correction according to the fourth embodiment is for the purpose of correcting the average energy (that is, adjusting the level of (2) to a predetermined value) among the above, and the energy difference between the particles in the continuous beam. This correction (that is, matching the levels (1) and (3)) will be described in the fifth embodiment.
Since the acceleration voltage in the section B equally applies energy to all particles regardless of the waveform, the voltage may be corrected so that the integrated value of the corrected acceleration voltage matches the desired correction value.
FIG. 6 shows an example of correcting the integral value by changing the correction time while keeping the correction voltage constant as one of the acceleration voltage correction methods for matching the integral values. This correction voltage pattern can be easily configured using a switching circuit such as an IGBT. There are other ways to match the integral values
Change the voltage at a constant time.
A switching circuit cuts out the integrated value from an arbitrary waveform (such as a sine wave). However, since these are well-known techniques for electronic circuits, detailed description thereof is omitted here.
[0023]
T1 in FIGS. 6A, 6B, and 6C is a monitoring time for predicting the correction amount of the acceleration voltage average value. T2 is the time during which the leading particle is present in the accelerator, and T2-T1 is the average value correctable time. The correction is performed as follows. First, based on the data obtained by sampling the acceleration voltage up to time T1, the acceleration voltage waveform in the entire T2 time is predicted, and the integral value (correction amount = VTo) of the error amount of the acceleration voltage obtained therefrom is obtained (FIG. 6). (b)). At this time, the correction amount can be predicted in a short time by using a conversion coefficient created based on a database of sampling data obtained in the past. If the correction amount is divided by the correction voltage V1, the necessary correction time Tp can be obtained, and the acceleration voltage may be applied during this time.
Of course, V1 is selected so that Tp <T2-T1.
By such correction, there is an effect that the average energy of the beam can be set to a desired value even if an inexpensive power source with a little accuracy is used, and the beam loss lost due to the deviation of the beam energy can be reduced.
[0024]
On the other hand, the maximum correction amount of the integral value (particle energy) is a product Ec (= Vc · Tc) of the acceleration voltage Vc and the circulation time Tc in the emission energy. Since this amount can be corrected by rotating the particles once more, it can also be corrected by adjusting the number of rotations. For example, if the correction value ΔE = 3Ec + Eh, it is possible to correct 3Ec by rotating around three extra times, so the remaining Eh may be corrected. This is shown in FIG. It can be seen that in order to reach the predetermined energy, only the amount that cannot be corrected by the circulation (ie, Vh) needs to be corrected.
By correcting in this way, the correction power supply voltage can be reduced, the power supply cost can be reduced, and the cross-sectional area of the correction core (second acceleration core 19 in FIG. 3) can be reduced, so that the core cost is reduced. There is an effect. Although the correction described in this embodiment is not shown, it is executed by a pulse correction circuit provided in the acceleration voltage correction circuit 118 of FIG.
[0025]
Embodiment 5 FIG.
In the fifth embodiment of the invention, the average energy of the beam is not corrected, but the energy distribution of the particles due to the difference in the influence of the acceleration voltage variation due to the position of the particles in the beam described in the fourth embodiment (that is, This relates to a correction for the difference between (1) and (3) in FIG. FIG. 8 shows the correction voltage of the particle energy distribution resulting from the fluctuation of the acceleration voltage and the corrected particle energy distribution. Since the energy difference is given to the particles in the sections A and C described in the fourth embodiment (the sections A, B, and C are the same as those in the fourth embodiment, the description is omitted). The correction is adjusted within this range. As shown in FIG. 8B, there are three adjustment methods: section A only (301), section C only (302), and A and C (303).
[0026]
When the correction is made in the section A or C (301, 302), it is necessary to correct the voltage so that the acceleration voltage becomes constant in this section. By this correction, the energy in the beam becomes constant as shown in FIG.
To keep the acceleration voltage constant,
The acceleration voltage is monitored and fed back so that the acceleration voltage becomes constant.
When the acceleration voltage change pattern is constant, feed-forward from the previous acceleration voltage change pattern is performed to output a precorrected level.
There is a way.
[0027]
Embodiment 6 FIG.
As for the correction in the section C (302 in FIG. 8B) described in the fifth embodiment, in addition to (1) and (2) described in the fifth embodiment, position information of the emitted beam is fed back. There is also a way to do it. FIG. 9 shows such a configuration. In the figure, the beam position detection electrodes 21a and 21b are arranged on both sides of the track near the exit side of the exit septum 11 (also referred to as the exit port) while being shifted in the direction of the diameter of the orbit. The beam position detection electrodes 21a and 21b can also be used as septum electrodes. The currents of both electrodes are measured by the current detection means A. When the beam position approaches the electrode 21a, the current I1 increases. When the beam position approaches the electrode 21b, the current I2 increases.
[0028]
If the beam is incident on the center X0 of the septum 11 when the beam has a predetermined energy, the direction deflected by the deflection magnetic field 15 changes in a positive or negative direction when the energy changes.
As a result, the beam current incident on the beam position detection electrodes 21a and 21b changes corresponding to the change in the incident position of the beam as shown in FIG. The horizontal axis of FIG. 10 indicates the distance in the direction from the electrodes 21a to 21b (position where the beam passes). If the accelerating voltage is changed so that both currents are minimized or one level is a predetermined low level, the beam emission efficiency can be improved.
[0029]
In this configuration, since it is not necessary to feed back the acceleration voltage signal, voltage correction by the acceleration voltage monitor may be approximate, and the accuracy required for monitoring can be greatly relaxed.
In Embodiments 4, 5, and 6, beam energy control can be performed at higher speed and with higher accuracy by combining 4 and 6, or 4 and 5, or 4 and 5, and 6. As described in the third embodiment, this means that the smaller the power required for correction, the faster the element that can be used. For example, the control of 4 is handled by a power switching element such as an IGBT, and for 5 and 6, the rough control is performed by the switching element, and a portion requiring a high-speed response that cannot be followed by the switching element is required. A power amplifier using an FET or the like may be used. At that time, as described in the third embodiment, the core controlled by the power amplifier is formed of a high permeability material, and the required power is minimized, thereby enabling higher speed control.
As described above, by combining the fourth, fifth, and sixth embodiments, it is possible to suppress the power of the power source that is required to be high speed, and it is possible to increase the speed. There is an effect that more efficient emission becomes possible.
[0030]
Embodiment 7 FIG.
  In the embodiments so far, the acceleration voltage is monitored to obtain the integral value. However, in order to accurately obtain the integrated value of the acceleration voltage, an ultra-high accuracy monitor is required as described above. However, high-accuracy measurement of the accelerating voltage is often difficult to use in a noisy environment because the influence of noise is inevitable.
  Therefore, a method for monitoring particle energy using particle arrival time (corresponding to particle velocity) instead of obtaining particle energy by monitoring the integral value of the acceleration voltage will be described with reference to FIG. In the figure, an electrode 22 (incident beam detector) placed so as to surround the trajectory and an electrode (exit beam detector) 23 placed around (or near) the exit position are provided around (or near) the entrance position. As the beam passes through these electrodes, a charge is induced on the electrodes having a polarity opposite to the charge polarity of the beam particles.
  The detector voltage due to the induced charge is as shown in FIG. That is, the voltage V1 is generated at the detector at the incident position while the beam is incident, and the voltage V2 is generated at the detector at the output position while the beam is emitted. The time ΔT from when the beam is incident to when it is emitted is determined by the velocity of the particles depending on the energy of the beam. If the number of laps in the beam accelerator is the same, the energy can be calculated back from ΔT. The determination of whether or not the number of laps is the same depends on the acceleration voltage monitor. However, since the monitoring only needs to have a resolution equivalent to one acceleration voltage, the accuracy requirement is greatly eased. Perform the above correctionThingsThis is called particle velocity correction means.
  Finally, the relationship between the present embodiment and claim 7 will be specifically described. The “charged particle incident position detector provided in the passage” according to claim 7 is a device that reads a change in electrostatic capacity or magnetic field accompanying the passage of the beam, and its output can not only detect the beam position, It can also be used as a monitor for beam transit time. Therefore, when the output is taken on the time axis, a beam passage timing monitor is obtained as shown in FIG. That is, “the time from when the output of the incident position detector is generated until when the output of the output position detector is generated” is the timing of signal extinction of the output position detector in FIG.
(T0−H2) − (t0−ΔT−H1) = ΔT + (H1−H2),
  On the other hand, “the time from when the output of the incident position detector disappears until the output of the output position detector disappears” corresponds to ΔT in FIG. That is, controlling so that this time becomes the same is nothing but controlling so that H1 = H2.
On the other hand, if the acceleration voltage is the same from the beginning to the end, the time required for acceleration of the first particle and the final particle shown in FIG. 5 becomes equal, and H1 = H2, but if the acceleration voltage changes, H1 = H2. Don't be. That is, the acceleration voltage can be corrected by performing control so that H1 = H2.
[0031]
H1 in FIG. 12A indicates the length of time that the incident beam passes through the incident beam detector 22. H2 indicates the length of time that the outgoing beam passes through the outgoing beam detector 23.
FIG. 12B shows a method for measuring not only the energy of the head beam but also the energy distribution in the beam. Before the incident beam enters the accelerator, for example, a pulse voltage is applied to an electrostatic deflector (not shown) at a constant interval, so that the particle flow is cut off at a constant interval as shown in the figure. This incident time interval is set to f1 = f2 = f3 = f4. When the beam energy is constant in the entire section, the fragmented pulse time width F at the time of beam emission is equal to f. If f1> F1 in the figure, the energy of the last beam is smaller (slower) than the first beam in this region. That is, by measuring the pulse width at the time of emission and comparing it with that at the time of incidence, the increase / decrease in the acceleration voltage can be known, and the acceleration voltage can be kept constant by feeding back this signal to the acceleration voltage.
In this measurement, it is not necessary to measure the absolute values V1 and V2 of the voltage due to the charge induced in the detector, and it is only necessary to measure the voltage rising timing, so that the influence of noise can be greatly reduced. . For this reason, there is an effect that energy measurement can be easily performed with high accuracy.
[0032]
Embodiment 8 FIG.
In the first to seventh embodiments described so far, by means of controlling the beam energy to be constant, any part of the beam is similarly accurately entered into the exit septum passage to improve the emission efficiency. I was letting. However, even if the energy is not made constant, any part can enter the passage similarly by bending the beam trajectory according to the part of the beam. This configuration will be described with reference to FIG. In the figure, a beam deflector (also referred to as a beam deflector) 24 and a beam deflector control power supply 25 are used. In order to correct the deflection of the beam caused by the error in the integrated value of the acceleration voltage, the trajectory is corrected by adding a corresponding correction deflection electric field, and control is performed to improve the beam emission efficiency. This is referred to as second control means. At this time, it goes without saying that the method described in the sixth and seventh embodiments may be used as a method of feedback control or feedforward control.
[0033]
Embodiment 9 FIG.
In the eighth embodiment, the beam deflector 24 is newly attached to deflect the beam. However, the beam can be deflected by changing the operating condition of the accelerator component.
14 and 15, among the accelerator components, the excitation power source 299 of the deflection magnetic field 15 or the electromagnet power source 300 of the electromagnet 4 is controlled using the above-described method (this is referred to as third control means), and the beam A configuration for improving the emission efficiency is shown. In these structures, since it is not necessary to newly attach the beam deflector 24, the cost can be reduced.
[0034]
【The invention's effect】
In the FFAG betatron according to the present invention, since the voltage integral value of the acceleration voltage is corrected, there is an effect that high accuracy is not required for the voltage control accuracy of the acceleration voltage.
Moreover, the emission efficiency of charged particles is improved by appropriately correcting the acceleration voltage.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an FFAG betatron according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining the operation of FIG. 1;
FIG. 3 is a configuration diagram of an FFAG betatron according to a second embodiment of the present invention.
FIG. 4 is a characteristic diagram for explaining the operation of the third embodiment of the present invention.
FIG. 5 is an explanatory diagram for explaining the operation of a fourth embodiment of the present invention.
FIG. 6 is an explanatory diagram for explaining the operation of a fourth embodiment of the present invention.
FIG. 7 is an explanatory diagram for explaining the operation of a fourth embodiment of the present invention.
FIG. 8 is an explanatory diagram for explaining the operation of the fifth embodiment of the present invention.
FIG. 9 is an explanatory diagram illustrating the configuration of an FFAG betatron according to a sixth embodiment of the present invention.
FIG. 10 is an explanatory diagram for explaining the operation of FIG. 9;
FIG. 11 is an explanatory diagram illustrating a configuration of an FFAG betatron according to a seventh embodiment.
12 is an explanatory diagram for explaining the operation of the apparatus of FIG.
FIG. 13 is an explanatory diagram illustrating the configuration of an FFAG betatron according to an eighth embodiment of the present invention.
FIG. 14 is an explanatory diagram for explaining the operation of the FFAG betatron according to the ninth embodiment of the present invention.
FIG. 15 is an explanatory diagram illustrating the configuration of an FFAG betatron according to a ninth embodiment of the present invention.
FIG. 16 is an explanatory diagram illustrating the structure of a FFAG betatron.
FIG. 17 is a horizontal sectional view of FIG. 16;
FIG. 18 is an explanatory diagram for explaining the operation of FIG. 16;
FIG. 19 is an explanatory diagram for explaining the operation of FIG. 16;
20 is a circuit diagram of a power supply device used in the FFAG betatron of FIG.
[Explanation of symbols]
1 electron gun, 2 electrostatic deflector, 3 ring-shaped vacuum vessel,
4 electromagnets, 5 acceleration gaps, 6 acceleration cores,
11 exit septum, 15 deflection magnetic field device, 16 voltmeter,
18 first drive power source, 19 second acceleration core,
20 Second drive power supply, 21a, 21b Beam position detector,
177 Acceleration voltage correction circuit,
188 correction circuit, 299 excitation power supply,
300 Electromagnet power supply.

Claims (10)

An annular vacuum vessel that forms a path for charged particles;
Charged particle incident means for injecting the charged particles into the passage;
A magnetic field generating means that generates a magnetic field that is arranged substantially perpendicular to the passage and guides the incident charged particles into the passage;
An annular central conductor having an acceleration gap in a direction along the passage, an acceleration voltage inducing means arranged to intersect the annular central conductor and inducing an acceleration voltage in the acceleration gap;
An exit for emitting the charged particles to the outside from the passage;
Voltage measuring means for measuring the acceleration voltage;
Integration means for obtaining an integral value of the acceleration voltage measured by the voltage measurement means between the time when the charged particles are incident and an arbitrary time before the emission time;
An FFAG betatron comprising accelerating voltage correcting means for correcting an output of the accelerating voltage inducing means after the arbitrary time point based on the obtained integral value.   The accelerating voltage inducing means includes an accelerating core that induces an accelerating voltage in the central conductor and a core driving power source that excites the accelerating core, and the accelerating voltage correcting means corrects the output of the core driving power source. The FFAG betatron according to claim 1, wherein the FFAG betatron is present. The acceleration core includes a first acceleration core that generates a predetermined acceleration voltage, and a second acceleration core that generates a correction acceleration voltage for correcting an integral value of the acceleration voltage,
The core drive power source includes a first drive power source for exciting the first acceleration core, and a second drive power source for exciting the second acceleration core,
3. The FFAG betatron according to claim 2, wherein the acceleration voltage correction unit corrects an output of the second drive power supply. 4.   4. The FFAG betatron according to claim 3, wherein the magnetic material constituting the second acceleration core has a magnetic permeability higher than that of the magnetic material constituting the first acceleration core. 5. The accelerating voltage correcting unit is configured to apply a predetermined predetermined voltage pulse time to be applied to the second acceleration coil after all of the charged particles are incident and before a part of the charged particles are emitted. The FFAG betatron according to claim 3, further comprising a pulse correction circuit that corrects an integral value of the acceleration voltage by changing a width.   The acceleration voltage correcting means is configured such that the integral value of the acceleration voltage is equal within a time period in which a part of the charged particles is incident and a part is not incident or a part is emitted and a part is not emitted. The FFAG betatron according to claim 3, wherein the FFAG betatron is corrected so that An annular vacuum vessel that forms a path for charged particles;
Magnetic field generating means that is substantially orthogonal to the path and guides the charged particles into the path;
An annular central conductor having an acceleration gap in a direction along the passage, an acceleration voltage inducing means arranged to intersect the annular central conductor and inducing an acceleration voltage in the acceleration gap;
An exit port through which the charged particles exit from the passage and exit to the outside;
The incident position detector of charged particles is provided in the passageway, by the emitting position detector provided near said exit, the output of the output position detector is generated from the output of the incident position detector is generated Until the output of the incident position detector disappears and the output of the output position detector disappears. A FFAG betatron comprising particle velocity correcting means for correcting the output of the means. A deflection magnetic field device that is provided in the vicinity of the exit and applies a correction deflection magnetic field;
2. The FFAG betatron according to claim 1, further comprising third control means for controlling the deflection magnetic field device or the magnetic field generating means in accordance with an output signal of the integrating means.   A beam position detector that outputs a position signal by measuring a radial position of the charged particles in the passage by a current flowing into an electrode provided on the exit side of the charged particles; The FFAG betatron according to any one of claims 1 to 6, wherein the acceleration voltage correction means is adjusted by a signal.   A beam position detector that outputs a position signal by measuring a radial position of the charged particles in the passage by a current flowing into an electrode provided on the exit side of the charged particles; 8. The FFAG betatron according to claim 7, wherein the particle velocity correcting means is adjusted by a signal.

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