JP7535972B2 - Charged particle beam transport device - Google Patents

Description

The present invention relates to a charged particle beam transport device.

Patent Document 1 describes a technology for reducing beam divergence caused by the space charge effect of a charged particle beam. This patent document states that "an electron beam device characterized by irradiating an ion beam into the trajectory region of an electron beam to neutralize the space charge formed by the electron beam and reduce the space charge effect," and that "the ion generating means is characterized by changing the ion beam density according to the magnitude of the current density of the electron beam along the trajectory of the electron beam."

JP 2007-19195 A

Patent Document 1 describes an apparatus that efficiently reduces the space charge effect by adjusting the irradiation position of the ion beam according to the current density of the electron beam. However, the apparatus described in Patent Document 1 cannot neutralize the space charge in response to the variation in the amount of space charge in the circumferential direction of the charged particle beam. If the amount of space charge varies in the circumferential direction of the charged particle beam, the amount of beam divergence varies in the circumferential direction of the charged particle beam.

The object of the present invention is to reduce the variation in the amount of beam divergence in the circumferential direction of a charged particle beam.

The present invention is a charged particle beam transport device in a linear accelerator, characterized in that it comprises a plurality of measuring devices arranged on the sides of the path of the charged particle beam in a sealed chamber and in different radial directions of the charged particle beam to measure the amount of divergence of the charged particle beam, a plurality of neutralizing agent outlets arranged on the sides of the path of the charged particle beam and in different radial directions of the charged particle beam corresponding to the plurality of measuring devices to release a space charge neutralizing agent to the charged particle beam to neutralize space charge, a neutralizing agent flow regulator for adjusting the amount of the space charge neutralizing agent released from each of the plurality of neutralizing agent outlets toward the charged particle beam, and a control device for controlling the neutralizing agent flow regulator based on the measurement results of the plurality of measuring devices, and causing the plurality of neutralizing agent outlets to radiate different amounts of the space charge neutralizing agent toward the charged particle beam.

The present invention can reduce the variation in the amount of beam divergence in the circumferential direction of a charged particle beam.

1 is a schematic diagram illustrating the configuration of a linear accelerator including a charged particle beam transport device according to a first embodiment. 1 is a schematic diagram of a charged particle beam transport device as viewed from the beam axis direction. 4 is a flowchart showing a flow of processing by the charged particle beam transport device according to the first embodiment. FIG. 11 is a schematic diagram of a linear accelerator including a charged particle beam transport device according to a second embodiment.

The following describes the examples using the drawings.

First Embodiment
A first embodiment of the present invention will be described below with reference to Figures 1 to 3. Figure 1 is a schematic diagram of a linear accelerator including a charged particle beam transport device 3 according to the first embodiment. The linear accelerator shown in Figure 1 includes a charged particle beam generator 2 that generates a charged particle beam 1, and a charged particle beam transport device 3 that transports the charged particle beam 1.

The charged particle beam generating device 2 may be, for example, a microwave ion source, an ECR (Electron Cyclotron Resonance) ion source, a duoplasmatron, or an electron gun. In this embodiment, a microwave ion source is used as the charged particle beam generating device 2.

The plasma 4 generated by microwaves in the charged particle beam generating device 2 is extracted by the potential difference with the extraction electrode 5. This generates the charged particle beam 1. In this embodiment, the charged particle beam 1 is composed of hydrogen ions as charged particles.

The charged particle beam transport device 3 is a device that transports the generated charged particle beam 1. The charged particle beam transport device 3 includes a sealed chamber 3a. The charged particle beam 1 generated by the charged particle beam generating device 2 is injected into the sealed chamber 3a and transported through the sealed chamber 3a.

A focusing coil 6 is provided along the outer wall of the sealed chamber 3a. The charged particle beam 1 is focused by the focusing coil 6 within the sealed chamber 3a and is then injected into the post-stage accelerator 7. The focusing coil 6 may be, for example, a magnetic pole made of a magnetic material. However, even if the focusing coil 6 is provided, due to the repulsive force between the charged particles that make up the charged particle beam 1 (in other words, due to the space charge effect), the emittance, which determines the amount of divergence of the charged particle beam 1, increases.

The charged particle beam 1 transported by the charged particle beam transport device 3 is injected into the post-accelerator 7. The post-accelerator 7 may be, for example, a high-frequency accelerator, such as an RFQ (Radio Frequency Quadrupole) or a DTL (Drift Tube Linac), or a combination of these. The post-accelerator 7 may also be an electrostatic accelerator, such as a Cockcroft-Walton type or a Van De Graaff type.

An absorber 9 is provided inside the sealed chamber 3a (specifically, near the beam exit port to the post-accelerator 7). The divergent beam 8 that diverges inside the sealed chamber 3a and contains unwanted ions is received by the absorber 9. This prevents the divergent beam 8 from entering the post-accelerator 7.

For example, the divergent beam 8 includes a beam portion diverged by the space charge effect formed by the charged particle beam 1, and unwanted ions other than hydrogen ions, such as deuterium. Deuterium ions and the like have a larger mass than hydrogen ions, so they diverge without being focused by the focusing coil 6. In the linear accelerator shown in FIG. 1, the absorber 9 is shaped to have a thickness in the direction of beam travel of the charged particle beam 1, and a through hole is provided through which the charged particle beam 1 passes, and the through hole is shaped like a cone (the hole diameter becomes smaller the further downstream in the beam path of the charged particle beam 1), so that the unwanted ions that are not focused can be stopped efficiently.

In the above-mentioned linear accelerator, in order to reduce beam divergence due to the space charge effect, the charged particle beam transport device 3 is configured to include a gas cylinder 10 that stores gas as a space charge neutralizing agent, a plurality of gas inlets 12 as neutralizing agent outlets for introducing gas from the gas cylinder 10 into the sealed chamber 3a (i.e., into the charged particle beam 1), and flow regulators 11 as neutralizing agent flow regulators for adjusting the amount of gas introduced into the sealed chamber 3a from each of the plurality of gas inlets 12.

The flow regulator 11 may be, for example, a gas solenoid valve provided in a gas flow path that communicates with each gas inlet 12. The gas solenoid valve includes a solenoid, a plunger which is a movable iron piece, and a valve, and operates the plunger by passing an electric current through the solenoid, thereby controlling the opening and closing of the valve. In such a gas solenoid valve, the amount of gas flowing through the gas solenoid valve can be adjusted by controlling the opening and closing of the valve.

The gas from the gas cylinder 10 is introduced into the sealed chamber 3a through the gas inlet 12 with the flow rate adjusted by the flow rate regulator 11. The ionized electrons generated by the reaction between the charged particle beam 1 and the gas are accumulated on the orbit by the attractive force of the electric charge of the charged particle beam 1, thereby neutralizing the space charge.

As a specific example, when a hydrogen ion beam having a positive charge is used as the charged particle beam 1, hydrogen gas can be used as the gas introduced into the sealed chamber 3a. In this case, the hydrogen ion beam as the charged particle beam 1 collides with the electrons of the hydrogen gas introduced into the sealed chamber 3a, and the electrons are stripped from the hydrogen gas. As a result, the hydrogen gas is split into positively charged hydrogen ions and negatively charged electrons. Since the hydrogen ions have a positive charge like the charged particle beam 1, they are repelled by the repulsive force between them and the charged particle beam 1. On the other hand, the electrons gather near the path of the charged particle beam 1 due to the attractive force between them and the charged particle beam 1. Then, an attractive force is generated between the hydrogen ion beam as the charged particle beam 1 and the electrons gathered in its vicinity, and the repulsive force between the charged particles (hydrogen ions) that make up the charged particle beam 1 is reduced (this is also expressed as "space charge is neutralized"). This suppresses the divergence of the charged particle beam 1 due to the space charge effect.

When a negatively charged electron beam or an anion beam is used as the charged particle beam 1, positively charged cations produced by the reaction between the charged particle beam 1 and the gas accumulate near the path of the charged particle beam 1, neutralizing the space charge. In other words, the space charge reduction method of introducing a gas can be applied to both positively and negatively charged charged particle beams 1.

The amount of space charge neutralization is determined by the amount of ionized electrons or ionized ions of the gas introduced into the sealed chamber 3a, so it is possible to adjust the amount of space charge neutralization by adjusting the amount of gas introduced (the total amount of gas introduced from the multiple gas inlets 12).

The total amount of space charge neutralizing gas introduced is adjusted according to the amount of current of the charged particle beam 1 measured by the current monitors 15a and 15b. Here, the current monitors 15a and 15b are, for example, non-contact CTs (Current Transformers) and measure the total amount of current of the charged particle beam 1. For example, the current monitors 15a and 15b are configured to include a circular or cylindrical porcelain core through whose internal space the charged particle beam 1 passes, and a winding wound around the porcelain core. When the charged particle beam 1 passes through the internal space of the porcelain core, a magnetic flux is generated in the porcelain core, and this magnetic flux generates a secondary current in the winding. The current of the charged particle beam 1 is measured by measuring the secondary current. The total amount of current measured by the current monitors 15a and 15b is read by the control device 14. The control device 14, which will be described in detail later, is provided in the charged particle beam transport device 3 and controls the flow rate regulator 11 to control the amount of gas introduced into the sealed chamber 3a from each gas inlet 12.

The current monitor 15a serving as the first current detector is provided near the extraction electrode 5. That is, the current monitor 15a measures the total current amount of the charged particle beam 1 entering the sealed chamber 3a. The current monitor 15b serving as the second current detector is provided downstream of the current monitor 15a in the path of the charged particle beam 1. In this embodiment, the current monitor 15b is provided near the beam exit of the sealed chamber 3a. That is, in this embodiment, the current monitor 15b measures the total current amount of the charged particle beam 1 exiting the sealed chamber 3a.

As the charged particle beam 1 diverges, the total current amount measured by the current monitor 15b becomes smaller than the total current amount measured by the current monitor 15a. Therefore, the difference between the total current amount measured by the current monitor 15a and the total current amount measured by the current monitor 15b is an index showing the divergence amount of the charged particle beam 1. In other words, the beam loss rate in the sealed chamber 3a can be calculated from the difference between the total current amount measured by the current monitor 15a and the total current amount measured by the current monitor 15b. Here, the beam loss rate is the ratio of the amount of the charged particle beam exiting the sealed chamber 3a to the amount of the charged particle beam entering the charged particle beam transport device 3 (which can also be rephrased as the amount of charged particles, density, or current value of the beam).

If the total amount of gas introduced into the sealed chamber 3a is insufficient, the space charge effect becomes large, and not only unnecessary charged particles but also necessary charged particles are scattered and stopped by the absorber 9, resulting in a high beam loss rate. On the other hand, if the total amount of gas introduced is too large, the reaction between the charged particle beam 1 and the gas increases, resulting in a high beam loss rate.

Therefore, the control device 14 calculates the beam loss rate from the current values measured by the current monitors 15a and 15b, and controls the flow regulator 11 according to the calculated beam loss rate. This appropriately adjusts the total amount of introduced gas (in other words, an amount of gas according to the beam loss rate is introduced into the sealed chamber 3a), suppressing the beam loss rate, i.e., the divergence of the charged particle beam 1 due to the space charge effect.

The charged particle beam transport device 3 is also provided with a vacuum pump (not shown) for removing impurities from the sealed chamber 3a and creating a vacuum, and a vacuum gauge 16 for measuring the degree of vacuum in the sealed chamber 3a. The degree of vacuum in the sealed chamber 3a may change due to the condition of the vacuum pump, and the density of the space charge neutralizing gas may be excessive or insufficient. Therefore, in addition to or instead of the above-mentioned beam loss rate, the control device 14 may determine the total amount of gas introduced into the sealed chamber 3a according to the degree of vacuum measured by the vacuum gauge 16. Specifically, the greater the degree of vacuum, the smaller the amount of gas introduced into the sealed chamber 3a, so the control device 14 controls the total amount of gas introduced to be increased, and the smaller the degree of vacuum, the larger the amount of gas introduced into the sealed chamber 3a, so the control device 14 controls the total amount of gas introduced to be decreased.

Here, in the circumferential direction of the charged particle beam 1, there may be variations in the amount of space charge due to differences in current density. For example, when viewed from the direction of travel of the charged particle beam 1, the amount of space charge is greater on the lower side than on the upper side of the charged particle beam 1. When variations in the amount of space charge occur, there is variation in the amount of beam divergence in the circumferential direction of the charged particle beam 1. For example, when viewed from the direction of travel of the charged particle beam 1, the amount of beam divergence is greater on the lower side than on the upper side of the charged particle beam 1.

Figure 2 shows the charged particle beam 1 passing through the sealed chamber 3a, viewed from the direction of travel. In this embodiment, in order to reduce the variation in the amount of beam divergence in the circumferential direction of the charged particle beam 1, multiple measuring devices 13 and multiple gas inlets 12 are arranged to the sides of the charged particle beam 1 in the sealed chamber 3a, as shown in Figure 2.

The measuring device 13 measures the amount of divergence of the charged particle beam 1. The measuring device 13 may be, for example, an ammeter including an electrode, and is arranged to the side of the path of the charged particle beam 1. The divergent beam 8 (divergent charged particles) that has diverged and deviated from the path of the charged particle beam 1 is incident on the electrode of the measuring device 13. This generates a current in the electrode, and the measuring device 13 measures this current. It can be said that the larger the current value measured by the measuring device 13, the greater the amount of beam divergence.

Specifically, the multiple measuring instruments 13 are provided on the sides of the charged particle beam 1 in different radial directions of the charged particle beam 1. In the example of FIG. 2, measuring instrument 13a is provided in the radial direction from the center of the charged particle beam 1 toward the upper side, measuring instrument 13b is provided in the radial direction from the center of the charged particle beam 1 toward the right side, measuring instrument 13c is provided in the radial direction from the center of the charged particle beam 1 toward the lower side, and measuring instrument 13d is provided in the radial direction from the center of the charged particle beam 1 toward the left side. Note that, although four measuring instruments 13 are provided in this embodiment, two, three, or five or more measuring instruments 13 may be provided.

The gas inlets 12 are provided on the sides of the charged particle beam 1 in different radial directions of the charged particle beam 1 in correspondence with the multiple measuring instruments 13. Corresponding to the measuring instruments 13 means that the gas inlets 12 are provided in the same radial direction as the measuring instruments 13. In the example of FIG. 2, the gas inlet 12a is provided in the radial direction from the center of the charged particle beam 1 to the upper side in correspondence with the measuring instrument 13a, the gas inlet 12b is provided in the radial direction from the center of the charged particle beam 1 to the right side in correspondence with the measuring instrument 13b, the gas inlet 12c is provided in the radial direction from the center of the charged particle beam 1 to the lower side in correspondence with the measuring instrument 13c, and the gas inlet 12d is provided in the radial direction from the center of the charged particle beam 1 to the left side in correspondence with the measuring instrument 13d. In this embodiment, four gas inlets 12 are provided, but two, three, or five or more gas inlets 12 may be provided in correspondence with the measuring instruments 13.

In this embodiment, the multiple measuring devices 13 are arranged on the same vertical plane perpendicular to the traveling direction of the charged particle beam 1. That is, the multiple measuring devices 13 are arranged side by side along the circumferential direction of the charged particle beam 1. In other words, the distance from the entrance of the charged particle beam 1 in the sealed chamber 3a to each measuring device 13 is the same. The multiple gas inlets 12 are also arranged on the same vertical plane perpendicular to the traveling direction of the charged particle beam 1. However, the multiple measuring devices 13 do not have to be arranged on the same vertical plane perpendicular to the traveling direction of the charged particle beam 1 as long as they are arranged on the side of the charged particle beam 1 and in different radial directions of the charged particle beam 1. That is, the distances from the entrance of the charged particle beam 1 in the sealed chamber 3a to each measuring device 13 may be different from each other. The multiple gas inlets 12 do not have to be arranged on the same vertical plane perpendicular to the traveling direction of the charged particle beam 1 according to each measuring device 13.

When the amount of space charge in the circumferential direction of the charged particle beam 1 varies, that is, when the amount of beam divergence in the circumferential direction of the charged particle beam 1 varies, the amount of beam divergence measured by the multiple measuring instruments 13 will differ from each other. For example, if the amount of beam divergence is greater on the lower side than on the upper side of the charged particle beam 1, the amount of beam divergence measured by the measuring instrument 13c will be greater than the amount of beam divergence measured by the measuring instrument 13a. In response to this, the control device 14 controls the flow regulator 11 based on the measurement results of the multiple measuring instruments 13 to adjust the amount of gas introduced into the sealed chamber 3a from the multiple gas inlets 12. Specifically, the greater the amount of beam divergence measured by the measuring instrument 13, the greater the amount of gas introduced from the gas inlet 12 corresponding to that measuring instrument 13, and the smaller the amount of beam divergence measured by the measuring instrument 13, the less the amount of gas introduced from the gas inlet 12 corresponding to that measuring instrument 13. If the amount of space charge in the circumferential direction of the charged particle beam 1 varies and the amount of beam divergence in the circumferential direction of the charged particle beam 1 differs, different amounts of gas will be introduced into the sealed chamber 3a from the multiple gas inlets 12.

Specifically, a conversion table showing the relationship between the amount of emission of the charged particle beam 1 measured by the measuring device 13 and the amount of gas introduced into the sealed chamber 3a from the gas inlet 12 is stored in advance in a memory (not shown) of the charged particle beam transport device 3. The conversion table may be created by an administrator of the charged particle beam transport device 3, etc. The control device 14 refers to the conversion table and determines the amount of gas to be introduced from each gas inlet 12 based on the measured value of each measuring device 13.

In this embodiment, as described above, the control device 14 determines the total amount of gas to be introduced into the sealed chamber 3a based on at least one of the beam loss rate obtained from the measurements of the current monitors 15a and 15b and the degree of vacuum in the sealed chamber 3a obtained from the measurements of the vacuum gauge 16. Therefore, in this embodiment, the control device 14 adjusts the flow rate ratio of the gases introduced from each gas inlet 12 while keeping the determined total amount of introduced gas constant based on the measurements of each measuring device 13.

In this embodiment, even if the amount of space charge (i.e., the amount of beam divergence) varies in the circumferential direction of the charged particle beam 1, more gas is introduced from the gas inlet 12 corresponding to the position where the amount of space charge is large, by the control of the control device 14. The gas introduced into the sealed chamber 3a from the gas inlet 12 has a higher concentration in the vicinity of the gas inlet 12. In other words, by introducing more gas from the gas inlet 12 corresponding to the position where the amount of space charge is large, a state can be created in which the gas concentration is high at the position where the amount of space charge is large and the gas concentration is low at the position where the amount of space charge is small. In other words, more electrons can be introduced into the position where the amount of space charge is large and the amount of beam divergence is large, thereby more strongly suppressing the divergence of the charged particle beam 1. This reduces the variation in the amount of space charge in the circumferential direction of the charged particle beam 1, and reduces the variation in the amount of beam divergence in the circumferential direction of the charged particle beam.

Next, the flow of the process for adjusting the introduced gas flow rate to neutralize space charge according to this embodiment will be explained with reference to Figure 3.

First, the control device 14 calculates the beam loss rate based on the measured values of the current monitors 15a and 15b. The control device 14 also reads the measured value of the vacuum gauge 16 to obtain the degree of vacuum in the sealed chamber 3a (step S101).

Next, the control device 14 determines whether the beam loss rate and vacuum degree obtained in step S101 are within a preset tolerance range (step S102).

If it is determined in step S102 that the measured beam loss rate and vacuum level are not within the acceptable range, the process proceeds to step S103, where the control device 14 controls the flow regulator 11 to adjust the flow rate of the introduced gas so that the total amount of introduced gas is a preset amount based on the measured beam loss rate and vacuum level.

If it is determined in step S102 that the amount is within the acceptable range, the control device 14 measures the amount of divergent beam 8 in each radial direction of the charged particle beam 1 based on the measured values of the multiple measuring instruments 13 (step S104).

Next, it is determined whether the radial dependency of the amount of divergent beam 8 measured in step S104 (i.e., the difference in the amount of beam divergence between each radial direction) is within an acceptable range (step S105).

If it is determined in step S105 that the amount is not within the acceptable range, the process proceeds to step S106, where the control device 14 controls the flow regulator 11 based on the radial dependency of the amount of the diverging beam 8 so that a preset flow rate ratio of the introduced gas is achieved, thereby adjusting the flow rate of the gas introduced from each gas inlet 12.

If it is determined in step S105 that the flow rate is within the acceptable range, the flow rate adjustment of the introduced gas is terminated.

Second Embodiment
In the first embodiment, a gas is used as the space charge neutralizer, but in the second embodiment, an electron beam (electrons) or an ion beam is used as the space charge neutralizer. In the first embodiment, electrons or ions are obtained from a gas by colliding the gas with a charged particle beam 1, but in the second embodiment, electrons or ions for neutralizing the space charge are directly introduced into a sealed chamber 3a. A charged particle beam transport device 3' according to the second embodiment will be described with reference to FIG. 4. In the description of the second embodiment, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof will be omitted.

Figure 4 is a schematic diagram of a linear accelerator including a charged particle beam transport device 3' according to the second embodiment. Compared to the charged particle beam transport device 3 according to the first embodiment, the charged particle beam transport device 3' is provided with multiple beam irradiation devices 17 instead of the gas cylinder 10, flow regulator 11, and multiple gas inlets 12. Although the vacuum gauge 16 is not shown in Figure 4, the charged particle beam transport device 3' according to the second embodiment may also have a vacuum gauge.

Below, an example will be described in which the charged particle beam 1 has a positive charge and an electron beam is irradiated from the beam irradiation device 17. The beam irradiation device 17 includes an electron gun 18 that generates an electron beam 19, a plurality of electrodes 20 that accelerate the electron beam 19 from the electron gun 18, and a beam irradiation port 17a that is the exit of the electron beam 19 and serves as a neutralizing agent discharge port. The electrode 20 may be configured as an electrostatic lens to converge the electron beam. The beam irradiation device 17 is capable of adjusting the amount of electrons irradiated from the beam irradiation port 17a in response to an instruction from the control device 21. That is, in the second embodiment, the beam irradiation device 17 functions as a neutralizing agent flow regulator.

The multiple beam irradiation devices 17 (more specifically, the beam irradiation ports 17a) are provided on the sides of the path of the charged particle beam 1 in the sealed chamber 3a, in different radial directions of the charged particle beam 1. That is, in the second embodiment, the gas inlet port 12 of the first embodiment shown in FIG. 2 is replaced with the beam irradiation port 17a.

In the second embodiment, the control device 21 also controls the multiple beam irradiation devices 17 based on the measurement results of the multiple measuring devices 13 to adjust the amount of electrons irradiated from the multiple beam irradiation ports 17a into the sealed chamber 3a. Specifically, the larger the amount of beam divergence measured by the measuring device 13, the larger the amount of electrons irradiated from the beam irradiation port 17a corresponding to the measuring device 13 is, and the smaller the amount of beam divergence measured by the measuring device 13, the smaller the amount of electrons irradiated from the beam irradiation port 17a corresponding to the measuring device 13 is. If the amount of space charge in the circumferential direction of the charged particle beam 1 varies and the amount of beam divergence in the circumferential direction of the charged particle beam 1 differs, different amounts of electrons will be irradiated into the sealed chamber 3a from the multiple beam irradiation ports 17a.

Specifically, a conversion table showing the relationship between the amount of divergence of the charged particle beam 1 measured by the measuring device 13 and the amount of electrons irradiated from the beam irradiation port 17a into the sealed chamber 3a is stored in advance in a memory (not shown) of the charged particle beam transport device 3'. The control device 14 determines the amount of electrons to be irradiated from each beam irradiation port 17a based on the measurement value of each measuring device 13 while referring to the conversion table. Note that, in the second embodiment, the total amount of irradiated electrons determined based on at least one of the beam loss rate obtained from the measurement value of the current monitors 15a and 15b and the degree of vacuum in the sealed chamber 3a obtained from the measurement value of the vacuum gauge 16 is kept constant, and the ratio of the amount of electrons introduced from each beam irradiation port 17a is adjusted based on the measurement value of each measuring device 13.

The beam irradiation device 17 irradiates the electron beam from the beam irradiation port 17a into the sealed chamber 3a at a relatively gentle rate. Therefore, the electrons introduced into the sealed chamber 3a have a higher concentration in the vicinity of the beam irradiation port 17a. In other words, by introducing more electrons from the beam irradiation port 17a corresponding to the position where the amount of space charge is large, a state can be created in which the electron concentration is high at the position where the amount of space charge is large and the electron concentration is low at the position where the amount of space charge is small. In other words, by introducing more electrons into the position where the amount of space charge is large and the amount of beam divergence is large, the divergence of the charged particle beam 1 can be more strongly suppressed. This reduces the variation in the amount of space charge (i.e., the amount of beam divergence of the charged particle beam 1) in the circumferential direction of the charged particle beam 1.

When the charged particle beam 1 is composed of negatively charged charged particles, the space charge effect can be reduced by irradiating a positively charged cation beam from the beam irradiation device 17.

In addition, instead of the beam irradiation device 17, a plasma introduction device having a plasma irradiation port as a neutralizing agent discharge port may be provided, and plasma containing positive ions and electrons as a space charge neutralizing agent instead of electrons or ions may be introduced into the sealed chamber 3a. Even in this case, the plasma introduction device is capable of adjusting the amount of plasma irradiated from the plasma irradiation port in response to instructions from the control device 21, and the plasma introduction device functions as a neutralizing agent flow rate regulator.

According to this, when the charged particle beam 1 has a positive charge, the space charge is neutralized by the electrons contained in the plasma, and when the charged particle beam 1 has a negative charge, the space charge is neutralized by the positive ions contained in the plasma. In other words, the space charge reduction method that introduces plasma can be applied to both positively and negatively charged charged particle beams 1.

The charged particle beam 1 generated and accelerated by the linear accelerator described in the first or second embodiment can be used for various purposes. For example, the charged particle beam 1 whose divergence is suppressed by the present invention can be applied to a nuclear fusion system (or a nuclear fusion reactor) that generates nuclear fusion power. In this case, the charged particle beam transport device 3 according to the present invention is a device that constitutes a part of the nuclear fusion system. Also, the charged particle beam 1 whose divergence is suppressed by the present invention can be applied to a particle beam therapy system that performs particle beam therapy. In this case, the charged particle beam transport device 3 according to the present invention is a device that constitutes a part of the particle beam therapy system. In such a particle beam therapy system, for example, the charged particle beam 1 from the charged particle beam transport device 3 according to the present invention is input to a synchrotron or the like, and the further accelerated charged particle beam 1 is irradiated to a treatment target (e.g., cancer cells).

REFERENCE SIGNS LIST 1 Charged particle beam, 2 Charged particle beam generator, 3 Charged particle beam transport device, 3a Sealed chamber, 4 Plasma, 5 Extraction electrode, 6 Converging coil, 7 Post-accelerator, 8 Diverging beam, 9 Absorber, 10 Gas cylinder, 11 Flow regulator, 12 Gas inlet, 13 Measuring device, 14, 21 Control device, 15a, 15b Current monitor, 16 Vacuum gauge, 17 Beam irradiation device, 17a Beam irradiation port, 18 Electron gun, 19 Electron beam, 20 Electrode.

Claims (7)

A charged particle beam transport device in a linear accelerator, comprising:
a plurality of measuring devices for measuring the divergence of the charged particle beam, the measuring devices being disposed on the sides of a path of the charged particle beam in a sealed chamber and in different radial directions of the charged particle beam;
a plurality of neutralizing agent outlets, which are provided on the sides of a path of the charged particle beam in different radial directions of the charged particle beam corresponding to the plurality of measuring devices, and which discharge a space charge neutralizing agent for neutralizing a space charge into the charged particle beam;
a neutralizing agent flow rate regulator for regulating an amount of the space charge neutralizing agent discharged from each of the plurality of neutralizing agent discharge ports toward the charged particle beam;
a control device that controls the neutralizing agent flow regulator based on the measurement results of the plurality of measuring devices to emit different amounts of the space charge neutralizing agent from the plurality of neutralizing agent outlets toward the charged particle beam;
A charged particle beam transport device comprising: 2. The charged particle beam transport apparatus according to claim 1,
the control device determines the amount of the space charge neutralizing agent to be discharged from each of the neutralizing agent discharge ports by referring to a conversion table showing a relationship between the amount of divergence of the charged particle beam measured by the measuring device and the amount of the space charge neutralizing agent to be discharged toward the charged particle beam;
A charged particle beam transport device characterized by: 3. The charged particle beam transport apparatus according to claim 1,
a first current detector for measuring a total current of the charged particle beam;
a second current detector that is disposed downstream of the first current detector in a path of the charged particle beam and that measures a total current amount of the charged particle beam;
Further equipped with
The control device determines a total amount of the space charge neutralizing agent to be released from the plurality of neutralizing agent release ports according to a difference between a total amount of current measured by the first current detector and a total amount of current measured by the second current detector.
A charged particle beam transport device characterized by: 4. The charged particle beam transport apparatus according to claim 1,
a vacuum gauge for measuring the degree of vacuum in the sealed chamber;
Further equipped with
The control device determines a total amount of the space charge neutralizer to be released from the plurality of neutralizer release ports in accordance with the degree of vacuum measured by the vacuum gauge.
A charged particle beam transport device characterized by: 2. The charged particle beam transport system according to claim 1,
the neutralizing agent outlet is a gas inlet for introducing a gas as the space charge neutralizing agent into the charged particle beam;
A charged particle beam transport device comprising: 2. The charged particle beam transport system according to claim 1,
The neutralizer discharge port is a beam irradiation port that irradiates the charged particle beam with an electron beam or an ion beam as the space charge neutralizer.
A charged particle beam transport device comprising: 2. The charged particle beam transport system according to claim 1,
The neutralizer discharge port is a plasma irradiation port that irradiates plasma as the space charge neutralizer to the charged particle beam.
A charged particle beam transport device comprising: