JP2024058747A - Charged particle beam transport device, method for manufacturing the charged particle beam transport device, and method for neutralizing a charged particle beam - Google Patents

Abstract

[Problem] To provide a charged particle beam transport device capable of reducing beam divergence due to space charge and loss due to beam neutralization at the same time, a method for manufacturing the charged particle beam transport device, and a method for neutralizing a charged particle beam. [Solution] A charged particle beam transport device 20 includes collimators 13a, 13b whose inner diameter decreases toward the convergence part of a charged particle beam 1, and injection ports 9b1, 9b2, 9b3, 9b4 for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the collimators 13a, 13b. [Selected Figure] Figure 1

Description

The present invention relates to a charged particle beam transport device, a method for manufacturing a charged particle beam transport device, and a method for neutralizing a charged particle beam.

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 a device that aims to efficiently reduce the space charge effect by adjusting the irradiation position of the ion beam depending on the current density of the electron beam.

However, the device described in Patent Document 1 has the problem that only the irradiation position is adjusted, and the irradiated neutralizing agent spreads spatially, so the concentration of the neutralizing agent ions in the beam convergence part where the current density is high cannot be sufficiently increased. This effect is particularly noticeable when a neutral gas is used as the neutralizing agent. In addition, the device described in Patent Document 1 has the problem that it cannot neutralize the space charge according to the space charge distribution caused by the variation in current density in the beam diameter direction.

Due to the above factors, in areas with high space charge, the degree of space charge neutralization is insufficient, causing the beam to diverge and leading to beam loss. On the other hand, in areas with low space charge, the beam is excessively neutralized due to the reaction between the beam and the neutralizing agent, which also leads to beam loss.

The present invention provides a charged particle beam transport device that can simultaneously reduce beam divergence due to space charge and reduce losses due to beam neutralization, a method for manufacturing a charged particle beam transport device, and a method for neutralizing a charged particle beam.

The present invention includes multiple means for solving the above problems, and one example is a charged particle beam transport device that includes a focusing structure whose inner diameter decreases toward the focusing part of the charged particle beam, an injection port for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the focusing structure, and a control device that controls the amount of space charge neutralizing agent injected.

The present invention can reduce both beam divergence due to space charge and losses due to beam neutralization. Problems, configurations, and effects other than those described above will become clear from the description of the embodiments below.

1 is a schematic diagram of a linear accelerator including a charged particle beam transport device according to a first embodiment. FIG. 4 is a diagram showing a flow of control of the injection amount of a space charge neutralizer according to the first embodiment. 13 is a schematic diagram showing the arrangement of an injection port for a space charge neutralizer and a beam distribution meter of a charged particle beam transport device according to a second embodiment. FIG. FIG. 11 is a schematic diagram showing a modified example of the charged particle beam transport device according to the second embodiment. FIG. 11 is a schematic diagram showing a modified example of the charged particle beam transport device according to the second embodiment. FIG. 11 is a schematic diagram illustrating an example of a collimator of a charged particle beam transport device according to a third embodiment. FIG. 11 is a schematic diagram showing a modified example of a collimator of the charged particle beam transport device according to the third embodiment.

Below, embodiments of the charged particle beam transport device, the manufacturing method of the charged particle beam transport device, and the neutralization method of the charged particle beam of the present invention will be described with reference to the drawings. Note that in the drawings used in this specification, identical or corresponding components are given the same or similar reference numerals, and repeated explanations of these components may be omitted.

First Embodiment
A first embodiment of a charged particle beam transport apparatus, a method for manufacturing the charged particle beam transport apparatus, and a method for neutralizing a charged particle beam according to the present invention will be described with reference to FIGS. 1 and 2. FIG.

First, the overall configuration of the linear accelerator 30 including the charged particle beam transport device will be described with reference to FIG. 1. FIG. 1 is a schematic diagram of the configuration of the linear accelerator including the charged particle beam transport device according to the first embodiment.

The charged particle beam transport device 20 shown in FIG. 1 is a device for injecting a charged particle beam 1 generated by a charged particle beam generator 4 composed of an ion source or the like into a post-stage accelerator 5, and is composed of a vacuum chamber 2, focusing coils 3a, 3b, a neutralizing agent reservoir 7, an injection amount control device 8, injection ports 9a, 9b, a vacuum gauge 10, a beam distribution meter 11, a beam current meter 12, collimators 13a, 13b, and a vacuum exhaust pump 14.

When manufacturing such a charged particle beam transport device 20, at least the steps of providing collimators 13a, 13b whose inner diameters become smaller toward the convergence part of the charged particle beam 1, and providing injection ports 9a, 9b for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the collimators 13a, 13b are performed.

Here, the charged particle beam generating device 4 is a device that generates the charged particle beam 1, and the type of the device can be, for example, a microwave ion source, an ECR (Electron Cyclotron Resonance) ion source, a duoplasmatron, an electron gun, etc. In this embodiment, the configuration of a linear accelerator that employs a microwave ion source will be described as an example.

The plasma generated by microwaves in the charged particle beam generator 4 is extracted by the potential difference with the extraction electrode 6, generating the charged particle beam 1.

The charged particle beam 1 is focused by focusing coils 3a and 3b in the vacuum chamber 2 and is then injected into the post-stage accelerator 5. Here, the focusing coils 3a and 3b can be equipped with magnetic poles made of a magnetic material.

The post-stage accelerator 5 is, for example, a high-frequency accelerator, such as an RFQ (Radio Frequency Quadruple) or a DTL (Drift Tube Linac), and can be used alone or in combination. Alternatively, it can be an electrostatic accelerator, such as a Cockcroft-Walton type or a Van de Graaff type.

The charged particle beam 1 injected from the charged particle beam generator 4 into the vacuum chamber 2 is converged by the focusing coils 3a and 3b and adjusted into a shape that can be injected into the post-stage accelerator 5. During this process, divergence occurs due to the Coulomb repulsion between the charged particles that make up the charged particle beam 1, i.e., the space charge effect, so that as the beam current value increases, a divergence force that exceeds the focusing force of the focusing coils 3a and 3b is generated.

A method of neutralizing the space charge is to inject a neutral gas or plasma into the area through which the charged particle beam 1 passes. When a neutral gas is injected, the charged particle beam 1 collides with the neutral gas, ionizing the neutral gas and emitting electrons. When the charged particle beam 1 has a positive charge, the electrons emitted by ionization are attracted to the beam orbit by the Coulomb force between the charged particle beam 1 and the neutral gas. On the other hand, the ionized gas is pulled away from the beam orbit by the repulsion caused by the Coulomb force between the charged particle beam 1 and the neutral gas. As a result of the above action, ions with an opposite charge to the charged particle beam 1 are accumulated on the orbit, neutralizing the space charge. When plasma is injected, the space charge is neutralized by a similar action. In this embodiment, an example in which a neutral gas is used as a neutralizing agent will be described, but the details of the case of injecting plasma are the same as those of the case of introducing a neutral gas, so a description will be omitted.

When there is a shortage of neutralizing agent, the charged particle beam 1 diverges due to insufficient neutralization of the space charge. On the other hand, when there is an excess of space charge neutralizing agent, the charged particles in the charged particle beam 1 combine with ions of the opposite charge, resulting in a large loss of the charged particle beam 1 due to beam neutralization. For this reason, in the charged particle beam transport device, it is necessary to suppress beam divergence due to the space charge effect to a level that is permissible under the injection conditions of the post-stage accelerator 5 while minimizing the loss rate of the charged particle beam 1.

Therefore, in the charged particle beam transport device 20 of this embodiment, the neutralizing agent concentration is increased in the convergence part where the space charge is higher than in other parts. Here, the "convergence part" refers to the "connection part between the charged particle beam generation device 4 and the charged particle beam transport device 20" which is the entrance side of the charged particle beam 1 into the charged particle beam transport device 20, and/or the "connection part between the charged particle beam transport device 20 and the post-stage accelerator 5" which is the exit side.

In this first embodiment, the injection amount of the neutral gas stored in the neutralizing agent reservoir 7 is adjusted by an injection amount control device 8 that controls the injection amount of the neutral gas as a space charge neutralizing agent, and the neutralizing agent is injected from injection ports 9a and 9b, thereby neutralizing the space charge at the entrance side and/or exit side of the charged particle beam 1, where the space charge is particularly high.

Furthermore, in this embodiment, in order to generate a neutralizing agent distribution corresponding to the distribution of space charge caused by the diverging and converging trajectories of the charged particle beam 1, collimators 13a and 13b with tapered shapes are provided to match the diverging and converging trajectories.

Collimators 13a and 13b are structures whose inner diameter becomes smaller toward the convergent portion of the charged particle beam 1. Collimator 13b is provided on the outlet side of the charged particle beam 1, and is a structure whose inner diameter becomes smaller toward the outlet. In contrast, collimator 13a is provided on the entrance side of the charged particle beam 1, and is a structure whose inner diameter becomes smaller toward the entrance.

The inlet 9a is an opening for injecting a space charge neutralizing agent into the space surrounded by the collimator 13a, and the inlet 9b is an opening for injecting a space charge neutralizing agent into the space surrounded by the collimator 13b to neutralize the space charge. The concentration of the neutralizing agent can be increased as the inner diameter of the collimators 13a and 13b becomes smaller. This makes it possible to increase the space charge neutralization rate in the area where the charged particle beam 1 converges and the space charge becomes high.

The amount of neutralizing agent injected and the shapes of the collimators 13a and 13b are determined in advance based on beam simulation and gas distribution simulation. Here, in the beam simulation, a beam trajectory calculation that takes into account the space charge effect using a method such as PIC (Particle In Cell) is used. In the gas distribution simulation, the mean free path of the neutral gas used as the neutralizing agent is considered to be sufficiently long, and the gas distribution is calculated using a simulator that calculates it as a molecular flow.

The length of the collimators 13a and 13b in the transport direction depends on the design trajectory of the beam, and as shown in Figure 1, the collimator 13b on the exit side is not necessarily longer than the collimator 13a on the entrance side.

As mentioned above, in the charged particle beam transport device 20, it is necessary to suppress beam divergence due to the space charge effect so that the shape of the charged particle beam 1 falls within the tolerance of the post-stage accelerator 5.

Therefore, the amount of space charge at each spatial position on the orbit of the charged particle beam 1 is evaluated based on a beam simulation, and the required space charge neutralization rate at each spatial position is determined. In addition, a gas distribution simulation is used to evaluate the neutral gas distribution for the shape of the collimators 13a and 13b, and the collimators 13a and 13b are determined so that the neutral gas distribution is closer to the space charge distribution evaluated by the above beam simulation.

Furthermore, the beam distribution under the conditions where the required space charge neutralization rate is achieved is calculated in advance by beam simulation, and the amount of neutral gas injected is determined so that the actual beam distribution measured by the beam distribution meter 11 approaches the calculated value.

More specifically, the injection amount control device 8 can adjust the injection amount of the space charge neutralizer so that the beam distribution in the cross section in the transport direction has a desired shape based on the measurement results of the beam distribution meter 11 that measures the distribution of the charged particle beam 1, by decreasing the injection amount of the space charge neutralizer compared to the judgment timing when it is determined that the beam distribution is narrower than a first predetermined range, and by increasing the injection amount of the space charge neutralizer compared to the judgment timing when it is determined that the beam distribution is wider than a second predetermined range that is wider than the first predetermined range.

The beam distribution meter 11 may be either a non-contact measuring device that measures the electromagnetic waves generated on the beam orbit or the potential of an electrode excited by the charged particle beam 1, or a contact measuring device such as a Faraday cup or a wire chamber.

In actual operation, the amount of neutralizing agent required to be injected is highly likely to change due to changes in the current amount of the charged particle beam 1 over time and changes in the exhaust speed of the vacuum exhaust pump 14 installed in the vacuum chamber 2.

Therefore, the injection amount control device 8 can adjust the flow rate of the space charge neutralizing agent based on the measurement result of the beam current value (increase or decrease in the total current amount) by the beam ammeter 12 that measures the current of the charged particle beam 1, in addition to or instead of the measurement result by the beam distribution meter 11. Furthermore, the flow rate of the space charge neutralizing agent can be adjusted based on the measurement result of the vacuum degree by the vacuum gauge 10 that measures the vacuum degree inside the charged particle beam transport device 20 (change in the concentration of the neutralizing agent due to change in the vacuum exhaust speed).

For example, the amount of space charge neutralizer injected can be adjusted to reduce the amount of space charge neutralizer injected when it is determined that the beam current value is smaller than a first predetermined value or larger than a second predetermined value that is larger than the first predetermined value, and further, the amount of space charge neutralizer injected can be adjusted to reduce the amount of space charge neutralizer injected when it is determined that the degree of vacuum is lower than a third predetermined value or higher than a fourth predetermined value.

The beam current meter 12 may be a non-contact type CT (Current Transformer) or the like. The vacuum gauge 10 may have a variety of known configurations.

Even when adjusting the amount of neutralizing agent injected using control based on the measurement results of the beam ammeter 12 and vacuum gauge 10, it is desirable to adjust the amount injected so that the beam distribution measured by the beam distribution meter 11 ultimately becomes the target distribution (see Figure 2).

In addition, it is desirable to provide the vacuum exhaust pump 14, which evacuates the inside of the charged particle beam transport device 20, at the intermediate portion between the inlet collimator 13a and the outlet collimator 13a, i.e., at the equidistant portion or around it, at a distance from the injection ports 9a and 9b.

Next, the method for neutralizing the charged particle beam 1 according to this embodiment will be described with reference to FIG. 2. FIG. 2 is a flow chart showing the injection amount control of the neutralizing agent according to this embodiment.

First, the injection amount control device 8 calculates the amount of neutralizing agent to be injected based on the degree of vacuum measured by the vacuum gauge 10 and the beam current measured by the beam current meter 12 as described above (step S101).

Next, the implantation amount control device 8 determines whether the beam current and vacuum degree obtained in step S101 are within a preset tolerance range (step S102).

If it is determined in step S102 that the amount is not within the allowable range, the process proceeds to step S103, where the injection amount control device 8 adjusts the injection amount of the neutralizing agent so that the injection amount becomes the injection amount preset for the beam current and vacuum degree (step S103). After that, the process returns to step S101, and the effect of the injection is confirmed.

In contrast, if it is determined in step S102 that the amount is within the acceptable range, the injection amount control device 8 waits for a certain period of time until the distribution of the injected neutralizing agent within the vacuum chamber 2 stabilizes (step S104).

Next, the beam distribution is measured using the beam distribution meter 11 (step S105).

Then, the injection amount control device 8 determines whether the difference between the beam distribution measured in step S105 and the target beam distribution is within an acceptable range (step S106).

If it is determined in step S106 that the measured beam distribution is not within the acceptable range, the process proceeds to step S107, where the injection amount control device 8 compares the measured beam distribution with the target distribution, and controls the injection amount to a preset amount so that if the beam divergence is large, the injection amount is increased, and if the beam divergence is small, the injection amount is decreased taking into account beam loss (step S107). After that, the process returns to step S105, and the effect of the injection is confirmed.

In contrast, if it is determined in step S106 that the amount is within the acceptable range, control of the injection amount of neutralizing agent is terminated.

In each step in FIG. 2, since it is desirable to adjust the beam distribution at a minimum, steps S101 to S104 may be omitted and only steps S105 to S107 may be executed, but it is desirable to execute all of them as shown in FIG. 2.

It is desirable to execute the flow in FIG. 2 at predetermined intervals during the generation of the charged particle beam 1.

Next, we will explain the effects of this embodiment.

The charged particle beam transport device 20 of the first embodiment of the present invention described above includes collimators 13a, 13b whose inner diameters become smaller toward the convergence portion of the charged particle beam 1, and injection ports 9a, 9b for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the collimators 13a, 13b, thereby increasing the concentration of the neutralizing agent in the convergence portion.

This makes it possible to adjust the amount of space charge neutralizer injected to reduce excess or deficiency in space charge neutralization according to the space charge distribution in the beam orbit direction associated with the diverging/converging orbit of the charged particle beam and the space charge distribution in the circumferential direction relative to the beam orbit associated with the charge distribution of the charged particle beam, thereby reducing losses due to divergence of the charged particle beam and beam neutralization compared to conventional methods.

Such a charged particle beam transport device 20 is preferably suitable for use in a linear accelerator, and can be applied to an ion source in a nuclear fusion power reactor, neutron capture therapy (BNCT: boron neutron capture therapy), or a particle beam therapy device using a synchrotron accelerator.

In addition, the collimator 13b is provided on the exit side of the charged particle beam 1, and the inner diameter becomes smaller toward the exit, so that the neutralization rate of the portion of the charged particle beam 1 converging toward the rear-stage post-accelerator 5 can be more effectively increased.

Furthermore, the collimator 13a is provided on the entrance side of the charged particle beam 1, and the inner diameter becomes smaller toward the entrance, thereby making it possible to further increase the neutralization rate of the converging portion of the charged particle beam 1 extracted from the entrance side of the charged particle beam generating device 4.

In addition, because collimators 13a and 13b have a tapered shape, the space charge neutralizer introduced is introduced more smoothly to the exit side or entrance side where it converges more tightly along the tapered surface, achieving more effective neutralization.

The system further includes a beam distribution meter 11 for measuring the distribution of the charged particle beam 1, and an injection amount control device 8 for controlling the injection amount of the space charge neutralizer. The injection amount control device 8 adjusts the injection amount of the space charge neutralizer so that the beam distribution in the cross section in the transport direction has a desired shape. In particular, when it is determined that the beam distribution is narrower than a first predetermined range, the injection amount of the space charge neutralizer is reduced from the determined timing, and when it is determined that the beam distribution is wider than a second predetermined range that is wider than the first predetermined range, the injection amount of the space charge neutralizer is increased from the determined timing, thereby adjusting the charged particle beam 1 to a beam shape more suitable for the post-stage accelerator 5.

In addition, by providing a vacuum exhaust pump 14 that evacuates the inside of the charged particle beam transport device 20 in the middle between the inlet collimator 13a and the outlet collimator 13b, the space charge neutralizer that is introduced is evacuated early, and it is possible to reliably prevent the amount of the introduced agent from deviating from the expected amount.

Furthermore, the device is further provided with a beam ammeter 12 for measuring the current of the charged particle beam 1, and an injection amount control device 8 for controlling the injection amount of the space charge neutralizing agent, and the injection amount control device 8 adjusts the flow rate of the space charge neutralizing agent based on the measurement result of the beam current value by the beam ammeter 12, or further includes a vacuum gauge 10 for measuring the degree of vacuum in the charged particle beam transport device 20, and an injection amount control device 8 for controlling the injection amount of the space charge neutralizing agent, and the injection amount control device 8 adjusts the flow rate of the space charge neutralizing agent based on the measurement result of the degree of vacuum by the vacuum gauge 10, thereby realizing the injection of the space charge neutralizing agent suitable for the state of the charged particle beam 1.

In this embodiment, the amount of space charge neutralizer injected is adjusted based on the results measured by the beam distribution meter 11, the beam current meter 12, and the vacuum gauge 10. However, it is also possible to control the amount of space charge neutralizer injected without a measurement system based on the results obtained in advance by simulation.

Second Embodiment
A charged particle beam transport apparatus, a manufacturing method thereof, and a method for neutralizing a charged particle beam according to a second embodiment of the present invention will be described with reference to Figs. 3 to 5. The same components as those in the first embodiment are designated by the same reference numerals, and a description thereof will be omitted. The same applies to the following embodiments. Figs. 3 to 5 are schematic diagrams showing the arrangement of an injection port for a space charge neutralizing agent and a beam distribution meter in the charged particle beam transport apparatus according to the second embodiment.

In the present embodiment shown in FIG. 3, multiple injection ports 9b1, 9b2, 9b3, and 9b4 are provided, and the injection amount control device 8 controls the injection amount for each of the multiple injection ports 9b1, 9b2, 9b3, and 9b4 arranged to the side of the beam independently according to the spatial charge distribution in a plane perpendicular to the beam axis of the charged particle beam 1.

When the charged particle beam 1 is actually transported, the state of the charged particle beam 1 can cause a bias in the beam current distribution, resulting in an asymmetric space charge distribution in a plane perpendicular to the beam axis. Therefore, the injection amount control device 8A can perform space charge neutralization corresponding to the asymmetric space charge distribution by independently controlling the injection amount ratio according to the positions of the injection ports 9b1, 9b2, 9b3, and 9b4.

In Figure 3, an example is described in which four beam distribution meters 11a, 11b, 11c, and 11d and four neutralizing agent injection ports 9b1, 9b2, 9b3, and 9b4 are arranged at symmetrical positions at 90 degrees to the side of the charged particle beam 1.

In this case, the beam distribution meters 11a, 11b, 11c, 11d and the injection ports 9b1, 9b2, 9b3, 9b4 do not necessarily need to be arranged on the same plane. Each of the four beam distribution meters 11a, 11b, 11c, 11d and the injection ports 9b1, 9b2, 9b3, 9b4 is connected to the injection amount control device 8A, and based on the beam distribution measured by the beam distribution meter 11, the injection amount is controlled so as to increase the injection amount ratio of the neutralizing agent from the injection ports 9b1, 9b2, 9b3, 9b4 on the side with the larger beam divergence.

For example, the injection amount ratio is adjusted while maintaining the total injection amount of the vertical injection ports 9b2 and 9b4 based on the amount of beam divergence evaluated from the beam distribution measured by the beam distribution meters 11a and 11c. Similarly, for other directions, the injection amount ratio of the neutralizing agent from the direction with the largest divergence is increased while maintaining the total injection amount.

In this embodiment, as shown in FIG. 4, a single beam distribution meter 11a, 11d may be installed in the perpendicular direction of a line connecting a pair of opposing injection ports 9b1, 9b2, 9b3, 9b4, and the injection amount control device 8B may adjust the injection amount of the space charge neutralizer from the injection ports 9b1, 9b2, 9b3, 9b4. In other words, this embodiment can be established even with half the number of beam distribution meters 11 compared to FIG. 3. Also, the number of opposing injection ports 9b1, 9b2, 9b3, 9b4 and the beam distribution meters 11a, 11d may be greater than in FIG. 3 or FIG. 4.

Also, as shown in FIG. 5, the beam distribution meters 11a1, 11b1, 11c1, and 11d1 may be contact type detectors, and the injection amount control device 8C may adjust the injection amount of the space charge neutralizer from the injection ports 9b1, 9b2, 9b3, and 9b4. In the case of the contact type beam distribution meters 11a1, 11b1, 11c1, and 11d1, the area to which the beam halo portion 15 diverged from the charged particle beam 1 extends is measured, and the injection amount ratio of the injection ports 9b1, 9b2, 9b3, and 9b4 in the same axial direction as the opposing beam distribution meters 11a1, 11b1, 11c1, and 11d1 is adjusted according to the divergence area of the beam halo portion 15.

The rest of the configuration and operation are substantially the same as those of the charged particle beam transport device, the method for manufacturing the charged particle beam transport device, and the method for neutralizing a charged particle beam of the first embodiment described above, and details are omitted.

The charged particle beam transport device, the manufacturing method of the charged particle beam transport device, and the neutralization method of the charged particle beam of the second embodiment of the present invention also provide substantially the same effects as the charged particle beam transport device, the manufacturing method of the charged particle beam transport device, and the neutralization method of the charged particle beam of the first embodiment described above.

In addition, the injection amount control device 8A independently controls the injection amount ratio according to the positions of the injection ports 9b1, 9b2, 9b3, and 9b4, so that even if the beam is biased, it is possible to inject a more appropriate amount of space charge neutralizing agent to correct the bias.

Third Embodiment
A charged particle beam transport apparatus, a manufacturing method thereof, and a method for neutralizing a charged particle beam according to a third embodiment of the present invention will be described with reference to Fig. 6 and Fig. 7. Fig. 6 and Fig. 7 are schematic diagrams showing an example of a collimator of the charged particle beam transport apparatus according to the third embodiment.

As shown in FIG. 6, instead of the collimator 13b of the first embodiment, a collimator 16 having a stepped structure in which the diameter decreases in accordance with the convergence trajectory of the charged particle beam 1 is used. By injecting a neutralizing agent through an injection port 9b toward the inside of such a collimator 16, the concentration of the neutralizing agent in the convergence part of the charged particle beam 1 with a high space charge can be increased. The entrance side can also have a stepped structure, but it is not necessary for the entrance side and the exit side to have the same structure.

In FIG. 7, as in FIG. 6, a collimator 17 with a smaller inner diameter is provided in accordance with the convergence trajectory of the charged particle beam 1, thereby increasing the concentration of the neutralizing agent at the convergence part of the charged particle beam 1 with a high space charge. In FIG. 7, the entrance side can also have a stepped structure, and it does not have to have the same structure. However, a stepped structure with fine steps as in FIG. 6 or similar to the smooth tapered structure as in FIG. 1 allows the concentration distribution of the neutralizing agent to change more smoothly, thereby making it possible to increase the efficiency of space charge neutralization.

In this embodiment, the design of the structure and the amount of neutralizing agent injected into the space charge can be determined in the same manner as in embodiment 1. The amount of neutralizing agent injected is also controlled in the same manner according to the control flow in FIG. 2.

The rest of the configuration and operation are substantially the same as those of the charged particle beam transport device, the method for manufacturing the charged particle beam transport device, and the method for neutralizing a charged particle beam of the first embodiment described above, and details are omitted.

The charged particle beam transport device, the manufacturing method of the charged particle beam transport device, and the neutralization method of the charged particle beam of the third embodiment of the present invention also provide substantially the same effects as the charged particle beam transport device, the manufacturing method of the charged particle beam transport device, and the neutralization method of the charged particle beam of the first embodiment described above.

＜Other＞
The present invention is not limited to the above-described embodiment, but includes various modified examples. The above-described embodiment has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to the embodiment having all of the described configurations.

It is also possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. It is also possible to add, delete, or replace part of the configuration of each embodiment with the configuration of another embodiment.

The present invention may take the following forms:

(1) A charged particle beam transport device comprising a focusing structure whose inner diameter decreases toward the focusing part of the charged particle beam, and an injection port for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the focusing structure.

(2) In the charged particle beam transport device described in (1), the focusing structure is provided on the outlet side of the charged particle beam in the charged particle beam transport device, and the inner diameter becomes smaller toward the outlet.

(3) In the charged particle beam transport device described in (1) or (2), the focusing structure is further provided on the entrance side of the charged particle beam in the charged particle beam transport device, and the inner diameter becomes smaller toward the entrance.

(4) In the charged particle beam transport device described in any one of (1) to (3), the focusing structure has a tapered shape.

(5) The charged particle beam transport device according to any one of (1) to (4) further includes a distribution measuring device for measuring the distribution of the charged particle beam and a control device for controlling the injection amount of the space charge neutralizer, and the control device adjusts the injection amount of the space charge neutralizer so that the beam distribution in the cross section in the transport direction has a desired shape.

(6) In the charged particle beam transport device described in (5), the control device reduces the injection amount of the space charge neutralizer from the determined timing when it is determined that the beam distribution is narrower than a first predetermined range, and increases the injection amount of the space charge neutralizer from the determined timing when it is determined that the beam distribution is wider than a second predetermined range that is wider than the first predetermined range.

(7) In the charged particle beam transport device described in any one of (1) to (6), the focusing structure is provided on the entrance side and the exit side of the charged particle beam, and a vacuum exhaust section for evacuating the inside of the charged particle beam transport device is provided in the middle part between the focusing structure on the entrance side and the focusing structure on the exit side.

(8) The charged particle beam transport device according to any one of (1) to (7) further comprises a current measuring device for measuring the current of the charged particle beam and a control device for controlling the injection amount of the space charge neutralizer, and the control device adjusts the flow rate of the space charge neutralizer based on the measurement result of the beam current value by the current measuring device.

(9) The charged particle beam transport device according to any one of (1) to (8) further includes a vacuum gauge for measuring the degree of vacuum within the charged particle beam transport device and a control device for controlling the injection amount of the space charge neutralizer, and the control device adjusts the flow rate of the space charge neutralizer based on the result of the measurement of the degree of vacuum by the vacuum gauge.

(10) The charged particle beam transport device according to any one of (1) to (9), further comprising a control device that has a plurality of the injection ports and independently controls the injection amount of the space charge neutralizer at each of the plurality of injection ports.

(11) A method for manufacturing a charged particle beam transport device, comprising the steps of providing a focusing structure whose inner diameter decreases toward the focusing portion of the charged particle beam, and providing an injection port for injecting a space charge neutralizing agent that neutralizes space charge toward the space surrounded by the focusing structure.

(12) A method for neutralizing a charged particle beam, comprising providing a focusing structure whose inner diameter decreases toward the focusing portion of the charged particle beam, and injecting a space charge neutralizing agent that neutralizes the space charge toward the space surrounded by the focusing structure.

Reference Signs List 1...charged particle beam 2...vacuum chamber 3a, 3b...focus coil 4...charged particle beam generator 5...post-stage accelerator 6...extraction electrode 7...neutralizing agent reservoir 8, 8A, 8B, 8C...injection amount control device 9a, 9b, 9b1, 9b2, 9b3, 9b4...injection port 10...vacuum gauge (vacuum degree measuring device)
11, 11a, 11a1, 11b, 11b1, 11c, 11c1, 11d, 11d1...beam distribution meter (distribution measuring instrument)
12...Beam ammeter (current measuring device)
13, 13a, 13b, 16, 17...Collimator (focusing structure)
14...Vacuum exhaust pump (vacuum exhaust part)
15... Beam halo section 20... Charged particle beam transport device 30... Linear accelerator

Claims (12)

A charged particle beam transport device, comprising:
a focusing structure having an inner diameter that decreases toward a focusing portion of the charged particle beam;
an injection port for injecting a space charge neutralizing agent for neutralizing space charge toward a space surrounded by the focusing structure. 2. The charged particle beam transport system according to claim 1,
The focusing structure is provided on an outlet side of the charged particle beam in the charged particle beam transport device, and the inner diameter becomes smaller toward the outlet. 3. The charged particle beam transport system according to claim 2,
The focusing structure is further provided on an entrance side of the charged particle beam in the charged particle beam transport device, and the inner diameter becomes smaller toward the entrance. 4. The charged particle beam transport system according to claim 1,
The focusing structure has a tapered shape. 4. The charged particle beam transport system according to claim 1,
a distribution measuring device for measuring a distribution of the charged particle beam;
A control device for controlling the injection amount of the space charge neutralizer,
The control device adjusts the amount of the space charge neutralizer injected so that the beam distribution in a cross section in the transport direction has a desired shape. 6. The charged particle beam transport system according to claim 5,
The control device reduces the amount of space charge neutralizing agent injected compared to the determined timing when it is determined that the beam distribution is narrower than a first predetermined range, and increases the amount of space charge neutralizing agent injected compared to the determined timing when it is determined that the beam distribution is wider than a second predetermined range that is wider than the first predetermined range. 4. The charged particle beam transport system according to claim 3,
a vacuum exhaust section for evacuating the inside of the charged particle beam transport device to a vacuum, the vacuum exhaust section being provided in an intermediate portion between the focusing structure on the entrance side and the focusing structure on the exit side. 4. The charged particle beam transport system according to claim 1,
a current measuring device for measuring a current of the charged particle beam;
A control device for controlling the injection amount of the space charge neutralizer,
The control device adjusts the flow rate of the space charge neutralizer based on a measurement result of a beam current value by the current measuring device. 4. The charged particle beam transport system according to claim 1,
a vacuum level measuring device for measuring a vacuum level within the charged particle beam transport device;
A control device for controlling the injection amount of the space charge neutralizer,
The control device adjusts a flow rate of the space charge neutralizer based on a result of measurement of the degree of vacuum by the vacuum measuring device. 4. The charged particle beam transport system according to claim 1,
The injection port is provided in a plurality of ports,
The charged particle beam transport device further comprises a control device that independently controls the injection amount of the space charge neutralizer at each of the plurality of injection ports. A method for manufacturing a charged particle beam transport device, comprising the steps of:
providing a focusing structure having an inner diameter that decreases toward a focusing portion of the charged particle beam;
providing an injection port for injecting a space charge neutralizer toward a space surrounded by the focusing structure. A method for neutralizing a space charge of a charged particle beam in a charged particle beam transport device, comprising:
A method for neutralizing a charged particle beam, comprising: injecting a space charge neutralizing agent toward a space surrounded by a focusing structure having an inner diameter smaller toward a focusing portion of the charged particle beam.

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