JP7300197B2 - Ion source and multi-ion generator equipped with it - Google Patents

Description

The present invention relates to an ion source and a multi-ion generator including the same.
This application claims priority based on Japanese Patent Application No. 2019-071409 filed in Japan on April 3, 2019, the content of which is incorporated herein.

In order to further improve the therapeutic effect of heavy ion radiotherapy, a multi-ion irradiation method has been proposed in which several kinds of ions are used for treatment. In order to develop this method at heavy ion beam cancer treatment facilities equipped with compact treatment devices, which are becoming popular nationwide, it is necessary to generate four types of ions (He, C, O, Ne) and switch between them. A compact multi-ion generation system that can quickly perform

K. Takahashi et al., Proc. of the 15th Annual Meeting of ParticleAccelerator Society of Japan, Nagaoka, Japan, 2018, p.408 E.D.Donets, E.E.Donets, and D.E.Donets, Review of Scientific Instruments, Volume73, Number2, 2002, p.696

So far, a method of switching the ion species by controlling the gas supply system of one ECR ion source has been tried, but experiments have confirmed that it takes several minutes to switch the ion species. (Non-Patent Document 1). In addition, an EBIS ion source, which has a completely different structure from the ECR ion source, is known. larger than the source (Non-Patent Document 2).

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a miniaturized ion source so that the ion species to be supplied can be switched in a short time, and a multi-ion generator equipped with the same. do.

In order to solve the above problems, the present invention employs the following means.

(1) An ion source according to an aspect of the present invention includes an electron source, an anode electrode and a cathode electrode for extracting a hollow electron beam from the electron source, a drift tube surrounding a passing region of the extracted hollow electron beam, a repeller for reversing the traveling direction of the hollow electron beam that has passed through the passage area toward the electron source; and gas supply means for supplying a raw material gas to the passage area, wherein , the repeller, and the gas supply means are all arranged outside the drift tube.

(2) In the ion source described in (1) above, the anode electrode comprises a first anode electrode that adjusts the amount of the hollow electron beam to be generated, and a second anode electrode that forms an ion trap in the central axis direction of the drift tube. and a second anode electrode.

(3) The ion source according to either (1) or (2) above may further include magnetic field generating means disposed around the outer wall surface of the drift tube.

(4) A multi-ion generator according to an aspect of the present invention is a multi-ion generator comprising a plurality of ion sources according to any one of (1) to (3), an ion channel for extracting generated ions from an ion source, wherein the ion extracting means connects at least one of the plurality of ion sources to a predetermined ion extracting portion; a connected ion source changing means for changing the ion source to which the channel is connected.

(5) In the multiple ion generation device described in (4) above, the connected ion source changing means is fixed to one end of the ion flow path connected to the ion extraction section, and rotates the ion flow path. and the other end of the ion flow path rotated such that the distances from the plurality of ion sources are equal to each other from the rotation axis is one of the plurality of ion sources. It may be arranged so as to be connectable with the passage area.

(6) A multi-species ion generator according to another aspect of the present invention comprises the ion source according to any one of (1) to (3) above, and the ion source via a first gas flow path. and gas supply means connected to each of a plurality of second gas flow paths branched from the first gas flow path, wherein the conductance C of the first gas flow path is equal to the above It is equal to or greater than the ratio V/(Δt) between the volume V of the ion source and the evacuation time Δt of the ion source.

(7) In the multiple ion generator described in (6) above, it is preferable that the evacuation time Δt is 1 second or less.

(8) In the multiple ion generator according to any one of (6) and (7) above, each of the plurality of second gas flow paths may be provided with a mass flow controller for adjusting the gas flow rate.

ADVANTAGE OF THE INVENTION According to this invention, the ion source miniaturized so that switching of the ion species to supply can be performed in a short time, and the multi-ion generation apparatus provided with the same can be provided.

1 is a configuration diagram of a popular compact therapeutic device including the multi-ion generating device of the present invention; FIG. 1 is a cross-sectional view of an ion source according to first and second embodiments of the present invention; FIG. 1(a) and 1(b) are a side view and a cross-sectional view of the multi-ion generating device according to the first embodiment of the present invention; FIG. FIG. 3 is a diagram comparing the ion source of FIG. 2 and a compact ECR ion source for heavy ion radiotherapy. It is a figure which shows the relationship of the operation timing of a synchrotron, an injector, and the multispecies ion generator of this invention. It is a block diagram of the multi-ion generation apparatus which concerns on 2nd embodiment of this invention. 4(a) and 4(b) are graphs showing simulation results of electron trajectories and electron distributions in an ion source as examples of the present invention. 5 is a graph showing a simulation result of time change of the number of accumulated electrons in the ion source as an example of the present invention. (a) It is a graph which shows the ionization cross section data table of various ion produced|generated as an Example of this invention. (b) and (c) are graphs showing simulation results of valence distribution ratios of various ions generated as examples of the present invention.

DETAILED DESCRIPTION OF THE INVENTION An ion source according to an embodiment to which the present invention is applied and a multi-species ion generator including the ion source will be described in detail below with reference to the drawings. In addition, in the drawings used in the following explanation, in order to make the features easier to understand, the characteristic portions may be enlarged for convenience, and the dimensional ratios of each component may not necessarily be the same as the actual ones. do not have. Also, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate modifications within the scope of the invention.

<First Embodiment>
FIG. 1 is a configuration diagram of a popular compact therapeutic device including a multi-ion generator 150 according to the first embodiment of the present invention. The popular compact therapeutic device is mainly composed of a multi-ion generator 150 , a popular compact injector 160 and a popular synchroton 170 .

The multiple ion generator 150 mainly includes a plurality of ion sources 100 and an ion extraction means (device) 120 for extracting ions generated from each of the ion sources 100 . As the ion source 100, a compact electron beam ion source (EBIS) for generating light ions is used.

FIG. 2 is a cross-sectional view of the ion source 100. As shown in FIG. The ion source 100 mainly includes an electron source 101, an anode electrode 102 and a cathode electrode 103 that extract a hollow electron beam EB from the electron source 101, a drift tube 105 surrounding a passing region 104 of the extracted hollow electron beam EB, A repeller 106 for reversing the traveling direction of the hollow electron beam EB that has passed through the passing region 104 toward the electron source 101 side, and a vacuum chamber 110 are provided. The electron source 101 , the anode electrode 102 , the cathode electrode 103 and the repeller 106 are all arranged outside the space surrounded by the drift tube 105 inside the vacuum chamber 110 . A space surrounded by the drift tube 105 is hollow.

Outside the drift tube 105 , a magnetic field generating means (magnetic field generating device) 107 such as an electromagnet or a permanent magnet is arranged so as to surround the drift tube 105 .
The anode electrode 102 may include a first anode electrode that adjusts the amount of the hollow electron beam EB that is generated, and a second anode electrode that forms an ion trap along the central axis of the drift tube 105 .

An electron beam EB extracted from an electron source 101 on a cathode electrode (cathode) 103 by an anode electrode (anode) 102 moves in the drift tube 105 along the direction of the magnetic field generated by the magnetic field generating means 107 . A hollow (annular) electron beam EB can be formed by appropriately designing an electron gun having an annular electron source 101, a cathode electrode 103, and an anode electrode . This hollow-shaped electron beam EB suppresses the potential drop in the drift tube 105 caused by the space charge effect, and makes it possible to store more electrons than in the case of a linear beam. The kinetic energy of the generated electron beam EB can be adjusted by changing the potential difference between the cathode electrode 103 and the drift tube 105 .

When the hollow electron beam EB passes through the reveller anode 108 and reaches the repeller 106 set to the same or lower voltage as that of the electron source 101, it is reversed and starts moving in the opposite direction, and returns to the electron source 101. reach the periphery of By this repetition, electrons having favorable energy are accumulated in the drift tube 105 for generating ions.

Due to the space charge effect of the accumulated electrons, a potential distribution is formed in the radial direction (r direction) in the hollow portion of the drift tube 105, and the potential on the central axis 105C passing through the hollow portion is equal to the potential of the drift tube 105. decrease in comparison. In addition to the potential distribution in the r direction, by setting the potentials of the anode electrode 102 and the repeller anode 108 to potentials higher than those of the drift tube 105, a potential distribution is also given in the axial direction (s direction), Potential wells necessary for confinement are formed.

A gas to be ionized is supplied from outside the ion source 100 into the drift tube 105 . The supplied gas collides with electrons accumulated therein to produce singly charged ions. The singly charged ions produced are confined in a potential well formed within the drift tube 105 . The longer the confinement time τ, the more singly charged ions change to multiply charged ions by successive ionization.

In order to achieve the required confinement time τ (20 to 200 ms) for generating the desired multiply charged ions, the area around the drift tube 105 in the ion source 100 must be maintained at a high degree of vacuum. For that purpose, a NEG (Non-evaporated getter) pump is arranged around the drift tube. The generated multiply charged ions are taken out of the ion source 100 by the extraction electrode 109 .

FIG. 3( a ) is a side view of the multiple ion generation device 150 of the present embodiment viewed from the ion extraction port side of the ion source 100 . FIG. 3(b) is a cross-sectional view of the multiple ion generator 150 of FIG. 3(a) taken along a plane containing the α-α line. The multi-species ion generator 150 mainly includes a plurality of (here, four) ion sources 100 and ion extraction means 120 for extracting ions generated from each of the ion sources 100 . It is assumed that as many ion sources 100 are installed as the number of ion species that need to be produced. Ion species to be generated include, for example, He, C, O, and Ne.

The ion extraction means 120 changes the ion flow path (deflector) 122 that connects at least one of the plurality of ion sources 100 to a predetermined ion extraction part 121, and the ion source 100 to which the ion flow path 122 is connected. and a connected ion source changing means 123 for changing the ion source.

The connected ion source changing means 123 is not particularly limited. For example, as shown in FIG. and a rotating shaft 124 that rotates the . In this case, the plurality of ion sources 100 are arranged such that the distances from the rotation axis 124 are equal to each other, and the other end 122b of the rotated ion flow path is located in one of the passage regions of the plurality of ion sources 100. 104 are arranged so as to be connectable.

When rotating the rotating shaft 124 in a vacuum, a magnetically coupled rotary introducer can be used as a manipulator, and a stepping motor can be used for the rotating drive. The time required for switching ions is less than about 1 second required for rotating the ion channel 122 . The ion flow path 122 should be designed such that the selected ion source does not change the downstream dispersion function.

4A and 4B are cross-sectional views of the ion source 100 and the compact ECR ion source for heavy ion radiotherapy, respectively, shown in FIG. The dimension L1 of the ion source 100 in the passage direction of the electron beam EB is about 1/4 of the maximum dimension L2 of the ECR ion source 500. Therefore, when the ion source 100 is used, the installation space can be greatly reduced. can.

FIG. 5 is a diagram showing the relationship between the operation timings of the synchrotron, injector, and multi-species ion generator 150 of the present invention. The synchrotron operates with a period of the order of 10 seconds, and ions are supplied from the injector during the time width of 100 μs at the beginning of the period. In this time span of 100 μs, the compact multi-ion generation system supplies ions to the downstream injector. The ions to be supplied can be switched between the end of the supply of certain ions and the timing of the next supply (10 seconds corresponding to one cycle of the synchrotron).
Then, at the timing of the next supply, it is possible to supply ions different from those in the previous period.

As described above, the ion source according to this embodiment is miniaturized by arranging the electron source 101, the anode electrode 102 , the repeller 106, etc. outside the drift tube and making the inside of the drift tube hollow. be. Therefore, it is possible to install a plurality of ion sources 100 according to the present embodiment in an installation space for one conventional ECR ion source, and easily realize a multi-ion generator 150 having a plurality of ion sources 100. be able to. A plurality of different ions can be simultaneously generated by driving the plurality of ion sources 100 respectively. Therefore, according to the multi-species ion generator of the present embodiment, it is possible to switch the ion species to be supplied in a shorter time than in the case where a single ion source sequentially generates a plurality of ions.

<Second embodiment>
FIG. 6 is a configuration diagram of a multiple ion generator 210 according to a second embodiment of the present invention. The multiple ion generator 210 includes an ion source 200, an exhaust means 212 connected to the ion source 200 via a first gas flow path 211, and a plurality of second gas flow paths branched from the first gas flow path 211. gas supply means 214 connected to each of 213 . The plurality of gas supply means 214 has a function of supplying source gases of ions different from each other. It is assumed that the ion source 200 is configured similarly to the ion source 100 of the first embodiment.

The multi-species ion generator 210 is configured to switch the generated ions by quickly evacuating the gas lines and the ion source 200 . Specifically, first, when changing the generated ions, the valves V2, V3, V4, and V5 in front of the cylinder are closed, V1 is opened, and the gas lines and the vacuum chamber 110 in the ion source 200 are evacuated. conduct. In order to quickly evacuate, conduits serving as the first gas flow path 211 and the second gas flow path 213 should have a large inner diameter, and the vacuum chamber 110 should be kept at an ultra-high vacuum. After the evacuation is completed, the valve of the gas cylinder to be used is opened, V1 is closed, and the supply gas is switched.

Each of the plurality of second gas flow paths is provided with a mass flow controller that adjusts the gas flow rate. Valves V2, V3, V4, and V5 may have this mass flow controller function. The ion switching time performed by this valve operation is about the same as the exhaust time constant τevac determined by the volume of the inter-valve conduit (the first gas flow path 211 and the second gas flow path 213) and the volume of the ion source 200. Become. This time constant τevac is, for example, 1 second when the volume of the ion source 200 is 0.4 L, the inner diameter of the inter-valve conduit is 9 mm, and the length is 200 mm. With this exhaust time constant, the amount of residual gas can be reduced to 1/100 of the amount before the exhaust is started 4.7 seconds after the ion source 200 is exhausted. It becomes possible. The suction/exhaust performance of the vacuum chamber 110 is mainly affected by the conductance C of the first gas flow path 211 . When evacuation is performed for a time equal to or less than the time constant τevac, the conductance C of the first gas flow path 211 is determined by the volume V of the ion source 200 (volume of the vacuum chamber 110) and the evacuation of the ion source 200 (vacuum chamber 110). It has the relationship of the following formula (1) with the time Δt.
C≧V/(Δt) (1)
That is, the conductance C of the first gas flow path 211 is equal to or greater than the ratio V/(Δt) between the volume V of the ion source 200 and the evacuation time Δt of the ion source 200 . The exhaust time Δt in this embodiment is preferably about 1 second or less.

Hereinafter, the effects of the present invention will be made clearer by way of examples. It should be noted that the present invention is not limited to the following examples, and can be modified as appropriate without changing the gist of the invention.

As an embodiment of the present invention, a simulation using a three-dimensional PIC code was performed for electron trajectories and electron distribution in an ion source. FIG. 7A is a diagram showing electron trajectories when the ion source is driven. The magnetic field distribution obtained by numerical analysis of the solenoid is used. Calculations are made using 10 ⁷ particles, and the trajectories of 10 ² particles among them are plotted. FIG. 7(b) is a graph showing the r((x ² +z ² ) ^1/2 ) direction dependence of the electron beam current density j in the cross section of the ion source. These results show that the ion source of the present invention can form a hollow electron beam.

As an embodiment of the present invention, a simulation of the change in the number of accumulated electrons in the ion source over time was performed. FIG. 8 is a graph showing the results. From the change in the number of accumulated electrons in the ion source over time, it can be seen that the number of electrons in the drift tube reaches 1.5×10 ¹¹ . This result shows that even for Ne ⁷⁺ ions (q=7) with the highest ion valence, a maximum of N˜10 ¹⁰ is stored in the drift tube. Also, if the transport efficiency from the multi-ion generation system to the synchrotron for multi-turn injection is assumed to be 10%, it can be seen that N˜10 ⁹ ions can be supplied to the synchrotron.

FIG. 9(a) is a graph showing ionization cross sections of various ions generated as an example of the present invention. FIGS. 9B and 9C are graphs showing simulation results of valence distribution ratios of various ions generated as examples of the present invention.

Regarding the potential of each electrode, the cathode: 0 V, the first anode electrode: 1.5 kV, the second anode electrode: 1.7 kV, the drift tube: 1.3 kV, the liberal anode: 1.7 kV, the liberal: -100 V, the extraction electrode. : -4 kV. The average electron beam energy in the drift tube obtained under these conditions was 660 eV. This energy is sufficient for the sequential ionization generation of He ²⁺ , C ⁴⁺ , C ⁵⁺ , Q ⁶⁺ and Ne ⁷⁺ as shown in FIG. 9(a).

FIG. 9(b) shows n _q /n ₀ , which is the ratio of the number of generated ions n _q to the total number of generated ions _n for carbon ions, and j τ which is the product of the electron beam current density j and the confinement time τ. as a function of By adjusting the value of jτ in the target area in the figure, a maximum value of n _q /n ₀ =0.83 for C ⁴⁺ and n _q /n ₀ =0.62 for C ⁵⁺ can be obtained.

Similarly, as shown in FIG. 9(c), He ²⁺ has n _q /n ₀ =1.0, and O ⁶⁺ has n _q /n ₀ =1.0 (K nuclei cannot be ionized at 660 eV, q=6 ), Ne ⁷⁺ can obtain a maximum value of n _q /n ₀ =0.49. In ^order to achieve this target area jτ value (=0.2-2 C/cm ² ), from FIG. , which is a common value for EBIS and can be easily achieved with the ion source of the present invention.

DESCRIPTION OF SYMBOLS 100, 200... Ion source, 101... Electron source, 102... Anode electrode 103... Cathode electrode, 104... Passage area, 105... Drift tube 105C... Central axis, 106 ... Repeller 107 ... Magnetic field generating means 108 ... Reveler anode 109 ... Extraction electrode
110 Vacuum chamber 120 Ion extraction means 121 Ion extraction unit 122 Ion channel 122a One end of ion channel 122b Other end of ion channel
123... Connected ion source changing means 124... Rotating shaft, 150, 210... Multi-ion generator, 160... Injector 170... Popular synchroton, 180... Treatment room, 211 First gas flow path 212 Exhaust means 213 Second gas flow path 214 Gas supply means 500 ECR ion source EB Hollow electron beam

Claims (8)

an electron source;
an anode electrode and a cathode electrode for extracting a hollow electron beam from the electron source;
a drift tube surrounding a passing region of the extracted hollow electron beam;
a repeller for reversing the traveling direction of the hollow electron beam that has passed through the passage area toward the electron source;
gas supply means for supplying source gas to the passage area,
An ion source, wherein the electron source, the anode electrode, the repeller, and the gas supply means are all arranged outside the drift tube. 3. The anode electrodes include a first anode electrode for adjusting the amount of the hollow electron beam to be generated, and a second anode electrode for forming an ion trap in a central axis direction of the drift tube. 1. The ion source according to 1. 3. The ion source according to claim 1, further comprising magnetic field generating means arranged around the outer wall surface of said drift tube. A multiple ion generator comprising a plurality of the ion sources according to any one of claims 1 to 3,
Further comprising ion extracting means for extracting the generated ions from each of the ion sources,
The ion extracting means includes an ion channel that connects at least one of the plurality of ion sources with a predetermined ion extracting portion, and a connected ion source change that changes the ion source to which the ion channel is connected. A multiple ion generator characterized by comprising: means. The connected ion source changing means is fixed to one end side of the ion flow path connected to the ion extracting section, and has a rotation shaft for rotating the ion flow path,
The plurality of ion sources are equidistant from the rotation axis, and the other end of the rotated ion channel can be connected to any one of the plurality of ion sources. 5. The multi-ion generator according to claim 4, wherein the multi-ion generator is arranged in the . an ion source according to any one of claims 1 to 3;
exhaust means coupled to the ion source via a first gas flow path;
gas supply means connected to each of a plurality of second gas flow paths branched from the first gas flow path,
The multiple ion generator, wherein the conductance C of the first gas flow path is equal to or greater than the ratio V/(Δt) between the volume V of the ion source and the evacuation time Δt of the ion source. 7. The multiple ion generator according to claim 6, wherein the exhaust time .DELTA.t is 1 second or less. 8. The multiple ion generator according to claim 6, wherein each of the plurality of second gas flow paths is provided with a mass flow controller for adjusting gas flow rate.

Images