JP6668281B2 - Ion source and ion beam generation method - Google Patents

Description

  Embodiments described herein relate generally to an ion source that outputs an ion beam and an ion beam generating method.

  An ion beam composed of carbon ions, etc., was applied to the patient's affected part (cancer) by irradiation with a particle beam therapy device or a patient who received a drug containing boron. The development of ion beam-based therapeutic devices, such as boron neutron capture therapy (BNCT), which performs treatment by neutron irradiation, is being actively conducted.

  In general, in a treatment apparatus using an ion beam, ions extracted from an ion source are accelerated by an electrostatic field using a linear accelerator to generate an ion beam. Then, the ion beam that has been accelerated by a synchrotron (circular accelerator) to a predetermined set energy by orbital acceleration is used for the treatment.

  As a linear accelerator that accelerates low-energy ions extracted from an ion source with an electric field, a high-frequency quadrupole linear accelerator that can output a high-energy ion beam while suppressing divergence due to the space charge effect peculiar to charged particles is widely used. ing.

JP 2011-233478 A

  In a normal accelerator facility equipped with both an ion source and a linear accelerator, there is a problem that the entire facility becomes large and complicated. If a high-energy ion beam can be supplied by the ion source alone without using a linear accelerator, the configuration of the acceleration facility can be simplified and made compact.

  In addition, if a large current and high energy ion beam can be output, the ion beam can be directly used for a treatment device such as BNCT. However, in the conventional electrostatic acceleration using a linear accelerator, the viewpoint of the pressure resistance performance is considered. Therefore, there is a limit to the energy of the ion beam that can be output.

  The present invention has been made in view of such circumstances, and has as its object to provide an ion source and an ion beam generation method capable of outputting a high-current and high-energy ion beam without using a linear accelerator.

  The ion source according to the embodiment of the present invention has a cylindrical outer magnetic portion, and a columnar shape that is disposed at a fixed space in the center of the outer magnetic portion and generates a magnetic field between the outer magnetic portion. An inner magnetic part, comprising an anode disposed on the closed side of the space, and a cathode disposed on the open side, applying an electric field in a direction perpendicular to the magnetic field, and supplied to the space. A hole thruster for accelerating ions in the plasma generated by ionizing the gas, a columnar inner anode arranged with one end open, and an outer cathode arranged around the inner anode, The ion beam flowing from the Hall thruster is accelerated and moved in the direction of the open end of the inner anode by Lorentz force generated by a current flowing between the electrodes and a self-magnetic field generated by the current, and the Open part A plasma focus unit for outputting by compression, characterized in that it comprises a.

  According to the embodiments of the present invention, an ion source and an ion beam generation method capable of outputting a high-current and high-energy ion beam without using a linear accelerator are provided.

FIG. 2 is a longitudinal sectional view showing the configuration of the ion source according to the first embodiment. FIG. 2 is a perspective view illustrating a configuration of a hall thruster according to the embodiment. FIG. 4 is an explanatory view showing a state in which plasma is generated in a Hall thruster and ions of the plasma are accelerated. FIG. 3 is an explanatory diagram showing a state where an ion beam is accelerated in a plasma focus unit. Explanatory drawing which shows the state where an ion beam is accelerated in a guide tube. FIG. 6 is a longitudinal sectional view showing a configuration of a modification of the ion source according to the first embodiment. 4 is a flowchart illustrating an ion beam generation method according to the first embodiment. FIG. 6 is a longitudinal sectional view illustrating a configuration of an ion source according to a second embodiment. FIG. 9 is a longitudinal sectional view illustrating a configuration of an ion source according to a third embodiment.

(1st Embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
An ion source 10 according to the first embodiment shown in FIG. 1 includes a hole thruster 11 for accelerating ions of plasma generated in a space to which gas is supplied, and a hole thruster via insulating portions 12 (12a, 12b). A plasma focus unit 13 that communicates with the inner electrode 30 and applies an electric voltage between the inner anode 30 and the outer cathode 32 that are open at one end to accelerate and compress the ion beam flowing from the Hall thruster 11; And a guide tube 15 for applying a magnetic field perpendicular to the traveling direction of the ion beam and accelerating the ion beam in a collisionless state.

  The ion source 10 according to the first embodiment accelerates the ion beam accelerated by the Hall thruster 11 in the plasma focus unit 13 and compresses the ion beam. In addition, a high energy ion beam can be output.

A specific configuration will be described.
The Hall thruster 11 includes an outer magnetic part 16, an outer dielectric 19, an inner magnetic part 20, an inner dielectric 23, an anode 25, and a cathode 26.

  The outer magnetic portion 16 includes a cylindrical outer magnetic core 18 made of iron or the like, an annular outer coil 17 a wound along the inner peripheral surface of the outer magnetic core 18, and an outer peripheral surface of the outer magnetic core 18. And an annular outer coil 17b wound along. In the outer magnetic core 18, a magnetic field is generated in the axial direction.

  The outer dielectric 19 is formed in an annular shape, and is arranged on the inner peripheral surface of the outer magnetic part 16 coaxially with the outer magnetic part 16. The outer dielectric 19 is an insulating member that prevents charged particles from flowing through the outer coil 17. As a material of the outer dielectric 19, a ceramic material such as boron nitride is exemplified.

  The inner magnetic section 20 is formed in a columnar shape, and is arranged at the center of the cylindrical outer magnetic section 16 with the outer magnetic section 16 coaxially with a certain space therebetween.

  The inner magnetic section 20 includes a cylindrical inner magnetic core 21 and an inner coil 22 wound in an annular shape on the outer peripheral surface of the inner magnetic core 21. In the inner magnetic core 21, a magnetic field in the axial direction is generated in a direction opposite to the magnetic field generated in the outer magnetic core 18.

  The outer magnetic core 18 and the inner magnetic core 21 are connected to form a magnetic circuit, and a radial magnetic field is generated in the space of the hole thruster 11 in the radial direction from the outer magnetic part 16 to the inner magnetic part 20. Note that a permanent magnet may be used instead of the outer magnetic portion 16.

  The inner dielectric 23 is formed in an annular shape, and is disposed coaxially with the inner magnetic unit 20 on the outer peripheral surface of the inner magnetic unit 20. The inner dielectric 23 prevents charged particles from flowing through the inner coil 22 and, like the outer dielectric 19, is made of a ceramic material such as boron nitride.

  An annular space formed between the outer magnetic part 16 and the inner magnetic part 20 becomes a plasma region for generating plasma. The closing portion 27 closes one of the hall thrusters 11.

  The anode 25 is an annular electrode (anode) provided near the closing portion 27 through the inner magnetic portion 20 as a center. A gas supply pipe 24 is connected to the anode 25, and a gas for ionization is supplied into the space through the anode 25. The gas used for ionization is appropriately selected depending on the type of ion beam used, and for example, hydrogen, xenon, and argon are used.

  The cathode 26 is an annular electrode (cathode) provided on the open side (beam exit side) of the hall thruster 11 and adjacent to the outer magnetic section 16. By applying a voltage between the anode 25 and the cathode 26, an electric field is generated in the axial direction of the Hall thruster 11.

  The cathode 26 is preferably a hollow cathode capable of supplying electrons to the space inside the hall thruster 11. By using the hollow cathode, plasma can be generated in the Hall thruster 11 at a lower voltage.

  FIG. 2 is a perspective view showing the configuration of the hall thruster 11 in the present embodiment. Note that FIG. 2 omits some components such as the closing portion 27 and the like.

  A plurality of gas supply ports 35 for supplying gas into the space are provided on the side surface of the annular anode 25 in the circumferential direction, and the ionization gas input from the gas supply pipe 24 flows into the space. .

  The cathode 26 (hollow cathode) is formed in a hollow annular shape, and a plurality of heaters 33 are arranged in the space of the cathode 26. A substrate (not shown) for emitting thermoelectrons is inserted into the heater 33.

  A secondary gas for ionization is supplied to the inside of the heater 33, and thermal electrons are emitted from the substrate heated by the heater 33, whereby the secondary gas is ionized and plasma is generated inside the cathode 26.

  A plurality of electron supply ports 34 are provided in the inner peripheral surface of the cathode 26 in the circumferential direction, and electrons generated by ionization of the secondary gas are supplied from the electron supply ports 34 into the space of the hole thruster 11.

  The electrons supplied from the cathode 26 promote ionization of the gas supplied into the space of the hole thruster 11. Some of the electrons supplied from the cathode 26 have a role of neutralizing the ion beam accelerated and output by the hole thruster 11.

  FIG. 3 is an explanatory diagram showing a state in which plasma is generated in the hole thruster 11 and ions in the plasma are accelerated.

  In the Hall thruster 11, a radial magnetic field generated by the outer magnetic section 16 and the inner magnetic section 20 and an axial electric field generated by applying a voltage between the anode 25 and the cathode 26 are generated. . The electrons supplied from the cathode 26 are confined in the space by a field (close field) where the magnetic field and the electric field are orthogonal to each other, and perform a drift motion in the circumferential direction. This phenomenon is called the Hall effect. The gas supplied from the anode 25 is ionized by the electrons confined in this space, and plasma is generated.

  The positive ions in the generated plasma are electrostatically accelerated by the electric field and output from the hole thruster 11. At this time, some of the electrons supplied from the cathode 26 are output from the hole thruster 11 together with the ion beam to neutralize the ion beam.

Returning to FIG. 1, the description will be continued.
The insulating section 12 (12a, 12b) couples the hole thruster 11 and the plasma focus section 13 coaxially via an insulating material, and connects the hole thruster 11 and the plasma focus section 13 with each other.

  Specifically, the cathode 26 of the hole thruster 11 and the outer cathode 32 of the plasma focus unit 13 are connected using the cylindrical insulating part 12a. Then, the inner magnetic portion 20 of the hole thruster 11 and the inner anode 30 of the plasma focus portion 13 are coupled using the columnar insulating portion 12b.

  As a material of the insulating portion 12, an insulating material such as NC nylon, Teflon (registered trademark), or Delrin is used. Further, similarly to the outer dielectric 19 and the inner dielectric 23 of the hole thruster 11, a ceramic material such as boron nitride may be used.

  Since the space between the hole thruster 11 and the plasma focus unit 13 is communicated via the insulating unit 12, the ion beam accelerated and output by the hole thruster 11 smoothly proceeds to the plasma focus unit 13.

The plasma focus unit 13 includes an inner anode 30 and an outer cathode 32.
The inner anode 30 is formed in a column shape, one end is open, and the other end is connected to the insulating part 12b. The tip portion 31 of the inner anode 30 is formed such that its diameter decreases toward the opening portion, for example, in a conical shape.

  The outer cathode 32 is formed in a hollow cylindrical shape, and is arranged around the inner anode 30. One end of the outer cathode 32 is connected to the guide tube 15, and the other end is connected to the insulating part 12a.

  The diameter of the outer cathode 32 is formed to be narrower at the opening in order to guide the ion beam traveling in the space of the plasma focus unit 13 to the opening of the inner anode 30 (the part where the inner anode 30 is cut off).

  A voltage is applied between the inner anode 30 and the outer cathode 32 arranged coaxially. A current is supplied to the inner anode 30 via a current path 36 (see FIG. 4) laid inside the insulating section 12 and the inner magnetic section 20.

  FIG. 4 is an explanatory diagram showing a state where the ion beam is accelerated in the plasma focus unit 13. In the hole thruster 11, a large amount of ions generated by ionization are accelerated, and a group of ion beams is output in a plasma state. Therefore, the group of ion beams will be appropriately referred to as "plasma" below.

  The ion beam output from the Hall thruster 11 enters a space formed between the electrodes of the plasma focus unit 13.

  A self-magnetic field is generated in the circumferential direction of the plasma focus unit 13 by causing a radial current to flow through the plasma by the voltage applied to the inner anode 30 and the outer cathode 32. The plasma is accelerated and moved in the axial direction by the Lorentz force generated by the self magnetic field and the current flowing through the plasma. The acceleration by the self magnetic field is called a magnetic piston.

  As the plasma accelerates in the axial direction, a thin layer of compressed gas (shock wave front) is formed in front of the plasma, and this layer precedes the magnetic piston. The front of this shock wave sweeps the gas existing in the space of the plasma focus unit 13 to ionize it.

  Then, the plasma that has reached the distal end portion 31 of the inner anode 30 by accelerating movement in the axial direction is radially compressed (pinched) by Lorentz force at the open portion where the inner anode 30 is interrupted. At this time, the plasma becomes high temperature and high density, and the kinetic energy in the axial direction is converted into thermal energy by the compression effect. Then, the compressed plasma is propagated inside the induction tube 15 in a high energy state.

  As described above, the plasma focus unit 13 further accelerates and compresses the ion beam accelerated by the hole thruster 11 by Lorentz force, and outputs high-energy plasma.

  In a general plasma focus device, an insulator is formed on the surface of the anode, and by applying a voltage between the electrodes, a creeping discharge occurs at a position where the anode is in contact with the insulator. Then, the plasma having no initial velocity is accelerated by Lorentz force.

  On the other hand, the plasma focus unit 13 according to the first embodiment flows a high-speed ion beam (for example, 80 k (m / s)) accelerated by the upstream Hall thruster 11 and further accelerates using the Lorentz force. Therefore, an ion beam with higher energy can be generated as compared with a general plasma focus apparatus.

Returning to FIG. 1, the description will be continued.
The guide tube 15 is connected to a beam outlet of the plasma focus unit 13 and transfers the plasma (ion beam) compressed by the plasma focus unit 13 into the guide tube 15 due to a pressure difference from the inside of the guide tube 15 having a low pressure. Propagate.

  Further, the internal space communicated with the hole thruster 11, the plasma focus unit 13, and the guide tube 15 is maintained in a vacuum state of 1 Pa or less, and the length of the guide tube 15 becomes shorter than the mean free path of ions and electrons. Set as follows.

  The vertical magnetic field generator 14 is provided so as to sandwich the guide tube 15, and generates a magnetic field perpendicular to the traveling direction of the ion beam.

  FIG. 5 is an explanatory diagram showing a state in which the ion beam is accelerated in the guide tube 15.

  The plasma (ion beam) propagated from the plasma focus unit 13 into the guide tube 15 passes through the vertical magnetic field applied to the guide tube 15. At this time, an electric field is induced by the compression of the magnetic field, and the plasma is further accelerated.

  By setting the length of the guide tube 15 shorter than the mean free path of ions and electrons, the plasma propagating in the guide tube 15 has no collision, and the high energy state is maintained.

  Then, the ion beam output from the guide tube 15 is supplied to a treatment device using the beam, an accelerator provided at a subsequent stage, and the like.

  FIG. 6 is a configuration diagram showing a modification of the ion source 10 according to the first embodiment.

  In this modification, a deflecting unit 37 that separates the ion beam and the electrons is provided at the beam exit of the guide tube 15. Examples of the deflection unit 37 include an electrostatic deflector, an electrostatic lens, and a deflection electromagnet.

  When a hollow cathode is used as the cathode 26 of the Hall thruster 11, the beam output from the guide tube 15 includes an ion beam and electrons for neutralizing ions. Control is complicated if the beam contains electrons.

  Therefore, by separating electrons using the deflection unit 37, only the ion beam can be extracted, and the ion source 10 can be easily applied to a particle beam therapy system, a BNCT, or a neutron source.

  FIG. 7 is a flowchart illustrating the ion beam generation method according to the first embodiment (see FIG. 1 as appropriate).

  A gas for ionization is supplied to the space in the hall thruster 11 via the anode 25 (S10). A voltage is applied between the anode 25 and the cathode 26 to generate an electric field in a direction orthogonal to the radial magnetic field generated by the outer magnetic section 16 and the inner magnetic section 20 (S11).

When the electrons are supplied from the cathode 26, the electrons are confined in the space by the close field, the gas is ionized by the confined electrons, and plasma is generated (S12, S13).
Then, the ions are accelerated by the electric field in the hall thruster 11 and enter the plasma focus unit 13 (S14).

When a voltage is applied between the inner anode 30 and the outer cathode 32 and a radial current flows through the plasma (ion beam), a self-magnetic field is generated in the circumferential direction of the plasma focus unit 13 (S15).
The plasma is accelerated and moved in the axial direction of the plasma focus unit 13 by the Lorentz force generated by the self magnetic field and the current flowing through the plasma (S16).

Then, the plasma is compressed at the opening of the inner anode 30 (S17).
The plasma propagates to the guide tube 15 due to the pressure difference between the inside of the guide tube 15 (S18).

  The ion beam is accelerated without collision by the electric field induced when the ion beam passes through the vertical magnetic field, and the ion beam is output (S19, S20).

  As described above, an ion beam is generated using the Hall thruster 11 capable of outputting a large current beam (about several hundred mA), and the ion beam is generated by the plasma focus unit 13 and the guide tube 15 communicated via the insulating unit 12. By accelerating, a high-current and high-energy ion beam can be output without using a linear accelerator. For this reason, the output ion beam can be used for a therapeutic device such as a particle beam therapy device or a BNCT that requires a large current ion beam.

(2nd Embodiment)
Subsequently, a case where the ion source 10 according to the present embodiment is applied to a rocket engine in the field of aerospace will be described.

  FIG. 8 shows a configuration diagram of an ion source 10 according to the second embodiment. In FIG. 8, portions having the same configuration or function as those of the first embodiment (FIG. 1) are denoted by the same reference numerals, and redundant description will be omitted.

  In the ion source 10 according to the second embodiment, the guide tube 15 is not provided, and the diameter of the outer cathode 32 in the plasma focus unit 13 is formed so as to be narrow at the open portion of the inner anode 30, and the beam output port is opened from the open portion. Form so as to spread out. The periphery of the plasma focus unit 13 is covered with an insulator 38 to prevent electrification.

  The plasma compressed in the open portion diverges in a region where the diameter of the outer cathode 32 increases, and the ion beam is discharged to the outside.

  In addition, by using a hollow cathode as the cathode 26, the ion beam output from the Hall thruster 11 is neutralized, so that charging of the hull to which the ion source 10 is applied can be prevented.

  As a propulsion system used for a general rocket engine, there are an electrostatic propulsion system and an electromagnetic propulsion system. The electrostatic propulsion system is a system that applies an electrostatic electric field and accelerates the ionized propellant by the electrostatic field, as exemplified by a hall thruster. On the other hand, an electromagnetic propulsion system is a system that accelerates a propellant by a combined action of an electric field and a magnetic field, as exemplified by a MPD (Magneto Plasma Dynamic) thruster.

  Electrostatic propulsion systems use a lot of power to improve the thruster's propulsion performance, but spacecraft that fly in space have limited available power, making it difficult to obtain large thrust. Become. On the other hand, the electromagnetic propulsion system has a higher thrust density than propulsion by electrostatic acceleration, but has a problem that a large-scale spare ionization device is required.

  On the other hand, the ion source 10 according to the second embodiment generates an ion beam using the hole thruster 11 and can discharge the beam accelerated by the plasma focus unit 13 to about 100 k (m / s). An ion beam having a high pumping speed up to the above can be output with low power consumption.

(Third embodiment)
FIG. 9 shows a configuration diagram of an ion source 10 according to the third embodiment. In FIG. 9, portions having the same configuration or function as those of the second embodiment (FIG. 8) are denoted by the same reference numerals, and redundant description will be omitted.

  The ion source 10 according to the third embodiment further includes a solenoid 39 that is disposed outside the plasma focus unit 13 along the axial direction and applies a magnetic field in the axial direction.

  The solenoid 39 serving as an external magnetic field is stronger than a self magnetic field generated in the plasma focus unit 13. Therefore, when the ions are not sufficiently magnetized, the ion beam is further accelerated by the magnetic pressure difference in the axial direction.

  On the other hand, if the electric field lines and the magnetic field lines are not perpendicular when the ions are sufficiently magnetized, a component of the motion along the axial magnetic field appears. As a result, the ion beam performs cyclotron motion along the axial direction. Thereby, the divergence of the ion beam is suppressed and discharged.

  As described above, by applying an external magnetic field in the axial direction of the plasma focus unit 13 by the solenoid 39, the ion beam can be accelerated and the divergence of the ion beam can be suppressed and output.

  According to the ion source of each embodiment described above, the ion beam accelerated by the Hall thruster is accelerated and compressed in the plasma focus unit, so that a large current and high energy ion beam can be used without using a linear accelerator. Can be output.

  Although several embodiments of the present invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 10 ... Ion source, 11 ... Hall thruster, 12 (12a, 12b) ... Insulation part, 13 ... Plasma focus part, 14 ... Vertical magnetic field generation part, 15 ... Induction tube, 16 ... Outside magnetic part, 17 (17a, 17b) ... Outer coil, 18 ... Outer magnetic core, 19 ... Outer dielectric, 20 ... Inner magnetic part, 21 ... Inner magnetic core, 22 ... Inner coil, 23 ... Inner dielectric, 24 ... Gas supply pipe, 25 ... Anode, 26 ... Cathode, 27 ... Closed part, 30 ... Inner anode, 31 ... Tip, 32 ... Outer cathode, 33 ... Heater, 34 ... Electron supply port, 35 ... Gas supply port, 36 ... Current path, 37 ... Deflection section, 38 ... insulator, 39 ... solenoid.

Claims (12)

A cylindrical outer magnetic portion, a columnar inner magnetic portion disposed at a fixed space in the center of the outer magnetic portion and generating a magnetic field between the outer magnetic portion, and a closed side of the space. An anode disposed on the open side, and a cathode disposed on the open side, comprising applying an electric field in a direction orthogonal to the magnetic field, and ionizing the gas supplied to the space to generate plasma in the plasma. Hall thrusters that accelerate ions,
A column-shaped inner anode arranged with one end open, and an outer cathode arranged around the inner anode, the ion beam flowing from the Hall thruster, and a current flowing between the two electrodes And a plasma focus unit that accelerates and moves in the direction of the open end of the inner anode by Lorentz force generated by a self-magnetic field generated by the current, compresses and outputs at the open portion of the inner anode, and Ion source.   The ion source according to claim 1, further comprising an insulating unit that couples the hole thruster and the plasma focus unit through an insulating material. An induction tube for propagating the ion beam compressed by the plasma focus unit,
The ion source according to claim 1, further comprising: a vertical magnetic field generation unit provided in the guide tube and configured to generate a magnetic field perpendicular to a traveling direction of the ion beam.   The ion source according to claim 3, wherein the length of the guide tube is provided to be shorter than the mean free path of the ions and electrons.   5. The cathode according to claim 1, wherein the cathode of the Hall thruster ionizes a secondary gas supplied into the cathode to supply electrons into the space formed in the Hall thruster. 6. The ion source according to claim 1.   The ion source according to claim 5, wherein the cathode of the Hall thruster has a plurality of electron supply ports for supplying electrons. The tip of the inner anode has a conical shape,
The ion source according to any one of claims 1 to 6, wherein a diameter of the outer cathode is formed to be narrower at the open portion of the inner anode. It further includes an insulating unit that is coupled via an insulating material and communicates the hole thruster and the plasma focus unit,
The inner anode, the insulating portion and the ions according to any one of claims 1 to 7 in which current through a current path that is laid inside the inner magnetic portion is characterized in that it is provided source. An induction tube for propagating the ion beam compressed by the plasma focus unit,
Is connected to the beam outlet of the guide tube, the ion source according to any one of claims 1 to 8, characterized in that said further and a deflection unit for separating an ion beam and an electron.   2. The ion source according to claim 1, wherein a diameter of the outer cathode is formed so as to be narrower at the opening of the inner anode and expand toward the beam output port from the opening.   The ion source according to claim 10, further comprising a solenoid that is disposed outside the plasma focus unit and applies a magnetic field in an axial direction. Using a Hall thruster to accelerate the plasma ions generated in the gas-supplied space;
Accelerating and compressing the ion beam output from the hole thruster by applying a voltage between the inner anode and the outer cathode, one end of which is open, using a plasma focus unit communicated with the hole thruster; And a method for generating an ion beam.