JP2015138640A - negative ion source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative ion source device which enables the increase in the efficiency of using a promoting substance.SOLUTION: A negative ion source device 100 comprises: a chamber 108; a gas-supply source 122 for supplying a material gas into the chamber 108; a plasma generating part 112 located on one end side of the chamber 108 for generating plasma by using the material gas supplied from the gas-supply source 122; a cesium supply source 118 for promoting the generation of negative ions, and supplying cesium having reactivity with atmospheric air into the chamber 108; a plasma electrode 116 located on the other end side of the chamber 108, and having a through-hole 116a which allows negative ions generated in the chamber 108 to be withdrawn out of the chamber 108; and a temperature-control part 128 for creating, on the other side of the chamber 108, a temperature lower than that of a wall part on the one end side of the chamber 108.

Description

  The present invention relates to a negative ion source device.

  As an ion source device used for an accelerator or the like, for example, a plasma sputtering type negative ion source device using a solid as a raw material (see Patent Document 1) or a negative ion beam generating a negative ion beam using a gas (for example, hydrogen gas) as a raw material. Ion source devices are known. The latter negative ion source device includes, for example, a chamber, a filament for generating plasma in the chamber, a hydrogen gas supply unit for supplying hydrogen gas into the chamber, and a cesium for supplying cesium vapor into the chamber. A supply source and a plasma electrode for extracting negative ions generated in the chamber out of the chamber are provided. Since an electric current is passed through the filament, thermoelectrons are emitted from the heated filament and collide with hydrogen gas in the chamber to generate plasma. And the negative ion is produced | generated when the slow electron in plasma or the electron of the plasma electrode surface reacts with a hydrogen molecule, a hydrogen atom, or a hydrogen ion.

  Since the work function is reduced on the surface of the substance to which cesium has adhered, cesium has a function of promoting the generation of negative ions. Therefore, when cesium is supplied into the chamber by the cesium supply source, the amount of negative ions extracted from the negative ion source is increased. Thus, the cesium supplied in the vapor state into the chamber gradually accumulates in a solid or liquid state on the wall surface of the chamber as the negative ion source device is operated.

JP 2004-030966 A

  However, if a large amount of a promoting substance that promotes the production of negative ions such as cesium is deposited on the wall surface of the chamber, the proportion of the promotion substance that contributes to the production of negative ions decreases.

  Therefore, an object of the present invention is to provide a negative ion source device capable of increasing the utilization efficiency of a promoting substance.

  A negative ion source device according to one aspect of the present invention includes a chamber, a source gas supply unit that supplies source gas into the chamber, and a source gas that is located at one end of the chamber and is supplied by the source gas supply unit A plasma generating unit that generates plasma using a gas, a promoting substance supply unit that promotes the generation of negative ions and that has a reactivity with the atmosphere, and is provided on the other end side of the chamber. And an electrode having a through hole capable of extracting negative ions generated in the chamber to the outside of the chamber and a temperature lower than the temperature of the wall portion on one end side of the chamber on the other end side of the chamber A temperature adjustment unit.

  In the negative ion source device according to one aspect of the present invention, the temperature adjusting unit generates a temperature lower than the temperature of the wall portion on one end side of the chamber on the other end side of the chamber. Therefore, when the promotion substance supplied into the chamber by the promotion substance supply unit takes a vapor state, the promotion substance is liable to be liquefied or solidified in a region (low temperature region) that has become low temperature by the temperature adjustment unit. It ’s easier to get together. Since the low temperature region is on the other end side of the chamber where the electrode is located, when the promoting substance in the low temperature region receives heat from the surroundings and evaporates, the promoting substance is supplied to the electrode. Thereby, the production | generation of a negative ion is accelerated | stimulated in an electrode. As described above, the accelerating substance that tends to adhere to the wall surface of the chamber is collected in the vicinity of the electrode and is used to promote the generation of negative ions. As a result, the utilization efficiency of the promoting substance can be increased.

  The temperature adjustment unit may be a cooling pipe through which the refrigerant flows.

  The cooling pipe may be arranged so as to surround an imaginary straight line connecting the plasma generation unit and the through hole. In this case, the promoting substance is easily collected in a balanced manner on the inner peripheral surface of the chamber.

  A negative ion source device according to one aspect of the present invention is located on the outer peripheral side of a chamber in a state separated from the outer peripheral surface of the chamber, and forms a predetermined magnetic field in the chamber, and cooling that cools the magnet May be further included. In this case, it is possible to suppress excessive heat generation of the magnet during operation of the negative ion source device by the cooling unit that cools the magnet. In addition, since the magnet and the outer peripheral surface of the chamber are separated from each other, it is possible to suppress the heat of the magnet from being transmitted to the chamber and the chamber from excessively generating heat.

  The negative ion source device according to one aspect of the present invention may further include a heating unit that heats the chamber wall. In this case, the temperature of the chamber can be prevented from becoming lower than a predetermined target value by the heating unit adjusting the temperature of the chamber. For this reason, the temperature of the plasma in the chamber can be maintained at a predetermined value.

  ADVANTAGE OF THE INVENTION According to this invention, the negative ion source apparatus which can raise the utilization efficiency of a promoting substance can be provided.

FIG. 1 is a diagram schematically showing a neutron capture therapy apparatus. FIG. 2 is a diagram illustrating the negative ion source device according to the present embodiment. FIG. 3 is a diagram illustrating a negative ion source device according to a first modification. FIG. 4 is a diagram illustrating a negative ion source device according to a second modification. 5 is a cross-sectional view taken along line VV in FIG. FIG. 6 is a diagram showing a negative ion source device according to a third modification.

  Embodiments of the present invention will be described with reference to the drawings. However, the following embodiments are exemplifications for explaining the present invention and are not intended to limit the present invention to the following contents. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

First, the neutron capture therapy apparatus 1 including the negative ion source apparatus 100 according to one embodiment of the present invention is taken as an example, and an outline of the neutron capture therapy apparatus 1 will be described with reference to FIG. The neutron capture therapy device 1 is a device used to perform cancer treatment using boron neutron capture therapy (BNCT), and to a tumor of a patient 50 to which boron ( ¹⁰ B) is administered. Irradiate neutron beam N.

  The neutron capture therapy apparatus 1 includes a cyclotron 2. The cyclotron 2 is an accelerator that generates a charged particle beam R by accelerating negative ions (also referred to as negative ions) generated by the negative ion source device 100. The cyclotron 2 has a capability of generating a charged particle beam R having a beam radius of 40 mm and 60 kW (= 30 MeV × 2 mA), for example. The neutron capture therapy apparatus 1 is not limited to the cyclotron 2 as an accelerator, and a synchrotron, a synchrocyclotron, a linac, or the like may be used.

  The charged particle beam R emitted from the cyclotron 2 travels toward the target 6 through the beam duct 3. A plurality of quadrupole electromagnets 4 and scanning electromagnets 5 are provided along the beam duct 3. The scanning electromagnet 5 scans the charged particle beam R and controls the irradiation position of the charged particle beam R with respect to the target 6.

  The neutron capture therapy apparatus 1 includes a control unit (calculation means) S. The control unit S is an electronic control unit having a CPU, a ROM, a RAM, and the like, and comprehensively controls the neutron capture therapy apparatus 1.

  The control unit S is connected to a current monitor M that measures in real time the current value of the charged particle beam R irradiated to the target 6 (that is, charge and irradiation dose rate), and neutron capture therapy according to the measurement result. Control of each part of the apparatus 1 is performed. As the current monitor M, for example, a non-destructive DCCT (Direct Current Current Transformer) that can be measured without affecting the charged particle beam R can be used.

  The target 6 receives a charged particle beam R and generates a neutron beam N. The target 6 has a disk shape with a diameter of 160 mm, for example. The target 6 may be formed of, for example, beryllium (Be), lithium (Li), tantalum (Ta), or tungsten (W). The target 6 is not limited to a plate shape (solid) and may be liquid.

  The shield 7 shields the generated neutron beam N and gamma rays generated by the generation of the neutron beam N from being emitted to the outside of the neutron capture therapy apparatus 1. The moderator 8 has a function of decelerating the neutron beam N (attenuating the energy of the neutron beam N). The moderator 8 is configured by laminating first and second moderators 8A and 8B. The first moderator 8A mainly decelerates fast neutrons contained in the neutron beam N. The second moderator 8B mainly decelerates epithermal neutrons contained in the neutron beam N.

  The collimator 9 forms an irradiation field of the neutron beam N (irradiation range in a plane orthogonal to the traveling direction of the neutron beam N), and has an opening 9a through which the neutron beam N passes. The neutron beam N generated by the target 6 passes through the moderator 8 and then partially passes through the opening 9 a of the collimator 9, while the remaining part is shielded by the peripheral part that defines the opening 9 a of the collimator 9. As a result, the neutron beam N that has passed through the collimator 9 is formed into a shape corresponding to the shape of the opening 9a.

  The neutron dose measuring device 10 is a device that measures the dose and dose distribution of the neutron beam N irradiated to the patient 50 on the treatment table 51.

  Next, the configuration of the negative ion source device 100 will be described with reference to FIG. The negative ion source device 100 includes a negative ion source 102 and a vacuum box 104. The negative ion source 102 and the vacuum box 104 are connected by an insulating flange 106.

  The negative ion source 102 includes a chamber 108, a magnet 110, a plasma generation unit 112, a cesium introduction unit 114, a plasma electrode 116, and a temperature adjustment unit 128.

  The chamber 108 is connected to a vacuum pump (not shown) and can hold the inside in a vacuum state. The chamber 108 includes a main body 108a having a cylindrical shape, and a lid 108b provided on one end side of the main body 108a. The main body 108 a forms the side wall of the chamber 108. At both ends of the main body portion 108a, flange portions 108c and 108d that protrude outward are provided. The lid part 108b is detachably attached to a collar part 108c located on one end side of the main body part 108a, and opens or closes one end (open end) of the main body part 108a.

  The magnet 110 has a function of confining the plasma generated in the chamber 108 in the chamber 108. A plurality of magnets 110 are arranged on the outer peripheral surface side of the main body portion 108a. More specifically, the magnet 110 is positioned on the outer peripheral side of the chamber 108 in a state of being separated from the outer peripheral surface of the main body portion 108a. A cooling path (cooling part) (not shown) is provided between the magnet 110 and the outer peripheral surface of the main body part 108a. In order to cool the magnet 110 or the wall portion of the main body 108a, a coolant such as water is circulated in the cooling path.

  The plasma generation unit 112 includes a main body 112a and a pair of filaments 112b extending outward from the end surface of the main body 112a (the other end side of the chamber 108 and the plasma electrode 116 side). The main body portion 112a is attached to the inner wall surface of the lid portion 108b. A DC power supply (not shown) is connected to the main body 112a. The DC power supply applies a voltage and a current to the filament 112b to generate heat, and causes a potential difference between the filament 112b and the chamber 108 (main body portion 108a).

  The cesium introduction part 114 is provided in the lid part 108b so as to penetrate the lid part 108b. The tip of the cesium introduction part 114 is located in the chamber 108. A cesium supply source 118 is connected to the cesium introduction unit 114, and in this embodiment, cesium is supplied to the chamber 108 in a gas (vapor) state.

  The plasma electrode 116 is disposed between the insulating flange 120 provided on the flange portion 108d located on the other end side of the main body portion 108a and the insulating flange 106 on the vacuum box 104 side. The plasma electrode 116 is connected to a power source (not shown) having a variable voltage. By controlling the power supply to control the magnitude of the voltage applied to the plasma electrode 116, the plasma distribution in the chamber 108 is controlled, and the amount of negative ions extracted from the chamber 108 is controlled. The plasma electrode 116 has a through hole 116a through which negative ions generated in the chamber 108 can be drawn out of the chamber 108 (in this embodiment, the vacuum box 104 side). The plasma electrode 116 generates heat, for example, at about 250 ° C. when energized.

  A pipe 116 b connected to the gas supply source 122 is provided in the vicinity of the plasma electrode 116. That is, the pipe 116 b is located on the other end side of the chamber 108. The gas supply source 122 includes a source gas source (hydrogen gas source) and an inert gas source (argon gas source). That is, the source gas and the inert gas from the gas supply source 122 are supplied into the chamber 108 from the other end side of the main body 108a through the pipe 116b.

  The temperature adjustment unit 128 is disposed on the inner wall surface of the chamber 108 (main body unit 108a). The temperature adjustment unit 128 is a cooling pipe through which a coolant such as water flows, for example. The temperature adjustment unit 128 has a function of generating a temperature lower than the temperature of the wall portion on one end side of the chamber 108 on the other end side of the chamber 108. The temperature adjustment unit 128 is located on the other end side (the plasma electrode 116 or the vacuum box 104 side) of the chamber 108 from the center in the axial direction of the chamber 108 (main body 108a). That is, the temperature adjustment unit 128 is located on the other end side of the chamber 108 with respect to 1/2 of the total length in the axial direction of the chamber 108 (main body portion 108a). The temperature adjustment unit 128 may be located on the other end side of the chamber 108 with respect to 1/3 of the full length, or may be located on the other end side of the chamber 108 with respect to 1/4 of the full length. . Alternatively, the temperature adjustment unit 128 may be located within 2 cm in a linear distance from the plasma electrode 116 or may be located within 1 cm.

  The temperature adjustment unit 128 may have an annular shape extending in the circumferential direction along the inner peripheral surface of the main body 108a. In this case, the temperature adjustment unit 128 surrounds an imaginary straight line connecting the plasma generation unit 112 and the through hole 116 a of the plasma electrode 116.

  The vacuum box 104 is located on the downstream side of the chamber 108 from which the negative ion beam is extracted (the other end side of the chamber 108). The vacuum box 104 can hold the inside in a vacuum state, like the chamber 108. In the vacuum box 104, an electrode 124 such as an extraction electrode, a Faraday cup (not shown) for measuring the beam amount of the negative ion beam, a steering coil (not shown) for changing the trajectory of the negative ion beam, and the like are arranged. ing.

  In the negative ion source device 100 described above, when generating negative ions, the chamber 108 and the vacuum box 104 are first evacuated by a vacuum pump. Next, a source gas (hydrogen gas) is supplied into the chamber 108 from the gas supply source 122, and cesium gas is supplied into the chamber 108 from the cesium supply source 118. The amount of cesium supplied by the cesium supply source 118 may be adjusted according to the amount of the negative ion beam to be extracted. Since the work function is reduced on the surface of the substance to which cesium has adhered, cesium has a function of promoting the generation of negative ions.

  Next, a current is passed through the plasma generation unit 112, and a voltage is applied between the plasma generation unit 112 and the chamber 108. When a voltage is applied between the filament 112b heated by the current flow and the chamber 108, thermoelectrons are emitted from the filament 112b to the chamber 108, and arc discharge occurs. The thermoelectrons collide with the hydrogen gas filled in the chamber 108 and eject electrons to make the hydrogen gas into plasma.

  Among electrons existing in the plasma, fast electrons and slow electrons are discriminated by a magnet. Negative ions are generated by the reaction of slow electrons or electrons on the surface of the plasma electrode 116 with hydrogen molecules, hydrogen atoms, or hydrogen ions in the plasma. The negative ions thus generated are drawn out of the chamber 108 through the opening of the plasma electrode 116 and introduced into the cyclotron 2 via the vacuum box 104.

  Through the above steps, a coolant such as water is caused to flow inside the temperature adjustment unit 128. Therefore, a temperature lower than the temperature of the wall portion on one end side of the chamber 108 is generated on the other end side of the chamber 108 by the temperature adjusting unit 128. For example, the temperature in the vicinity of the temperature adjustment unit 128 may be 100 ° C. or less. The temperature of the wall portion at one end of the chamber 108 may be about 200 ° C. in response to heat from plasma generated in the chamber. Therefore, the cesium gas supplied from the cesium supply source 118 into the chamber 108 is difficult to adhere to the inner wall surface of the chamber 108, but easily deposits in the vicinity of the temperature adjustment unit 128.

  In the present embodiment as described above, the temperature adjustment unit 128 generates a temperature on the other end side of the chamber 108 that is lower than the temperature of the wall portion on the one end side of the chamber 108. Therefore, the cesium gas supplied into the chamber 108 by the cesium supply source 118 is likely to be liquefied or solidified in a region (low temperature region) that has become low temperature by the temperature adjustment unit 128, and as a result, tends to collect in the low temperature region. Since the low temperature region is on the other end side of the chamber 108 where the plasma electrode 116 is located, cesium gas is supplied to the plasma electrode 116 when cesium in the low temperature region receives heat from the surroundings and evaporates. Thereby, generation of negative ions is promoted in the plasma electrode 116. As described above, cesium that tends to adhere to the wall surface of the chamber 108 is collected in the vicinity of the plasma electrode 116 and is used to promote the generation of negative ions. As a result, it is possible to increase the utilization efficiency of cesium.

  In the present embodiment, the temperature adjustment unit 128 is disposed so as to surround an imaginary straight line connecting the plasma generation unit 112 and the through hole 116 a of the plasma electrode 116. Therefore, cesium is easily collected on the inner peripheral surface of the chamber 108 with a good balance.

  In the present embodiment, the magnet 110 is positioned on the outer peripheral side of the chamber 108 in a state of being separated from the outer peripheral surface of the chamber 108, and the magnet 110 is cooled by a cooling path (cooling unit) (not shown). Therefore, the cooling unit can suppress excessive heat generation of the magnet 110 when the negative ion source device 100 is in operation. In addition, since the magnet 110 and the outer peripheral surface of the chamber 108 are separated from each other, it is possible to suppress the heat of the chamber 108 from being transmitted to the magnet 110 and the magnet 110 from excessively generating heat.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to above-described embodiment. For example, you may utilize the temperature adjustment parts 130-134 (refer FIGS. 3-6) of the form different from the temperature adjustment part 128 shown by FIG. Each will be specifically described below.

  The temperature adjusting unit 130 shown in FIG. 3 is formed integrally with the main body 108 a of the chamber 108. The temperature adjustment unit 130 has a double tube structure having an outer tube extending along a predetermined axis and an inner tube extending along the axis inside the outer tube. In the example shown in FIG. 3, the tip of the temperature adjusting unit 130 is located in the chamber 108 (main body 108a). In such a temperature adjustment unit 130, the refrigerant flows from one of the inner tube and the outer tube to the other, thereby performing heat exchange with the chamber 108 (main body unit 108 a). In this way, the temperature adjustment unit 130 generates a temperature on the other end side of the chamber 108 that is lower than the temperature of the wall portion on one end side of the chamber 108.

  The main body part 108a may be provided with a plurality of temperature adjustment parts 130. Adjacent ones of the plurality of temperature adjusting parts 130 may be arranged at substantially equal intervals in the circumferential direction of the main body part 108a. In this case, cesium is easily collected on the inner peripheral surface of the chamber 108 in a balanced manner.

  The temperature adjusting unit 132 shown in FIGS. 4 and 5 is formed integrally with the main body 108 a of the chamber 108. The temperature adjustment unit 132 is different from the temperature adjustment unit 130 in FIG. 3 in that the tip of the temperature adjustment unit 132 extends to the inside of the chamber 108 (main body 108a). A plurality of temperature adjustment units 132 may be provided in the main body unit 108a. FIG. 5 shows a state in which four temperature adjustment units 132 are provided in the main body unit 108a.

  The temperature adjusting unit 134 shown in FIG. 6 is formed integrally with the main body 108 a of the chamber 108. The temperature adjustment unit 132 is different from the temperature adjustment unit 130 in FIG. 3 in that the tip of the temperature adjustment unit 132 extends to the inside of the chamber 108 (main body 108a) and a flange is provided at the tip. The main body part 108a may be provided with a plurality of temperature adjusting parts 134.

  The negative ion source device 100 according to this embodiment may further include a heating unit (for example, a heater) that heats the wall portion of the chamber 108. In this case, the temperature of the chamber 108 (main body part 108a) can be suppressed from becoming lower than a predetermined target value by the heating unit adjusting the temperature of the chamber 108 (main body part 108a). Therefore, the temperature of the plasma in the chamber 108 can be maintained at a predetermined value.

  DESCRIPTION OF SYMBOLS 1 ... Neutron capture therapy apparatus, 100 ... Negative ion source apparatus, 108 ... Chamber, 108a ... Main body part, 108b ... Lid part, 110 ... Magnet, 112 ... Plasma generation part, 112b ... Filament, 116 ... Plasma electrode, 116a ... Through Hole 118, cesium supply source, 122 ... gas supply source, 128, 130, 132, 134 ... temperature adjusting unit.

Claims (5)

A chamber;
A source gas supply unit for supplying source gas into the chamber;
A plasma generating unit that is located on one end side of the chamber and generates plasma using the source gas supplied by the source gas supply unit;
An accelerating substance supply unit for accelerating the production of negative ions and supplying an accelerating substance having reactivity with the atmosphere into the chamber;
An electrode located on the other end side of the chamber and having a through-hole capable of extracting negative ions generated in the chamber out of the chamber;
A negative ion source device comprising: a temperature adjusting unit that generates a temperature lower than a temperature of a wall portion on one end side of the chamber on the other end side of the chamber.   The negative ion source device according to claim 1, wherein the temperature adjustment unit is a cooling pipe through which a refrigerant flows.   The negative ion source device according to claim 2, wherein the cooling pipe is disposed so as to surround an imaginary straight line connecting the plasma generation unit and the through hole. A magnet that is positioned on the outer peripheral side of the chamber in a state of being separated from the outer peripheral surface of the chamber, and that forms a predetermined magnetic field in the chamber;
The negative ion source device according to claim 1, further comprising a cooling unit that cools the magnet.   The negative ion source device according to claim 1, further comprising a heating unit that heats a wall portion of the chamber.

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