JP6538005B2 - Negative ion source device - Google Patents

Description

  One aspect of the present invention relates to a negative ion source device.

  As an ion source device used for an accelerator etc., for example, a plasma sputter type negative ion source device using a solid as a raw material and a negative ion source device generating a negative ion beam using a gas (for example, hydrogen gas) as a raw material ing. 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 in the chamber, and a cesium supply for supplying cesium in the chamber A source and a plasma electrode for drawing negative ions generated in the chamber out of the chamber. Since current flows through the filament, the heated filament emits thermal electrons and collides with hydrogen gas in the chamber to generate plasma. Then, negative ions are generated by the reaction of low-speed electrons in the plasma or electrons on the surface of the plasma electrode with hydrogen molecules, hydrogen atoms, or hydrogen ions.

  Cesium has a function to promote the formation of negative ions because the work function is lowered on the surface of the substance to which cesium is attached. Therefore, when cesium is supplied into the chamber by the cesium source, the amount of negative ions extracted from the negative ion source is increased. The cesium thus supplied in the vapor state in the chamber gradually deposits in the solid or liquid state on the wall of the chamber as the negative ion source device operates.

  Patent Document 1 discloses that heating of the chamber suppresses deposition of a promoter promoting formation of negative ions such as cesium on the wall of the chamber, and promotes deposition of cesium on the plasma electrode. Negative ion source devices capable of

JP, 2015-138640, A

  However, if the amount of promoter deposited on the plasma electrode is too large, the amount of negative ions extracted from the negative ion source will decrease. The above-described negative ion source device can not adjust the amount of promoting substance deposited on the plasma electrode, which may reduce the amount of negative ions extracted from the negative ion source.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a negative ion source device capable of suppressing a decrease in the amount of negative ions extracted from the negative ion source.

  A negative ion source device according to one aspect of the present invention includes a hollow chamber in which negative ions are generated inside, a source gas supply unit that supplies a source gas serving as a source of negative ions in the chamber, and one end of the chamber Side of the plasma generation unit that generates plasma using the source gas supplied by the source gas supply unit, the electrons in the plasma are guided to the other end of the chamber, and negative ions are A negative ion generating unit to be generated, an accelerating agent supply unit for supplying an accelerating agent for accelerating the generation of negative ions into the chamber, and the other end of the chamber are provided on the other end side of the chamber. A temperature control unit for controlling the temperature of the chamber wall by performing at least one of heating and cooling, and a temperature control unit for controlling the temperature control unit. Comprising a control unit, a temperature control unit controls the temperature adjustment portion based on the value that changes according to the amount of promoter material deposited on the electrode.

  Since the negative ion source device according to one aspect includes the temperature control unit, it is possible to control the temperature of the wall of the chamber. Since the state (gas, liquid, or solid) of the promoter substance supplied into the chamber changes with temperature, the promoter substance deposited on the chamber wall and electrode by adjusting the temperature of the chamber wall It is possible to control the amount of For example, when the temperature control unit heats the wall of the chamber, the promoter is less likely to deposit on the wall of the chamber, and thus the promoter is likely to be deposited on the electrode. On the other hand, when the temperature control unit cools or reduces the amount of heating of the chamber wall, the promoter is likely to be deposited on the chamber wall, so the promoter is less likely to be deposited on the electrode. In addition, since the temperature control unit controls the temperature control unit based on the value that changes in accordance with the amount of the promoting substance, indirectly grasp the amount of the promoting substance deposited on the electrode and adjust it to an appropriate amount. Can. Therefore, it is possible to suppress a decrease in the amount of negative ions extracted from the negative ion source.

  In one form, the negative ion source device further includes a current measurement unit provided downstream of the electrode and measuring a current value of negative ions extracted by the electrode, and the temperature control unit is measured by the current measurement unit. The temperature adjustment unit may be controlled based on the fluctuation of the current value. Since the current value changes in accordance with the amount of promoter deposited on the electrode, the amount of promoter deposited on the electrode can be known by measuring the current value. Further, according to this configuration, since the temperature control unit is controlled based on the fluctuation of the current value, the amount of the promoting substance deposited on the electrode can be indirectly adjusted to an appropriate amount. Therefore, it is possible to suppress a decrease in the amount of negative ions extracted from the negative ion source.

  In one form, the temperature control unit may reduce the amount of heating by the temperature adjustment unit when the current value decreases. According to this configuration, since the promoting substance is easily deposited on the wall of the chamber, the amount of the promoting substance deposited on the electrode can be reduced. Therefore, even if the amount of promoter deposited on the electrode exceeds the appropriate amount, the amount of promoter can be adjusted to an appropriate amount, and the amount of negative ions extracted from the negative ion source can be reduced. It is possible to suppress.

  In one form, the temperature control unit may be divided into a plurality of divided temperature control units along the extension direction of the chamber, and each divided temperature control unit may be capable of temperature control independently. Since the plasma generating unit that emits heat is provided on one end side of the chamber, the temperature distribution in the chamber is likely to vary in the extending direction of the chamber. According to this configuration, the temperature distribution in the chamber can be maintained more uniformly because each divided temperature control unit can be adjusted independently. In addition, since any temperature distribution can be formed in the extension direction of the chamber, it is possible to deposit a promoter on a specific part of the wall of the chamber.

  In one form, the promoter supply may be provided at the center of one end of the chamber. According to this configuration, a predetermined distance is maintained between the promoting substance supply unit and the side wall connecting the one end side and the other end side of the chamber, so the accelerating substance supplied from the promoting substance supply unit is the side wall of the chamber. Can be suppressed from adhering to Therefore, it is possible to further improve the utilization efficiency of the promoting substance.

  According to the present invention, a negative ion source device is provided which can suppress a decrease in the amount of negative ions extracted from the negative ion source.

Fig. 1 schematically shows a neutron capture therapy device comprising a negative ion source device according to an aspect of the present invention. It is a figure showing roughly the negative ion source device concerning one form of the present invention. It is a perspective view which shows the chamber and temperature control part of a negative ion source device roughly. It is a figure which shows typically temperature distribution of the wall part of a chamber when not adjusting temperature by a temperature control part. It is a figure which shows typically temperature distribution of the wall part of a chamber at the time of temperature-controling by a temperature control part.

  Hereinafter, various embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference numerals.

First, taking a neutron capture therapy apparatus 1 provided with a negative ion source apparatus 100 according to an embodiment of the present invention as an example, the outline of the neutron capture therapy apparatus 1 will be described with reference to FIG. The neutron capture therapy apparatus 1 is an apparatus used for performing cancer treatment using boron neutron capture therapy (BNCT), and is used to treat the tumor of a patient 50 who has received boron ( ¹⁰ B). The neutron beam N is irradiated.

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

  The charged particle beam R emitted from the accelerator 2 travels toward the target 6 through the beam duct 3. A plurality of quadrupole magnets 4 and a scanning electromagnet 5 are provided along the beam duct 3. The scanning electromagnet 5 scans the charged particle beam R to control the irradiation position of the charged particle beam R on the target 6.

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

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

  The target 6 is irradiated with the charged particle beam R to generate a neutron beam N. The target 6 has, for example, a disk shape having a diameter of 160 mm. 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 (solid), and may be liquid.

  The shield 7 shields the generated neutron beam N, the gamma ray generated with the generation of the neutron beam N, and the like 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 the 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 the epithermal neutron contained in the neutron beam N.

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

  The neutron dosimetry apparatus 10 is an apparatus for measuring the dose and the dose distribution of the neutron beam N irradiated to the patient 50 on the treatment table 51.

  Subsequently, the configuration of the negative ion source device 100 will be described with reference to FIG. The negative ion source device 100 comprises 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 hollow chamber 108, a magnet 110, a plasma generation unit 112, a cesium introduction unit 114, a plasma electrode 116, a temperature control unit 128, and a temperature control unit 130.

  The chamber 108 is connected to a vacuum pump (not shown) and can hold the inside in a vacuum state. The chamber 108 has a cylindrical main body portion 108 a and a lid portion 108 b provided on one end side of the main body portion 108 a. The main body portion 108 a has a cylindrical shape, and forms a side wall of the chamber 108. The main body portion 108 a is formed with a plurality of groove portions 109 for disposing the temperature adjustment portion 128. The groove portion 109 (see FIG. 3) extends in the circumferential direction of the main body portion 108a, and is provided separately in the axial direction of the main body portion 108a. At both ends of the main body portion 108a, flange portions 108c and 108d projecting outward are respectively provided. The lid portion 108b is detachably attached to the collar portion 108c located on one end side of the main body portion 108a, and opens or closes one end (release end) of the main body portion 108a. A plurality of groove portions 109 for disposing the temperature adjustment portion 128 may be formed in the lid portion 108 b as well.

  The magnet 110 is comprised from the 1st magnet 110A and the 2nd magnet (negative ion production | generation part) 110B. The first magnet 110A has a function of generating a magnetic field for confining the plasma generated in the chamber 108 in the chamber 108. The second magnet 110 </ b> B has a function of generating a magnetic field that blocks electrons of a predetermined energy or more. The first magnet 110A and the second magnet 110B are disposed on the outer peripheral surface of the main body portion 108a, and the first magnet 110A is provided on one end side (the side on which the plasma generating portion 112 is provided) in the axial direction of the main body portion 108a. The second magnet 110B is provided on the other end side (the side on which the plasma electrode 116 is provided). The magnet 110 is held by a magnet holder (not shown), and the magnet holder is provided with a cooling pipe (not shown) for cooling the magnet 110. A refrigerant such as water is circulated in the cooling pipe. The magnet 110 may be in direct contact with the refrigerant to be cooled without using the cooling pipe.

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

  The cesium introduction unit (promoting substance supply unit) 114 is provided at the center of one end side of the chamber 108. In the present embodiment, the cesium introducing unit 114 is provided at the center of the lid 108 b so as to penetrate the lid 108 b. The tip of the cesium introducing unit 114 is located in the chamber 108. A cesium supply source 118 is connected to the cesium introducing unit 114, and in the present embodiment, cesium is supplied to the chamber 108 in a gas (vapor) state. In addition, the state of the cesium supplied is not limited to gas, You may be supplied by arrange | positioning solid cesium in a chamber. Further, the type of promoter is not limited to cesium, and any substance having a function of reducing the work function on the surface of the attached substance may be used. Further, the position at which the cesium introducing portion 114 is provided is not limited to the central portion on one end side of the chamber 108, and may be provided in any portion of the chamber 108.

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

  In the vicinity of the plasma electrode 116, a pipe 116b connected to a gas supply source (source gas supply unit) 122 is provided. That is, the pipe 116 b is located on the other end side of the chamber 108. The gas 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 of the gas supply source 122 are supplied into the chamber 108 from the other end side of the main body 108 a through the pipe 116 b.

  The temperature control unit 128 adjusts the temperature of the wall 108 e of the chamber 108 by performing at least one of heating and cooling. The temperature adjustment unit 128 is provided on the wall 108 e. The detailed description of the temperature adjustment unit 128 will be described later.

  The temperature control unit 130 is an electronic control unit having a CPU, a ROM, a RAM, and the like, and controls the temperature adjustment unit 128. The temperature control unit 130 may be included in the control unit S (see FIG. 1) that controls the entire neutron capture therapy apparatus 1 or may be provided separately from the control unit S. The detailed description of the temperature control unit 130 will be described later.

  The vacuum box 104 is located downstream of the chamber 108 where the negative ion beam is extracted (the other end of the chamber 108). Similar to the chamber 108, the vacuum box 104 can hold the inside in a vacuum state. In the vacuum box 104, an electrode 124 such as an extraction electrode, a current measurement unit 132 for measuring the current value of the negative ion beam, a steering coil (not shown) for changing the trajectory of the negative ion beam, and the like are arranged.

  The current measurement unit 132 is disposed in the vacuum box 104 and measures the current value of the negative ion beam extracted from the chamber 108. The current measuring portion 132 has a movable portion, and is disposed on an extension line (a line from which the negative ion beam is drawn) CL of the through hole 116 a of the plasma electrode 116 when the current value of the negative ion beam is measured. Ru. When the current value is not measured, the current measurement unit 132 is housed at a position not interfering with the negative ion beam. That is, when the current value is not measured, the current measurement unit 132 retracts to a position separated from the extension line CL of the through hole 116a. For example, a Faraday cup or the like can be used to measure the current value of the negative ion beam.

  In the negative ion source device 100 described above, when generating negative ions, first, the inside of the chamber 108 and the vacuum box 104 is evacuated by a vacuum pump. Next, the source gas (hydrogen gas) is supplied into the chamber 108 by the gas supply source 122, and the cesium gas is supplied into the chamber 108 by the cesium supply source 118. The amount of cesium supplied by the cesium source 118 may be adjusted according to the amount of negative ion beam desired to be extracted. Cesium has a function to promote the formation of negative ions because the work function is lowered on the surface of the substance to which cesium is attached.

  Next, current is supplied to the plasma generation unit 112, and a voltage is applied between the plasma generation unit 112 and the chamber 108. The application of a voltage between the filament 112 b heated by the flow of the current and the chamber 108 causes the filament 112 b to emit thermal electrons to the chamber 108 to cause an arc discharge. The thermions collide with the hydrogen gas filling the chamber 108 and eject electrons to plasmify the hydrogen gas. The generated plasma is confined in the chamber 108 by the magnetic field generated by the first magnet 110A.

  In the plasma, high speed electrons, which are high energy electrons, and low speed electrons, which have low energy, are mixed. The second magnet 110 </ b> B generates a magnetic field blocking high-speed electrons having energy higher than a predetermined energy, and allows high-speed electrons to stay on one end side of the chamber 108 (the side on which the plasma generation unit 112 is provided). In addition, the second magnet 110B allows slow electrons having energy lower than a predetermined energy to enter the other end side of the chamber 108 (the side on which the plasma electrode 116 is provided). Thus, among the electrons present in the plasma, the high speed electrons and the low speed electrons are discriminated by the second magnet 110B. Although not only electrons but also hydrogen atoms and hydrogen molecules are present in the plasma, hydrogen atoms and hydrogen molecules are hard to be affected by the magnetic field generated by the magnet 110 and can freely move back and forth in the chamber 108. At the other end of the chamber 108, negative ions are generated by the reaction of low-speed 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 through holes 116 a of the plasma electrode 116 and introduced into the accelerator 2 through the vacuum box 104.

  Next, the temperature adjustment unit 128 and the temperature control unit 130 will be described in detail.

  In the present embodiment, the temperature control unit 128 includes both a heating unit and a cooling unit. The temperature adjustment unit 128 can adjust the amount of heating of the wall 108 e using the heating unit and the cooling unit. When reducing the heating amount, the temperature control unit 128 reduces (or stops) the output of the heating unit and increases the output of the cooling unit. Conversely, when the heating amount is to be increased, the temperature adjustment unit 128 may increase the output of the heating unit and reduce (or stop) the output of the cooling unit. The temperature adjustment unit 128 may include only one of the heating unit and the cooling unit. Even in this case, the amount of heating can be reduced by reducing or stopping the output of the heating unit, and the amount of heating can be increased by decreasing or stopping the output of the cooling unit.

  Here, the temperature adjustment unit 128 will be described in detail with reference to FIG. FIG. 3 is a perspective view schematically showing the chamber 108 and the temperature control unit 128 of the negative ion source device 100. As shown in FIG.

  As shown in FIG. 3, the temperature control unit 128 includes a plurality of heaters 128 a for heating the wall 108 e of the chamber 108 as a heating unit, and a plurality of cooling pipes 128 b for cooling the wall 108 e of the chamber 108 as a cooling unit. And a plurality of temperature sensors 128 c that detect the temperature of the wall 108 e of the chamber 108. The heater 128 a, the cooling pipe 128 b, and the temperature sensor 128 c are respectively disposed in the groove portion 109 formed in the main body portion 108 a of the chamber 108. The heater 128a and the cooling pipe 128b extend so as to wrap around the circumferential direction of the main body portion 108a one by one, and are alternately arranged in a state of being separated by a fixed distance in the extending direction of the chamber 108. The temperature sensor 128c is disposed between the heater 128a and the cooling pipe 128b. For example, a sheath heater can be used as the heater 128a. For example, a refrigerant such as cooling water can be allowed to flow through the cooling pipe 128 b. Further, for example, a thermocouple or the like can be used for the temperature sensor 128c. The temperature adjusting unit 128 can adjust the temperature of the wall 108 e of the chamber 108 in the range of, for example, about 10 ° C. to 250 ° C.

  The temperature control unit 128 can be divided into a plurality of divided temperature control units 129 along the extension direction of the chamber 108. Each divided temperature adjustment unit 129 includes at least one set of a heater 128a and a cooling pipe 128b, and can be independently controlled by a temperature control unit 130 described later. Here, in the state in which the temperature adjustment unit 128 is “divided”, one divided temperature adjustment unit 129 can set unique temperature adjustment conditions without being affected by the other divided temperature adjustment unit 129. It is a state. Specifically, the state in which the heater 128a is divided refers to a state in which a current is independently supplied to the divided portion and not electrically connected to other portions. The state in which the cooling pipe 128 b is divided means that each divided portion has an independent inlet and outlet for the refrigerant. Further, “independently control” means that temperature adjustment of only one divided temperature adjustment unit 129 can be performed under predetermined conditions. For example, in one divided temperature adjustment unit 129, control can be performed such that the wall portion 108e of the chamber 108 is heated by the heater 128a, and in the other divided temperature adjustment unit 129, the wall portion 108e of the chamber 108 is cooled by the cooling pipe 128b. is there.

  The temperature control unit 128 is also disposed on the lid 108 b of the chamber 108 (see FIG. 2). In the lid portion 108b, for example, the heaters 128a and the cooling pipes 128b extending linearly may be alternately disposed, and the temperature sensor 128c may be disposed between the heater 128a and the cooling pipes 128b. The arrangement of the temperature control unit 128 in the lid 108 b is not limited to the above. For example, the annular heater 128 a and the cooling pipe 128 b may be arranged concentrically.

  The temperature control unit 130 controls the temperature adjustment unit 128 based on the value that changes according to the amount of the promoting substance (cesium) deposited on the plasma electrode 116. More specifically, the temperature control unit 130 controls the heater 128a based on the fluctuation of the current value of the negative ion beam measured by the current measurement unit 132 and the temperature of the chamber wall 108e measured by the temperature sensor 128c. And control the cooling pipe 128b. That is, in the present embodiment, the current value of the negative ion beam is used as the “value that changes in accordance with the amount of the promoting substance deposited on the plasma electrode 116”. Here, the "variation in current value" means that the current value increases or decreases. The temperature control unit 130 may control the temperature adjustment, for example, when the current value increases or decreases beyond a predetermined threshold. The threshold may be determined, for example, by a specific numerical value, or may be determined by the rate of increase or decrease from the target current value. In addition, the temperature control unit 130 may perform the following control. Since the current value of the negative ion beam can be increased or decreased by the arc discharge power, the fluctuation of the negative ion beam current can be suppressed by adjusting the arc discharge power. However, when the deposition amount of the promoting substance on the surface of the plasma electrode 116 deviates from the optimum amount, the current value of the negative ion beam decreases from the target value, and the response of the current value of the negative ion beam to the arc discharge power is poor. Become. That is, even if the arc discharge power is set to a high value in order to increase the current value of the reduced negative ion beam to the target value again, the rate of increase of the current value of the negative ion beam decreases. If the deposition amount of the promoting substance on the surface of the plasma electrode 116 deviates further from the optimum amount, the current value of the negative ion beam does not increase even if the arc discharge power is set to a high value, and it decreases with time. Therefore, a threshold is provided for the rate of increase of the current value of the negative ion beam by the arc discharge power, and when the rate of increase falls below the threshold, the deposition amount of the promoting substance on the surface of the plasma electrode 116 deviates from the optimal amount. Judge and carry out control of temperature adjustment.

  Here, the control content in the case where the temperature control unit 130 controls the temperature adjustment unit 128 based on the fluctuation of the current value of the negative ion beam measured by the current measurement unit 132 will be described. When the discharge amount in the plasma generation unit 112 and the flow rate of the gas supplied from the gas supply source 122 are constant, the beam amount of the negative ion beam extracted from the chamber 108 depends on the change in the amount of cesium deposited on the plasma electrode 116 Increase or decrease. Therefore, in order to keep the amount of negative ion beam constant, it is necessary to keep the amount of cesium deposited on the plasma electrode 116 at an appropriate amount. When the amount of cesium deposited on the plasma electrode 116 becomes too large, the amount of negative ion beam decreases, and the current value measured by the current measurement unit 132 decreases. In such a case, when the amount of cesium deposited on the plasma electrode 116 is reduced, the temperature of the plasma electrode 116 is increased to separate excess cesium from the plasma electrode 116, and the chamber 108 is operated by the temperature control unit 128. The temperature of the wall 108e is reduced. As a result, the excess cesium deposited on the plasma electrode 116 separates from the plasma electrode 116 and tends to be deposited on the wall 108 e of the chamber 108.

  On the other hand, when the amount of cesium deposited on the plasma electrode 116 decreases too much, the beam amount of the negative ion beam decreases, and the current value measured by the current measurement unit 132 decreases. In such a case, when the amount of cesium deposited on the plasma electrode 116 is increased, the temperature control unit 128 raises the temperature of the wall 108 e of the chamber 108. As a result, the cesium deposited on the wall portion 108 e can be released, and the cesium can be supplied to the plasma electrode 116, so that the cesium can be easily deposited on the plasma electrode 116. Thus, by adjusting the temperature of the wall 108 e of the chamber 108 by the temperature adjusting unit 128, the amount of cesium deposited on the plasma electrode 116 can be indirectly adjusted to an appropriate amount. In addition, since cesium can be circulated between the wall 108 e of the chamber 108 and the plasma electrode 116, the utilization efficiency of cesium can be enhanced and the amount of cesium supplied from the cesium supply source 118 can be reduced. Furthermore, the ability to release the cesium deposited on the wall 108 e of the chamber 108 can reduce the frequency of maintenance of the chamber 108.

  The increase and decrease of the current value measured by the current measurement unit 132 and the increase and decrease of the amount of cesium deposited on the plasma electrode 116 do not necessarily coincide with each other. For example, when the current value measured by the current measurement unit 132 decreases, the amount of cesium deposited on the plasma electrode 116 increases when the amount of cesium deposited on the plasma electrode 116 increases, and the amount of cesium deposited on the plasma electrode 116 The decreased current value may be increased by decreasing. Therefore, in actual control, the temperature control unit 130 first causes the temperature adjustment unit 128 to increase or decrease the temperature of the wall 108 e of the chamber 108, and confirms the tendency of the current value measured by the current measurement unit 132 to change. Do. After that, the temperature control unit 130 determines whether to increase or decrease the temperature of the wall 108 e to increase the decreased current value, and controls the temperature adjustment unit 128. In this control, even if the temperature of the wall 108 e is first raised temporarily, if the temperature of the wall 108 e is finally lowered, the temperature of the wall 108 e decreases. To be controlled. On the contrary, even when the temperature of the wall 108e is first lowered, if the temperature of the wall 108e is finally raised, the temperature of the wall 108e is controlled to rise. .

  The temperature control unit 130 can independently control each divided temperature adjustment unit 129 so that the temperature distribution of the wall 108 e of the chamber 108 becomes uniform. Here, with reference to FIG. 4 and FIG. 5, an example of operation | movement of the temperature control part 128 in said process is demonstrated. FIG. 4 is a view schematically showing the temperature distribution of the wall portion 108 e of the chamber 108 when the temperature control unit 128 does not perform temperature control. FIG. 5 is a view schematically showing the temperature distribution of the wall 108 e of the chamber 108 when the temperature control unit 128 performs temperature control.

  The plasma generating unit 112 disposed in the chamber 108 has a high temperature when generating a plasma. For this reason, as shown, for example in FIG. 4, the temperature distribution of the wall 108e of the chamber 108 varies. The temperature control unit 130 controls the divided temperature adjustment units 129 of the temperature adjustment unit 128 based on the temperature measured by the temperature sensor 128 c. For example, in a relatively high temperature portion, cooling is performed using the cooling pipe 128b, or the temperature of the wall portion 108e is reduced by reducing the output of the heater 128a. Further, in the relatively low temperature portion, the temperature of the wall portion 108 e is raised by increasing the output of the heater 128 a. Thereby, as shown in FIG. 5, the temperature distribution of the wall 108e of the chamber 108 can be made uniform. Therefore, localized deposition of cesium on the wall 108 e of the chamber 108 can be suppressed.

  The temperature control unit 130 may not control the divided temperature adjustment units 129 so that the temperature distribution of the wall 108 e of the chamber 108 is uniform. For example, when it is desired to deposit cesium on a specific portion of the wall 108 e, the temperature control unit 130 may control each division temperature adjustment unit 129 so as to intentionally form a low temperature portion.

  As described above, in the negative ion source device 100 according to the present embodiment, since the temperature control unit 128 is provided, it is possible to adjust the temperature of the wall 108 e of the chamber 108. Since the state of cesium supplied into the chamber 108 changes with temperature, adjusting the temperature of the wall 108 e of the chamber 108 allows the amount of cesium deposited on the wall 108 e of the chamber 108 and the plasma electrode 116 It is possible to control.

  The negative ion source device 100 further includes a current measurement unit 132 provided downstream of the plasma electrode 116 and measuring the current value of negative ions extracted by the plasma electrode 116. The temperature control unit 130 is a current measurement unit. The temperature control unit 128 is controlled based on the fluctuation of the current value measured at 132. Since the current value changes according to the amount of cesium deposited on the plasma electrode 116, the amount of cesium deposited on the plasma electrode 116 can be known by measuring the current value. Further, according to this configuration, since the temperature adjustment unit 128 is controlled based on the fluctuation of the current value, the amount of cesium deposited on the plasma electrode 116 can be indirectly adjusted to an appropriate amount. Therefore, it is possible to suppress a decrease in the amount of negative ions extracted from the negative ion source 102.

  In addition, the temperature control unit 130 reduces the amount of heating by the temperature adjustment unit 128 when the current value decreases. As a result, cesium is easily deposited on the wall 108 e of the chamber 108, so the amount of cesium deposited on the plasma electrode 116 can be reduced. Therefore, even if the amount of cesium deposited on the plasma electrode 116 exceeds an appropriate amount, the amount of cesium can be adjusted to an appropriate amount, and the amount of negative ions extracted from the negative ion source 102 is reduced It is possible to suppress

  Further, the temperature adjustment unit 128 is divided into a plurality of divided temperature adjustment units 129 along the extension direction of the chamber 108, and each divided temperature adjustment unit 129 can independently perform temperature adjustment. Since the plasma generating unit 112 that emits heat is provided on one end side of the chamber 108, the temperature distribution in the chamber 108 is likely to vary in the extension direction of the chamber 108. According to this configuration, the temperature distribution in the chamber 108 can be maintained more uniformly because each divided temperature control unit 129 can be adjusted independently. In addition, since any temperature distribution can be formed in the extension direction of the chamber 108, it is possible to deposit cesium on a specific location of the wall portion 108e of the chamber 108.

  Further, the cesium introducing unit (promoting substance supply unit) 114 is provided at the center of one end side of the chamber 108. As a result, a predetermined distance is maintained between the cesium introducing portion 114 and the side wall connecting the one end side and the other end side of the chamber 108, so the cesium supplied from the cesium introducing portion 114 adheres to the side wall of the chamber 108 Can be suppressed. Therefore, it is possible to further increase the utilization efficiency of cesium.

  As mentioned above, although embodiment of this invention was described, this invention can employ | adopt a various deformation | transformation aspect, without being limited to said embodiment. For example, in the above embodiment, although the negative ion source device 100 is used for a neutron capture and treatment device, it can be applied to an accelerator or a neutral beam injection device for fusion plasma heating.

  Moreover, in said embodiment, although the temperature control part 128 has both a heating part and a cooling part, you may have only any one. For example, in the above-described embodiment, the temperature adjustment unit 128 includes the heater 128 a as a heating unit, but the temperature adjustment unit 128 may not include the heater 128 a. In this case, the temperature of the wall 108 e of the chamber 108 can be adjusted by controlling the flow rate of the refrigerant flowing through the cooling pipe 128 b using heat generation in the plasma generation unit 112 instead of the heater 128 a.

  Alternatively, the temperature control unit may include a mechanism simultaneously provided with the functions of the heating unit and the cooling unit. For example, instead of the heater 128a, pipes may be provided as in the case of the cooling pipe 128b, and a mechanism capable of adjusting the temperature of the fluid to be supplied to each pipe may be provided to cause each pipe to function as a heating unit and a cooling unit. In this case, the temperature of the wall 108 e of the chamber 108 can be adjusted by controlling the temperature and flow rate of the fluid flowing through the piping.

  Moreover, the shape of the temperature control part 128 is not limited to said embodiment, It can change arbitrarily. For example, the heater 128 a and the cooling pipe 128 b may be disposed along the extension direction of the chamber 108 or may be disposed to spirally wrap around the chamber 108. Since the temperature distribution of the wall 108 e of the chamber 108 is likely to vary in the stretching direction, the heater 128 a and the cooling pipe 128 b extend along the circumferential direction of the chamber 108 in order to make the temperature distribution more uniform. It is preferable that it is arrange | positioned. Furthermore, the order in which the heater 128a, the cooling pipe 128b, and the temperature sensor 128c are disposed is not particularly limited, and can be arbitrarily changed. Also, the temperature sensor 128c may be omitted.

  In addition, the temperature control unit 128 may be provided in part of the region in the extension direction of the chamber 108 and the temperature control unit 128 may not be provided in the other part. Alternatively, only a heating portion may be provided in a part of the region in the extension direction of the chamber 108, and only a cooling portion may be provided in the other portion. In addition, in the region in the extension direction of the chamber 108, both the heating unit and the cooling unit may be provided in part, and only one of the cooling unit and the heating unit may be provided in the other part.

  The temperature adjustment unit 128 is divided into a plurality of divided temperature adjustment units 129, and each divided temperature adjustment unit 129 is preferably independently temperature-controllable, but is divided into a plurality of divided temperature adjustment units 129. It does not have to be. For example, in a configuration in which the piping is spirally wound along substantially the entire length in the extension direction of the chamber 108, and there is one inlet and one outlet for fluid and only the same fluid can flow, the temperature control unit 128 It does not correspond to an undivided, independently controllable configuration. Further, the configuration in which the pipe and the heater extend in the extension direction of the chamber also corresponds to a configuration in which the temperature control unit 128 is not divided.

  In the above embodiment, the temperature control unit 130 measures the negative ion beam measured by the current measurement unit 132 provided in the vacuum box 104 as “a value that changes according to the amount of the promoter deposited on the electrode”. The temperature control unit 128 is controlled based on the current value of the current control unit, but the temperature control unit 128 is controlled based on the current value of the charged particle beam R measured by the current monitor M provided in the middle of the beam duct 3. Good. Furthermore, the temperature control unit 130 may control the temperature adjustment unit 128 based on a change in the thickness of cesium deposited on the plasma electrode 116 or the emission spectrum of plasma instead of the current value.

DESCRIPTION OF SYMBOLS 1 ... neutron capture therapy apparatus, 2 ... accelerator, 3 ... beam duct, 4 ... 4 pole electromagnet, 5 ... scanning electromagnet, 6 ... target, 7 ... shield, 8 ... moderator, 9 ... collimator, 10 ... neutron dose measurement apparatus , 50: patient, 51: treatment table, 100: negative ion source device, 102: negative ion source, 104: vacuum box, 106: insulating flange, 108: chamber, 108a, main body portion, 108b, lid portion, 108c, 108d ... ridge portion 109 groove portion 110A first magnet 110B second magnet (negative ion generation portion) 112 plasma generation portion 114 cesium introduction portion (promoting substance supply portion) 116 plasma electrode (electrode 116a: through hole 116b: piping 118: cesium supply source 120: insulating flange 122: gas supply source (raw material gas supply unit) 124: electrode 128 Temperature adjustment unit 128a Heater 128b Cooling tube 128c Temperature sensor 129 Division temperature adjustment unit 130 Temperature control unit 132 Current measurement unit M Current monitor N Neutron beam R Charge Particle beam, S ... control unit.

Claims (5)

A hollow chamber in which negative ions are generated;
A source gas supply unit configured to supply a source gas serving as a source of the negative ions into the chamber;
A plasma generation unit provided on one end side of the chamber for generating plasma using the source gas supplied by the source gas supply unit;
A negative ion generation unit which guides electrons in the plasma to the other end side of the chamber and generates the negative ions from materials of the electrons and the negative ions;
An accelerator supply unit for supplying an accelerator into the chamber for promoting the formation of negative ions;
An electrode having a through hole provided on the other end side of the chamber and capable of extracting negative ions generated in the chamber to the outside of the chamber;
A temperature control unit for controlling the temperature of the wall of the chamber by performing at least one of heating and cooling;
A temperature control unit that controls the temperature adjustment unit;
The said temperature control part controls the said temperature control part based on the value which changes according to the quantity of the said promotion substance deposited on the said electrode, Negative ion source apparatus. And a current measuring unit provided downstream of the electrode and measuring a current value of negative ions extracted by the electrode,
The negative ion source device according to claim 1, wherein the temperature control unit controls the temperature adjustment unit based on a change in current value measured by the current measurement unit.   The negative ion source device according to claim 2, wherein the temperature control unit reduces the heating amount by the temperature adjustment unit when the current value decreases. The temperature control unit is divided into a plurality of divided temperature control units along the extension direction of the chamber,
The negative ion source device according to any one of claims 1 to 3, wherein each of the divided temperature control units is capable of temperature control independently.   The negative ion source device according to any one of claims 1 to 4, wherein the promoting substance supply unit is provided at a center of the one end side of the chamber.

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