JP2018073680A - Accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accelerator capable of ensuring the uniformity of a voltage gradient in an accelerating tube even when a high-current ion beam is accelerated and thereby capable of maintaining an ion beam diameter, and a neutron generator including the accelerator.SOLUTION: An accelerator includes: a charged particle source; an accelerating tube which includes a plurality of electrodes and in which a charged particle emitted from the charged particle source is accelerated; and a voltage supply mechanism supplying a DC voltage to each of the electrodes. The voltage supply mechanism includes a plurality of stages of series resonant circuits connected in series therein, each of the series resonant circuits including an SiC-MOSFET. The output voltages of the plurality of stages of series resonant circuits are separately supplied to the respective electrodes.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an accelerator that obtains a charged particle beam by accelerating charged particles.

  For example, in order to obtain a neutron beam, an ion beam having a large current is extracted by an accelerator as shown in Patent Document 1 and irradiated to a beryllium target.

  As shown in FIG. 5, the accelerator 100A includes an ion source 1A and a cylindrical acceleration tube 2A in which an electric field for accelerating ions is formed. The acceleration tube 2A includes a plurality of electrodes 21A and insulators 2IA formed of a ring-shaped conductor, which are alternately arranged in the axial direction. The voltage supply mechanism 3E applies each electrode 21A to the acceleration tube 2A. A predetermined voltage is applied to each.

  In order to accelerate the ion beam so that it does not collide with the inner wall surface in the acceleration tube 2A, the voltage gradient from the base end side in contact with the ion source 1A of the acceleration tube 2A to the tip side where the ion beam is emitted is constant. It is necessary to form an electric field so that For this reason, as shown in FIG. 5, the voltage supply mechanism 3E uses a cockcroft power supply 3A and a voltage applied by the cockcroft power supply 3A to generate a high voltage for the electrode 21A at the tip of the acceleration tube 2A. And a voltage dividing circuit 3B for voltage division.

  For example, as shown in FIGS. 5 and 6, the voltage dividing circuit 3B includes a plurality of voltage dividing resistors connected between the electrodes.

Japanese Patent Laying-Open No. 2015-53187

  However, if a voltage is applied to each electrode 21A by the voltage dividing circuit 3B as described above, it is difficult to reduce the impedance of the electrode 21A portion. Therefore, if the beam current has a large current value exceeding several milliamperes, the voltage The uniformity of the gradient may be lost. Then, it becomes difficult to maintain a predetermined ion beam diameter.

  However, in order to reduce the impedance, an intermediate output terminal IT for outputting an intermediate voltage other than the rated output extraction terminal RT is provided from the cockcroft power supply 3A as shown in FIG. 7 without using the voltage dividing circuit 3B. If different voltages are applied to the electrodes, the step-up rectification operation of the cockcroft power supply 3A itself becomes unstable and adversely affects the operation of the accelerator 100A itself.

  For this reason, conventionally, a different voltage must be applied to each electrode 21A of the accelerating tube, and a voltage dividing circuit 3B, which is extra hardware, has to be used to realize a uniform voltage gradient.

  The present invention has been made in view of the above-described problems. An accelerator capable of ensuring the uniformity of the voltage gradient in the acceleration tube and maintaining the ion beam diameter even when accelerating a large current ion beam, and the accelerator An object of the present invention is to provide a neutron generating apparatus using a neutron.

  That is, the accelerator according to the present invention includes a charged particle source and a plurality of electrodes, and supplies a DC voltage to each of the acceleration tube and the plurality of electrodes in which charged particles emitted from the charged particle source are accelerated. A supply mechanism, wherein the voltage supply mechanism is configured by connecting a plurality of series resonant circuits including SiC-MOSFETs in series, and an output voltage of the plurality of series resonant circuits is applied to the plurality of electrodes. It is characterized by being supplied separately.

  If this is the case, the voltage that can be boosted by one series resonant circuit by applying a SiC-MOSFET having a high element breakdown voltage can be made larger than that of a conventional product using a Si-MOSFET, and the cockcroft circuit can be reduced in number of series. Compared to the above, the DC high voltage required for the accelerator can be obtained at a much lower manufacturing cost. Further, the voltage that can be applied for each stage of the series resonant circuit can be changed in proportion, and there is no need to provide a voltage dividing circuit using a voltage dividing resistor as in the prior art. For this reason, an appropriate voltage can be supplied to each electrode of the accelerating tube with a small impedance, and even if a high-current charged particle beam is extracted by realizing a uniform voltage gradient in the accelerating tube, the inner surface of the accelerating tube is charged. Particles can be prevented from colliding and a desired beam diameter can be secured.

  In order to be able to apply an appropriate voltage to each electrode according to the electric field to be formed and the characteristics of the accelerating tube, the output voltage of the series resonance circuit at any stage is configured to be supplied to any one of the electrodes. It only has to be.

  For example, in order to realize boosting at each stage with a simple circuit configuration, the series resonant circuit includes a half bridge circuit composed of two SiC-MOSFETs, a series drive circuit including the resonant circuit, and the series drive circuit. What is necessary is just to be provided with the connected power transmission coil, the power reception coil which receives electric power from the said power transmission coil, and the rectifier circuit connected to the said power reception coil.

  In order to increase the boost amount per stage and reduce the number of stages where the series resonant circuits are connected in series, the rectifier circuit may be a boost type rectifier circuit such as a cockcroft circuit.

  As described above, according to the accelerator according to the present invention, a voltage proportional to the number of stages can be output by a series resonant circuit connected in series in a plurality of stages, and it is not necessary to use a voltage dividing resistor. A desired voltage can be applied. Therefore, even when a charged particle beam with a large current is drawn out, a uniform voltage gradient can be realized in the accelerating tube, and collision of charged particles on the inner surface of the accelerating tube can be eliminated, and a desired beam diameter can be obtained.

The schematic diagram which shows the accelerator which concerns on 1st Embodiment of this invention. The circuit block diagram which shows the series resonance circuit connected in multiple steps of series of 1st Embodiment. The schematic diagram shown about the detail of the series resonance circuit of 1st Embodiment. The circuit block diagram which shows the series resonance circuit connected in multiple stages of the accelerator which concerns on 2nd Embodiment of this invention. The schematic diagram which shows the conventional accelerator. The circuit diagram which shows an example of the voltage dividing circuit used for the conventional accelerator. The circuit diagram which shows the cockcroft circuit which provided the terminal which outputs a voltage in the middle.

  The accelerator 100 according to the first embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the accelerator 100 applies different voltages to the ion source 1 that is a charged particle source, the acceleration tube 2 whose base end is connected to the ion source 1, and each part of the acceleration tube 2. And a voltage supply mechanism 3 to be used.

  The ion source 1 emits an ion beam made of positively charged particles. This ion source 1 is grounded.

  The acceleration tube 2 has a cylindrical shape as shown in FIG. 1, and the conductor portions and the insulator portions 2I constituting the electrodes 2F, 21, 22, 23, 24, 25, 26, 2R are alternately in the axial direction. It is provided side by side. Each of the conductor portion and the insulator portion 2I has a ring shape. A negative voltage is applied to the conductor portion, and the ion beam extracted from the ion source 1 is accelerated in the acceleration tube 2 and emitted from the tip.

  The electrodes 2F, 21, 22, 23, 24, 25, 26, 2R are arranged at equal intervals along the axial direction, and the proximal electrode 2R and the distal electrode 2F are the central electrode 21. 22, 22, 23, 24, 25, and 26, the outer shape is formed larger. In the following description, the proximal electrode 2F is also referred to as a proximal flange, and the distal electrode 2R is also referred to as a distal flange. For each of the electrodes 2F, 21, 22, 23, 24, 25, 26, 2R, a lower voltage is applied with a constant gradient from the proximal end side toward the distal end side.

  As shown in FIGS. 1 and 2, the voltage supply mechanism 3 is a negative DC voltage applied to each electrode 2F, 21, 22, 23, 24, 25, 26, 2R of the acceleration tube 2 from a commercial AC power source. Are respectively generated and applied. The voltage supply mechanism 3 includes a plurality of series resonance circuits 4, and each series resonance circuit 4 is connected in series in a plurality of stages. Each series resonant circuit 4 is connected to a three-phase full-wave rectifier circuit 45 that converts an AC voltage supplied from a commercial AC power source into a DC voltage.

  The series resonance circuit 4 is a so-called insulation type DC-DC converter, and includes a half bridge circuit 4A composed of two SiC-MOSFETs 46 and a resonance circuit 4B composed of a capacitor and a coil as shown in FIG. A drive circuit 41, a power transmission coil 42 connected to the series drive circuit 41, a power reception coil 44 that receives power from the power transmission coil 42, and a rectifier circuit 45 connected to the power reception coil 44. . As shown in FIG. 2, a common insulator 43 is disposed between each power receiving coil 44 and each power transmitting coil 42, and its thickness dimension is 30 mm. The SiC-MOSFET 46 can increase the device withstand voltage compared to the Si-MOSFET, and drives the power transmission coil 42 at a high voltage of about 800 Vp-p. The output of the first stage series resonance circuit 4 connected to the proximal flange of the accelerating tube 2 is grounded to the ground potential (± 0 V), and the voltage is lowered by 2 kV for each stage. In the first embodiment, since the 140-stage series resonance circuit 4 is connected in series, −280 kV is applied from the last-stage series resonance circuit 4 connected to the tip flange of the acceleration tube 2. Further, the electrodes 21, 22, 23, 24, 25, and 26 at the center of the acceleration tube 2 are −40 kV, −80 kV, −120 kV, −160 kV, −200 kV, −240 kV from the proximal end side to the distal end side. Is applied.

  According to the accelerator 100 of the first embodiment configured as described above, the series resonant circuit 4 including the SiC-MOSFET 46 is provided in a plurality of stages connected in series, thereby being proportional to the number of stages of the series resonant circuit 4. Different DC voltages can be output. Moreover, since the element breakdown voltage of the SiC-MOSFET 46 is large and the power transmission coil 42 can be driven at a high voltage of about 800 Vp-p, the high voltage from the rectifier circuit 45 can be achieved without increasing the turns ratio of the power transmission coil 42 and the power reception coil 44 so much. The voltage can be taken out.

  Accordingly, since the dielectric strength between the power receiving coil 44 and the power transmitting coil 42 can be increased, a DC high voltage of several hundred kV to several MV is generated as the output of the series resonance circuit 4 at the final stage without using a cockcroft circuit. be able to.

  Furthermore, even if a voltage is output from the rectifier circuit 45 in the series resonant circuit 4 at an arbitrary stage between the first stage and the final stage, the voltage output from the series resonant circuit 4 at the final stage is not more than a specified current. Is not unstable. Further, unlike the prior art, it is not necessary to provide a voltage dividing circuit for supplying a high voltage first and dividing the voltage into the electrodes 2F, 21, 22, 23, 24, 25, 26, 2R.

  For these reasons, even when a high-current ion beam is accelerated in the acceleration tube 2, the voltage gradient in the acceleration tube 2 is kept uniform, ions that collide with the inner wall surface are eliminated, and a desired beam diameter is secured. Can do.

  Next, an accelerator 100 according to a second embodiment of the present invention will be described with reference to FIG. Note that members corresponding to those described in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 4, the accelerator 100 according to the second embodiment differs from the accelerator 100 according to the first embodiment in the configuration of the rectifier circuit 45 and the number of stages of the series resonant circuit 4. More specifically, a cock loft circuit is used as the rectifier circuit 45, and the boosting amount per stage is larger than that in the first embodiment, and the voltage is lowered by 10 kV per stage. . For this reason, 28 stages of series resonant circuits 4 are connected in series so that -280 kV is obtained as the output of the series resonant circuit 4 at the final stage. The output of each series resonance circuit 4 is configured to supply a voltage to the outside via the rated voltage extraction terminal of the cockcroft circuit.

  With such an accelerator 100 according to the second embodiment, a high voltage similar to that of the first embodiment can be obtained while reducing the number of stages of the series resonant circuit 4.

  Further, since the voltage is output from the rated voltage extraction terminal of the cockcroft circuit, the output voltage at the final stage does not become unstable.

  Further, the accelerator 100 according to the second embodiment does not require the use of a voltage dividing circuit as in the first embodiment, and thus can provide a so-called large beam loading while maintaining a uniform acceleration electric field gradient.

  Other embodiments will be described.

  The charged particle source is not limited to an ion source from which positive ions are ejected, and may be an ion source from which negative ions are ejected.

  The external output of each DC resonance circuit may be performed only from a part of the DC resonance circuits as shown in each embodiment, or a voltage may be supplied to the outside from all the DC resonance circuits. Further, the electrodes of the acceleration tube are not limited to those provided at equal intervals. The arrangement of the electrodes may be determined according to the electric field formed in the acceleration tube, and the voltage corresponding to each electrode may be supplied from the voltage supply mechanism.

  In addition, various modifications and combinations of the embodiments may be made without departing from the spirit of the present invention.

100 ... Accelerator 1 ... Ion source (charged particle source)
2 ... Accelerating tube 3 ... Voltage supply mechanism 4 ... Series resonance circuit

Claims (4)

A charged particle source;
An accelerating tube comprising a plurality of electrodes and for accelerating charged particles emitted from the charged particle source;
A voltage supply mechanism for supplying a DC voltage to each of the plurality of electrodes,
The voltage supply mechanism is configured by connecting a series resonant circuit including a SiC-MOSFET in a plurality of stages in series,
An accelerator, wherein output voltages of a plurality of stages of series resonance circuits are separately supplied to the plurality of electrodes.   The accelerator according to claim 1, wherein an output voltage of a series resonance circuit of an arbitrary stage is configured to be supplied to one of the electrodes. The series resonant circuit is
A half-bridge circuit composed of two SiC-MOSFETs, and a series drive circuit including a resonance circuit;
A power transmission coil connected to the series drive circuit;
A power receiving coil for receiving power from the power transmitting coil;
The accelerator of Claim 1 or 2 provided with the rectifier circuit connected to the said receiving coil.   The accelerator according to claim 3, wherein the rectifier circuit is a cockcroft circuit.