JP7771018B2 - Accelerated particle generating device and accelerated particle generating method - Google Patents

Description

Embodiments of the present invention relate to an accelerated particle generating device and an accelerated particle generating method that apply a pulse voltage to accelerating parallel plate electrodes using an optical switch that turns on when light is incident on them to form an electric field and accelerate charged particles.

Conventional accelerators use electrostatic fields or radio frequency energy to form an accelerating electric field and accelerate charged particles. However, as the strength of the accelerating electric field is increased, discharge occurs according to an empirical rule known as Paschen's law in electrostatic fields and the Kilpatrick discharge limit in radio frequency energy. While it is possible to improve the discharge voltage by improving the degree of vacuum, surface treatment, and increasing the acceleration frequency, the realistic acceleration gradient is limited to approximately 1 MV/m for acceleration using electrostatic fields and approximately 40 MV/m for acceleration using radio frequency energy, and discharge may occur at gradients greater than this.

Furthermore, when accelerating particles with large masses, such as ions, it takes time for the particle velocity to approach the relativistic velocity β = 1. For this reason, when accelerating ions using radio-frequency energy, the acceleration efficiency decreases further as the acceleration phase must be adjusted to match the gradually changing particle velocity, resulting in an acceleration gradient of several hundred kV/m to several MV/m. As a result, the equipment must be huge, covering an area of several hundred square meters or more, which is an obstacle to the widespread use of accelerators.

U.S. Pat. No. 5,757,146 Special table 2013-504150 publication

As a means of avoiding the aforementioned decline in acceleration efficiency and achieving a high acceleration gradient, the Dielectric Wall Accelerator (DWA) has been proposed (Patent Document 1). This is a type of accelerator that uses pulse voltage (Patent Document 2), and generates an accelerating electric field between electrodes by propagating a pulse voltage generated by a switching element. Because it is easy to create multiple stages by stacking the acceleration electrodes, there is no need to apply a large voltage corresponding to the particle energy, as is the case with acceleration using an electrostatic field. Furthermore, by synchronizing the switching timing of the switching elements with the particle beam, it is possible to achieve an acceleration gradient of tens of MV/m or more, even for particles with large masses such as ions.

However, due to discrepancies in the propagation path length of the pulse voltage to the accelerating parallel plate electrodes or differences in the laser optical path length, the timing at which the particle beam passes through the accelerating parallel plate electrodes may be inappropriate, resulting in the particle beam not being accelerated properly. In other words, the timing at which the switching element is turned on may differ from the timing at which the particle beam passes through the accelerating parallel plate electrodes, resulting in the issue of not being able to accelerate the particles as designed.

Embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide an accelerated particle generation device and an accelerated particle generation method that enable a charged particle beam to efficiently acquire energy from the accelerating electric field generated between multiple accelerating parallel plate electrodes, thereby accelerating the charged particles as designed.

An accelerated particle generator according to an embodiment of the present invention includes a beam source that generates a beam of charged particles, multiple acceleration parallel plate electrodes through which the charged particle beam from the beam source passes and accelerates, multiple high-voltage power supplies that generate high voltages to apply voltages to each of the acceleration parallel plate electrodes, a light source that generates light, and multiple optical switches connected to the acceleration parallel plate electrodes and the high-voltage power supplies, respectively, that turn on when irradiated with light from the light source and apply voltage from the high-voltage power supplies as a pulse voltage to the acceleration parallel plate electrodes. The accelerated particle generator is characterized by including an optical path length adjustment mechanism that adjusts the optical path length of the optical path through which light passes between the multiple optical switches, thereby matching the timing of application of the pulse voltage to the acceleration parallel plate electrodes with the timing of the charged particle beam passing through the acceleration parallel plate electrodes.

An accelerated particle generation method according to an embodiment of the present invention provides an accelerated particle generation device having a beam source that generates a beam of charged particles, multiple acceleration parallel plate electrodes through which the charged particle beam from the beam source passes and accelerates, multiple high-voltage power supplies that generate high voltages to apply voltages to each of the acceleration parallel plate electrodes, a light source that generates light, and multiple optical switches connected to the acceleration parallel plate electrodes and the high-voltage power supplies, respectively, that turn on when irradiated with light from the light source and apply voltage from the high-voltage power supplies as a pulse voltage to the acceleration parallel plate electrodes, and adjusts the optical path length of the optical path through which light passes between the multiple optical switches to synchronize the timing of application of the pulse voltage to the acceleration parallel plate electrodes with the timing of the charged particle beam passing through the acceleration parallel plate electrodes.

According to an embodiment of the present invention, a charged particle beam can efficiently acquire energy from the accelerating electric field generated between multiple accelerating parallel plate electrodes, accelerating the charged particles as designed.

FIG. 1 is a configuration diagram showing an accelerated particle generation device according to a first embodiment. FIG. 2 is a perspective view showing the connection relationship around the accelerating parallel plate electrode shown in FIG. 1 . FIG. 10 is a configuration diagram showing an accelerated particle generation device according to a second embodiment. FIG. 4 is an electrical circuit diagram showing the circuit configuration of the voltage monitor of FIG. 3 . 5 is a graph showing the time distribution of a pulse voltage applied to an accelerating parallel plate electrode measured by the waveform measuring device of the voltage monitor of FIGS. 3 and 4 . 4 is a graph showing the time distribution of the pulse voltage applied to each accelerating parallel plate electrode measured by each voltage monitor of FIG. 3; 4 is a flowchart showing an optical path length adjustment procedure and a charged particle acceleration procedure executed by the control means of FIG. 3 .

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[A] First embodiment (FIGS. 1 and 2)
Fig. 1 is a configuration diagram showing an accelerated particle generator according to the first embodiment. The accelerated particle generator 10 shown in Fig. 1 is a photoconductive switching type accelerator using optical switches that are turned on by the incidence of light, and is configured to include a beam source 11, a plurality of acceleration parallel plate electrodes (e.g., acceleration parallel plate electrodes 12A and 12B), a plurality of high-voltage power supplies (e.g., high-voltage power supplies 13A and 13B), a ground electrode 14, a laser source 15 as a light source, a plurality of optical switches (e.g., optical switches 16A and 16B), an optical path length adjustment mechanism 17, and a beam energy measurement device 18.

Beam source 11 generates a beam of charged particles (charged particle beam P), such as protons, electrons, or ions. High-voltage power supply 13A generates a high voltage to apply a voltage (pulse voltage, described below) to acceleration parallel plate electrode 12A, and high-voltage power supply 13B generates a high voltage to apply a voltage (pulse voltage, described below) to acceleration parallel plate electrode 12B. Furthermore, laser source 15 generates a laser beam L as light.

Optical switches 16A and 16B are rapidly and instantaneously switched from OFF to ON when laser light L is incident from laser source 15. Optical switch 16A is electrically connected to high-voltage power supply 13A via high-voltage propagation path 19A and to accelerating parallel plate electrode 12A via switch voltage propagation path 20A. Optical switch 16B is electrically connected to high-voltage power supply 13B via high-voltage propagation path 19B and to accelerating parallel plate electrode 12B via switch voltage propagation path 20B.

When optical switch 16A is turned ON by the incidence of laser light L, it applies a pulse voltage, which is a pulse waveform of the high voltage from high-voltage power supply 13A, to acceleration parallel plate electrode 12A via switch voltage propagation path 20A. When optical switch 16B is turned ON by the incidence of laser light L, it applies a pulse voltage, which is a pulse waveform of the high voltage from high-voltage power supply 13B, to acceleration parallel plate electrode 12B via switch voltage propagation path 20B.

As shown in Figures 1 and 2, the acceleration parallel plate electrodes 12A, 12B and the ground electrode 14 allow the charged particle beam P from the beam source 11 to pass through and accelerate the beam. That is, when a pulse voltage is applied to the acceleration parallel plate electrode 12A by the high-voltage power supply 13A and the optical switch 16A, the acceleration parallel plate electrode 12A forms an acceleration electric field between itself and the acceleration parallel plate electrode 12B, accelerating the charged particle beam P flowing within this acceleration electric field. Then, when a pulse voltage is applied to the acceleration parallel plate electrode 12B by the high-voltage power supply 13B and the optical switch 16B, the acceleration parallel plate electrode 12B forms an acceleration electric field between itself and the ground electrode 14, further accelerating the charged particle beam P flowing within this acceleration electric field.

Here, the ground electrode 14 is an electrode installed downstream of the acceleration parallel plate electrodes 12A and 12B and has a zero potential. The beam energy measuring device 18 is installed downstream of the ground electrode 14 and measures the beam energy of the charged particle beam P accelerated by passing through the acceleration parallel plate electrodes 12A, 12B and the ground electrode 14. The beam energy E of this charged particle beam P is E = N x Q x V, where V is the voltage of the pulse voltage applied to the acceleration parallel plate electrodes 12A and 12B, N is the number of acceleration parallel plate electrodes (N = 2 in the first embodiment), and Q is the valence (charge) of the charged particle beam P.

The optical path length adjustment mechanism 17 comprises a fixed reflecting mirror 21 that reflects the laser beam L and is fixedly installed, and a movable reflecting mirror 22 that reflects the laser beam L. The laser beam L emitted from the laser source 15 passes through the optical switch 16A, turning this optical switch 16A on, and is then reflected sequentially by the fixed reflecting mirror 21 and the movable reflecting mirror 22, before passing through the optical switch 16B and turning this optical switch 16B on.

The optical path length adjustment mechanism 17 moves the movable reflecting mirror 22 to adjust the optical path length K of the laser optical path along which the laser L passes between the optical switches 16A and 16B. The optical path length K of the laser optical path between the optical switches 16A and 16B is adjusted so that K = CT, where T is the transit time of the charged particle beam P between the acceleration parallel plate electrodes 12A and 12B and C is the velocity of the laser L. This makes it possible to match the timing of application of the pulse voltage to the acceleration parallel plate electrodes 12A and 12B (particularly the acceleration parallel plate electrode 12B) with the timing of the charged particle beam P passing through the acceleration parallel plate electrodes 12A and 12B (particularly the acceleration parallel plate electrode 12B).

As configured as above, the first embodiment provides the following effect (1).
(1) The optical path length adjustment mechanism 17 adjusts the optical path length K of the laser light path through which the laser L passes between the optical switches 16A and 16B by moving the movable reflecting mirror 22, thereby matching the timing of applying a pulse voltage to the acceleration parallel plate electrodes 12A and 12B (particularly the acceleration parallel plate electrode 12B) with the timing of the charged particle beam P passing through the acceleration parallel plate electrodes 12A and 12B (particularly the acceleration parallel plate electrode 12B). Therefore, when the acceleration parallel plate electrodes 12A and 12B form an acceleration electric field to accelerate the charged particle beam P by each of the optical switches 16A and 16B sequentially applying a pulse voltage to the acceleration parallel plate electrodes 12A and 12B, the charged particle beam P can efficiently obtain energy from the acceleration electric fields formed between the acceleration parallel plate electrodes 12A and 12B and between the acceleration parallel plate electrode 12B and the ground electrode 14. As a result, the accelerated particle generator 10 equipped with the optical path length adjustment mechanism 17 can accelerate the charged particles as designed.

[B] Second embodiment (FIGS. 3 to 7)
3 is a block diagram showing an accelerated particle generation apparatus according to a second embodiment. In this second embodiment, parts similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the description thereof will be simplified or omitted.

The accelerated particle generator 25 of this second embodiment differs from the first embodiment in that it is configured by adding multiple voltage monitors (e.g., voltage monitors 26A and 26B) as voltage measurement means and a control means 27 that controls the optical path length adjustment mechanism 17, etc., to the accelerated particle generator 10 of the first embodiment.

Voltage monitor 26A is electrically connected to acceleration parallel plate electrode 12A via electrode voltage propagation path 28A and measures the pulse voltage applied to acceleration parallel plate electrode 12A when optical switch 16A is turned ON. Voltage monitor 26B is electrically connected to acceleration parallel plate electrode 12B via electrode voltage propagation path 28B and measures the pulse voltage applied to acceleration parallel plate electrode 12B when optical switch 16B is turned ON. As shown in Figure 4, these voltage monitors 26A and 26B are configured with a voltage divider circuit 29 as a voltage divider and a waveform measurement device 30; specifically, an EO probe (Electrical-Optical Probe) is preferred.

The voltage divider circuit 29 comprises multiple (e.g., two) capacitors 31 and 32 connected in series at the end of the electrode voltage propagation paths 28A and 28B that propagate the pulse voltage from the accelerating parallel plate electrodes 12A and 12B, and a load resistor 33 connected in parallel to these capacitors 31 and 32. The pulse voltage applied to the accelerating parallel plate electrodes 12A and 12B is divided by this voltage divider circuit 29. By connecting a waveform measuring device 30 between the capacitors 31 and 32 of the voltage divider circuit 29, the pulse voltage applied to the accelerating parallel plate electrodes 12A and 12B is divided by the voltage divider circuit 29, and the waveform is output to the waveform measuring device 30 for measurement.

Figure 5 shows the waveform (time distribution) of the pulse voltage applied to acceleration parallel plate electrodes 12A and 12B measured by waveform measurement device 30. Time distribution 34 of the pulse voltage applied to acceleration parallel plate electrodes 12A and 12B requires a certain rise time Sa to reach its maximum height and then drops after a certain time Sb. Next, time distribution 35A of the pulse voltage applied to acceleration parallel plate electrode 12A and time distribution 35B of the pulse voltage applied to acceleration parallel plate electrode 12B are shown in Figure 6. If the rise time in time distribution 35A of the pulse voltage applied to acceleration parallel plate electrode 12A is t1 and the rise time in time distribution 35B of the pulse voltage applied to acceleration parallel plate electrode 12B is t2, then the time difference Δt = |t1 - t2| between them depends on (is proportional to) the optical path length K of the laser optical path between optical switches 16A and 16B.

The control means 27 shown in FIG. 3 controls the operation (movement) of the movable reflector 22 of the optical path length adjustment mechanism 17 based on the measured values of the voltage monitors 26A and 26B (time distributions 35A and 35B of the pulse voltage applied to the accelerating parallel plate electrodes 12A and 12B by the optical switches 16A and 16B) and the transit time T for the charged particle beam P to pass between adjacent accelerating parallel plate electrodes 12A and 12B. Furthermore, this control means 27 controls the start and stop of the beam source 11, laser source 15, and high-voltage power supplies 13A and 13B. The control means 27 also receives input of the measured beam energy of the charged particle beam P from the beam energy measurement device 18.

Regarding the movement control of the movable reflecting mirror 22 described above, the control means 27 first obtains the transit time T of the charged particle beam P between the accelerating parallel plate electrodes 12A and 12B, which is determined in advance by simulation or the like, and compares this transit time T with the time difference Δt between the rise times t1 and t2 in the time distributions 35A and 35B of the pulse voltage applied to the accelerating parallel plate electrodes 12A and 12B. Next, when Δt > T, the control means 27 moves the movable reflecting mirror 22 so as to shorten the optical path length K of the laser optical path, and when Δt < T, moves the movable reflecting mirror 22 so as to lengthen the optical path length K of the laser optical path. The control means 27 repeatedly measures the pulse voltage using the voltage monitors 26A and 26B and controls the movement of the movable reflecting mirror 22 of the optical path length adjustment mechanism 17, moving the movable reflecting mirror 22 so that the difference between the time difference Δt and the transit time T is minimized (preferably so that the time difference Δt and the transit time T are the same).

Next, the procedure for adjusting the optical path length K of the laser optical path and the procedure for accelerating the charged particle beam P will be described mainly with reference to FIG.
First, parameters of each device, such as the voltage values of the high-voltage power supplies 13A and 13B and the output value of the laser source 15, are set, and the control means 27 acquires the transit time T for the charged particle beam P to pass between the accelerating parallel plate electrodes 12A and 12B, and sets the optical path length K of the laser optical path between the optical switches 16A and 16B (S1). Next, the control means 27 applies voltage to each of the optical switches 16A and 16B in the OFF state using the high-voltage power supplies 13A and 13B (S2).

Next, the control means 27 causes the laser source 15 to emit laser L (S3), applies a pulse voltage to the acceleration parallel plate electrode 12A using the optical switch 16A, and subsequently applies a pulse voltage to the acceleration parallel plate electrode 12B using the optical switch 16B. Next, the voltage monitor 26A measures the pulse voltage applied to the acceleration parallel plate electrode 12A and outputs it to the control means 27, and subsequently, the voltage monitor 26B measures the pulse voltage applied to the acceleration parallel plate electrode 12B and outputs it to the control means 27 (S4).

Next, the control means 27 determines whether the time difference Δt between the rise times t1 and t2 in the time distributions 35A and 35B, which are waveforms of the pulse voltages measured by the voltage monitors 26A and 26B, matches a set value (the transit time T for the charged particle beam P to pass between the accelerating parallel plate electrodes 12A and 12B) (S5). In step S5, if Δt > T, the control means 27 performs a calculation to shorten the optical path length K of the laser optical path, and if Δt < T, performs a calculation to lengthen the optical path length K (S6).

The control means 27 adjusts the optical path length K of the laser optical path by moving the movable reflecting mirror 22 of the optical path length adjustment mechanism 17 so that the optical path length K is the corrected optical path length K calculated in step S6 (S7). The control means 27 repeatedly executes steps S3 to S7, moving the movable reflecting mirror 22 of the optical path length adjustment mechanism 17 to adjust the optical path length K of the laser optical path so that the difference between Δt and T is minimized, and preferably so that Δt matches T.

Then, the control means 27 activates the beam source 11 (S8), causing the charged particle beam P to pass through the acceleration parallel plate electrodes 12A and 12B and the ground electrode 14, and sequentially accelerating the charged particle beam P by the acceleration electric field formed between the acceleration parallel plate electrode 12A and the acceleration parallel plate electrode 12B, and the acceleration electric field formed between the acceleration parallel plate electrode 12B and the ground electrode 14. The beam energy of the charged particle beam P accelerated by these acceleration electric fields is measured by the beam energy measuring device 18 (S9), and the measured value is output to the control means 27.

If the beam energy of the charged particle beam P measured by the beam energy measuring device 18 has increased by a predetermined value or more, the control means 27 completes the adjustment of the optical path length K of the laser optical path by the optical path length adjustment mechanism 17 (S10). If the increase in the beam energy of the charged particle beam P measured by the beam energy measuring device 18 is less than a predetermined value, the control means 27 suggests that consideration be given to whether other measures besides adjusting the optical path length K by the optical path length adjustment mechanism 17 are necessary.

As configured as above, the second embodiment provides the following effect (2).
(2) The optical switch 16A, 16B, which is turned on by the incidence of the laser beam L and applies a pulse voltage to each of the acceleration parallel plate electrodes 12A, 12B, is adjusted by the control means 27 by moving the movable reflecting mirror 22 of the optical path length adjusting mechanism 17 based on the measured value of the pulse voltage applied to the acceleration parallel plate electrodes 12A, 12B measured by the voltage monitors 26A, 26B, respectively (i.e., based on the time difference Δt between the rise times t1 and t2 in the measured time distributions 35A, 35B of the applied pulse voltage). This allows the application timing of the pulse voltage to the acceleration parallel plate electrodes 12A, 12B (particularly the acceleration parallel plate electrode 12B) to be matched with the passing timing of the charged particle beam P through the acceleration parallel plate electrodes 12A, 12B (particularly the acceleration parallel plate electrode 12B) with high precision. Therefore, the charged particle beam P passing through the accelerating parallel plate electrodes 12A, 12B and the ground electrode 14 can more efficiently obtain energy from the accelerating electric field formed by these electrodes 12A, 12B, 14. As a result, the accelerated particle generator 25 equipped with the optical path length adjustment mechanism 17 and the voltage monitors 26A and 26B can accurately accelerate the charged particle beam P as designed.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in a variety of other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, such substitutions, changes, and combinations are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims.

For example, the light emitted from the light source is not limited to the laser L from the laser source 15, but may also be light from an LED that is focused by an optical system.

10...accelerated particle generator, 11...beam source, 12A, 12B...accelerating parallel plate electrodes, 13A, 13B...high-voltage power supply, 15...laser source (light source), 16A, 16B...optical switch, 17...optical path length adjustment mechanism, 22...movable reflector, 25...accelerated particle generator, 26A, 26B...voltage monitor (voltage measurement means), 27...control means, 29...voltage divider circuit (voltage divider), 30...waveform measurement device, 31, 32...capacitor, 33...load resistance, K...optical path length, L...laser (light), P...charged particle beam

Claims (6)

a beam source for generating a beam of charged particles;
a plurality of parallel plate accelerating electrodes for passing and accelerating the charged particle beam from the beam source;
a plurality of high voltage power supplies that generate high voltages to apply voltages to the accelerating parallel plate electrodes;
a light source that generates light;
a plurality of optical switches connected to the accelerating parallel plate electrode and the high voltage power supply, respectively, and turned on when irradiated with light from the light source, and applying a voltage from the high voltage power supply to the accelerating parallel plate electrode as a pulse voltage,
An accelerated particle generating device characterized by being configured with an optical path length adjustment mechanism that adjusts the optical path length of the optical path through which light passes between the multiple optical switches, thereby matching the timing of applying a pulse voltage to the acceleration parallel plate electrodes with the timing of the charged particle beam passing through the acceleration parallel plate electrodes. a voltage measuring means for measuring a pulse voltage applied to the accelerating parallel plate electrodes;
2. The accelerated particle generating device according to claim 1, further comprising: a control means for controlling the operation of the optical path length adjustment mechanism based on the measurement value by the voltage measurement means and the time it takes for the charged particle beam to pass between the adjacent parallel plate electrodes of the accelerating electrode. The accelerated particle generator described in claim 1 or 2, characterized in that the optical path length adjustment mechanism is configured with a movable reflecting mirror that reflects light and is movable. The accelerated particle generating device described in claim 2, characterized in that the voltage measuring means is configured to include a voltage divider that divides the pulse voltage applied to the accelerating parallel plate electrodes, and a waveform measuring device that measures the waveform of the pulse voltage divided by this voltage divider. The accelerated particle generating device described in claim 4, characterized in that the voltage divider comprises a plurality of capacitors connected in series at the end of the propagation path for propagating the pulse voltage from the accelerating parallel plate electrodes, and a load resistor connected in parallel to these capacitors, and is configured so that the pulse voltage between the plurality of capacitors is output to a waveform measuring device. a beam source for generating a beam of charged particles;
a plurality of parallel plate accelerating electrodes for passing and accelerating the charged particle beam from the beam source;
a plurality of high voltage power supplies that generate high voltages to apply voltages to the accelerating parallel plate electrodes;
a light source that generates light;
a plurality of optical switches connected to the accelerating parallel plate electrode and the high-voltage power supply, respectively, and turned on when irradiated with light from the light source, and applying a voltage from the high-voltage power supply to the accelerating parallel plate electrode as a pulse voltage;
A method for generating accelerated particles, characterized by adjusting the optical path length of the optical path through which light passes between the plurality of optical switches, and matching the timing of applying a pulse voltage to the accelerating parallel plate electrodes with the timing of the charged particle beam passing through the accelerating parallel plate electrodes.