JP7606682B2 - Charged Particle Transport Device - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. Website address: https://jps200908.award-con.com/ Website posting date: August 28, 2020 (Reiwa 2) Meeting name: The Physical Society of Japan, 2020 Fall Meeting (Physical Properties) Date held: September 8-11, 2020 (Reiwa 2) Website address: https://doi.org/10.1016/j.fusengdes.2021.112712 Website posting date: June 14, 2021 (Reiwa 3)

The present invention relates to a charged particle transport device.

In the field of accelerator applications, an accelerated beam is irradiated onto a target, and secondary charged particles generated by the reaction between the beam and the target are used. For example, various particles with positive or negative charges, such as muons, positrons, antiprotons, charged mesons, and unstable nuclei, are used. When using these, it is necessary to selectively and quickly transport the charged particles to be used from near the target, where a large number of various particles that cause noise are generated, to the usage location, which requires an environment with little unnecessary particles and radiation that cause background noise.

In addition, one of the major goals of chemistry is to clarify the processes of various chemical reactions, and reaction dynamics is a field that clarifies reactions at the atomic level. In reaction dynamics, in order to clarify reactions, it is essential to investigate the kinetic energy distribution of particles after a reaction, and to do so, it is necessary to quickly transport the particles after the reaction to a location where the kinetic energy distribution can be observed.

Conventionally, methods for transporting charged particles include the coaxial ion guide method (see, for example, Patent Document 1), in which AC and DC potentials are simultaneously applied to multiple coaxial ring electrodes to trap the charged particles in a ring shape, and the electrode potential is gradually switched to gradually move the ring-shaped trapping point to transport the particles. However, this method has the problem that it takes time to transport the trapped charged particles, making it impossible to observe short-lived particles.

To solve this problem, methods have been developed for quickly transporting particles after a reaction to an observation site, such as a method in which a current is passed through a solenoid coil wrapped around a tube, and the magnetic field generated by this transports the charged particles through the inside of the tube (see, for example, non-patent documents 1 to 3), a method in which a pulsed current is passed through a wire passing through the center of the tube, and the magnetic field generated by this transports the charged particles while converging them (see, for example, non-patent document 4), and a method in which the lens effect of an electric or magnetic field is used to image-transfer and transport the charged particles (see, for example, non-patent documents 5 and 6).

Methods have also been proposed for transporting charged particles using interactions between charged particles and matter. For example, there is a so-called ion guide method (see, for example, Non-Patent Document 7) in which a charged particle beam is injected into a gas, the gas is charged by ionization, and the electric potential distribution formed by the ionized gas acts on the charged particles to transport them along the beam axis. There is also a method in which a rod-shaped or wire-shaped insulator is charged by irradiating it with the charged particle beam to be transported, and the electric potential distribution formed by the charged insulator forms a central force electric field, so that the charged particles are transported by wrapping them around the insulator (see, for example, Non-Patent Document 8).

In addition, a Monte Carlo calculation code (PHITS) has been developed that uses nuclear reaction models and nuclear data to simulate various radiation behaviors in various materials (see, for example, non-patent document 9).

Special table 2016-516986 publication

Takuya Shimoyama, "Accumulation and transport of positrons for antihydrogen synthesis," Master's thesis, University of Tokyo, [online], March 2009, [Retrieved October 7, 2020], Internet〈URL: http://radphys4.c.u-tokyo.ac.jp/theses/master/Shimoyama-mthes.pdf〉 K. Nakahara, Y. Miyake, K. Shimomura, P. Strasser, K. Nishiyama, N. Kawamura, H. Fujimori, S. Makimura, A. Koda, K. Nagamine, T. Ogitsu, A. Yamamoto, T. Adachi, K. Sasaki, K. Tanaka, N. Kimura, Y. Makida, Y. Ajima, K. Ishida, and Y. Matsuda,“The super omega muon beamline at J-PARC,” Nuclear Instruments and Methods in Physics Research A, 2009, 600, p.132-134 Y. Makida, Y. Ikedo, T. Ogitsu, K. Shimomura, Y. Miyake, M. Yoshida, T. Adachi, R. Kadono, N. Kawamura, P. Strasser, A. Koda, H. Fujimori, K. Nishiyama, H. Ohhata, T. Okamura, R. Okada, and T. Orikasa, “Performance of a superconducting magnet system operated in the Super Omega Muon beam line at J-PARC”, [online], 17 February 2015, AIP Conf. Proc., 1573, 438, [Retrieved October 7, 2020], Internet〈URL: https://doi.org/ 10.1063/1.4860734〉 J. Hylen et al., “The Hadron Hose: Continuous Toroidal Focusing for Conventional Neutrino Beams”, Nucl. Instrum. Meth. A498, 2003, p.29-51, [Retrieved October 12, 2020], Internet〈URL: https://arxiv.org/abs/hep-ex/0210051〉 K. Shimomura, A. Koda, P. Strasser, N. Kawamura, H. Fujimori, S. Makimura, W. Higemoto, K. Nakahara, K. Ishida, K. Nishiyama, K. Nagamine, Y. Miyake, “Superconducting muon channel at J-PARC,” Nuclear Instruments and Methods in Physics Research A, 2009, 600, p.192-194 Mikhail Yavor, “Transporting Charged Particle Beams in Static Fields”, Advances in Imaging and Electron Physics, 2009, Volume 157, p.95-139 Ken Takayama, "II Introduction to Accelerator Physics", High Energy Accelerator Seminar OHO'92, [online], 1992, p24-26, [Retrieved October 7, 2020], Internet <URL: http://accwww2.kek.jp/oho/OHOtxt/OHO-1992/txt-1992-%E2%85%A1.pdf> D. S. Prono, G. J. Caporaso, A. G. Cole, R. J. Briggs, Y. P. Chong, J. C. Clark, R. E. Hester, E. J. Lauer, R. L. Spoerlein, and K. W. Struv, “Electron-Beam Guiding and Phase-Mix Damping by an Electrostatically Charged Wire”, [online], 29 August 1983, Phys. Rev. Lett. 51, 723, [Retrieved October 7, 2020], Internet〈URL: https://doi.org/10.1103/PhysRevLett.51.723〉 Tatsuhiko Sato, Yosuke Iwamoto, Shintaro Hashimoto, Tatsuhiko Ogawa, Takuya Furuta, Shin-ichiro Abe, Takeshi Kai, Pi-En Tsai, Norihiro Matsuda, Hiroshi Iwase, Nobuhiro Shigyo, Lembit Sihver and Koji Niita, “Features of Particle and Heavy Ion Transport code System (PHITS) version 3.02”, J. Nucl. Sci. Technol., 2018, 55(5-6), p.684-690

In the charged particle transport methods described in Non-Patent Documents 1 to 3, while the charged particles are being transported, it is necessary to continue to pass a current through a solenoid coil wound around a tube whose length corresponds to the distance to be transported, and heat is generated from the solenoid coil. For this reason, in cases where a solenoid coil must be placed in a vacuum or where an extremely low temperature target is used in the observation of charged particles, as described in Non-Patent Document 2, it is necessary to use an expensive superconducting coil or the like to suppress heat generation from the solenoid coil, or a large-scale cooling device to cool the solenoid coil, resulting in the problem of high equipment costs.

The method described in Non-Patent Document 4 also requires a large current of 1000 A to flow through the wire, which generates a lot of heat, resulting in high equipment costs for cooling. In addition, the methods using the lens effect of electric or magnetic fields described in Non-Patent Documents 5 and 6 have the problem that the focal length of each lens changes depending on the particle energy, narrowing the range of particle energies that can be effectively transported, resulting in poor transport efficiency.

In addition, the methods described in Non-Patent Documents 7 and 8 that use interactions between particles and materials require a considerable amount of beam to be irradiated in advance to ionize or charge gases, insulators, etc., and have the problem that charged particles cannot be transported when the current value is small. In addition, since the potential distribution for confining particles depends on the magnitude of the interaction with the material and the current value of the charged particles, there is a problem that the transport efficiency decreases when transporting charged particles with a variable current amount, such as transporting pulsed particles.

The present invention was made with a focus on these problems, and aims to provide a charged particle transport device that can reduce equipment costs and transport charged particles efficiently regardless of the amount of charged particles.

The inventors focused on the fact that in muon-catalyzed nuclear fusion reactions, in which muons, a type of elementary particle, aid in the nuclear fusion reaction of hydrogen isotope nuclei, muons that have once aided in a reaction are released once after nuclear fusion and then aid in another nuclear reaction again. While developing a device that uses a solid hydrogen target to observe post-nuclear reaction muons (regenerated muons) that are isotropically emitted from the target surface, they came up with the idea of a new transport device that is not only capable of transporting muons emitted from the target surface to observation equipment, but can also be applied to transport other charged particles, leading to the invention.

In other words, the charged particle transport device according to the present invention has an elongated inner conductor, an outer conductor that is spaced apart from the inner conductor, covers all or part of the side of the inner conductor, and is arranged to extend along the length of the inner conductor, and a potential difference applying means that is provided to be able to apply a potential difference between the inner conductor and the outer conductor, and is configured so that when the potential difference is applied by the potential difference applying means, a force toward the inner conductor is always applied to the charged particles in the space between the inner conductor and the outer conductor, allowing the charged particles to move along the length of the inner conductor while circling around the inner conductor.

The charged particle transport device according to the present invention can transport charged particles based on the following principle. That is, as shown in Fig. 1, the outer conductor is a long and thin tube, and the inner conductor is disposed inside the outer conductor, with a gap between them, coaxially with the outer conductor. In this case, the outer conductor covers the entire periphery of the side surface of the inner conductor. Here, the radius of the inner conductor is r _in and the radius of the outer conductor is r _ex , and a potential difference applying means applies a potential V _in to the inner conductor and a potential V _ex to the outer conductor. In this case, for simplicity of explanation, the potential V _in of the inner conductor is negative, and the outer conductor is grounded so that V _ex = 0 V.

In this case, if the distance from the central axis of the inner conductor is r, a log-shaped electrostatic potential distribution V _ES (r) along the radial direction r, as shown in equation (1), is formed in the space between the inner conductor and the outer conductor.

V _ES (r)=V _ex -(V _in -V _ex )×{log(r/r _ex )/log(r _ex /r _in )} (1)

The potential distribution for a charged particle having a positive charge q is the distribution of q·V _ES (r) shown in FIG. 2, and a central force toward the inner conductor is always applied to the charged particle.

Therefore, when a charged particle has a velocity component along the length of the inner conductor, the charged particle will move in a spiral trajectory, revolving around the inner conductor and moving at a constant speed along the length of the inner conductor, due to the balance with the centrifugal force. If the mass of the charged particle is m and the angular momentum is L, the centrifugal potential V _cf (r) of the orbital motion is expressed by equation (2), and the motion of the charged particle in the r direction is defined by the effective potential V _eff (r) shown in equation (3).

V _cf (r)＝(1/2)×(L ² /m)×1/r ² (2)

V _eff (r)＝q・V _ES (r)＋V _cf (r) (3)

FIG. 2 shows an example of the distribution of the centrifugal potential V _cf (r) in equation (2) and the effective potential V _eff (r) in equation (3).

As shown in Figure 2, the motion of a charged particle in the r direction reciprocates from a certain minimum radius to a certain maximum radius due to the effective potential V _eff (r), and the position is determined by the stored energy E of the charged particle in the r direction. In addition, when the stored energy E of the charged particle is greater than the minimum value of the effective potential V _eff (r), the minimum radius of the orbit is greater than the radius r _in of the inner conductor, and the maximum radius of the orbit is smaller than the radius r _in of the outer conductor, the charged particle is allowed to continue reciprocating in the r direction. Therefore, in a plane perpendicular to the inner conductor, the orbit of the charged particle becomes a cycloidal orbit that revolves around the inner conductor, as shown in Figure 3.

Thus, with the charged particle transport device of the present invention, the charged particles follow a spiral trajectory in which they move at a constant speed along the length of the inner conductor while orbiting around the inner conductor. Once the charged particles enter this trajectory, as shown in FIG. 2, they do not collide with the inner conductor or the outer conductor. Furthermore, since the motion of the charged particles along the length of the inner conductor is simply uniform motion, the charged particles can be transported indefinitely while remaining on the spiral trajectory.

Here, we have described the case where the inner conductor and the outer conductor are coaxial tubes, but as long as the same principle can be applied, they are not limited to coaxial tubes and may have other configurations. For example, the inner conductor and the outer conductor may be made of one or more conductors, and the cross section perpendicular to the length direction may be a circle, an ellipse, a triangle, a rectangle, a polygon, or a ring having any of these shapes. In addition, the inner conductor and the outer conductor may have unevenness on their surfaces.

In addition, here, the potential _Vin of the inner conductor is set to negative, and the potential _Vex of the outer conductor is set to the ground potential, but the potentials of the conductors may be set in any way as long as a potential difference is provided between the inner conductor and the outer conductor so that the charged particles can be transported. For example, to transport positive charged particles, the potential _Vin of the inner conductor is set to be lower than the potential _Vex of the outer conductor, and conversely, to transport negative charged particles, the potential _Vin of the inner conductor is set to be higher than the potential _Vex of the outer conductor, thereby applying a central force to the charged particles, and the charged particles can be transported according to the above principle.

In this way, the charged particle transport device of the present invention can transport charged particles simply by creating a potential difference between the inner conductor and the outer conductor. This requires less power than when current is passed through a coil or wire, and heat generation can be largely suppressed. This means that expensive superconducting coils and cooling devices are not required, even in special environments such as vacuum or extremely low temperatures, and equipment costs can be reduced.

The charged particle transport device according to the present invention can transport even large current charged particles by, for example, providing a potential difference between the inner conductor and the outer conductor that is sufficient to overcome the space charge generated by the charged particles and prevent the charged particles from colliding with the inner and outer conductors when the charged particles are injected into the space between the inner conductor and the outer conductor. In this way, the charged particle transport device according to the present invention does not require a beam to be irradiated in advance, and can efficiently transport charged particles regardless of the amount of charged particles, from small currents to large currents. In addition, since the potential difference between the inner conductor and the outer conductor can be instantly adjusted, even charged particles with a variable amount of current can be efficiently transported by adjusting the potential difference according to the type of charged particle.

The charged particle transport device according to the present invention can be used, for example, to transport charged particles such as muons generated using an accelerator or the like from the position where the charged particles are generated to the position where the charged particles are observed. A lot of noise that interferes with observation is also generated near the position where the charged particles are generated, but the charged particle transport device according to the present invention can transport the charged particles to a position away from the position where they are generated, thereby reducing noise during observation.

In the charged particle transport device according to the present invention, the inner conductor and the outer conductor may be partially curved along the length direction. In this case, it is preferable that a potential difference different from that of the straight portion can be applied between the inner conductor and the outer conductor of the curved portion in order to transport the desired charged particles along the curved portion. The curved portion may be provided so as to bend the extension direction of the inner conductor and the outer conductor at any angle, and may be provided along any curve or three-dimensional curvature. By providing the curved portion, the desired charged particles can be bent and transported along the curved portion. In addition, particles with higher energy than the charged particles cannot bend the curved portion and collide with the outer conductor, so that background noise can be reduced when observing the desired charged particles.

In the charged particle transport device according to the present invention, the inner conductor and/or the outer conductor may form a potential variable section in which a predetermined section along the length direction can be applied with a potential different from that of the other sections, and the potential difference applying means may be configured to apply a different potential difference between the section of the potential variable section and the other sections between the inner conductor and the outer conductor. In this case, by adjusting the potential of the potential variable section, a filter effect can be obtained that removes, reflects or passes the charged particles depending on the energy, angular momentum or a combination thereof possessed by the charged particles.

In addition, when the potential variable section is included, it is preferable that the potential difference applying means is configured to be capable of changing the potential difference in the section of the potential variable section. This can improve the controllability of the filter effect on the charged particles. Furthermore, the inner conductor and/or the outer conductor may have two or more potential variable sections spaced apart from each other along the length direction, and the potential difference applying means may be configured to be capable of applying a potential difference to the section of each potential variable section so that the charged particles can be confined between two of the potential variable sections. This makes it possible to trap charged particles in the section between two of the potential variable sections, or to emit the trapped charged particles as a pulse at any timing.

The charged particle transport device according to the present invention may have a magnetic field application means provided outside the outer conductor so as to be able to apply a magnetic field to the space between the inner conductor and the outer conductor. In this case too, by adjusting the magnetic field applied by the magnetic field application means, a filter effect can be obtained that removes, reflects, or passes the charged particles depending on the energy, angular momentum, or a combination thereof possessed by the charged particles. In addition, by using it in combination with a potential variable section, the controllability of the filter effect can be increased by the combination of a magnetic field and an electric field.

In this case, it is preferable that the magnetic field application means is configured to be capable of changing the magnetic field applied to the space. This allows for improved control of the filter effect on the charged particles. Furthermore, two or more of the magnetic field application means may be provided at intervals along the length of the outer conductor, and the magnetic field applied to the space by any two of the magnetic field application means may be configured to confine the charged particles in the space. This allows for the charged particles to be trapped in the space between the inner conductor and the outer conductor, and for the trapped charged particles to be emitted as a pulse at any timing.

The present invention provides a charged particle transport device that can reduce equipment costs and efficiently transport charged particles regardless of the amount of charged particles.

1 is a perspective view showing the principle of a charged particle transport device according to the present invention; 4 is a graph showing the principle of the charged particle transport device according to the present invention, illustrating the electric potential distribution and the effective potential distribution in a cross section perpendicular to the length direction of the inner conductor and the outer conductor. 1 is a cross-sectional view perpendicular to the length direction of an inner conductor and an outer conductor, showing the principle of a charged particle transport device according to the present invention, in which a trajectory of a charged particle is projected. 1 is a perspective view showing a charged particle transport device according to an embodiment of the present invention; 11 is a perspective view showing a modified example of the charged particle transport device according to the embodiment of the present invention, in which an external conductor has a potential variable portion. FIG. 1A and 1B are a longitudinal sectional view and a transverse sectional view showing a modified example of a charged particle transport device according to an embodiment of the present invention, in which an inner conductor and an outer conductor have potential variable portions. 1A and 1B are a longitudinal sectional view and a transverse sectional view showing a modified example of a charged particle transport device according to an embodiment of the present invention, the modified example having a magnetic field application means. 1A and 1B are a longitudinal sectional view and a transverse sectional view showing a modified example of the charged particle transport device according to the embodiment of the present invention, in which the inner conductor and the outer conductor each have two potential variable parts. 1A and 1B are a perspective view and a cross-sectional view, respectively, showing a modified example of a charged particle transport device according to an embodiment of the present invention in which a plurality of inner conductors are sandwiched between an outer conductor made of two parallel plates. 1 is a cross-sectional view showing an experimental apparatus for a muon catalyzed nuclear fusion experiment used in a simulation of a charged particle transport device according to an embodiment of the present invention. 1 is a perspective view showing a model of a charged particle transport device according to an embodiment of the present invention used in a simulation of a muon catalyzed nuclear fusion experiment. 1 is a side view showing a simulation result of a trajectory of a muon emitted from a solid hydrogen target arranged at one end of an outer conductor of a charged particle transport device according to an embodiment of the present invention. FIG. 12A and 12B are side views showing simulation results of a muon trajectory using the model shown in FIG. 11 in the charged particle transport device according to the embodiment of the present invention when (a) there is no thermal shield and (b) there is a thermal shield. 12 is a graph showing a change in arrival rate versus muon kinetic energy, obtained from a simulation result of a muon trajectory using the model shown in FIG. 11 in the charged particle transport device according to the embodiment of the present invention. 12A and 12B are side views showing the results of a simulation of a muon trajectory when a model of a charged particle transport device according to an embodiment of the present invention has curved portions in the middle of the inner conductor and outer conductor of the model shown in FIG. 11, in which (a) the same potential is applied to the straight portion and the inner conductor of the curved portion, and (b) a higher potential is applied to the inner conductor of the curved portion than to the inner conductor of the straight portion. 12A is a side view showing the results of a simulation of a muon trajectory using a model of a charged particle transport device according to an embodiment of the present invention having a potential variable part in the outer conductor of the model shown in FIG. 11 , and FIG. 12B is a graph showing the change in the arrival rate at each potential relative to the muon kinetic energy, for each potential difference (filter potential) between the outer conductor other than the potential variable part and the potential variable part. 12 is a graph showing the change in the arrival ratio at each potential of the solid hydrogen target with respect to the kinetic energy of muons when the potential of the solid hydrogen target is changed using the model shown in FIG. 11 of the charged particle transport device according to the embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings and examples.
4 to 17 show a charged particle transport device according to an embodiment of the present invention.
As shown in FIG. 4, the charged particle transport device 10 has an inner conductor 11 , an outer conductor 12 , and a potential difference applying means 13 .

The inner conductor 11 is elongated and has a circular cross section. The inner conductor 11 is made of, for example, copper wire. The outer conductor 12 is elongated and tubular, with an inner diameter larger than the outer diameter of the inner conductor 11, and is arranged so that the inner conductor 11 is inserted inside and extends along the length of the inner conductor 11. The outer conductor 12 is arranged coaxially with the inner conductor 11 with a gap between them. The outer conductor 12 covers the entire periphery of the side of the inner conductor 11.

The potential difference applying means 13 is provided so as to be capable of applying a potential difference between the inner conductor 11 and the outer conductor 12. This is configured so that a force (see the arrow in FIG. 4) toward the inner conductor 11 is always applied to the charged particle 1. That is, the potential difference applying means 13 is configured so as to make the potential of the inner conductor 11 lower than the potential of the outer conductor 12 when transporting a positive charged particle 1, and conversely, to make the potential of the inner conductor 11 higher than the potential of the outer conductor 12 when transporting a negative charged particle 1. In a specific example shown in FIG. 4, the potential difference applying means 13 is provided so as to ground the outer conductor 12 and to be capable of applying a potential V to the inner conductor 11.

The charged particle 1 may be any type of particle, ranging from elementary particles to macro-sized particles, such as electrons, positrons, protons, antiprotons, negative muons, positive muons, charged mesons, charged leptons, charged baryons, charged ions, charged molecules, charged aerosols, and charged microparticles. In addition, the space between the inner conductor 11 and the outer conductor 12 is preferably a vacuum.

The charged particle transport device 10 is configured such that when a potential difference is applied between the inner conductor 11 and the outer conductor 12 by the potential difference applying means 13, the charged particle 1 can move along the length of the inner conductor 11 while circling around the inner conductor 11 in the space between the inner conductor 11 and the outer conductor 12 based on the principle shown in Figures 1 to 3.

Next, the operation will be described.
The charged particle transport device 10 can move the charged particle 1 on a helical orbit 1a revolving around the inner conductor 11 at a constant speed along the length of the inner conductor 11. Therefore, once the charged particle 1 enters the helical orbit 1a, it can be transported indefinitely while remaining on the helical orbit 1a, without colliding with the inner conductor 11 or the outer conductor 12, as long as the inner conductor 11 and the outer conductor 12 continue.

The charged particle transport device 10 can transport the charged particles 1 simply by creating a potential difference between the inner conductor 11 and the outer conductor 12. This reduces the required power and almost completely suppresses heat generation compared to when current is passed through a coil or wire. This eliminates the need for expensive superconducting coils and cooling devices, even in special environments such as vacuum or extremely low temperatures, and reduces equipment costs. In addition, there is no need to irradiate the beam in advance, and the charged particles 1 can be transported efficiently regardless of the amount of charged particles 1, from small currents to large currents. In addition, since the potential difference between the inner conductor 11 and the outer conductor 12 can be adjusted instantly, even if the amount of current of the charged particles 1 changes, the charged particles 1 can be transported efficiently by adjusting the potential difference according to the type of charged particles 1.

In the charged particle transport device 10, the inner conductor 11 and the outer conductor 12 may be partially curved along the length direction. In this case, it is preferable that the radius of curvature of the curved portion is larger than the radius of the outer conductor 12. In addition, in order to transport the desired charged particle 1 along the curved portion, it is preferable that a potential difference different from that of the straight portion can be applied between the inner conductor 11 and the outer conductor 12 of the curved portion. In particular, it is preferable that the smaller the radius of curvature of the curved portion, the larger the potential difference. The curved portion may be provided so as to bend the extension direction of the inner conductor 11 and the outer conductor 12 at any angle, and may be provided along any curve or three-dimensional curvature. By providing the curved portion, the desired charged particle 1 can be bent and transported along the curved portion. In addition, particles with higher energy than the charged particle 1 cannot bend the curved portion and collide with the outer conductor 12, so that background noise when observing the desired charged particle 1 can be reduced. In this way, since a curved portion capable of transporting the charged particle 1 can be provided, the design freedom of the charged particle transport device 10 can be increased.

As shown in FIG. 5, in the charged particle transport device 10, the outer conductor 12 may have a predetermined section along the length that forms a potential variable section 21 that is provided so that a potential different from that of the other sections can be applied, and the potential difference applying means 13 may be configured to apply a different potential difference between the section of the potential variable section 21 and the other sections between the inner conductor 11 and the outer conductor 12. As shown in FIG. 6, the potential variable section 21 may be provided in a predetermined section of the inner conductor 11 and the outer conductor 12. In a specific example shown in FIG. 6, the inner conductor 11 has an outer tube 22a that is provided with an interval only in a predetermined section, and a rod-shaped insert 22b inserted inside the outer tube 22a, and is provided so that a different potential can be applied to the outer tube 22a and the insert 22b, and the predetermined section where the insert 22b is exposed forms the potential variable section 21. The potential variable section 21 may be provided only in the inner conductor 11.

In the case of having this potential variable section 21, for example, by reducing the potential difference in the section of the potential variable section 21, the force of attraction to the inner conductor 11 can be weakened, and the high-energy charged particle 1 can be caused to collide with the outer conductor 12 (see the dashed trajectory 1b in FIG. 5), and only the low-energy charged particle 1 can be selectively transported. In addition, by increasing the potential difference in the section of the potential variable section 21, the force of attraction to the inner conductor 11 can be strengthened, and the low-energy charged particle 1 can be caused to collide with the inner conductor 11, and only the high-energy charged particle 1 can be selectively transported. In addition, the charged particle 1 can be reflected by making the potential difference in the section of the potential variable section 21 a potential difference of the opposite sign to the potential difference in the other sections. In this way, by adjusting the potential of the potential variable section 21, a filter effect can be obtained that removes, reflects, or passes the charged particle 1 depending on the energy, angular momentum, or a combination thereof possessed by the charged particle 1.

7, the charged particle transport device 10 may have a magnetic field application means 23 provided outside the outer conductor 12 so as to apply a magnetic field to the space between the inner conductor 11 and the outer conductor 12. The magnetic field application means 23 may be, for example, a solenoid coil. In this case, by adjusting the magnetic field applied by the magnetic field application means 23, a filter effect can be obtained that removes, reflects, or passes the charged particle 1 according to the energy, angular momentum, or a combination thereof possessed by the charged particle 1. The magnetic field application means 23 may have a magnetic yoke arranged around the coil so that the magnetic field applied to the space between the inner conductor 11 and the outer conductor 12 becomes stronger. In addition, the magnetic field application means 23 may have a potential variable section 21 as shown in FIG. 5 and FIG. 6. In this case, the controllability of the filter effect can be improved by the combination of the magnetic field and the electric field. In a specific example shown in FIG. 7, the charged particle 1 is configured as a Wien filter in which the magnetic field and the electric field applied to the charged particle 1 are approximately orthogonal to each other. Therefore, a filter function according to the charge-to-mass ratio, which is the ratio of the charge to the mass of the charged particle 1, can be added.

Also, as shown in FIG. 8, in the charged particle transport device 10, the inner conductor 11 and the outer conductor 12 may have two or more potential variable sections 21 as shown in FIG. 6 spaced apart from each other along the length direction, and the potential difference applying means 13 may be configured to be capable of changing the potential difference in the section of each potential variable section 21 and to be capable of applying a potential difference to the section of each potential variable section 21 so as to confine the charged particle 1 between two of the potential variable sections 21. In a specific example shown in FIG. 8, there are two potential variable sections 21. Note that each potential variable section 21 may be provided only on the inner conductor 11 or only on the outer conductor 12.

8, for example, a charged particle 1 can be trapped in the section between the potential variable sections 21 (particle storage section 24) as follows. That is, first, one potential variable section 21 is set to a state in which the charged particle 1 passes, and the other potential variable section 21 is set to a state in which the charged particle 1 is reflected, and the charged particle 1 is made to enter the particle storage section 24 from one potential variable section 21. When the charged particle 1 is present in the particle storage section 24, the one potential variable section 21 is switched to a state in which the charged particle 1 is reflected, whereby the charged particle 1 can be trapped in the particle storage section 24. By trapping the charged particle 1, the presence of the charged particle 1 is localized, so that it is possible to measure the lifetime of the charged particle 1 by detecting the decay secondary particles emitted from the particle storage section 24, measure the spin and fine structure constant of the charged particle 1 by applying a magnetic field or microwaves to the particle storage section 24, cool the charged particle 1 by inserting a substance such as a thin film or gas into the particle storage section 24, and efficiently measure the repeated interaction between the inserted substance and the charged particle 1.

In addition, when the charged particle 1 is trapped in the particle storage section 24, any of the potential variable sections 21 can be switched to a state in which the charged particle 1 passes at any timing, thereby making it possible to emit the trapped charged particle 1 as a pulse at that timing. In addition, by controlling the potential setting of the potential variable section 21 that allows the charged particle 1 to pass at this time so that only a specific energy passes, it is also possible to select charged particles 1 of a specific energy from among the trapped charged particles 1 and extract them as a pulse. For this reason, in order to periodically emit pulses of the charged particle 1, the potential difference applying means 13 may be configured to be capable of periodically changing the potential difference in the section of any of the potential variable sections 21.

In addition, the charged particle transport device 10 may have two or more magnetic field application means 23 as shown in FIG. 7, instead of the potential variable section 21, spaced apart from each other along the length direction of the outer conductor 12. In this case, too, it is possible to trap the charged particles 1 and emit the trapped charged particles 1 as pulses at any timing. In order to emit pulses of the charged particles 1 periodically, the magnetic field of any of the magnetic field application means 23 may be configured to be periodically changeable.

As shown in FIG. 9, in the charged particle transport device 10, the inner conductors 11 may be multiple, rod-shaped or linear, and arranged parallel to each other, and the outer conductors 12 may be two parallel plates that extend along the length of each inner conductor 11 and are arranged to sandwich each inner conductor 11 at a distance from each inner conductor 11. Each outer conductor 12 covers one side of each inner conductor 11. In this case, as shown in FIG. 9(b), by applying a potential difference between the inner conductor 11 and the outer conductor 12 by the potential difference applying means 13, a potential distribution (see equipotential lines 2 in the figure) is formed in the space between the inner conductor 11 and the outer conductor 12 such that a force toward the inner conductor 11 is always applied to the charged particle 1, and the charged particle 1 can be transported along an orbit 1c that revolves around one inner conductor 11 or an orbit 1d that revolves across multiple inner conductors 11.

[About the simulation]
In the following, a simulation was performed using commercially available ion optical design software SIMION (manufactured by Scientific Instrument Services) for the charged particle 1 transported by the charged particle transport device 10. In the simulation, a muon catalyzed nuclear fusion experiment using a solid hydrogen target was assumed, and electrodes to which a voltage can be applied (inner conductor, outer conductor, solid hydrogen target) were arranged, an arbitrary voltage was set to form an electric field, and a muon (weight 0.11 au) was arranged as the charged particle 1 within the electric field, and the subsequent trajectory of the muon was obtained.

As shown in FIG. 10, an actual muon catalyzed nuclear fusion experiment is carried out as follows. That is, first, a rectangular plate-shaped solid hydrogen target 32 is placed inside a rectangular box-shaped thermal shield 31. Here, the surface of the solid hydrogen target 32 is coated with deuterium or tritium, deuterium or tritium is added, and it is cooled to an extremely low temperature. In addition, the charged particle transport device 10 shown in FIG. 4 is placed on the side of the solid hydrogen target 32 so as to extend in a direction parallel to the surface of the solid hydrogen target 32. At this time, the end of the outer conductor 12 of the charged particle transport device 10 on the side of the solid hydrogen target 32 is placed inside the thermal shield 31, and a circular metal foil 33 for muon detection is placed on the opposite end of the outer conductor 12. The metal foil 33 is made of titanium, is connected to the inner conductor 11, and is at the same potential as the inner conductor 11.

In the experiment, high-energy negative muon particles are bombarded by an accelerator into the back surface of the solid hydrogen target 32 from a direction perpendicular to the back surface. As a result, negative muon particles decelerated to about 10 keV are isotropically emitted from the surface of the solid hydrogen target 32 by the Ramsauer-Townsend effect, which is a low-temperature quantum effect, and the muon catalyzed nuclear fusion reaction. Of the emitted muon particles, some of those that enter the inside of the outer conductor 12 from the end on the side of the solid hydrogen target 32 are transported through the space between the inner conductor 11 and the outer conductor 12 to the opposite end, where they hit the metal foil 33 and are detected. In order to simulate this muon catalyzed nuclear fusion experiment, a model shown in FIG. 11 was created. In the model shown in FIG. 11, the outer diameter of the inner conductor 11 is 1 mm, the inner diameter of the outer conductor 12 is 56 mm, the radius of the metal foil 33 is 58 mm, and the length of the inner conductor 11 and the outer conductor 12 is about 1.1 m.

First, to confirm that the charged particle transport device 10 can transport the charged particle 1, a solid hydrogen target 32 was placed at one end of the outer conductor 12 perpendicular to the length direction of the inner conductor 11 and the outer conductor 12, and the trajectory of the muon emitted from its center was determined by simulation. In the simulation, a potential of +10 kV was applied to the solid hydrogen target 32 and the inner conductor 11, and the outer conductor 12 was set to ground potential (0 V).

The results of the simulation are shown in Figure 12. Figure 12 shows an example of the potential distribution formed by the solid hydrogen target 32, the inner conductor 11, and the outer conductor 12 (see equipotential lines 2 in the figure), as well as the orbits of 10-30 keV muons moving in response to it. As shown in Figure 12, it was confirmed that some of the muons emitted from the solid hydrogen target 32 entered an orbit that revolved in the space between the inner conductor 11 and the outer conductor 12, and were transported to the end opposite the solid hydrogen target 32. Orbit 1e in the figure is the orbit of a 10 keV negative muon emitted at an elevation angle of 15 degrees, and orbit 1f in the figure is the orbit of a 30 keV negative muon emitted at an elevation angle of 15 degrees.

In addition, muons, which are elementary particles, are unstable particles that decay with a lifetime of 2.2 microseconds, but can be transported a distance of several meters within that lifetime. In reality, many noise particles such as electrons, positrons, and photons with various energies are present near the solid hydrogen target 32 exposed to high-energy particles. In the charged particle transport device 10, negative muons are not lost due to factors other than their lifetime, but the noise particles become smaller in inverse proportion to the square of the distance, so that background noise can be significantly reduced by transporting them a few meters. For example, when the amount of photons (noise) due to the incidence of one muon was calculated using PHITS described in Non-Patent Document 9, it was 2.7×10 ⁻³ at a position where the transport distance by the charged particle transport device 10 was 400 mm, and 1.5×10 ⁻⁴ at a position where the transport distance was 1100 mm. In addition, by increasing the transport distance of the muons, the space for arranging shielding materials to shield the noise can be increased, so that noise can be further reduced. In this way, the charged particle transport device 10 can efficiently transport only particles having a specific energy, mainly consisting of negative muons, to a location away from the solid hydrogen target 32, making it possible to conduct experiments and observations using negative muons in an environment with little noise.

Using the model shown in FIG. 11, which assumes a muon-catalyzed nuclear fusion experiment, the trajectory of the muon emitted from the solid hydrogen target 32 was obtained by simulation. In the simulation, a potential of +10 kV was applied to the inner conductor 11, the solid hydrogen target 32 and the outer conductor 12 were set to ground potential (0 V), and other conditions were the same as in Example 1. The trajectories of the muons obtained by the simulation are shown in FIG. 13. FIG. 13(a) shows the trajectories when there is no thermal shield 31 to protect the solid hydrogen target 32, and FIG. 13(b) shows the trajectories when a more precise simulation was performed with the addition of a thermal shield 31 to protect the solid hydrogen target 32. As shown in FIGS. 13(a) and (b), it was confirmed that some of the muons emitted from the solid hydrogen target 32 entered the space between the inner conductor 11 and the outer conductor 12, drew a trajectory 1a that rotated in that space, and were transported to the metal foil 33 on the opposite side of the solid hydrogen target 32.

Using the model shown in FIG. 11, a simulation was performed for muons having any kinetic energy emitted from the solid hydrogen target 32, and the arrival rate of muons that reached the metal foil 33 by the charged particle transport device 10 was obtained. The simulation conditions were the same as in Example 2. In the simulation, the trajectories of 100,000 muons were obtained for each of multiple kinetic energies in the range of 0.25 to 30 keV, and it was confirmed how many of them reached the metal foil 33. Note that in the simulation, only muons that have a component that is directed in the opposite direction to the direction of the solid hydrogen target 32, that is, toward the charged particle transport device 10, were used. Here, the number of muons that reached the metal foil 33 obtained in the simulation was divided by the number of muons simulated (here, 100,000), and the arrival rate was determined (the same applies below).

The change in the arrival rate with respect to the kinetic energy of the muons is summarized and shown in Figure 14. As shown in Figure 14, in the range of 0.25 to 30 keV, it was confirmed that the arrival rate decreases as the kinetic energy of the muons increases. It was also confirmed that the arrival rate at this time was approximately 0.004 to approximately 0.15. When no potential difference is applied between the inner conductor 11 and the outer conductor 12, that is, when the inner conductor 11, the outer conductor 12, and the solid hydrogen target 32 are at 0 V, the arrival rate can be calculated using the solid angle corresponding to the surface area of the metal foil 33, and is approximately 0.002. From this, it can be said that the arrival rate is approximately 2 to 70 times higher with the charged particle transport device 10, and the transport efficiency of the charged particles is improved.

The trajectory of muons emitted from the solid hydrogen target 32 was obtained by simulation using a model having curved parts in the middle of the inner conductor 11 and the outer conductor 12 of the model shown in FIG. 11. In the model used, curved parts (curvature radius R = 144 mm) were inserted at the ends of the inner conductor 11 and the outer conductor 12 on the metal foil 33 side, where the inner conductor 11 and the outer conductor 12 were curved at a constant curvature so that the extension direction of each was bent by 90 degrees. In the simulation, the trajectory of muons was obtained for two cases: when a potential of +10 kV was applied to the inner conductor 11 of the straight part and the curved part, and when a potential of +10 kV was applied to the inner conductor 11 of the straight part and +30 kV was applied to the inner conductor 11 of the curved part. The kinetic energy of the muons was 10 keV. In both cases, the solid hydrogen target 32 and the outer conductor 12 were at ground potential (0 V), and other conditions were the same as in Example 2.

The trajectories of the muons obtained by simulation for each case are shown in Figures 15(a) and (b), respectively. When a potential of +10 kV was applied to the inner conductor 11 of the straight section 25a and the curved section 25b shown in Figure 15(a), it was confirmed that more muons were unable to bend at the curved section 25b and collided with the outer conductor 12, and fewer muons reached the metal foil 33, compared to when a potential of +10 kV was applied to the straight section 25a and +30 kV was applied to the curved section 25b shown in Figure 15(b).

For each simulation shown in FIG. 15, the arrival rate was calculated from the number of muons that reached the metal foil 33. In addition, a simulation was performed in which the radius of curvature of the curved portion 25b was halved (R = 72 mm), and a potential of +10 kV was applied to the inner conductor 11 of the straight portion 25a and +30 kV was applied to the inner conductor 11 of the curved portion 25b, and the arrival rate was calculated. For comparison, a simulation was also performed in which the curved portion 25b was not provided, and the arrival rate was calculated. The ratio of the arrival rate (relative arrival rate) for each case with the curved portion 25b was calculated, assuming that the arrival rate for the case without the curved portion 25b was 1, and the results are shown in Table 1. Note that the distance from the solid hydrogen target 32 to the metal foil 33 (the length of the inner conductor 11) was the same in all cases.

As shown in Table 1, even if the radius of curvature of the curved portion 25b is changed, the relative arrival rate hardly changes, and it was confirmed that within the range of the radius of curvature in this simulation, the radius of curvature does not have a significant effect on the arrival rate. In contrast, it was confirmed that when the potential of the inner conductor 11 of the curved portion 25b is increased above the potential of the straight portion 25a, that is, when the potential difference between the inner conductor 11 and the outer conductor 12 is made larger in the curved portion 25b than in the straight portion 25a, the relative arrival rate is significantly improved. This is thought to be because when the potential difference between the inner conductor 11 and the outer conductor 12 is made larger in the curved portion 25b, the force that attracts muons to the inner conductor 11 becomes stronger in the curved portion 25b, and the number of muons that cannot bend can be reduced.

When the curved portion 25b is provided, the solid hydrogen target 32 and the metal foil 33 have the advantage that they cannot be seen in a straight line. In other words, in addition to the required muons, the solid hydrogen target 32 also emits various high-energy particles and X-ray particles as secondary radiation, but charged particles 1 with higher energy than muons travel straight without bending at the curved portion 25b, and X-ray particles travel straight without bending in the electromagnetic field. For this reason, by providing the curved portion 25b, noise particles traveling straight can be shielded and only the required muons can be made to enter the metal foil 33, greatly reducing background noise during observation. In this way, when the curved portion 25b is provided, the arrival rate is lower than when the curved portion 25b is not provided, but the background noise can be reduced, so it is considered effective to insert the curved portion 25b when the decrease in the arrival rate is smaller than the decrease in the background noise.

As shown in Figure 5, a model having a potential variable section 21 capable of changing the potential in part of the outer conductor 12 of the model shown in Figure 11 was used to obtain the trajectory of muons emitted from the solid hydrogen target 32 by simulation. In the simulation, a potential of +10 kV was applied to the inner conductor 11, and the potential of the potential variable section 21 was changed in 1 kV increments from 0 kV to -10 kV. In addition, the solid hydrogen target 32 and the outer conductor 12 other than the potential variable section 21 were set to ground potential (0 V), and the other conditions were the same as in Example 2.

Figure 16(a) shows the trajectories of muons when the potential of the potential variable section 21 is 5 kV. Figure 16(b) shows the arrival rate for each potential difference (filter potential) between the outer conductor 11 other than the potential variable section 21 and the potential variable section 21 when the kinetic energy of the muon is set to 0.5 to 20 keV and the potential of the potential variable section 21 is changed. As shown in Figure 16(a), when a potential of the opposite sign to that of the inner conductor 11 is applied to the potential variable section 21, the force attracting the muon to the inner conductor 11 becomes stronger due to the formed potential distribution (see equipotential line 2 in the figure). Therefore, muons with high energy (see trajectory 1g) pass through the potential variable section 21, but muons with low energy (see trajectory 1h) collide with the inner conductor 11 or are reflected toward the solid hydrogen target 32, and are unable to pass through the potential variable section 21. As shown in FIG. 16(b), it was confirmed that the arrival rate changes depending on the potential of the potential variable section 21 and the energy of the muon, and in particular, the arrival rate of muons with low energy changes significantly depending on the potential of the potential variable section 21. From this, it is possible to obtain a filter effect that removes muons with low energy by adjusting the potential of the potential variable section 21. It is also believed that the kinetic energy distribution of muons can be obtained by performing observations while changing the potential of the potential variable section 21.

11, a simulation was performed by changing the potential of the solid hydrogen target 32 to obtain the arrival ratio. In the simulation, the potential (V _C ) of the inner conductor 11 was set to +10 kV, and the potential (V _T ) of the solid hydrogen target 32 was set to 0 kV, 1 kV, 5 kV, and 10 kV. The outer conductor 12 was set to ground potential (0 V), and the other conditions were the same as in Example 2.

The muon kinetic energy was set to 0.25 to 20 keV, and the arrival rate at each potential was determined when the potential of the solid hydrogen target 32 was changed, and is shown in Figure 17. As shown in Figure 17, it was confirmed that the arrival rate changes depending on the potential of the solid hydrogen target 32 and the muon energy, and in particular, the arrival rate of muons with low energy changes significantly depending on the potential of the solid hydrogen target 32. From this, it can be seen that by adjusting the potential of the solid hydrogen target 32, a filter effect that removes low-energy muons can be obtained. It is also believed that the kinetic energy distribution of muons can be obtained by performing observations while changing the potential of the solid hydrogen target 32.

1 Charged particle 1a (spiral) orbit 1b-1g orbit 2 Equipotential line

10: Charged particle transport device 11: Inner conductor 12: Outer conductor 13: Potential difference applying means

21 potential variable section 22a outer tube 22b insert 23 magnetic field application means 24 particle storage section 25a straight section 25b curved section

31 Thermal shield 32 Solid hydrogen target 33 Metal foil

Claims (8)

an inner conductor consisting of a single elongated conductor ;
an outer conductor arranged to cover all or a part of a side surface of the inner conductor with a gap between the outer conductor and the inner conductor and extend along a longitudinal direction of the inner conductor;
a potential difference applying means for applying a predetermined potential to the inner conductor and applying a potential difference between the inner conductor and the outer conductor;
A charged particle transport device characterized in that, when the potential difference is applied by the potential difference application means, a charged particle takes a helical trajectory in the space between the inner conductor and the outer conductor, moving along the length of the inner conductor while circling around the inner conductor, and a force toward the inner conductor is constantly applied to the charged particle so as to maintain the helical trajectory . the outer conductor is elongated and tubular;
2. The charged particle transport device according to claim 1, wherein the inner conductor is disposed inside the outer conductor and coaxially with the outer conductor. 3. The charged particle transport device according to claim 1 , wherein the inner conductor and the outer conductor have a cross section perpendicular to the longitudinal direction that is circular, elliptical, triangular, rectangular, polygonal, or annular having any of these outer shapes. The charged particle transport device according to any one of claims 1 to 3, characterized in that the inner conductor and the outer conductor are partially curved along their length. 5. The charged particle transport device according to claim 1, further comprising a magnetic field applying means provided outside the outer conductor so as to be able to apply a magnetic field to the space between the inner conductor and the outer conductor. an elongated inner conductor;
an outer conductor arranged to cover all or a part of a side surface of the inner conductor with a gap between the outer conductor and the inner conductor and extend along a longitudinal direction of the inner conductor;
a potential difference applying means provided so as to be able to apply a potential difference between the inner conductor and the outer conductor;
a magnetic field applying means provided outside the outer conductor so as to be capable of applying a magnetic field to a space between the inner conductor and the outer conductor;
When the potential difference is applied by the potential difference applying means, a force directed toward the inner conductor is constantly applied to the charged particles in the space between the inner conductor and the outer conductor, so that the charged particles can move along the length of the inner conductor while revolving around the inner conductor.
A charged particle transport device comprising: 7. The charged particle transport device according to claim 5 , wherein the magnetic field applying means is configured to be able to change the magnetic field applied to the space. The charged particle transport device according to claim 7, characterized in that the magnetic field application means is provided in two or more locations spaced apart from each other along the longitudinal direction of the outer conductor, and is configured to be able to confine the charged particles within the space by the magnetic field applied to the space by any two of the magnetic field application means.