JP5682903B2 - Air-core type cyclotron - Google Patents

Description

  The present invention relates to a cyclotron that accelerates charged particles, and more particularly to an air-core type cyclotron that uses an air-core coil.

  As a cyclotron capable of accelerating protons to 250 to 300 MeV (mega electron volt), one described in Patent Document 1 below is known. In this cyclotron, the mass of charged particles approaching the speed of light increases in proportion to the Lorentz factor due to the relativistic effect. An isochronous magnetic field is created that is an increased magnetic field (with a positive gradient outward).

  In addition, in this cyclotron, in the isochronous magnetic field that is stronger toward the outer side, if acceleration is performed as it is, acceleration particles diverge in the direction perpendicular to the acceleration plane, and acceleration particles collide with the device and acceleration cannot be continued. Are provided with a plurality of ferromagnetic pole pieces (pole tips) for changing the magnetic field strength in the circumferential direction (the direction of particle rotation) and causing the acceleration particles to obtain a convergence force in the vertical direction. Each pole tip is formed in a fan shape that is spirally curved so as to have an incident angle (spiral angle) with the accelerating particles in order to obtain a stronger convergence force, and is equidistant from each other in the circumferential direction of the acceleration plane. It is arranged to strengthen the magnetic field in the part with the ball chip (hill), weaken the magnetic field in the part without the ball (valley), and focus the accelerating particles in the vertical direction (and in the horizontal direction). A cyclotron that creates such a magnetic field that is strong and weak in the direction of rotation (azimuth angle direction) is called an AVF (Azimuthally Varying Field) cyclotron.

Japanese Patent No. 3456139

In such a cyclotron, a normal conducting iron core coil is used to create an isochronous magnetic field, and the average magnetic field on the orbit can only be increased to a maximum of about 1.6 T (Tesla). Further, since a ferromagnetic material is used as the ball chip, there is a limit to the energy of charged particles that can be converged. Therefore, in such a cyclotron, the protons are only accelerated to 250 to 300 MeV, and heavy particle beams (such as carbon hexavalent positive ions ¹² C ⁶⁺⁾ that have recently been remarkably useful in the irradiation treatment of cancer. (Radiation) cannot be sufficiently accelerated to a state having energy of about 400 MeV / nucleon (accelerated to about 70% of the speed of light) that can be used for cancer treatment.

  Currently, the five-year survival rate of all cancers (malignant tumors) in Japan has exceeded 50% (percent), but it remains the top intractable disease of Japanese people. According to "Cancer Statistics '07" (Cancer Research Promotion Foundation), about 1 in 2 men and 1 in 3 women will be diagnosed with cancer in their lifetime. About 1 in 4 men and 1 in 6 women die of cancer. With the progress of an aging society, the number of cancer patients is still on the rise, and is expected to exceed 5 million in 2015 (approximately double in about 10 years from 2003).

  Also, if cancer patients who were treated in outpatient or hospitalization were not required for treatment, they would not be paid (medical expenses), and if a person who died of cancer had lived to the average life expectancy There is a trial calculation that the amount of money (loss profit) that should have been obtained from the above is about 3 trillion yen in medical expenses and about 7 trillion yen in lost profits. Therefore, it can be said that society's loss due to cancer is about 10 trillion yen per year (about 2% of Japan's gross domestic product). On the other hand, it is needless to say that cancer countermeasures are important from the viewpoint of reducing social costs because cancers that can be cured are increasing due to improvements in screening techniques and treatment techniques.

  Cancer treatment can be broadly divided into surgery, internal medicine, and radiation therapy, but radiation therapy that irradiates the affected area with radiation is relatively low in cost, and is becoming a major part of cancer treatment in Europe and the United States as well as in Japan. . High-energy X-rays mainly using electron beam linac are used as external therapeutic radiation, but in recent years, proton beams and heavy particle beams such as carbon beams can perform more effective treatment. It is attracting attention as.

  Comparing the characteristics of proton beams and carbon beams, the killing effect of proton cells on cancer cells is equivalent to that of conventional X-rays, but it is superior because the dose distribution is sharper than X-rays and irradiation can be concentrated on the affected area. . On the other hand, the dose distribution of carbon rays is sharper than that of proton rays, and treatment with precise dose distribution is possible while avoiding normal tissues and important organs, and the cell lethal effect is about three times that of proton rays. Therefore, it can be applied to cancer with higher radiation resistance. In addition, cancer cells grow rapidly, and the central part of the cancer tissue that has grown to some extent becomes deficient in oxygen due to decreased blood flow, so the effects of X-rays and proton beams on such hypoxic cells are insufficient. However, the effect of heavy particle beams has been recognized.

  Therefore, heavy ion beam radiation therapy is effective for the treatment of sites that are difficult to perform surgery or excision (liver, hilar region, skull base, eyeball, AVM, etc.), and has become an extremely low-invasive treatment method. According to the past results, therapeutic effects can be expected for about 60% of solid cancers. In addition, due to the concentration of dose distribution and good cell killing effect, the number of times of irradiation is reduced to reduce the physical burden and cost burden of the patient, and due to the low invasiveness, the hospitalization period and hospitalization period are reduced. The quality of life of patients (Quality Of Life, QOL) can be improved.

  Thus, as a device capable of emitting heavy particle beams useful for cancer treatment, the current cyclotron cannot be used, and a synchrotron is being adopted. However, the synchrotron has a very large scale for sufficiently accelerating heavy particles (for example, about 1000 coils are arranged and controlled along a circle having a diameter of about 50 m (meter)), and the installation cost is enormous. However, the operating cost is expected to increase due to the cooling of a large number of coils, the complexity of control, the increase in the number of operators, the great power consumption, and the like.

  At such a scale, even though it is useful for cancer treatment, it will not gain momentum, so it is desirable to reduce the size of heavy particle accelerators and reduce running costs. It is conceivable to construct a heavy particle accelerator by expanding the scale of the cyclotron as in Patent Document 1 as few as few. However, the formation of the magnetic field by the iron core and the normal conducting coil is limited to about 1.6 T, in which iron magnetic saturation does not occur. Based on this assumption, when designing a cyclotron capable of accelerating heavy particle beams up to 400 MeV / nucleon In order to form an isochronous magnetic field, a magnet (47 thousand tons) having a pole face (magnetic pole surface) with a diameter of at least about 13 m is required, and even if actually created, it takes time to stabilize the magnetic field. In addition, a large amount of heat is generated and a huge cooling device is required. In addition, due to the increased energy of the accelerating particles, the pole tip for convergence must be installed in a huge and complicated shape. Therefore, a cyclotron with such a large scale eventually becomes extremely complex and large, although not as much as a synchrotron.

Accordingly, the invention according to claim 1 is a circumferential direction in which the heavy particles can be stably accelerated until they have energy that can be used for cancer treatment or the like while being small in size and low in installation cost and operation cost. It is an object of the present invention to provide an air-core type cyclotron that can efficiently form a high magnetic field having high and low strength .
The inventions of claims 2 and 3 can be stably accelerated until the heavy particles have energy that can be used for cancer treatment, etc., while being small in size and low in installation cost and operation cost. It is an object of the present invention to provide an air-core type cyclotron with further improved strength and durability.

In order to achieve the above object, the invention according to claim 1 is directed to a pair of main coil units that are opposed to each other in the axial direction and that form an isochronous magnetic field in the radial direction, and are opposed to each other in the circumferential direction. Each of the spiral sector coil units includes three or more spiral sector coils, and each of the spiral sector coils includes an oxide superconducting conductor. Is an air-core coil wound along a curved sector, and is arranged so as to be rotationally symmetric with each other, and the sector in each spiral sector coil has a tangent on the side intersecting the circumferential direction, in which spiral angle is an angle in the radial direction passing through the contact point of the tangent line is characterized in that it is formed to be less than 90 degrees

In order to achieve the above object, the invention according to claim 2 is directed to a pair of main coil units that are opposed to each other in the axial direction and that form an isochronous magnetic field in the radial direction, and are opposed to each other in the circumferential direction. Each of the spiral sector coil units includes three or more spiral sector coils, and each of the spiral sector coils includes an oxide superconducting conductor. Is an air-core coil wound along a curved sector, and is arranged so as to be rotationally symmetric with each other, and each of the spiral sector coils has an outer shape obtained by smoothly connecting a plurality of curvature radius curves. It is characterized by being formed by winding an oxide superconducting conductor around a jig .

To achieve the above object, an invention according to claim 3, in the above invention, each of the spiral sector coils, in which the bending radius being formed to be a predetermined value or more is there.

According to a fourth aspect of the present invention, in order to achieve the object of efficiently forming a strong isochronous magnetic field in addition to the above object, in the above invention, the main coil unit comprises an oxide superconducting conductor in a ring shape. An air core main split coil wound around is arranged in a plurality of axial directions.

In order to achieve the object of efficiently forming a stronger magnetic field by suppressing the amount of coil wire used, in addition to the above object, the invention described in claim 5 is the above invention. Thus, the inner diameter of the main split coil farther from the main split coil is smaller than the outer diameter of the main split coil close to another main coil unit.

In addition to the above-described object, the invention described in claim 6 is directed to the above-described invention, in order to achieve the object of forming a high magnetic field or magnetic field distribution capable of accelerating heavy particles at high speed with a more efficient sharpness. The pair of spiral sector coil units and / or the pair of main coil units are arranged mirror-symmetrically with each other.

In order to achieve the object of forming a strong magnetic field while being easy to operate, compact and energy saving, in addition to the above object, the invention according to claim 7 is the above invention, wherein the oxide superconductor is a bismuth-based material. It is an oxide superconductor or RE-123 series oxide superconductor (REBa ₂ Cu ₃ O _7-δ , RE is a rare earth element containing yttrium).

  According to the present invention, a plurality of air-core spiral sector coils in which an oxide superconducting conductor is wound so as to follow a spirally curved fan shape are arranged so as to be rotationally symmetric with each other. Facing each other. Therefore, a compact isochronous high magnetic field and magnetic field distribution that can accelerate to energy that can be used for cancer treatment etc. for heavy particles while being small and low in installation cost and operation cost. The cyclotron that can be formed can be provided.

It is a perspective explanatory view of the coil system in the air core type cyclotron of the present invention. It is a plane explanatory view of the coil system of FIG. It is a partial end surface explanatory drawing of the main coil unit in FIG. It is a graph which shows the magnetic field etc. which are formed by the main coil unit of FIG. It is a plane explanatory view of the spiral sector coil in FIG. (A) is a schematic side view of Hill Valley, (b) is a schematic plan view showing the trajectories of charged particles in the radial sector type, and (c) is a motion of charged particles across the edge of Hill Valley. It is a schematic diagram which shows a state. (A) is a schematic side view showing an integration path, (b) is a schematic plan view of a spiral sector type hill valley, and (c) is a partially enlarged view showing the trajectory of charged particles in (b). It is a plane schematic diagram. It is a graph which shows the relationship between the spiral angle of the spiral sector coil of FIG. 5, and a radial direction position. 2 is a drawing-substituting photograph showing a magnetic field strength distribution on an acceleration plane formed by the coil system of FIG. 1. 1 shows (a) a circumferential intensity distribution in a circular orbit of each radius, (b) a radial intensity distribution, and (c) a radial flutter distribution of the magnetic field on the acceleration plane formed by the coil system of FIG. It is a graph.

  Hereinafter, an example of an embodiment according to the present invention will be described with reference to the drawings as appropriate. In addition, the said form is not limited to the following example.

≪Overall structure≫
FIG. 1 is a perspective view of a coil system 1 of an air core type cyclotron (hereinafter referred to as “cyclotron”) of the present invention, and FIG. 2 is a plan view of the coil system 1. The cyclotron has a coil system 1 inside a cover (not shown), an ion source (not shown) that generates charged particles and makes it enter the vicinity of the center of the coil system 1, and an illustration that is arranged outside the coil system 1. In synchronism with a predetermined cycle of rotation (rotation frequency) of the charged particles, a cooling device (not shown) that cools the coil system 1 to a predetermined temperature, a vacuum pump (not shown) that evacuates the inside of the cover, An acceleration electrode (not shown) that applies an impulse magnetic field for acceleration, a control device (not shown) that controls these, and a power supply device (power source) (not shown) that supplies power to these electrodes are included. In addition, you may further provide the magnetic body for a shield which reduces the magnetic field intensity to the exterior.

  The coil system 1 includes a pair of main coil units 2 and 2 and a pair of spiral sector coil units 4 and 4 which are accommodated therein. The main coil units 2 are arranged vertically (in the axial direction) so as to face each other in a mirror symmetry, and the spiral sector coil units 4 are also arranged vertically in a state facing each other in a mirror symmetry. The centers of the main coil units 2 to the spiral sector coil units 4 are arranged on the same vertical line.

≪Main coil unit≫
Each main coil unit 2 includes a main split coil 21, a first correction split coil 22, and a second correction split coil 23 each having a perforated disk shape (ring shape). The main split coil 21, the first correction split coil 22, and the second correction split coil 23 are arranged so that their centers are located on the same vertical line.

  3 is a partial end view of the main coil unit 2. The Y axis is a vertical line passing through the centers of the main split coil 21, the first correction split coil 22, and the second correction split coil 23, and the X axis is the main axis. It is a symmetrical centerline of the coil unit 2. The main split coil 21 has a rectangular cross section of 0.149135 m in length and 0.390949 m in width, and is arranged in parallel with the Y axis so that the lower surface is 0.065000 m above the Y axis. The inner diameter (radius) of the main split coil 21 is 1.094110 m.

  The main split coil 21 is formed by winding a superconducting wire made of a superconducting conductor in a circular shape (air core) so as to fill the cross section in a state where the center is located on the Y axis, and further winding the superconducting wire in a ring shape. It is formed by covering with a shield (not shown). The main split coil 21 is electrically connected to the power source. A cooling medium (not shown) is sealed in the shield or connected to the cooling apparatus, and the cooling apparatus can cool the cooling medium to 20 K (Kelvin) and send it to the shield. It has become.

  The main split coil 21 has a cross section with a larger area than the first correction split coil 22 and the second correction split coil 23. The main split coil 21 has an aspect ratio (aspect ratio) of: Horizontal = 1: 2 and over 1: 3. The main split coil 21 has a larger outer diameter and inner diameter than the first correction split coil 22 and the second correction split coil 23.

  In addition, the width of the superconducting wire is about 1 cm (centimeter), the thickness is 200 μm (micrometer) including the substrate and stabilized copper, and the space factor including the insulating coating on the surface of the superconducting wire is 0. The load factor is about 0.7.

  Further, the material of the superconducting wire may be metal (nickel titanium, niobium tin, etc., superconducting state at 4.2K), oxide (bismuth, thallium, mercury, RE-Ba-Cu-O, etc.), 77K. The superconducting state can be used at 20K, and the superconducting state with good characteristics can be used. However, since the critical temperature is high and the superconducting state is high at a relatively high temperature, and the critical magnetic field is high, the oxide superconducting conductor can be used. It is preferable to use, among oxide superconducting conductors, although the manufacturing cost is relatively high, but it is mechanically resistant to magnetic fields and heat resistant and corrosion resistant nickel-based alloys (Hastelloy, registered trademark, the same shall apply hereinafter) etc. are used as wire constituent materials. It is more preferable to use an oxide superconducting conductor that has good strength and whose main component can be represented by RE-Ba-Cu-O.

A specific example of the former bismuth-based oxide superconducting wire is Bi2223 (Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10-δ ) manufactured by Sumitomo Electric Industries, Ltd. The bismuth-based oxide superconducting wire is preferably a bismuth-based 2223-phase oxide superconducting conductor containing Bi2223 (in addition to (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _10-δ ) or a bismuth-based 2223 phase oxide. superconducting conductor _{((Bi, Pb) 2 Sr} 2 Ca 1 Cu 2 O 8-δ, Bi 2 Sr 2 Ca 1 Cu 2 O 8-δ) is used.

On the other hand, specific examples of the latter RE-Ba-Cu-O-based oxide superconducting wire include YBCO (YBa ₂ Cu ₃ O _7-δ ) manufactured by American Superconductor Corporation (AMSC). In this embodiment, YBCO is used.

Here, in the oxide superconducting conductor whose main component can be represented by RE-Ba-Cu-O, RE is at least one of rare earth elements such as Y (yttrium), Sm (samarium), Gd (gadolinium), and Ho (holmium). Or any combination of two or more, Ba is barium, Cu is copper, and O is oxygen. Preferably, the oxide superconductor is an yttrium oxide superconductor having RE of Y, more preferably a Y-123 oxide such as YBa ₂ Cu ₃ O _7-δ , or YBa ₂ Cu. _It is assumed that all or part of Y in ₃ O _7-δ is replaced with another rare earth metal (RE-123 oxide superconductor).

  The oxide superconducting conductor is formed on a substrate (wire constituent material) having crystal orientation on the surface. The substrate is preferably Cu (copper), Ni (nickel), Ti (titanium), Mo (molybdenum), Nb (niobium), Ta (tantalum), W (tungsten), Mn (manganese), Fe (iron) , Ag (silver), or a metal layer made of an alloy thereof, or more preferably, a metal layer made of stainless steel, Inconel, or Hastelloy.

Furthermore, an intermediate layer made of a metal oxide is preferably arranged between the oxide superconductor and the substrate. The intermediate layer has a pyrochlore structure, a rare earth-C structure, a perovskite structure, or a fluorite structure. For example, BaZrO ₃ (Zr is zirconium), Y ₂ O ₃ , MgO (Mg is magnesium), SrTiO ₃ (SrTiO ₃ ). Is strontium, Ti is titanium), YSZ (yttria stable zirconia), or Ln-MO-based compounds such as Gd ₂ Zr ₂ O ₇ (Ln is one or more lanthanoid elements, M is Sr · Zr · Ga (gallium) ) One or more elements selected from the group of The intermediate layer is formed by a sputtering method, an electron beam evaporation method, or the like, but is preferably formed by an IBAD method (Ion Beam Assisted Deposition).

  The main split coil 21 is arranged 0.130000 m away from the mirror-symmetric main split coil 21.

  On the other hand, the first correction split coil 22 and the second correction split coil 23 are formed and designed in the same manner as the main split coil 21 except for the dimensions and arrangement.

  The first correction split coil 22 has an inner diameter of 1.0086602 m, a width (width of the cross section) of 0.084736 m, and a thickness (length of the cross section) of 0.069711 m, and is in a state (horizontal) along the main split coil 21. The first correction split coil 22 at a symmetrical position is arranged with an interval of 0.330000 m (0.165000 m away from the X axis). Therefore, the first correction split coil 22 is arranged in a state of being aligned with the main split coil 21 and the main split coil 21 in its axial direction, and the inner diameter or outer diameter thereof is made smaller than the outer diameter of the main split coil 21. It is located inside the outer diameter of the main split coil 21 (as viewed in the radial direction and radial direction of the coil).

  The second correction split coil 23 has an inner diameter of 0.387893 m, a width of 0.516684 m, and a thickness of 0.011931 m, and is 0.330002 m with respect to the second correction split coil 23 at the symmetrical position in a state along the main split coil 21. They are arranged at intervals (0.0165001 m away from the Y axis). Accordingly, the inner diameter or outer diameter of the second correction split coil 23 is smaller than the outer diameter of the main split coil 21 or the first correction split coil 22, and the outer diameter of the main split coil 21 or the first correction split coil 22 is smaller. It is arranged more inside.

  In the upper main coil unit 2, the lower surface of the first correction split coil 22 having an inner diameter or an outer diameter larger than the outer diameter is disposed below the lower surface of the second correction split coil 23. The lower surface of the main split coil 21 having an outer diameter larger than the inner diameter or the outer diameter is disposed below the lower surface of the main coil 22, and the main split coil 21 and the first correction split coil are viewed as the upper main coil unit 2 as a whole. 22, The bottom surface of the second correction split coil 23 has a mountain shape that rises upward. The same applies to the upper surface of the lower main coil unit 2.

  Further, an isochronous magnetic field for particle acceleration is formed in a portion sandwiched between the main coil units 2 and 2 that are symmetrical to each other. In the cyclotron having the coil unit 1, the central plane between the main coil units 2 and 2 (a plane perpendicular to the paper surface including the X axis in FIG. 3) is an acceleration plane for charged particles. In this cyclotron, the center plane between the spiral sector coil units 4 and 4 and the acceleration plane also coincide.

  The main split coil 21, the first correction split coil 22, and the second correction split coil 23 are electrically connected to the common power source via a switch (not shown), respectively. A voltage is applied by the power source to be excited, and an isochronous magnetic field is generated together with other exciting coils. The energization currents of the main split coil 21, the first correction split coil 22, and the second correction split coil 23 are 420A (ampere), 398A, and 432A in this order (the operation current may be less than these energization currents). The horizontal plane including the Y axis is the center in the vertical direction of the isochronous magnetic field.

  The computer as the control device of the cyclotron operates the cooling device when forming the isochronous magnetic field, and the cooling medium is a temperature at which the main split coil 21, the first correction split coil 22, and the second correction split coil 23 are in a superconducting state. Cool by conduction cooling to (20K) to stabilize the temperature of the cooling medium. Then, a voltage is gradually applied, and a current is passed through the main split coil 21, the first correction split coil 22, and the second correction split coil 23 until the above-described energization current is reached. When the above-described energizing current is generated and the current is stabilized by the superconducting state, the application of voltage is stopped, and a transition is made to a steady state in which an isochronous magnetic field is formed in which charged particles are accelerated in a spiral orbit.

≪Magnetic field formed by main coil unit≫
FIG. 4 shows the magnetic field generated by the main coil units 2 and 2. The generated magnetic field (DESIGN) of the main coil units 2 and 2 has less error (ERROR) than the ideal magnetic field (TARGET) capable of accelerating the carbon hexavalent positive ions ¹² C ⁶⁺ to 400 MeV / nucleon at a constant rotational frequency. It is in a state (maximum of about 0.1T).

Regarding an ideal magnetic field, generally, the magnetic field and the orbital radius of a particle are given by the following [Equation 1]. Where Bρ is the magnetic rigidity [Tm], p is the (relativistic) momentum [MeV / c], Z is the number of charges (here 6), and E is the kinetic energy (here 400). [MeV / u], E ₀ is the static energy (931) [MeV / u], and A is the mass number (here 12).

≪Spiral sector coil unit≫
Each spiral sector coil unit 4 includes a plurality of spiral sector coils 41. Each spiral sector coil 41 is an air-core coil wound so as to follow a curved sector shape, and is formed of an oxide superconducting wire like the main split coil 21 and covered with a shield (not shown) so as to be cooled. It is connected to the power supply so that it can be energized. The spiral sector coils 41 are arranged so as to be rotationally symmetric with respect to each other so that the convex side due to the curvature is the positive side in the clockwise direction, and are arranged at equal intervals in the circumferential direction. For each spiral sector coil 41, the convex side may be arranged on the negative side in the clockwise direction.

  FIG. 5 shows details of the spiral sector coil 41. Each spiral sector coil 41 has a width of 5 cm and a thickness of 5 cm throughout. 5 is a circle with a radius of 1060 mm (millimeters), and the two-dot chain line is a circle with a radius of 1100 mm.

  Further, each of the spiral sector coils 41 has a bending radius of a predetermined value (here, 3 cm) in view of mechanical characteristics that the oxide superconducting wire may be broken if it is bent excessively and may interfere with the superconducting characteristics. ) Designed to be above. Specifically, the oxide superconducting wire is wound so as to fill a winding space formed by a combination of a block and an arc-shaped block having a bending radius of a predetermined value or more. More specifically, three arc-shaped blocks (inside Arc-1 arranged on the outside and Arc-2, Arc-3 arranged on the outside, and a continuum of straight blocks connected so as to bend gradually at an angle from Arc-1 to Arc-2 (Brick-OUT-1 to Brick-OUT-19), a straight block (Brick-OUT-20) connecting Arc-2 and Arc-3, and an angle from Arc-1 to Arc-3. A winding space is formed from a set of straight blocks (Brick-IN-1 to Brick-IN-16) connected so as to bend gradually. Here, the continuous body of the straight block and the connection body of the arc-shaped block imitate the external shape in which a plurality of curvature radius curves are smoothly connected, and each spiral sector coil 41 has such an external shape. It is formed by winding an oxide superconducting wire around a jig (not shown).

  Further, each spiral sector coil 41 has a boundary of a strong magnetic field portion (hill, hill) generated between the spiral sector coil 41 at the mirror symmetry position with respect to the spiral trajectory of the accelerated particles (within a predetermined range). ) It is formed in a spiral shape having a predetermined angle. Since the spiral sector coils 41 are arranged at equal intervals in the circumferential direction, a relatively strong magnetic field (hill) is generated between the upper and lower spiral sector coils 41, and the spiral sector coils 41 are relatively in a portion where the spiral sector coils 41 are not present. A weak magnetic field (valley) is generated. A spiral is generated so that the incident angle of the accelerated particles from the valley to the hill (the angle between the speed direction of the accelerated particle when the hill enters and the tangential direction of the hill boundary) is within a predetermined range (here, 20 to 90 degrees). Brick-OUT-1 to Brick-OUT-20 (the shape on the hill incidence side) of the sector coil 41 are mainly formed. Further, the spiral sector coil 41 mainly has a Brick-IN-1 so that the angle between the accelerating particle and the hill boundary tangent to the valley from the hill is also within a predetermined range (here, 20 to 90 degrees). Brick-IN-16 (shape on the valley incident side) is formed.

  Each spiral sector coil 41, like the main split coil 21, etc., is connected to a power source and has a cooling device. Based on the command of the computer, the cooling temperature is stabilized and a predetermined energizing current (here, 320A) is supplied. Applying or shifting to a superconducting steady state generates a circumferentially increasing / decreasing magnetic field for accelerating particle convergence in an isochronous magnetic field.

≪Magnetic field formed by spiral sector coil unit≫
The magnetic field generated by the spiral sector coil units 4 and 4 thus formed brings about a strong convergence force on the accelerated particles in the isochronous magnetic field, as will be described below.

  That is, as schematically shown in FIG. 6 (a), when the magnetic pole gap is a hill and narrow and wide, the charged particle (Ion) has a circular orbit as shown in FIG. 6 (b). Taking a distorted orbit from (Circle), the particles enter and leave the hill part at an angle of κ. In this case, as shown in FIG. 6A, the magnetic field lines are distorted at the boundary between the hill and the valley, and the azimuth component of the magnetic field is generated in the vicinity thereof. Here, first, consider the case of FIG. 6B (radial sector type) in which the boundary between the hill and the valley is linear along the radial direction. Based on this case, the consideration when the boundary between the hill and the valley is spiral along the radial direction (spiral sector type) will be described later.

  When the geometric problem is solved using the relationship of “ω = q / mB” and “Bρ = const.” In FIG. 6A, the following [Equation 2] is obtained.

As shown in FIG. 6C, when a particle having a velocity v crosses an edge at an angle α, the equation of motion of the particle in the z direction is expressed by the following [Equation 3]. Here, _Bh is a value in a direction perpendicular to the edge of the horizontal component of the magnetic field, and has a finite value near the edge. Further, when a parameter “s = vt” is introduced, an equation that gives a change in the amount of motion p _{z in} the z direction is the following [Equation 4] from [Equation 3].

The total amount of change Δp _z of the momentum in the z direction when crossing the edge is expressed by the following [Equation 5] using the parameters defined in FIG.

  On the other hand, according to Stokes' theorem, the closed integration along P1-P2-P3-P4-P1 is “▽ × B = 0”, so the following [Equation 6] is obtained. The integration along P2-P3 has a magnetic field value of 0, and the integration along P3-P4 is 0 because both the magnetic field and the integration path are orthogonal. Accordingly, the following [Equation 7] is obtained, and eventually [Equation 8] is obtained.

  From [Equation 8], when α is positive (in the case of FIG. 6C), the particles undergo a focusing action. Therefore, the focal length f is given by the following [Equation 9], and focusing by oblique incidence is given by the following [Equation 10]. Here, ΔB is the difference in magnetic field strength between Hill and Valley.

  Once these values are determined, the betatron frequency can be determined using the transfer matrix. The transfer matrix for one unit of motion in the z direction is given by the product of the transfer matrices for free movement in the hill, focusing at the edge, free movement in the valley, and focusing at the edge, It is given by FOFO as shown in [Formula 11] below.

  When this matrix product is executed and the following relation of [Equation 12] is used, [Equation 13] is eventually obtained. Here, μ is an amount called a phase advance.

Accordingly, the betatron frequency in the z direction is the following [Expression 14] and [Expression 15], and is given by the sum of -β ² γ ² and flutter F ² .

  In each spiral sector coil unit 4, an oblique incident angle of acceleration particles with respect to a boundary between hills and valleys generated by upper and lower spiral sector coils 41 is increased, that is, the boundary draws a spiral from the center of the acceleration plane to the outside. Each spiral sector coil 41 is formed so as to have such a spiral shape.

  FIG. 7B schematically shows hills and valleys (spiral sector type) or circular orbits having spiral boundaries, and FIG. 7C shows the relationship between the circular orbit and acceleration orbit (equilibrium orbit).

  The angle formed by ε in FIG. 7B, that is, the tangent line of the Hill Valley boundary line, and the perpendicular line (radius passing through the contact point) passing through the contact point with respect to the circular orbit passing through the contact point of the tangent line is called a spiral angle. With respect to the deviation angle κ between ε and the circular orbit, the oblique incident angle is ε + κ when entering the hill and ε−κ when leaving. When entering, it receives convergence, and when it exits, it receives divergence. This indicates that it is AG (Alternating Gradient) convergence that alternately repeats convergence and divergence. κ is given by [Expression 2] as in the case of the radial sector type. The magnitude of convergence / divergence at the edge is given by the following [Equation 16], and the transfer matrix is given by FODO as shown in [Equation 17].

  Therefore, the spiral sector type phase advance is represented by the following [Equation 18].

Therefore, the betatron frequency in the z direction of the spiral sector type AVF cyclotron is the following [Equation 19] or [Equation 20], and the term of ² tan ² ε is added to the factor of the term by the radial sector type F ^2. become. In the cyclotron having the coil unit 1, since ε is 50 degrees, the value of this factor becomes as large as 4, and a strong convergence force can be obtained. From the viewpoint of setting such a value of the betatron frequency to an appropriate magnitude, ε is preferably set to 20 to 40 degrees outside the half in the radial direction.

  In order to generate a magnetic field to which a spiral angle ε of less than 90 degrees is applied at various radii on the acceleration plane in this way, the shape (outer shape, winding direction) of each spiral sector coil 41 has a bending radius set to a predetermined value. Although it is described above, similarly, it is formed into a spirally curved sector having a spiral angle ε of less than 90 degrees (around 60 degrees) with respect to various radii. FIG. 8 shows the relationship between the radial position and the spiral angle ε.

≪Magnetic field in acceleration plane≫
FIG. 9 shows an acceleration plane magnetic field (in plan view) formed by a pair of main coil units 2 and 2 and a pair of spiral sector coil units 4 and 4 housed therein, and FIG. The magnetic field distribution in the circumferential direction in the circular orbit of each radius of the plane is shown, FIG. 10B shows the magnetic field distribution from the center of the acceleration plane to the radial direction (radial direction), and FIG. 10C shows the acceleration plane. The distribution of flutter from the center to the radial direction is shown.

  From these, in the acceleration plane, an isochronous magnetic field whose strength increases from about 4T to about 7T as it goes to the outer peripheral portion, and a strong portion (hill) and a weak portion (valley) AVF magnetic field in the circumferential direction. The boundary between the hill and the valley is formed in a spiral shape so that the spiral angle ε, which is the angle between the tangent line and the radial direction, is less than 90 degrees and tilts from the radial direction, and the flutter is sufficiently secured. I understand that The flutter will be described in detail. At the radial position r = 0.28 m, the peak is 0.15, and as the diameter increases, the beam extraction position r = 1.06 m has 0.07, which is 0.06 or more. The desired value of is obtained.

Therefore, in the cyclotron provided with the coil unit 1, a magnetic field distribution capable of accelerating the carbon hexavalent ions, which are heavy particles, to about 400 MeV / nucleon can be formed on the acceleration plane. Therefore, acceleration of heavy particles necessary for heavy particle beam cancer treatment can be performed by a cyclotron having the coil system 1. The dimensions of the coil system 1 itself are about 4 m in diameter x about 2 m in height, and the coil system 1 and cyclotron can be made very compact, such as an installation area of about several tens of square meters (m ² ) including peripheral devices. It can be downsized. Furthermore, the coil system 1 and the cyclotron are small, and both the main split coil 21, the first correction split coil 22, the second split coil 23, and both the spiral sector coils 41 constituting the coil system 1 are air-core. Therefore, it is possible to reduce the amount of materials required for manufacturing (particularly relatively expensive superconducting wire), to simplify the structure of the shield for cooling, etc. It can be reduced, operation control can be made relatively simple, introduction cost and operation cost can be made low, maintenance can be easily performed, and maintenance cost can be reduced. Can also be inexpensive.

  In addition, both the main split coil 21, the first correction split coil 22, the second split coil 23, and both the spiral sector coils 41 are placed in a superconducting state, and excitation is performed in the superconducting state. In addition, Joule heat generation does not occur and the cooling energy of the cooling medium can be relatively small, and the amount of electric power required for operation can be reduced. In addition, since it is small and air-core, the amount of cooling medium is small, and Joule heat is not generated, so that the time from the stop state to the high magnetic field state (particle acceleration possible state) can be shortened, Particle acceleration can be performed efficiently. Further, since no Joule heat is generated, the main split coil 21, the first correction split coil 22, the second split coil 23, and the spiral sector coil 41 can be prevented from being thermally deformed, and the magnetic field distribution can be prevented. Thus, stable isochronous magnetic field or AVF magnetic field can be formed, or stable operation of particle acceleration can be ensured. Due to the above characteristics, the spread of particle accelerators capable of accelerating heavy particle beams can be promoted, and a great effect can be achieved such as an increase in hospitals capable of performing heavy particle beam cancer treatments.

≪Change example≫
In addition, the other form of this invention which mainly consists of changing the said form is illustrated. The number of coils can be changed variously, and can be 1, 2, or 4 or more in one side main coil unit, or 3 or less or 5 or more in one side spiral sector coil unit. The coils may not be divided into the main split coil and the correction split coil based on the cross-sectional area, but may have the same cross-sectional area, or each coil may have various cross-sectional areas. Further, the main split coil may be arranged farther from the accelerating magnetic field than the correction split coil. The dimensions and arrangement of the various coils can be finely adjusted or changed according to the magnetic gradient shape, the height of the magnetic flux density, or the like. One main coil unit does not need to be composed only of coils that are mirror-symmetric with respect to all the coils in the other main coil unit, and is additionally provided with a fine adjustment coil that is not in the other main coil unit. Any configuration may be adopted as long as it includes a coil that is mirror-symmetric with respect to the plurality of coils belonging to the other main coil unit, and the same applies to the spiral sector coil unit.

  The various coils in the main coil unit are configured by using pancake coils formed by winding a strip-shaped superconducting wire around a pancake. Each of the main split coil and the correction split coil is configured to have a stacked structure (as a stacked pancake coil) by stacking a plurality of disk-shaped (annular) pancake coils having a hole in the center. Even in a cyclotron including such a main coil unit, a high-strength isochronous magnetic field can be formed in a small, low-cost and easy-to-use apparatus. Moreover, by forming the pancake coil or its laminate, electromagnetic force can be applied to the wire component (Hastelloy) as a compressive stress during excitation, and the mechanical strength of each coil can be increased. It can be raised to avoid buckling, further improving durability, and generating a high magnetic field in a more stable state. Note that pancake coils can be used alone without being stacked, and the number of layers can be varied, or the thickness, number of turns, and type / dimension of the wire for each layer can be varied. The main coil unit is a solenoid coil. , A pancake coil, or a combination of laminated pancake coils.

  The temperature of the cooling medium may be other than 20K. The isochronous magnetic field may be made of a coil not using a superconducting wire or an oxide superconducting wire or a ferromagnetic material.

  According to the air core type cyclotron of the present invention, an extremely strong isochronous magnetic field and an AVF magnetic field can be provided by a small and low cost configuration. The air core type cyclotron of the present invention can be used for various medical institutions. In addition to being applicable to medical accelerators, it can also be used to create experimental cyclotrons that can be easily introduced in research institutions that do not have the largest scale. An air core type cyclotron capable of acceleration has various uses.

  In particular, in the case of a heavy particle accelerator for cancer treatment, as described below, the air-core type cyclotron of the present invention efficiently performs irradiation of heavy particle beams that are very effective against cancer. It is possible to treat a large number of cancer patients and provide an improvement in QOL, and the social cost is significantly reduced.

  That is, by irradiating heavy particles such as carbon hexavalent ion beams at two horizontal and vertical gates, it is possible to concentrate a position with a high energy absorption amount at the position of the cancer affected area. The level is much higher than that of gamma rays, and it can have a steep boundary compared to proton rays, reducing the burden on treatment other than the affected area and reducing the burden of treatment. The dose can be concentrated to make the biological effect (cell killing effect) on cancer cells about 3 times that of X-rays or protons, and the effect can be increased with a relatively short irradiation time. The number of irradiations can be reduced, the treatment period and hospitalization period can be shortened, or the rehabilitation period can be made unnecessary or extremely short, but there are very few physical burdens and cost burdens compared to surgical excision and other radiation treatments. Treatment It can be. In addition, due to the concentration of the dose, there are cases where it is effective against hypoxic cancer (large tumors after the middle stage) and radiation resistant cancer (cancers such as adenocarcinoma and osteosarcoma) It can also be used to treat intractable cancer. In addition, the possibility of treatment can be found even by elderly people and other disease holders by the fact that surgery is unnecessary in principle because of low burden (expansion of patients to be treated) and to improve the patient's QOL. As a result, the Social Cost can be reduced. According to the air-core type cyclotron of the present invention, it is possible to promote the spread of equipment that exhibits such remarkable effects.

1 Coil system 2 Main coil unit 4 Spiral sector coil unit 41 Spiral sector coil

Claims (7)

A pair of main coil units facing in the axial direction and forming an isochronous magnetic field in the radial direction;
It has a pair of spiral sector coil units that are opposed to each other in the axial direction and form a magnetic field that is strong and weak in the circumferential direction.
Each spiral sector coil unit includes three or more spiral sector coils,
Each spiral sector coil is an air-core coil in which an oxide superconducting conductor is wound along a curved fan shape, and is arranged so as to be rotationally symmetrical with each other .
The sector in each spiral sector coil is formed such that a spiral angle, which is an angle formed between a tangent line on a side intersecting the circumferential direction and a radial direction passing through a contact point of the tangent line, is less than 90 degrees. An air core type cyclotron. A pair of main coil units facing in the axial direction and forming an isochronous magnetic field in the radial direction;
It has a pair of spiral sector coil units that are opposed to each other in the axial direction and that form a magnetic field with strength in the circumferential direction
Each spiral sector coil unit includes three or more spiral sector coils,
Each spiral sector coil is an air-core coil in which an oxide superconducting conductor is wound along a curved fan shape, and is arranged so as to be rotationally symmetrical with each other.
The air core according to claim 1 , wherein each spiral sector coil is formed by winding an oxide superconducting conductor around a jig having an outer shape in which a plurality of curvature radii curves are smoothly connected. Type cyclotron. The air-core type cyclotron according to claim 1 or 2, wherein each of the spiral sector coils is formed so that a bending radius is not less than a predetermined value. 4. The main coil unit according to any one of claims 1 to 3 , wherein air-core main split coils formed by winding oxide superconducting conductors in a ring shape are arranged in a plurality of axial directions. Air core type cyclotron. In the respective said main coil unit, with respect to the outer diameter of the main split coil near the other main coil unit, the inner diameter of the distant main split coil than the main split coils, characterized in that it is smaller claims Item 5. The air-core type cyclotron according to item 4 . The air-core type cyclotron according to any one of claims 1 to 5 , wherein the pair of spiral sector coil units and / or the pair of main coil units are arranged in mirror symmetry with each other. . The oxide superconductor is a bismuth-based oxide superconductor or an RE-123-based oxide superconductor (REBa ₂ Cu ₃ O _7-δ , RE is a rare earth element including yttrium). The air-core type cyclotron according to any one of claims 1 to 6 .