Unipolar induction acceleration cell, and induction accelerator and induction acceleration method for charged particle beam using same

Abstract

[Problem] To provide a unipolar induction acceleration induction acceleration cell in which a reset voltage of a magnetic body is not allowed to affect a charged particle beam, and to provide an acceleration device and an acceleration method for a charged particle beam that use the acceleration cell to perform induction-acceleration of a DC charged particle beam existing over one round of a ring of an accelerator. [Solution] The present invention provides a configuration of a unipolar induction acceleration cell which is an induction acceleration cell characterized by further comprising: a first diode group composed of a plurality of first diodes disposed to connect ends of a metallic beam pipe, which is divided by a first insulator provided in a band shape in the circumferential direction of the beam pipe, the plurality of first diodes being disposed in parallel and at equal intervals in the circumferential direction; and a second diode group composed of a plurality of second diodes disposed to connect ends of a metallic outer cylinder of the induction acceleration cell, the outer cylinder being divided by a second insulator disposed in a band shape around the beam pipe, the plurality of second diodes being disposed in parallel and at equal intervals.

Description

Unipolar induction acceleration cell, induction accelerator for charged particle beam using same, and induction acceleration method

[0001] The present invention relates to a unipolar induction acceleration cell that does not affect the reset voltage of a magnetic material on a charged particle beam, and further to an acceleration device and acceleration method for a charged particle beam that uses the same to inductively accelerate a DC charged particle beam that exists around a ring of an accelerator.

[0002] Conventional induction acceleration cell and induction acceleration synchrotron technologies are fully disclosed in Patent Document 1 and Non-Patent Documents 1-3.

[0003] As shown in Figure 1 (Figure 2 in Reference 1, Figure 2 in Reference 2), conventional induction cells (confinement induction cells and acceleration induction cells) have the same structure in principle as induction accelerating cavities for linear induction accelerators that have been made up to now.

[0004] The induction accelerating cells of the cited documents 1 and 2 are here again described as the existing induction accelerating cell 1, and the symbols and names of the symbols have been formally changed as necessary.

[0005] The principle of induced voltage generation will be explained using an existing induction accelerating cell 1. The existing induction accelerating cell 1 has a double structure consisting of a beam pipe 2, which is an inner cylinder, and an outer cylinder 3, with a magnetic material 3a inserted inside the outer cylinder 3 to create inductance. The portion of the beam pipe 2 connected to a vacuum duct 5 through which a charged particle beam 4 passes is made of a first insulator 2a such as ceramic. Since the existing induction accelerating cell 1 generates heat when operated at high repetition rates, insulating oil or the like for cooling is sometimes circulated inside the outer cylinder 3, and a seal 3b such as plastic is required between the outer cylinder 3 and the beam pipe 2.

[0006] A switching power supply 6 that generates a pulse voltage 6a is connected to the primary electrical circuit of an existing induction accelerating cell 1, and the generation of the electric field 2c can be freely controlled by turning the switching power supply 6 on and off externally.

[0007] That is, when a pulse voltage 6a is applied from a switching power supply 6 to the primary-side electric circuit surrounding the magnetic body 3a, a primary current 3c (core current) flows, exciting the magnetic body 3a, and the magnetic flux density penetrating the toroidal-shaped magnetic body 3a increases over time. At this time, an electric field 2c is induced on the secondary side, which are both ends 2b, 2b of the conductor beam pipe 2, with the first insulator 2a in between, according to Faraday's law of induction. This electric field 2c becomes an accelerating electric field. The part where this accelerating electric field occurs is called an acceleration gap 2d.

[0008] In the existing induction accelerating cell 1, in order to eliminate magnetic saturation of the magnetic body 3a, it was necessary to apply a negative induction voltage (reset voltage) opposite to the voltage (positive induction voltage (set voltage)) that accelerates the charged particle beam 4. Furthermore, the existing induction accelerating cell 1 only had a single acceleration gap 2d. Therefore, it was not possible to have the charged particle beam 4 present in the acceleration gap 2d during the time period when the reset voltage was applied. Therefore, it was theoretically impossible to inductively accelerate a DC charged particle beam that had been uniformly accumulated around the entire circumference of the accelerator ring.

[0009] Japanese Patent Application Laid-Open No. 2006-310013 (All-ion accelerator and its control method) Japanese Patent Application Laid-Open No. 2007-165220 (Induction accelerator and charged particle beam acceleration method)

[0010] K. Takayama and RJ Briggs, Induction Accelerators (Springer, 2011). K. Takayama, 'Evolution of Induction Synchrotrons', Reviews in Physics 10, 100083 (2023). Ken Takayama, commentary, 'Evolution and Applications of Induction Synchrotrons', Journal of the Physical Society of Japan 75, 666 (2020).

[0011] Therefore, the present invention aims to provide a unipolar induction acceleration cell that does not affect the reset voltage of a magnetic material on a charged particle beam, and further to provide an acceleration device and acceleration method for a charged particle beam that uses the same to induce and accelerate a DC charged particle beam that exists around the entire ring of the accelerator.

[0012] (1) A unipolar induction accelerating cell further comprising: a first diode group consisting of a plurality of first diodes arranged in parallel at equal intervals in the circumferential direction between ends of a metal beam pipe separated by a first insulator provided in a band shape in the circumferential direction of the metal beam pipe; and a second diode group consisting of a plurality of second diodes arranged in parallel at equal intervals in the circumferential direction between ends of the metal outer tube of the induction accelerating cell separated by a second insulator provided in a band shape around the beam pipe. More specifically, the induction acceleration cell has a double structure consisting of a metal beam pipe that is an inner cylinder and a metal outer cylinder, and a magnetic material is inserted inside the outer cylinder to create inductance, a portion of the beam pipe that is connected to a vacuum duct through which the charged particle beam passes is made of a first insulator, a switching power supply that generates a pulse voltage is connected to a primary coil that is a primary electric circuit surrounding the magnetic material, and the generation of an electric field is controlled by turning the switching power supply on and off externally, when the pulse voltage is applied from the switching power supply to the primary coil, a primary current flows, the magnetic material is excited, and the magnetic flux density penetrating the toroidal shaped magnetic material increases over time, an electric field is induced on both ends of the beam pipe, which are secondary sides across the first insulator, according to Faraday's law of induction, and an acceleration gap that becomes an accelerating electric field is provided, and a set voltage that gives a positive induced voltage that accelerates the charged particle beam and a reset voltage that eliminates saturation of the magnetic material are applied in the induction acceleration cell, further a first diode group consisting of a plurality of first diodes arranged in parallel at equal intervals in the circumferential direction between ends of the beam pipe separated by the first insulator arranged in a band shape in the circumferential direction of the beam pipe; and a second diode group consisting of a plurality of second diodes arranged in parallel at equal intervals between ends of the outer tube separated by a second insulator arranged in a band shape around the beam pipe on the outer tube, wherein the first diode group is turned on when a set voltage between the primary coil terminals is turned off and a negative reset voltage is generated, and the second diode group is automatically opened.(2) An induction accelerator for a charged particle beam, characterized in that two unipolar induction accelerating cells according to (1) are used to induce acceleration of a direct current charged particle beam stored in a storage ring. (3) A method for induction acceleration of a charged particle beam, characterized in that two unipolar induction accelerating cells according to (1) are used to induce acceleration of a direct current charged particle beam stored in a storage ring.

[0013] The present invention makes it possible to provide a unipolar induction acceleration cell that does not affect the reset voltage of a magnetic material on a charged particle beam, and further provides an acceleration device and acceleration method for a charged particle beam that uses the same to inductively accelerate a DC charged particle beam that exists around the entire ring of the accelerator.

[0014] By connecting the ends of the beam pipe separated by the first insulator and the ends of the outer tube separated by the second insulator with a diode, a passive short circuit is possible, and the charged particle beam is not subjected to the negative reset voltage. Also, a power semiconductor element, which is an active element, can be used to forcibly short circuit or open the beam, and like a diode, the charged particle beam is not subjected to the negative reset voltage.

[0015] The most noteworthy application at present is the EUV CW free electron laser. In particular, the FEL is attracting attention as a light source for EUV lithography in VLSI semiconductor manufacturing. Currently, AMSL in the Netherlands is the only supplier of a 13.5 nm EUV light source in the world. However, the laser-driven light source it supplies has extremely low power efficiency (0.1%) for industrial use, high equipment costs (20 billion yen), maintenance costs for the liquid tin target irradiation chamber and EUV optical system, an excessively large number of parts (20,000), and the need for highly skilled operators. In comparison, the induction-acceleration storage ring-driven EUV CW free electron laser offers the following notable advantages: (1) FEL output is polarized; (2) high efficiency (up to 20%); (3) high average power (up to kW); (4) relatively low cost (up to 5 billion yen); and (5) the potential for shorter wavelengths beyond 13.5 nm.

[0016] 4A is a schematic cross-sectional view of an existing induction accelerating cell 1; FIG. 4B is a schematic cross-sectional view of a unipolar induction accelerating cell 1a of the present application; and FIG. 4C is an explanatory diagram of a gap. (A) is a schematic perspective view of a beam pipe, illustrating a first insulator and a first diode group; (B) is a schematic front view of a unipolar induction accelerating cell, illustrating a second insulator and a second diode group. FIG. 4A shows the diode operation sequence of a unipolar induction accelerating cell. In FIG. 4B, the upper row shows the voltage pattern generated between both ends of the primary coil of the unipolar induction accelerating cell, and the lower row shows the acceleration voltage pattern received by the circulating charged particle beam. The vertical axis represents voltage value, and the horizontal axis represents time. This shows the acceleration pattern of a charged particle beam using two unipolar induction accelerating cells. (A) is the operation sequence of a first unipolar induction accelerating cell, and (B) is the operation sequence of a second unipolar induction accelerating cell. In both cases, the upper row shows the voltage pattern generated between both ends of the primary coil of the unipolar induction accelerating cell, and the lower row shows the acceleration voltage pattern received by the circulating charged particle beam. (C) is the sum of the acceleration voltages of the two unipolar induction accelerating cells, which is the acceleration voltage effectively applied to the DC charged particle beam. The vertical axis represents the voltage value, and the horizontal axis represents time.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0018] 2 and 3, the unipolar induction accelerating cell 1a of the present invention is the same as the existing induction accelerating cell 1 shown in Fig. 1, except that a second insulator 3d is provided on the outer cylinder 3, and a first diode group 7 is provided across the first insulator 2a, and a second diode group 8 is provided across the second insulator 3d. The unipolar induction accelerating cell 1a is driven by the same voltage control by the switching power supply 6 as the existing induction accelerating cell 1.

[0019] The first diode group 7 is composed of a plurality of first diodes 7a arranged in parallel at equal intervals in the circumferential direction between the ends 2b, 2b of the beam pipe 2, which are separated by a first insulator 2a arranged in a band shape in the circumferential direction of the metal beam pipe 2.

[0020] The second insulator 3d is arranged in a strip shape surrounding the beam pipe 2 in the metal outer cylinder 3 of the existing induction accelerating cell 1. The second diode group 8 is composed of a plurality of second diodes arranged in parallel connection at equal intervals between the ends 3e, 3e of the outer cylinder 3 separated by the second insulator 3d. The second insulator 3d may be provided not only on the side surface as shown in FIG. 2 but also on the circumferential portion of the outer cylinder 3.

[0021] The first diode 7a and the second diode 8a are not particularly limited as long as they are high-voltage diodes, such as SiC diodes, that have a withstand voltage greater than the set voltage 9 and the reset voltage 9a. The first diode 7a and the second diode 8a are respectively arranged in opposite directions between the ends of the acceleration gap 2d (first gap) and the second gap 3f, which are topologically arranged in series on a closed circuit.

[0022] The second diode 8a may be installed inside the outer cylinder 3 by connecting the end 3e of the outer cylinder 3.

[0023] The unipolar induction accelerating cell 1a configured as shown in Figures 2 and 3 is passively controlled and maintained by the first diode 7a and the second diode 8a so as to be in the voltage state of the acceleration gap 2d (first gap) shown in Figure 4(A). At this time, the charged particle beam 4 is not subjected to the reset voltage 9a shown in the upper part of Figure 4, but is subjected to only the acceleration voltage 10 shown in the lower part of Figure 4.

[0024] That is, as shown in FIG. 4A, the first diode group 7 to be used is turned on at the timing (t=0) when the set voltage 9 between the primary coil terminals is turned off and a negative reset voltage 9a is generated. This shorts out the acceleration gap 2d. As a result, the acceleration gap 2d no longer has any effect on the circulating DC charged particle beam 4 (lower part of FIG. 4B). In other words, the charged particle beam 4 is not decelerated during the reset period of the magnetic body 3a. Meanwhile, the second diode group 8 is automatically opened at this timing (t=0). As a result, a reverse current flows through the primary coil, the magnetic body 3a is reset by the reset voltage 9a, and the operating point returns to the initial value on the BH curve.

[0025] As a result of continuously generating the set voltage 9 and reset voltage 9a, a unipolar acceleration voltage 10 is applied to the circulating DC charged particle beam 4 for half of its residence time in the storage ring, resulting in the pattern of acceleration voltages 10 applied to the circulating charged particle beam 4 shown in the bottom of Figure 4(B). t=0 in Figure 4(A) is the diode on timing, and the vertical colored band to the right of it indicates the diode turn-on time (up to 5 nsec). +V is the forward voltage state, and -V is the reverse voltage state.

[0026] As shown in FIG. 5, by using two unipolar induction accelerating cells 1a (a first unipolar induction accelerating cell 1a and a second unipolar induction accelerating cell 1a), a direct current charged particle beam 4 stored in the storage ring can be induction accelerated.

[0027] Specifically, by operating two unipolar induction accelerating cells 1a continuously with an operating phase shift of 180 degrees as shown in FIGS. 5(A) and 5(B), a positive set voltage 9, i.e., a continuous accelerating voltage 10, can be applied to the DC charged particle beam 4 throughout the entire time the beam stays in the storage ring, as shown in FIG. 5(C).

[0028] REFERENCE SIGNS LIST 1 Existing induction accelerating cell 1a Unipolar induction accelerating cell 2 Beam pipe 2a First insulator 2b End 2c Electric field 2d Acceleration gap 3 Outer cylinder 3a Magnetic material 3b Seal 3c Primary current 3d Second insulator 3e End 3f Second gap 4 Charged particle beam 5 Vacuum duct 6 Switching power supply 6a Pulse voltage 7 First diode group 7a First diode 8 Second diode group 8a Second diode 9 Set voltage 9a Reset voltage 10 Acceleration voltage

Claims

1. An induction acceleration cell having a double structure consisting of a metal beam pipe which is an inner cylinder and a metal outer cylinder, a magnetic material is inserted inside the outer cylinder to create inductance, a part of the beam pipe connected to a vacuum duct through which a charged particle beam passes is made of a first insulator, a switching power supply which generates a pulse voltage is connected to a primary coil which is a primary electric circuit surrounding the magnetic material, and the generation of an electric field is controlled by turning the switching power supply on and off from the outside, when the pulse voltage is applied from the switching power supply to the primary coil, a primary current flows, the magnetic material is excited, and the magnetic flux density penetrating the toroidal magnetic material increases over time, an electric field is induced on the secondary side which is both ends of the beam pipe, on either side of the first insulator, according to Faraday's law of induction, and an acceleration gap which becomes an accelerating electric field is provided, and a set voltage which gives a positive induced voltage which accelerates the charged particle beam and a reset voltage which eliminates saturation of the magnetic material are applied, further comprising: A unipolar induction accelerating cell comprising: a first diode group consisting of a plurality of first diodes arranged in parallel connection at equal intervals in the circumferential direction between ends of the beam pipe separated by the first insulator provided in a band in the circumferential direction of the beam pipe; and a second diode group consisting of a plurality of second diodes arranged in parallel connection at equal intervals between ends of the outer tube separated by a second insulator arranged in a band on the outer tube surrounding the beam pipe, wherein the first diode group is turned on when a set voltage between the primary coil terminals is turned off and a negative reset voltage is generated, and the second diode group is automatically opened.

2. An induction accelerator for a charged particle beam, characterized in that two unipolar induction accelerating cells as claimed in claim 1 are used to induction-accelerate a direct current charged particle beam stored in a storage ring.

3. A method for induction acceleration of a charged particle beam, comprising the steps of: accelerating a direct current charged particle beam stored in a storage ring by using two unipolar induction acceleration cells as claimed in claim 1.

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