Synchrotron radiation light-source apparatus and method of manufacturing same

Abstract: A synchrotron radiation light-source apparatus is provided in which the characteristics of synchrotron radiation generated from deflecting electromagnets can be made uniform, and emittance can be made smaller to increase brightness. The synchrotron radiation light-source apparatus, for bending the traveling direction of an electron beam by deflecting electromagnets and for emitting synchrotron radiation includes, deflecting electromagnets which cause a negative value (-dBy/dx) of a magnetic-field gradient gradually increase after gradually decreasing in the traveling direction of the electron beam, that is, along the length of the deflecting electromagnets so as to form a smooth recessing distribution, or to increase in a step-like manner after decreasing in a step-like manner.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION: The present invention relates to a synchrotron radiation light source apparatus and a method of manufacturing the same. DESCRIPTION OF THE RELATED ART: One known type of this apparatus is the synchrotron radiation light-source apparatus, shown in Fig. 8, which is described, for example, in the "1-2 GeV Synchrotron Radiation Source, Conceptual Design Report (July 1986)", page 23, published by Lawrence Berkeley Laboratory, University of California, Berkeley. In Fig. 8, reference numeral 1 denotes an orbiting trajectory of an electron beam; reference numeral 2 denotes bending magnets disposed at predetermined intervals with respect to the orbiting trajectory 1; reference numeral 3 denotes a focusing quadruple magnet, disposed on the orbiting trajectory 1 before and after the bending magnets 2, for converging beams; and reference numeral 4 denotes a defocusing quadruple magnet. Fig. 9 shows a betatron function within the bending magnets 2. Fig. 10 shows the coordinate system of the synchrotron radiation light-source apparatus. The horizontal axis S in Figur 9 indicates the coordinates along the S axis in Fig. 10. Reference letter ℓ B denotes the length of the bending magnet. The operation of the synchrotron radiation light-source apparatus will now be explained. The orbit 1 of an electron beam is bent by the bending magnets 2; the electron beam is converged by the focusing quadruple magnet 3 and the defocusing quadruple magnet 4, while emitting synchrotron radiation (referred to as SR), and passes and encircles within a limited area along a closed orbit. The widths along the X and Y axes in the limited area along the closed orbit, i.e., beam sizes, are such that a value called emittance is multiplied by the square root of the betatron function values along the X and Y axes. Since the distribution of the betatron function along the closed orbit is determined by the bend angle and the magnetic-field gradient of the bending magnet 2, by the magnetic-field gradient of the focusing quadruple 3, by the magnetic-filed gradient of the defocusing quadruple magnet 4, and by the positions at which the electromagnets are positioned, its value of the betatron function differs depending upon the position on the closed orbit. Also, emittance is determined uniquely for the SR light-source apparatus on the basis of the bend angle and the magnetic-field gradient of the bending magnet 2; by the magnetic-field gradient of the focusing quadruple magnet 3; by the magnetic-field gradient of the defocusing quadruple magnet 4; by the positions at which the electromagnets are positioned; and by the beam energy. Regardless of the position on the closed orbit, the size of the emittance is the same. Emittance is obtained by multiplying a value obtained by integrating a function H(s) (shown in equation (1) below) which is only in the bending magnets 2 by a value which is dependent on the beam energy. H(s) = (π(s) 2 + (β(s)π ' (s) - β ' (s)π(s)/2) 2 )/2 π ρ β (s) where β(s) is the betatron function along the X axis, ρ is the bend radius, and π(s), called a dispersion function, is a function whose value, similarly to the betatron function, varies depending upon its position on the closed orbit. Although π(s) does not vary much with respect to changes in the magnetic-field gradients of the bending magnets 2, the focusing quadruple magnet 3 and the defocusing quadruple magnet 4, β(s) is a monotonous decreasing function with respect to a negative value of the magnetic-field gradient at position s. Therefore, in the conventional SR light-source apparatus, by making the bending magnets 2 have a fixed, negative magnetic-field gradient, the value of β(s) is made small at the bending magnets 2 as shown in Fig. 9 so that emittance is made smaller. However, in the conventional synchrotron radiation light-source apparatus, since the bending magnets 2 are made to have only a fixed magnetic-field gradient, the betatron function has no fixed area along the S axis within bending magnets 2. Consequently, the beam size is not fixed. As a result, a problem arises, for example, the characteristics of synchrotron radiation generated from the bending magnets 2 differ depending upon the position at which they are extracted. SUMMARY OF THE INVENTION The present invention has been achieved to solve the above-described problem of the prior art. It is an object of the present invention to provide a synchrotron radiation light-source apparatus in which the characteristics of synchrotron radiation generated from the bending magnets 2 can be made uniform, emittance can be reduced to increase brightness, and it is easy to manufacture, and a method of manufacturing the same. A synchrotron radiation light-source apparatus in accordance with one aspect of the present invention comprises bending magnets making a negative value of the magnetic-field gradient of the bending magnet gradually increase after being gradually decreasing along the travelling direction of the electron beam, thereby forming a recessed contribution of said magnetic field gradient along the length of said bending magnet. As an example, a bending magnet comprises a pair of coils facing each other with the orbit of the electron beam in between, each of the coils being formed as an air-core bending magnet formed in such a way that they are twisted in opposite directions with the orbit of the electron beam as a reference so that the gap between the coils becomes greater toward the exterior of the orbit at both ends of the coils which serve as the entrance and exit for the electron beam. As another embodiment, a bending magnet includes a pair of magnetic poles facing each other with the orbit of the electron beam in between, each of these magnetic poles being formed in such a way that the gap between the magnetic poles becomes gradually narrower in the interior of the orbit, and becomes gradually wider in the exterior of the orbit toward both ends of the coils which serve as the entrance and exit for the electron beam, and the gap between the magnetic poles becoming constant. As an example, each of the magnetic poles is formed in such a way that a plurality of semi-circular plates are stacked with the angle of the arc varied along the orbit of the electron beam. The synchrotron radiation light-source apparatus in accordance with the present invention can comprise a bending magnet for causing a negative value of the magnetic-field gradient to decrease in a step-like manner, and then increase in a step-like manner along the travelling direction of the electron beam. As an example, the bending magnet is formed by combining two or more types of iron cores. According to a second aspect of the present invention, there is provided a method of manufacturing a synchrotron radiation light-source apparatus for generating synchrotron radiation by bending the orbit of an electron beam by means of a bending magnet, the method comprising the step of forming the bending magnet causing a negative value of the magnetic-field gradient to gradually decrease and then gradually increase along the orbit of said electron beam, thereby forming a recessed distribution of said magnetic field gradient along the length of said bending magnet. The bending magnet can be formed by twisting a pair of facing coils with the orbit of said electron beam in between in opposite directions with the orbit of said electron beam as a reference, so that the gap between the coils becomes greater toward the exterior of said orbit at both ends of the coils which serve as the entrance and exit for the electron beam. Alternatively, the bending magnet can be formed by using a pair of magnetic poles facing each other in which a plurality of semi-circular plates are stacked with the orbit of the electron beam in between with the angle of each arc along the orbit of said electron beam varied. As a further alternative, the bending magnet can be formed by combining two or more types of iron cores having magnetic poles with different shapes. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph illustrating the distribution of the magnetic-field gradient of a bending magnet of a synchrotron radiation light-source apparatus in the travelling direction of an electron beam in accordance with a first embodiment of the present invention; Fig. 2 is a graph illustrating the betatron function along the X axis within the bending magnet having the magnetic-field gradient shown in Fig. 1; Fig. 3A is a graph illustrating in more detail the bending magnet of the synchrotron radiation light-source apparatus in accordance with the first embodiment of the present invention; Fig. 3B is a side view thereof from a direction at right angles with the electron beam orbit; and Fig. 3C is a side view thereof from a direction of the electron beam orbit; Fig. 4A and 4B are respectively a side view from a direction of the electron beam orbit illustrating another embodiment of the bending magnet of the synchrotron radiation light-source apparatus in accordance with the present invention, and a side view from a direction at right angles with to electron beam orbit; Fig. 5 is a perspective view illustrating still another embodiment of the bending magnet of the synchrotron radiation light-source apparatus in accordance with the present invention; Fig. 6 is a graph illustrating the distribution of the magnetic-field gradient of the bending magnet of a synchrotron radiation light-source apparatus in the travelling direction of an electron beam in accordance with a second embodiment of the present invention; Fig. 7 is a perspective view illustrating in more detail the bending magnet of the synchrotron radiation light-source apparatus in accordance with the second embodiment of the present invention; Fig. 8 is an illustration of one cycle of the synchrotron radiation light-source apparatus; Fig. 9 is a graph illustrating the distribution of the magnetic-field gradient of a bending magnet of a conventional synchrotron radiation light-source apparatus in the travelling direction of the electron beam; and Fig. 10 is an illustration of a coordinate system of the synchrotron radiation light-source apparatus. DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be explained below with reference to the accompanying drawings. FIRST EMBODIMENT Fig. 1 is a graph illustrating the distribution of the magnetic-field gradient of a bending magnet of a synchrotron radiation light-source apparatus in a beam travelling direction in accordance with a first embodiment of the present invention. Fig. 2 is a graph illustrating the betatron function along the X axis within the bending magnet having the magnetic-field gradient shown in Fig. 1. As shown in Fig. 1, the synchrotron radiation light-source apparatus comprises bending magnet which cause a negative value (-dBy/dx) of a magnetic-field gradient to gradually increase after gradually decreasing in the travelling direction of the electron beam, that is, along the length of the bending magnet, so as to form a smooth recessed distribution rd. Since, as described above, the betatron function β (s) along the X axis at position s within the bending magnet is a monotonous decreasing function with respect to the negative value of the magnetic-field gradient at position s, as shown in Fig. 2, the betatron function β (s) along the X axis at position s within the bending magnet becomes uniform and nearly fixed, small values in most areas as a result of the negative value of the magnetic-field gradient being distributed in a recessing manner. Consequently, the size of the electron beam within the bending magnet becomes constant, and therefore the characteristics of synchrotron radiation generated within the bending magnet can be made uniform. Also, since the betatron function value becomes a small value within the bending magnet, emittance can be reduced and brightness can be increased. SECOND EMBODIMENT Figs. 3A, 3B and 3C illustrate in more detail the bending magnet of the synchrotron radiation light-source apparatus in accordance with the first embodiment of the present invention; Fig. 3A is a plan view thereof; Fig. 3B is a side view from a direction at right angles to the electron beam orbit; and Fig. 3C is a side view from a direction of the electron beam orbit. In these Figures, a bending magnet 12 is formed of an air-core coil which is widely used in a superconducting bending magnet or the like. As shown in the Figures, the bending magnet 12 comprises a pair of upper and lower coils 12A and 12B, these coils being twisted in opposite directions with the travelling direction of the electron beam as a reference. In other words, as shown in Fig. 3C seen from a side opposite to the travelling direction of the electron beam, the upper coil 12A is formed in such a way that the central portion thereof is twisted into a smallest amount in the clockwise direction with the orbiting trajectory 11 of the electron beam as an axis. In contrast, the lower coil 12B is formed in such a way that the central portion thereof is twisted into a smallest amount in the counter clockwise direction with the orbiting trajectory 11 of the electron beam as an axis. In other words, the coils 12A and 12B are formed in such a way that the gap between the coils becomes greater toward the exterior of the orbit 11 at both ends of the coils which serve as the entrance and exit for the electron beam. Therefore, in the bending magnet 12, since the entrance and exit for the electron beam of the upper coil 12A and the lower coil 12B for generating deflecting magnetic fields are twisted in opposite directions into a largest amount, the negative values of the magnetic-field gradient form a recessing distribution along the travelling direction of the electron beam, as shown in Fig. 1, and the betatron function along the X axis within the bending magnet 12 can be made uniform, small values, as shown in Fig. 2, making it possible to reduce emittance and increase brightness. In addition, in this embodiment, the upper and lower coils 12A and 12B can be manufactured easily and at a low cost by merely bending coils. THIRD EMBODIMENT Figs. 4A and 4B illustrate another embodiment of the bending magnet of the synchrotron radiation light-source apparatus in accordance with the present invention. Fig. 4A is a side view from a direction of the electron beam orbit; Fig. 4B is a side view from a direction at right angles to the electron beam orbit. Although this bending magnet is not shown clearly in the Figures, similarly to the bending magnet shown in Fig. 10, it is as a whole curved along the electron beam orbit. As shown in Fig. 10, a bending magnet 22 of the synchrotron radiation light-source apparatus of this embodiment comprises a yoke 22A, coils 22B and 22C wound around portions facing the yoke 22A, and magnetic poles 22D and 22E mounted in the coils 22B and 22C, respectively. The magnetic poles 22D and 22E are formed to show top-bottom symmetry in such a way that the arc of stacked plates in which a plurality of semi-circular, thin plates 22F are stacked are made to face each other. Furthermore, as regards the arcs of the semi-circular, thin plates, which form the magnetic poles 22D and 22E, as shown in Figs. 4A and 4B, the gap between the magnetic poles becomes gradually narrower in the interior of the orbit 11, and becomes gradually wider in the exterior of the orbit 11, from the center of the bending magnet 22 toward both ends of the coils which serve as the entrance and exit for the electron beam, and the gap between the magnetic poles becomes constant. That is, the rotational angle of the arcs becomes gradually larger toward both ends of the coils. Therefore, in the bending magnet 22, the negative values of the magnetic-field gradient form a recessing distribution along the travelling direction of the electron beam in the section between the magnetic poles 22D and 22E for generating deflecting magnetic fields, as shown in Fig. 1. The betatron function along the X axis within the bending magnets 22 can be made uniform, small values, as shown in Fig. 2. Also, emittance can be reduced and brightness can be increased in the same manner as in the above-described embodiments. In addition, in this embodiment, a complex surface that the magnetic poles face can be realized by gradually varying the angle of the arcs of a plurality of semi-circular plates stacked along the beam orbit, and the apparatus can be manufactured easily and at a low cost. Also, it is possible to vary the changes in the angle of the arcs of a plurality of semi-circular stacked plates along the beam orbit as required. Although the magnetic poles 22D and 22E of the bending magnet 22 are formed of a plurality of thin stacked plats, they may be formed of thick plates or blocks. For example, a bending magnet 23 shown in Fig. 5, having magnetic poles 22F and 22G, may be used generally as bending magnet. The surfaces of these magnetic poles 22F and 22G, which face each other, with the beam orbit 11 in between, become gradually narrower in the interior of the orbit 11, and become gradually wider in the exterior of the orbit 11, from the center of the bending magnet 23 toward both ends of the coils which serve as the entrance and exit for the electron beam, and the gap between the magnetic poles becomes constant in the orbit 11. FOURTH EMBODIMENT Fig. 6 is a graph illustrating the distribution of the magnetic-field gradient of the bending magnet of the synchrotron radiation light-source apparatus in the travelling direction of the electron beam in accordance with the second embodiment of the present invention. In this embodiment, as shown in Fig. 6, a bending magnet is provided which forms a square, recessing distribution in which the negative value (-dBy/dx) of the magnetic-field gradient decreases in a step-like manner along the travelling direction of the electron beam, and then increases in a step-like manner. Although the accuracy attainable by this embodiment is slightly lower than that of the first embodiment, advantages equivalent to those of the above-described embodiments can be realized. In addition, in this embodiment, since the magnetic field gradient forms a square, recessing distribution, two types of iron cores 24A and 24B having magnetic poles with different shapes as a bending magnet 24 shown in Fig. 7, may be combined to form the electronic bending magnet. Therefore, since a complex construction is unnecessary, this embodiment has an advantage, in particular, in that a bending magnet can be manufactured easily and at low cost, though the uniformity of synchrotron radiation characteristics is inferior to that of the above-described embodiments. Although two types of iron cores having magnetic poles with different shapes are combined to form a bending magnet shown in Fig. 7, three or more types of iron cores having magnetic poles with different shapes may be combined so that the magnetic-field gradient may be varied in two or more steps. Also, the bending magnet in which the negative value of the magnetic-field gradient is varied in a step-like manner may be used in which the angle of the arcs of a plurality of semi-circular stacked plates of the bending magnet 22, shown in Figs. 4A and 4B, is varied properly.

Claims: A synchrotron radiation light-source apparatus for emitting synchrotron radiation by bending the orbit of an electron beam by means of a bending magnet, said apparatus comprising a bending magnet (12, 22, 23, 24) causing a negative value of the magnetic-field gradient to gradually decrease and then gradually increase along the traveling direction of said electron beam, thereby forming a recessed distribution (rd) of said magnetic field gradient along the length (l B ) of said bending magnet. A synchrotron radiation light-source apparatus according to claim 1, wherein said bending magnet (12) comprises a pair of coils (12A, 12B) facing each other with the orbit of said electron beam (11) in between, each of said coils being formed as an air-core bending magnet formed in such a way that they are twisted in opposite directions with the orbit of said electron beam as a reference so that the gap between the coils becomes greater toward the exterior of said orbit at both ends of the coils (12A, 12B) which serve as the entrance and exit for the electron beam (11). A synchrotron radiation light-source apparatus according to claim 1, wherein said bending magnet (22) includes a pair of magnetic poles (22B, 22C) facing each other with the orbit of said electron beam (11) in between, each of these magnetic poles being formed in such a way that the gap between the magnetic poles becomes gradually narrower in the interior of the orbit, and becomes gradually wider in the exterior of the orbit toward both ends of the coils which serve as the entrance and exit for the electron beam, and said gap between the magnetic poles becoming constant. A synchrotron radiation light-source apparatus according to claim 3, wherein each of the magnetic poles of said bending magnet (22) is formed by stacking a plurality of semi-circular plates (22D, 22E) with the angle of each arc along the traveling direction of said electron beam varied. A synchrotron radiation light-source apparatus according to claim 1, wherein said bending magnet (24) is adapted for causing a negative value of a magnetic-field gradient to decrease in a step-like manner along the traveling direction of the electron beam (11), and then to increase in a step-like manner. A synchrotron radiation light-source apparatus according to claim 5, wherein said bending magnet (24) is formed by combining two or more types of iron cores (24A, 24B, 24C) having magnetic poles with different shapes. A method of manufacturing a synchrotron radiation light-source apparatus for generating synchrotron radiation by bending the orbit of an electron beam by means of a bending magnet, said method comprising the step of: forming said bending magnet (12, 24) causing a negative value of the magnetic-field gradient to gradually decrease and then gradually increase along the traveling direction of said electron beam, thereby forming a recessed distribution (rd) of said magnetic field gradient along the length (l B ) of said bending magnet (12, 24). A method of manufacturing a synchrotron radiation light-source apparatus for generating synchrotron radiation according to claim 7, wherein said bending magnet (22) is formed by using a pair of magnetic poles facing each other in which a plurality of semi-circular plates (22D,22E) are stacked with the orbit of said electron beam in between with the angle of each arc along the orbit of said electron beam varied. A method of manufacturing a synchrotron radiation light-source apparatus for generating synchrotron radiation according to claim 7, wherein said bending magnet (24) is formed by combining two or more types of iron cores having magnetic poles with different shapes. A method of manufacturing a synchrotron radiation light-source apparatus for generating synchrotron radiation according to claim 7, wherein said bending magnet (12) is formed by twisting a pair of facing coils with the orbit of said electron beam in between in opposite directions with the orbit of said electron beam as a reference so that the gap between the coils becomes greater toward the exterior of said orbit at both ends of the coils which serve as the entrance and exit for the electron beam.

Inventors: YAMAMOTO YUICHI, YAMAMOTO, YUICHI, Yamamoto, Yuichi, c/o Mitsubishi Denki K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: H05H7
IPC codes: G21K1, H05H7, H05H13