A circular accelerator having an ion beam accelerating device

Abstract: The ion beam accelerating device of the invention comprises an accelerating cavity (2) having a plurality of magnetic cores (20) provided therein, and high frequency magnetic field generating means (35) provided for respective magnetic cores for inducing magnetic field within respective magnetic cores. The accelerating cavity comprises an accelerating cavity outer conductor having a space therein, accelerating cavity inner conductors inside of which an ion beam passes through each of the inner conductors penetrating one of the side walls of the accelerating cavity outer conductor, and a plurality of magnetic cores surrounding the accelerating cavity inner conductors within the accelerating cavity outer conductor. By providing a high frequency magnetic field generating means for each magnetic core or group thereof, impedance mismatching between the high frequency power supply and the accelerating cavity can be minimized, thereby improving the utilization factor of the high frequency power, and consequently it is possible to increase the gap voltage in the cavity.

Description: The present invention relates to a circular accelerator having an ion beam accelerating device for providing energy to charged particles, and in particular, to an ion beam accelerating device suitable for application to a medical use or physical experiments. First of all, an accelerating cavity to be used for accelerating ion beams will be described in the following. Because a proton which is a lightest mass of ions is about 2000 times heavier than that of an electron, thereby the relativistic effect of ions is small. Therefore, an ion velocity is generally slow, and in addition, the ion velocity undergoes a substantial change during acceleration. Thereby, in order to accelerate an ion beam to a predetermined energy level, a magnetic core-loaded accelerating cavity in which magnetic cores are installed is used by advantageously decreasing its resonant frequency in accordance with its magnetic permeability of the loaded magnetic cores. There are two types in this magnetic substance-loaded accelerating cavity: one is a tuned-type accelerating cavity which uses a magnetic core having a low magnetic loss, and controls the magnetic permeability of the magnetic core by applying a bias magnetic field by using a bias current so that the magnetic permeability thereof is tuned to the revolution frequency; and the other is an untuned-type accelerating cavity which actively makes use of a magnetic loss, and can broaden a resonance frequency band, although its cavity voltage is lowered, thus requires no bias device. One of such a prior art accelerating cavity and its power supply method has been described in "High Frequency Accelerating Cavity for Proton Synchrotron" p.V-19 to V-30, the High Energy Accelerating device Seminar OHO'89. Fig. 1 indicates a schematic diagram of a conventional untuned-type accelerating cavity 3 and its power supply. In the drawing of Fig. 1, accelerating cavity 3 is comprised of accelerating cavity outer conductor 10, accelerating cavity inner conductor 11A the inside of which ion beam 60 passes through and which inner conductor is disposed to penetrate one of the side walls of the accelerating cavity outer conductor 10, accelerating cavity inner conductor 11B which is disposed to penetrate the other side wall of the accelerating cavity outer conductor 10, eight pieces of magnetic toroidal magnetic cores 20 each disposed around the outer surface of the accelerating cavity inner conductor 11A within the accelerating cavity outer conductor 10, and a gap formed between the accelerating cavity inner conductors 11A and 11B. Each side wall at both end portions of the accelerating cavity outer conductor 10 is connected to either of accelerating cavity inner conductors 11A and 11B. The other ends of the accelerating cavity inner conductors 11A and 11B are connected respectively to a vacuum duct of a circular accelerating device. A high-frequency power which is output from a high-frequency power source 30 is supplied across the accelerating cavity inner conductor 11A and the accelerating cavity outer conductor 10 both in combination constitute a coaxial structure. This power supply method will be referred to as a direct coupling or direct power supply arrangement. By means of this direct power supply arrangement, high-frequency current 41 is caused to generate between the accelerating cavity inner conductor 11A and the accelerating cavity outer conductor 10. This high frequency current 41 induces high frequency magnetic field 42. Then, the high frequency magnetic field 42 and the toroidal magnetic cores 20 disposed within the accelerating cavity outer conductor 10 are inductively coupled to generate an accelerating voltage in the gap 12. By way of example, the accelerating cavity disclosed in the JP-A Laid-Open No.63-76299 is arranged to supply electric power using the same power supply arrangement as in the prior art accelerating cavity 3 of Fig. 1. An article entitled 'Induction Linear Accelerators and their Applications' by J.E. Leiss, published in IEEE Transactions on Nuclear Science, Vol. NS-26 No. 3, June 1979 discloses an acceleration arrangement in which toroidal magnetic cores extended around the path of a particle beam to be accelerated. Each core was connected to a separate modulator to transmit high frequency power to the beam. A cavity inner conductor for the beam extended through the toroidal cores and the arrangement also had a cavity outer conductor surrounding the cores, the side walls of the cavity outer conductor being penetrated by the cavity inner conductor. As mentioned above, the article by J.E. Leiss was concerned with a linear accelerator. The present invention is concerned with a circular accelerator in which the injected ion beam moves in a circular path under the influence of bending magnets. The article entitled 'High Frequency Accelerating Cavity for Proton Synchrotron' was concerned with such a circular accelerator. According to a first aspect of the invention, there is provided a circular accelerator having an injector for injecting an ion beam into the accelerator, bending magnets for causing the injected ion beam to move in a circular path and an ion beam accelerating device for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor having a space therein, a cavity inner conductor penetrating side walls of said cavity outer conductor and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores disposed in the space within said cavity outer conductor and surrounding said cavity inner conductor; wherein: the ion beam accelerating device further comprises: a high frequency power transmission unit provided for each of said plurality of magnetic cores for generating a respective magnetic field; an amplifier included in each high frequency power transmission unit; and high frequency power sources respectively connected to corresponding ones of said amplifiers. According to a second aspect of the invention there is provided a circular accelerator having an injector for injecting an ion beam into the accelerator, bending magnets for causing the injected ion beam to move in a circular path and an ion beam accelerating device for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor having a space therein, a cavity inner conductor penetrating side walls of said cavity outer conductor and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores disposed in the space within said cavity outer conductor and surrounding said cavity inner conductor; wherein: the ion beam accelerating device further comprises: a high frequency power transmission unit provided for each of said plurality of magnetic cores for generating a respective magnetic field; an amplifier included in each of said high frequency power transmission units; and a high frequency power source; and a power supply splitter for distributing output power from said high frequency power source to each of said amplifiers. According to a third aspect of the present invention there is provided a circular accelerator having an injector for injecting an ion beam into the accelerator, bending magnets for causing the injected ion beam to move in a circular path and an ion beam accelerating device for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor having a space therein, a cavity inner conductor penetrating side walls of said cavity outer conductor and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores disposed in the space within said cavity outer conductor and surrounding said cavity inner conductor; wherein: the ion beam accelerating device further comprises: a high frequency power transmission unit for generating a respective magnetic field; an amplifier included in each of said high frequency power transmission units; and a high frequency power source; and a power supply splitter for distributing output power from said high frequency power source to each of said amplifiers; wherein the plurality of magnetic cores form a plurality of groups disposed in the space within said cavity outer conductor and surrounding said cavity inner conductor, and: one of said high frequency power transmission units is provided for each group of magnetic cores. The invention may thus enable an ion beam accelerating device for a circular accelerator to be produced which has an improved utilisation factor of high frequency power. The invention may also enable an ion beam accelerating device for a circular accelerator to be provided which can increase the accelerating voltage. Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawing wherein: Fig. 1 is a schematic block diagram illustrative of arrangements of a prior art accelerating cavity and its power; Fig. 2 is a schematic block diagram of an ion beam accelerating device of one embodiment of the invention; Fig. 3(a) is an equivalent circuit of the ion beam accelerating device of the one embodiment of the invention; Fig. 3(b) is another equivalent circuit of Fig. 3(a) which is divided into a number of n; Fig. 4 is a schematic block diagram of an accelerating device which uses an ion beam accelerating device of a second embodiment of the invention; Fig. 5 is a detailed configuration of the ion beam accelerating device of Fig. 4; Fig. 6 is a cross-sectional view of the ion beam accelerating device as taken along VI-VII section in Fig. 5; Fig. 7 is a schematic block diagram of an ion beam accelerating device of a third embodiment of the invention; and Fig. 8 is a schematic block diagram of an ion beam accelerating device of a fourth embodiment of the invention. EMBODIMENTS OF THE PRESENT INVENTION: The inventors of the present invention have discussed in detail the characteristics of the prior art accelerating cavity 3 shown in Fig. 1 and of the JP-A Laid-Open No. 63-76299. As a result, the inventors have discovered a critical problem associated with these prior art accelerating cavities, that is, their utilization factors in use of the high frequency electric power are very low. The present invention has been contemplated to solve this newly discovered critical problem. The result of the aforementioned discussion will be described in detail in the following. With reference to Fig. 1, in the prior art accelerating cavity 3, an accelerating voltage V to be generated in gap 12 will be given by equation 1, where P is a net cavity power, and Z is a cavity impedance. V = 2PZ When impedance Z of accelerating cavity 3 is nearly equal to impedance Z d of the magnetic core, an accelerating voltage V d occurring in the gap 12 will be expressed by means of Z d as follows. V d = 2PZ d = 2 4Z d Z 0 (Z d +Z 0 ) 2 Z d P g Further, P will be given by the following equation 3, P = (1-Γ) 2 P g = 4Z d Z 0 (Z d +Z 0 ) 2 P g where, assuming Z a pure resistance, when Z〉Z o , Γ=(Z-Z o )/(Z+Z o ), and when Z〈Z o, Γ=(Z o -Z)/(Z o +Z), and where Γ is a voltage reflection coefficient, Z o is a characteristic transmission impedance (=50Ω), and P g is an output power from the high frequency power supply. Impedance Z d of the magnetic cores to be installed within the accelerating cavity 3 is generally large, thereby impedance Z of the accelerating cavity 3 is determined almost by Z d. There is such a relationship between power transmission impedance Z o and impedance Z of the accelerating cavity 3 that Z=Z d »Z o , thereby causing an impedance mismatching to occur therebetween. Thereby, assuming, for example, Z=1 kΩ, a net cavity power P becomes less than 20% of an output power P g from the high frequency power supply 30. The rest of power is reflected to the high frequency power supply 30 to be consumed therein, thereby the utilization coefficient of the high frequency power is very low. The same problem is noted in the accelerating cavity disclosed in the JP-A Laid-Open No. 63-76299 as described in the prior art accelerating cavity 3 of Fig. 1. As the result of the thorough and extensive study to try to solve the problem associated with the prior art, it is discovered that an inductive coupling by use of inductance of the magnetic cores will also cause an accelerating voltage to occur in the accelerating cavity. The inventors have successfully improved the utilization factor or efficiency in the sue of the high frequency power supply greatly through this inductive coupling, that is, by supplying a high frequency power to each one of the plurality of magnetic cores or for each group thereof. Preferred embodiments of the invention will be described in detail in the following. EMBODIMENT 1: With reference to Fig. 2, an ion beam accelerating device of a first embodiment of the invention will be described below. The ion beam accelerating device of the first embodiment is comprised of accelerating cavity 2 having a plurality of magnetic cores 20 in the number of n mounted therein, and a plurality of high frequency magnetic field generating unit 35 in the number of n. The accelerating cavity 2 which is of an untuned type includes accelerating cavity outer conductor 10, accelerating cavity inner conductors 11C and 11D the inside of which ion beam 60 passes through, and a plurality of magnetic toroidal cores 20 which are disposed to surround the accelerating inner conductors 11C and 11D, respectively, in a space within the accelerating cavity outer conductor 10. More particularly, toroidal magnetic cores in the number of n/2 are mounted around the accelerating cavity inner conductors 11C and 11D, respectively. Each one of the plurality of toroidal magnetic cores 20 has a same magnetic permeability. An impedance of each of the plurality of the magnetic cores 20 is Z d /n. Each of the accelerating cavity inner conductors 11C and 11D is disposed to penetrate a different side wall of the accelerating cavity outer conductor 10 to oppose each other with a gap therebetween. Gap 12 provided between 11C and 11D of the accelerating cavity inner conductors is disposed in the forward direction of ion beam 60 at the center of the accelerating cavity outer conductor 10. The side walls 25 and 26 of the accelerating cavity outer conductor 10 are connected respectively to 11C and 11D of the accelerating cavity inner conductors. High frequency magnetic field generating unit 35 include a plurality of power supply lines 34 in the number of n provided respectively for the plurality of toroidal magnetic cores 20, and winding portions 33 connected respectively to the plurality of power supply lines 34 and wound around the plurality of toroidal magnetic cores respectively to induce high frequency magnetic fields therein. Each of the power supply lines 34 includes high frequency power source 30A, amplifier 32 one end of which is connected to an output terminal of the high frequency power source 30A, and coaxial cable 14 connected to an output terminal of the amplifier 32. Internal conductor 15 of each coaxial cable 14 is wound around each toroidal magnetic core 20 to form winding portion 33, and its tip is in contact with the accelerating cavity outer conductor 10. A hole in the accelerating cavity outer conductor 10 through which the internal conductor 15 of the coaxial cable penetrates is hermetically sealed with electrical insulator 27 which insulates the internal conductor 15 of the coaxial cable from the accelerating cavity outer conductor 10. An outer conductor (shield) 16 of the coaxial cable 16 is connected to the accelerating cavity outer conductor 10. A high frequency power from the high frequency power source 30A is amplified by amplifier 32, and an amplified high frequency power is supplied through coaxial cable 14 to toroidal magnetic core 20. Since internal conductor 15 is wound around toroidal magnetic core 20, a high frequency current flowing through the internal conductor 15 induces high frequency magnetic field 42 inside the toroidal core 20. By means of the high frequency magnetic field 42 thus induced in each toroidal core, a high frequency power can be supplied to the accelerating cavity 2 more efficiently thereby producing a greater accelerating voltage in gap 12. Thereby, ion beam 60 is accelerated by this accelerating voltage every time it passes through the gap 12. With reference to Fig. 3(a), there is indicated an equivalent circuit of the accelerating cavity of the first embodiment of the invention, as viewed from the high frequency magnetic field generating unit 35. In this embodiment of the invention, since a high frequency power is supplied to the accelerating cavity 2 via a plurality of toroidal magnetic cores 20 in the number of n, it can be said that there exists an inductive coupling between the high frequency power supply and the accelerating cavity 2, which makes use of the inductance of toroidal magnetic cores 20. Further, the equivalent circuit of Fig. 3(a) can be expressed in terms of inductance L/n which is an inductance of each toroidal magnetic core 20 as indicated in Fig. 3(b). Impedance Z n of the accelerating cavity 2 connected to one of the power supply lines 34 is equal to Z d /n which is an impedance of one of the toroidal magnetic cores 20. Therefore, the accelerating cavity 2 of the first embodiment of the invention comprising the plurality of toroidal magnetic cores 20 in the number of n can be construed that the same is comprised of a plurality of accelerating cavities in the number of n connected in series, each cavity having impedance Z d /n. Assuming that one coaxial cable 14 transmits a high frequency power P g /n, then, an accelerating voltage V n to be generated in the gap 12 is given by the following equation 4. V n = 2PZ n = n 2 4 Z d n Z 0 ( Z d n +Z 0 ) 2 Z d n P g n ≃ n V d (Z d >> Z 0 , n) Therefore, the accelerating cavity 2 according to this embodiment of the invention can generate an accelerating voltage greater than √n times that in the prior art direct coupling accelerating cavity. By way of example, in the prior art accelerating cavity to which the high frequency power is supplied through direct coupling, only a single power supply line is provided, and a net impedance Z of the accelerating cavity equals to impedance Z d of a plurality of magnetic cores in the number of n. In the present embodiment of the invention, however, load impedance Z n in each one of the plurality of power supply lines 34 in the number of n is given by Z d /n which is an impedance of each one of the plurality of toroidal magnetic cores 20. Namely, according to the present embodiment of the invention, the load impedance Z n in the power supply line 34 is substantially reduced to approach the characteristic impedance Z 0 of the power supply line. Thereby, the impedance mismatching between the power supply line 34 and the load can be substantially decreased, in consequence, reducing the reflection power. In the high frequency magnetic field generation unit 35, supply of the high frequency power to the accelerating cavity 2 is substantially increased and the reflection power which is wasted is substantially decreased. Thereby, the consumption of the reflection power in the high frequency power source 30 is reduced, and in turn, the utilization efficiency of the high frequency power is improved accordingly. Further, by winding each inner conductor 15 of the coaxial power supply lines around each magnetic core, high frequency magnetic field 42 can be induced efficiently inside the magnetic core. In addition, since the magnetic core is formed into a toroidal shape, leakage magnetic flux can be minimized, thereby capable of inducing a large high frequency magnetic field 42 within the accelerating cavity 2. Through this high frequency magnetic field 42, the transmitted high frequency power can be supplied into the accelerating cavity 2, thereby producing a greater accelerating voltage in the gap 12. Hereinabove, this embodiment of the invention has been described by way of example of the untuned type accelerating cavity, however, it is not limited thereto, and the same effect and advantage of the invention will be obtained using a tuned type accelerating cavity as well. The same will apply with the following embodiments. EMBODIMENT 2: With reference to Fig. 4, there is illustrated a circular accelerator 1 for use in medical treatment to which an ion beam accelerating device 13 of a second embodiment of the invention is applied. The circular accelerating device 1 is comprised of injector 51 for injecting ion beam 60 which has been accelerated by injector accelerating device 50, bending magnet 52 for bending orbit of the ion beam 60 injected from the injector 51, quadrupole magnet 53 for diverging or converging the ion beam 60, extractor 54 for extracting ion beam 60 to an experimental laboratory or medical treatment room 70, and ion beam accelerating device 13 which is disposed along toroidal vacuum duct 55 the inside of which the ion beam 60 passes through. Ion beam 60 after having been accelerated by injector accelerating device 50 is injected into the circular accelerating device 1 through injector 51. After it has been accelerated to a predetermined energy level, ion beam 60 is extracted from the circular accelerating device 1 through extractor 54. The extracted ion beam is utilized in the experimental laboratory or medical treatment room 70. The ion beam accelerating device 13 of the second embodiment of the invention will be described with reference to Figs. 5 and 6 in the following. The ion beam accelerating device 13 of the second embodiment comprises accelerating cavity 2 having eight members of toroidal magnetic cores 20 mounted therein, and high frequency magnetic field generation unit 35A. The foregoing accelerating cavity 2 is of untuned-type accelerating cavity having the same construction as that of the first embodiment of the invention. The other ends of respective accelerating cavity inner conductors 11C and 11D are connected to vacuum duct 55 of the circular accelerating device 1. High frequency magnetic field generation unit 35A is comprised of a single high frequency power source 30B for producing a high frequency power instead of the plurality of high frequency power source 30A provided in the first embodiment of the invention, and power splitter 31 with one input and eight output pins with the one input pin thereof being connected to the output of the high frequency power source 30B. Eight power supply (transmission) lines 34 and eight winding portions 33 thereof are provided respectively for respective toroidal magnetic cores 20 likewise the first embodiment of the invention. Each of the power supply lines 34 includes a coaxial cable 14 and an amplifier 32. Each amplifier 32 is connected to one of the eight output pins of the power splitter 31. Arrangements and electric connections of inner conductor 15 and outer conductor 16 of each coaxial cable 14 are the same as in the first embodiment of the invention. A high frequency power output from the high frequency power source 30B is splitted into eight high frequency power supplies by the power splitter 31. Each splitted high frequency power is amplified by each amplifier 32. Each amplification and each phase of each of the amplified eight high frequency power supplies are the same from each other, respectively. Amplified respective high frequency power supplies are transmitted via respective coaxial cables 14 to respective toroidal magnetic cores 20. Since inner conductor 15 of each coaxial cable is wound around each toroidal magnetic core 20, a high frequency current flowing through the inner conductor 15 will efficiently induce high frequency magnetic field 42 within each toroidal magnetic core 20. Through this high frequency magnetic field 42 induced in each magnetic core, the high frequency power is effectively supplied into the accelerating cavity 2. Thus, an accelerating voltage is produced in gap 12 between accelerating cavity inner conductors 11C and 11D. Therefore, ion beam 60 is accelerated by this accelerating voltage when it passes through the gap 12. An equivalent circuit of the second embodiment of the invention and its resultant accelerating voltage will be described in the following. With reference to Fig. 3(b), an equivalent circuit of the second embodiment of the invention corresponds to an instance when parameter n=8. Therefore, accelerating voltage V 8 to be generated in the gap 12 in this instance will be given by substituting its parameter n in equation (4) so that n=8, and thus, by the following equation 5, V 8 = 2PZ 8 = 8 2 4 Z d 8 Z 0 ( Z d 8 +Z 0 ) 2 Z d 8 P g 8 ≃ 8 V d (Z d >> Z 0 ) where, V d is the accelerating voltage that the direct-coupled accelerating cavity produces. Thereby, the accelerating cavity 2 according to the second embodiment of the invention can produce an accelerating voltage about 3 times as great as V d . Now, as for an impedance of the second embodiment of the invention, impedance Z 8 of the accelerating cavity 2 with respect to a single power supply line 34 is Z d /8 which is an impedance of a single magnetic core 20. Namely, according to the second embodiment of the invention, load impedance Z 8 in the power supply line 34 is reduced likewise in the first embodiment, and approaches Z 0 which is the characteristic impedance of the power supply line. Thereby, the utilization factor or efficiency of the high frequency power in the second embodiment of the invention can be improved significantly likewise in the first embodiment. Further, since that each magnitude and phase of each high frequency power which is transmitted through each coaxial cable 14 are the same, and that the direction of winding of each inner conductor 15 is the same, each magnitude and phase of each high frequency magnetic field 42 induced in each of the eight toroidal magnetic cores 20 are all the same. Further, the inner conductor 15 of the coaxial power supply line wound around the toroidal magnetic core 20 can efficiently induce a high frequency magnetic field in each magnetic core. In addition, since the magnetic core is formed into the toroidal shape, leakage of magnetic flux is minimized. Thereby, a large net high frequency magnetic field 42 can be obtained in the accelerating cavity 2 according to the invention. Through this high frequency magnetic field 42, the transmitted high frequency power is enabled to be supplied to the accelerating cavity 2 at a high efficiency, thereby ensuring a high accelerating voltage to be generated therein. Further, since each power supply line 34 is provided with each amplifier 32, the high frequency power source 30B may have a small output rating. Thereby, small capacity power splitter 31 and amplifier 32 can be used. Thereby, the high frequency magnetic field generation unit 35A can be reduced in size, thus a more compact ion beam accelerating device 13 can be provided. Further, it is not necessary to synchronize respective high frequency power supplies to be output from respective amplifiers 32 since the power splitter 31 is connected to a single high frequency power source 30B. In the case of the first embodiment, however, since a plurality of individual high frequency power sources 30 are provided, it becomes necessary to provide additional means for synchronizing respective high frequency power supplies output from respective amplifiers 32. According to the second embodiment of the invention, since such additional means for synchronizing respective outputs is not necessary, a more compact configuration of equipment than that of the first embodiment can be achieved. EMBODIMENT 3: With reference to Fig. 7, another ion beam accelerating device 13A of a third embodiment of the invention will be described. In the third embodiment of the invention, a plurality of power supply lines 34 are provided for respective toroidal magnetic cores 20 in the same way as in the second embodiment of the invention. According to the third embodiment, through the use of the same action of inductive coupling as in the second embodiment, there have been achieved an improved utilization efficiency in use of the power supplied and a greater accelerating voltage. EMBODIMENT 4: With reference to Fig. 8, still another ion beam accelerating device 13B of a fourth embodiment of the invention will be described in the following. Accelerating cavity 2 according to the fourth embodiment of the invention is of an untuned-type accelerating cavity having the same configuration as the second embodiment except for core winding portions. In the fourth embodiment, eight members of toroidal magnetic cores 20 are grouped into four groups each having two members of cores, and respective power supply lines 34 are provided for respective groups thereof. High frequency magnetic field generating unit 35B includes high frequency power source 30B which outputs a high frequency power, power splitter 31B having one input and four output pins the input pin thereof being connected to the high frequency power source 30B, respective power supply lines 34 connected to respective output pins of the splitter 31B, and respective winding portions 33 connected to the other ends of the respective power supply lines 34. Coaxial cable 14 is electrically connected in the same way as in the second embodiment, however, in the fourth embodiment, an internal conductor 15 of each coaxial cable 14 is wound around two adjacent members of toroidal magnetic cores 20. An equivalent circuit of the fourth embodiment is obtained according to the equivalent circuit of the first embodiment of the invention indicated in Fig. 3 by substituting parameter n so that n=4. Therefore, a resultant accelerating voltage V 4 generated in gap 12 will be given, by substituting n=4 in equation 4, by the following equation 6, V 4 = 2PZ 4 =4 2 4 Z d 4 Z 0 ( Z d 4 +Z 0 ) 2 Z d 4 P g 4 ≃ 2V d (Z d >>Z 0 ) where, V d is the accelerating voltage that the direct coupling accelerating cavity generates. As is obvious from equation 6, the accelerating cavity 2 of the fourth embodiment can produce about two-fold accelerating voltage of V d . Now, regarding impedance of the fourth embodiment, in terms of a single power supply line 34, impedance Z 4 of the accelerating cavity 2 becomes Z 4 /4 which is an impedance of two magnetic cores 20. Namely, according to the fourth embodiment of the invention, likewise the first embodiment, load impedance Z 4 in each power supply line 34 decreases to approach the characteristic impedance Z 0 of the power supply line. Thereby, according to the fourth embodiment likewise the first embodiment, the utilization efficiency in use of the high frequency power is substantially improved. As noted in the fourth embodiment in which the plurality of magnetic cores are divided into groups each having the same number of magnetic cores and respective power supply lines 34 are provided for respective groups, the same advantage and result of the invention can be attained through the same action due to inductive coupling, thereby ensuring an improved utilization efficiency of the power and a greater accelerating voltage to be obtained. Further, the number of groups to divide the magnetic cores is not limited to four, and any number of groups may be adopted within the scope of the invention. By way of example, when a plurality of magnetic cores are assumed to be in one group having a single power supply line 34 and a single high frequency power source 30B, then such an arrangement will exhibit the same characteristic and performance as the direct coupling arrangement.

Claims: A circular accelerator having an injector (51) for injecting an ion beam into the accelerator, bending magnets (52) for causing the injected ion beam to move in a circular path and an ion beam accelerating device (13) for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor (10) having a space therein, a cavity inner conductor (11C, 11D) penetrating side walls (25, 26) of said cavity outer conductor and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores (20) disposed in the space within said cavity outer conductor (10) and surrounding said cavity inner conductor (11C, 11D); characterised in that: the ion beam accelerating device further comprises: a high frequency power transmission unit (34) provided for each of said plurality of magnetic cores (20) for generating a respective magnetic field; an amplifier (32) included in each high frequency power transmission unit; and high frequency power sources (30A) respectively connected to corresponding ones of said amplifiers (32). A circular accelerator having an injector (51) for injecting an ion beam into the accelerator, bending magnets (52) for causing the injected ion beam to move in a circular path and an ion beam accelerating device (13) for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor (10) having a space therein, a cavity inner conductor (11C, 11D) penetrating side walls (25, 26) of said cavity outer conductor (10) and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores (20) disposed in the space within said cavity outer conductor (10) and surrounding said cavity inner conductor (11C, 11D); characterised in that: the ion beam accelerating device further comprises: a high frequency power transmission unit (34) provided for each of said plurality of magnetic cores for generating a respective magnetic field; an amplifier (32) included in each of said high frequency power transmission units; and a high frequency power source (30B); and a power supply splitter (31) for distributing output power from said high frequency power source to each of said amplifiers. An accelerator according to claim 2, having a pair of said accelerating cavity inner conductors (11C, 11D) disposed axially in spaced apart relationship with respect each other, each cavity inner conductor penetrating a different side wall (25, 26) of said cavity outer conductor (10). A circular accelerator having an injector (51) for injecting an ion beam into the accelerator, bending magnets (52) for causing the injected ion beam to move in a circular path and an ion beam accelerating device (13) for accelerating the ion beam, the ion beam accelerating device comprising: a cavity outer conductor (10) having a space therein, a cavity inner conductor (11C, 11D) penetrating side walls (25, 26) of said cavity outer conductor (10) and providing a passage for an ion beam to pass through the inside thereof, a plurality of magnetic cores (20) disposed in the space within said cavity outer conductor (10) and surrounding said cavity inner conductor (11C, 11D); characterised in that: the ion beam accelerating device further comprises: a high frequency power transmission unit (34) for generating a respective magnetic field; an amplifier (32) included in each of said high frequency power transmission units; and a high frequency power source (30B); and a power supply splitter (31) for distributing output power from said high frequency power source to each of said amplifiers; wherein the plurality of magnetic cores (20) form a plurality of groups disposed in the space within said cavity outer conductor (10) and surrounding said cavity inner conductor (11C, 11D), and: one of said high frequency power transmission units (34) is provided for each group of magnetic cores (20). An accelerator according to any one of the preceding claims wherein each said high frequency power transmission unit includes at least one coaxial cable (14), the inner conductor (15) of the or each coaxial cable (14) being wound around a respective one of said plurality of magnetic cores (20), and wherein said cavity outer conductor (16) and the outer conductor (10) of each of said plurality of coaxial cables (14) are electrically connected. An accelerator according to any one of the preceding claims, wherein said plurality of magnetic cores (20) have a toroidal shape and said cavity inner conductor(s) (11C, 11D) penetrate the plurality of said magnetic cores (20).

Inventors: HIROTA JUNICHI, IWASHITA YOSHIHISA, HIROTA, JUNICHI, IWASHITA, YOSHIHISA
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1995
Main classification: H05H7
IPC codes: H05H9, H05H7