- Email: [email protected]
The fast extraction kicker for J-PARC with a novel pulse compression system
Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
The fast extraction kicker for J-PARC with a novel pulse compression system Kunio Koseki n, Hiroshi Matsumoto High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 30 August 2013 Received in revised form 2 December 2013 Accepted 9 December 2013 Available online 27 December 2013
A fast extraction kicker magnet for the main ring of J-PARC has been developed. A lumped constant type magnet is employed for its structural simplicity and stability in high-voltage operation. A disadvantage of the lumped constant type, a slow rise time, was alleviated by the adoption of a newly developed magnetic pulse compression system. The effectiveness of the magnetic pulse compression system in sharpening the excitation current was confirmed both by a circuit simulation and experimentally. The newly developed fast extraction kicker system was operated successfully with a 30 kV charging voltage of the pulsed power supply. The required rise time of less than 1.1 μs was achieved in the measurement. & 2013 Elsevier B.V. All rights reserved.
Keywords: Kicker magnet Magnetic pulse compression Saturable inductor
1. Introduction One of the most important experimental projects at the main ring synchrotron of J-PARC [1] is the T2K experiment [2]. Eight proton beams are accelerated up to 30 GeV and extracted by five kicker magnets in a synchronous manner. Because the extraction is performed within a single circulation of the beams, the deflecting magnetic field generated by the kickers must be excited within 1.1 μs. The layout of J-PARC is depicted in Fig. 1. The design parameters of the main ring synchrotron are summarized in Table 1. The main ring synchrotron began operation in 2010, at which time only six proton beams were extracted because the fast extraction kicker system could not satisfy the required rise time. After intensive investigation, it was found that a parasitic inductance of the pulse forming network (PFN) disturbed the sharp rise of the excitation current by forming a resonant structure with an energy storage capacitor at a relatively lower frequency. The effect is more serious in a low-impedance PFN circuit because the energy storage capacitance is larger. Thus, it was concluded that the reason of the slow rise time of the fast extraction kicker system was the characteristic impedance of as low as 5 Ω. To recover eight-bunch operation in the main ring, a new kicker power supply with reduced parasitic inductance in the PFN circuit has been developed [3]. To minimize the cost and the length of the upgrade term, high-voltage transmission cables installed for the existing system were reutilized. Thus, the characteristic impedance of the new kicker power supply was chosen
n
Corresponding author. Tel.: þ 81 29 864 5200 4698. E-mail address: [email protected] (K. Koseki).
0168-9002/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2013.12.040
to be 5 Ω as in the existing system. Moreover, it was decided to develop a new fast extraction kicker magnet with a sufficiently large aperture for a future upgrade of the beam intensity. Because of its structural simplicity and stability in high-voltage operation, the fast extraction kicker employs a lumped constant magnet, which is equipped with a ferrite-loaded single-turn coil. The rise time of the lumped constant magnet is determined by the ratio of the coil inductance and the characteristic impedance of the system. Therefore, achieving a sharp rise time is difficult in a low-impedance system. Moreover, it is impossible to fully eliminate the disturbing effect induced by the parasitic inductance in the PFN circuit. To overcome the disadvantage of the lumped constant magnet, utilization of a saturable inductor as a magnetic pulse compression (MPC) system [4–6] was evaluated. The MPC system acts as a magnetic switch that sharpens the rise time of the output pulses by utilizing the nonlinearity of the ferromagnetic core materials. It was thought that successful adoption of the MPC system would achieve a sharp rise in the excitation current with a simple circuit configuration even in a low-impedance kicker system. In this paper, the operational principles of the MPC system to sharpen the rise time of the excitation current of the fast extraction kicker magnet of J-PARC are reported in detail. Moreover, the results of the successful high-voltage operation for evaluation of the performance of the newly developed MPC system with the lumped constant magnet are reviewed. 2. Simulation study The conceptual circuit schematic of the fast extraction kicker system is depicted in Fig. 2. The pulsed power supply consists of
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K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
two thyratrons, a blumlein pulse forming network, and a pulse transformer. The excitation current generated by the pulsed power supply is transmitted by high-voltage coaxial cables to the magnet. The kicker magnet employs the lumped constant type. Lumped constant type kicker magnets are widely used for various extraction systems in accelerators [7,8]. Structural simplicity, which contributes to reliability in high-voltage operation, is the main advantage of the lumped constant type. This section describes simulations that were performed based on the circuit schematic depicted in Fig. 2 to evaluate the rise time of the excitation current. In the circuit simulation, parameters as summarized in Table 2 were employed. The parasitic inductance of the PFN circuit was modeled as a series inductance of 20 nH to the energy storage capacitor.
Therefore, the excitation current to the magnet, Imag, is expressed as Z τrise 1 V mag dt; ð1Þ I mag ¼ Lmag 0
2.1. Characteristic of lumped constant magnet
where Lmag is the inductance of the magnet and Vmag is the applied voltage across the magnet. A circuit simulation was performed to evaluate Eq. (1) and other effects from the pulsed power supply. The saturable inductor depicted in Fig. 2 as a MPC system was removed from the simulation for simplicity. The excitation current waveform from the circuit simulation is shown in Fig. 3. Fig. 4 shows the applied voltage across the kicker magnet. From a comparison of Figs. 3 and 4, the validity of Eq. (1) is confirmed. Moreover, it can be seen that the slowly rising leading edge of the applied voltage to the kicker magnet is one of the reasons for the slow rise time of the excitation current. A natural approach is to apply a higher voltage to the magnet over a shorter period of time to achieve a faster rise time of the excitation current.
The lumped constant kicker magnet is a single-turn coil loaded with ferrite cores, so the impedance is treated as an inductance.
2.2. Magnetic switch In the previous section, it was noted that the slowly rising leading edge of the applied voltage to the magnet disturbs the sharp rising of the excitation current. Therefore, adoption of a MPC system as a solution for sharpening the rise time of the excitation current was evaluated. The MPC system utilizes the nonlinearity of ferromagnetic core materials and acts as a magnetic switch. During the rising period of the applied voltage, the high impedance of the MPC system is maintained by the unsaturated core materials of the inductors. Therefore, no excitation current flows to the kicker magnet. Once the voltage reaches its peak value, the core materials are saturated. At this time, the excitation current starts to flow with relatively higher applied voltage. Consequently, the rise of the excitation current, which is defined as the integral of the applied voltage, is sharpened. To evaluate the pulse sharpening effect by the MPC system, a circuit simulation was performed. The results are shown in Figs. 5–8.
Fig. 1. Layout of J-PARC.
Table 1 Design parameters of the main ring of J-PARC. Injection energy
3 GeV
Extraction energy Circumference Average radius Repetition rate Revolution period at 30 GeV
30 GeV 1567.5 m 249.475 m 0.3 Hz 5.2 μs
Table 2 Parameters employed in the circuit simulation. Characteristic impedance
5Ω
PFN inductance PFN capacitance Magnet inductance Low pass filter resistance Low pass filter capacitance Damping resistor of filter
500 nH 20 nF 3 μH 5Ω 20 nF 50 Ω
Fig. 2. Conceptual circuit schematic of the fast extraction kicker system.
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
65
Fig. 7. Simulated voltage waveform applied to the MPC system. Fig. 3. Simulated excitation current waveform.
Fig. 8. Simulated voltage waveform applied to the kicker magnet. Fig. 4. Simulated voltage applied to the lumped constant type kicker magnet. Table 3 Design parameters of the magnetic pulse compression system. Initial inductance
380 μH
Total cross sectional area Core material Saturation flux density
2.86 10 3 m2 FT-3M 1.23 T
Fig. 5. Simulated current waveform to the kicker magnet with the MPC system.
Fig. 9. Comparison of the simulated current waveforms. The dashed and solid lines show the rise of the excitation current waveform with and without the MPC system, respectively.
Fig. 6. Simulated input voltage waveform to the load system.
In the simulation, a saturable inductor based on the parameters summarized in Table 3 was used. The input voltage transmitted from the pulsed power supply is depicted in Fig. 6. Before the saturation of the MPC system, most of the input voltage is applied only to the MPC system (see Fig. 7) because the impedance of the saturable inductor is sufficiently higher than that of the kicker magnet. Therefore, no excitation current flows during this period. At the point at which the input
voltage reaches its peak value, the MPC system becomes saturated and its impedance drops to a negligibly small value. Then, most of the input voltage is applied only to the kicker magnet (see Fig. 8). Thus, the rising of the excitation current is sharpened by the relatively higher voltage applied to the kicker magnet. To illustrate the effectiveness of the MPC system, an enlarged view of the simulated excitation currents during the rise period is depicted in Fig. 9. The rise time of the excitation current is calculated as 695 ns for the case with the MPC system (dashed line) and 930 ns for the case without (solid line). Therefore, the result is 235 ns faster with the MPC system. Thus, the effectiveness
66
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
Fig. 10. Cross sectional view of the kicker magnet.
Table 4 Design parameters of the fast extraction kicker system. Extraction energy
30 GeV
Total kick angle Horizontal aperture Vertical aperture Magnet inductance Charging voltage Excitation current Rise time Flatness Flat-top length
6.08 mrad 150 mm 130 mm 3 μH 33 kV 6.5 kA o 1.1 μs (1–99%) o 1% 4.5 μs Fig. 12. Measured voltage waveform applied to the saturable reactor and the kicker magnet.
Fig. 11. Circuit schematic of the load system.
of the MPC system for sharpening the current rise is confirmed. In the calculation, the rise time of the excitation current is defined as the time it takes to rise from 1% to 99% of peak value.
3. Evaluation The fast extraction kicker system has been developed. To obtain sufficient field uniformity in the horizontal direction, an H-shaped magnet loaded with NiZn ferrites (CMD5005, [9]) is employed
Fig. 13. Measured voltage waveform applied to the kicker magnet.
(see Fig. 10). Design parameters of the developed fast extraction kicker system are summarized in Table 4. To evaluate the performance of the MPC system by saturable inductors in the newly developed kicker system, the excitation current and the voltages (Vin and Vmag in Fig. 11) were measured during high-voltage operation with a voltage of 30 kV charged to the PFN. The results are shown in Figs. 12–14. During the rise time of the input voltage, Vin, no voltage is applied to the kicker magnet because the high impedance of the MPC system is maintained with unsaturated core materials of the saturable inductors (see Fig. 13). Thus, no excitation current flows
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
67
bunch operation, a new kicker power supply and magnet have been developed. A lumped constant type kicker magnet is employed for its structural simplicity and resulting stability during high-voltage operation. By simulating the circuit, it was found that a slowly rising voltage applied to the kicker magnet disturbed the sharp rise of the excitation current. Therefore, adoption of a MPC system by saturable inductors was investigated. A circuit simulation confirmed the ability of the MPC system to sharpen the rising current. Through a system evaluation with a voltage of 30 kV charged to the PFN, the effectiveness of the saturable inductors for the pulse compression in the kicker magnet system was also confirmed. A rise time of 1 μs, which is less than the required value of 1.1 μs, was achieved in the measurement. Fig. 14. Measured excitation current waveform. The rise time of the excitation current was measured from 1% to 99% of the full strength. The required rise time of less than 1.1 μs was achieved in this measurement.
to the kicker magnet (see Fig. 14). Once the input voltage reaches a certain value, the core materials of the MPC system become saturated and the impedance of the MPC system drops to a negligibly small value. Then, most of the input voltage is applied to the kicker magnet. Thus, with a relatively higher applied voltage, the excitation current starts to flow to the kicker magnet. This results in a sharp rising of the excitation current. The rise time during which the excitation current increases its value from 1% to 99% of the maximum value was measured to be 1 μs in this operation. 4. Conclusion The main ring synchrotron began operation in 2010, at which time only six proton beams were extracted because the fast extraction kicker system could not satisfy the required rise time. To recover eight-
Acknowledgments The authors are grateful for the continuous support by Professor H. Kobayashi and Professor M. Yoshioka. References [1] Accelerator Technical Design Report for J-PARC, KEK Report, 2002–13, 2003. [2] T2K collaboration, The T2K experiment, Nuclear Instruments and Methods Physics Research A, 659, 2011, pp. 106–135. [3] K. Koseki, Nuclear Instruments and Methods Physics Research A 729 (2013) 3. [4] W.S. Melville, The use of saturable reactors as discharge devices for pulse generators, Proceedings of the IEE Radio Section, vol. 98, part. 3, 1951, pp. 185– 207. [5] Dongdong Zhang, et al., IEEE Transactions on Dielectrics and Electrical Insulation 18 (4) (2011) 1151. [6] Jaegu Choi, Journal of Electrical Engineering and Technology 5 (3) (2010) 484. [7] R.S. Shinde, et al., IEEE Transactions on Applied Superconductivity 12 (1) (2002) 262. [8] E.B. Forsyth, et al., The RHIC injection fast kicker, in: Proceedings of the PAC, 1995. [9] Ceramic Magnetics Inc., 〈http://www.cmi-ferrite.com/〉.
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
The fast extraction kicker for J-PARC with a novel pulse compression system Kunio Koseki n, Hiroshi Matsumoto High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 30 August 2013 Received in revised form 2 December 2013 Accepted 9 December 2013 Available online 27 December 2013
A fast extraction kicker magnet for the main ring of J-PARC has been developed. A lumped constant type magnet is employed for its structural simplicity and stability in high-voltage operation. A disadvantage of the lumped constant type, a slow rise time, was alleviated by the adoption of a newly developed magnetic pulse compression system. The effectiveness of the magnetic pulse compression system in sharpening the excitation current was confirmed both by a circuit simulation and experimentally. The newly developed fast extraction kicker system was operated successfully with a 30 kV charging voltage of the pulsed power supply. The required rise time of less than 1.1 μs was achieved in the measurement. & 2013 Elsevier B.V. All rights reserved.
Keywords: Kicker magnet Magnetic pulse compression Saturable inductor
1. Introduction One of the most important experimental projects at the main ring synchrotron of J-PARC [1] is the T2K experiment [2]. Eight proton beams are accelerated up to 30 GeV and extracted by five kicker magnets in a synchronous manner. Because the extraction is performed within a single circulation of the beams, the deflecting magnetic field generated by the kickers must be excited within 1.1 μs. The layout of J-PARC is depicted in Fig. 1. The design parameters of the main ring synchrotron are summarized in Table 1. The main ring synchrotron began operation in 2010, at which time only six proton beams were extracted because the fast extraction kicker system could not satisfy the required rise time. After intensive investigation, it was found that a parasitic inductance of the pulse forming network (PFN) disturbed the sharp rise of the excitation current by forming a resonant structure with an energy storage capacitor at a relatively lower frequency. The effect is more serious in a low-impedance PFN circuit because the energy storage capacitance is larger. Thus, it was concluded that the reason of the slow rise time of the fast extraction kicker system was the characteristic impedance of as low as 5 Ω. To recover eight-bunch operation in the main ring, a new kicker power supply with reduced parasitic inductance in the PFN circuit has been developed [3]. To minimize the cost and the length of the upgrade term, high-voltage transmission cables installed for the existing system were reutilized. Thus, the characteristic impedance of the new kicker power supply was chosen
n
Corresponding author. Tel.: þ 81 29 864 5200 4698. E-mail address: [email protected] (K. Koseki).
0168-9002/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nima.2013.12.040
to be 5 Ω as in the existing system. Moreover, it was decided to develop a new fast extraction kicker magnet with a sufficiently large aperture for a future upgrade of the beam intensity. Because of its structural simplicity and stability in high-voltage operation, the fast extraction kicker employs a lumped constant magnet, which is equipped with a ferrite-loaded single-turn coil. The rise time of the lumped constant magnet is determined by the ratio of the coil inductance and the characteristic impedance of the system. Therefore, achieving a sharp rise time is difficult in a low-impedance system. Moreover, it is impossible to fully eliminate the disturbing effect induced by the parasitic inductance in the PFN circuit. To overcome the disadvantage of the lumped constant magnet, utilization of a saturable inductor as a magnetic pulse compression (MPC) system [4–6] was evaluated. The MPC system acts as a magnetic switch that sharpens the rise time of the output pulses by utilizing the nonlinearity of the ferromagnetic core materials. It was thought that successful adoption of the MPC system would achieve a sharp rise in the excitation current with a simple circuit configuration even in a low-impedance kicker system. In this paper, the operational principles of the MPC system to sharpen the rise time of the excitation current of the fast extraction kicker magnet of J-PARC are reported in detail. Moreover, the results of the successful high-voltage operation for evaluation of the performance of the newly developed MPC system with the lumped constant magnet are reviewed. 2. Simulation study The conceptual circuit schematic of the fast extraction kicker system is depicted in Fig. 2. The pulsed power supply consists of
64
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
two thyratrons, a blumlein pulse forming network, and a pulse transformer. The excitation current generated by the pulsed power supply is transmitted by high-voltage coaxial cables to the magnet. The kicker magnet employs the lumped constant type. Lumped constant type kicker magnets are widely used for various extraction systems in accelerators [7,8]. Structural simplicity, which contributes to reliability in high-voltage operation, is the main advantage of the lumped constant type. This section describes simulations that were performed based on the circuit schematic depicted in Fig. 2 to evaluate the rise time of the excitation current. In the circuit simulation, parameters as summarized in Table 2 were employed. The parasitic inductance of the PFN circuit was modeled as a series inductance of 20 nH to the energy storage capacitor.
Therefore, the excitation current to the magnet, Imag, is expressed as Z τrise 1 V mag dt; ð1Þ I mag ¼ Lmag 0
2.1. Characteristic of lumped constant magnet
where Lmag is the inductance of the magnet and Vmag is the applied voltage across the magnet. A circuit simulation was performed to evaluate Eq. (1) and other effects from the pulsed power supply. The saturable inductor depicted in Fig. 2 as a MPC system was removed from the simulation for simplicity. The excitation current waveform from the circuit simulation is shown in Fig. 3. Fig. 4 shows the applied voltage across the kicker magnet. From a comparison of Figs. 3 and 4, the validity of Eq. (1) is confirmed. Moreover, it can be seen that the slowly rising leading edge of the applied voltage to the kicker magnet is one of the reasons for the slow rise time of the excitation current. A natural approach is to apply a higher voltage to the magnet over a shorter period of time to achieve a faster rise time of the excitation current.
The lumped constant kicker magnet is a single-turn coil loaded with ferrite cores, so the impedance is treated as an inductance.
2.2. Magnetic switch In the previous section, it was noted that the slowly rising leading edge of the applied voltage to the magnet disturbs the sharp rising of the excitation current. Therefore, adoption of a MPC system as a solution for sharpening the rise time of the excitation current was evaluated. The MPC system utilizes the nonlinearity of ferromagnetic core materials and acts as a magnetic switch. During the rising period of the applied voltage, the high impedance of the MPC system is maintained by the unsaturated core materials of the inductors. Therefore, no excitation current flows to the kicker magnet. Once the voltage reaches its peak value, the core materials are saturated. At this time, the excitation current starts to flow with relatively higher applied voltage. Consequently, the rise of the excitation current, which is defined as the integral of the applied voltage, is sharpened. To evaluate the pulse sharpening effect by the MPC system, a circuit simulation was performed. The results are shown in Figs. 5–8.
Fig. 1. Layout of J-PARC.
Table 1 Design parameters of the main ring of J-PARC. Injection energy
3 GeV
Extraction energy Circumference Average radius Repetition rate Revolution period at 30 GeV
30 GeV 1567.5 m 249.475 m 0.3 Hz 5.2 μs
Table 2 Parameters employed in the circuit simulation. Characteristic impedance
5Ω
PFN inductance PFN capacitance Magnet inductance Low pass filter resistance Low pass filter capacitance Damping resistor of filter
500 nH 20 nF 3 μH 5Ω 20 nF 50 Ω
Fig. 2. Conceptual circuit schematic of the fast extraction kicker system.
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
65
Fig. 7. Simulated voltage waveform applied to the MPC system. Fig. 3. Simulated excitation current waveform.
Fig. 8. Simulated voltage waveform applied to the kicker magnet. Fig. 4. Simulated voltage applied to the lumped constant type kicker magnet. Table 3 Design parameters of the magnetic pulse compression system. Initial inductance
380 μH
Total cross sectional area Core material Saturation flux density
2.86 10 3 m2 FT-3M 1.23 T
Fig. 5. Simulated current waveform to the kicker magnet with the MPC system.
Fig. 9. Comparison of the simulated current waveforms. The dashed and solid lines show the rise of the excitation current waveform with and without the MPC system, respectively.
Fig. 6. Simulated input voltage waveform to the load system.
In the simulation, a saturable inductor based on the parameters summarized in Table 3 was used. The input voltage transmitted from the pulsed power supply is depicted in Fig. 6. Before the saturation of the MPC system, most of the input voltage is applied only to the MPC system (see Fig. 7) because the impedance of the saturable inductor is sufficiently higher than that of the kicker magnet. Therefore, no excitation current flows during this period. At the point at which the input
voltage reaches its peak value, the MPC system becomes saturated and its impedance drops to a negligibly small value. Then, most of the input voltage is applied only to the kicker magnet (see Fig. 8). Thus, the rising of the excitation current is sharpened by the relatively higher voltage applied to the kicker magnet. To illustrate the effectiveness of the MPC system, an enlarged view of the simulated excitation currents during the rise period is depicted in Fig. 9. The rise time of the excitation current is calculated as 695 ns for the case with the MPC system (dashed line) and 930 ns for the case without (solid line). Therefore, the result is 235 ns faster with the MPC system. Thus, the effectiveness
66
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
Fig. 10. Cross sectional view of the kicker magnet.
Table 4 Design parameters of the fast extraction kicker system. Extraction energy
30 GeV
Total kick angle Horizontal aperture Vertical aperture Magnet inductance Charging voltage Excitation current Rise time Flatness Flat-top length
6.08 mrad 150 mm 130 mm 3 μH 33 kV 6.5 kA o 1.1 μs (1–99%) o 1% 4.5 μs Fig. 12. Measured voltage waveform applied to the saturable reactor and the kicker magnet.
Fig. 11. Circuit schematic of the load system.
of the MPC system for sharpening the current rise is confirmed. In the calculation, the rise time of the excitation current is defined as the time it takes to rise from 1% to 99% of peak value.
3. Evaluation The fast extraction kicker system has been developed. To obtain sufficient field uniformity in the horizontal direction, an H-shaped magnet loaded with NiZn ferrites (CMD5005, [9]) is employed
Fig. 13. Measured voltage waveform applied to the kicker magnet.
(see Fig. 10). Design parameters of the developed fast extraction kicker system are summarized in Table 4. To evaluate the performance of the MPC system by saturable inductors in the newly developed kicker system, the excitation current and the voltages (Vin and Vmag in Fig. 11) were measured during high-voltage operation with a voltage of 30 kV charged to the PFN. The results are shown in Figs. 12–14. During the rise time of the input voltage, Vin, no voltage is applied to the kicker magnet because the high impedance of the MPC system is maintained with unsaturated core materials of the saturable inductors (see Fig. 13). Thus, no excitation current flows
K. Koseki, H. Matsumoto / Nuclear Instruments and Methods in Physics Research A 739 (2014) 63–67
67
bunch operation, a new kicker power supply and magnet have been developed. A lumped constant type kicker magnet is employed for its structural simplicity and resulting stability during high-voltage operation. By simulating the circuit, it was found that a slowly rising voltage applied to the kicker magnet disturbed the sharp rise of the excitation current. Therefore, adoption of a MPC system by saturable inductors was investigated. A circuit simulation confirmed the ability of the MPC system to sharpen the rising current. Through a system evaluation with a voltage of 30 kV charged to the PFN, the effectiveness of the saturable inductors for the pulse compression in the kicker magnet system was also confirmed. A rise time of 1 μs, which is less than the required value of 1.1 μs, was achieved in the measurement. Fig. 14. Measured excitation current waveform. The rise time of the excitation current was measured from 1% to 99% of the full strength. The required rise time of less than 1.1 μs was achieved in this measurement.
to the kicker magnet (see Fig. 14). Once the input voltage reaches a certain value, the core materials of the MPC system become saturated and the impedance of the MPC system drops to a negligibly small value. Then, most of the input voltage is applied to the kicker magnet. Thus, with a relatively higher applied voltage, the excitation current starts to flow to the kicker magnet. This results in a sharp rising of the excitation current. The rise time during which the excitation current increases its value from 1% to 99% of the maximum value was measured to be 1 μs in this operation. 4. Conclusion The main ring synchrotron began operation in 2010, at which time only six proton beams were extracted because the fast extraction kicker system could not satisfy the required rise time. To recover eight-
Acknowledgments The authors are grateful for the continuous support by Professor H. Kobayashi and Professor M. Yoshioka. References [1] Accelerator Technical Design Report for J-PARC, KEK Report, 2002–13, 2003. [2] T2K collaboration, The T2K experiment, Nuclear Instruments and Methods Physics Research A, 659, 2011, pp. 106–135. [3] K. Koseki, Nuclear Instruments and Methods Physics Research A 729 (2013) 3. [4] W.S. Melville, The use of saturable reactors as discharge devices for pulse generators, Proceedings of the IEE Radio Section, vol. 98, part. 3, 1951, pp. 185– 207. [5] Dongdong Zhang, et al., IEEE Transactions on Dielectrics and Electrical Insulation 18 (4) (2011) 1151. [6] Jaegu Choi, Journal of Electrical Engineering and Technology 5 (3) (2010) 484. [7] R.S. Shinde, et al., IEEE Transactions on Applied Superconductivity 12 (1) (2002) 262. [8] E.B. Forsyth, et al., The RHIC injection fast kicker, in: Proceedings of the PAC, 1995. [9] Ceramic Magnetics Inc., 〈http://www.cmi-ferrite.com/〉.