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Journal Articles

Vacuum tube operation analysis under multi-harmonic driving and heavy beam loading effect in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*

Nuclear Instruments and Methods in Physics Research A, 835, p.119 - 135, 2016/11

 Times Cited Count:3 Percentile:36.52(Instruments & Instrumentation)

A magnetic alloy loaded cavity is used to generate multi-harmonic rf voltage in J-PARC RCS. However, a vacuum tube operation analysis under the multi-harmonic driving is very complicated because many variables should be solved with a self consistency. At the conventional operation analysis, a hand work by tracing the constant current curve of the tube was performed, or an appropriate single harmonic wave form was assumed. We have developed a numerical analysis code which calculates the vacuum tube operation automatically and it realizes the multi-harmonic vacuum tube operation analysis. The code is verified at the high power beam acceleration test and we confirm the calculation results are consistent with the measurement ones. We can calculate the vacuum tube operation precisely by using the code, and it will contribute to improving the quality of the beam in the high intensity proton synchrotron.

Journal Articles

Simulation of phase modulation for longitudinal emittance blow-up in J-PARC MR

Yamamoto, Masanobu; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Schnase, A.*; Shimada, Taihei; Takagi, Akira*; Takata, Koji*; et al.

JPS Conference Proceedings (Internet), 8, p.012015_1 - 012015_6, 2015/09

The J-PARC MR provides a coasting proton beam for nuclear physics experiments by slow extraction. The longitudinal emittance should be enlarged until the MR flat top to mitigate the microwave instability. We have investigated a Phase Modulation (PM) method by using a High Frequency Cavity (HFC) to increase the emittance. We have performed extensive simulation studies to find the appropriate parameters of the PM through the particle tracking simulation. We found that the effective HFC frequency has linear dependence with the PM frequency, where the emittance is smoothly enlarged. Furthermore, we found that the required HFC voltage is inverse proportional to the square root of the duration time of the PM. These PM properties will be used for the design of the HFC. We describe the particle tracking simulation results of controlled emittance blow-up by the PM.

Journal Articles

High intensity single bunch operation with heavy periodic transient beam loading in wide band RF cavities

Tamura, Fumihiko; Hotchi, Hideaki; Schnase, A.*; Yoshii, Masahito*; Yamamoto, Masanobu; Omori, Chihiro*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; et al.

Physical Review Special Topics; Accelerators and Beams, 18(9), p.091004_1 - 091004_8, 2015/09

 Times Cited Count:4 Percentile:36.33(Physics, Nuclear)

The RCS in the J-PARC was originally designed to accelerate two high intensity bunches, while some of neutron experiments in the MLF and a muon experiment using MR beams require a single bunch operation mode. The beam intensity in the single bunch operation has been limited by longitudinal beam losses due to the rf bucket distortions by the wake voltage of the odd harmonics in the wide band MA cavities. We installed an additional rf feedforward system to compensate the wake voltages of the odd harmonics (h=1,3,5). The longitudinal beam losses during the single bunch acceleration disappeared with feedforward for the odd harmonics. We also confirmed that the beam quality in the single bunch acceleration are similar to that of the normal operation with two bunches. Thus, high intensity single bunch acceleration at the intensity of 2.3$$times$$10$$^{13}$$ protons per bunch has been achieved in the J-PARC RCS.

Journal Articles

Ribbon thickness dependence of the magnetic alloy core characteristics in the accelerating frequency region of the J-PARC synchrotrons

Nomura, Masahiro; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takata, Koji*; Toda, Makoto*; Yoshii, Masahito*; et al.

Nuclear Instruments and Methods in Physics Research A, 749, p.84 - 89, 2014/06

 Times Cited Count:1 Percentile:11.75(Instruments & Instrumentation)

We have been developing high shunt impedance Magnetic Alloy (MA) cores. The MA core shunt impedance is a key parameter to achieve a higher field gradient for increasing a beam power. We increase the MA core shunt impedance by two different ways. One way is applying an external magnetic field during annealing to increase the MA core magnetic properties. The other way is using thinner ribbons to reduce the eddy current. In this paper, we discuss the latter way.

Journal Articles

Momentum loss during slow extraction in the J-PARC MR and its countermeasures

Tamura, Fumihiko; Yamamoto, Masanobu; Omori, Chihiro*; Yoshii, Masahito*; Schnase, A.*; Nomura, Masahiro; Tomizawa, Masahito*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.125 - 129, 2014/06

For the slow extraction in the J-PARC MR, the rf voltage ins the cavities is turned off after finishing the acceleration to obtain a coasting beam. During the debunching process, the average momentum decrease due to the longitudinal coupling impedances in the MR. The decelatation continues until a well debunchedbeam is foarmed. The deceraration causes a reduction of the extraction efficiency due to the chromatic effects. In the J-PARC MR, a momentum loss has been observed at a relatively low beam power. To achieve higher beam power with keeping the high extraction efficiency, measures against the momentum loss are necessary. In this article, we report the observations and simulation results of the momentum losses. We adopt the rf feedforward method to cancel the wake voltage in the cavity as a measure of the momentum loss. By the feedforward, the momentum loss is significantly reduced. We achieve a high extraction efficiency, 99.5%, at the beam power of 20 kW.

Journal Articles

Study of high impedance magnetic alloy core

Nomura, Masahiro; Yamamoto, Masanobu; Shimada, Taihei; Tamura, Fumihiko; Omori, Chihiro*; Toda, Makoto*; Hasegawa, Katsushi*; Hara, Keigo*; Yoshii, Masahito*; Schnase, A.*

Proceedings of 10th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.217 - 220, 2014/06

J-PARC RCS and MR employ RF cavities loaded with Magnetic Alloy (MA) cores. To achieve the high shunt impedance, we measured the shunt impedance with changing the core filling factor, ribbon thickness, and magnetization process. The shunt impedance was reduced in despite of the filling factor increase because the strong winding tension deteriorate the magnetic property. The MA core with thin ribbons and the MA core that is magnetized by a rotation process show high permeability in the accelerating frequency region, and those MA cores show the high shunt impedance consequently.

Journal Articles

Various usages of wall current monitors for commissioning of RF systems in J-PARC synchrotrons

Tamura, Fumihiko; Yamamoto, Masanobu; Schnase, A.; Yoshii, Masahito*; Omori, Chihiro*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hara, Keigo*; Hasegawa, Katsushi*

Proceedings of 1st International Beam Instrumentation Conference (IBIC 2012) (Internet), p.63 - 65, 2013/06

Wall current monitors (WCM) for RF system commissioning are installed in the J-PARC synchrotrons, the RCS and the MR. The WCM signals are used for diagnosis to adjust the RF system parameters. For the diagnosis, the WCM signals are taken by an oscilloscope with the revolution clock signal generated by the LLRF control system, and slices of the WCM waveform with lengths of the revolution periods are generated. By stacking the slices, one can get a mountain plot, which shows motions of bunches and variations of the bunch shapes. Also, time variations of the bunching factor, which are important for acceleration of high intensity proton beams, are obtained. The harmonic analysis is performed on the WCM signal and the cavity voltage monitor signal. By using complex amplitudes of them, one can calculate the impedance seen by the beam. The RF parameters for high intensity beams have been successfully adjusted by using these analyses.

Journal Articles

Inner diameter change over the years of MA cores of RF-cavities at the J-PARC 3 GeV synchrotron

Shimada, Taihei; Nomura, Masahiro; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*; Schnase, A.*; et al.

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2750 - 2752, 2013/06

no abstracts in English

Journal Articles

Commissioning of beam loading compensation system in the J-PARC MR

Tamura, Fumihiko; Omori, Chihiro*; Yamamoto, Masanobu; Yoshii, Masahito*; Schnase, A.*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2540 - 2542, 2013/06

Beam loading compensation is indispensable to accelerate high intensity proton beams in the J-PARC MR. The MA-loaded rf cavities in the MR are driven by the single harmonic (h = 9) rf signals, while the cavity frequency response covers also the neighbor harmonics (h = 8, 10). The wake voltage induced by the beam consists of the three harmonics (h = 8, 9, 10). We employ the rf feedforward method to compensate the beam loading of these harmonics. The full-digital feedforward system was developed for the MR. We have successfully commissioned the feedforward patterns for all of eight cavities by using high intensity beams with 1.0$$times$$10$$^{14}$$ ppp. We present the commissioning results. The impedance seen by the beam is reduced and the longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, high power beam operation at the beam power of 200 kW has been achieved.

Journal Articles

Influence of core winding tension and ribbon quality on the MA core RF characteristics

Nomura, Masahiro; Schnase, A.*; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*

Proceedings of 4th International Particle Accelerator Conference (IPAC '13) (Internet), p.2747 - 2749, 2013/06

During the development of Magnetic Alloy (MA) cores for RF cavities, the core shunt impedance was increased by lowering a core winding tension to improve the electrical insulation between MA ribbon layers. The lower winding tension reduced the core filling factor. The core shunt impedance might be reduced according to the core filling factor reduction. We study the influence of improving the electrical insulation and lowering the core winding tension on the core shunt impedance.

Journal Articles

Multiharmonic RF feedforward system for compensation of beam loading and periodic transient effects in magnetic-alloy cavities of a proton synchrotron

Tamura, Fumihiko; Omori, Chihiro*; Yamamoto, Masanobu; Yoshii, Masahito*; Schnase, A.*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*

Physical Review Special Topics; Accelerators and Beams, 16(5), p.051002_1 - 051002_12, 2013/05

 Times Cited Count:5 Percentile:42.24(Physics, Nuclear)

Beam loading compensation is a key for acceleration of a high intensity proton beam in the MR of J-PARC. Magnetic alloy loaded rf cavities with a Q value of 22 are used to achieve high accelerating voltages. The cavity is driven by a single harmonic (h = 9) rf signal while the cavity frequency response also covers the neighbor harmonics (h = 8, 10). Therefore the wake voltage induced by the high intensity beam consists of the three harmonics, h = 8, 9, 10. We employ the rf feedforward method to compensate the beam loading ofthese three harmonics (h = 8, 9, 10). The full-digital multiharmonic feedforward system was developed for the MR. The commissioning of the feedforward system has been performed by using high intensity beams with 1.0$$times$$10$$^{14}$$ protons per pulse. The longitudinal oscillations due to the beam loading are reduced. By the beam loading compensation, stable high power beam operation is achieved.

Journal Articles

Iterative Kappa magnet pole shape optimization for MA core annealing

Schnase, A.; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Omori, Chihiro*; Shimada, Taihei; Tamura, Fumihiko; Toda, Makoto*; Yamamoto, Masanobu; Yoshii, Masahito*

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1204 - 1208, 2012/08

Journal Articles

Commissioning of multiharmonic feedforward system for J-PARC MR

Tamura, Fumihiko; Omori, Chihiro*; Yamamoto, Masanobu; Yoshii, Masahito*; Schnase, A.; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hasegawa, Katsushi*; Hara, Keigo*

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.89 - 93, 2012/08

For acceleration of high intensity proton beam, it is important to compensate the beam loading due to the wake voltages in accelerating cavities. The Q-value of the magnetic-alloy cavity in the J-PARC MR is set to 22 to cover the frequency sweep of the accelerating harmonic ($$h$$=9) without tuning bias loop. The cavity bandwidth also covers the neighbor harmonics ($$h$$=8, 10). Thus, the wake voltage consists of the accelerating harmonic ($$h$$=9) and the neighbor harmonics ($$h$$=8, 10). We employ the RF feedforward method to compensate the multiharmonic beam loading. The full-digital feedforward system has been developed for the MR. We present the commissioning results of the system with high intensity (1.0$$times$$10$$^{14}$$ ppp) proton beams.

Journal Articles

Measurement of inner diameters of MA cores of RF-cavities of J-PARC 3 GeV synchrotron and diameter change over the years

Shimada, Taihei; Suzuki, Hiromitsu; Yamamoto, Masanobu; Schnase, A.; Toda, Makoto*; Omori, Chihiro*; Hara, Keigo*; Hasegawa, Katsushi*; Nomura, Masahiro; Tamura, Fumihiko; et al.

Proceedings of 9th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1143 - 1145, 2012/08

The RF cavities of J-PARC 3 GeV synchrotron use 198 MA cores. Buckling occurred in some cores since the operation starting on the October of 2007. We have measured the inner diameters of the cores as a part of the investigation to determine the cause of the buckling when the cavities were disassembled for maintenance. We noticed that deformations of the inner shapes of the cores related to its manufacturing process and that inner diameters change over year were not measured in the most of the cores without buckled cores. Furthermore, the effective manufacturing process of cores to avoid the buckling has be established. We are going to replace old type cores with new type cores in shutdown periods in summer every year.

Journal Articles

Simulation of controlled longitudinal emittance blow-up in J-PARC RCS

Yamamoto, Masanobu; Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Takagi, Akira*; et al.

Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.2952 - 2954, 2012/05

In J-PARC RCS, the high intensity beam is delivered to the MR. The longitudinal beam emittance at the RCS extraction should be optimized to avoid the beam loss after the MR injection. In order to match the longitudinal emittance shape between the RCS and the MR, it is desirable to enlarge the longitudinal emittance during the RCS acceleration. We have performed the particle tracking simulation for the controlled longitudinal emittance blow up in the RCS.

Journal Articles

RF feedforward system for beam loading compensation in the J-PARC MR

Tamura, Fumihiko; Yamamoto, Masanobu; Schnase, A.; Yoshii, Masahito*; Omori, Chihiro*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hara, Keigo*; Hasegawa, Katsushi*

Proceedings of 3rd International Particle Accelerator Conference (IPAC '12) (Internet), p.3924 - 3926, 2012/05

For acceleration of high intensity proton beams in the J-PARC MR, beam loading compensation is important. In the MA-loaded RF cavity in the MR, which has a $$Q$$-value in the order of 20, the wake voltage consists of the accelerating harmonic ($$h$$ = 9) and the neighbor harmonics ($$h$$ = 8, 10). We employ the RF feedforward method for the beam loading compensation, like in the J-PARC RCS, in which the impedance seen by the beam is greatly reduced by the feedforward. The full-digital feedforward system developed for the MR has a similar architecture to that of the RCS. The system compensates the beam loading of the important three harmonics ($$h$$ = 8, 9, 10). We present the structure of the RF feedforward system. Also, we report the preliminary results of the beam tests.

Journal Articles

A Convenient way to find an electrical insulation break of MA cores in J-PARC synchrotrons

Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Hara, Keigo*; Hasegawa, Katsushi*; Omori, Chihiro*; Toda, Makoto*; Yoshii, Masahito*

Nuclear Instruments and Methods in Physics Research A, 668, p.83 - 87, 2012/03

 Times Cited Count:4 Percentile:36.4(Instruments & Instrumentation)

We employ magnetic alloy core loaded RF cavities for the Japan Proton Accelerator Research Complex synchrotrons to achieve a high accelerating voltage. To improve the electrical insulation of MA cores, we conceptualized a convenient way to find an electrical insulation break by measuring the DC resistance in the radial directions of MA cores. We modified the core manufacturing process by evaluating the electrical insulation of MA cores from the radial resistance data, and thus we could improve the electrical insulation of MA cores.

Journal Articles

Impedance measurements of RF cavities in J-PARC synchrotrons

Nomura, Masahiro; Tamura, Fumihiko; Schnase, A.; Yamamoto, Masanobu; Hasegawa, Katsushi*; Shimada, Taihei; Hara, Keigo*; Toda, Makoto*; Omori, Chihiro*; Yoshii, Masahito*

Proceedings of 8th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1263 - 1266, 2011/12

J-PARC 3 GeV RCS and 50 GeV MR employ Magnetic Alloy (MA) loaded RF cavities to achieve a high accelerating voltage. RCS RF cavities employ MA un-cut cores and MR use MA cut cores. We report the impedance measurement results of the RCS RF cavities loaded MA cores without epoxy resin and effectiveness of coating of MR cutting core surface to prevent rusting. We also report the RF systems affected by the great East Japan earthquake.

Journal Articles

Condition of MA cut cores in the RF cavities of J-PARC main ring after several years of operation

Nomura, Masahiro; Schnase, A.; Shimada, Taihei; Tamura, Fumihiko; Yamamoto, Masanobu; Sato, Tomonori; Yamamoto, Masahiro; Ezura, Eiji*; Hara, Keigo*; Hasegawa, Katsushi*; et al.

Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.107 - 109, 2011/09

J-PARC 3 GeV Rapid Cycling Synchrotron (RCS) and 50 GeV Synchrotron (MR) employ the Magnetic Alloy (MA) loaded RF cavities. We observed the impedance reductions of MR RF cavities. Opening the RF cavities, we found that the impedance reductions were caused by the corrosion on the core cutting surfaces. The copper ions in the cooling water from hollow conductors of main magnets might accelerate the corrosion process.

Journal Articles

Performance of multi-harmonic RF feedforward system for beam loading compensation in the J-PARC RCS

Tamura, Fumihiko; Yamamoto, Masanobu; Omori, Chihiro*; Schnase, A.; Yoshii, Masahito*; Nomura, Masahiro; Toda, Makoto*; Shimada, Taihei; Hara, Keigo*; Hasegawa, Katsushi*

Proceedings of 2nd International Particle Accelerator Conference (IPAC 2011) (Internet), p.2733 - 2735, 2011/09

The beam loading compensation is a key part for acceleration of high intensity proton beams in the J-PARC RCS. In the wide-band MA-loaded RF cavity, the wake voltage consists of not only the accelerating harmonic component but also the higher harmonics. The higher harmonic components cause the RF bucket distortion. We employ the RF feedforward method to compensate the multi-harmonic beam loading. The full-digital feedforward system is developed, which compensates the first three harmonic components of the beam loading. We present the results of the beam test with a high intensity proton beam ($$2.5times 10^{13}$$ ppp). The impedance seen by the beam is greatly reduced, the impedance of the fundamental accelerating harmonic is reduced to less than 25 $$Omega$$ in a full accelerating cycle, while the shunt resistance of the cavity is in the order of 800 $$Omega$$. The performance of the feedforward system is promising for achievement of the design beam power, 1 MW, in the future.

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