Spatial polarization distribution measurements of gamma rays produced by inverse Compton scattering

Yang, Y.*; Taira, Yoshitaka*; Shizuma, Toshiyuki*; Omer, M.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.194 - 196, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-MOPB063

Study of operation above half-integer random resonance in the J-PARC RCS

Kojima, Kunihiro; Harada, Hiroyuki; Okabe, Kota; Chimura, Motoki; Saha, P. K.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.2244 - 2247, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-WEPS003

In the 3-GeV rapid cycling synchrotron of the Japan Proton Accelerator Research Complex, the beam power ramp-up aiming to surpass the design of 1 MW enhances the space charge effect and pushes the beam toward the structure resonance. To mitigate the beam loss, the operating point is required to be apart from the structure resonance corresponding to the beam power ramp-up, although any changes in the operating point lead to an increase in the beam loss due to the approach to other resonances. We recently compensated the horizontal half-integer resonance located just above the current operating point to address this issue, and we are now ready to explore a higher tune region than that. We confirmed in a tune survey that the vertical half-integer and linear sum resonances are substantially excited. In addition, the linear sum resonance is found to be well compensated by making a vertical local bump in the arc section.

Development of the diagnostic and transport beamline for the muon linac low-velocity section

Nakazawa, Yuga*; Cicek, E.*; Ishida, Katsuhiko*; Futatsukawa, Kenta*; Shimomura, Koichiro*; Otani, Masashi*; Kimura, Masato*; Kamioka, Shusei*; Yamazaki, Takayuki*; Mibe, Tsutomu*; et al.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.1163 - 1166, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-TUPS156

At the Japan Proton Accelerator Research Complex (J-PARC), low-emittance muon beams with a linear accelerator (linac) are proposed as a new approach to precisely measure the anomalous magnetic moment and electric dipole moment of the muon. Low-emittance muon beams can also be employed as new probes for non-destructive imaging techniques to see through structures. In the low-velocity section of the muon linac, a radio-frequency quadrupole linac (RFQ) and an interdigital H-mode drift tube linac (IH-DTL) are used to accelerate muons to = v/c = 0.08 and 0.28, respectively, at an operating frequency of 324 MHz. To reduce construction costs, the IH-DTL employs the alternating phase focusing (APF) method, which uses the transverse focusing force derived from the RF electric field. Because the APF method limits the transverse and longitudinal acceptances simultaneously, careful beam diagnostics and commissioning are essential to suppress the emittance growth derived from beam mismatches. As a result of the beam simulation, by conducting appropriate beam matching, the normalized rms emittance of 0.3 -mm-mrad and the transmission to the downstream detector of 97% was obtained. In this paper, the results of the tracking simulation and the development status of the diagnostic and transport beamlines in the low-velocity section are described.

Development of the beam separation test device to evaluate the electric field of non-destructive electrostatic septum

Nagayama, Shota; Kinsho, Michikazu; Harada, Hiroyuki; Yamada, Ippei; Chimura, Motoki; Kojima, Kunihiro; Yamamoto, Kazami; Shimogawa, Tetsushi*; Sato, Atsushi*

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.1025 - 1028, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-TUPB028

Slow extraction method of synchrotrons is used in nuclear and particle physics experiments, radiation therapy, and many other applications. In the slow extraction process, beam loss at the septum electrode, which separates the extracted beam from the circumferential side, induces activation and damage to the device. To solve this problem, we have devised an electric field measurement device named "Beam separation test device" to evaluate the two-dimensional electric field distribution of the nondestructive electrostatic septum that we are developing. The device consists of a prototype septum, horizontal and vertical wire scanners, and an electron gun installed on a movable stage fixed to a drive unit. This device measures the electric field by injecting an electron beam into the electric field and measuring the bending angle of the beam orbit. In developing this device, an additional optics system was designed to make a narrow electron beam to improve the measurement accuracy of the electric field distribution. In addition, we designed a beam dump that reduces secondary electron emission by utilizing energy loss when particles collide with materials. According to calculations of secondary electron emission, this beam dump can reduce secondary-emission into the chamber by up to 98%.

Performance of the diode stack with resistors to suppress beam instability at the J-PARC RCS

Shobuda, Yoshihiro; Saha, P. K.; Yamada, Ippei; Okabe, Kota

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.2240 - 2243, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-WEPS002

Beam instability in the 3-GeV Rapid Cycling Synchrotron (RCS) at the Japan Proton Accelerator Research Complex (J-PARC) is primarily caused by the impedance of its eight kickers. The kicker design, with one end shorted and the other open, saves power during beam extraction but excites instability. To mitigate this, we developed a diode stack with resistors installed at the open ends of four kickers. This configuration effectively suppresses instability for smaller-emittance beams delivered to J-PARC's Main Ring (MR).

Development of a compact high voltage pulse power supply of MARX-type for muon linac klystron

Takayanagi, Tomohiro; Fuwa, Yasuhiro; Otani, Masashi*; Shimomura, Koichiro*; Mibe, Tsutomu*; Kondo, Yasuhiro; Futatsukawa, Kenta*; Cicek, E.*; Nakazawa, Yuga*; Tokuchi, Akira*; et al.

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.1884 - 1886, 2025/11

https://doi.org/10.18429/JACoW-IPAC2025-WEPB062

We have been developing a compact pulse power supply with high output and high frequency specifications: output voltage of 75 kV, current of 40 A, main pulse width of 50 us, and repetition frequency of 25 Hz for short pulse waveforms. This power supply is used to drive klystron for muon linac, which requires high stability and reliability. It uses a next-generation power semiconductor SiC-MOSFET with excellent characteristics of ultra-high withstand voltage of 13 kV and low loss, which was realized through the technological development of wide band gap semiconductor devices. Combining this SiC-MOSFET with the Marx circuit that generates ultra-high voltage pulses will realize a more compact pulse power supply with lower losses than conventional ones. In addition, future ap-plications in portable accelerators are also possible. In this presentation, the circuit design of the Marx power supply will be reported.

Neutron target for high-intensity operation at J-PARC MLF

Haga, Katsuhiro; Naoe, Takashi; Kogawa, Hiroyuki; Wakui, Takashi; Kinoshita, Hidetaka; Harada, Masahide

Proceedings of 16th International Particle Accelerator Conference (IPAC25) (Internet), p.3245 - 3249, 2025/06

https://doi.org/10.18429/JACoW-IPAC2025-FRXD1

In April 2024, the beam power at MLF attained 950 kW for the first time for long term user operation, and the beam power at the 3 GeV rapid cycle synchrotron (RCS) outlet was raised to 1 MW. This accomplishment means that the goal of the stable operation of the neutron source with 1 MW was almost achieved at last, and it's time to go on to the new stage of the neutron source R&D. There are two major challenges for the mercury target in the next stage. One is to attain the long-term operation of a mercury target. The service life of the target vessel is primarily determined by cavitation damage that occurs on the inner surface due to the injection of high-intensity pulsed proton beams. Until now, the vessel has been replaced annually to inspect the extent of the damage. However, based on the damage data obtained during 1 MW high-power operation, it has been determined that the vessel can withstand long-term operation for more than two years. Therefore, a new target vessel, which was replaced in 2024, is scheduled to be used for an extended period through 2027. Furthermore, since there are plans to increase the pulse intensity of the RCS in the future, it will be necessary to develop more effective pitting damage suppression techniques and new target vessels that can withstand even stronger proton beam pulses. In this presentation, the present status of the neutron source of MLF and future operation plans will be shown.