Pulse shape discrimination in JSNS

Dodo, Taku; Haga, Katsuhiro; Harada, Masahide; Hasegawa, Shoichi; Kasugai, Yoshimi; Kinoshita, Hidetaka; Masuda, Shiho; Meigo, Shinichiro; Sakai, Kenji; Suzuya, Kentaro; et al.

Progress of Theoretical and Experimental Physics (Internet), 2025(2), p.023H02_1 - 023H02_8, 2025/02

https://doi.org/10.1093/ptep/ptaf016

Dataset of nuclide production from nuclear capture reaction of negative muon based on Monte Carlo simulation

Yamaguchi, Yuji; Harada, Masahide; Haga, Katsuhiro

JAEA-Data/Code 2024-008, 91 Pages, 2024/08

JAEA-Data-Code-2024-008.pdf:1.24MB
JAEA-Data-Code-2024-008-appendix(CD-ROM).zip:0.09MB

We have produced a dataset of the yields of radionuclides produced by the nuclear capture of negative muons applying Monte Carlo calculation due to scarce experimental data for the sake of radiation safety of experimental facilities which can provide negative muons. The dataset covers all the stable targets of natural elements. The use of the dataset is described in an example of radioactive estimation for a negative-muon-irradiated sample. The dataset reported is fundamental data expected to be utilized in experiments with negative muons of various fields including radiation safety.

Technical note for the cavitation damage inspection for interior surface of the mercury target vessel, 2; Damage depth measurement for cavitation erosion

Naoe, Takashi; Wakui, Takashi; Kinoshita, Hidetaka; Kogawa, Hiroyuki; Teshigawara, Makoto; Haga, Katsuhiro

JAEA-Technology 2023-022, 81 Pages, 2024/01

JAEA-Technology-2023-022.pdf:9.87MB

In the liquid mercury target system for the pulsed spallation neutron source of Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC), pressure waves that is generated by the high-energy proton beam injection simultaneously with the spallation reaction, resulting severe cavitation erosion damage on the interior surface of the mercury target vessel. Because the bubble of pressure wave-induced cavitation collapsing near the interior surface of the mercury target vessel with applying the large amplitude of localized impact on the surface. Since the wall thickness of the beam entrance portion of the target vessel is designed to be 3 mm to reduce thermal stress due to the internal heating, the erosion damage has the possibility to cause the vessel fatigue failure and mercury leakage originated from erosion pits during operation. To reduce the erosion damage by cavitation, a technique of gas microbubble injection into the mercury for pressure wave mitigation, and double-walled structure of the beam window of the target vessel has been applied. A specimen was cut from the beam window of the used mercury target vessel in order to investigate the effect of the damage mitigation technologies on the vessel, and to reflect the consideration of operation condition for the next target. We have observed cavitation damage on interior surface of the used mercury target vessel by cutting out the disk shape specimens. Damage morphology and depth of damaged surface were evaluated and correlation between the damage depth and operational condition was examined. The result showed that the erosion damage by cavitation is extremely reduced by injecting gas microbubbles and the damage not formed inside narrow channel of the double-walled structure for relatively high-power operated target vessels.

Optimization of mercury flow with microbubbles in the target-vessel design by means of machine learning

Kogawa, Hiroyuki; Futakawa, Masatoshi; Haga, Katsuhiro; Tsuzuki, Takayuki*; Murai, Tetsuro*

JAEA-Technology 2022-023, 128 Pages, 2022/11

JAEA-Technology-2022-023.pdf:9.0MB

In a mercury target of the J-PARC (Japan Proton Accelerator Research Complex), pulsed proton beams repeatedly bombard the flowing mercury which is confined in a stainless-steel vessel (target vessel). Cavitation damage caused by the propagation of the pressure waves is a factor of the life of the target vessel. As a measure to reduce damages, we developed a bubbler to inject the gas microbubbles into the flowing mercury, which can reduce the pressure waves. To operate the mercury target vessel stably with the 1 MW high-intensity proton beams, further reduction of the damage is required. The bubbler setting position should be closer to the beam window to increase the bubble population, which could enhance the reduction effect on the pressure waves and damage. However, the space at the beam window of the target vessel is restricted. The bubbler design and setting position as well as the vane design for the mercury flowing pattern are optimized by means of a machine learning technique to get more suitable bubble distribution, increasing in bubble population and optimizing bubble size nearby the beam window of the target vessel. The results of CFD analyses performed with 1000 cases were used for machine learning. Since the flow rate of mercury affects the temperature of the target vessel, this was used for the constraint condition. As a result, we found a design of mercury target vessel that can increase the bubble population by ca. 20% higher than the current design.

Development of the high-power spallation neutron target of J-PARC

Haga, Katsuhiro; Kogawa, Hiroyuki; Naoe, Takashi; Wakui, Takashi; Wakai, Eiichi; Futakawa, Masatoshi

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 13 Pages, 2022/03

The cross-flow type target was developed as the basic design of mercury target in J-PARC, and the design has been improved to realize the MW-class pulsed spallation neutron source. When the high-power and short-pulsed proton beam is injected into the mercury target, pressure waves are generated in mercury by rapid heat generation. The pressure waves induce the cavitation damages on the target vessel. Two countermeasures were adopted, namely, the injection of microbubbles into mercury and the double walled structure at the beam window. The bubble generator was installed in the target vessel to absorb the volume inflation of mercury and mitigate the pressure waves. Also, the double walled target vessel was designed to suppress the cavitation damage by the large velocity gradient of rapid mercury flow in the narrow channel of double wall. Finally, we could attain 1 MW beam operation with the duration time of 36.5 hours in 2020, and achieved the long term stable operation with 740 kW from April in 2021. This report shows the technical development of the high-power mercury target vessel in view of thermal hydraulics to attain 1 MW operation.

The JSNS detector

Ajimura, Shuhei*; Haga, Katsuhiro; Harada, Masahide; Hasegawa, Shoichi; Kasugai, Yoshimi; Kinoshita, Hidetaka; Masuda, Shiho; Meigo, Shinichiro; Sakai, Kenji; Suzuya, Kentaro; et al.

Nuclear Instruments and Methods in Physics Research A, 1014, p.165742_1 - 165742_15, 2021/10

https://doi.org/10.1016/j.nima.2021.165742

Unified mercury radioactivity monitoring system at J-PARC and its operation experiences

Harada, Masahide; Sekijima, Mitsuaki*; Morikawa, Noriyuki*; Masuda, Shiho; Kinoshita, Hidetaka; Sakai, Kenji; Kai, Tetsuya; Kasugai, Yoshimi; Muto, Giichi*; Suzuki, Akio*; et al.

JPS Conference Proceedings (Internet), 33, p.011099_1 - 011099_6, 2021/03

https://doi.org/10.7566/JPSCP.33.011099

In MLF at J-PARC, a unified mercury radioactivity monitor (UHAM) is installed to find an indication of failure of the mercury target and loop system by detecting radioactive materials leaked from the system with a -ray energy analysis with Germanium semi-conductor detectors (Ge detectors). It is composed of three units of sampling port and radiation monitors: (1) HAM for interstitial helium gas layer between the mercury vessel and surrounding water shroud of the mercury target, (2) CAM for atmosphere in the hot cell where the target loop is operated and (3) VAM for helium gas in the helium vessel where the target vessel is installed. Once any leakages of radioactive materials are detected, an alarm signal is issued immediately to the accelerator control system to stop beam operation. Software and hardware have been upgraded yearly. For example, two Ge detectors are used for HAM for redundancy, NaI Scintillation detectors are also used as supplemental for the Ge detector to keep availability of the system for high counting rate event. In April 2015, the UHAM activated when a small water coolant leakage from the water shroud of the mercury target occurred. VAM detected an abnormal increase of the counting rate in the helium vessel. It was also indicated that the measured radioactive nuclides were generated from the activation of the coolant (water) in the water shroud and not from the mercury.

Periodic level measurements of Materials and Life science experimental Facility in J-PARC

Harada, Masahide; Sakai, Motonobu*; Kurosawa, Takashi*; Haga, Katsuhiro

JPS Conference Proceedings (Internet), 33, p.011098_1 - 011098_5, 2021/03

https://doi.org/10.7566/JPSCP.33.011098

Materials and Life science experimental Facility (MLF) in J-PARC has a high-intense spallation neutron source and a high-intense muon source induced by 3-GeV and 1MW proton beam. To reduce beam loss, components of proton, neutron and muon beam lines are precisely aligned. However, a settlement of MLF caused by a building construction, installation of heavy shields, earthquakes, consolidation of basement, instrument installation (weight increase), and so on, was assumed in the design stage. Therefore, periodic level measurements in MLF was started from the design stage. A few tens of level measuring points are installed inside and outside MLF. The level measurements were done once per month in the construction stage and per year after operation start. In the construction stage of MLF, it was found that the MLF building largely settled by construction of the building and installation of many shields. And it was also found that The Great East Japan Earthquake on March 11, 2011, caused large settlements of MLF attached buildings. Figure 1 shows fluctuations of measured levels at representative points in each area from December 2011. No critical deterioration (small changes within 1.0 mm) could be detected. However, a few local settlements are found in the MLF building. In the presentation, periodic level measurement results at MLF will be introduced.

New design of high power mercury target vessel of J-PARC

Wakui, Takashi; Wakai, Eiichi; Kogawa, Hiroyuki; Naoe, Takashi; Hanano, Kohei*; Haga, Katsuhiro; Shimada, Tsubasa*; Kanomata, Kenichi*

Materials Science Forum, 1024, p.145 - 150, 2021/03

https://doi.org/10.4028/www.scientific.net/MSF.1024.145

To realize a high beam power operation at the J-PARC, a mercury target vessel covered with water shroud was developed. In the first step, to realize an operation at 500 kW, the basic structure of the initial design was followed and the connection method between the mercury vessel and the water shroud was changed. Additionally, the operation at a beam power of 500 kW was realized in approximately eight months. In the second step, to realize the operation at 1 MW, the new structure in which only rear ends of vessels were connected was investigated. Cooling of the mercury vessel is used to reduce thermal stress and thick vessels of the water shroud are used to increase stiffness for the internal pressure; therefore, it was adopted. The stress in each vessel was lower than the allowable stress based on the pressure vessel code criteria prescribed in the Japan Industrial Standard, and confirmation was obtained that the operation with a beam power of 1 MW could be conducted.

Conceptual design of an abnormality sign determination system for the general control system of the Materials and Life Science Experimental Facility at J-PARC

Sakai, Kenji; Oi, Motoki; Teshigawara, Makoto; Naoe, Takashi; Haga, Katsuhiro; Watanabe, Akihiko*

Journal of Neutron Research, 22(2-3), p.337 - 343, 2020/10

https://doi.org/10.3233/JNR-190133

For operating a spallation neutron source and a muon target safely and efficiently, a general control system (GCS) operates within Materials and Life Science Experimental Facility (MLF). GCS administers operation and interlock processes of many instruments under various operation status. Since the first beam injection in 2008, it has operated stably without any serious troubles for more than ten years. GCS has a data storage server storing operational data on status around target stations. It has functioned well to detect and investigate unusual situations by checking data in this server. For continuing stable operation of MLF in future, however, introduction of abnormality sign determination system (ASDS) will be necessary for picking up potential abnormalities of target stations caused by radiation damages, time-related deterioration and so on. It will judge abnormalities from slight state transitions of target stations based on analysis with various operational data throughout proton beams, target stations, and secondary beams during long-term operations. This report mentions present status of GCS, conceptual design of ASDS, and installation of an integral data storage server which can deal with various data for ASDS integrally.