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Journal Articles

Two-parameter model for optimizing target beam distribution with an octupole magnet

Meigo, Shinichiro; Oi, Motoki; Fujimori, Hiroshi*

Physical Review Accelerators and Beams (Internet), 23(6), p.062802_1 - 062802_24, 2020/06

 Times Cited Count:0 Percentile:100(Physics, Nuclear)

As hadron accelerators for such as the ADS and spallation neutron source achieve increasing beam power, damage to targets is becoming increasingly severe. To mitigate this damage, nonlinear beam optics based on octupole magnets is attractive. Nonlinear optics can decrease the beam-focusing hazard due to failure of the rastering magnet. As a side effect of nonlinear optics, the beam size is known to expand drastically compared with linear optics. Nonlinear effects have been studied via a simplified filament model that ignores beam-divergence spread at the octupole magnet. In this study, a new generalized model is proposed for application to an octupole magnet, regardless of the filament-model approximation. It is found that the transverse distribution obtained by beam tracking can be specified by the introduction of only two parameters, namely the normalized octupole strength of $$K^{*}_8$$ and the $$cot phi$$ of the phase advance. To achieve the two antagonistic requirements of reduction of the beam-peak density and minimization of the beam loss, the transverse distribution is surveyed for a large range of beam position. It is found that a bell-shaped distribution with $$K^{*}_8 sim$$ 1 and $$cot phi sim$$ 3 can satisfy requirements. This result is applied to beam transport in the spallation neutron source at J-PARC. The calculation result given by the present model shows good agreement with the experimental data, and the peak current density is reduced by 50% compared with the linear-optics case.

Journal Articles

New design and fabrication technology applied in mercury target vessel #8 of J-PARC

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

JPS Conference Proceedings (Internet), 28, p.081002_1 - 081002_6, 2020/02

A mercury target vessel of J-PRAC is designed with a triple-walled structure consisting of the mercury vessel and a double-walled water shroud with internal and external vessels. During the beam operation at 500 kW in 2015, small water leakages from a water shroud of the mercury target vessel occurred twice. Design, fabrication and inspection processes were improved based on the lessons learned from the target failures. The total length of welding lines at the front of the mercury target vessel decreases drastically to approximately 55% by adopting monolithic structure cut out from a block of stainless steel by the wire-electrical discharge machining. Thorough testing of welds by radiographic testing and ultrasonic testing was conducted. The fabrication of the mercury target vessel #8 was finished on September 2017 and the beam operation using it started. Stable beam operation at 500 kW has been achieved and it could experience the maximum beam power of 1 MW during a beam test.

Journal Articles

Development of profile monitors on target for high-intensity proton accelerators

Meigo, Shinichiro; Takei, Hayanori; Matsuda, Hiroki; Yuri, Yosuke*; Yuyama, Takahiro*

Proceedings of 16th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.515 - 519, 2019/07

no abstracts in English

Journal Articles

Ultrasonic inspection technique for weld part of mercury target vessel for spallation neutron source

Wakui, Takashi; Wakai, Eiichi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Takada, Hiroshi; Shintaku, Yohei*; Li, T.*; Kanomata, Kenichi*

Choompa Techno, 30(5), p.16 - 20, 2018/10

A mercury target vessel has been used for the spallation neutron source at J-PARC. It has a complicated multi-layered structure composed of a mercury target and a surrounding double-walled water shroud, which is assembled with thin plates (minimum thickness of 3 mm) by welding. Thus, welding inspection during the manufacturing process is important. We investigated the applicability of new ultrasonic inspections using specimens (thickness of 3 mm) with defects to improve the accuracy of welding inspection for the mercury target vessel. Immersion ultrasonic testing using a probe (frequency of 50 MHz) could detect a spherical defect with a diameter of 0.2 mm. The size was smaller than target value of 0.4 mm. The length of unwelded region estimated using the phased array ultrasonic testing corresponded with the actual length (0.8 - 1.5 mm).

Journal Articles

Development of profile monitors on target for high-intensity proton accelerators

Meigo, Shinichiro; Takei, Hayanori; Matsuda, Hiroki; Yuri, Yosuke*; Yuyama, Takahiro*

Proceedings of 15th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.1035 - 1039, 2018/08

no abstracts in English

Journal Articles

Beam instruments for high power spallation neutron source and facility for ADS

Meigo, Shinichiro

Proceedings of 61st ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams (HB 2018) (Internet), p.99 - 103, 2018/07

As the increase of beam power, beam instruments play an essential role in the Hadron accelerator facility. In J-PARC, the pitting erosion on the mercury target vessel for the spallation neutron source is one of a pivotal issue to operate with the high power of the beam operation. Since the erosion is proportional to the 4th power of the beam current density, the minimization of the peak current density is required. To achieve low current density, the beam-flattening system by nonlinear beam optics in J-PARC, by which the peak density was successfully reduced by 30% than the density with the conventional case optics. Since the ADS requires a very powerful accelerator with the beam power such as 30 MW, a robust beam profile monitor is required, especially for the observation of the beam status on the target continuously. A candidate material for the beam monitor was developed by using heavy-ion of Ar beam to give the damage efficiently.

Journal Articles

Neutron source

Takada, Hiroshi

Kasokuki Handobukku, p.330 - 333, 2018/04

Spallation neutron source provides thermal and cold neutrons for materials researches. Those neutrons are obtained by slowing down the neutrons generated in a neutron production target by injecting high energy protons in surrounding reflector and moderators. This article introduces basic characteristics of the neutron production target at first, and then explains the characteristics of moderator, especially the design to generate high intensity and high quality neutron pulses with narrow width in the moderators used in the 1-MW spallation neutron source at J-PARC. Furthermore, the design procedure of the spallation neutron source is described.

Journal Articles

Profile monitor on target for spallation neutron source

Meigo, Shinichiro; Matsuda, Hiroki; Takei, Hayanori

Proceedings of 6th International Beam Instrumentation Conference (IBIC 2017) (Internet), p.373 - 376, 2018/03

no abstracts in English

Journal Articles

Current status of pulsed spallation neutron source of J-PARC

Takada, Hiroshi

JAEA-Conf 2017-001, p.51 - 56, 2018/01

A pulsed spallation neutron source of Japan Proton Accelerator Research Complex (J-PARC) is aimed at promoting a variety of cutting-edge materials researches at state-of-the-art neutron instruments with neutrons generated by a 3-GeV proton beam with a power of 1-MW at a repetition rate of 25 Hz. In 2015, for the first time it received 1-MW equivalent proton beam pulse, and the beam power for user program was ramped up to 500 kW. The moderator system of the neutron source was optimized to use (1) 100% para-hydrogen for increasing pulse peak intensity with decreasing pulse tail, (2) cylindrical shape with 14 cm diam. $$times$$ 12 cm long for providing high intensity neutrons to wide neutron extraction angles of 50.8 degrees, (3) neutron absorber made from Ag-In-Cd alloy to make pulse widths narrower and pulse tails lower. As a result, it gives highest intensity pulsed neutrons per incident proton in the world. Towards the goal to achieve the target operation at 1-MW for 5000 h in a year, efforts to mitigate cavitation damages at the target vessel front with injecting gas micro-bubbles into the mercury target are under way. Also, improvement of structural target vessel design is an urgent issue since there was failure twice at the water shroud of the mercury target due to the thermal stress during operating periods at 500 kW in 2015.

Journal Articles

Cavitation damage prediction for the JSNS mercury target vessel

Naoe, Takashi; Kogawa, Hiroyuki; Wakui, Takashi; Haga, Katsuhiro; Teshigawara, Makoto; Kinoshita, Hidetaka; Takada, Hiroshi; Futakawa, Masatoshi

Journal of Nuclear Materials, 468, p.313 - 320, 2016/01

BB2014-2665.pdf:3.4MB

 Times Cited Count:5 Percentile:35.96(Materials Science, Multidisciplinary)

Mercury target vessel in the JSNS, which is made of 316L SS, is damaged owing to the pressure wave-induced cavitation resulting from the proton beam bombardment. The cavitation damage decreases the structural integrity of the target vessel and is currently a dominant factor to decide the service life in compared with the radiation damage. Injecting microbubbles into mercury is one of the prospective techniques to mitigate the pressure waves and cavitation damage. In the JSNS, a microbubble generator with a gas circulation system was installed and has been operated since October 2012. The effects of microbubble injection into mercury on pressure wave mitigation were studied using a laser Doppler vibrometer. The result showed that the vibrational velocity of the target vessel is clearly reduced according to the increase of void fraction. An average peak vibrational velocity under 340 kW operation with the void fraction of 0.1% was reduced to 1/4 of that without injecting microbubbles.

Journal Articles

Gigacycle fatigue behaviour of austenitic stainless steels used for mercury target vessels

Naoe, Takashi; Xiong, Z.; Futakawa, Masatoshi

Journal of Nuclear Materials, 468, p.331 - 338, 2016/01

BB2014-2666.pdf:0.65MB

 Times Cited Count:11 Percentile:14.02(Materials Science, Multidisciplinary)

Mercury enclosure vessel of the JSNS made of an austenitic stainless steel suffers radiation damage in the proton and neutron environment. In addition to the radiation damage, the vessel suffers the cyclic impact loading caused from the pressure waves. The JSNS target vessel suffers higher than 2$$times$$10$$^8$$ cyclic loading. Furthermore, strain rate of the beam window portion of the target vessel reaches to 50s$$^{-1}$$ at the maximum, which is much higher than the conventional fatigues. Very high cycle fatigue strengths up to 10$$^9$$ cycles for solution annealed (SA) and 10% cold-worked 316L (CW) were investigated through the ultrasonic fatigue test. The result showed that the fatigue strengths of SA and CW tested in high-strain rate were higher than that of the conventional fatigue. On the other hand, the fatigue failure occurred regardless of material and temperature in the very high-cycle region ($$10^7 sim 10^9$$ cycles) at the stress amplitude of below the conventional fatigue limit.

Journal Articles

Research and development of high intensity beam transport to the target facilities at J-PARC

Meigo, Shinichiro; Oi, Motoki; Ikezaki, Kiyomi*; Kawasaki, Tomoyuki; Kinoshita, Hidetaka; Akutsu, Atsushi*; Nishikawa, Masaaki*; Fukuda, Shimpei

Proceedings of 12th International Topical Meeting on Nuclear Applications of Accelerators (AccApp '15), p.255 - 260, 2016/00

Journal Articles

Inner observation of canning Cadmium by energy-selective neutron imaging at NOBORU

Harada, Masahide; Parker, J. D.*; Oikawa, Kenichi; Kai, Tetsuya; Shinohara, Takenao

JPS Conference Proceedings (Internet), 8, p.035002_1 - 035002_5, 2015/09

We found that Cadmium (Cd) was not only a suitable thermal neutron absorber as a poison material in a pulsed spallation neutron source, but also had a long life time with a small sacrifice in neutron intensities at an intense source. Therefore, we decided to use Cd as the poison material in the first moderator in JSNS/J-PARC. In the development stage of JSNS, canning of a Cd plate by an Al-alloy with the Cold Isostatic Pressing method failed and the Al-alloy cover of the Cd plate was broken. In order to correct the manufacturing process, we have to observe the inside of the sample to find the reason for failure. To investigation the inside of the canning Cd plate non-destructively, we applied the energy selective neutron imaging method. We measured the transmission of the canning Cd plate used by the micro-pixel chamber ($$mu$$PIC) neutron detector at NOBORU (BL10) in JSNS. As a result, several vacancies could be found and the distribution of the amount of Cd could be also obtained.

Journal Articles

Cavitation erosion induced by proton beam bombarding mercury target for high-power spallation neutron sources

Futakawa, Masatoshi; Naoe, Takashi; Kogawa, Hiroyuki; Haga, Katsuhiro; Okita, Kohei*

Experimental Thermal and Fluid Science, 57, p.365 - 370, 2014/09

AA2014-0181.pdf:1.48MB

 Times Cited Count:8 Percentile:46.64(Thermodynamics)

A liquid mercury target system for a megawatt-class spallation neutron source is being developed in the world. Proton beam is injected to the mercury target to induce spallation reaction. The moment the proton beams bombard the target, pressure waves are generated in the mercury by the thermally shocked heat deposition. The pressure waves excite the mercury target vessel and negative pressure that may cause cavitation along the vessel wall. Gas-bubbles will be injected into the flowing mercury to mitigate the pressure waves and suppress the cavitation inception. The injected gas-bubbles conditions were examined and the effects were predicted experimentally and theoretically from the viewpoints of macroscopic time-scale and microscopic time-scale, i.e. in the former is dominant the interaction between the structural vibration and the pressure in mercury, and in the later is essential the pressure wave propagation process.

Journal Articles

Small gas bubble experiment for mitigation of cavitation damage and pressure waves in short-pulse mercury spallation targets

Riemer, B. W.*; Wendel, M. W.*; Felde, D. K.*; Sangrey, R. L.*; Abdou, A.*; West, D. L.*; Shea, T. J.*; Hasegawa, Shoichi; Kogawa, Hiroyuki; Naoe, Takashi; et al.

Journal of Nuclear Materials, 450(1-3), p.192 - 203, 2014/07

 Times Cited Count:8 Percentile:33.27(Materials Science, Multidisciplinary)

Populations of small helium gas bubbles were introduced into a flowing mercury experiment test loop to evaluate mitigation of beam-pulse induced cavitation damage and pressure waves. The test loop was developed and thoroughly tested at the Spallation Neutron Source (SNS) prior to irradiations at the Los Alamos Neutron Science Center - Weapons Neutron Research Center (LANSCE-WNR) facility. Twelve candidate bubblers were evaluated over a range of mercury flow and gas injection rates by use of a novel optical measurement technique that accurately assessed the generated bubble size distributions. Final selection for irradiation testing included two variations of a swirl bubbler provided by Japan Proton Accelerator Research Complex (J-PARC) collaborators and one orifice bubbler developed at SNS. Bubble populations of interest consisted of sizes up to 150 $$mu$$m in radius with achieved gas void fractions in the 10$$^{-5}$$ to 10$$^{-4}$$ range. The nominal WNR beam pulse used for the experiment created energy deposition in the mercury comparable to SNS pulses operating at 2.5 MW. Nineteen test conditions were completed each with 100 pulses, including variations on mercury flow, gas injection and protons per pulse. The principal measure of cavitation damage mitigation was surface damage assessment on test specimens that were manually replaced for each test condition. Damage assessment was done after radiation decay and decontamination by optical and laser profiling microscopy with damaged area fraction and maximum pit depth being the more valued results. Damage was reduced by flow alone; the best mitigation from bubble injection was between half and a quarter that of flow alone. Other data collected included surface motion tracking by three laser Doppler vibrometers (LDV), loop wall dynamic strain, beam diagnostics for charge and beam profile assessment, embedded hydrophones and pressure sensors, and sound measurement by a suite of conventional and contact microphones.

Journal Articles

Experimental investigation of characteristics of impinging jet heat transfer and application to JSNS moderator design

Aso, Tomokazu; Monde, Masanori*; Sato, Hiroshi; Hino, Ryutaro; Tatsumoto, Hideki; Kato, Takashi

Nippon Genshiryoku Gakkai Wabun Rombunshi, 5(3), p.179 - 189, 2006/09

no abstracts in English

Journal Articles

Numerical analysis for heat transfer from a Cd poison in cryogenic hydrogen

Tatsumoto, Hideki; Kato, Takashi; Aso, Tomokazu; Hasegawa, Shoichi; Ushijima, Isamu*; Otsu, Kiichi*; Ikeda, Yujiro

LA-UR-06-3904, Vol.2, p.426 - 434, 2006/06

In JSNS, Cadmium has been selected as a poison material in a hydrogen moderator to obtain narrow neutron pulse. The concern to adopt to Cd is how to bond Cd and Al alloy plate. R&Ds for bonding have been performed. But good bonding has not been obtained. Consequently, heat transfer between Cd poison and cryogenic hydrogen was studied for the case of insufficient bonding. The heat transfers for various bonding ratios were analyzed by CFD code (STAR-CD) without any turbulence model. The temperature rise in Cd poison for insufficient bonding was estimated. As a result, even the case of the bonding ratio of only 5 %, the maximum temperature of Cd is around 75K. Therefore, the expected heat transfer between the Cd poison and the hydrogen should be sufficient for insufficient bonding. Then, it is found that the any bonding method should be available for manufacturing method of Cd poison.

Journal Articles

Estimation of JSNS moderator flowing condition based on impinging jet heat transfer

Aso, Tomokazu; Monde, Masanori*; Sato, Hiroshi; Tatsumoto, Hideki; Kato, Takashi; Ikeda, Yujiro

LA-UR-06-3904, Vol.2, p.385 - 394, 2006/06

no abstracts in English

Journal Articles

Design result of the cryogenic hydrogen circulation system for 1 MW pulse spallation neutron source (JSNS) in J-PARC

Aso, Tomokazu; Tatsumoto, Hideki; Hasegawa, Shoichi; Ushijima, Isamu*; Otsu, Kiichi*; Kato, Takashi; Ikeda, Yujiro

AIP Conference Proceedings 823, p.763 - 770, 2006/05

no abstracts in English

Journal Articles

Evaluation of mechanical properties and microstructure in ion-irradiated surface layer

Naoe, Takashi*; Futakawa, Masatoshi; Naito, Akira*; Kogawa, Hiroyuki; Ikeda, Yujiro; Motohashi, Yoshinobu*

JSME International Journal, Series A, 48(4), p.280 - 285, 2005/10

Target vessel materials used in spallation neutron source will be exposed to proton and neutron irradiation and mercury immersion environments. In order to evaluate the surface degradation of the vessel candidate materials due to such environment, the triple-ion beam irradiation taking the spallation reaction into account and mercury immersion tests were carried out. Mechanical properties of the gradient surface layer ware evaluated by the inverse analysis with multi-layer model that considers distribution of surface characteristic was applied to the load and depth curves measured by using the instrumented indentation machine. Transmission electron microscopic observations ware performed to evaluate the changes of microstructure in irradiated surface layer using focused ion-beam cut micro-specimen. It was confirmed that the ductility loss is enhanced by the irradiation and mercury immersion, and simulated stress and strain curves of the ion-irradiated surface layer ware adequately in good agreement with the curves of experimental equivalent neutron-irradiated material.

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