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Aoki, Kazuhiro; Tanaka, Yukumo; Yoshida, Takumi; Shimada, Koji; Sakai, Toru*; Kametaka, Masao*; Seshimo, Kazuyoshi
Oyo Chishitsu, 62(2), p.64 - 81, 2021/06
Co-seismic surface ruptures in the Fukushima-ken Hamadori Earthquake of Mw 6.7 on April 11, 2011 exposed approximately 14 km trending NNW-SSE from Nameishi to northwest of Ishizumi Tsunaki of Tabito Town, Iwaki City and were newly named the Shionohira Fault. However, no surface ruptures appeared along an N-S trending active Kuruma fault extending 5 km south of the Shionohira Fault. Because of the proximity and similar strike, two locations in Shionohira Fault and one location in Kuruma fault were selected as the study area for the fault activity evaluation. The present study reports the results of a series of geological and drilling surveys, core observation, XRD, isotope, and fluid inclusion analyses, and water permeability test. The results obtained from the three locations offer a fundamental data base that can be utilized for fault activity evaluation by summarizing the geological, mineralogical, and fluid property characteristics of fault fracture zone.
Kitamura, Akihiro; Kurikami, Hiroshi; Sakuma, Kazuyuki; Malins, A.; Okumura, Masahiko; Machida, Masahiko; Mori, Koji*; Tada, Kazuhiro*; Tawara, Yasuhiro*; Kobayashi, Takamaru*; et al.
Earth Surface Processes and Landforms, 41(12), p.1708 - 1726, 2016/09
Times Cited Count：18 Percentile：54.02(Geography, Physical)Sediment erosion and transport processes that are considered to be important in predicting the future radioactive material distribution through sediment-sorbed form in Fukushima Prefecture are simulated. Since large portion of the sediment is considered to be supplied into the rivers, it is important to trace their migration process in terms of each river basin. We choose five river basins, namely the Odaka, the Ukedo, the Maeda, the Kuma, and the Tomioka, from north to south, because of their importance in contamination aspects and prediction studies. The results are summarized as comprehensive dataset of sediment migration for particular river basins in typical typhoon events that account for the most of annual soil erosion. Detail calculations implemented for the amount of sediment supplied in to the river, deposited on river and dam beds, and exported to the ocean.
Nishikiori, Ryo; Kojima, Atsushi; Hanada, Masaya; Kashiwagi, Mieko; Watanabe, Kazuhiro; Umeda, Naotaka; Tobari, Hiroyuki; Yoshida, Masafumi; Ichikawa, Masahiro; Hiratsuka, Junichi; et al.
Plasma and Fusion Research (Internet), 11, p.2401014_1 - 2401014_4, 2016/03
One of critical issues for high-energy high-current beam acceleration in ITER and JT-60SA is the high voltage holding which is dominated by vacuum discharges. The past results suggest that vacuum discharge occurs beyond the threshold of the dark current. The dark current can be derived from F-N theory where electric field enhancement factor beta is included. Though, beta could only be evaluated from the experiment previously. Therefore, the method to decide beta without experiment is required. This time dark currents were measured at three different areas to compare beta in different electric field. As a result, the effective electric field 
E, where E is average electric field, were found to be almost constant for different areas although the beta is largely different. By applying E, beta can be evaluated analytically, leading to the analytical prediction of the dark current and voltage holding capability without the measurements.
Ishizawa, Akihiro*; Idomura, Yasuhiro; Imadera, Kenji*; Kasuya, Naohiro*; Kanno, Ryutaro*; Satake, Shinsuke*; Tatsuno, Tomoya*; Nakata, Motoki*; Nunami, Masanori*; Maeyama, Shinya*; et al.
Purazuma, Kaku Yugo Gakkai-Shi, 92(3), p.157 - 210, 2016/03
The high-performance computer system Helios which is located at The Computational Simulation Centre (CSC) in The International Fusion Energy Research Centre (IFERC) started its operation in January 2012 under the Broader Approach (BA) agreement between Japan and the EU. The Helios system has been used for magnetised fusion related simulation studies in the EU and Japan and has kept high average usage rate. As a result, the Helios system has contributed to many research products in a wide range of research areas from core plasma physics to reactor material and reactor engineering. This project review gives a short catalogue of domestic simulation research projects. First, we outline the IFERC-CSC project. After that, shown are objectives of the research projects, numerical schemes used in simulation codes, obtained results and necessary computations in future.
Hanada, Masaya; Kojima, Atsushi; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.
Review of Scientific Instruments, 87(2), p.02B322_1 - 02B322_4, 2016/02
Times Cited Count：14 Percentile：54.22(Instruments & Instrumentation)In International Thermo-nuclear Experimental Reactor (ITER) and JT-60 Super Advanced (JT-60 SA), the D
ion beams of 1 MeV, 40 A and 0.5 MeV, 22 A are required to produce 3600 s and 100 s for the neutral beam injection, respectively. In order to realize such as powerful D ion beams for long duration time, Japan Atomic Energy Agency (JAEA) has energetically developed cesium (Cs)-seeded negative ion sources (CsNIS) and electro-static multi-aperture and multi-stage accelerators (MAMuG accelerator) which are chosen as the reference design of ITER and JT-60 SA. In the development of the CsNIS, a 100s production of the H ion beam has been demonstrated with a beam current of 15 A by modifying the JT-60 negative ion source. At the higher current, the long pulse production of the negative ions has been tried by the mitigation of the arcing in the plasma inside the ion source. As for the long pulse acceleration of the negative ions in the MAMuG accelerator, the beam steering angle has been controlled to reduce the power loading of the acceleration grids A pulse duration time has been significantly extended from 0.4 s to 60 s at reasonable beam power for ITER requirement. The achieved pulse duration time is limited by the capacity of the power supplies in the test stand. In the range of 
60 s, there are no degradations of beam optics and voltage holding capability in the accelerator. It leads to the further extension of the pulse duration time at higher power density. This paper reports the latest results of development on the negative ion source and accelerator at JAEA.
Kojima, Atsushi; Hanada, Masaya; Tobari, Hiroyuki; Nishikiori, Ryo; Hiratsuka, Junichi; Kashiwagi, Mieko; Umeda, Naotaka; Yoshida, Masafumi; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.
Review of Scientific Instruments, 87(2), p.02B304_1 - 02B304_5, 2016/02
Times Cited Count：13 Percentile：51.98(Instruments & Instrumentation)Optimization techniques of the vacuum insulation design have been developed in order to realize a reliable voltage holding capability of Multi-Aperture Multi-Grid accelerators for giant negative ion sources for nuclear fusion. In this method, the nested multilayer configuration of each acceleration stage in the MAMuG accelerator can be uniquely designed to satisfy the target voltage within given boundary conditions. The evaluation of the voltage holding capabilities of each acceleration stages were based on the past experimental results of the area effect and the multi-aperture effect on the voltage holding capability. Moreover, total voltage holding capability of multi-stage was estimated by taking the multi-stage effect into account, which was experimentally obtained in this time. In this experiment, the multi-stage effect appeared as the superposition of breakdown probabilities in each acceleration stage, which suggested that multi-stage effect can be considered as the voltage holding capability of the single acceleration gap having the total area and aperture. The analysis on the MAMuG accelerator for JT-60SA agreed with the past gap-scan experiments with an accuracy of less than 10% variation.
Hiratsuka, Junichi; Hanada, Masaya; Kojima, Atsushi; Umeda, Naotaka; Kashiwagi, Mieko; Miyamoto, Kenji*; Yoshida, Masafumi; Nishikiori, Ryo; Ichikawa, Masahiro; Watanabe, Kazuhiro; et al.
Review of Scientific Instruments, 87(2), p.02B137_1 - 02B137_3, 2016/02
Times Cited Count：4 Percentile：20.41(Instruments & Instrumentation)To understand the physics of the negative ion extraction/acceleration, the heat load density profile on the acceleration grid has been firstly measured in the ITER prototype accelerator where the negative ions are accelerated to 1 MeV with five acceleration stages. In order to clarify the profile, the peripheries around the apertures on the acceleration grid were separated into thermally insulated 34 blocks with thermocouples. The spatial resolution is as low as 3 mm and small enough to measure the tail of the beam profile with a beam diameter of 16 mm. It was found that there were two peaks of heat load density around the aperture. These two peaks were also clarified to be caused by the intercepted negative ions and secondary electrons from detailed investigation by changing the beam optics and gas density profile. This is the first experimental result, which is useful to understand the trajectories of these particles.
Yoshida, Masafumi; Hanada, Masaya; Kojima, Atsushi; Kashiwagi, Mieko; Umeda, Naotaka; Hiratsuka, Junichi; Ichikawa, Masahiro; Watanabe, Kazuhiro; Grisham, L. R.*; Tsumori, Katsuyoshi*; et al.
Review of Scientific Instruments, 87(2), p.02B144_1 - 02B144_4, 2016/02
Times Cited Count：10 Percentile：43.85(Instruments & Instrumentation)Time evolution of spatial profile of negative ion production during an initial conditioning phase has been experimentally investigated in the JT-60 negative ion source. Up to 0.4 g Cs injection, there is no enhancement of the negative ion production and no observation of the Cs emission signal in the source, suggesting the injected Cs is mainly deposited on the water-cooled wall near the nozzle. After 0.4 g Cs injection, enhancement of the negative ion production appeared only at the central segment of the PG. The calculation of the Cs neutral/ion trajectories implied that a part of Cs was ionized near the nozzle and was transported to this area. The expansion of the area of the surface production was saturated after ~2 g Cs injection corresponding to 6000 s discharge time. From the results, it is found that Cs ionization and its transport plays an important role for the negative ion production.
Kojima, Atsushi; Umeda, Naotaka; Hanada, Masaya; Yoshida, Masafumi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Akino, Noboru; Komata, Masao; Mogaki, Kazuhiko; et al.
Nuclear Fusion, 55(6), p.063006_1 - 063006_9, 2015/06
Times Cited Count：45 Percentile：90.00(Physics, Fluids & Plasmas)Significant progresses in the extension of pulse durations of powerful negative ion beams have been made to realize the neutral beam injectors for JT-60SA and ITER. In order to overcome common issues of the long pulse production/acceleration of negative ion beams in JT-60SA and ITER, the new technologies have been developed in the JT-60SA ion source and the MeV accelerator in Japan Atomic Energy Agency. As for the long pulse production of high-current negative ions for JT-60SA ion source, the pulse durations have been successfully increased from 30 s at 13 A on JT-60U to 100 s at 15 A by modifying the JT-60SA ion source, which satisfies the required pulse duration of 100 s and 70% of the rated beam current for JT-60SA. This progress was based on the R&D efforts for the temperature control of the plasma grid and uniform negative ion productions with the modified tent-shaped filter field configuration. Moreover, the each parameter of the required beam energy, current and pulse has been achieved individually by these R&D efforts. The developed techniques are useful to design the ITER ion source because the sustainment of the cesium coverage in large extraction area is one of the common issues between JT-60SA and ITER. As for the long pulse acceleration of high power density beams in the MeV accelerator for ITER, the pulse duration of MeV-class negative ion beams has been extended by more than 2 orders of magnitude by modifying the extraction grid with a high cooling capability and a high-transmission of negative ions. A long pulse acceleration of 60 s has been achieved at 70 MW/m
(683 keV, 100 A/m) which has reached to the power density of JT-60SA level of 65 MW/m.
Kojima, Atsushi; Hanada, Masaya; Yoshida, Masafumi; Umeda, Naotaka; Hiratsuka, Junichi; Kashiwagi, Mieko; Tobari, Hiroyuki; Watanabe, Kazuhiro; Grisham, L. R.*; NB Heating Technology Group
AIP Conference Proceedings 1655, p.060002_1 - 060002_10, 2015/04
Times Cited Count：6 Percentile：86.35(Physics, Applied)In this paper, the recent activities on the new test stand are reported toward demonstration of the long pulse production for 22A, 100s negative ion beams. As for the temperature control of the plasma grid, a prototype of the grid with cooling/heating by circulating a high-temperature fluorinated fluid has been improved to cover the full extraction area by using 5 segments of the PG. These grids were found to have a capability to control the temperature with a time constant of 10s as well as the prototype grid. As a result, 15A negative ion beams for 100s have been achieved.
Hiratsuka, Junichi; Hanada, Masaya; Umeda, Naotaka; Kojima, Atsushi; Kashiwagi, Mieko; Watanabe, Kazuhiro; Tobari, Hiroyuki; Yoshida, Masafumi
Plasma and Fusion Research (Internet), 10(Sp.2), p.3405045_1 - 3405045_4, 2015/04
To produce high current density (
200 A/m), high-energy ( 1 MeV) negative ion beams for long pulse duration time (1 hour) for International Thermo-nuclear Experimental Reactor (ITER), the suppression of the direct interception of the negative ions with the grids has been carefully investigated with studying the deflection angle by aperture displacement technique. The non-linear dependence of the deflection angle appears at the aperture diameter of 14 mm on a steering control grid (SCG). From this dependence, the aperture diameter and the offset distance of the SCG has been designed to be 16 mm and 0.7 mm, respectively and tested in a prototype accelerator for ITER. Each of the beamlets on the multiple apertures is properly steered with compensation of the deflection due to the residual magnetic field in the accelerator and the grid power loading was significantly reduced. It resulted in a 10% enhancement of the accelerated beam current.
Murakami, Haruyuki; Kizu, Kaname; Tsuchiya, Katsuhiko; Koide, Yoshihiko; Yoshida, Kiyoshi; Obana, Tetsuhiro*; Takahata, Kazuya*; Hamaguchi, Shinji*; Chikaraishi, Hirotaka*; Natsume, Kyohei*; et al.
IEEE Transactions on Applied Superconductivity, 24(3), p.4200205_1 - 4200205_5, 2014/06
Times Cited Count：25 Percentile：72.73(Engineering, Electrical & Electronic)Central Solenoid (CS) of JT-60SA are designed with the Nb
Sn cable in conduit conductor. CS model coil (CSMC) was manufactured by using the real manufacturing jigs and procedure to validate the CS manufacturing processes before starting mass production. The dimensions of the CSMC are the same as real quad-pancake. The cold test of the CSMC was performed and the test results satisfied the design requirements. These results indicate that the manufacturing processes of the JT-60SA CS has been established. In this paper, the development and the validation of the CS manufacturing processes are described.
Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Kojima, Atsushi; Yoshida, Masafumi; Taniguchi, Masaki; Dairaku, Masayuki; Maejima, Tetsuya; Yamanaka, Haruhiko; Watanabe, Kazuhiro; et al.
Review of Scientific Instruments, 85(2), p.02B320_1 - 02B320_3, 2014/02
Times Cited Count：29 Percentile：73.78(Instruments & Instrumentation)The negative ion extractor for high power and long-pulse operations is newly developed toward the neutral beam injector (NBI) for heating & current drive of future fusion machines such as ITER, JT-60 Super Advanced (SA) and DEMO reactor. The satisfactory cooling capability is designed in the thermal analysis. A negative ion production and a suppression of electrons are experimentally validated for this new extractor. As the results, the negative ion current shows increases by a factor of 1.3 with suppressing the electron current. The beam divergence angle is also maintained small enough, 4 mrad.
Kojima, Atsushi; Hanada, Masaya; Yoshida, Masafumi; Tobari, Hiroyuki; Kashiwagi, Mieko; Umeda, Naotaka; Watanabe, Kazuhiro; Grisham, L. R.*
Review of Scientific Instruments, 85(2), p.02B312_1 - 02B312_5, 2014/02
Times Cited Count：13 Percentile：49.24(Instruments & Instrumentation)The negative ion source for JT-60SA is designed to produce high power and long pulse beams with a beam energy of 500 keV, a negative ion current of 22A and a pulse duration of 100s. One of the key issues toward long pulse production of such high-current beams is the control of the surface temperature on the plasma grid (PG) where cesium is layered. In order to optimize cesium layer on PG for long pulse duration, we have developed an actively cooled PG where fluorinated fluids having high boiling point of 270
C is circulated. While the surface temperature of the PG in the JT-60 negative ion source has been kept at 170C for 100s with ramp-up time of 7s, stable long pulse beam extractions of 100s have been obtained. This current density is 90% of the required current density for JT-60 SA. The further increase of the current density is expected by optimizing the arc discharge power.
Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Kashiwa, Yoshitoshi; Yoshizawa, Norio; Yoshida, Kiyoshi; Hasegawa, Mitsuru*; Kuno, Kazuo*; Nomoto, Kazuhiro*; Horii, Hiroyuki*
Fusion Engineering and Design, 88(6-8), p.551 - 554, 2013/10
Times Cited Count：8 Percentile：51.69(Nuclear Science & Technology)The programme of constructing JT-60SA device is progressing under the framework of the Broader Approach project. Superconducting poloidal field (PF) coil system, which was decided to be procured by Japan, consists of a central solenoid (CS) with four solenoid modules and six equilibrium field (EF) coils. Each of EF coil has individual diameters, 4.5 to 12 m. Fabrication of EF4 coil, which is set at the lowermost of torus, was started from the beginning of 2009 as a first EF coil. EF4 coil has ten double pancake (DP) coils, and sizes of circularity were measured for all DP coil after curing process. Maximum error of circularity was 3.1 mm, which was nearly a half of the design tolerance, 6 mm. After stacking these DP coils, winding pack of EF4 was completed in the spring of 2012. After optimizing the positions of DP coils to cancel the error of circulation which each DP coil has, error of radial current centre of DP coils will be achieved in the range between + 0.2 to - 0.4 mm. Structural analysis of terminal structure was also performed. Terminal part has a pair of conductors bended toward the lower side of winding pack. A side of them (positive terminal) was covered by stainless steel armor to prevent the movement by electromagnetic force because a length of conductor was longer due to starting from the top of winding pack. Another side (negative terminal) was not covered by armor in the first design because this length was relatively short. However, it was clear on the structural analysis that mechanical strength of insulation around this terminal was not sufficient. Therefore, we also reinforced this side with stainless steel. From this April, fabrication of EF coils with large bore (larger than 8 m of diameter) will be started at the facility built in JAEA Naka site. In this paper, we will discuss about technological problem during the fabrication of large bore EF coils, such as temperature control at the winding process.
Kojima, Atsushi; Hanada, Masaya; Yoshida, Masafumi; Inoue, Takashi; Watanabe, Kazuhiro; Taniguchi, Masaki; Kashiwagi, Mieko; Umeda, Naotaka; Tobari, Hiroyuki; Grisham, L. R.*; et al.
Fusion Engineering and Design, 88(6-8), p.918 - 921, 2013/10
Times Cited Count：7 Percentile：47.55(Nuclear Science & Technology)In this paper, the recent activities are reported toward demonstration of the long pulse production. As for the improvement of uniform beam current profile, a symmetric magnetic field configuration for the source plasma production, a so-called tent-shaped filter, was found to be effective to improve the uniformity of the beam current profile. A similar configuration is applied to the JT-60 negative ion source whose plasma size is 1220 mm 
564 mm. An estimation from trajectory calculations of primary electrons with the symmetric magnetic field configuration showed that the primary electrons were distributed uniformly in a longitudinal direction. As for the temperature control of the plasma grid, a prototype of the grid with cooling/heating by circulating a high-temperature fluorinated fluid has been developed. This grid was found to have a capability to control the temperature with a time constant of 10 s by considering the physical properties of the fluid.
Kizu, Kaname; Murakami, Haruyuki; Tsuchiya, Katsuhiko; Yoshida, Kiyoshi; Nomoto, Kazuhiro*; Imai, Yoshio*; Minato, Tsuneaki*; Obana, Tetsuhiro*; Hamaguchi, Shinji*; Takahata, Kazuya*
IEEE Transactions on Applied Superconductivity, 23(3), p.4200104_1 - 4200104_4, 2013/06
Times Cited Count：23 Percentile：69.96(Engineering, Electrical & Electronic)The maximum magnetic field, current and voltage of CS for JT-60SA are 8.9 T, 20 kA and 10 kV, respectively. NbSn conductor with high field and high current density was developed. The outer diameter and height of CS are 2 and 1.6 m, respectively. Several components were newly developed and tested. To increase the supplying flux, winding diameter should be maximized as possible. The butt type joint was developed that can minimize the joint space. DGEBA epoxy used for main binder of insulation showed sufficient tensile strength even though the 
ray irradiation of 100 kGy. Insulation characteristics of 44 stack sample applying double of operational stress with operational cycle showed the larger withstand voltage than 21 kV. According to these results, the fabrication of CS can be started.
Yoshida, Kazuhiro*; Sakata, Hideyuki*; Sago, Hiromi*; Shiraishi, Tadashi*; Oyama, Kazuhiro*; Hagiwara, Hiroyuki*; Yamano, Hidemasa; Yamamoto, Tomohiko
Proceedings of 8th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-8) (USB Flash Drive), 9 Pages, 2012/12
To prevent the vortex cavitations, asymmetric flow in the upper plenum due to the radial slit with upper internal structure (UIS) has been mitigated by installing a cylindrical structure named as dummy plug instead of the fuel handling machine only used for refueling period. In this study, the extended brim and the division plate at the slit of UIS have been proposed in order to improve flow pattern in upper plenum for the purpose of the vortex cavitation prevention.
Tsuchiya, Katsuhiko; Kizu, Kaname; Murakami, Haruyuki; Yoshida, Kiyoshi; Kurihara, Kenichi; Hasegawa, Mitsuru*; Kuno, Kazuo*; Nomoto, Kazuhiro*; Horii, Hiroyuki*
IEEE Transactions on Applied Superconductivity, 22(3), p.4202304_1 - 4202304_4, 2012/06
Times Cited Count：8 Percentile：43.88(Engineering, Electrical & Electronic)no abstracts in English
Hasegawa, Mitsuru*; Horii, Hiroyuki*; Nomoto, Kazuhiro*; Imai, Yoshio*; Murai, Takashi*; Minato, Tsuneaki*; Kuno, Kazuo*; Tsuchiya, Katsuhiko; Murakami, Haruyuki; Kizu, Kaname; et al.
Proceedings of 24th International Cryogenic Engineering Conference (ICEC 24) and International Cryogenic Materials Conference 2012 (ICMC 2012) (CD-ROM), p.571 - 574, 2012/05
JT-60U magnet system will be upgraded to the superconducting coils (JT-60SA) in the Broader Approach project. JT-60SA magnet system has 18 Toroidal Field coils, a Central Solenoid with 4 modules and 6 Equilibrium Field (EF) coils. This paper describes the manufacturing procedure of EF4 coil, that is the first manufactured EF coil of JT-60SA. The winding pack of EF4 coil was successfully manufactured within geometrical tolerance requirements.
