Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a BC thin film

Norimatsu, Wataru*; Matsuda, Keita*; Terasawa, Tomoo; Takata, Nao*; Masumori, Atsushi*; Ito, Keita*; Oda, Koji*; Ito, Takahiro*; Endo, Akira*; Funahashi, Ryoji*; et al.

Nanotechnology, 31(14), p.145711_1 - 145711_7, 2020/04

https://doi.org/10.1088/1361-6528/ab62cf

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of BC on SiC and graphene on BC had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on BC acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on BC was highly boron doped, and the hole concentration could be controlled over a wide range of 210 to 210 cm. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Turbulent transport reduction induced by transition on radial electric field shear and curvature through amplitude and cross-phase in torus plasma

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku*; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*

Scientific Reports (Internet), 7(1), p.14971_1 - 14971_8, 2017/11

https://doi.org/10.1038/s41598-017-14821-y

Development of prototype reactor maintenance, 2; Application to piping support of sodium-cooled reactor prototype

Arai, Masanobu; Kunogi, Kosuke; Aizawa, Kosuke; Chikazawa, Yoshitaka; Takaya, Shigeru; Kubo, Shigenobu; Kotake, Shoji*; Ito, Takaya*; Yamaguchi, Akira*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 6 Pages, 2017/04

Applications for maintenance program on piping support of prototype fast breeder reactor Monju are studied. Based on degradation mechanism, snubbers in Monju primary cooling system showed lifetime more than the plant lifetime of 30 years by experiments conservatively. For the first step during construction, visual inspection on accessible all supports could be available. In that visual inspection, mounting conditions and damages of all accessible supports could be monitored. One of major features of the Monju primary piping system is large thermal expansion due to large temperature difference between maintenance and operation conditions. Thanks to that large thermal expansion, integrity of the piping support could be monitored by measuring piping displacement. When technologies of piping displacement monitoring are matured in Monju, visual inspection on piping support could be shifted to piping displacement monitoring. At that stage, the visual inspection could be limited only on representative supports.

Field test around Fukushima Daiichi Nuclear Power Plant site using improved Ce:Gd(Al,Ga)O scintillator Compton camera mounted on an unmanned helicopter

Shikaze, Yoshiaki; Nishizawa, Yukiyasu; Sanada, Yukihisa; Torii, Tatsuo; Jiang, J.*; Shimazoe, Kenji*; Takahashi, Hiroyuki*; Yoshino, Masao*; Ito, Shigeki*; Endo, Takanori*; et al.

Journal of Nuclear Science and Technology, 53(12), p.1907 - 1918, 2016/12

https://doi.org/10.1080/00223131.2016.1185980

The Compton camera was improved for use with the unmanned helicopter. Increase of the scintillator array from 44 to 88 and expanse of the distance between the two layers contributed to the improvements of detection efficiency and angular resolution, respectively. Measurements were performed over the riverbed of the Ukedo river of Namie town in Fukushima Prefecture. By programming of flight path and speed, the areas of 65 m 60 m and 65 m 180 m were measured during about 20 and 30 minutes, respectively. By the analysis the air dose rate maps at 1 m height were obtained precisely with the angular resolution corresponding to the position resolution of about 10 m from 10 m height. Hovering flights were executed over the hot spot areas for 10-20 minutes at 5-20 m height. By using the reconstruction software the -ray images including the hot spots were obtained with the angular resolution same as that evaluated in the laboratory (about 10).

Experimental identification of electric field excitation mechanisms in a structural transition of tokamak plasmas

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.

Scientific Reports (Internet), 6, p.30720_1 - 30720_7, 2016/08

https://doi.org/10.1038/srep30720

In this Letter, we report model verifications for a key physics for the L-H transition. Radial electric field excitation, using discharges having a two-step transition. Examining time derivative of Poissons equation, it is found that the sum of the loss cone loss current and neoclassical bulk viscosity current agrees the experimentally observed current in the order of magnitude at the first transition. Following second transition and an ambipolar condition in the L-mode cannot be explained by the models.

Experimental measurement of vortex cavitation around a suction pipe inlet

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kurihara, Akikazu; Kunugi, Tomoaki*

Konsoryu, 30(2), p.189 - 196, 2016/06

https://doi.org/10.3811/jjmf.30.189

Study on surface tension modeling for mechanistic evaluation of vortex cavitation

Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki; Kawamura, Takumi*; Nakamine, Yoshiaki*

Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 6 Pages, 2014/11

The authors have been studied the vortex cavitation in sodium-cooled fast reactors. In this paper, the authors present a modified evaluation method for vortex cavitation, in which a surface tension is modeled mechanistically. Namely, the cavity radius is calculated in consideration of radial pressure distribution, saturated vapor pressure and the pressure jump condition at an interface. As the basic validation of the developed surface tension model, numerical analyses of a simple experiment under various velocity conditions are performed. The evaluation results give qualitatively appropriate tendency, that is, the cavity radius becomes larger with the higher liquid velocity and/or lower reference pressure which cause the larger pressure drop at the vortex. In addition, the authors evaluate the influence of the kinematic viscosity which plays an important role in the vortex cavitation occurrences in the experiments.

Present status of J-PARC linac

Oguri, Hidetomo; Hasegawa, Kazuo; Ito, Takashi; Chishiro, Etsuji; Hirano, Koichiro; Morishita, Takatoshi; Shinozaki, Shinichi; Ao, Hiroyuki; Okoshi, Kiyonori; Kondo, Yasuhiro; et al.

Proceedings of 11th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.389 - 393, 2014/10

http://www.pasj.jp/web_publish/pasj2014/proceedings/PDF/FSP0/FSP021.pdf

no abstracts in English

Dynamics of edge limit cycle oscillation in the JFT-2M tokamak

Kobayashi, Tatsuya*; Ito, Kimitaka*; Ido, Takeshi*; Kamiya, Kensaku; Ito, Sanae*; Miura, Yukitoshi; Nagashima, Yoshihiko*; Fujisawa, Akihide*; Inagaki, Shigeru*; Ida, Katsumi*; et al.

Nuclear Fusion, 54(7), p.073017_1 - 073017_14, 2014/07

https://doi.org/10.1088/0029-5515/54/7/073017

In the JFT-2M tokamak, limit-cycle oscillation among several variables is observed before L-to-H transition. Spatiotemporal dynamics of the LCO is analyzed in detail. Zonal fows are not seen, and modulation in edge-localized poloidal flow and density gradient is observed. Modulation is also seen in Reynolds stress, caused by that in turbulence intensity and turbulence wavenumber. However, flow acceleration is not able to be explained by the modulation in the Reynolds stress. Rapid inward propagation in density gradient and turbulence packet is also observed. Characteristics of the propagation are veried by means of turbulence spreading theory and diffusion theory.

Preliminary experiment for internal structure visualization of HTTR using cosmic ray muons

Takegami, Hiroaki; Takamatsu, Kuniyoshi; Ito, Chikara; Hino, Ryutaro; Suzuki, Keiichi*; Onuma, Hiroshi*; Okumura, Tadahiko*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(1), p.7 - 16, 2014/03

https://doi.org/10.3327/taesj.J13.010

One of the important problems for controlling of the Fukushima Daiichi Nuclear Power Plant is removing of fuel debris. As this preparation, the nondestructive inspection method for grasping the position of fuel debris is required. Therefore, we focused on a nondestructive inspection method using cosmic-ray muons. In this study, the applicability of this method for internal visualization of reactor was confirmed by preliminary test of internal visualization of High Temperature Engineering Test Reactor (HTTR). By using cosmic-ray muons, major components in the HTTR, such as concrete wall and reactor core, can be observed from the outside of a containment vessel. From the results, it appears that the inspection method with muons is a candidate method for searching the fuel debris in a reactor. Based on the results, we also proposed some improvements of this system for inspection at the Fukushima Daiichi Nuclear Power Station.