Simulation of discharge in insulating gas from initial partial discharge to growth of a stepped leader using the percolation model

Sasaki, Akira; Kato, Susumu*; Takahashi, Eiichi*; Kishimoto, Yasuaki*; Fujii, Takashi*; Kanazawa, Seiji*

Japanese Journal of Applied Physics, 55(2), p.026101_1 - 026101_10, 2016/02

https://doi.org/10.7567/JJAP.55.026101

A percolation model of discharge, which can reproduce stochastic behaviors of initial partial discharge to the growth of a stepped leader, is presented. The model uses macroscopic cells, from which a network of electric circuits is defined, and the spatial and temporal evolutions of the electric field and current in the discharge medium are calculated. For each cell, one of two states, either insulator or conductor, which corresponds to neutral gas or ionized plasmas, respectively, is decided. The decision is made on the basis of probability for each calculation cell at each time step, taking the effects of local electric field and current, which enhance ionization and sustain the discharge channel, respectively, into account. The stochastic behavior of discharge is discussed, in conjunction with the characteristic feature of ionization, that is, the ionization occurs not only ahead of the streamer tip where the electric field is enhanced but randomly in the discharge medium.

Detailed deposition density maps constructed by large-scale soil sampling for -ray emitting radioactive nuclides from the Fukushima Dai-ichi Nuclear Power Plant accident

Saito, Kimiaki; Tanihata, Isao*; Fujiwara, Mamoru; Saito, Takashi*; Shimoura, Susumu*; Otsuka, Takaharu*; Onda, Yuichi*; Hoshi, Masaharu*; Ikeuchi, Yoshihiro*; Takahashi, Fumiaki; et al.

Journal of Environmental Radioactivity, 139, p.308 - 319, 2015/01

https://doi.org/10.1016/j.jenvrad.2014.02.014

Development of a GEM-TPC for H-dibaryon search experiment at J-PARC

Sako, Hiroyuki; Ahn, J. K.*; Baek, K. H.*; Bassalleck, B.*; Fujioka, H.*; Guo, L.*; Hasegawa, Shoichi; Hicks, K.*; Honda, R.*; Hwang, S. H.*; et al.

Journal of Instrumentation (Internet), 9(4), p.C04009_1 - C04009_10, 2014/04

https://doi.org/10.1088/1748-0221/9/04/C04009

A TPC has been developed for J-PARC E42 experiment to search for H-dibaryon in (, ) reaction. An event with 2 and 2 protons decaying from H-dibaryon is searched for inside the TPC. The TPC has octagonal prism shape drift volume with about 50 cm diameter with 55 cm drift length filled with Ar-CH (90:10) gas. At the end of the drift volume, 3-layer GEMs are equipped. In order to analyze momenta of produced particles, the TPC is applied with 1 T dipole magnetic field parallel to the drift electric field with a superconducting Helmholz magnet. In order to maximize the acceptance of H-dibaryon events, a diamond target is installed inside the TPC drift volume, in a cylindrical hole opened from the top to the middle of the drift volume. Since extremely high-rate beam is directly injected into the TPC drift volume to the target, a gating grid and GEMs are adopted to suppress positive-ion feedback.

Cryogenic structures of superconducting coils for fusion experimental reactor "ITER"

Nakajima, Hideo; Shimamoto, Susumu*; Iguchi, Masahide; Hamada, Kazuya; Okuno, Kiyoshi; Takahashi, Yoshikazu

Teion Kogaku, 48(10), p.508 - 516, 2013/10

https://doi.org/10.2221/jcsj.48.508

JAEA is procuring both structural materials and structural design of Toroidal Field (TF) coil and Central Solenoid (CS) for ITER. Although 316LN is used in the most parts of the superconducting magnets system, the cryogenic stainless steels, JJ1 and JK2LB, which were newly developed by JAEA and Japanese steel companies, are used in the highest stress area of TF coil case and whole CS conductor jackets, respectively. These two materials became commercially available based on demonstration of productivity and weldability of materials, and evaluations of 4 K mechanical properties of trial products including welded parts. In order to simplify quality control in mass production, JAEA has used materials specified in the material section of "Codes for Fusion Facilities - Rules on Superconducting Magnet Structure (2008)" issued by the Japan Society of Mechanical Engineers (JSME). The design of structural materials, production technology and quality control are described in this paper.

Single-shot observation of growing streamers using an ultrafast camera

Takahashi, Eiichi*; Kato, Susumu*; Furutani, Hirohide*; Sasaki, Akira; Kishimoto, Yasuaki*; Takada, Kenji*; Matsumura, Satoshi*; Sasaki, Hiroyasu*

Journal of Physics D; Applied Physics, 44(30), p.302001_1 - 302001_4, 2011/08

https://doi.org/10.1088/0022-3727/44/30/302001

A recently developed ultrafast camera that can acquire frames per second was used to investigate positive streamer discharge. It enabled single-shot evaluation of streamer evolution without the need to consider shot-to-shot reproducibility. This camera was used to investigate streamers in argon. Growing branches, the transition when a streamer forms a return stroke, and related phenomena were clearly observed.

Percolation simulation of laser-guided electrical discharges

Sasaki, Akira; Kishimoto, Yasuaki*; Takahashi, Eiichi*; Kato, Susumu*; Fujii, Takashi*; Kanazawa, Seiji*

Physical Review Letters, 105(7), p.075004_1 - 075004_4, 2010/08

https://doi.org/10.1103/PhysRevLett.105.075004

A three-dimensional simulation of laser guided-discharges based on the percolation is presented. The model includes both local growth of a streamer due to the enhanced electric field at the tip and propagation of a leader by remote ionization such that caused by runaway electrons. The stochastic behavior of the discharge through preformed plasma channel is reproduced by the calculation, which shows complex path with detouring and bifurcation. The probability of guiding is investigated with respect to the ionized, conductive fraction along the channel.

Numerical modeling of atomic-molecule processes for discharge and lighting

Kato, Susumu*; Takahashi, Eiichi*; Sasaki, Akira; Kishimoto, Yasuaki*

Purazuma, Kaku Yugo Gakkai-Shi, 84(8), p.477 - 483, 2008/08

https://ci.nii.ac.jp/naid/110006881125

no abstracts in English

Current status of the control system for J-PARC accelerator complex

Yoshikawa, Hiroshi; Sakaki, Hironao; Sako, Hiroyuki; Takahashi, Hiroki; Shen, G.; Kato, Yuko; Ito, Yuichi; Ikeda, Hiroshi*; Ishiyama, Tatsuya*; Tsuchiya, Hitoshi*; et al.

Proceedings of International Conference on Accelerator and Large Experimental Physics Control Systems (ICALEPCS '07) (CD-ROM), p.62 - 64, 2007/10

J-PARC is a large scale facility of the proton accelerators for the multi-purpose of scientific researches in Japan. This facility consists of three accelerators and three experimental stations. Now, J-PARC is under construction, and LINAC is operated for one year, 3GeV synchrotron has just started the commissioning in this October the 1st. The completion of this facility will be next summer. The control system of accelerators established fundamental performance for the initial commissioning. The most important requirement to the control system of this facility is to minimize the activation of accelerator devices. In this paper, we show that the performances of each layer of this control system have been achieved in the initial stage.

The Japanese approach to developing clay-based repository concepts; An Example of design studies for the assessment of sealing strategies

Sugita, Yutaka; Fujita, Tomoo; Takahashi, Yoshiaki*; Kawakami, Susumu; Umeki, Hiroyuki; Yui, Mikazu; Uragami, Manabu*; Kitayama, Kazumi*

Physics and Chemistry of the Earth, 32(1-7), p.32 - 41, 2007/00

https://doi.org/10.1016/j.pce.2006.04.029

The H12 repository concept for vitrified high-level radioactive waste was developed based on a multi-barrier system with the emphasis on robust engineered barrier performance to ensure its feasibility for a wide range of geological conditions typically observed in Japan. The buffer is clay-based and plays a very important role in the engineered barrier system (EBS). The decision to use a volunteer siting process requires maximum flexibility of the repository concept to allow it to be adapted to potential sites and hence a wide range of variants of the basic H12 repository design has been developed. In order to evaluate the feasibility and the applicability of different repository options to specific siting environments, NUMO has established a set of "design factors" which classify the aspects that need to be considered when evaluating the pros and cons of different repository options. A Na-type bentonite from Japan is used as the reference material for all clay-based repository components (buffer, backfill, clay plug, etc.). The characteristics of this bentonite (thermal, mechanical, chemical, hydraulic) have been examined with consideration of various practical constraints (limitation on the repository footprint, the influence of saline water, the interaction of hyperalkaline leachates and practical working environment, etc.). Clay-based seals, which close off the tunnels after emplacement of the EBS, may also be key components for assessment of the repository. Full analyses considering all engineered barrier components (buffer, backfill, clay plug, concrete lining, tunnel, concrete plug, host rock) that may be used in a repository will be an essential future task. As a first step towards this goal, a numerical analysis focusing on hydraulic behaviour at the intersections of the disposal tunnels and the main tunnel is presented to illustrate how the design requirements of clay-based seals can be determined.

Discussion on sealing performance required to disposal system; Hydraulic analysis considering intersections of tunnels

Sugita, Yutaka*; Fujita, Tomoo; Takahashi, Yoshiaki*; Kawakami, Susumu; Umeki, Hiroyuki; Yui, Mikazu; Uragami, Manabu*

JNC TN8400 2005-016, 49 Pages, 2005/09

JNC-TN8400-2005-016.pdf:5.45MB

The sealing performance of a repository should be considered in the safety assessment of the geological disposal system of the high level radioactive waste. Nuclear Waste Management Organization of Japan and Japan Nuclear Cycle Development Institute are examining the sealing performance of the closure components (backfilling material and clay plug) to present the concept on the sealing performance required to the disposal system, and to develop the direction for the future R&D programme for the design requirements of the closure components of the presented concepts.The first step of this examination reviewed the current status of the domestic and the international sealing technologies, summarized the repository components and the repository environments, and performed the hydraulic analysis considering components on the intersections of a main tunnel and a disposal tunnel in a disposal panel and in and around the engineered barrier system (EBS). Since all tunnels connect in the underground facility, understanding of hydraulic behaviour at the intersections of the tunnels is the important issue to estimate migration of radionuclides from the EBS, and to evaluate the required sealing performance for the disposal system. The considering components in the analysis model are the intersections of the disposal tunnel and the main tunnel, the waste package, the EBS, the backfilling material, the clay plug, the concrete plug, the excavated disturbed zone, the tunnel lining and the host rock. Alteration of the concrete material (tunnel lining and concrete plug) is described as variation of the hydraulic conductivity of it. Sites of emplacement of the clay plug are the disposal tunnel and the main tunnel. No clay plug condition is also analysed. Effect of the clay plug is discussed by the results of these analyses.