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WIDE-FIELD IMAGING WITH MOSAIC CCD CAMERAS
OKAMURA S.,DOI M.,KAWASAKI W.,KOMIYAMA Y.,SHIMASAKU K.,YAGI M.,YASUDA N.,KASHIKAWA N.,SEKIGUCHI M. The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
An outline is given of our development of mosaic CCD cameras. Hardware and data reduction software of two operational cameras are described. Scientific objectives of wide-field imaging with the cameras are briefly described.
Studies on electron Bernstein wave heating in CHS and LHD at NIFS
Y. Yoshimura,H. Igami,S. Ferrando-Margalet,K. Nagasaki,S. Kubo,T. Shimozuma,M. Isobe,C. Suzuki,A. Shimizu,T. Akiyama,C. Takahashi,K. Nagaoka,S. Nishimura,T. Minami,K. Matsuoka,S. Okamura,T. Mutoh 한국진공학회 2007 한국진공학회 학술발표회초록집 Vol.16 No.2
Characteristics of second harmonic ECCD on CHS
yasuo Yoshimura,H. Matsushita,H. Igami,K. Nagasaki,K. Matsuoka,K. Ohkubo,K. Nagaoka,M. Isobe,S. Kobayashi,S. Okamura,S. Kubo,S. Nishimura,T. Minami,T. Akiyama,T. Notake,T. Shimozuma,A. Shimizu,C. Suzu 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
Second harmonic electron cyclotron current drive (ECCD) has been investigated on CHS (Compact Helical System) by using a 2-D steerable EC-beam injection system. The direction of the plasma current, which is the sum of bootstrap current and EC-driven current, is clearly reversed by a reversal of the EC-beam injection direction. The direction of driven current is consistent with expectation in the case of low-field side injection of EC wave. So far, a driven current up to 6 kA has been obtained when bootstrap current is less than 2 kA. It is confirmed that right-hand polarization and low density are effective for ECCD.
Plasma-Confinement Physics Study in Compact Helical System
stoichi Okamura,A. Fujisawa,A. Shimizu,C. Takahashi,C. Suzuki,H. Iguchi,H. Nakano,H. Matsushita,K. Nagaoka,K. Matsuo,K. Ida,K. Toi,K. Nakamura,K. Matsuoka,M. Yoshinuma,M. Isobe,M. Takeuchi,R. Ikeda,S. 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
In a CHS experiment, various types of transport barrier have been studied. An internal transport barrier (ITB) for electrons in a stellarator was first found in CHS, and the ITB for improved ion confinement was also found. H-mode (edge transport barrier) study in CHS showed many common features in transition to tokamak experiments, although the magnetic surface quantities are very different. Discharges with a combination of ETB and ITB were also found. Two heavy ion beam diagnostics in CHS showed a new direct measurement of zonal flow structure in toroidal confinement. The relation between the fluctuation and the transport barrier was also studied.
Structural and Magnetic Properties of Co₂MnSi Heusler Alloy Films
W. C. Lim,S. Okamura,N. Tezuka,K. Inomata,J. Y. Bae,H. J. Kim,T. W. Kim,T. D. Lee 한국자기학회 2006 Journal of Magnetics Vol.11 No.1
Recently half-metallic full-Heusler alloy films have attracted significant interests for spintronics devices. As these alloys have been known to have a high spin polarization, very large TMR ratio is expected in magnetic tunnel junctions. Among these alloys, CO₂MnSi full-Heusler alloy with a high spin polarization and a high Curie temperature is considered a good candidate as an electrode material for spintronic devices. In this study, the magnetic and structural properties of CO₂MnSi Heusler alloy films were investigated. TMR characteristics of magnetic tunnel junctions with a CO₂MnSi/SiO₂/CoFe structure were studied. A maximum MR ratio of 39% with SiO₂ substrates and 27% with MgO(100) substrates were obtained. The lower MR ratio than expectation is considered due to off-stoichiometry and atomic disorder of CO₂MnSi electrode together with oxidation of the electrode layer.
Takahashi, N.,Kajihara, T.,Okamura, C.,Kim, Y.,Katagiri, Y.,Okushima, Y.,Matsunaga, S.,Hwang, I.,Umeda, M. Current Biology Ltd ; Elsevier Science Ltd 2013 Current biology Vol.23 No.18
Plant roots respond to various internal and external signals and adjust themselves to changes of environmental conditions. In the root meristem, stem cells produce daughter cells that continue to divide several times. When these latter cells reach the transition zone, they stop dividing and enter the endocycle, a modified cell cycle in which DNA replication is repeated without mitosis or cytokinesis. The resultant DNA polyploidization, named endoreduplication, is usually associated with an increase of nuclear and cell volume and with cell differentiation [1-4]. At the transition zone, cytokinin signaling activates two transcription factors, type-B ARABIDOPSIS RESPONSE REGULATOR 1 (ARR1) and ARR12, and induces SHY2/IAA3, a member of the Aux/IAA family of auxin signaling repressors. This inhibits auxin signaling and reduces the expression of auxin efflux carriers, resulting in cell division arrest [5]. Such counteracting actions of two hormones are assumed to determine meristem size. However, it remains unknown whether cytokinins additionally control meristem size through an auxin-independent pathway. Here we show that, in Arabidopsis, the cytokinin-activated ARR2 directly upregulates the expression of CCS52A1, which encodes an activator of an E3 ubiquitin ligase, anaphase-promoting complex/cyclosome (APC/C) [6], thereby promoting the onset of the endocycle and restricting meristem size. Our genetic data revealed that CCS52A1 function is independent of SHY2-mediated control of auxin signaling, indicating that downregulation of auxin signaling and APC/C-mediated degradation of cell-cycle regulators cooperatively promote endocycle onset, and thus fine tune root growth.
ryosuke Ikeda,C. Suzuki,G. Matsunaga,K. Toi,M. Takeuchi,S. Okamura 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
For the purpose of transport simulation, low temperature plasmas having similar dimensionless parameters to those of high temperature plasmas are produced by 2.45 GHz microwaves up to and 30 kW at low toroidal field (Bt < 0.1 T) in the Compact Helical System (CHS). In the configuration where the fundamental electron cyclotron resonance layer is placed near the last closed flux surface, electron density exceeds the ordinary (O)-mode cutoff density by a factor of 2 . 3 in hydrogen plasmas. The deposition of microwave power occurs in the interior region beyond the (O)-mode and extraordinary (X)-mode cutoff layers through which electron cyclotron waves (ECW) cannot penetrate. This suggests that a mode conversion of ECW to electron Bernstein wave (B-mode) would occur. Moreover, superimposition of ECW power was performed on target over-dense plasmas which have a steep density gradient at the upper hybrid resonance layer. In this condition, the mode conversion efficiency of superimposed ECW power was theoretically estimated to be about 50 . 60 %. The absorption rate of superimposed ECW power reached up to about 30 %.
Cryogenic system for COMET experiment at J-PARC
Ki, T.,Yoshida, M.,Yang, Y.,Ogitsu, T.,Iio, M.,Makida, Y.,Okamura, T.,Mihara, S.,Nakamoto, T.,Sugano, M.,Sasaki, K.i. Heywood Co ; Elsevier Science Ltd 2016 Cryogenics Vol.77 No.-
Superconducting conductors and cryogenic refrigeration are key factors in the accelerator science because they enable the production of magnets needed to control and detect the particles under study. In Japan, a system for COMET (Coherent Muon to Electron Transition), which will produce muon beam lines, is under the construction at J-PARC (Japan Proton Accelerator Research Complex). The system consists of three superconducting magnets; the first is a pion-capture solenoid, the second is a muon-transport solenoid, and the third is a detector solenoid. It is necessary to cool down the magnets efficiently using two-phase helium and maintain them securely at 4.5K. For stable cryogenic refrigeration of the magnets, a suitable cooling method, structures, and the irradiation effect on materials should be investigated. In this paper, we focus on the development of an overall cryogenic system for cooling the capture and transport solenoids. A conduction-cooling method is considered for cooling the capture and transport solenoids because of the advantages such as the reduction of total heat load, fewer components, and simplified structure. To supply cryogenic fluids (4.5K liquid helium and 58K gas helium) and currents to the conduction-cooled magnets subjected to high irradiation, cryogenic components (cooling paths in the magnets, transfer tubes, and a current lead box) are developed. Based on the environment of high irradiation, the conditions (temperature and pressure) of helium in cooling paths are estimated, as well as the temperature of the capture magnet. We develop a dynamic model for quench simulation and estimate the maximum pressure in the cooling pipe when the capture magnet quenches. We conclude with a discussion of the next steps and estimated challenges for the cryogenic system.