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Hysteresis and fast timescales in transport relations of toroidal plasmas
Itoh, K.,Itoh, S.-I.,Ida, K.,Inagaki, S.,Kamada, Y.,Kamiya, K.,Dong, J.Q.,Hidalgo, C.,Evans, T.,Ko, W.H.,Park, H.,Tokuzawa, T.,Kubo, S.,Kobayashi, T.,Kosuga, Y.,Sasaki, M.,Yun, G.S.,Song, S.D.,Kasuya, International Atomic Energy Agency 2017 Nuclear fusion Vol.57 No.10
<P>This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradient–flux relation. The key finding is that hystereses were observed simultaneously in both the the gradient–flux and gradient–fluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation <img ALIGN='MIDDLE' ALT='$\delta T_{\rm m}$ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102021/nfaa796aieqn001.gif'/> in heating modulation experiments. The hysteresis introduces the term <img ALIGN='MIDDLE' ALT='$\delta T_{\rm m}$ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102021/nfaa796aieqn002.gif'/>, which depends on the harmonic number <I>m</I> in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for ‘the heating heats turbulence’ is that the external source <I>S</I> in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on confinement. Finally, the impacts of transport hysteresis on the control system are assessed. Control systems must be designed so as to protect the system from sudden plasma loss.</P>
Extension of the operational regime of the LHD towards a deuterium experiment
Takeiri, Y.,Morisaki, T.,Osakabe, M.,Yokoyama, M.,Sakakibara, S.,Takahashi, H.,Nakamura, Y.,Oishi, T.,Motojima, G.,Murakami, S.,Ito, K.,Ejiri, A.,Imagawa, S.,Inagaki, S.,Isobe, M.,Kubo, S.,Masamune, S IOP 2017 Nuclear fusion. Fusion nucléaire. &n.Illiga Vol.57 No.10
<P>As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, <I>T</I> <SUB>i</SUB> and <I>T</I> <SUB>e</SUB>, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value <img ALIGN='MIDDLE' ALT='$\left\langle \beta \right\rangle $ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102023/nfaa7fc2ieqn001.gif'/>. The high <img ALIGN='MIDDLE' ALT='$\left\langle \beta \right\rangle $ ' SRC='http://ej.iop.org/images/0029-5515/57/10/102023/nfaa7fc2ieqn002.gif'/> regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.</P>
Current Challenges and Future Opportunities for Child and Adolescent Psychiatry in Japan
Masaru Tateno,Takahiko Inagaki,Takuya Saito,Anthony P. S. Guerrero,Norbert Skokauskas 대한신경정신의학회 2017 PSYCHIATRY INVESTIGATION Vol.14 No.5
Japan has been facing a serious shortfall of child and adolescent psychiatric workforce relative to increasing service needs. Likely because of a combination of limited workforce supply and limited trust or perception of effectiveness, mental health services are under-utilized by the educational and child welfare systems. Child and adolescent psychiatry (CAP) has not been a formally established specialty in Japan. The lack of basic structure in the specialty most likely contributes to a lack of training facilities, limited exposure to and interest in the specialty, and hence an inadequate workforce. To date, there exists no standardized training program for CAP in Japan and each training hospital determines its own teaching curriculum and training content. Clinical experience in CAP varies greatly among hospitals. To solve current problems in child and adolescent psychiatry in Japan, we advocate for the development and establishment of a more standardized child and adolescent psychiatry training system that is akin to what exists in the US and that teaches and evaluates according to specific competencies. Through standardizing care and education and ultimately improving workforce, the quality of mental health services can be raised. The tragic and costly consequences of unidentified and untreated mental illness in youth can be avoided by taking timely evidence based actions in partnership with others.
Kobayashi, T.,Ida, K.,Inagaki, S.,Tsuchiya, H.,Tamura, N.,Choe, G.H.,Yun, G.S.,Park, H.K.,Ko, W.H.,Evans, T.E.,Austin, M.E.,Shafer, M.W.,Ono, M.,Ló,pez-bruna, D.,Ochando, M.A.,Estrada, T.,Hidalg IOP 2017 Nuclear fusion. Fusion nucléaire. &n.Illiga Vol.57 No.7
<P>In this contribution we analyze modulation electron cyclotron resonance heating (MECH) experiment and discuss higher harmonic frequency dependence of transport coefficients. We use the bidirectional heat pulse propagation method, in which both inward propagating heat pulse and outward propagating heat pulse are analyzed at a radial range, in order to distinguish frequency dependence of transport coefficients due to hysteresis from that due to other reasons, such as radially dependent transport coefficients, a finite damping term, or boundary effects. The method is applied to MECH experiments performed in various helical and tokamak devices, i.e. Large Helical Device (LHD), TJ-II, Korea Superconducting Tokamak Advanced Research (KSTAR), and Doublet III-D (DIII-D) with different plasma conditions. The frequency dependence of transport coefficients are clearly observed, showing a possibility of existence of transport hysteresis in flux-gradient relation.</P>
Formation of metallic NbSe2 nanotubes and nanofibers
T.Tsuneta,T.Toshima,K.Inagaki,T.Shibayama,S.Tanda,S.Uji,M.Ahlskog,P.Hakonen,M.Paalanen 한국물리학회 2003 Current Applied Physics Vol.3 No.6
We succeed in synthesizing NbSe2 nanotubes along with nanofibers by chemical vapor transportation. They are stable crystalline systems and can be synthesized reproducibly in a nearly equilibrium reacting process. We have investigated these nanosize structures of NbSe2 by transmission electron microscopy and electron diffraction. Both of the structures have a similar size of 100–200 nm in diameter. While nanotubes consist of rolled-up NbSe2 layers, nanofibers are a pile of thin flat layers. We propose a mechanism of the formation of NbSe2 nanotubes and nanofibers on the basis of deseleniditive transition from a NbSe3 fiber-shaped crystal. We also measured electrical resistance of the nanofibers with conductive atomic force microscopy and demonstrated that the material show metallic behavior at room temperature. 2003 Elsevier B.V. All rights reserved.