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RISS 인기검색어
- 검색키워드
- 저자 : T. Tokuzawa (검색결과 3 건)
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- 유료
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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>
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Recent progress in Large Helical Device experiments
Akio Komori,T. Shimozuma,T. Ido,T. Kobuchi,T. Seki,T. Ozaki,T. Fujita,T. Watari,T. Akiyama,T. Tokuzawa,T. Uda,T. Minami,Y. Nakamura,Y. Torii,Y. Sakamoto,Y. Takeiri,Y. Nagayama,Y. Oka,Y. Narushima,Y. Y 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
In the Large Helical Device (LHD), some reactor-oriented experiments, i.e. high beta, high ion temperature, steady state operation, have produced remarkable progress in recent experimental campaigns. By optimizing the rotational transform, an average beta value of 4.3 %, which is the highest on record for helical devices, was achieved. The ICRF sustained steady-state discharges for more than 30 minutes, these were also successfully performed with the aid of the magnetic axis swing technique for the reduction of the heat load to the plasma-facing component. In the discharge, the total input energy to the plasma reached 1.3 GJ, which also established a new record.1
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Tanaka, K.,Nagaoka, K.,Murakami, S.,Takahashi, H.,Osakabe, M.,Yokoyama, M.,Seki, R.,Michael, C.A.,Yamaguchi, H.,Suzuki, C.,Shimizu, A.,Tokuzawa, T.,Yoshinuma, M.,Akiyama, T.,Ida, K.,Yamada, I.,Yasuhar IOP 2017 Nuclear fusion Vol.57 No.11
<P>Surveys of the ion and electron heat transports of neutral beam (NB) heating plasma were carried out by power balance analysis in He and H rich plasma at LHD. Collisionality was scanned by changing density and heating power. The characteristics of the transport vary depending on collisionality. In low collisionality, with low density and high heating power, an ion internal transport barrier (ITB) was formed. The ion heat conductivity (<I>χ</I> <SUB>i</SUB>) is lower than electron heat conductivity (<I>χ</I> <SUB>e</SUB>) in the core region at <I>ρ</I> < 0.7. On the other hand, in high collisionality, with high density and low heating power, <I>χ</I> <SUB>i</SUB> is higher than <I>χ</I> <SUB>e</SUB> across the entire range of plasma. These different confinement regimes are associated with different fluctuation characteristics. In ion ITB, fluctuation has a peak at <I>ρ</I> = 0.7, and in normal confinement, fluctuation has a peak at <I>ρ</I> = 1.0. The two confinement modes change gradually depending on the collisionality. Scans of concentration ratio between He and H were also performed. The ion confinement improvements were investigated using gyro-Bohm normalization, taking account of the effective mass and charge. The concentration ratio affected the normalized <I>χ</I> <SUB>i</SUB> only in the edge region (<I>ρ</I> ~ 1.0). This indicates ion species effects vary depending on collisionality. Turbulence was modulated by the fast ion loss instability. The modulation of turbulence is higher in H rich than in He rich plasma.</P>
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