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Transient Electron Heat Transport in LHD
https://ir.soken.ac.jp/records/522
https://ir.soken.ac.jp/records/522bfcfbb86742747ea98e6abe9559221f5
名前 / ファイル  ライセンス  アクション 

要旨・審査要旨 (301.6 kB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  Transient Electron Heat Transport in LHD  
タイトル  
タイトル  Transient Electron Heat Transport in LHD  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
YAKOVLEV, MYKHAYLO
× YAKOVLEV, MYKHAYLO 

フリガナ 
ヤコブレフ, ミカイロ
× ヤコブレフ, ミカイロ 

著者 
YAKOVLEV, Mykhaylo
× YAKOVLEV, Mykhaylo 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（学術）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第897号  
研究科  
値  物理科学研究科  
専攻  
値  10 核融合科学専攻  
学位授与年月日  
学位授与年月日  20050930  
学位授与年度  
値  2005  
要旨  
内容記述タイプ  Other  
内容記述  A decrease in global energy confinement with increase in the heating power is observed in the Large Helical Device (LHD) even in the inward shifted (R<SUB>ax</SUB>, = 3.5m) magnetic configuration where the heat transport predicted by the neoclassical theory is small. Moreover, the flattening of temperature profile inside the low order rational surface and saturation of core T<SUB>e</SUB> are observed with respect to increase of the heating power. These observations suggest that the turbulence and rational surfaces play an important role on heat transport in the LHD. The turbulence is usually driven by plasma free energy and thus it restricts the gradients of the local thermodynamic variables in a plasma. When the turbulencedriventransport is dominant, the heat flux is not proportional to electron temperature gradient ∇T<SUB>e</SUB> but is a nonlinear function of electron temperature T<SUB>e</SUB> and ∇T<SUB>e</SUB>. The effect of magnetic configuration on transport is also important because it influences the turbulence in many aspects. In addition, the magnetic field structure (e.g. magnetic island) directly affects the over all plasma confinement. In this thesis, the nonlinearity in the heat transport and effect of the rational surfaces are studied by using the transient transport analysis in the LHD. <br /> The perturbative analysis is recognized as a powerful tool to study an effect of turbulence on transport and its unique feature makes possible to study the transport in the almost flat electron temperature region, where the usual analysis based on the calculated power deposition and measured gradients is not applicable. To study the transport features of the confined plasmas, the heat pulse propagation experiments are performed by onaxis electron cyclotron heating (ECH) power modulation on the LHD plasmas with neutral beam injection (NBI). The heat pulse propagation can not be explained by transport features obtained from the steady state analysis. Requirement of larger (35 times) heat diffusivity to reproduce the heat pulse propagation in Coand balanced NBI plasmas indicates the nonlinearity of the heat transport. The analysis method for the heat pulse propagation based on the nonlinear dependence of heat diffusivity X<SUB>e</SUB> on T<SUB>e</SUB> and ∇T<SUB>e</SUB> is established. One of the first principle turbulence transport model, the critical temperature gradient scale length model, is tested for quantitative understanding of nonlinearity of heat transport in the LHD. The critical temperature gradient scale length model with optimized parameters, which is obtained from the heat pulse propagation, can also explain the results of the cold pulse propagation experiment. <br /> The effect of the rational surface on the heat transport is found to be more important in the counter dominant NBI heated plasmas. A unique feature of heat pulse propagation is observed near the m/n = 2/1 rational surface (m, n are the poloidal and toroidal mode numbers, respectively). A simultaneous response of the temperature perturbation on radially separated flux surfaces is observed. This nonmonotonic heat pulse propagation can not be explained even if the heat transport is strongly nonlinear. The change in the magnetic field topology due to enlargement of a magnetic island structure is used to explain this nonmonotonic heat pulse propagation phenomenon. The estimated Opoint position of the island is located near the m/n = 2/1 rational surface. The m/n = 2/l island healing with decrease in electron collisionality is also observed as was predicted by theories. The magnetic island enlargement is considered to be related to a direction and profile of plasma current mainly driven by NBI. The simple equation of heat pulse propagation in slab geometry with timedependent boundary conditions is used to evaluate the heat diffusivity inside the magnetic island. The estimated electron heat diffusivity inside an m/n = 2/l magnetic island has same order as X<SUB>e</SUB> obtained from the power balance analysis in the Co NBI plasmas. <br /> The core T<SUB>e</SUB> flattening region in the presence of the m/n = 2/1 island is found to be a stiff structure. No increase in ∇T<SUB>e</SUB> is observed with respect to the change in the power of onaxis ECH. High power ECH above a critical value injection can break this stiff structure, and steep T<SUB>e</SUB> profile is formed just inside the rational surface. The role of the m/n 2/1 rational surface and presence of an island in the formation of internal transport barrier (ITB) is discussed in CtrNBI plasmas, where the enlargement of the m/n =2/1 island is indicated.  
所蔵  
値  有 