H. Hasegawa

S. Ishiguro

National Institute for Fusion Science (NIFS-Repository)

Recently, it is reported that ﬁlamentary coher-ent structures are formed intermittently in non-uniformplasma such as scrape-oﬀ layer (SOL) of magnetic con-ﬁnement fusion devices1). In such kind of structure, mi-croscopic mechanics such as sheath formation betweenplasma and divertor plate, charge separation, and insta-bility induced by shear ﬂow are believed to have an inﬂu-ence on macroscopic dynamics. Thus, the purpose of thisstudy is the development of a holistic code which con-nects microscopic mechanics with macroscopic dynamicsand computes such a hierarchy system self-consistently.First, as an initial stage of the study, we have developeda three dimensional electrostatic plasma particle code2)and investigated microscopic mechanics in such struc-tures with the code.In Fig. 1 we present the conﬁguration of the simu-lation. An ambient magnetic ﬁeld is directed along thepositive z axis (equivalent to the toroidal direction). Thestrength of magnetic ﬁeld has a gradient along the posi-tive x axis (equivalent to the counter radial direction) as2LxB0/(3Lx − x) where Lx, Ly, and Lz are the systemsize in the x, y, and z directions and B0 is the magneticﬁeld strength at x = Lx. Particle absorbing boundaryis placed at x = 0 as the shaded planes shown in Fig. 1.The plane at x = 0 corresponds to the ﬁrst wall. Inthe y (equivalent to the poloidal direction) and z direc-tions, periodic boundary condition is applied. A coherentstructure is initially set as a column along the externalmagnetic ﬁeld (as shown in Fig. 1). The initial densityconﬁguration of the structure in the cross section is givenby the Gaussian distribution with the width δb. A moredetailed description of parameters is shown in Ref. [3].Figure 2 shows electron density distributions in thex-y plane at z = Lz/2 at ωpet = 100, 800, 1,500,2,200, and 2,900 where the system size Lx × Ly × Lzis 64λDe × 64λDe × 16λDe. The initial radius of thestructure is δb = 4.0λDe. The structure is initially lo-cated at around (x, y) = (48λDe, 32λDe). As shown inFig. 2, the structure evolves to a mushroom-shaped pro-ﬁle. This fact is in agreement with previous result of thetwo-dimensional reduced ﬂuid model simulations4).Fig. 1: Conﬁguration of the simulation.Fig. 2: Electron density distributions in the x-y planeat z = Lz/2 at ωpet = 100, 800, 1,500, 2,200, and 2,900.1) Krasheninnikov, S. I. et al.: J. Plasma Phys. 74(2008) 679 and references therein.2) Ishiguro, S. and Hasegawa, H.: J. Plasma Phys. 72(2006) 1233.3) Hasegawa, H. and Ishiguro, S.: Plasma Fusion Res. 7(2012) 2401060.4) Bian, N. et al.: Phys. Plasmas 10 (2003) 671.394§23. Development of Holistic Simulation Model for Plasma Coherent StructuresIshiguro, S., Hasegawa, H.

Development of Holistic Simulation Model for Plasma Coherent Structures

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