A. Wakasa

M. Yokoyama

S. Matsuoka

S. Murakami

S. Satake

National Institute for Fusion Science (NIFS-Repository)

Recent LHD experiments have achieved highelectron temperature (Te) reaching 20 keV at theplasma core, and such high Te plasmas are called CERC(Core Electron-Root Conﬁnement) plasmas1). A CERCplasma is characterized by its high Te with the steepTe gradient of the electron internal transport barrier(eITB) and the large positive (electron-root) radialelectric ﬁeld (Er). The neoclassical transport (NC) isstill important in helical devices, since it increases dueto the helically-trapped particles in the low collisionalityplasmas. The NC particle ﬂux plays a key role to deter-mine the ambipolar Er in helical devices. Although theion ﬁnite orbit width (FOW) eﬀect on ion NC transportcalculations has attracted much attention in recentstudies, electron NC transport has been so far evaluatedwithout FOW eﬀect due to the small mass of electrons.In CERC plasmas, however, the electron neoclassicaltransport needs to be evaluated with electron FOWeﬀect because the FOW eﬀect of the helically-trappedelectron increases in proportion to T 7/2e . For thispurpose, we have extended a numerical NC transportcalculation code, FORTEC-3D (F3D)2), to be appli-cable to the electron. F3D solves the drift kineticequation based on δf Monte-Carlo method. In F3D,particle orbits including the radial drift are traced, andthe NC transport thus obtained involves the FOW eﬀect.Benchmark calculation of electron FORTEC-3DWe have carried out benchmark calculations amongF3D, DCOM/NNW (DCN), and GSRAKE codes. Thelatter two numerical codes are widely used for the NCtransport analysis based on the local NC transportcalculation which neglects the FOW eﬀect. It has beenconﬁrmed that results of F3D agree well with thoseobtained by DCN and GSRAKE for the low Te and highcollisionality plasma. Numerical results for a high Te (5keV at the core) and low collisionality plasma are shownin Fig.13). As shown in this ﬁgure, while the particleﬂux rapidly increases at around Er = 0 for both DCNand GSRAKE, the F3D result shows similar but slightincrease at the positive Er. This indicates that theFOW eﬀect involves two diﬀerent physical mechanisms;(1) the poloidal resonance not at Er = 0 but at theﬁnite Er, and (2) the collisionless detrapping whichleads to the reduction of the particle ﬂux at the poloidalresonance.Transport analysis of LHD high Te plasmaWe have implemented the transport analysis for a 0 2 4 6 8 10 12 14-20 -15 -10 -5  0  5  10  15  20Γ [× 1018  m-2 s-1 ]Er [kV/m]ρ = 0.5GSRAKEDCOMF3DFig. 1: The Er dependence of the particle ﬂux at ρ =0.5 calculated by F3D, DCN, and GSRAKE.-5 0 5 10 15 0  0.2  0.4  0.6  0.8  1E r [kV/m]ρexpFORTEC-3DDCOM/NNWFig. 2: The radial proﬁle of Er obtained by F3D andDCN. Experimental observations are also plotted.CERC plasma including electron FOW eﬀect for the ﬁrsttime by using F3D4). The time evolution of Er is solvedsimultaneously with calculating the electron NC trans-port by F3D and referring to the ion particle ﬂux database obtained by DCN. Results of F3D is compared toexperimental observations and DCN results in Fig.2. Itis shown that Er at the core of approximately ρ < 0.2,where the CERC plasma has its characteristic Te gradi-ent and the electron-root Er, has a similar radial pro-ﬁle observed in the LHD experiment. The NC ﬂuxesthere also show larger diﬀerences from those of DCNat the core compared to the values approximately at0.3 < ρ < 0.6. This suggests that the electron FOWeﬀect aﬀects the ambipolar Er for CERC plasmas. Onthe other hand, Er of F3D at the edge shows the ion-root(weak, negative) value and it does not agree with the ex-perimental observations of the electron-root one. Moredetailed analyses on the NC transport and Er for CERCplasmas are being performed. The reason why the dif-ference between Er of F3D and the experiment arises atthe edge will be investigated.1) e.g., Yokoyama, M., et al., Fus. Sci. Tech., 50 (2006) 3272) Satake, S., et al., Plasma Fus. Res., 1 (2006) 0023) Matsuoka, M., et al., Phys. Plasmas, 18 (2011) 0325114) Matsuoka, M., et al., Plasma Fus. Res., 6 (2011) 1203016189§3. Calculation of the Electron Neoclassical Transport with Finite Orbit Width Effect and the Radial Electric FieldMatsuoka, S., Satake, S., Yokoyama, M., Wakasa, A. (Kyoto Univ.), Murakami, S. (Kyoto Univ.)

Calculation of the Electron Neoclassical Transport with Finite Orbit Width Effect and the Radial Electric Field

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)