30E02P
中高密度ヘリカルプラズマにおける両極性径電場・新古典エネルギー拡散の検証と装置間比較
Inter-Machine Validation Study of Neoclassical Transport Modeling inMedium- to High-Density Stellarator-Heliotron Plasmas
M.Yokoyama, A.Dinklage1, J.L.Velasco2, et al.,
LHD Experiment Group, W7-AS Team1, TJ-II Team2
National Institute for Fusion Science, Japan,
Max-Planck-Institut fur Plasmaphysik, Germany1,
The National Fusion Laboratory, CIEMAT, Spain2
In order to test a recently concluded
benchmarking of calculations of NC transportcoefficients [1], and extending previous studiesof electron energy transport at low densities [2],this study compares experimental findings
with NC transport predictions for medium- tohigh-density S-H plasmas.
The focus is put on recent experiments
conducted in LHD and TJ-II also involving
findings from Wendelstein 7-AS (W7-AS) [3]. In
3D magnetic configurations, radial electricfields (Er) must arise to satisfy the ambipolar
condition which is not intrinsically satisfied as
inaxisymmetrictokamaks.
Inthelong-mean-free-path (lmfp) at sufficiently highdensities above a few times 1019 m-3, Er is well
predicted by the NC ambipolarity condition andis found to be in the so-called ion-root. Er has
particular impact on the energy fluxes of theions.
Dedicated experiments performed in LHD andTJ-II can be summarized as follows. In LHD,
discharges with high heating power withne>3x1019 m-3, Te,i>1 keV have been obtained.
The variation of the heating power (ion/electron
heating ratio as well), density and magnetic
configuration forms a systematic database. In
TJ-II, obtained parameters have been
ne~4x1019 m-3,, Te~300 eV and Ti~120 eV. The
NC particle and energy fluxes are evaluated byconvoluting the mono-energetic transportcoefficients calculated by DKES [4] in W7-AS
and TJ-II, and by DGN/LHD [5] in LHD.
It is found that the measured negative Er is
consistent with NC ambipolar ion-root
conditions for all devices. Higher density andcomparable
temperatures
towards
reactor-relevant S-H plasmas tend to weaken
the bifurcation capability of Er as reported forelectron-root conditions [2]. Differently, in TJ-II
the experimentally observed Er is morenegative than the predicted NC ambipolar Er.
Steady-state energy balance analyses wereperformed using the integrated transport code,
TASK3D [6] for LHD, and by ASTRA [7] inTJ-II. For W7-AS, the experimentally
determined particle and energy fluxes werecompared to NC fluxes with transportcoefficients from DKES and found to beconsistent with NC theory up to 2/3 of theminor radius. For an example of LHD
discharge, it is found that the ion energy flux isclose to the NC energy flux up to 2/3 of theplasma radius. However, since the NC energy
flux has a strong dependence on the value of Er,more systematic survey utilizing the databasewould be required for a conclusive statement.
In TJ-II, the ion energy flux has been found tobe beyond the prediction of local NC theory.
References[1] Beidler C D et al., Nucl. Fusion 51 (2011) 076001.
[2] Yokoyama M et al., Nucl. Fusion 47 (2007) 1213.
[3] Baldzuhn J et al., Plasma Phys. Control. Fusion 40(1998) 967.
[4] Hirshman S P et al., Phys. Fluids 29 (1986) 2951.
[5] Wakasa A et al., Contrib. Plasma Phys. 50 (2010)582.
[6] Yokoyama M et al., Plasma and Fusion Res. 7 (2011)2403011.
[7] Pereverzev GV, IPP 5/98, Max-Planck Institut fürPlasmaphysik (2002).
[8] Tribaldos V et al, Plasma Phys. Control. Fusion 47(2005) 545.

Acknowledgement

This work has been conducted based on IEA
Implementing
Agreementon
Cooperationin
DevelopmentofStellarator-Heliotron
Concept
http://iea-shc.nifs.ac.jp/. It has been supported byNIFS/NINS under the project, “Promotion of theInternational Collaborative Research Network
Formation”.