24aE25P
LHDのエルゴディック層における炭素不純物の発光強度・イオン温度・フロー速度の空間分布
Spatial profiles of emission intensity, ion temperature and flow velocity ofcarbon impurities in the ergodic layer of LHD
大石鉄太郎1,2，森田繁1,2，黄賢礼1，張洪明2，後藤基志1,2，LHD実験グループ1
Tetsutarou Oishi1,2, Shigeru Morita1,2, Xianli Huang1, Hongming Zhang2, Motoshi Goto1,2
and the LHD Experiment group1
1核融合研，2総研大核融合
1NIFS, 2SOKENDAI

Effects of edge stochastic magnetic fields on theimpurity transport have attracted attention widely.
Reduction of the cross-field impurity transport, so
called “impurity screening”, has been observed inLarge Helical Device (LHD) which has a thickstochastic magnetic field layer called “ergodiclayer” located outside the core plasma.
Theoretically it is said that a parallel impurity
momentum balance in the ergodic layer determines
direction and quantity of the impurity flow, which
could be one of key mechanisms of the impurity
screening. Therefore, a precise measurement on
the spatial profile of impurity flows is required as
an experimental approach to investigate theimpurity transport in such stochastic magnetic field.
A space-resolved spectroscopy using a 3 m
normal incidence vacuum ultraviolet (VUV)
spectrometer was developed to measure the VUVemission profiles in wavelength range of 300-3200
Å from impurities in the ergodic layer [1]. The
optical axis is perpendicular to the magnetic axis ata horizontally-elongated poloidal cross section.
Vertical profiles of emission intensity, ion
temperature and ion flow are derived by measuring
the Doppler profile of impurity line spectra.
Observed flow velocity is a projection along eachobservation chord, which is approximately directedalong the plasma major radius.
The impurity flows were derived by theDoppler shift of the CIV spectra with thewavelength of 1548.20 × 2 Å.
The VUV
spectroscopy was attempted for hydrogen
discharges with magnetic axis position of Rax, =3.60 m at toroidal magnetic field of Bt, = 2.75 T.
Figure 1 shows a vertical profile of the flow
velocity of carbon impurity ions measured for ahigh-density discharge with the line-averaged
electron density of 6.3 × 1013 cm-3. The horizontal
axis, Z, indicates positions of observation chords

evaluated at the major radius, R, of 3.60 m. The
impurity flows toward outboard direction wereclearly observed around Z = ±480 mm close to
top and bottom edges of the horizontally-elongatedpoloidal cross section of the plasma.
The
directions of the flows are consistent with those
calculated by a three-dimensional simulation code
EMC3-EIRINE qualitatively. The code predicts
that a friction force between bulk ions and impurity
ions becomes dominant in the parallel impurity
momentum balance in the ergodic layer when theelectron density increases [2].
It results inimpurity flows toward the divertor plates causing
the impurity screening phenomena.
This work was partially supported by the LHD
project financial support (NIFS14ULPP010),
Grant-in-Aid for Young Scientists (B) 26800282,
and JSPS-NRF-NSFC A3 Foresight Program in theField of Plasma Physics (NSFC: No.11261140328,
NRF: No.2012K2A2A6000443).
[1] T. Oishi et al., Applied Optics 53 (2014) 6900.
[2] M. Kobayashi et al., Nuclear Fusion 53 (2013)
033011.

Figure 1. Vertical profile of the flow velocity ofcarbon impurity ions in the ergodic layer derived by
the Doppler shift of the CIV spectra with thewavelength of 1548.20 × 2 Å.