04pC09
高パワー加熱を用いた LHD 長時間放電における不純物挙動
Impurity behavior in LHD long pulse discharges with high power heating
中村幸男, 田中謙治, 吉村信次, 吉沼幹朗, 鈴木千尋, 田村直樹, B.J. Peterson
NAKAMURA Yukio, TANAKA Kenji, YOSHIMURA Shinji, YOSHINUMA Mikiro, SUZUKI Chihiro,
TAMURA Naoki, Byron Jay PETERSON

核融合研
NIFS
Impurity behavior has been mainly investigated sofar in long pulse discharges with low NBI heating power(< 3 MW). The upgrade of NBI heating systems (Pnbi ~10 MW, td ~ 5 s) enables us to maintain highperformance plasmas for long time. Now we can study
impurity behavior in long pulse discharges with hightemperature plasma. Here, we report the experimental
results in long pulse discharges with high NBI heatingpower (Pnbi = 3~10 MW).
Figure 1 shows a typical long pulse discharge withhigh NBI heating power. In the early stage of thisdischarge, the total heating power is about 10 MW andthe heating power steps down to 6 MW at around 6 s.
The line averaged radiation intensity (AXUVD signal)and the intrinsic impurity line intensity (Fe XXIII) at thecentral chord of plasma increase gradually and seem tobe saturated. The step down of heating power brings out
a discontinuous rise of the radiation and the impurity line
intensity. The measurements of local radiation powerwith bolometer arrays show a hollow profile in the highpower phase and a peaked profile in the low power phase,as shown in Fig. 2, where the normalized radiation
profiles are plotted for various heating powers. The
peaked radiation profile also appears in a quasi-steadystate discharge with 6 MW. As found in the previous

study [1,2], there is an impurity accumulation window inthe operational regime of hydrogen discharges on LHD
and the plasma parameters in these discharges
corresponds to those in the accumulation window.
However, no peaked radiation profile is observed in thehigh power discharge with 10 MW. Another importantfeature is to enhance the radiation in the edge plasma
region.
According to neoclassical theory of impurity
transport in helical plasma, the convection term depends
on radial electric field (positive: outward, negative:inward) and normalized temperature gradient (outward).
In these discharges, the radial electric fields are negative
and almost the same. For hydrogen discharges withvarious heating powers (3~10 MW), we measured
radiation profiles in the range of accumulation window.
Figure 3 shows the dependence of radiation peaking
factor on the normalized electron temperature gradient.
Although the temperature gradient depends on theheating power, the normalized temperature gradient does
not change largely. However, no peaking of radiation isobserved in the discharges with high heating power (10MW). Such a drastic change suggests that there is a new
type of outward convection (due to plasma turbulenceetc.) in the core region for high power heating. This may
be related to impurity hole observed in high Ti mode inLHD. Further investigations on carbon density profileand density fluctuation will be discussed.
4.0(!=0.945)

114893 (Pnbi ~ 2.5 MW)
114887 (Pnbi ~ 6 MW)
114884 (Pnbi ~ 10 MW)

3.0(!=0.54) / S

rad

1.0

rad

0.5

2.0

1.0S

Normalized Radiation Profile

1.5

0.0

0.0

0.2

0.4

0.6!

0.8

1.00.00.00.5
1.0-dT /d! / T (!=0.5)
e1.5eFig. 2. Radiation profiles for Fig. 3. Dependence of radiation
various heating powers
peaking factor on
normalized Te gradientFig. 1. NBI long pulse discharge with different heating
powers of 6 MW and 10 MW

References[1] Y. Nakamura et al., PPCF 44 (2002) p.2121[2] Y. Nakamura et al., NF 43 (2003) p.219