Speaker
Naoki Tamura
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1079.pdf
Initial Results on Impact of Background Hydrogen Isotope
on Impurity Behavior in the EC-heated LHD plasmas
N. Tamura1, 2, C. Suzuki1, K. Mukai1, 2, H. Funaba1, M. Yoshinuma1, 2, K. Ida1, 2,
T. Fornal3, A. Czarnecka3, M. Kubkowska3 and LHD Experiment Group1
1
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Japan,
2
The Graduate University for Advanced Studies (SOKENDAI), Toki, Japan,
3
Institute of Plasma Physics and Laser Microfusion, Warsaw, Poland
A first assessment of the impact of background hydrogen isotope on the impurity behavior
in EC-heated plasmas of the LHD has been performed. In the case of Hydrogen (H) plasmas, no
impurity accumulation has been observed up to 3.2 x 1019 m-3 as a line-averaged electron density
nebar with 2.1 MW ECH. The plasma was generally terminated as intended. On the other hand, in
the case of Deuterium (D) plasmas under the similar condition, the nebar of 3.0 x 1019 m-3 with 1.7
MW ECH, a plasma radiation suddenly started to increase, and then the plasma was finally
collapsed. During this event, there is no external fueling. This is a clear indication of the occurrence
of impurity accumulation, which can be also supported by the temporal behavior of the intensity of
line emissions from highly-ionized impurities externally introduced into the core plasmas. As
shown in Fig. 1, the decay time of the Li-like intensity from the Vanadium impurity ion, which was
introduced into the core plasma by the TESPEL method [1], in such high-density D plasma more
than doubled (0.848 s à 1.812 s), as compared to that in the similar-density H plasma. And, in
comparison with the H plasma, the rise time (time required to reach maximum) of the Vanadium
Li-like intensity in the D plasma is also increased. In general, the rise and decay time of the line
emission from the highly-ionized impurity
reflect mainly the diffusivity and convection
velocity, respectively. Therefore, the
experimental result clearly indicates that such
high-density D plasma has a lower impurity
diffusivity and larger impurity inward
convection velocity, as compared with the H
Fig. 1 Temporal evolution of Vanadium Li-like integrated
plasma under the similar condition. counts measured with a VUV spectrometer.
[1] S. Sudo and N. Tamura, Rev. Sci. Instrum. 83 023503 (2012).
*This work is supported by a Grant-in-Aid for Young Scientists from a Toray scientific foundation and a Grant-in-Aid
for Scientific Research (B) (Nos. 15H03759, and 15H04234) from Japan Society for the Promotion of Science and a
budgetary Grant-in-Aid (ULHH007, ULHH012) of the National Institute for Fusion Science.
