7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Characteristics of toroidally asymmetric behavior of divertor heat load related
to three-dimensionally localized radiation structure in impurity seeded plasmas
on LHD
Kiyofumi Mukai1, 2, Gakushi Kawamura1, 2, Suguru Masuzaki1, 2, Yuki Hayashi1, 2,Hirohiko Tanaka3, Byron J Peterson1, 2, Tetsutarou Oishi4, Chihiro Suzuki1, 2,Masahiro Kobayashi1, 2, and Koyo Munechika5
1
National Institute for Fusion Science, 2 SOKENDAI, 3 IMaSS, Nagoya University,4Graduate School of Engineering, Tohoku University, 5 Tokyo Institute of Technology
e-mail (speaker): mukai.kiyofumi@nifs.ac.jp

In fusion reactors, huge power exhaust toward divertor
region is mitigated by divertor detachment using
impurity seeding. Although divertor heat load reduction
in all toroidal sections is preferable, toroidallyasymmetric heat load reduction was observed in various
toroidal devices. The asymmetry is caused by thelocalization of the radiative cooling. While themeasurement of the localized radiation structure isrequired for the detailed investigation of the asymmetry,
toroidal arrays of resistive bolometers [1] and/or divertor
Langmuir probes [2] is generally used to speculate theasymmetry.
In this study, the three-dimensionally localized structureof the radiative cooling was extracted [3] using Principal
Component Analysis (PCA) from two-dimensionalradiation images measured with an InfraRed imaging
Video Bolometer (IRVB) [4, 5]. The IRVB has 520
channels (26 in toroidal and 20 in radial). Typical
two-dimensional radiation images in nitrogen (N2)seeded plasmas with toroidally-asymmetric heat load
reduction and in neon (Ne) seeded plasmas withtoroidally-symmetric heat load reduction are shown in
Figure 1 (a) and (b), respectively. It is difficult to discuss
the difference between the images through directcomparison. Therefore, PCA was applied to 34 images
each in N2 seeded plasmas and in Ne seeded plasmas. As
the result, a radiation feature in N2 seeded plasmas wasfound as one of the principal components as shown in
Figure 1 (c). The three-dimensional transport code
EMC3-EIRENE indicated that the ionization in one ofthe divertor legs is enhanced in nitrogen seedingcompared with Ne seeding due to the difference in thefirst ionization energy. The magnetic field lines from thedivertor leg were along the extracted radiation structure
and were terminated by the divertor where the heat loaddecreased due to the N2 seeding. These results indicatethat three-dimensionally localized structure of radiative
cooling was detected experimentally. The toroidallyasymmetric behavior with the different impurity seedingis also presented in the talk.
References[1] M.L. Reinke et al., , PSFC Research Report
PSFC/RR-14-3, MIT, Cambridge, 2014.
[2] H. Tanaka et al., Nucl. Mater. Energy 12 (2017)241-246.
[3] K. Mukai et al., Nucl. Mater. Energy 33 (2022)

101294.
[4] B.J. Peterson et al., Rev. Sci. Instrum. 72 (2001)
923–926.
[5] K. Mukai et al., Rev. Sci. Instrum. 89 (2018) 10E114.

Figure 1 Typical radiation images of IRVB in (a) N2and (b) Ne seeded plasmas. (c) Principal component
extracted from 68 images of N2 and Ne seeded plasmas.
A dashed ellipse indicates the localized structure in N2
seeded plasmas.