S15-2
Spectroscopic modeling for high Z impurities with their atomic processes andtransport from wall to core plasma in LHD
LHDにおける壁からコアでの高Ｚ不純物の原子過程と輸送の分光モデル
Izumi Murakami1, Daiji Kato1, Chihiro Suzuki1, Hiroyuki A. Sakaue1, Hisamichi Funaba1 et al.
村上泉1, 加藤太治1，鈴木千尋1，坂上裕之1，舟場久芳1，野上啓祐2, 剣持貴弘3, 酒井康弘2，
古屋謙治4，本橋健次5, 後藤基志1，田村直樹1，須藤滋1，森田繁1，LHD実験グループ1
1

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu, Japan
核融合科学研究所 〒509-5292 岐阜県土岐市下石町322-6
2
Department of Physics, Toho University, Miyama, Funabashi, Chiba 274-8510, Japan
東邦大学理学部 〒274-8510 千葉県船橋市三山2-2-1
3Faculty of Life and Medical Sciences, Doshisha University, Tatara-Miyakodani, Kyotanabe, Kyoto 610-0394, Japan
同志社大学生命医科学部〒610-0394 京都府京田辺市多々羅都谷1-3
4Interdisciplinary Graduate School of Enginnering Sciences, Kyushu University,Motook, Nishi-ku, Fukuoka, Japan
九州大学総合理工学府 〒819-0395福岡市西区元岡744
5Faculty of Science and Engineering, Toyo University, 2100 Kujirai, Kawagoe, Saitama 350-8585, Japan
東洋大学理工学部〒350-8585 埼玉県川越市鯨井2100
Qunatitative tungsten study with reliable atomic modeling is important for successful achievement of ITER.
We have developed tungsten atomic modeling for understanding the tungsten behavior in fusion plasmas.
The modeling is applied to the analysis of tungsten extreme ultraviolet (EUV) spectra observed fromplasmas of Large Helical Device (LHD) and compact electron beam ion trap (CoBIT). We found EUVemission peaks at 1.5-4 nm of W22+ - W33+ ions are useful to determine the charge state distribution.
Unresolved transition array (UTA) feature are reproduced by our model. Transport calculation helps tounderstand tungsten behavior in LHD plasma. We obtained mean velocities of sputtered tungsten atom byion beam experiments and the result indicates importance of atomic structure for tungsten kinetics.

1. Introduction
Tungsten is used as plasma-facing material in
ASDEX Upgrade [1] and JET [2] to support ITER
project because of high melting point and low
sputtering yield by hydrogen. However, tungsten
is sputtered by impurities from limiter [3] ordivertor plates and accumulated in core plasma.
Tungsten causes large radiation power loss andcools plasma. It is important for stable operationof ITER to study the influx and transport oftungsten ions with a spectroscopic method.
Previous studies on tungsten atomic modeling
have not fully explained the tungsten EUV
spectra, e.g. an unresolved transition array (UTA)seen at 4.5-7.0 nm in plasma with electron
temperature Te <1.5 keV [4], which corresponds
to edge plasma temperature for ITER. Since theUTA is composed of numerous transitions, it has
been difficult to analyze the UTA. We need areliable atomic model for tungsten over wide
temperature range.
We have developed a tungsten atomic modelwith detailed atomic structure, and we applied themodel to analyze EUV spectra measured fromCoBIT plasmas [5] with tungsten hexacarbonyl

vapor and from the LHD plasmas with tungsten
pellet injection. The CoBIT experiments wellcontrol the charge distribution of tungsten ions.
The information from the CoBIT spectra is
helpful to understand EUV spectra in the LHD.
2. Tungsten Atomic Model
We have constructed a collisional-radiative (CR)model for tungsten ions. Atomic data in the CR
model are calculated with the HULLAC atomiccode [6]. We consider electron configurations withprincipal quantum number n up to 6 including
inner-shell excited states for atomic structure andup to 20,000 J-resolved fine-structure levels areincluded for one ion in the CR model. As atomicprocesses, electron-impact ionization, excitationand de-excitation processes, and radiative decay areincluded. Recombination processes are ignored.
Here we examine Wq+ ions with q = 20-45, which
are N-shell ions with outermost electron in n = 4
shell for the ground state, and they are seen in LHD
plasma with Te < 3 keV.
3. EUV Spectroscopic Measurements
Tungsten EUV spectra at 1.5-4 nm wavelengthregion were measured in CoBIT with various
electron beam energies. The charge states ofobserved emission peaks were determined. Using
the CR model, we calculated EUV spectra with thephysical condition of CoBIT, i.e., ne = 1016 m-3 andmono-energy electron distribution and identified
emission peaks as 6g–4f, 5g–4f, 5f–4d, and 5p–4dtransitions of W19+–W33+ ions [7]. The peakwavelengths shift shorter for higher charge states
and they are useful to determine the charge state
distribution in LHD plasmas.
For LHD plasmas, tungsten was injected as animpurity pellet or a tracer-encapsulated solid pellet(TESPEL) in NBI heated discharges. A pellet wasablated in the vicinity of normalized minor radius
ρ~0.8, and tungsten was ionized and transferred
into a core plasma region. After pellet injection
electron temperature dropped due to large
radiation loss by tungsten at the central region andrecovered with NBI heating. Tungsten EUV
spectra at 1.5-4 nm were measured in LHD, whichwere similar to the spectra measured in CoBIT. Wecalculated spectra using the CR model with theplasma condition of LHD and synthesized spectrawith ion abundances determined to match with themeasured spectra. Obtained charge distributions
are shown in Fig. 1 for two cases. Our model
calculations well reproduce the LHD spectra. We
also synthesized spectra at 4-7 nm with thedetermined ion abundance and the two-peak UTA
feature is obtained as shown in Fig.2.

4. Tungsten Behavior in LHD
We performed tungsten transport calculation withthe STRAHL code [8] for the discharge analyzed
above to demonstrate tungsten behavior in the LHD
plasma. In this calculation we use ionization andrecombination rates from ADAS [9], since we needcomplete sets of these rates from neutral to fully
ionized tungsten ion. Constant diffusion coefficient
D=0.1m2/s and spatial dependent inward convection
velocity up to -2 m/s at ρ=0.5-1.0 are assumed.
Obtained spatial and temporal distributions oftungsten ions reasonably explain the obtained
charge state distributions.
5. Mean Velocity of Sputtered Tungsten Atom
We measured tungsten velocity sputtered fromtungsten target irradiated by ion beam to understandbehavior of sputtered tungsten atom [10]. The mean
normal velocities are dependent on energy
difference between the work function and ionization
potential of the excited states. This indicates thatdetailed atomic structure of sputtered tungsten atom
influence tungsten kinetics and need to consider thiseffect in particle simulations for divertor plasmas.
6. Summary
We have developed tungsten atomic modeling tounderstand tungsten behavior in fusion plasma andanalyze EUV spectra measured in LHD plasmas.
AcknowledgmentsThe authors acknowledge all members of the LHD
Experiment Group for their technical support and fruitful
discussions. This work is supported partly by JSPS
Grant-in-Aid for Scientific Research (A) 23246165 and(B) 23340183, JSPS Grant-in-Aid for Young Scientists(B) 23740412, and the JSPS-NRF-NSFC A3 Foresight
Program in the field of Plasma Physics (NSFC: No.
11261140328).

Fig.1 Obtained charge distribution for tungsten ions inLHD plasma discharge 112880 at t = 4.64 s (Te = 0.7keV) and t = 4.80 s (Te = 1.4 keV).

Fig.2. Synthesized spectra using obtained charge
distributions for LHD plasma.

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