富山大学水素同位体科学研究センター研究報告29 ･ 30 : 65‑70, 2010.

Effect of simultaneous implantatiOn on deuterium retention in tungsten

yasuhisa Oyal, sachiko Suzukil, Makoto Kobayashil, Rie Kuratal, shoji Miyamoto2,

Naoaki Yoshida2, NaokoAshikawa3, Akio Sagara3, Yuji Hatano4 and Kenji OkunoI
Radioscience Research Laboratoyy, FacultyofScience, Shizuoka UniversiO!, Shizuoka
422‑8529, Japan

Research InstitutejTor AIPlied Mechanics, Kyushu UniversiO?, Fukuoka, 81 6‑8580, Japan
National InstitutejTor Fusion Science, Glj:u, 509‑5292, JapanHydrogen Isotope Research Centef: UniversiOJ ofToyama, Toyama 930‑8555, Japan

Deuterium retention in tungsten irradiated simultaneously with deuterium, helium andcarbon ions was investlgated by TDS. Effect of irradiation pre‑damage on the deuterium
retention was examined by microstmcture obseⅣation with taking account of the TDSresults. It was found that deuterium was preferentially trapped by intrinsic defects for
simultaneous C+ and D2+ implanted山ngsten･ The deuterium trapplng by ion‑induced

defects was enhanced by the ion implantation.

In the case of simultaneous implantation with He+, the deuterium retention has largely
changed･ Especially, in the case of He+ and D2+ simultaneous implantation, the deuterium
retention increased compared to the sequential implantation. However, the triple ions
(He+‑D2+‑C+) implantation, the deuterium retention was almost the same as that f♭r the only

D2+ implanted tungsten, indicatlng the dynamic desorptlOn WOuld be enhanced･

Keywords: tritium retention, plasma‑surface interactions, tungsten, simultaneous
i mp 1 antationof the plasma facing components･

I. Introduction

Tb predict hydrogen isotope recycling,

Plasma facing materials play an key role inincluding tritium, it is important to elucidate themaintaining high purity D‑T plasma and theireffects of simultaneous implantation of carbon

selections are qulte important. Recently, theand/or helium on hydrogen isotope retention

combination of several different materials as
andノor recycling fbr山ngsten. The sputterlng

plasma facing materials for the first wall,
divertor and bafnes was deemed to be one of theyield ofW under implantation with C and D ionsas a function of the C fraction in the incident

best solutions [1‑3]. Therefわre, the assessment of

nux has been studied and it was shown that
tritium retention under simultaneous ionsdeuterium retention is limited by the number of
implantation circumstance is one of the criticalavailable traps [5]. Besides, implanted carbon
issues. Tungsten is considered as one of thecandidates

fわr

ITER

divertor

components

because of its low sputtering yield and low

exists in several chemical fbms in tungsten. At

higher temperatures, WC layer is fbmed [6],which was confirmed by chemical shift of XPS

tritium retention l114]. In addition, carbon is[7]. h addition, the implantation or helium
considered to be used fわr high heat load reglOnS

produced by the D‑T nuclear reaction will65

Y. Oya, S. Suzuki, M. Kobayashi, R. Kurata, S. Miyamoto, N. Yoshida, N. Ashikawa, A. Sagara, Y. Hatanoand K. Okuno

introduce damages and/or bubbles into theDesorbed gaseous molecules were detected bytungsten, indicatlng that the deuterium retention

quadruple mass spectrometers･ The TEM

is also expected to change upon simultaneousobseⅣations (JEM 2000EX, JASCO Inc.) WereHe+

thealso perf♭med at the Institute of Applied

deuterium retention behaviors fわr various ion

Mechanics, Kyushu Universlty tO analyze theimplantation conditions were studied andmicrostructure change by various ion

simultaneous implantation effect on deuteriumimplantations. The depth profiles of D and C

retention is discussed. The correlation between

were analyzed by GD‑OES at Universlty Of

these retention behaviors and microstructure

Tbyama.

i汀adiation･In

thepresents山dy,change is also discussed.

III. Results and discussion

ⅠⅠ. Experimental
Stress‑relieved山ngsten samples with size

Figure 1 shows the D2 TDS spectra f♭rof 10 mm in diameter and 0.5 mm in thickness
were used. Prior to implantation, the samples

tungsten simultaneously implanted with C and D

ions. The C'/D'nux ratio was fixed at 0.2, 1,

were polished mechanically to mi汀Or丘nish
and 2. In the case of C十/D十‑ 0.2, the TDS
surfaces and pre‑heated at 1173

K for 10

spectrum was clearly different from otherminutes in vacuum to remove surface impurities

spectra. The TDS spectmm was characterized byand damages induced by the polishing process.

desorptlOnS peaks at ‑500 and ‑800 K with aThe triple ions implantation system has been set
shoulder at〜950K.; Note that this TDS

up at Shizuoka University. This system also
spectmm is similar to the spectmm obseⅣed f♭rfeatures a TDS chamber which is connected withtungsten sequentially lmplanted with C and D
an implantation chamber through a gate valveions. For the C+/D十‑ 1 and l･8 cases, the higher

via a load lock chamber. CO2 gas Was used as aC+Source

topreventhydrogendesorptlOn Stage at ‑ 800 K disappeared andimpurlty
only one large desorptlOn peak was fわund at 〜contamination. A ExBmass separator was
350 ‑500 K, which was similar to the deso叩tlOn

installed at the head of the C'gun･ 10 keV C', 3obseⅣed f♭r tungsten.

keV D2+ and 3 keV He十ions were independentlycontrolled. The D2'flux was set to be lx1018

Dm 2 S l and its mlenCe Was reached to be lxlO22 D1〕 '▲ '▲0 5 0m‑2･ The angles of incidence with respect to theL･ Sz･ t T白トLOt/JICJuO!1dJOSJa

surface normal were 0 degrees for the C'ionsand 15 degrees fわr the others. The implantation

area was set to 4 mm x4mm. The sample
holder is equlpped with a ceramic heater to heat

the samples up to 1300 K. The ion implantation
experiment was done at room temperature. A氏eran ion implantation, the sample was transferred

into an TDS chamber. The sample was heated up
to 1173 良 with a heating rate ofO･5 K s‑1, and300400500600700800900 1000 1100Temperature / KFig.1 The D2 TDS spectra fb∫ simultaneouslyimplanted tungsten with D and C ions withvarious C+/D+什ux ratio.

66

Effect of simultaneous implantation on deuterium retention in tungsten

つJつJ2 ーー
505050N･tnGoNOtJuO!1u31adヽヽヽヽ ヽ､‑̲̲ ◇‑■‑‑■

0.5

1.0

1.5

2.0

Flux ratio orC+/D+
Fig.2 Summary of deuterium retention for thesimultaneously Implanted tungsten with various

Fig･ 4 The diffraction pattem for the C+‑D2+
simultaneous implanted sample after annealing

c+/D'nux ratio.

at 1073 K.
The deuterium retentions for the simultaneously

implanted tungsten with various C'/D'nux

dislocations and the dislocation loops appeared

after the ion implantation. Microscopic damage

ratios are summarized in Fig. 2. 1t was clear thatat matrix was gradually annihilated around 973
the highest deuterium retention was achieved f♭r

K and most of damage was annihilated at 1073
the sample with C+/D+什ux ratio of O･2･ The data

was scattered as increaslng the C'/D'flux ratio･
However, we believe that the deuterium

retention would be converged above 1017 D m‑2by increaslng the C'/D'flux ratio･ Fig･ 3 shows

K. However, the dislocations existed at 1073 K.
The ele'ctron diffraction pattem for C'‑D2'implanted山ngsten a洗er annealing at 1073 良(Fig. 4) was clearly different from the originaltungsten indicatlng the formation of a WC layer

microstmcture changes caused by isochronalannealing (10 min.) for the C'‑D2'simultaneousimplantedsample.

Itwas

fわund

that

after the simultaneous implantation.

theFig･ 3 Micros加cture change caused by isochronal annealing fわr the C十一D2+ simultaneous implantedsamnle.

67

Y1 0ya, S･ Suzuki, M･ Kobayashi, RI Kurata, S･ Miyamoto, N. Yoshida, N.Ashikawa, A. Sagara, Y. Hatano and K. Okuno

T･ SN･ tuZo8TOt/aTeluOl dJOSaG
3.0(;)C

Lo o o 0 8 ′hV 4 2 0□●C十一He+‑D2+

2.5

由mDHe'‑D2'

口篭△C十一D2十 A [D⊥ 2･0■■l

享1.500 1.00.5'号

0.00102030

4050300

Depth /nm

500700900

1 100

Temperature / K
3.02.5(b)DFig. 6 The D2 TDS spectmm f♭r triple ions2.0(C+‑He+‑D2+) implanted tungsten. The TDSl､･ヽ

･‑spectra for the dual ions (He'‑D2') and (C'‑D2')

ヨ1･50U l.0
implanted tungsten samples were also shown fわr

0.5

compari son.
･一箪や.:.:き■::…g<…

0.0
0

1020

30

4050

Depth /nm

which is almost consistent with the estimation

by SRIM code. The carbon concentration nearFigl 5 The depth profiles ofC and D for tungsten

the surface reglOn decreased at temperature ofsimultaneously lmplanted with C+ and D2+ at

673 K, indicatlng the dynamic desorptlOn towardvarious temperahres.

the outside of the sample. The amount or

The depth profiles of C and D after various

retained deuterium decreased as the implantation

temperature increased. These results show that
implantation temperatures were observed by

GD‑OES･ As shown in Fig. 5, carbon was

the dynamic desorpt10n aS CDx would beoccu汀ed.

aggregated near the surface region around 20 nm,

To evaluate helium implantation effTect, triple

C十一D2+ simultaneous

CLHe'‑D2'simultaneous

implantation

impl antationFig･ 7 TEM micrographs f♭r C十一D2十and C+‑He+‑D2十simultaneous implanted tungsten samples a鮎r ion

implantation and TDS experiment68Effect of simultaneous implantation on deuterium retention in tungsten

ions(C十,He+andD2十)implantation

wasmicrostructure observation with taking accountperf♭med. Fig. 6 shows the D2 TDS spectra fわror TDS results. It was fわund that the deuterium

triple ions implanted sample with the flux ratio

was preferentially trapped by intrinsic defectsofC十:He十:D十:‑o･2:0･2: 1 ･ The D2 TDS spectra fわr

including grain boundary for simultaneous C'

the He+‑D2+ (He+:D+‑0.2:1) and C十一D2+

and D2+ implanted山ngsten･ The deuterium(C+:D十‑0.2: 1) simultaneous implanted samples

trapplng by ion‑induced defects was enhanced

were also shown fわr comparison. It was fわundby the ion implantation･was

In the case of simultaneous implantation withconcentrated in lower temperature side less thanHe+, the deuterium retention has largely changed･

1100 K. The deuterium retention by dual ions

Especially,implantation of C+‑D2+ and triple ions were

simultaneous implantation, the deuterium

almost the same. However, the deuterium

retention increased compared to the sequential

retention by He十一D2+ implantation was about 2･5

implantation. However, the triple ions

that

theD2

desorption

temperature

inthecaseofHe+

andD2+times as large as those by triple ions

(He十一D2十一C+) implantation, the deuterium

implantation and C+‑D2+ dual ions implantations･retention was almost the same as that for theThese results indicate that the dynamic

only D2+ implanted tungsten, indicatlng thedeso叩tlOn

dynamic desorptlOn WOuld be enhanced･aSCDxduring

thetriple

ions

implantation reduces the deuterium retention.
Fig. 7 summarizes TEM micrographs fbr血e

Ackmowledgememts

c十一D2十and C+‑He十一D2+ simultaneous implanted

tungsten samples after ion implantation and TDS

This study was supported by a Grand‑in‑aid

for scientific research infusion by Ministry ofexperiment. It has been fわund that He bubble

Education, Science and Culture, Japan, by thewasfbmedintheC十一D2十simultaneousimplanted tungsten and this bubbles wereJOlnt usage/research program of the Hydrogen
Isotope Research Center, University of Tbyama

aggregated by heating. The di於action pattem

after TDS experiment was quite different among(No.HRC2009‑02 &03) and by the Center fわrlnstmmental AnalysIS at Shizuoka Universlty･these samples. The different structure wasformed for the dual ion implanted sample,

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