Deuterium Retention in Ion-Damaged ITER-Grade Tungsten Exposed toLow-Energy, High-Flux Pure and Helium-Seeded Deuterium Plasmas
低エネルギー・高フラックスプラズマ曝露下での ITER グレード W 中の重水素滞留挙動 －照射欠陥および He の影響－
V.Kh. Alimov1,2, Y. Hatano1, B. Tyburska-Püschel3, K. Isobe2, M. Matsuyama1, T. Yamanishi2
V.Kh. Alimov1,2, 波多野雄治 1, B. Tyburska-Püschel3, 磯部兼嗣 2, 松山政夫 1, 山西敏彦 2
1

Hydrogen Isotope Research Center, University of Toyama, Toyama 930-8555, Japan
富山大学水素同位体科学研究センター 〒930-8555 富山市五福 3190
2Tritium Technology Group, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
日本原子力研究開発機構トリチウム工学研究グループ 〒319-1195 茨城県那珂郡東海村白方白根 2-4
3Max-Planck-Institut für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany
Samples prepared from polycrystalline ITER-grade tungsten were damaged by irradiation with 20 MeV W ions atroom temperature to a fluence of 1.4×1018 W/m2. Due to the irradiation, displacement damage peaked near theend-of-range, 1.35 μm beneath the surface, at 0.89 displacements per atom. The damaged as well as undamaged W
samples were exposed to low-energy, high-flux (1022 D/m2s) pure D and helium-seeded D plasmas to an ion fluenceof 3×1026 D/m2 at various temperatures. Trapping of deuterium was examined by the D(3He,p)4He nuclear reaction
at 3He energies varied from 0.69 to 4.0 MeV allowing determination of the D concentration at depths up to 6 μm. It
has been found that (i) addition of 5% helium ions into the D plasma at exposure temperatures of 440-650 K
significantly reduces the D concentration at depths of 0.5-6 µm compared to that for the pure plasma exposure; (ii)generation of the W-ion-induced displacement damage significantly increases the D concentration at depths up to
2 µm (i.e., in the damage zone) under following exposure both to the pure D and helium-seeded D plasmas.

1. Introduction
Due to its favorable physical properties, tungsten(W) is employed as a candidate material for
plasma-facing high heat-flux structures in future
fusion reactors. As plasma-facing material in thefusion reactors, W will be subject to intensive
fluxes of energetic deuterium (D) and tritium (T)particles as well as helium (He) ions and 14 MeV
neutrons (n) from the D–T fusion reaction. Neutron
irradiation causes modification of the W
microstructure and creates displacements in thebulk. One of the ways to investigate the influence ofn-produced defects on the hydrogen isotope
inventory is to simulate displacement damage intungsten using irradiation with energetic ions. The
objective of this work are comparison studies of D
retention at displacement damage in ITER-grade W
exposed to pure D and He-seeded D plasmas atelevated temperatures.
2. ExperimentalPolycrystalline ITER-grade W (A.L.M.T. Corp.,
Japan) is deformed (rolled, swaged and/or forged)
followed by appropriate heat-treatments to obtainbetter mechanical properties after the sintering
process. In consequence, the W microstructure
consists of anisotropically elongated grains along
the deformation axis. The grain size is 1-3 µm in
section and up to 5 µm in length. Individual

elongated cracks observed between grains are dueto the deformation treatments. Tungsten samples
were so prepared by the manufacturer that theirradiated surfaces were perpendicular to
deformation axis.
Some of the W samples were irradiated with 20
MeV ions to a fluence of 1.4×1018 W/m2 at room
temperature. As a result, the near-surface layer ofthe samples was damaged to 0.89 displacements peratom (dpa) at the damage peak situated at a depth of
1.35 µm. The damage profile was calculated using
the program SRIM-2008 [1] with a displacement
energy of 90 eV [2].
The damaged as well as undamaged W samples
were exposed to low-energy, high-flux pure andhelium-seeded deuterium plasmas at elevatedtemperatures (440-720 K) [3]. For exposure to thepure D plasma, plasma beam with species of D2+(over 80%) and D+ (less than 20%) was obtained. Abias voltage of -80 V was applied to the W sample,
resulting in incident energy of 76 eV for D2+, taking
into account the plasma potential of about -4 V. Theincident deuterium ion flux was fixed at 1022 D/m2s.
The concentration of He ions in the He-seeded D
plasma was 10% [4]. The samples were exposed tothe pure D and He-seeded D plasmas to a D ionfluence of 3×1026 D/m2.
Deuterium depth profiles in the plasma-exposed
W samples were analyzed by the D(3He,p)4He

3. Results
The D depth profile in the undamaged
ITER-grade W exposed to the pure D plasma attemperatures of 460 and 560 K is characterized by aconcentration of 0.1-0.2 at.% at depths of 1-6 μm(in the sub-surface layer). Concentration minima at
depths up to 1 µm (Fig. 1a) may be connected withthe appearance of small blisters and accompanying
porosity development [6]. At Texp = 640 K, the Dconcentration in the sub-surface layer does notexceed 10-2 at.%. A further increase of the exposure
temperature leads to a decrease of the Dconcentration (Fig. 1a).

10126010-110-210-310-4D concentration (at.%)

110010-110-210-310-4Texp = 460 K

Texp = 640 K

Texp = 560 K

Texp = 720 K

12326

4562Texp = 440 K
Texp = 650 K

345100Texp = 540 K

exp

10-110-210-310-4Texp = 640 K
Texp = 710 Ka10110010-110-210-310-4123264562D-He plasma (Φ = 3x10 D/m ) → ITER-grade W
damaged to 0.89 dpa
Texp = 445 K
Texp = 545 K
Texp = 640 K

bdamage

123456Depth (mm)b2

D plasma (Φ = 3x10 D/m ) → ITER-grade W
damaged to 0.89 dpa
T = 440 K

0Texp = 540 K

1210D-He plasma (Φ = 3×10 D/m ) → ITER-grade W

02610damagea0102

D plasma (Φ = 3×10 D/m ) → ITER-grade W

D concentration (at.%)Damage (dpa)

D concentration (at.%)10

slowly decreasing into the bulk. As the exposure
temperature increases up to 650 K, the near-surface
D concentration decreases to about 0.2 at.%,whereas the sub-surface D concentration becomes
below 5×10-4 at.% (Fig. 1b).
Generation of ion-induced displacement damage
and following exposure both to pure D plasma and
D-He plasma significantly increases the Dconcentration at depths up to 2 µm (i.e., in thedamage zone) (Fig. 2). However, for all exposure
temperatures, the D concentrations at depths of 4-6µm in the undamaged and damaged W samples arecomparable in a value (Figs. 1 and 2).
D concentration (at.%)Damage (dpa)nuclear reaction. To determine the D concentration
at larger depths, an analyzing beam of 3He ions withenergies varied from 0.69 to 4.0 MeV was used.
The proton yields measured at different 3He ion
energies allow measuring the D depth profile atdepths of up to 6 μm [5].

6Depth (μm)

Fig. 1. Depth profiles of deuterium retained inundamaged ITER-grade W after exposure to pure D
plasma (76 eV D2+) (a) and He-seeded D plasma {76 eV(D2+ + 10% He+)} (b) with D ion fluence of 3×1026 D/m2
at various temperatures.

Seeding of helium ions into the D plasma at
exposure temperatures of 440-650 K significantly
reduces the D concentration at depths of 0.5-6 μm(Fig. 1b). At Texp = 440 K, the D concentration is
described by a sharp near-surface concentration
maximum of about 1 at.%, and, at depths above
0.5 μm, by a concentration of about 3×10-2 at.%Fig. 2. Depth profiles of deuterium retained in
ITER-grade W, damaged to 0.89 dpa by irradiation with20 MeV W ions at room temperature, after exposure topure D plasma (76 eV D2+) (a) and He-seeded D plasma{76 eV (D2+ + 10% He+)} (b) with D ion fluence of3×1026 D/m2 at various temperatures.
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