24P077-P
Deuterium Ion Driven Permeation through Tungsten
タングステン中の重水素透過特性に関する研究
Heun Tae Lee, Han Yee Peng, Yusuke Ohtsuka and Yoshio Ueda
Lee Heun Tae, Peng Han Yee，大塚裕介，上田良夫
Graduate School of Engineering, Osaka University
Yamadaoka 2-1, Suita, Osaka 565-0871, Japan
大阪大学工学研究科 〒565-0871 大阪府吹田市山田丘2-1
Tungsten is the present material choice for the ITER divertor, as well as candidate armour material for DEMO. It is
important to understand hydrogen interaction with tungsten to estimate recycling and permeation behavior, as well as
in-vessel tritium inventory. To study hydrogen diffusion, surface recombination, and trapping processes in tungsten, ion
driven permeation experiments have been performed. Specifically, permeation experiments under mixed ion irradiation
with helium and carbon species were done to determine the effects of impurities in the plasma. In addition, the effect ofdifferent tungsten microstructure was examined.

1. Introduction
Tungsten (W) is the present material choice for
the ITER divertor, as well as candidate armour
material for DEMO. To assess the safety andoperational cycle of future fusion devices adetailed understanding of hydrogen (H, D, T)
transport in tungsten is required. We have
performed deuterium ion driven permeation
experiments through tungsten to determine howchanges in plasma and material parameters will
impact the hydrogen transport in tungsten. On theplasma side, we have introduced helium andcarbon impurities and studied their effects. On thematerial side we have examined the effect ofdifferent tungsten microstructure. This poster
presentation will provide an overview summaryof these experimental results.
2. Experimental
Details of the irradiation device, HiFIT, can befound in previous publication [1] and a brief
description follows. A microwave plasma discharge
was extracted and focused into a beam composed ofboth D atoms and ions. Typical ion flux was ~1.5 x1020 D m2 s-1. For He/D mixed irradiation, He gas
was introduced into the source resulting in 2 % He
in the incident flux. For C/D mixed irradiation, Cimpurities in the beam were introduced by placing
graphite plates or rings inside the ion source.
Details of determining the carbon fraction in theincident beam can be found in Ref. [1].
The permeation setup [2] consists of a W
specimen sealed by placing it between two standard
conflat flanges and a copper gasket. The specimen
was irradiated at incident angle of 15 degrees
through an 8 mm diameter aperture. A highresolution quadrupole mass spectrometer (MKSmicrovision plus) with a mass range 1-6 amu wasused to monitor changes in the mass 3 (HD or H3)
and mass 4 (D2) signals at the permeation side. The
signals were calibrated using a standard D2
calibration leak. Typical pressures duringexperiments were 10-4 and 10-6 Pascal in theirradiation and permeation chambers, respectively.
The specimen was heated from the rear side by
an infrared heater and the temperature measured bya spot welded thermocouple at the irradiation
surface. Temperature uncertainty was ±10 K for
D/He experiments and ±5 K for pure D and D/Cexperiments.
Three different types of W specimens wereinvestigated. Two polycrystalline specimens of
99.99 % purity manufactured by ALMT corp, Japan
with different grain sizes were obtained byannealing at 1573 K (W1) and re-crystallization at2273 K (W2). Following the annealing process, thespecimens were mechanically polished to thedesired thicknesses of 25 µm, 50 µm, and 75 µm. 50µm thick polycrystalline specimens annealed at1203 K (W3) were provided by IPP, Garching.
Details of the microstructure for this W3 specimen
have been previously discussed in Ref [3].
3. Results and Discussion
3.2 D-only irradiation
The principal aim of this work was to determine
the effect of W microstructure on D permeation anddiffusion [4]. From Figure 1, the difference in thesteady state permeation flux between tungsten
specimens with different grain sizes was inagreement within a factor of two. The largest
difference was observed at the limits of both highand low temperature. We tentatively concluded thatsteady state permeation flux was independent of
microstructure and estimate that grain boundary
effects will not contribute significantly to steadystate permeation in tungsten in the temperature
region of interest for ITER operation or future
blanket conditions.
3.2 He or C mixed ion irradiation
Under mixed He/D irradiation, a clear decrease in
the permeation flux was observed in comparison toD-only case; see Figure 2. In addition, thepermeation flux was observed to obey a square root
dependence to the incident flux. This was in directcontrast to D-only case, where the permeation flux
was linearly proportional to the incident flux over atemperature range 550 K < T < 1050 K [2]. Such ashift could be modeled by changes to the front
diffusivity which could be attributed to He bubbles
formed near the surface. It was further determinedthat hydrogen does not diffuse according toFrauenfelder’s [5] values in the implantation zone.
Under mixed C/D irradiation, an opposite trendof increased permeation was observed [6]. Mixed
C/D irradiation resulted in the formation of W/Cmixed layers near the surface, which could reducehydrogen diffusivity and/or recombination. A moredetailed treatment is presented in poster
presentation 24P078-P.
4. Summary
From D-only irradiation experiments withvarious W specimens with different grain sizes, it
was determined that diffusion through grainboundaries appear limited and will not affectpermeation behavior significantly. However, theyFig.2. Comparison of beam-on transient curves during
Pure D and He/D mixed irradiation. From Ref. [2].

will have an impact on tritium inventory if they are
preferential sites for precipitation due to large
buildup of solute concentration within the lattice.
Such conditions are expected under mixed
carbon-hydrogen irradiation.
Mixed ion (He/D and C/D) driven permeation intungsten was studied. Mixed material formation andmodification of the front surface could vary thesteady state permeation by factor ranging from 10-2
to 102. Significant finding was the modification in
the near surface by formation of He bubbles or C/W
mixed layers can significantly vary the steady-state
permeation flux. For He/D mixed ion irradiation,
more than an order of magnitude reduction inpermeation flux was observed. In contrast, for
mixed C/D mixed ion irradiation, more than twoorders of magnitude enhancement of permeation
flux was observed. These reduction (He/D) andenhancement (C/D) are strongly temperaturedependent, and is most significant at 800 K;
corresponding to the expected blanket first walltemperature in future fusion devices.
Acknowledgments
We thank E. Markina for providing us with W3
tungsten specimens from IPP, Garching.

Fig.1. Steady state permeation for three specimens
with different grain sizes. The thickness of W1 and W2
specimen was 25µm. The permeation flux for 50 µm W3
specimen has been multiplied by 2. Taken from Ref. [4].

References[1] Y. Ueda, H. Kikuchi, T. Shimada, A. Sagara, B.
Kyoh, and M. Nishikawa: Fusion Eng. and Design
61 (2002) 255.
[2] H.T. Lee, H. Tanaka, Y. Ohtsuka, and Y. Ueda: J.
Nucl. Mater. 415 (2011) S696.
[3] Yu. Gasparyan, M. Rasinski, M. Mayer, A. Pisarev,and J. Roth: J. Nucl. Mater. 417 (2011) 514.
[4] H.T. Lee. E. Markina, Y. Ohtsuka, and Y. Ueda: Phys.
Scr. T144 (2011), accepted.
[5] R. Frauenfelder: J. Vac. Sci & Tech 6 (1968) 388.
[6] H.Y. Peng, H.T. Lee, Y. Ohtsuka, and Y. Ueda: Phys.
Scr. T144 (2011), accepted.