BEHAVIOR OF HYDROGEN IMPLANTED IN FIRST WALL MATERIALS
Tetsuo Tanabeand Shosuke Imoto

Faculty of Engineering Osaka University
1. Introduction
It is one of the most important problem to estimate an
inventory and/or recycling of tritium at the first wall materialof CTR(Controlled Thermonuclear Reactor).
In order to clarifyhydrogen behavior in the first wall we have constructed a new
apparatus for measurements of (1) diffusion and permeation,(2)re-emission and (3) thermal desorption of hydrogen isotopes
implanted into metals.
In the present paper the preleminary
results of measurements of diffusion coefficient and permeation
rate of implanted hydrogen under ion bombardment are reported.
2. Experimental
Figure 1 shows the apparatus
for measurements of permeation
rate and diffusion coefficientof hydrogen under ion bombardment.
An analyzed deuetrium ion beam
accelerated to 20 keV are injected
to a specimen and deuterium which(a) Entire Systemcomes out to the other side bypermeation is analyzed by a quadropole mass analyzer(Q-mass ).
Maximum flux of the beam is about
9 x 10 18 D+/cm2• sec(l.4 A/m 2 ) andthe residual gas pressure duringimplantation is about 8 x 10-S Pa
at the inlet side and 1 x 10- 7 Pa
at the outlet side.
The diffusion coefficient wasdetermined by making least square(b) Details of specimen holder
fitting of permeation rate to thetheoretical relation derived fromFig.l Apparatus for Measurements
Pick's law for two cases.
The
first was obtained from the increasing
curve due to permeation of implanted
deuterium at the outlet side immediately after beam-on(injectio ncurve) and the second from the decreasing curve due to evolutionof implanted deuterium at the outlet side shortly after beam~off(evolution(Iyrve ).
Details of analysis have been represented
elsewhere.
3. Results and Discussion
Figure 2 shows the change of permeation rate with time underion bombardment for Ni at various temperatures.
When the beam
was turned on(t=O), permeation rate of deuterium is increased to a
maximum value, however, below 500°c the permeation rate decreased
for further irradiation.
The decreased permeation rate at nearlysteady state is smaller than the maximum value by factor of oneor two.
Such decrease in the permeation rate of Ni has neverbeen observed in ordinar~ 2 ?ydrogen permeation measurement withgaseous charging method.
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10'Fig.2 Change of <;leuteriu m permeat.i onrate for Ni of 0.1 mm thick

1.5· 2D
11 T X 1()3( K-1)

25Fig.3 Diffusio n coeffici ent of
deuterium for Ni determin ed
from injectio n, evolutio n andgaseous charging (Ref. 2)

The diffusi on coeffic ients obtaine d from the injecti on curve
for a virgin surface are in good agreeme nt with those obtainedfrom gaseous chargin g method (see fig. 3).
Howeve r, the diffusi on
coeffic ients obtaine d from the evoluti on curve after nearly establishing the steady state are much smaller than those from theinjecti on curve below 500°C.
This suggest s a strong effect ofsome radiati on damage induced by ion implan tation to the diffusion and permea tion of deuteri um in Ni.
Since permea tion rate is represe nted by the product of thediffusi on coeffic ient of the bulk and the surface concen tration
at the inlet side, the decreas e in the permea tion rate can be
attribu ted to the decreas e in diffusi on coeffic ient and/or insurface concen tration .
Under the bombard ment of energe tic
deuteriu m ions various types of irradia tion defects such asvacancy , disloca tion, inters titials and so on are produce d near
the project ed range, and they are inferre d to contrib ute to thedecreas e in permea tion rate in followi ng two ways.
The first
is increas e of re-emis sion rate of implant ed deuteriu m fromtheinjecte d side.
With increas ing fluence , vacanc ies produce d byirradia tionatn ear surface region will lead to the formati onofmicro-p ores or micro cracks piling up to the surface .
Implant ed
deuteriu m is then easy to diffuse out from the surface of the
inletside, resulti ng the decreas e of deuteriu m concen tration at nearsurface region.
The second is trappin g of deuteriu m by defects
which have diffuse d into the deeper region than the project ed
range.
The second seems likely the case, because the diffusi on
coeffic ient obtaine d from the evoluti on which are conside red
to beinfluen ced by radiati on damage s(see fig. 3) are remarka bly smaller
than those from the injecti on to a virgin surface .
Above 600°C
due to anneali ng of radiati on damage s, diffusi on of deuteriu misno more affecte d and permea tion rate is not decreas ed.
Thisalso seems to suggest the less effect of re-emis sion rate fromtheinjecte d side to permea tion rate.
4. Referen ces(1) N. Saitoh et al.: Techno l. Repts. Osaka Unive rsity, inpress(2) T. Tanabe et al.: Techno l. Repts. Osaka Univ.,2 7(1977) No.l374.

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