Deuterium and Hydrogen Retention Properties of the JT-60 and JT-60U
Divertor Tiles
Y. Hirohata1), T. Tanabe2), Y. Oya3), K. Shibahara4), M. Oyaidzu5), T. Arai6),
K. Masaki6), Y. Gotoh6), K. Okuno5), N. Miya6)
1) Hokkaido University, Sapporo, 060-8628 Japan2) Kyusyu University, Fukuoka, 912-9581 Japan3) The University of Tokyo, Tokyo, 113-0032 Japan
4) Nagoya University, Nagoya, 464-8603 Japan
5) Shizuoka University, Shizuoka, 422-8529 Japan
6) Japan Atomic Energy Research Institute, Ibaraki, 311-0913 JapanThe retention properties and depth profiles of deuterium and/or hydrogen in the graphite tiles
located in the divertor region used in the W-shaped divertor of JT-60U with inner side pumping and
JT-60 were investigated by thermal desorption spectroscopy (TDS) and secondary ion mass
spectroscopy (SIMS). Total amount of retained hydrogen in the samples used in JT-60 and hydrogenand deuterium in JT-60U was proportional to the thickness of the re-deposited layers. Assuming
homogeneous hydrogen distribution in the re-deposited layers and carbon density of 0.9 g/cm3, H/C in
the re-deposited layers was determined to be approximately 0.03 from this slope of the linear
relationships. This value is almost the same as that observed in the tiles of JT-60U and is much smaller
than those observed in JET and other devices. The re-deposited layers are very likely subjected to hightemperatures because of their poor thermal contact to the substrate owing to their porous structure.
Keywords: hydrogen, deuterium, retention, re-deposited layer, depth profile, JT-60, JT-60U
reactions

I. Introductionwas

implanted

into

depth

of

The accumulation of tritium in in-vessel

micrometer range, and tritium areal distribution

components of thermonuclear fusion devices is

was independent of carbon deposition profiles,

a major safety concern. Therefore, it is very

while H and D seem to be very much influenced

importantretentionby the carbon deposition as well as the surface

characteristics of hydrogen isotopes (T, D, H) in

temperature of the tile. Although most of thein-vessel components of current plasma devices

tiles[1-7]. We have been studying the retention of

re-deposited layer with the maximum thicknesshydrogen isotopes in plasma facing graphiteof 70 µm, for JT-60U erosion is dominant in thetiles exposed to both deuterium and hydrogenouter divertor region and redeposition in the

discharges in JT-60U by using various methods

inner divertor region [12].

issue

to

evaluate

used

in

JT-60

were

coveredwithunder the joint research between JapaneseIn this study, the retention properties ofuniversities and JAERI [8-11]. We have founddeuterium and/or hydrogen in the graphite tiles

that most of tritium produced by the D-D

located in the divertor region used in theJT-60U and JT-60 were investigated by TDS.
The

depth

profilesofhydrogen

and/or

TiC/Inconel(a)deuterium retained in the graphite tiles were
TiC/Moalso investigated by SIMS and Elastic Recoil

Graphite

Lower X-point
divertor tile
1Af14D-1, 1Af14D-2, 1Ag14D-1

Detection (ERDA).
(b)

1 2
InboardFig.1 shows the cross sectional view of thestructure and lower X-point configuration (a),including300

divertor

configuration

discharges

duringSampling
point

32
BBP P

OBDP
42

limiterhermocouple

DM4,5,6
3

9
8,
7,

DM

,
1,2

DM

4
,ID
ID3

January 1988 to October 1988. Most of the tiles

D2
, O
D3

the

2,
,ID
ID1

with

1
BP
11
BP

discharges

B
-1
g14D
1Af14D-2 1A
Private flux Outer strike
regionregionFig.1 Cross-sectional view of the vacuum
vessel of JT-60 (a) and sampling positions (b).

made by isotropic graphite (ETP-10, Ibiden) (b).
All tiles were exposed to total of 1800 hydrogen

A D

D,E: SIMS
A,B,C:Ram

CE

1Af14D-1
Inner strike
regionvacuum vessel of JT-60 with an open divertor
and sampling positions in three divertor tiles

3 4 5 6 7

1,O

II.A Samples

11 12 Sample
1~11:TDS
8 9 10OD

II. Experimental

X-point

Removedsamplewere covered with re-deposited layers of the
maximum thickness of 70 µm [13]. Operationaltemperature of the vacuum vessel and the basetemperature of the tiles were kept at 573 K.

InboardOutboard

Fig.2 Cross-sectional view of the divertor
region in JT-60U and sampling position

However, the surface temperature of the tilerose especially at the position where frequencyof the strike point hit for total of 300 divertor
discharges was large [14].
For TDS analysis, twelve samples (8mm ×
8mm × 1mm) were cut from the tiles to include
the surface area; six from the inner strike region(Sample 1~6), three from the private flux region(Sample 7~9), three from the outer strike region(Sample 10~12). One sample from which
re-deposited layers were completely removed(referred as a removed sample) was also
analyzed by TDS to compare hydrogen
retention in the re-deposited layers and that in
the substrate. Two samples (Sample D and E)
were analyzed by SIMS. Hydrogen depth
profile in the re-deposited layer of a tile locatedin the private flux region (similar position to

sample E) during different hydrogen discharge
campaign was also determined by ERDA.
Fig.2 shows the cross sectional view of the
JT-60U W-shaped divertor. The W-shaped
divertor was pumped from the inner slot bycryopumps. All tiles received 3600 shots ofdeuterium discharges during two discharge
campaigns from June 1997 to October 1998.
After each of two-deuterium discharge periods,
a hydrogen discharge experiment, of totally 700
shots, was carried out for detritiation before air
ventilation. Among the 3600 DD discharges,
about 300 shots of NBI heating were performed
with the output range of 14–23 MW. In thesedischarges, accordingly, the surface temperatureof the divertor tiles rose above 1300K [5]. The
NBI power for HH discharges was about half

compared to that for the DD discharges. Hence,mass numbers were 2(H2), 3(HD), 4(D2),the temperature increase during the HH

15(CH4),discharges would be much less than that during

30(C2H6), 32(C2D4), 36(C2D6) and 39(C3H8).

the DD discharges. The operational temperature

Here, the fragment ions of CH4, C2H4 and C3H8of the vacuum vessel and the base temperature

were used to evaluate the amount of retained Hof the tiles were also ~573 K. Boronization was

because the parental (main) ions of these gases

conducted twice during these campaigns.

overlap with other fragment ions.

19(CD3H),

20(CD4),26(C2H4),

Thirteen thermocouples were embedded in the

Depth profile of hydrogen concentration

divertor tiles 6 mm beneath the tile surface, towithin the depth of 0.3 µm, i.e., less than themonitor the tile temperatures during the

thickness of the re-deposited layer, wasdischarge.

conducted for only one sample (JT-60 sample)

Samples (5mm × 10mm × 1mm) for SIMS

by ERDA. Helium ions with energy of 1.7 MeV

measurements were cut from the tile surface

were used as a primary beam. Depth profiles ofarea just above the thermocouples; four samples

hydrogen,(ID1~ID4) from the inner divertor tiles, three

retained in the graphite tiles were analyzed by(OD1~OD3) from the outer divertor tiles, four

SIMS using 5 keV Cesium ions (Cs+) as a

(BP1, BP11, BP2, BP3) from the baffle plates,

primary beam. The sputtering rate by Cs+ ion

and nine(DM1~DM9) from the dome units

was approximately 1 µm/h. The beam of 32 µm

were prepared (see Fig.2). TDS analysis wasin diameter was rastered over 400 × 400 µm2

conducted for six samples (ID1, 2, 3, OD1, 3,

area. In order to eliminate the effect of crater

DM5, BP1, 3). Sample size was 8mm × 8mm ×edges, the negative secondary ion was collected

0.5mm. For ID1, an additional measurement

only from the center of the rastered area. The

after removing the re-deposited layers was also

ion intensities of H and D were normalized byconducted.

that of 12C for comparison.
and/orboron

andoxygenThe thickness of the re-deposited layers

II.B Analysis of the sample
Deuterium

deuterium,hydrogenretentionwasestimatedby

Scanning

Electronproperties were investigated by using a TDS

Microscope (SEM). Since the tile have roughapparatus. The sample was put on a sample

surface,holder and heated from room temperature to

re-deposited layer has an error of 1 µm.

themeasured

thicknessofthe1273 K with a constant ramp rate of 0.42 K/s,
and then was held at 1273 K for 10 min.

III. Results

Scanning mass range was from 1 to 55 amu. For

III.A. Hydrogen retention of graphite tiles

the JT-60 tiles exposed to only hydrogenused in JT-60

numbers

The most dominant species desorbed fromobserved by a Quadrupole Mass Spectrometer

the samples was H2 molecule. Hydrocarbons(QMS) during the heating were 2(H2), 15(CH4),

such as CH4, C2H4, C2H6 and C3H8 were also26(C2H4), 30(C2H6) and 39(C3H8). For thedesorbed as minor desorption species. Fractions

JT-60U tiles exposed to deuterium dischargesof H2 gas to the total amount of hydrogen atoms

following hydrogen discharges, the dominantretained in the samples are approximately

discharges,

thedominantmassand desorption rates of CH4 and H2 increased
with the thickness of the re-deposited layers.
Fig.3 shows the total amounts of hydrogen
desorbed from the sample as a function of theaverage thickness of the re-deposited layers.
The total amount of retained hydrogen in thesamples were 1.38~10.9 × 10

222

H/m . The

amount of hydrogen desorbed from the removed

14

2
22

appeared around 750 K and 973 K, respectively,

Amount of retained H (10 atoms/m )80~70 %. Desorption peaks of CH4 and H2
12
10
8
6
4
Strike point(Inner divertor)

2
Re-moved sample

0
0

10

20

30

40

50

60

70

Thickness of re-deposited layer (µm)

the samples with the re-deposited layers,

Fig.3 Total amounts of hydrogen desorbed
from the samples as a function of the
thickness of the re-deposited layers.

indicating that hydrogen was mainly retained inregion tile were also shown for comparison. The

the re-deposited layer. In addition, one can be

thickness of the re-deposited layers of D and E

note that the total amount of the retained

samples were 40 and 1 µm, respectively. The

hydrogen in the samples shows good linear

surface concentration was higher for the sample

relationshiptheE, but it decreased exponentially with the depth,

re-deposited layers except one sample. This

while the concentration of the sample D having

indicates

the thick re-deposited layers kept rather

sample was quite small compared to those fromwithhydrogenthewasthicknessretained

of
in

the

re-deposited layers uniformly with a constantconstant with the depth.

This again confirms

hydrogen concentration irrespective of their

the

that

thickness or poloidal position. From the slope ofconcentration in the re-deposited layers is

this straight line, we can determine hydrogenconstant. As shown in Fig.4, in the tile locatedconcentration in the re-deposited layers as

in the private flux region, where was covered

21

1.3x102

above

discussionthehydrogenwith only thin re-deposited layers, H/C ratiohydrogen distribution in the re-deposited layers

within the depth of 300 nm was observed to be

and carbon density of 0.90 g/cm3, H/C ratio in~0.05 by ERDA, while H/C ratio measured by

the re-deposited layers is ~0.03. Here, theTDS was ~0.031. Thus the surface hydrogencarbon density of the re-deposited layer was

retention for the tiles which was not covered

observed in JET [2,4,6] and other low
temperature operating machines [6,4,7] where
H/C is 0.1 ~ 0. 4. Fig.4 shows depth profiles of
SIMS represented by signal intensity ratios of
H/12C for the inner divertor tile (sample D) andthe private flux region tile (sample E) within thedepth of 1.7 µm.

Depth profiles of ERDA

represented by H/C ratio of the private flux

12[15]. This H/C ratio is much smaller than thoseSignal intensity ratio of H / C
measured by SIMS

measured by using both SEM and microbalance
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00

0.07
Private region (ERDA)
0.06
Private region(Sample E: 1 µm)

0.05
Inner divertor Region 0.04
(Sample D: 70µm)
0.03
0.02
0.01

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.00

H/C ratio measured by ERDA

H/m /1µm. Assuming homogeneous

Depth (µm)

Fig.4 Depth profiles of H/12C of sample D andE measured by SIMS and that of H/C ratio
measured by ERDA

with the thick re-deposited layers, was rather
high but hydrogen did not diffuse into the depth(a) Erosion region on the outer divertor(Sample:OD3)
0.6

and decreased rapidly with the depth. Assuming
H/12C ratio measured by SIMS proportional to
H/C by ERDA, the H/C of the sample D was

0.5
0.4

roughly 0.036 which was almost the same as

0.3

that measured by TDS.

0.2

H/C

0.1

III.B. Hydrogen and deuterium retentions ofgraphite tiles used in JT-60U
It was reported that the outer divertor tiles(b) Deposition region on the inner divertor(Sample:ID3)
0.06
0.05

inner divertor tiles were covered by deposited

0.04

on the dome top tile no significant deposition or

D/C

0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

were mostly eroded (up to 20 µm) while thelayers with maximum thickness of 60 µm and

H/C
D/C(H+D)/C

0.03(H+D)/C
0.02

H/C

erosion was observed [12]. Fig.5 compares
typical depth profiles of H/12C, D/12C and
12(H+D)/ C signal intensity ratios for (a) erosion
dominated region of the outer divertor tile
(OD3), (b) deposition dominated region of the

H/C
D/C(H+D)/C(H+D)/C

0.01

D/C
0.00
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0(c) Dome top (sample:DM5)
0.6
H/C
D/C
(H+D)/C

0.5

inner divertor tiles (ID3) and (c) the plasma
0.4

facing dome top tile (DM5). One can see that
the

H/12C

ratio

near

the

surfacewasapproximately one order of magnitude larger
than

that

of

D/12C

indicating

effective

replacement of deuterium retained in nearsurface regions. In addition, the ratio of H/12C,
D/12C and (H+D)/12C of the sample ID3 withthick re-deposited layer was one order ofmagnitude smaller than those of OD3 and DM5
samples and kept rather constant with the depth.
Similar result was observed in the tile used in
JT-60 (see Fig.4).

(H+D)/C

0.3

D/C

0.2

H/C

0.1
0.0
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Depth (µm)

Fig.5 Typical depth profiles of signal intensity
ratios of H/12C, D/12C and (H+D)/12C for (a)erosion dominated region of the outer divertor, (b)the deposition dominated region of the innerdivertor region and (c) the plasma facing dome
top tile.

desorption species. Main desorption peak of H2

Fig. 6 shows thermal desorption spectra ofappeared around 1070 K, while the desorption

H2, HD, D2 and CH4 for the ID3 sample coveredof HD and D2 were peaked at higher

by the re-deposited layers with the thickness oftemperatures than that of H2, reflecting the

60 µm. In addition to those dominant species,

deepervarious hydrocarbons such as CD4, CD3H, C2H4,

Desorption of CH4 was peaked around 700 K.

C2H6 and C3H8 were also desorbed as minor

The total retained amount (retention) of H+D

D

retention

profile(see

Fig.5).

2

Amount of desorbed gases (10 atoms/m )2

Desorption rate (10 molecules/m /s)

2.5

Inner divertor tile (ID3)

22

2.0

1.5

19

H2
HD
D2
CH4

1.0

0.5

0.0

400

600

800

1000

1200

14.0
H2
HD
D2
CH4 group
C2 group

12.0
10.0
8.0
6.0
4.0
2.0
0.0

BP1 ID1 ID2 ID3 DM5 OD1 OD3 BP3

20 14 60

Temperature (K)removedsampleThickness of re-deposited layer (µm)

Fig.7 Amount of H2, HD, D2 and CH4-group
and C2,3 groups desorbed gases from the tiles.

Fig.6 TDS spectra of H2, HD, D2 and CH4,
CHD3 and CD4 desorbed from the innerdivertor tile covered by the re-deposited layer
with the thickness of ~60µm.

eroded tile, showed the smallest retention,

was determined by integrating all mass spectra

nearly the same as that of the removed sample.

considering the number of H and D atoms

These results clearly indicate that hydrogen

included and their sensitivity. About 60% of theisotopes are mainly retained in the re-deposited

retained hydrogen was desorbed as hydrogenlayers.

molecules (H2, HD, D2) and the remaining 40%

the inner divertor tiles are plotted as a function

as hydrocarbon molecules.

of the thickness of the re-deposited layers. One

In Fig. 8, the total H+D retentions in

Fig. 7 compares the hydrogen retention for

can see very good linear relationship as alreadyall samples including ID1, the sample after thenoted in the HH tiles (see Fig.3). From the slope

removal of the re-deposited layer (named as theof the line i.e., 1.45x1021 H+D/m2/1µm,“removed sample”). The amount of retained(H+D)/C ratio in the re-deposited layers washydrogen isotopes is clearly correlated with thedetermined to be 0.032+0.003. Here measured

thickness of the deposited layers (from 2.3x1022

carbon density of the re-deposition layer (0.91

232

to 1.3x10 atoms/m ), i.e., ID3from the innerg/cm3) was used. This value is the same as that

60 µm in thickness [12] showed the largest
retention, and OD1 from the outer divertor tiles
with the erosion depth of about 20 µm showed
the smallest. The retention of the samples fromthe inner baffle plate was also larger than that of
the outer baffle plate. The total H+D retention
in the dome top tile was comparable to those of
OD3 and BP3. It is also important to note thatthe total H+D retention of the inner divertor tile
increased with the thickness of the re-depositedlayers (see Fig.8). The outer divertor tiles
showed much less retention and OD1, the mostRetention amount (1022atoms/m2)

divertor tiles covered with deposited layers of
14.0
ID3

12.0
10.0
8.0

ID1
ID2

6.0
4.0
Removal

2.0
0.0
-10

0

10

20

30

40

50

60

70

Thickness of re-deposited layer (µm)

Fig.8 Total amount of retained H and D atoms
in the inner divertor tiles vs. thickness of
re-deposited layers

observed in the divertor tiles exposed to the HH

IV. Discussion

discharges in the JT-60 (H/C ~0.03) and much

As appeared in Fig. 7 and 8, the H+D

smaller than those observed in JET and otherretention was different with sample positions

devices [2,4,6,8,16]. Such low retention is mostand clearly correlated to the thickness of thelikely owing to the temperature increase of thedeposition layers, showing nearly constantdivertor tiles during the discharge as discussed

concentration of 0.03 in (H+D)/C ratio in thelater. It is also important to note that the straight

re-deposited layers which was the same as thatcrosses at line crosses at -20 µm in the thickness

observed in the tile exposed to only HHof the re-deposited layers when the linear

discharge in JT-60 (see Fig.3) and is much

relationshipzerosmaller than those observed in JET and otherconcentration, in Fig. 8. This clearly indicatesdevices. In JT-60U, the operational temperaturethat the substrate also retained hydrogenand the base temperature of the tiles were kept

isotopes, as evidenced by the desorption of D

at 573 K, which was higher than other devices.

containing gases in TDS spectra of the removed

In addition, the poor thermal contact of thesample (see Fig.7). A similar result was

deposition

observed in the tiles exposed to only hydrogentemperature [12].

isextrapolatedtolayerscould

increase

their

The smallest retention was observed fordischarges in JT-60 (see Fig.3).
Fig. 9 compares the atomic ratio of

OD1 which was eroded with the thickness of 20

retained D and H (D/H) for all samples.

µm [13], because it was hit most frequently byInterestingly, D/H for most samples were nearly

the divertor strike points and experienced the

0.4 except for OD1 of 0.09.

highest temperature of ~1373 K [5] during DD

In more detail,D/H seems to correlate to the plasma loading

discharges. Thishistory of the samples, i.e., D/H for the innerretention is limited by both high heat load anddivertor tiles increased (0.38~0.45) towards theerosion of the tile during DD discharges. But

most common position for the divertor strikethe H retention shows no appreciable difference

point during DD discharges [12].

among OD3, BP3 and the removed sample asshown in Fig. 3.

means that D

dynamic

Thus, H retention during the

HH discharge plays an important role for the

0.8
0.7

consideration of hydrogen isotope retention.

D/H ratio

0.6
0.5Interestingly, the D/H ratio was almost the

0.4

same, 0.4+0.1 irrespective of the tile position

0.3

except the OD1.

0.2

On the other hand, the ratioof the number of the DD discharges and the HH

0.1

ones

0.0

BP1 ID1 ID2 ID3 DM5 OD1 OD3 BP3

removalSample name

Fig.9 Atomic ratio of retained D and H (D/H)

werearound

5.

If

the

retention

characteristic is not different in both discharges,
the D/H ratio is much higher (~5.0) than
measured value (~0.4). If the amount ofhydrogen retained in the removed sample is thesame as that of substrate of all samples, D/Hratio shall becomes large (see Fig.7), but still

DD discharges rose above 700K. The poor

these D/H ratios are considerably smaller thanthermal contact of the deposition layers to the

5.0. This indicates that the tile temperature

substrate could increase their temperature to

might be high during DD discharges. Still the

reduce their hydrogen retention further. The

D/H of 0.4 is too low, even the DD discharges

important role of temperature in reduction

contained around 10% of H.

This suggests

retention is also supported by less D retention inthat a part of the D retained during the DD

the sample located in the erosion-dominateddischarges was replaced by H during the HH

region, which was clearly heated up above

discharges.

1300K during the NBI heated DD discharges.

In addition, the HH discharges

very likely add the H dominated re-depositedThus, the present results indicate that tritium

layers on the D dominated deposition layers on

retention in the re-deposited carbon layers in thethe inner divertor tiles.

According to rough

ITER first wall could be reduced significantly

estimation, the HH discharges likely produced acomparing the current estimation based on thefew µm of deposition layers, though the

JET results, if the surface temperature could bethickness may vary in the tile position. In

substantially higher than 573 K.

addition, the lower temperature during the HH
discharges could result in higher H/C than D/C

Acknowledgementin the DD deposited layers. The depth profiles

The authors would like to thank the JT-60

well reflect such retention profiles of H and D.

team for their contribution to the operation andCorrespondingly,

the experiments of JT-60U.

thedesorption

peak

temperatures of HD and D2 are higher than thatof H2.

Thus the hydrogen retention in the

Reference

JT-60U or JT-60 divertor tiles reflects the[1] G. Federici, et.al., “In-vessel tritium

history of plasma exposure and/or temperatures.

retention and removal in ITER”, J.Nucl.Mater.,In this respect, one should be very careful for

266-269, 14 (1999) .

estimation of tritium retention from data

[2] J.P. Coad, et.al., “Erosion/deposition issues

obtained at lower temperatures.

at JET”, J.Nucl.Mater., 290-293, 224 (2001).

V. Conclusions
Deuterium and/or hydrogen retention in thegraphite tiles located in the divertor region of
JT-60 and JT-60U were investigated by TDS
and

SIMS.

The

H+D

retention

inthere-deposited layers on the tiles used in JT-60U
was ~0.03 in (H+D)/C ratio, which was thesame as that observed in the tile of JT-60 and ismuch smaller than those observed in JET andother devices. That is because, the temperaturesof the JT-60U divertor tiles during NBI heated[3] T.Tanabe, et.al., “Tritium retention ofplasma facing components in tokamaks”,
J.Nucl.Mater., 313-316, 478 (2003).
[4] R.-D.Penzhorn, et.al., “Tritium in plasma
facing components “, Fusion Eng. & Design,
56-57, 105 (2001).
[5] K.Masaki, et.al., “Tritium distribution in
JT-60U W-shaped divertor”, J.Nucl.Mater.,
313-316, 514 (2003).
[6] M.Mayer, et.al, “Hydrogen inventories innuclear fusion devices”, J.Nucl.Mater., 290-293,
381. (2001).

[7] M. Rubel et.al.”Thick co-deposition andW-shaped

dust in controlled fusion devices with carbon

J.Nucl.Mater., 313-316, 370 (2003).

wall”, Physica Scripta, T103, 20 (2003).

[13]Y.Gotoh, et.al., “Transmission electron[8]T. Tanabe, et.al., “Surface distribution of

microscopy of redeposition layers on graphite

tritium on graphite tiles of divertor area intiles used for open divertor armor of JT-60”,

JT-60U”, Fusion Sci.Tech., 41, 877 (2002).

J.Nucl.Mater., 329-333, 840 (2004).

[9] Y.Oya, et.al., “Hydrogen isotope behavior in[14] S.Tsuji, et.al., IAEA-CN-50/A-V-1, 265

in-vessel components used for DD plasma[15]Y.Ishimoto, private communications

operation of JT-60U by SIMS and XPS[16] V.Rohde, et.al., “On the formation of a-C:D

technique”, J.Nucl.Mater., 313-316, 209 (2003).

layers and parasitic plasmas underneath the roof[10]K.Masaki, et.al. “Retention characteristics

baffle of the ASDEX Upgrade divertor “,of hydrogen isotopes in JT-60U”, J.Nucl.Mater.,

J.Nucl.Mater., 313-316, 337 (2003).

337-339, 553 (2005)..
[11]Y.Hirohata, “Hydrogen retention in divertor
tiles used in JT-60 for hydrogen discharge
period”, J.Nucl.Mater., 337-339, 609 (2005)..
[12] Y.Gotoh, et.al., Analysis of erosion andre-deposition layers on graphite tiles used in thedivertorregionof

JT-60U,