J.P. Coad 1 H Workshop, Salamanca 3 June 2008

Local deposition of 13C tracer at the JET MkII-SRP outer divertor

J Paul Coad

Hydrogen Workshop, Salamanca, 2-3 June 2008

J.P. Coad 2 H Workshop, Salamanca 3 June 2008

Local deposition of 13C tracer at the JET MkII-SRP outer divertor

J. P. Coada, , L. K. Aho-Mantilab, M. I. Airilab, D. E. Holec, J. Likonend, A. Widdowsona and JET- EFDA Contributors[1]

•JET-EFDA Culham Science Centre OX14 3DB, Abingdon, UKaUKAEA/EURATOM Fusion Association, Culham Science Centre, Abingdon, OX14 3DB, U.K.

bAssociation EURATOM-Tekes, Helsinki University of Technology TKK, PO Box 4100, 02015, TKK, Espoo, Finland

d Dept. of Engineering and Design, University of Sussex, Brighton, BN1 9QH, East Sussex, UK eAssociation EURATOM-Tekes, VTT, PO Box 1000, 02044 VTT, Espoo, Finland

[1] See the Appendix of M.L. Watkins et al., Fusion Energy 2006 (Proc. 21st Int. Conf. Chengdu) IAEA, (2006)

Introduction13C puffing experiment in 2004Local deposition near the puffing portGeneral considerations of shadowing in the JET divertor• Mk I divertor 1994-5• Mk II divertors 1995 - present timeConclusions

J.P. Coad 3 H Workshop, Salamanca 3 June 2008

13C-methane puffing experiment in 2004

•31 similar pulses on last day of operation•ELMy H-mode discharges:- BT 1.2T, IP 1.2 MA, ~7.5 MW additional heating•Total of 4.3 1023

molecules 13C-methane puffed in outer divertor from 48 locations

Approximate line of W-stripe is shown as white dashes

J.P. Coad 4 H Workshop, Salamanca 3 June 2008

Field line plot showing strike points and SOL region for the 13C-puffing experiment

•Occasional sweeps of strike-point position for Langmuir probe data•Collector probe on reciprocating probe in SOL at top of machine

J.P. Coad 5 H Workshop, Salamanca 3 June 2008

JG

03

.67

6-1

c

Tile 1

Tile 3

Tile 4

Tile 8

Tile 7

Tile6

Amounts of 13C measured on divertor tiles by SIMS and IBA

Note: Measurements have been extrapolated, assuming toroidal symmetry

Tile 13C amount(%)

1 2.2% 3 0.7% 4 3.2% SRP 1.8% 6 2.5% 7 15.4% 8 0.9% Total 27.0%

SRP

Shadowing edge

J.P. Coad 6 H Workshop, Salamanca 3 June 2008

SIMS

IBA

poloidal distance around the divertor (mm)

0 500 1000 1500 2000

13C

dep

osit

ed /

cm

2 / 13

C i

njec

ted

10-8

10-7

10-6

10-5

10-4

10-3final fit

J Strachan et al

Modelling of SIMS and IBA data

J.P. Coad 7 H Workshop, Salamanca 3 June 2008

G7B

12345678

0a1a

J.P. Coad 8 H Workshop, Salamanca 3 June 2008

19-23(max) x1018 atoms/cm2

13-18.9 x1018 atoms/cm2

10-12.9 x1018 atoms/cm2

7-9.9 x1018 atoms/cm2

1-6.9 x1018 atoms/cm2

Total number deposited 13C in this area is ~215 x1018 atoms

Tungsten stripe13C injection

20mm

Cores cut for SIMS analysis

Deposition in shadow on tile 14OW G7B

J.P. Coad 9 H Workshop, Salamanca 3 June 200820mm

11063

11041 11047

0

200

400

600

800

1000

1200

1400

1600

1800

0 200 400 600 800 1000

11063

11041

11047

13CBe

O

12C

J.P. Coad 10 H Workshop, Salamanca 3 June 2008

13C deposition on 2ON G7A

J.P. Coad 11 H Workshop, Salamanca 3 June 2008

D and 13C concentrations

0

50

100

150

200

250

300

350

30 50 70 90 110 130 150 170

14OWG7B-D (x1e17) 2ONG7A-D (x1e17)

14OWG7B-13C (cts) 2ON G7A-13C (cts)

Distance on tile (poloidally), mm

Count rate

Ion Beam Analysis (Nuclear Reaction Analysis) data across tile depend on where line is relative to

injection point

J.P. Coad 12 H Workshop, Salamanca 3 June 2008

12C and 13C concentrations

0

50

100

150

200

250

300

350

30 50 70 90 110 130 150 170

2ON G7A-13C (cts) 2ON G7A-12C (x1e17)Distance on tile (poloidally), mm

Count rate

IBA data show film in

shadowed region is almost pure 13C (plus a

lot of H)

J.P. Coad 13 H Workshop, Salamanca 3 June 2008

Deposition at the JET Mk I divertor

JET MkI divertor operated 1994-5, first with C, then Be tiles

Pairs of tiles were mounted on water-

cooled poloidal bars, 196 bars toroidally.

There was a gap between each bar.

Tiles were in a “roof-top” arrangement

J.P. Coad 14 H Workshop, Salamanca 3 June 2008

Cross-section of tiles of the JET Mk I divertor, and deposition at the outer strike zone

• Exposed part of each tile in strike zone eroded• local re-deposition in the shadowed area

J.P. Coad 15 H Workshop, Salamanca 3 June 2008

Subsequent JET divertors have used large format tiles mounted to solid carriers, in

turn mounted on a water-cooled support structure

Pumping is only through the corners of the divertor, heavy deposition in these regions

No significant deposition in areas shadowed toroidally on

tiles

J.P. Coad 16 H Workshop, Salamanca 3 June 2008

Tritium remaining in the JET vessel after DTE1 in 1997

Rest of T assumed to be in flakes at bottom of vessel

Collected from the louvres and divertor floor

R-D Penzhorn, N Bekris, FZK, Karlsruhe

J.P. Coad 17 H Workshop, Salamanca 3 June 2008

G7B

12345678

0a1a

J.P. Coad 18 H Workshop, Salamanca 3 June 2008

Tile 3, exposed 1998-2001

Region of tile shadowed by adjacent tile

J.P. Coad 19 H Workshop, Salamanca 3 June 2008

JET septum 1998-2001

Almost complete separation of inner and outer divertor,

somewhat analogous to ITER

J.P. Coad 20 H Workshop, Salamanca 3 June 2008

100

Campaign averaged strikepoint position

0.8 mm

2.5 mm

15 mm

Source

Fit to sticking monitors:99% with sticking 0.9<1% with very low sticking

Hydrocarbon migration in JET

Migration to ITER pump ducts may not be large

Long term analysis in collaboration with TF FT

Recent analysis of septum shows low deposition !

Mayer, Rubel, Coad

J.P. Coad 21 H Workshop, Salamanca 3 June 2008

Conclusions

• Thick deposits of 13C-H found in shadowed zone where puffed methane enters divertor

• Overall 13C balance only marginally improved

• Pattern of deposition in JET may be influenced by particle flow

• Septum/PFR data in JET are encouraging for ITER dome, BUT this may be totally misleading