1. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 1 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Formation of mixed W/C and Mo/C layers in TEXTOR A. Litnovsky, V. Philipps, P. Wienhold, S. Richter, K. Krieger, G. Sergienko, A. Kirscher, A. Kreter, S. Droste, D. Borodin and TEXTOR Team

2. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 2 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Mixed layers in TEXTOR Naturally formed during the PWI experiments Can be observed after exposure of high-Z limiters in the SOL plasmas using Limiter Lock systems Example: twin limiters, castellated limiters

3. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 3 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Exposure of twin W/C limiter in the SOL plasmas of TEXTOR* W content in the deposit is the largest neat tangency point W found deposited locally on the carbon part of the limiter *M. Rubel, V. Philipps, A. Huber and T. Tanabe, Phys. Scr. T81 (1999) 61 Deuterium retention only in carbon deposition area W deposited in gaps of C rough surface despite of C net erosion area

4. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 4 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Exposures of castellated limiters: general parameters ExperimentExperiment 1 (Mo castellated limiter II) Experiment 2 (W castellated limiter III) No. of discharges3916 Duration of exposure219 s.112 s. Local T e, eV.~25 eV~ 20 eV Local N e, cm -3 2.5*10 12 6*10 12 Averaged fluence2.0×10 20 D/cm 2 2.2×10 20 D/cm 2 Bulk temperature of the limiter220-260 o C200-250 o C Temperature excursionsLocal heating of plasma closest edge up to 1600 o C Local heating of plasma closest edge up to 1500 o C Diagnostics used: He beam, fast probe, pyrometers, thermocouples, video observation system, spectroscopy (D, Mo, W)

5. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 5 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft EPMA Thickness, nm Mo C D B Mo C D B SIMS/DEKTAK Intensity, a.u. ~ 75 nm Investigations of deposited layers: Experiment 1 Plasma flow A B A: Plasma facing side of the gap SIMS (calibrated with Dektak) EPMA scan ~ 1.7 mm ~ 1.5 mm Measured spot (~ 30 nm) Measured spot (~ 30 nm)

6. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 6 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Investigations of deposited layers: Experiment 1: EPMA signals modeling ~ SIMS value At least ~50 at % Mo in the deposit are needed to suit with SIMS results for this location

7. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 7 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Distance along the gap, mm C, at/cm 2 Investigations of deposited layers: Experiment 2 Plasma flow A B A: Plasma facing side of the gap SIMS (calibrated with Dektak) EPMA scan ~ 1 mm EPMA value (without W mixing) ~ 25 nm EPMA value (without W mixing) ~ 25 nm NRA value ~ 42 nm NRA value ~ 42 nm SIMS/DEKTAK value ~ 50 nm SIMS/DEKTAK value ~ 50 nm EPMA modeled value (41 at. % W in the deposit) EPMA, NRA, SIMS/DEKTAK W castellated limiter NRA scan

8. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 8 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Investigations of deposited layers: Experiment 2 W castellated limiter: W mixing quantification 43,7% 69,6% 2,3% 36% 2,5% 41,6% 3,0% 27,3% 3,5% Observations: Strong W intermixing on the plasma-closest edges of gaps (>40 at. % of W); W-share decreases with the depth of the gap Looks like more W in plasma-shadowed gaps; More analyses to follow. open gap shadowed gap Plasma-

9. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 9 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Comparison of the experiments 1 and 2 What are these mixed deposits? Mo/CW/C N Mo /N C (gap edge) ~ 50 at % Mo N W /N C ( gap edge) ~ 40-70 at % W D/C < 0.1 D/C <<0.1 Less than 0.1% of impinging D flux trapped in gaps The properties of W/C and Mo/C mixed deposits are very similar

10. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 10 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Comparison of the experiments 1 and 2 Similarity of W/C and Mo/C layers: why so? Same geometry of studied samplesNo much difference between Mo and W for EPMA simulation: CKα absorption is similar Exposure in similar plasma conditions Y, cm 2 /mg Mo WC 19.2176

11. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 11 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Comparison of the experiments 1 and 2 Similarity of W/C and Mo/C layers: why so? Part II General feature: metal intermixing decreases with the gap depth C n+, D + C 0, D 0 Mo C 0, D 0 65 at.% Mo* 50 at.% Mo Very low D content: are W/C layers actually an issue for ITER? *A. Litnovsky et al, Proc. of 32nd EPS, ECA Vol. 29C, P- 1.015 (2005); A. Litnovsky et al., J. Nucl. Mater. in press

12. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 12 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Summary Mixed W/C and Mo/C deposits observed during investigations of twin W/C limiters and in the experiments with castellated limiters in TEXTOR Large share of metal (up to 70 at. %) in the intermixed layers W/C and Mo/C layers formed in gaps of castellated limiters are similar Metal share in the deposit decreases with distance from the metal source Generally low D-retention in studied mixed layers

13. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Slide 13 of 13 Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Thank you

14. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Additional slide Forschungszentrum Jülich in der Helmholtz-Gemeinschaft NRA spot size

15. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Additional slide Forschungszentrum Jülich in der Helmholtz-Gemeinschaft W mixing: detailed results

16. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Additional slide Forschungszentrum Jülich in der Helmholtz-Gemeinschaft SIMS measurement locations

17. Institut für Energieforschung - Plasmaphysik EURATOM Assoziation – FZJ TEC A. Litnovsky et al., Meeting of the EU TF PWI SEWG on mixed materials, JET, Culham, July 9, 2007 Additional slide Forschungszentrum Jülich in der Helmholtz-Gemeinschaft Encapsulated deposits* Thickness, nm Intensity, a.u. Substrate Deposit W-layer D C W 13 C SIMS spectra show an a:C-D deposit with a thickness of ~120 nm, covered with a ~ 100 nm thick layer of pure tungsten *A. Litnovsky et al., Phys. Scr. T128 (2007) 45;