TEC Trilateral Euregio Cluster 1 S. Brezinsek Spectroscopic determination of carbon erosion yields and the composition of chemically eroded molecular carbon species S. Brezinsek Institut für Plasmaphysik, Forschungszentrum Jülich GmbH, EURATOM Association, Trilateral Euregio Cluster, D Jülich, Germany Thanks to: A. Pospieszczyk, M. Stamp, G. Sergienko, A. Kirschner, P.T. Greenland, P. Wienhold I. Möller, U. Fantz, the TEXTOR-group and JET-EFDA contributors

TEC Trilateral Euregio Cluster 2 S. Brezinsek Outline  Motivation  Methods  Absorption spectroscopy on hydrocarbon molecules  Emission spectroscopy on hydrocarbon molecules  CD emission spectroscopy  C 2 emission spectroscopy  C 3 emission spectroscopy  Importance of C 2 - intrinsic hydrocarbon source at JET  Conclusion

TEC Trilateral Euregio Cluster 3 S. Brezinsek Motivation  Carbon is the plasma-facing material for the first divertor of ITER  good thermo-mechanical properties  chemical erosion Mass spectroscopy: Mix of CD x, C 2 D y, C 3 D z TEXTOR, Philipps 1989 ASDEX-U, Kallenbach 1994 Emission spectroscopy Mix of CD x, C 2 D y observed JET, Stamp 2001  Identification: species, location, a:C-D film characteristic  Quantification: individual contribution, total amount  Minimisation: optimum plasma and surface parameters  Spectroscopy as an in-situ tool

TEC Trilateral Euregio Cluster 4 S. Brezinsek Spectroscopic methods  Dissociation chain of hydrocarbon molecules is important CD 4 + CD 4 CD 3 + CD 3 CD 2 CDC CD 2 + CD + C+C+ C 2+ D2D2 D2D2 A part of the dissociation chain of CD 4 :  Emission spectroscopy: CD, CD +, C, D, D 2 can be measured  Absorption spectroscopy: CD 2, CD 3, CD 4 can be measured Interpretation:  calibration experiments  erosion-deposition modelling (ERO code)

TEC Trilateral Euregio Cluster 5 S. Brezinsek Absorption spectroscopy  Not yet tested in a tokamak – only in laboratory experiments Absorption experiment in TEXTOR in preparation  Database extended for CD 3 and CD 4  Detection of CD 3 (4.8 µm) and CD 4 (4.2 µm) in front of the inner limiter (graphite)

TEC Trilateral Euregio Cluster 6 S. Brezinsek Emission spectroscopy - CD Calibration: CD 4 injection through a gas inlet (stainless steel) simplified chain LCFS SOL

TEC Trilateral Euregio Cluster 7 S. Brezinsek Determination of the chemical erosion yield - accessible photon flux  CD: A-X band - inverse photon efficiencies D CD 4 A-X band Assumption: only CD 4 - total photon flux A-X spectrum simulation XB

TEC Trilateral Euregio Cluster 8 S. Brezinsek Interaction with the surface (i) Calibration: CD 4 injection through a gas inlet (stainless steel) After several shots: C 2 appeared in the spectrum! a-C:D layer is built up on the protection shield Additional parameters: - surface layer growth - geometry - temperature

TEC Trilateral Euregio Cluster 9 S. Brezinsek Interaction with the surface (ii) Calibration: CD 4 injection through a test limiter (graphite) C 2 always detectable in the spectrum (in correlation with the injection) Interpretation:  release of CD 4 from the secondary source (film)  intrinsic background  conversion factors?  yield determination? More data has to be analysed!

TEC Trilateral Euregio Cluster 10 S. Brezinsek Emission spectroscopy – C 2 (i)  Indirect measurement of C 2 D y via C 2 radicals  Dissocation of C 2 D y can lead to CD radicals C2D6C2D6 CD C2C2 dissociation chain ASDEX-U (outer divertor, L-mode) U. Fantz 2003  C 2 can be used to determine the contribution of C 2 D y  significant amount of C 2 D y ends up as CD Absorption spectroscopy: direct measurement of C 2 D y with y=1,2,4,5,6 CDC2C2

TEC Trilateral Euregio Cluster 11 S. Brezinsek Emission spectroscopy – C 2 (ii) Additional information about the initial species might be accessible via the rovibrational analysis of the spectrum  different dissoc. paths  different dissoc. energies  different rovibrational population  spectra simulation is not yet precise enough  molecular constants  resolution: ~500 K U. Fantz

TEC Trilateral Euregio Cluster 12 S. Brezinsek Emission spectroscopy – C 2 (iii)  Sublimation of carbon can lead to the release of carbon clusters  Emission of atomic C, C 2 and C 3 molecules  Energy of C I reflects the surface temperature Cluster formation observed in electron-beam experiments and laser ablation experiments on graphite targets T. Hirai 2003  Rovibrational temperature of C 2 molecules should reflect the surface temperature!  Should be lower than 3000 K  Sublimation experiments at DIII-D performed (Isler 2001)

TEC Trilateral Euregio Cluster 13 S. Brezinsek Emission spectroscopy – C 3  C 3 molecules have been observed in laser ablation experiments  Emission of C 3 has not yet been observed in tokamaks S. Arepalli 1999 C3C3 C2C2  Overlap of C 3 lines with lines of CD and CD +  C 3 emission at high temperatures (2000 K)

TEC Trilateral Euregio Cluster 14 S. Brezinsek JET divertor  Strong C 2 emission observed at different locations in the JET divertor here: corner region of the inner divertor Normal spectrumStrong C 2 emission spectrum

TEC Trilateral Euregio Cluster 15 S. Brezinsek JET divertor  Strong C 2 emission observed at different locations in the JET divertor Always:  on the shoulder of the inner divertor Near to the strike point:  L-mode: corner region of the inner divertor  H-mode: horizontal plate inner and outer divertor C2C2 C2C2 C2C2 P. Coad 2003 radius / m

TEC Trilateral Euregio Cluster 16 S. Brezinsek Conclusion  Emission spectroscopy can provide information about a-C:D layers  Observation of different molecular species is necessary: CD, C 2...  Interpretation is challenging owing to the indirect measurement  In-situ calibration of photon fluxes is important  Main release of CD 4 and C 2 D y from a-C:D layers likely (no C 3 )  Contribution of C 2 D y to the formation of CD has to be considered for  total hydrocarbon flux determination  erosion yield determination  Rovibrational analysis has to be improved (molecular data) to give information about the initial hydrocarbon species

TEC Trilateral Euregio Cluster 17 S. Brezinsek Total hydrocarbon flux determination higher hydrocarbons also contribute to  C : chem only methane family CD correction for ethane family add ethane family