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Impurity transport at JET On-going analysis from recent campaign

Impurity transport at JET On-going analysis from recent campaign. C. Giroud, C. Angioni, L. Carraro, P. Belo, I. Coffey, V. Naulin, M-E. Puiatti, M. Brix, H. Leggate, K. Lawson, A.D. Whiteford, M. Valisa. Experimental determination of transport coefficients.

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Impurity transport at JET On-going analysis from recent campaign

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  1. Impurity transport at JET On-going analysis from recent campaign C. Giroud, C. Angioni, L. Carraro, P. Belo, I. Coffey, V. Naulin, M-E. Puiatti, M. Brix, H. Leggate, K. Lawson, A.D. Whiteford, M. Valisa.

  2. Experimental determination of transport coefficients • Linear relationship assumed between impurity flux and density gradient Convection coefficient Vz >0 outwards Diffusion coefficient • Extrinsic impurities injected by laser ablation (Ni) or gas injection (Ne, Ar). • D and V determined individually by modelling of time evolution of spectroscopic data • Ni: soft x-ray and VUV • Ne and Ar: soft x-ray and VUV and also from charge exchange spectroscopy

  3. Time trace NCLASS: neoclassical coefficients calculated from NCLASS

  4. Discharges analysed so far A wide dataset of He, Ne, Ar, Ni has been collected: He still on-going analysis. many discharges cannot be analysed due to MHD, changing plasma conditions

  5. Measured peaking of impurity • Global density peaking used in this talk: • determined Vz and Dz • assume a constant source  nz(r) • definition global impurity density peaking: • also calculated corresponding peaking: with Dmeas, V=Vneo • for C, direct measurement of nz(r) Volume averaged

  6. Impurity peaking • Z dependence • For Argon, assumption V=Vneo with D=Dmeas does not reproduce peaking. • Variation in Argon peaking  More discharges to be analysed. Discharges without RF

  7. Diffusion coefficients r/a~0.6 r/a~0.15

  8. Transport coefficients: V r/a~0.15 r/a~0.6 C Ne Ar Ni Z V_ar measured different from neoclassical.

  9. Comparison L-mode and H-mode

  10. Comparison H-mode and Hybrid Ip/B Ptot Wdia ne Peaking varies for Argon: MHD ? Halpha Hybrid: black H-mode color (-15.5s)

  11. Effect of ICRH • Rf effect confirmed but local effectr/a~0.3 • Seem to be dependent on Z ! • Compatible with a neoclassical effect preliminary Carraro EPS 2007 Giroud EPS 2007 Belo

  12. Conclusion • Work on-going on the analysis of impurity transport experiments from 2006-2007 database. • Validation of consistent analysis technique and error analysis. • First results: • L-mode/H-mode : similar peaking • Hybrid/H-mode: same peaking from C to Ar. • ICRH effect: core effect and maybe due to neoclassical effect. • Ni transport analysis to be extended and He transport analysis started. • Beta scaling and neff scaling • Systematic comparison with theoretical models.

  13. Two very different Ni profiles ICRH dominant ion Peaked Ni profile ICRH dominant electron Slightly hollow Ni profile Steady-state profile [M-E. Puiatti PoP 13 2006]

  14. Recent development in turbulent transport theory • Two main electrostatic micro-instability considered ITG/TEM

  15. Recent development in turbulent transport theory • Three main mechanisms have been identified 1[J. Weiland NF 29 1989] 1[X. Garbet PRL 91 2003] 1[M. B. Isichenko PRL 1996] 2[X. Garbet PoP 12 2005] 2,3[C. Angioni C PRL. 96 2006] 1[D.R. Baker PoP 5 1998] 1[V. Naulin Phys Rev. E 2005] 2[M. Frojdh NF 32 1992]

  16. Pinch mechanisms in theory of turbulent impurity transport All contribute to the total turbulent pinch

  17. Illustration of complex Z dependence of turbulent transport GS2 [R/LTi=7, R/LTe=6, Te/Ti=0.88] • D and V calculated with the linear version of the gyrokinetic code GS2: • only the fastest growing mode is taken in the quasi – linear model, no neoclassical transport included. Trace impurity considered. • Nogeneral trend in Z of turbulent transport • specific calculation neededfor studied discharge [C. Angioni]

  18. Different dominant instability for peaked and flat Ni density ICRH dominant ion Peaked Ni profile ICRH dominant electron Slightly hollow Ni profile Steady-state profile GS2 [M-E. Puiatti PoP 13 2006]

  19. Measured Z dependence of impurity peaking #66134 • Ne, Ar and Ni injected • in ELMy H-mode • q0>1, 0.1 <neff <0.2 • Bt=2.9T, q95=7, • 2MW ICRH, 8.6MW NBI r/a =0.15 Neoclassic Peaking lower than neoclassical measure- ment stronger z dependence in core than at mid-radius r/a =0.55 Neoclassic Negative C peaking measure- ment

  20. #66134 Neoclassic Linear GK calculation reproduces trend of measured Z dependence Discharge ITG dominated R/LTi~5.8, R/LTe~6.3, R/Ln~0.3 and Te/Ti~1.1, n*~0.10 GS2 w/o Thermodiffusion GS2 GS2 Anomalous part: -R(V-Vneo)/(D-Dneo) Measurement

  21. Discharges analysed so far A wide dataset of He, Ne, Ar, Ni has been collected: He still on-going analysis. many discharges cannot be analysed due to MHD, changing plasma conditions Ti/Te

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