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T. Nakano J apan A tomic E nergy A gency

3Sep2013 ADAS Workshop Badhonnef, GE. W transport studies in JT-60U. T. Nakano J apan A tomic E nergy A gency. Tungsten: a candidate for PFCs in reactors. Tungsten: suitable for plasma facing components for reactors High melting point Low fuel retention

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T. Nakano J apan A tomic E nergy A gency

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  1. 3Sep2013 ADAS Workshop Badhonnef, GE W transport studies in JT-60U T. Nakano Japan Atomic Energy Agency

  2. Tungsten: a candidate for PFCs in reactors • Tungsten: • suitable for plasma facing components • for reactors • High melting point • Low fuel retention • Low sputtering yield (long life time) • Unsuitable • Highly radiative • Narrow operation window as PFCs • ( TDBTT< T <Trecrystalliation) • Neutron damage ( transformation, etc ) T~104 eV n~1020 m-3 Wq+ (q~40-60) Transport • Present study: • Suppression of W accumulation W divertor plates

  3. W divertor plates in JT-60U • W coated CFC tiles: • 50 m with Re multi-layer • 11 tiles (1/21 toroidal length ) Standard configuration W tiles Dome (C) Inner Div.(C) W tile Outer Div.(C) W exp. configuration W tile

  4. Diagnostics • Short-wavelength VUV spectrometer ( 0.5- 40 nm ) • On-axis : W XLVI intensity (core) • Long-wavelength VUV spectrometer ( 20 – 120 nm ) Off-axis: sensitivity calibration • Visible spectrometer • sensitivity calibration • PIN Soft X-ray (>3keV) • CXRS Toroidal rotation • TMS Te, ne • FIR, CO2 line density

  5. Identification of VUV spectrum (on-axis) Steps of spectral analysis: Wq+ spectrum <= FAC* Adjust Fractional Abundance (FA) Wq+ spectrum x FA Sum-up Comparison with observed spectrum x1/5 • W41+ - W52+ were identified • Isolated W45+ line (W XLVI) at 6.2 nm is used for W density *) M.F.Gu, Can. J. Phys. 86 (2008) 675. http://sprg.ssl.berkeley.edu/~mfgu/fac/

  6. 0.5 keV 4x1019 m-3 * ¼ picsFWHM

  7. Identification of VUV spectrum (on-axis) Steps of spectral analysis: Wq+ spectrum <= FAC* Adjust Fractional Abundance (FA) Wq+ spectrum x FA Sum-up Comparison with observed spectrum x1/5 • W41+ - W52+ were identified • Isolated W45+ line (W XLVI) at 6.2 nm is used for W density *) M.F.Gu et al., Astrophys. J. 582 (2003) 1241. http://sprg.ssl.berkeley.edu/~mfgu/fac/

  8. Evaluation of W44+ ionization / W45+ recombination rate Measurement Excitation rate I W45+(6.2 nm): 4s 2S1/2 - 4p 2P3/2 = I W44+(6.1 nm): 4s4s 1S0 - 4s4p 1P1 • Close excitation energy (199 ev and 204 eV) • Similar energy dependence ofCe Ioniz. Equi. (Ioniz.rate) (Recomb.rate) Calculation ~ 0.44

  9. Waveform of Negative Shear discharge with EC injection IP • Negative shear discharge • W accumulation occurs • Tedecrease • from 10 keV to 5 keV • During Te decrease, • IW45+ and IW44+ increases, and then decreases NB EC Te ne • Te -scan data for • W45+ / W44+ • Comparison with ionization equilibrium

  10. FAC calculation reproduced measured W45+/W44+ Cal: nW45+ /nW44+ = S44+ / a 45+ Exp: nW45+ /nW44+ = I45+ / I44+ / 0.44 Accuracy of ionization/recombination rates calculated with FAC were evaluated in JT-60U experimental data

  11. Waveform of W accumulation shot Ctr Co • Switch Co. to Ctr NBs. • With decreasing VT, W XLVI increases, while W I is constant. • W accumulation • The same phase between W XLVI and SX(5) • W XLVI is a measure inside the Sawtooth layer Systematic experiments on W accumulation against VT were performed

  12. Plasma rotation and central heating effective in avoiding W accumulation Radiation collapse Plasma rotation Central heating 3% Plasma current Neutral Beam T. Nakano and the JT-60 team, J. Nucl. Mater. S327 (2011) 415.

  13. Radiative power rates calculated with FAC 4f 4d 4s,4p n=3 n=2 • Radiative power ( line radiation ) is highest between 2 – 4 keV • Dominant charge states change at Te ~ 4 keV • from highly raditive n=4-shell to lowly radiative n=3-shell • Decrease of Lw *T Putterich et al Nucl. Fusion 50 (2010) 025012

  14. Comparison of calculated radiative power rate with NLTE5 workshop results** FAC calculation is in agreement with the NLTE5 results *T Putterich et al Nucl. Fusion 50 (2010) 025012 **Y Ralchenko et al AIP Proceedings 1161 (2009) 242

  15. Evaluated radiative power in agreement with bolometoric measurement Radiation collapse DPBOL= Pbefore – Pafter PNB = 15 MW Pradcore ~ 4 MW (Te ~ 5 – 6 keV ) Negative Feed-Back seems to result in radiation collapse: W accumulation => Radiation increase => Te decrease => Lw increase => Radiation increase => …

  16. Summary and Conclusions • W XLVI ( 6.2 nm ) intensity was measured with • absolutely calibrated VUV spectrometers. • Validity of Ioniz./Recomb. rate calculated with FAC was confirmed from W45+/W44+ density ratio • under ionization equilibrium with coronal model. • Quantitative measurement of • W density: ~ 10-3in W accumulation cases. • >> ITER allowable level (10-5). • W radiative power: agrees with bolometoric measurement

  17. Thank you!

  18. W63+(3s-3p,3p-3d) at 2 nm identified in JT-60U* JT-60U EBIT(NIST)** • 3s-3p lines at 7-8 nm identified in EBIT** were reproduced by the FAC calculation. • 3s-3p at 2.3 nm • 3p-3d at 2 nm The W63+ line at 2.3 nm will be a good diagnostic line for ITER high temperature plasma. Calculated by FAC 12 keV, 4x1019 m-3 Wavelength ( nm ) * J. Yanagibayashi, T. Nakano et al., accepted to J. Phys. B **Y. Ralchenko et al J. Phys. B 41 (2008) 021003

  19. Neutral Beam injectors • 11 positive-ion-based NBs (PNBs~85keV) • 2 co-tangential NB, 2ctr-tangential NBs, and 7 perp. NBs. • Combination of tangential and perpendicular NBs leads to • wide range of toroidal rotation. 2 ctr-tang. PNBs (~4.5MW) 7 perp. PNBs (~15.75MW) 2 co-tang. PNBs (~4.5MW)

  20. Comparison of time scales of atomic process:Colonal model is valid W46+ 3d10 7.8x10-16 1.2x10-17 Ionization Excitation W45+ 5 keV n=5 Radiative transition 4.4x1011 s-1 • tRadiative = 1 / 4.4x1011 = 2.3x10-12 s • tExcitation = 1 / 7.8x10-16 4x1019 = 3.2x10-5 s • tIonization = 1 / 1.2x10-17 4x1019 = 2.1x10-3 s • tRadiative << tExcitation <tIonization 4f 4d 4p ne 3d104s Deexcitation is dominated by radiative transition

  21. W generation Te~ 20 eV • W sputtering yield against D ~ 0.25% ( too high ) • Possible W sputtering mechanisms • by impurity ( C ) • by high energy particles during ELM

  22. High energy particles seem a key for W sputtering Te~ 20 eV • With decreasing VT, • Yphys.decreases • while Te increases • Opposite trend • Needs ELM-resolved data • With decreasing VT, ELM frequency becomes high and DWdia decreases* • Similar trend • between Yphys. and DWdia Time average ~ 1 s W sputtering is possibly due to high energy particles expelled during ELM *) K.Kamiya et al., Plasma Phys. Control. Fusion 48 (2006) A131.

  23. Tungsten in Fusion Research • Tungsten as a plasma-facing component • Merit : high melting point => compatible with high temperature fusion plasma • : low hydrogen (T) retention => safety, economy • : low sputtering yield => long lifetime • : low dust production • Demerit : high Z (74) • highly radiative ( allowable nW/ne < 10-5) • accumulation in the core plasma • Issues of W transport study • Understanding of • Transport in core plasma* • => accumulation mechanism in core plasma • Local transport in divertor, global migration,,, • Control of • W generation, W penetration, W accumulation,,, • Preparation of diagnostics at high Te ~ 15 keV ( ~ Wq+ : q > 60) • Evaluation of W density, W ion distribution*, radiative power,,, Cross section of ITER W Plasma Divertor • *present study

  24. Requirement for W atomic data=>calculation with an atomic structure code,FAC* ① 二電子性再結合断面積の計算 ② JT-60U, LHD スペクトルの解析 *) M.F.Gu et al., Astrophys. J. 582 (2003) 1241. http://sprg.ssl.berkeley.edu/~mfgu/fac/

  25. Significant difference in Ionization equilibrium 46+ 45+ 44+ FLYCHK code AUG* LLNL code 103 103 104 104 Te ( eV ) Te ( eV ) • Atomic data ( Ioniz./Recomb. rates ) are still to be checked • Atomic code calculation with FAC • Experimental validation in JT-60U plasmas *T Putterich et al Plasma Phys. Control. Fusion 50 (2008) 085016

  26. Ionization equilibrium:Difference between AUG* and FAC calculation 1 Still different: Shift to lower Te in AUG calculation 0.1 Fractional Abundance 0.01 Ionization equilibrium: Sq+=>(q+1)+ ･nWq+ = a (q+1)+=>q+ ･nW(q+1)+ S = Sdirect + Sexcit.autoioniz. a = aradiative + adie-electronic AUG* 45+ 46+ 44+ *present study FAC *T Putterich et al Plasma Phys. Control. Fusion 50 (2008) 085016

  27. Accurate recombination rates required=> Calculated with FAC Te ( eV ) *S Loch et al., Phys. Rev. A 72 (2005) 052716 **T Putterich et al., Plasma Phys. Control. Fusion 50 (2008) 085016

  28. W confinement time: ~ 0.5 s inside sawtooth layer • Present work: nWtotal = I WXLVI / Cexcite / ne / FFA(45+) / rST ( m-3 ) • GW = S/XB * IWI ( 1/s ) • tW = nWtotal * VpST / GW ( s )

  29. Significant W accumulation at negative toroidal rotation* IW XLVI / IWI ne(0) ( a.u.) Previous work*: W accumulation was evaluated in A.U. *) T. Nakano et al., Nucl. Fusion 49 (2009) 115024.

  30. Calculation model: Example for W 15+ Electron configuration: 4d10 4f11 5s2 4d10 4f11 5s1 5*1;5s=0 4d10 4f12 5s1 4d10 4f11 5s1 6*1 4d9 4f12 5s2 Excitation Atomic structure calculation Radiative transition Energy level: Excitation rate: Radiative transition rate: Coronal model

  31. Calculation model: Example for W 15+ • 4d10 4f11 5s2 • (Ground state) Electron configuration: 4d10 4f11 5s2 4d10 4f11 5s1 5*1;5s=0 4d10 4f12 5s1 4d10 4f11 5s1 6*1 4d9 4f12 5s2 • Excitation • Radiative transition • Coronal model Population normalized at the ground level • 4d9 4f12 5s2 Term Energy ( eV )

  32. Calculated W spectra

  33. JT-60U peripheral plasma: two peaks needed *) T. Nakano et al., Nucl. Fusion49 (2009) 115024.

  34. Contents • Introduction • Experimental set-up/Diagnostics • Absolute calibration of VUV spectrometers • Results • Evaluation of Ionization equilibrium • Quantitative evaluation of • W confinement time, density, radiative power • W generation • Conclusions

  35. Sensitivity Calibration of VUV spectrometers:“ Triple” Branching ratio method Visible Long-VUV Short-VUV Short-VUV

  36. Sensitivity Calibration of VUV spectrometers: • Absolute sensitivity ~ 6.2 nm was obtained • W XLVI is used for W density measurement

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