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

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 ( T DBTT < T <T recrystalliation ) Neutron damage ( transformation, etc ) 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 ( T DBTT < T <T recrystalliation ) Neutron damage ( transformation, etc ) Present study: Suppression of W accumulation Present study: Suppression of W accumulation T~10 4 eV n~10 20 m -3 W q+ (q~40-60) Transport W divertor plates Tungsten: a candidate for PFCs in reactors

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

Diagnostics  Short-wavelength VUV spectrometer ( 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 T e, n e  FIR, CO2 line density

* ) M.F.Gu, Can. J. Phys. 86 (2008) Identification of VUV spectrum (on-axis) W W 52+ were identified Isolated W 45+ line (W XLVI) at 6.2 nm is used for W density W W 52+ were identified Isolated W 45+ line (W XLVI) at 6.2 nm is used for W density 1.W q+ spectrum <= FAC* 2.Adjust Fractional Abundance (FA) 3.W q+ spectrum x FA 4.Sum-up 5.Comparison with observed spectrum Steps of spectral analysis:

0.5 keV 4x10 19 m -3 * ¼ picsFWHM

* ) M.F.Gu et al., Astrophys. J. 582 (2003) Identification of VUV spectrum (on-axis) W W 52+ were identified Isolated W 45+ line (W XLVI) at 6.2 nm is used for W density W W 52+ were identified Isolated W 45+ line (W XLVI) at 6.2 nm is used for W density 1.W q+ spectrum <= FAC* 2.Adjust Fractional Abundance (FA) 3.W q+ spectrum x FA 4.Sum-up 5.Comparison with observed spectrum Steps of spectral analysis:

I W45+ (6.2 nm): 4s 2 S 1/2 - 4p 2 P 3/2 = Excitation rate I W44+ (6.1 nm): 4s4s 1 S 0 - 4s4p 1 P 1 Close excitation energy (199 ev and 204 eV)  Similar energy dependence of C e Close excitation energy (199 ev and 204 eV)  Similar energy dependence of C e ~ 0.44 (Ioniz.rate) (Recomb.rate) Ioniz. Equi. Calculation Measurement Evaluation of W 44+ ionization / W 45+ recombination rate

Waveform of Negative Shear discharge with EC injection  Negative shear discharge -W accumulation occurs  T e decrease from 10 keV to 5 keV  During T e decrease, I W45+ and I W44+ increases, and then decreases T e -scan data for W 45+ / W 44+  Comparison with ionization equilibrium T e -scan data for W 45+ / W 44+  Comparison with ionization equilibrium EC NB IPIP TeTe nene

FAC calculation reproduced measured W 45+ /W 44+ Accuracy of ionization/recombination rates calculated with FAC were evaluated in JT-60U experimental data Accuracy of ionization/recombination rates calculated with FAC were evaluated in JT-60U experimental data Cal: n W 45+ / n W 44+ = S 44+ /  45+ Exp: n W 45+ / n W 44+ = I 45+ / I 44+ / 0.44

Waveform of W accumulation shot  Switch Co. to Ctr NBs.  With decreasing V T, 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 V T were performed Systematic experiments on W accumulation against V T were performed Ctr Co

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

Radiative power ( line radiation ) is highest between 2 – 4 keV Dominant charge states change at T e ~ 4 keV from highly raditive n=4-shell to lowly radiative n=3-shell  Decrease of L w Radiative power ( line radiation ) is highest between 2 – 4 keV Dominant charge states change at T e ~ 4 keV from highly raditive n=4-shell to lowly radiative n=3-shell  Decrease of L w Radiative power rates calculated with FAC4f *T Putterich et al Nucl. Fusion 50 (2010)

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

Evaluated radiative power in agreement with bolometoric measurement  P BOL = P before – P after P NB = 15 MW P rad core ~ 4 MW (T e ~ 5 – 6 keV ) Negative Feed-Back seems to result in radiation collapse: W accumulation => Radiation increase => T e decrease => L w increase => Radiation increase => … Negative Feed-Back seems to result in radiation collapse: W accumulation => Radiation increase => T e decrease => L w increase => Radiation increase => … Radiation collapse

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 W 45+ /W 44+ density ratio under ionization equilibrium with coronal model.  Quantitative measurement of -W density: ~ in W accumulation cases. >> ITER allowable level (10 -5 ). -W radiative power: agrees with bolometoric measurement

Thank you!

W 63+ (3s-3p,3p-3d) at 2 nm identified in JT-60U* Calculated by FAC 12 keV, 4x10 19 m -3 JT-60U Wavelength ( nm ) * J. Yanagibayashi, T. Nakano et al., accepted to J. Phys. B **Y. Ralchenko et al J. Phys. B 41 (2008) 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 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 W 63+ line at 2.3 nm will be a good diagnostic line for ITER high temperature plasma. The W 63+ line at 2.3 nm will be a good diagnostic line for ITER high temperature plasma.

2 co-tang. PNBs (~4.5MW) 21 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. 7 perp. PNBs (~15.75MW) 2 ctr-tang. PNBs (~4.5MW)

3d 10 4s 3d 10  Radiative = 1 / 4.4x10 11 = 2.3x s  Excitation = 1 / 7.8x x10 19 = 3.2x10 -5 s  Ionization = 1 / 1.2x x10 19 = 2.1x10 -3 s  Radiative <<  Excitation <  Ionization  Radiative = 1 / 4.4x10 11 = 2.3x s  Excitation = 1 / 7.8x x10 19 = 3.2x10 -5 s  Ionization = 1 / 1.2x x10 19 = 2.1x10 -3 s  Radiative <<  Excitation <  Ionization Comparison of time scales of atomic process: Colonal model is valid 4p n=5 4d 4f Excitation Ionization Radiative transition 4.4x10 11 s x x keV W 45+ W 46+ nene nene Deexcitation is dominated by radiative transition

W generation  W sputtering yield against D ~ 0.25% ( too high )  Possible W sputtering mechanisms by impurity ( C ) by high energy particles during ELM  W sputtering yield against D ~ 0.25% ( too high )  Possible W sputtering mechanisms by impurity ( C ) by high energy particles during ELM T e ~ 20 eV

High energy particles seem a key for W sputtering T e ~ 20 eV  With decreasing V T, Y phys. decreases while T e increases  Opposite trend  Needs ELM-resolved data  With decreasing V T, ELM frequency becomes high and  W dia decreases*  Similar trend between Y phys. and  W dia 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.

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 n W /n e < )  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 T e ~ 15 keV ( ~ W q+ : q > 60)  Evaluation of W density, W ion distribution*, radiative power,,, Tungsten in Fusion Research Cross section of ITER W Plasma Divertor *present study

* ) M.F.Gu et al., Astrophys. J. 582 (2003) 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

Significant difference in Ionization equilibrium T e ( eV ) FLYCHK code LLNL code *T Putterich et al Plasma Phys. Control. Fusion 50 (2008) Atomic data ( Ioniz./Recomb. rates ) are still to be checked  Atomic code calculation with FAC  Experimental validation in JT-60U plasmas Atomic data ( Ioniz./Recomb. rates ) are still to be checked  Atomic code calculation with FAC  Experimental validation in JT-60U plasmas AUG*

Ionization equilibrium: Difference between AUG* and FAC calculation *T Putterich et al Plasma Phys. Control. Fusion 50 (2008) Still different: Shift to lower T e in AUG calculation Fractional Abundance AUG* FAC Ionization equilibrium: S q+=>(q+1)+ ･ n W q+ =  (q+1)+=>q+ ･ n W (q+1)+ S = S direct + S excit.autoioniz.  =  radiative +  die-electronic *present study

*S Loch et al., Phys. Rev. A 72 (2005) **T Putterich et al., Plasma Phys. Control. Fusion 50 (2008) Accurate recombination rates required => Calculated with FAC PresentRef** IonizationFAC (DW)Loch code* (DW) Dielectronic Recombination W : FAC the others: ADPACK mod. ADPACK mod. ( x 0.39 ) Radiative RecombinationFAC T e ( eV )

W confinement time: ~ 0.5 s inside sawtooth layer Present work: n W total = I WXLVI / C excite / n e / F FA(45+) / r ST ( m -3 )  W = S/XB * I WI ( 1/s )  W = n W total * V p ST /  W ( s ) Present work: n W total = I WXLVI / C excite / n e / F FA(45+) / r ST ( m -3 )  W = S/XB * I WI ( 1/s )  W = n W total * V p ST /  W ( s )

* ) T. Nakano et al., Nucl. Fusion 49 (2009) Significant W accumulation at negative toroidal rotation* Previous work*: W accumulation was evaluated in A.U. I W XLVI / I WI n e (0) ( a.u.)

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 Coronal model Excitation Radiative transition Atomic structure calculation Energy level: Excitation rate: Radiative transition rate:

Calculation model: Example for W 15+ Term Energy ( eV ) Population normalized at the ground level 4d9 4f12 5s2 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

Calculated W spectra

JT-60U peripheral plasma: two peaks needed * ) T. Nakano et al., Nucl. Fusion 49 (2009)

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

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

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