A detailed study of carbon chemical erosion R C E O V D III D - PowerPoint PPT Presentation

O F Y W T I I S S A detailed study of carbon chemical erosion R C E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A in L-mode plasmas in the DIII-D divertor D I S D. G. Whyte, University of Madison - Wisconsin J.N. Brooks, Argonne National Laboratory P.C. Stangeby, University of Toronto N.H. Brooks , General Atomics 10th international workshop on carbon materials for fusion application September 17-19, 2003 Jülich, Germany 1 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C E O V D III –D N I S N I U N NATIONAL FUSION FACILITY Outline S A N D I E G O M N O A D I S • L-mode plasmas for carbon erosion studies • Erosion modeling and interpretation • Erosion with attached divertor plasma � Divertor tile vs. main-wall tile � Determination of Y chem at outer strikepoint � Atomic carbon velocity distribution • Effect of plasma detachment on carbon erosion. • Discussion & Summary 2 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C E O V H-mode plasma studies showed unexpected reduction D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S in carbon erosion in the DIII-D divertor Outer strikepoint (OSP) D 2 gas spectroscopy injection (a.u.) 10 ISP of new Upper divertor Brightness D- α 10 Y chem (%) (ph s -1 m -2 sr -1 ) D- β / D- α 10 20 1 10 19 0.1 CD / D- α OSP Lower divertor detached 0.1 10 -2 Year 10 -3 1992 2000 C 2 / D- α (x10) 80,000 90,000 100,000 Shot number 2000 3000 4000 time (ms) • Encouraging results on the use of carbon: � In-situ Y chem reduction at lower divertor. � Detachment, necessary for heat flux control, greatly reduces HC signals • …but tentative results: � Inconsistent plasma conditions over long-term study � ELMs in H-mode complicate interpretation of erosion and spectroscopy. 3 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C L-mode, simple-as-possible plasmas ideal E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S for carbon studies 1.6 10 5 105500 105502 • Low power leads to ~ 105503 1.2 10 5 105504 105505 I s (A/m 2 ) constant T surf ~375 K 105513 105506 8 10 4 105507 105508 + 105509 4 10 4 • No ELMs 0.0 0.90 1.00 1.10 1.20 Ψ n • Density control leads to Langmuir probe good detachment control DTS 10 21 100 n e (m -3 ) T e (eV) 10 10 20 • Multiple discharges 1 � Improved DTS statistics Γ i (m -2 s -1 ) 10 23 � Redundant divertor diagnosis 10 22 � Multiple C & HC 2.5 3.5 4.5 5.5 line-average density (10 19 m -3 ) emissions measured. 4 Carbon Workshop, Sept. 2003, Whyte

High resolution spectroscopy and O F Y W T I I S S R C E O V D III –D N I S N I U N NATIONAL FUSION FACILITY divertor sweeping diagnose erosion over S A N D I E G O M N O A D I S wide variety of surfaces High spectral resolution divertor spectroscopy (MDS) viewchords V1 V2 V3 V4 V5 V6 V7 #105505.2100 #105505.4900 baffle DTS 45 degree tile outer ring Row#1 Row#2 Row#3 Row#4 Langmuir probe clusters on lower divertor tiles • Absolute wavelength • Divertor tiles made from ATJ calibration from discharge graphite, an isostatically molded fine lamps during plasma shot grain graphite (+/- 0.001 nm ~ 300 m/s). • Multiple (>50) boronization layers • Can resolve T C < 0.5 eV. applied over +10 year lifetime. 5 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C WBC Monte-Carlo code is used to E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S interpret HC spectroscopy 43.5% CD 4 , 3.7% C 2 D 2 , 24.8% C 2 D 4 , • Full dissociation chains of methane & 11% C 2 D 6 , 16% C 3 D 6 higher order HC’s C atom • MOLDYN reflections vs. E trajectories • Full HC spectrum launched into OSP plasma (DTS) with sonic flow to plate. • Particle followed until redeposition or leave simulation zone (~5-10 cm) • Added C 2 and C 3 rates for C 2 spectroscopic interpretation. � Close to C for ionization & diss. CX negligible in H plasma • Excitation rates of CD, C 2 , C I and CI photon efficiency CII vs. T e, n e to calculate expected   XB emission --> photon efficiency. ∑ = X CI ,910 nm ( T e ) ∆ t i , CI n e     S CI ,910 nm i 6 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C Atomic carbon velocity distribution can E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S be an indicator of erosion source 1 WBC calculation of Thompson velocity • WBC computes emission distribution for emission-weighted atomic carbon velocity 100 eV D+ on carbon weighted f(v z ) arising from distribution (normal incidence_ HC dissociation into C I. f CI (v) • Thompson model with light- ion energy cutoff/correction predicts direct CI f(v z ) from D+ on C physical sputtering. 0 -10 0 10 20 v z (10 3 m/s) 1 / 2   E 3 / 2     E B + E df v ( E )   ∝ 1 −     ( E + E B ) 3   γ (1 − γ ) E dv       4m C m D γ = 2 ~ 0.49 ( m C + m D ) 7 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C E O The main/inner wall tiles has 5-6 times higher V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S Y chem than the inner divertor tiles V1 C II D- γ 2 V2 • V1 is a rare location for ISP, CD BD small particle/energy fluence. Spectral Intensity at ISP (10 19 ph s -1 m -2 sr -1 nm -1 ) 0 428 430 432 434 • Spectroscopy verifies C II C 2 0.8 High spectral resolution divertor ~identical ISP plasmas at two spectroscopy (MDS) viewchords V1 V2 V3 V4 V5 V6 V7 locations: #105505.2100 #105505.4900 0 T e ~ 10 eV 517 515 516 baffle 2 n e ~1.5x10 19 m -3 DTS 45 degree tile outer C I ring Row#1 Row#2 Row#3 Row#4 Langmuir probe clusters on lower divertor tiles 1 • Boron (BD) higher from 0 909 910 908 inner wall. D- α 100 C II 0 659 656 657 658 8 Carbon Workshop, Sept. 2003, Whyte wavelength (nm)

O F Y W T I I S S R C Attached outer strikepoint is dominated E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S by physical sputtering , Y chem = 0.3% Experiment 10 20 4 π x Brightness (ph s -1 m -2 ) WBC, Y chem =0.3% WBC, Y phys =1.8% 10 19 10 18 10 17 CD C 2 C I C II (431 nm) (516 nm) (910 nm) (514 nm) Incident plasma: T e =20 eV, E i ~5 T=100 eV, n e ~2.5x10 19 m -3 • • Matches of CD/C 2 ratio gives confidence in HC modeling. • Match of CII/CI ratio gives confidence in ion transport modeling. 9 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C Neither erosion model fits the E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S CI spectral features. Thompson velocity WBC calculation of distribution for emission-weighted • Calculated f(v z ) convoluted with 100 eV D+ on carbon atomic carbon velocity 1 (normal incidence_ distribution spectrometer instrumental function f CI (v) for comparison to measured CI spectra. • Discrepancy with sputtering models 0 -10 0 10 20 v z (10 3 m/s) unresolved. data � Physical: T eff ~ 1 eV OK, shift too large Thompson 1 Thompson, λ shifted � Chemical - WBC: shift OK, but chemical erosion, WBC Normalized intensity T eff ~3 eV too large. • N.B. chemical erosion can actually lead to higher T eff,CI than physical 0 sputtering -0.05 0 0.05 λ - λ 0 (nm) 10 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C WBC modeling predicts increasing E O V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S photon efficiency in detached plasmas CASE WBC-20 WBC-21 WBC-22 Plasma parameters at outer strikepoint • C 2 is particularly interesting Te (eV) 20 5 1 case: n e (m -3 ) 2.5e19 1.05e20 5.6e20 in 1 eV plasma no e- impact Photon-emission excitation rate coefficients (m 3 / s) ionization /dissociation but readily excited by e- impact C I (910 nm) 1.7e-15 1.5e-17 5.e-19 (E th ~2.4 eV). CD (431 nm) 5.6e-15 7e-15 1.5e-15 C 2 (516 nm) 2e-14 4e-14 1.16e-14 • In qualitative agreement with C + (514 nm) 5e-16 nil nil C 2 D 4 injection on JET at Photon efficiencies: Full hydrocarbon spectrum launched high density…C 2 most easily C I 4.4e-03 1.6e-3 1.7e-3 excited (Stamp et al.) CD 5.1e-2 0.45 0.22 1.1e-2 0.83 9.8 C 2 C II 4.2e-3 --- --- 11 Carbon Workshop, Sept. 2003, Whyte

O F Y W T I I S S R C E O Detachment strongly suppresses signatures of V D III –D N I S N I U N NATIONAL FUSION FACILITY S A N D I E G O M N O A D I S chemical erosion at the OSP detached • HC brightness decreases to or 10 18 Brightness (ph s -1 m -2 sr -1 ) below detection limits (open CD (431 nm) 10 17 SAPP symbols) in detachment. #105079 10 17 #105196 C 2 Swan band C 2 (516 nm) 10 16 at OSP 10 18 attached BD (433 nm) detached 10 17 10 21 100 n e (m -3 ) T e (eV) 10 10 20 1 2.5 3.5 4.5 5.5 line-average density (10 19 m -3 ) 515 516 517 wavelength (nm) 12 Carbon Workshop, Sept. 2003, Whyte