Edge Impurity Dynamics During an ELM Cycle in by M.R. Wade 1 in collaboration with K.H. Burrell, A.W. Leonard, T.H. Osborne, P.B. Snyder, J.T. Hogan, 1 and D. Coster 3 1 Oak Ridge National Laboratory General Atomics 3 Max-Planck-Institut für Plasmaphysik Presented at 46th Annual Meeting of Division of Plasma Physics Savannah, Georgia November 15 19, 4 88-4/MRW/rs
MOTIVATION The characterization of Type I ELMs has been an active area of research for the past 3 years as we seek to capture the beneficial aspects of ELMs (particle control) while mitigating their unfavorable effects (transient heat loads and erosion) Yet, while progress has been made, several issues with regard to the ELM cycle remain unresolved: What is trigger mechanism for the ELM? Snyder talk, Wed. PM Studies suggests that ELMs are triggered by ideal, moderate toroidal mode number instabilities (known as a peeling-ballooning mode) What causes the particle and energy loss? While peeling-ballooning theory can qualitatively reproduce some aspects of the measured losses, some other transport mechanism appears to be necessary to explain overall effect How do transport properties change during the inter-elm period? While it is known that improved edge confinement in H-mode is correlated with an increase ExB shear, the effect of Er on transport during the ELM cycle is unknown 88-4/MRW/rs
SUMMARY OF RESULTS Using temporally and spatially resolved measurements of the C+6 CER emission in the edge of an ELMing H mode, the following observations have been made: Each ELM causes a rapid (< 3 µs), localized (< 4 cm on the outboard midplane) expulsion of impurity density, energy, and momentum All species respond to the ELM in a similar manner over a wide range of edge conditions Density perturbation and convective energy loss is invariant over a wide range in edge collisionality Initial response to the ELM suggests a convective expulsion of plasma E r well near the separatrix disappears at the ELM, but redevelops very quickly Analysis indicates that the initial response to the ELM is rapid convective energy loss, followed by an increase in edge thermal transport associated with the change in E r at the ELM event 88-4/MRW/rs
HIGH TIME RESOLUTION CER MEASUREMENT ALLOWS DETAILED STUDY OF THE IMPURITY DYNAMICS DURING THE ELM CYCLE CER Spatial Resolution 3 mm for density, temperature 6 mm for toroidal and poloidal rotation (1 18 m 3 ) (kev) (km/s) 4 3 1.8.4. 1 Time resolution: 74 µs.1 m.5 m.65 m.71 m.77 m.84 m.9 m.96 m n C+6 T i v pol Central Tangential Chords EDGE Tangential Chords (km/s) 1 8 4. m.39 m.69 m.81 m.87 m.94 m.3 m v tor (a.u.) D α.9.95 3. 3.5 3.1 Time (s) 88-4/MRW/rs
(1 19 m 3 ) (km/s) (1 19 m 3 ) SIGNIFICANT AMOUNT OF IMPURITY DENSITY, ENERGY, AND MOMENTUM IS EXPELLED BY EACH ELM.5.4.3..1. 15 1 5-5 1 8 6 4 Before ELM After ELM n c+6 1. v pol n e.6.7.8.9 1. 1.1 Normalized Radius (kev) (km/s) (kev) 1.5 1..5. 1 6 1.5 1..5..6.7.8.9 1. 1.1 Normalized Radius Profile constructed from data taken across a set of reproducible ELMs during an outer gap sweep 1. T i v tor T e 88-4/MRW/rs
. 5. 6. 7 Norm aliz edf lux. 8.9 1.. 5. 6. 7 Norm aliz edf lux. 8.9 1. n C+6 and n e PERTURBATION NEARLY IDENTICAL; T i and T e PERTURBATION ARE SIMILAR AND CONSISTENT WITH PEELING BALLOONING EIGENMODE.4. n C+6 /n C+6 n e /n e Eigenmode structure calculated by ELITE (n = 6)..8.4 T i /T i T e /T e. 1.5 1..5..7 V pol /V pol V tor /V tor Eigenmode Amplitude (a.u.)..5.6.7.8.9 1. Normalized Poloidal Flux 88-4/MRW/rs
ORGANIZING TEMPORAL DATA WITH RESPECT TO ELM CYCLE IMPROVES TIME RESOLUTION AND PERTURBATION ANALYSIS.8 Data Normalized Radius =.94 (km/s) (kev) (1 19 m 3 ).4. 1..8.4. 1 1 1.5 1..5 n c+6 T i V pol D α. 1 5 Time Relative to ELM (ms) 5 1 88-4/MRW/rs
ORGANIZING TEMPORAL DATA WITH RESPECT TO ELM CYCLE IMPROVES TIME RESOLUTION AND PERTURBATION ANALYSIS.8 Data Fit Normalized Radius =.94 (km/s) (kev) (1 19 m 3 ).4. 1..8.4. 1 1 1.5 1. n c+6 T i V pol D α Linear Fit Before and After ELM.5. 1 5 Time Relative to ELM (ms) 5 1 88-4/MRW/rs
1 5 5 1 1 5 5 1 1 5 5 1 Time Relative to ELM (ms) ORGANIZING TEMPORAL DATA WITH RESPECT TO ELM CYCLE IMPROVES TIME RESOLUTION AND PERTURBATION ANALYSIS.8 Data Fit Normalized Radius =.94 (km/s) (kev) (1 19 m 3 ).4. 1..8.4. 1 1 1.5 1. n c+6 T i V pol D α nc+6 T i V pol.5. 1 5 Time Relative to ELM (ms) 5 1 88-4/MRW/rs
.7.8.9 1..6.7.8.9 1. Normalized Radius OVER A WIDE RANGE IN DENSITY, ELECTRON AND IMPURITY RESPONSE ARE NEARLY IDENTICAL Density perturbation constant as n e increases 1..8.6.4. n e..9 5.1 5.9 ν ped * e.4.7..5 nc nc 1..8.6.4. ne ne..6. Temperature perturbation decreases as ne increases 1..8.6.4 Ti Ti 1..8.6.4 Te Te....6.7.8.9 1. Normalized Radius..6.7.8.9 1. Normalized Radius 88-4/MRW/rs
..5 1. 1.5..5 3. Electron Pedestal Collisionalit y..5 1. 1.5..5 3. Electron Pedestal Collisionality PARTICLE LOSS AND CONVECTIVE ENERGY LOSS INSENSITIVE TO COLLISIONALITY WITH IONS AND ELECTRONS SHARING EQUALLY N N 1%.5..15.1 Impurities Electrons Ions Total N j N j W j W j W W 15%.5 W conv = 3 nj Tj dv Convective loss insensitive to ν ped *e..15 W cond = 3 conv cond T i n dv W j W j W j W j.1.5...5 1. 1.5..5 3. Electron Pedestal Collisionality..5 1. 1.5..5 3. Electron Pedestal Collisionality Conductive loss decreases with to ν ped *e 88-4/MRW/rs
...4.6.8 1. 1....4.6.8 1. 1....4.6.8 1. 1..6.7.8.9 1. ALTHOUGH PROFILES ARE NEARLY IDENTICAL, PERTURBATION CHANGES AS TOROIDAL FIELD DIRECTION IS CHANGED kev kev 1 19 m 3 1 8 6 4 4 3 1 5 4 3 1 n e T e T i...4.6.8 1. 1. Normalized Radius.5.4.3..1..5.4.3..1 B drift toward X-point B drift away from X-point T e T e T i T i..6.7.8.9 1. Normalized Radius 88-4/MRW/rs
COMPARISON OF TANGENTIAL AND VERTICAL VIEWS SUGGESTS POLOIDALLY LOCALIZED PASSIVE EMISSION DURING ELM Brightness (ph/s/m /sr) 4 1 17 1 17 Measured Signal with CER Beam Off Tangential Vertical T i ~ 1 kev on All Chords Path Length Through Shell (m).8.6.4.. Path Length Through Emitting Shell Between ρ =.9 and ρ = 1. Tangential Views (All Cases) Vertical Views Vertical Extent of Emitting Shell 3 cm cm 1 cm 5 cm 3 cm ± 5 cm 1.8.. R (m) Measured data requires emission shell to have limited vertical extent (<5 cm) Interaction with outer wall not ruled out but deemed unlikely source ± 1 cm ± 3 cm 88-4/MRW/rs
INITIAL RESPONSE TO ELM IS A RAPID DECREASE IN DENSITY AND SLIGHT INCREASES IN TEMPERATURE AND ROTATION VELOCITY (119 m 3).1.8.4. (kev) ρ =.67 ρ =.9 nc+6 6 4 4 6 1.5 ρ =.67 1. ρ =.9.5. (km/s) ρ =.99 ρ =.99 Ti 6 4 4 6 vpol 1 ρ =.9 ρ =.99 1 6 4 Time Relative to ELM) (ms 4 6 Dα 1..5. 6 4 4 6 Time Relative to ELM (ms) 88-4/MRW/rs
6 4 4 6 6 4 4 6 Time Relative to ELM ) (ms INITIAL RESPONSE TO ELM IS A RAPID DECREASE IN DENSITY AND SLIGHT INCREASES IN TEMPERATURE AND ROTATION VELOCITY (1 19 m 3 ) (kev) (km/s).1.8.4. 1.5 1..5. 1 1 1..5 6 4 4 6 n C+6 T i v pol D α ρ =.67 ρ =.9 ρ =.99 ρ =.67 ρ =.9 ρ =.99 ρ =.9 ρ =.99. 6 4 4 6 Time Relative to ELM (ms) 88-4/MRW/rs
6 4 4 6 6 4 4 6 6 4 4 6 Time Relative to ELM ) (ms FOLLOWING INITIAL RESPONSE, TEMPERATURE AND ROTATION VELCOITY DECREASE OVER A 1 MS TIME SCALE (1 19 m 3 ) (kev) (km/s).1.8.4. 1.5 1..5. 1 1 1. n C+6 T i v pol D α ρ =.67 ρ =.9 ρ =.99 ρ =.67 ρ =.9 ρ =.99 ρ =.9 ρ =.99.5. 6 4 4 6 Time Relative to ELM (ms) 88-4/MRW/rs
PRELIMINARY MODELING USING THE SOLPS (B-EIRENE) SCRAPE-OFF LAYER TRANSPORT CODE REPRODUCES SOME QUALITATIVE FEATURES Solps* edge transport code follows time-dependent evolution of edge plasma including impurities and neutrals *Schneider et al., Contrib. Plasma Phys 4 38 (). Reiter, J. Nucl. Mater. 196-198, 8 (199) Transport model for ELMs: Transport time dependence (schematic): Assume ELM only affects 1. Pre- ELM transport on outboard. Strong Enhancement (1 ms) at ELM midplane (green area) 3. Loss of barrier, x pre-elm value 4. slow improvement to pre-elm value D, χ 1 3 Time 88-4/MRW/rs
PRELIMINARY MODELING USING THE SOLPS (B-EIRENE) SCRAPE-OFF LAYER TRANSPORT CODE REPRODUCES SOME QUALITATIVE FEATURES nc+6 Evolution from solps (B-EIRENE) Separatrix ( 1 17 m 3 ) 1.8 1.5 1..9.6 n C+6 Data.3 Time 1 5 5 1 Time Relative to ELM (ms) 1.6 Core Radius ( 1 17 m 3 ) 1. n C+6 Modeling.8 HFS separatrix.4 LFS separatrix 5 5 Time Relative to ELM (ms) 88-4/MRW/rs
3. 3. 3.4 3.6 3.8 3.1 3.1 3. 3. 3.4 3.6 3.8 3.1 3.1 3. 3. 3.4 3.6 3.8 3.1 3.1 3. 3. 3.4 3.6 3.8 3.1 3.1 INTER-ELM PHASE CONSISTS OF TWO DISTINCT PHASES.4.1 m Recovery Phase t-t ELM <1 ms Density increases in SOL and near separatrix (kev) (1 19 m 3 ) (km/s)...8.4. 8 4 n C+6 T i v tor.5 m.84 m.9 m.65 m.71 m.77 m. m.39 m.69 m.87 m.94 m.3 m Improved Transport Phase t-t ELM >1 ms Gradients continue to increase throughout phase (km/s) 1 1 4 D α v pol 3. 3. 3.4 3.6 3.8 3.1 3.1 Time (s) 88-4/MRW/rs
E r SHEAR REDUCED SIGNIFICANTLY BY ELM EVENT 4 Er 1 Er = p Vθ B φ + Zen z Vφ Bθ z R =.36 m ρ =.8 R =.58 m ρ =.9 (kv/m) R =.68 m ρ =.93 R =.74 m R =.8 m ρ =.95 ρ =.97 4 1 5 5 1 Time Relative to ELM (ms) 88-4/MRW/rs
E r WELL NEAR SEPARATRIX OBITERATED BY ELM 3 Er 1 (kv/m) 1 t t ELM = 1 ms t t ELM = ms t t ELM =.5 ms 3.6.4... R-Rsep (m) 88-4/MRW/rs
SECONDARY E r WELL FORMS VERY QUICKLY AFTER ELM 3 Er 1 (kv/m) 1 t telm =.5 ms t telm = 1. ms t telm = 1.5 ms t telm =. ms 3.6.4... R-Rsep (m) 88-4/MRW/rs
3 E r AT PRIMARY WELL LOCATION STEADILY DECREASES AFTER ELM UNTIL WELL IS FORMED Er 1 (kv/m) 1 t telm = ms t telm = 3 ms t telm = 4 ms t telm = 5 ms 3.6.4... R-Rsep (m) 88-4/MRW/rs
E r SHEAR CONTINUES TO INCREASE THROUGHOUT INTER ELM PERIOD 3 Er 1 (kv/m) 1 t telm = 5 ms t telm = 6 ms t telm = 7 ms t telm = 8ms 3.6.4. R-R sep (m).. 88-4/MRW/rs
3 34 36 38 31 31 3 34 36 38 31 31 (a.u.) (a.u.) (kv/m) AS E r WELL DEEPENS THROUGHOUT INTER-ELM PERIOD, TRANSPORT CONTINUES TO IMPROVE INSIDE THE WELL REGION 1 1 3 1.6.5.4.3. E r P c+6 D α.1. 3 34 36 38 31 31 Time (ms) R=6.7 cm R=7.9 cm R=9.1 cm 88-4/MRW/rs
4 MAXIMUM PRESSURE GRADIENT IN EDGE INCREASES WITH E B SHEAR P c+6 (ρ =.95) 3 P e /1 (TANHFIT) (kpa/m) 1 P = 1 +.4 de r dr 1 3 4 de r/dr Just Inside Well Location (kv/m ) 88-4/MRW/rs
MAGNITUDE OF CONDUCTIVE ENERGY LOSS IS CORRELATED WITH E r CHANGE CAUSED BY ELM 5 Energy Loss Across ELM (kj) 15 1 5 Wtot Wconv Wcond W tot nearly constant W conv decreases slightly Increasing Density/Collisionality 8 1 1 14 16 18 Change in der/dr Across ELM (kv/m) Suggest T i,e variation is due to transport changes associated with magnitude of E r variation across ELM 88-4/MRW/rs
8 1 1 14 16 8 1 1 14 16 ELMING QUIESCENT TRANSITION OCCURS AFTER ELMS BECOME PRIMARILY CONVECTIVE 5 4 3 1..15.1.5..8.6.4. ν * e Dα Wconv / W Wcond / W ped. 8 1 1 14 Time (ms) Burrell talk, Mon. AM 16 88-4/MRW/rs
SUPPRESSION OF ELMS BY APPLICATION OF ASYMMETRIC FIELDS ONLY SEEN WHEN ELMS ARE PRIMARILY CONVECTIVE 3..5. 1.5 1..5 I-Coil On ped ν * e = 1.5.15 n c+6 ρ=.84 (kev) (1 19 m 3 ).1.5.8.7.6.5.4.3 T i cerftiv1/1.e3 115464 8 9 3 31 Time (ms) Moyer talk, Wed. PM ρ=.94 ρ=.84 ρ=.94 3 33 34 88-4/MRW/rs
SUMMARY OF RESULTS Using temporally and spatially resolved measurements of the C+6 CER emission in the edge of an ELMing H mode, the following observations have been made: Each ELM causes a rapid (< 3 µs), localized (< 4 cm on the outboard midplane) expulsion of impurity density, energy, and momentum All species respond to the ELM in a similar manner over a wide range of edge conditions Density perturbation and convective energy loss is invariant over a wide range in edge collisionality Initial response to the ELM suggests a convective expulsion of plasma E r well near the separatrix disappears at the ELM, but redevelops very quickly Analysis indicates that the initial response to the ELM is rapid convective energy loss, followed by an increase in edge thermal transport associated with the change in E r at the ELM event 88-4/MRW/rs