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ELM Suppression by Li Deposition on NSTX Graphite Divertor Surfaces. Office of Science. D. K. Mansfield a , H. W. Kugel a , R. Maingi b , M. G. Bell a , R. Bell a , E. Fredrickson a , R. Kaita a , J. Kallman a , S. Kaye a , B. LeBlanc a , D. Mueller a , S. Paul a , R. Raman c ,

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  1. ELM Suppression by Li Deposition on NSTX Graphite Divertor Surfaces Office of Science D. K. Mansfielda, H. W. Kugela, R. Maingib, M. G. Bella, R. Bella, E. Fredricksona, R. Kaitaa, J. Kallmana, S. Kayea, B. LeBlanca, D. Muellera, S. Paula, R. Ramanc, L. Roquemorea, S. Sabbaghd, H. Schneidera, C. H. Skinnera, V. Soukhanovskiie, J. Timberlakea, J. Wilgenb, L. Zakharova and the NSTX Team a Princeton Plasma Physics Laboratory, Princeton, NJ 08543 b Oak Ridge National Laboratory, Oak Ridge, TN 37831 c University of Washington,, Seattle, WA 98195 d Columbia University, New York, NY 10027 e Lawrence Livermore National Laboratory, Livermore, CA 94551 Supported by: DOE Contract DE-AC02-76CH03073 1

  2. Purpose : Study ELM Suppression by in situ Modification of NSTX Plasma Surface Interaction: Li on Graphite Lithium Evaporators with Shutters R/a = 1.46 BT = 0.5 T Ip = 800 kA PNBI = 4 MW Lower Single Null Type 1 ELMS B treated Graphite H. Kugel P2-58 2

  3. Newly-Installed Li Shutters Allow More Flexible Wall Conditioning and Improved Plasma Operations Previous Divertor PFC Conditioning Scenario Plasma 1 s • Disadvantages: • Window coatings • He co-deposition • & dilution Continuous Li Evaporation Li 10 min Li 10 min He 6.5 min He 6.5 min He 6.5 min He 6.5 min New Conditioning Scenario with Shutters Plasma 1 s • Advantages: • Windows clear • No He dilution • Shot cycle • shortened Shutters Closed Shutters Closed H. Kugel P2-58 C. Skinner P2-59 Time 3

  4. The Effects of Li Wall Conditioning on Inductive Flux Consumption Were Immediate and Pronounced 20 Fifth Deposition OH Coil Current (kA) First Deposition 116 mg (~100 nm) 0 No Li -20 1 No Li Plasma Current (MA) 4 NBI Power (MW) 0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Time (s) 4

  5. ELM Suppression by 5th Discharge With Li No ELMs Þ Immediate Increase in Stored Energy No Li No Li 1st Li 1st Li Da (A. U.) 5th Li 5th Li 2.5 Stored Energy (102 kJ) No Li 1st Li 5th Li No Li 5th Li 1st Li 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Time (s) 5

  6. How Does Wall Conditioning SuppressELMs? - By a Series of Omissions … Rate mg/min Recent mg Total mg No Li 129019 0 0 0 129021 * 16 116 116 129022 * 16 193 309 Da (A.U.) 129023 16 161 471 * * 129024 16 168 638 * * * 129025 16 171 809 * 0.2 0.3 0.4 Time (s) 6

  7. Complete ELM Suppression at Higher Li Evaporation Rates and Higher PFC Accumulations Þ Higher Confinement Rate mg/min Recent mg Total mg No Li 129019 Da (A.U.) 129038 No ELMS 70 767 5734 129041 No ELMS 70 970 8348 8 No Li 6 129038 129019 neL ( 1016 cm-2 ) 129041 4 PNBI (MW) 2 0 0 2.5 Beta Limit Stored Energy (102 kJ) No Li 129019 129041 129038 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Time (s) 7

  8. Pronounced Improvements in Discharge Parameters • Large Changes at Plasma Edge Due to Li 1.5 1.5 Li 129041 129019 Pronounced Pedestal Features 1.0 1.0 Ti (keV) Te (keV) 0.5 0.5 t = 515 ms t = 485 ms 0 0 10 250 ne (1019 m-3) Vtor (km/s) 5 150 t = 515 ms t = 485 ms 1.1 1.1 1.2 1.2 1.3 1.3 1.4 1.4 1.5 1.5 0 0 R (m) R (m) 8

  9. Reflectometry Shows Clear Modification of SOL Density by Lithium / ELMS 5 LCFS 4 3 ne (1012 cm-3) 129024 ELMs Total Lithium: 638 mg 129041 No ELMs Total Lithium : 8348 mg 2 1 0 Major Radius (m) 1.46 1.48 1.50 1.52 1.54 1.56 1.58 1.60 9

  10. The Same Intermittent ELM Behavior was Observed After Evaporation Ended as Li Lost Effectiveness 129019 No Li 129057 Taken Next Day No Evaporation 8348 mg Residual 10

  11. Summary and Conclusions • Actively modifying the plasma surface interaction in situ has completely eliminated ELMs. • ELMs disappeared in a series of omissions with no apparent change in either amplitude or frequency. • Thin films of Li (100 nm /discharge)can have pronounced effects on NSTX performance. • The evidence supports the view that wall conditioning by Li modifies both the SOL and pedestal properties. • Initial TRANSP run indicates increased current in outer region. • Stability analysis underway (S. Kaye) 11

  12. Extra Slides

  13. No ELMs Þ Metals Accumulate in Core Beta Limit With Li, No ELMs Zeff(0) From Metals No Li with ELMs Time (s)

  14. Possible ELMs Pacing with 40 mm Li Powder Injected into Plasma SOL/ Pedestal Powder Injector Li Velocity at SOL = 4.5 m/sec

  15. Lithium Edge Conditions Yield ELM Suppression • TRANSP Analysis Finds Increase in Edge Current No Li No Li Stability Analysis in Progress S. Kaye S. Kaye 10

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