1. NSTX-U Supported by Culham Sci Ctr York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAEA Inst for Nucl Res, Kiev Ioffe Inst TRINITI Chonbuk Natl U NFRI KAIST POSTECH Seoul Natl U ASIPP CIEMAT FOM Inst DIFFER ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep Coll of Wm & Mary Columbia U CompX General Atomics FIU INL Johns Hopkins U LANL LLNL Lodestar MIT Lehigh U Nova Photonics ORNL PPPL Princeton U Purdue U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Illinois U Maryland U Rochester U Tennessee U Tulsa U Washington U Wisconsin X Science LLC Effect of progressively increasing lithium conditioning on edge transport and stability in high triangularity NSTX H-modes R. Maingi, J.M. Canik, R.E. Bell, D.P. Boyle, A. Diallo, R. Kaita, S.M. Kaye, B.P. LeBlanc, S.A. Sabbagh, V.A. Soukhanovskii, and the NSTX Team 4 th International Symposium on Lithium Applications for Fusion Granada, Spain 28-30 September 2015

2. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Plasma characteristics and stability improved with increasing lithium evaporation in strongly shaped NSTX discharges 2 Lithium evaporated before each discharge –Deposition amount scanned, as also in weakly shaped discharges (No liquid lithium divertor results in this talk) Global characteristics changed –Recycling: D  declined in all measured views –Energy confinement (  E, H-factor) improved –When discharges were ELM-free, radiated power increased with time (several techniques were developed to deal with this problem) Edge n e, T e, pressure profiles changed –Reduction in edge n e gradient changed edge P’, which improved MHD stability in weakly shaped discharges; similar here 1.Effect on individual discharges 2.Trends vs. pre-discharge lithium 3.Effect on profiles 4.SOLPS edge transport analysis

3. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Low  (0.46) Low  (1.8) Low squareness I p =0.8 MA, q 95 =7.6 New dataset from highly shaped plasmas as envisioned in NSTX-U, and for future STs 3 High  (0.6) High  (2.2) High squareness I p =1 MA, q 95 =8.2

4. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Center of LITER deposition Outer Strike Point Center of LITER deposition very near (far from) outer strike point in high (low) triangularity discharges 4 Center of LITER deposition Outer Strike Point LITER Canisters R. Maingi, JNM 2015

5. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Performance of strongly shaped discharges improved more with increasing lithium (similar to weakly shaped discharges) 5 I p duration not quite optimized with higher Li Reduced P NBI Reduced dN/dt Comparable stored energy H-factor increased by 50% Increasing P rad Reduced recycling, long ELM-free phases Strong shaping No lithium 280 mg 550 mg

6. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 6 ELMs disappeared gradually with increasing lithium (also observed in weakly shaped discharges) Reference (no lithium) With lithium Divertor D  Higher fueling, lower NBI Higher fueling Higher fueling, lower NBI

7. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Lower divertor D  decreased rapidly with increasing Li deposition in highly shaped discharges 7 High shaping Low shaping Lower D  0 200 400 600 800 1000 Lithium dep. before discharge [mg] 5x drop in D  drop because of transition from detachment to high recycling to low recycling Possible geometric effect: lithium deposition closer to outer strike point and/or high flux expansion facilitates re-attachment at lower lithium deposition in highly shaped discharges

8. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 D  and neutral pressure decreased, and H97L increased with increasing pre-discharge lithium evaporation in all data 8 High shaping Low shaping Lower D   Lower Li-I Center Stack D  H97L Upper D   Midplane neutral pressure 0 200 400 600 800 1000 Lithium dep. before discharge [mg] 0 200 400 600 800 1000 Lithium dep. before discharge [mg]

9. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Edge profiles change markedly with increasing lithium in strongly shaped discharges (as in weakly shaped ones) 9 0 mg – 6 MW 150 mg – 5 MW 550 mg – 4 MW 132543 700 m5099 132556 900 mave 132588 556 ave

10. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Higher NBI power in strongly shaped discharges leads to higher edge temperature and pressure 10 550 mg – 4 MW 710 mg – 2 MW 132588 556 ave 129038 400 ave Strongly shaped Weakly Shaped

11. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Goal of SOLPS interpretive analysis is to assess recycling coefficient and radial transport changes with lithium 11 Generate grid based on discharge equilibrium Prescribe power and particle fluxes through inner boundary from data Vary free parameters to match measured midplane and divertor profiles –Separatrix location adjusted to match peak q div peak Plate recycling coefficient and radiation varied to match peak D  Extra power-balance iteration allows complex D(  ),  (  ) –No separation between D and v pinch, so diffusivities are ‘effective’ values, i.e. to get flux right Result: recycling coefficient drops f/0.99 to ~0.9 Result: transport increases in last 3% of  N, but decreases inside of that region

12. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Reference no-lithium discharge has low heat flux & high D  : code indicates partially detached state 12 132542 – 0.474 s 132543 - 0.8 s ELM-synced profiles Last 50% ELM cycle 132543 700 m5099  D  view truncated R < 0.41m  Factor of 2 uncertainty in D  data Data Model Data Model Data Model

13. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Shallow edge n e gradient, deeper temperature gradients, and higher heat flux/lower D  reproduced in modeling 13 ELM-free profiles 550mg Li pre-discharge 132588 556 ave Data Model  D  view truncated R < 0.41m  Factor of 2 uncertainty in D  data Data Model Data Model 132589 – 0.5 s 132588 – 0.65 s

14. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Particle transport reduced with increasing lithium Energy transport reduced a few cm insides of separatrix 14 Increasing lithium in direction of yellow arrow

15. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Comparison of lithium results from DIII-D, EAST and NSTX NSTXDIII-DEAST Delivery methodInter-shot evaporation, (Dropper) DropperDropper, (Morning evaporation) Pedestal WidthIncreased ? Pedestal HeightIncreased ? H-factorIncreased Unchanged Edge fluctuations DecreasedIncreased Radiated powerRamp during EFSteady during EF Effect on ELMsEliminatedDelayedEliminated RecyclingReducedUnchangedReduced

16. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Trend of improving discharge performance with increasing lithium observed in highly shaped plasmas 16 Recycling and neutral pressure decreased with increasing Li Energy confinement increased and edge stability improved with increasing Li Recycling coefficient dropped to ~ 0.9 from 0.99 (SOLPS) -Lithium deposition closer to strike point facilitates re-attachment? Transport increased in last 3% of  N, but decreased inside of that region (SOLPS) Change in edge profiles likely the key to ELM elimination, as in weakly shaped discharges (ELITE calcs. commencing) Impurity accumulation caused by reduction of edge fluctuations with Li in NSTX? Need to understand this!

17. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 THANK YOU FOR YOUR ATTENTION! Looking forward to conducting these types of experiments in NSTX-U! 17

18. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 No lithium 260 mg 700 mg 18 ELM-free H-mode induced by lithium wall conditioning in weakly shaped discharges Pre-Li, with-Li (260 mg), with-Li (700 mg) Lower NBI to avoid  limit Lower n e Similar stored energy H-factor increased by 40% Higher P rad /P heat Reduced recycling, ELM-free with higher Li D. Mansfield, JNM 2009; R. Maingi, PRL 2009 I p [MA] P NBI [MW] n e [10 19 m -3 ] W MHD [kJ] H97L P rad [MW] D  [au]

19. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Lithium improved performance of strongly shaped discharges, similar to weakly shaped ones 19 Strong shaping No lithium With lithium Duration extended Same P NBI Reduced dN/dt Higher stored energy Higher confinement Increasing P rad Reduced recycling, long ELM-free phases

20. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Intermediate lithium deposition results in intermediate effects on profiles 20  D  view truncated R < 0.41m  Factor of 2 uncertainty in D  amplitude 132558 – 0.644 s Data Model Data Model ELM-free profiles 280mg Li pre-discharge 132557 700 mave Data Model

21. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Lithium reduced recycling and improved confinement of both strongly and weakly shaped discharges 21 Strong shaping No lithium 550 mg Weak shaping No lithium 710 mg

22. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Similar effects on discharges observed with weak and strong shaping 22 Strong shaping No lithium Less lithium More lithium Duration extended Same and lower P NBI Reduced dN/dt Higher stored energy Higher confinement Increasing P rad Reduced recycling, long ELM-free phases

23. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 23 ELMs eliminated gradually during original low  experiment Reference (no lithium) With lithium Divertor D  Higher fueling, lower NBI

24. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 Power and particle exhaust a key challenge for future devices 24 Liquid metals are being studied at PPPL as an alternative to solid PFCs for future devices NSTX used lithium wall coatings (evaporative and liquid) to test the efficacy of lithium in particle and power exhaust -Lithium enables reduced recycling from PFCs -Lithium will be important research line in NSTX-Upgrade, which is scheduled to commence operation in 2015

25. NSTX-U ISLA 2015: Maingi oral28-30 Sep 2015 25 Flow chart of how lithium results in ELM elimination similar for highly and weakly shaped discharges Li coatings reduce recycling and core fueling (SOLPS) n e, P e gradient reduced P i gradient unchanged J bs, J || reduced - stabilizing (ELITE) Edge P e follows n e and T e ; peak P’ shifts farther from separatrix J bs, J || increased but far from separatrix; improves stability to kink/peeling modes (ELITE)  N from 0.95-1 (recycling region)  N from 0.8-0.94 n e and n e reduced T e fixed  e increased ETG (GS2)  e reduced strongly –  T stable (GS2) n e and n e T e and T e increased D eff reduced, most in ELM-free (SOLPS)