Boundary Physics Plan in NSTX Rajesh Maingi* For the NSTX Team *Oak Ridge National Laboratory Tokamak Planning Workshop PSFC, MIT Sept 17-19, 2007 Supported by Office of Science Culham Sci Ctr U St. Andrews York U Chubu U Fukui U Hiroshima U Hyogo U Kyoto U Kyushu U Kyushu Tokai U NIFS Niigata U U Tokyo JAERI Hebrew U Ioffe Inst RRC Kurchatov Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching ASCR, Czech Rep U Quebec College W&M Colorado Sch Mines Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics New York U Old Dominion U ORNL PPPL PSI Princeton U SNL Think Tank, Inc. UC Davis UC Irvine UCLA UCSD U Colorado U Maryland U Rochester U Washington U Wisconsin

R. Maingi - TPW 2 Increased Emphasis on Boundary physics in NSTX in FY09-FY13 Program organized into prioritized themes 1: Lithium as a divertor plasma-facing component Density and impurity control, heat flux handling Effect on plasma performance 2a: SOL and divertor physics Edge transport and turbulence; SOL width Divertor heat and particle flux optimization 2b: Pedestal and ELM Physics Characterization and theory comparison at low R/a Active control with resonant magnetic perturbations

R. Maingi - TPW 3 Lithium program motivation Provides density control and improves plasma peformance –Large density reduction and  E increase in CDX-U –Signs of improved  E and ELM control in NSTX Complements Mo/carbon PFC work at C-MOD/DIII-D –Substantial expertise in Li handling and use at PPPL  E and W MHD increased Large ELMs mitigated * Li evaporator results (NSTX 2007)

R. Maingi - TPW 4 Lithium program in NSTX proceeding in stages Li pellets : FY Li evaporator (LiTER): FY Li powder injection: FY Second Li evaporator: FY Liquid Li divertor (LLD): FY Divertor upgrade: FY –Builds on Li success in TFTR and CDX-U –Complements (and relies on) LTX mission of evaluating Li as the primary PFC

R. Maingi - TPW 5 Liquid lithium divertor module will be located at lower outboard divertor plate Goals –Low  : reduce n e by 50% –High  : reduce n e by 25% Features –15 cm wide –5 cm outboard of CHI gap –Desired T surface ~ o C Installation ~ summer 2008 Experiments in 2009 CHI gap

R. Maingi - TPW 6 Liquid lithium divertor module will be located at lower outboard divertor plate LLD  l = sec) CHI gap Goals –Low  : reduce n e by 50% –High  : reduce n e by 25% Features –15 cm wide –5 cm outboard of CHI gap –Desired T surface ~ o C Installation ~ summer 2008 Experiments in 2009

R. Maingi - TPW 7 Liquid lithium divertor module should provide density control in high flux expansion, high  shape LLD Goals –Low  : reduce n e by 50% –High  : reduce n e by 25% Broad D  profiles in high flux expansion (~ 20), high  l shape Divertor upgrade: FY –Second or upgraded LLD, or a cryopump –Long pulse PFC upgrade  l = sec) CHI gap

R. Maingi - TPW 8 Lithium program plan Install and characterize Liquid Lithium divertor (LLD) module Perform hydrogen retention and pumping efficiency studies Optimize efficiency of gas injector fueling New tools: LLD + diagnostics, Penning gauge near pumps, upgraded supersonic gas injector, programmable center stack gas injector LLD performance with higher power input, long pulse Utilize core fueling (pellets) New tools: new divertor diagnostics*, 2 nd NBI, D 2 pellet injector* Optimize divertor pumping and divertor PFC materials for long pulse Advanced core fueling (Compact toroids) New tools: New/additional LLD module* or cryopump, new PFCs, CT injector* * collaborator proposal

R. Maingi - TPW 9 Edge T & T Physics Elements  Motivated by the high divertor and first-wall heat loads expected in NHTX, ST-CTF, and ITER Sheath connected Sheath disconnected Analytic theory Correlate edge turbulence in the divertor and midplane regions –Compare with SOL widths Compare with analytic theory and numerical simulation of turbulence and SOL widths Investigate interaction between HHFW heating and edge turbulence near the RF antennas Measure effect of local poloidal electric fields on edge turbulence –Evaluate for SOL width control q SOL,mid [cm]

R. Maingi - TPW 10 Edge T & T Physics Plan Comparison of midplane and divertor turbulence characteristics with models Scaling of midplane n, T, , q with major parameters –Comparison with SOL width models –Comparison with turbulence characteristics Edge biasing with local electrodes and probes New tools: fast IR camera, upgraded reciprocating probe tips SOL turbulence and widths with higher input power Divertor turbulence with X-point probe Upgraded biasing capability, if warranted New tools: 2 nd NBI, new divertor diagnostics, X-point probe* * collaborator proposal

R. Maingi - TPW 11 Divertor and detachment physics emphasized in high power flux density spherical tori  ST effects: low ||, small R, large outboard side surface area  Power management through flux expansion and detachment may be required for dissipation Plan: –Full characterization of attached and detached divertor characteristics –Assessment of importance of private flux region in STs –2-D divertor physics measurements –Possible divertor modifications More closed divertor Possible X-divertor test

R. Maingi - TPW Lower divertor power accountability and transient loading studies Improved detachment control for long pulse discharges MARFE characterization studies Divertor performance dependence on geometry New tools: Fast IR camera, divertor bolometer Detachment and heat flux mitigation with higher input power and reduced densuty Private flux region physics studies Development of MARFE dynamic models New tools: X-point probe*, divertor imaging spectrometer, 2 nd NBI D divertor physics: parallel vs. perp. transport Closed divertor or X-divertor test? New tools: Divertor Thomson, 2-D divertor spectroscopy*, new divertor hardware Divertor and detachment Physics Plan * collaborator proposal

R. Maingi - TPW 13 ELM and Pedestal Physics Elements –Does the low R/a enable improved edge stability? –Do small ELMs in different devices have common physics? –Measure impact of ELMs on divertor and wall plasma fluxes –Optimize shape to avoid large ELMs –Control ELMs with Resonant Magnetic Perturbations Pedestal studies to reveal a/R dependence of gradients and widths –How to increase T ped ? D  [au] W MHD [kJ] Large (Type I) Mid (Type III) Small (Type V) Mixed (I + V)  Large ELMs at low collisionality motivate ELM and pedestal studies for NHTX and ST-CTF  Low R/a allows broader test of stability models for prediction of P’ limit for ITER

R. Maingi - TPW 14 ELM and Pedestal Physics plan: Assess edge stability of different ELM types and impact of aspect ratio Compare small ELM regimes with other devices Identify shape dependencies of ELM regimes Investigate effect of Lithium on ELMs Assess effects of RMP on edge stability Determine relation of pedestal and core stored energy Measure dependence of pedestal width on parameters Identify physics of Enhanced Pedestal H-modes, e.g. orbit squeezing physics Compare pedestal parameters with CPES and ESL codes New tools: Five additional edge Thomson channels Enhanced Pedestal H-mode

R. Maingi - TPW 15 ELM and Pedestal Physics plan: RMP effects of heat flux spreading Develop quasi-steady small ELM scenarios with high input power Investigate role of SOL current in ELM stability Extend Enhanced Pedestal H-modes New tools: Upgraded Edge rotation diagnostic, edge SXR* High m,n RMP impact on ELMs and heat flux Triggering of localized transport barriers with localized rotation control by RMP New tools: Internal Non-axisymmetric Control Coils (NCC) * collaborator proposal

R. Maingi - TPW 16 Boundary physics program time line FY09-FY13 5 year FY07 14 Midplane and divertor turbulence at higher PNBI Divertor turbulence with X-point probe Upgraded biasing for SOL control Midplane and divertor turbulence comp. with models Scaling of midplane widths Edge biasing for SOL control Compact Toroid Injector SWIFT ion flow + upgraded Penning gauge for particle balance Liquid lithium divertor module Upgraded LLD or cryopump SGI and center stack gas injector upgrades D 2 Pellet injector Divertor PFC long pulse upgrade Tools More edge TS chans Fast IR camera Divertor bolometry ERD upgrade X-point probe Edge SXR Divertor imaging spectrometer Divertor Thomson Divertor SXR Liquid Li with high input power Core fueling with pellets Optimize Liquid Li interactions Core fueling with CTs Characterize Liquid Li effects Hydrogen retention in liquid Li Optimized gas injector fueling Lithium T & T Detachment at higher PNBI Private flux region studies MARFE models 2-D divertor physics: new data and model comparison Closed divertor or X-divertor? Divertor power accounting Improved detachment control MARFE studies RMP effects on heat flux profile Long pulse small ELM regimes Extend EPH modes High m,n RMP studies Triggering of edge barriers ELM stability, small ELMs EPH modes, RMP effects Model comparison Divertor Pedestal & ELMs Non-axisymmetric Control Coils Second NBI

R. Maingi - TPW 17 Backup

R. Maingi - TPW 18 RMP can also de-stabilize ELMs in high  l discharges sec sec

R. Maingi - TPW 19 Lithium reduced L-mode density by 50% and H- mode density by 15% * Li evaporator results Pre-Li = Post-Li = t = 510ms H-mode L-mode

R. Maingi - TPW 20 Edge T & T Physics Details Sheath connected Sheath disconnected Analytic theory bounds ok n, T go down with I p q : 2.0cm (800kA) 1.1cm (900kA) 0.8cm (1MA)  T / q ~ 1!

R. Maingi - TPW 21 ELM and Pedestal Physics Details e * Type V ELM Enhanced Pedestal H-mode RMP coil concepts Pedestal R/a scan NSTX DIII-D MAST

R. Maingi - TPW 22 Large  p * reduction and  E increase observed in CDX-U with liquid Lithium Low  p * required more fueling  E increased with pump-out

R. Maingi - TPW 23 Large  p * reduction and  E increase observed in CDX-U with liquid Lithium Low  p * requires more fueling  E increased with pump-out