1 Boundary Physics Plan FY R. Maingi, H. Kugel* and the NSTX Team Oak Ridge National Laboratory * Princeton Plasma Physics Laboratory NSTX Five Year Plan Review Princeton Plasma Physics Laboratory 30 June - 2 July, 2003

2 Boundary physics activities have enabling technology goals and science goals Enabling technology - tailor edge plasma to optimize discharges –evaluate power handling needs and solutions –assess fueling and particle pumping needs –develop and evaluate wall conditioning techniques Science goals –characterize edge power and particle transport regimes parallel vs. cross-field do conventional aspect ratio models fit? –understand effect of ST features on boundary physics, e.g. large in/out B t ratio –pedestal asymmetry –target heat flux profiles large SOL mirror ratio and short connection length

3 Boundary goals are linked to IPPA goals 5-Year Objective: Make preliminary determination of the attractiveness of the spherical torus (ST), by assessing high-  T stability, confinement, self-consistent high bootstrap operation, and acceptable divertor heat flux, for pulse lengths much greater than energy confinement times. Implementing Approach : –Disperse Edge Heat Flux at Acceptable Levels –Study ST specific effects high mirror ratio high flux expansion

4 Boundary physics talk outline Fuel and impurity particle control –sources and sinks –wall conditioning techniques Power handling and mitigation –heat flux scaling and power balance –steady heat flux mitigation and off-normal event study H-mode, pedestal and ELM physics –profile shapes, gradients and widths –ELM characterization and control Edge, SOL, divertor and wall conditioning physics –nature of “classical” parallel transport and cross-field transport –ST kinetic effects

5 Fuel and impurity particle control will be improved Routine H-mode access enabled progress toward goals –higher  due to lower pressure peaking factor –long pulse due to low volt-second consumption rate, owing to high bootstrap fraction from edge pressure gradient Most reproducible H-mode access w/center stack gas puff –observe nearly monotonic n e, n C6+, n D rise with time Poloidal location of gas puffing affects H-mode Goal: make n e independent of time –progress toward ultra-low recycling Staged plan with parallel components –improve control of sources, aiming toward higher efficiency –improve control of sinks via wall conditioning and active pumping

6 Uncontrolled (non-disruptive) density rise in long pulse H-modes n e    m    sec  sec  sec  sec  I p [MA] P NBI /10 [MW] n e [10 19 m -3 ] D  [au] W MHD *10 [MJ] H98pby2  S NBI dN e /dt S gas [torr-l/s] Density control needed for improved current drive efficiency, transport studies, and power and particle handling research

7 Edge Carbon Density Increases Rapidly after L-H Core Carbon and Z eff Increase Slowly R. Bell (PPPL) CC  eff C ee DD #108728

8 Improved source control –more poloidal locations for gas (FY03-04) –supersonic gas nozzle (FY04) –Lithium pellets (FY04) –D 2 pellet injection (FY05) –CT injection? (FY06 ) New diagnostics –D  cameras for core fueling (FY04) –pellet diagnostics (FY06) –more edge Thomson channels (FY05,07) –divertor Langmuir probe upgrade (FY05) Fuel and impurity source control plan ?

9 Fuel and impurity sink control progresses toward ultra- low recycling Improved sink (density) control –improved boronization (FY03) high temp. TMB morning TMB between shots TMB –lithium pellets (FY04) –lithium coatings (FY04-06) –in-vessel cryopumps (FY06,FY04 ) –lithium module(FY08, FY06 ) New diagnostics –n C (r) f/CHERs, Z eff f/MPTS (FY03) –D  cameras for core fueling (FY04-05) –fast pressure gauges (FY04) –upgraded Langmuir probe array(FY05) –divertor SPRED (FY 07) ? ?

10 Power handling must be maintained for NSTX goal of several current diffusion times ST’s can have high heat flux because of high P heat /R – NSTX: P NBI ~ 7 MW, P RF ~ 6 MW, P heat /R ~ 15.3 Highest q peak in NSTX ~ 10 MW/m 2 –  T div ~ C in LSN –extrapolates to ~ 3 sec. pulse length limit (  T div ~ C) For T e < 2 keV, current diffusion time < 1 sec. –If T e increases, current diffusion time could approach few seconds Goal: assess power balance and survey heat flux in many scenarios (vs. shape, input parameters, etc.) Staged plan –quasi-steady power balance over next few years; evaluate PFCs –transient events in future

11 Peak heat flux increased with NBI power in LSN and was reduced in DND relative to LSN

12 Power handling and mitigation plan Experimental plan –Power balance studies (FY02+) divertor heat flux vs core and divertor radiation parallel vs perpendicular transport –Detailed comparison between single-nulls and double-nulls (FY04+) –Heat flux reduction studies (FY04+) –Impact of fast events, e.g. ELMs, IREs, and disruptions (FY05+) New Diagnostics –Cross-calibrate core bolometry with platinum-foils (FY04) –Add and optimize divertor bolometer channels (FY04-05) –Add one slow and one fast infrared cameras (FY04, FY05)

13 H-mode, pedestal and ELM physics background L-H transition physics (common with transport group) –P LH higher than scalings - trapped particles, poloidal damping? –I p and maybe B t dependence of P LH appears different –role of E X B shear? Pedestal: profile shapes, gradients and widths –density pedestal high and in/out asymmetry –pedestal T e < 400 eV, below predictions ELMs –Tokamak-like ELMs in double-null –Usually ELM-free or very large events in single-null –Fueling strongly affects ELM size(type?) Plan: characterization studies over next few years and optimization studies over longer term

sec sec sec sec   sec sec sec High n e and relatively low T e pedestal observed n e profile hollow after transition and fills in ms Moderate in/out n e asymmetry usually observed T e profile flattens initially and peaks later in time sec

Hz LSN DN  W/W 0 : 5-25%  W/W 0 : 1-4%   Time (s) D  (arb.) ELM behavior depends on operating conditions Higher Fueling Lower Fueling Bush (ORNL)

16 H-mode, pedestal and ELM physics plan Continue L-H mode transition parametric studies Pedestal studies –height, width, and maximum gradient scalings –role of fueling profile in setting density width ELM studies –role of shape and fueling –conductive vs. convective losses –optimization for density and impurity control New Diagnostics –extra edge Thomson channels (FY05, FY07) –MSE for edge durrent density (FY 06) –edge Helium line ratio (FY06) –improved time resolution in CHERs (FY08)

17 Edge, SOL, divertor and wall conditioning physics background Classical divertor heat flow regimes applicable? –high divertor T e, sheath-limited heat flow –low divertor T e, conduction-limited heat flow –detachment Impact of unique ST features –high SOL mirror ratio, short connection length, high flux expansion –in/out B t ratio and target; E X B flows Cross-field transport: diffusive vs. intermittent –intermittent transport appears strong in both L and H-modes –any cross-correlation with ELMs? Wall conditioning technique assessment Plan: near-term focus on nature of cross-field transport, and longer term on ST kinetic effects

18 Outer divertor probably attached (sheath/flux limit regime), but inner divertor probably detached I p [MA] P NBI /10[MW] W MHD *4[MJ] D  near ISP D  near OSP D  near ISP D  near OSP # time legend [sec] Heat flux profiles have outer peak -Probably attached Inner side detach- ment consistent with reversal of in/out D  profile during heat pulse -Similar to pre- cryopump at DIII-D Reduced recycling will probably re- attach ISP, so D  will go down More particles near OSP(?); need LP data to confirm

19 UEDGE modeling needed to estimate transport rates D  = 1 m 2 /sec,   = 3 m 2 /s Porter (LLNL) LLNL using diffusive cross- field transport UCSD examining convective cross-field transport

20 # GPI view Routine Intermittent Plasma Objects Observed with Gas Puff Imaging Diagnostic Radial vs. poloidal imaging Gas manifold Side-viewing re- entrant window Zweben (PPPL) Maqueda (LANL) H-mode L-mode Similar data from reflectometers (UCLA, ORNL) and edge reciprocating probe (UCSD)

21 Edge, SOL, and divertor physics plan Do classic divertor heat flow models apply? (FY03-04) –need UEDGE simulations for interpretation Continue edge turbulence studies (FY04+) –simulation and coupling with theory crucial (e.g. BOUT, DEGAS-2) Cross-field transport and SOL scaling with mid-plane reciprocating probe (FY04+) Experiments to test ST kinetic effects (FY06+) New Diagnostics –divertor Langmuir probe array with improved spatial resolution (FY05) –imaging spectrometer (FY06) –X-point reciprocating probe (FY06) –SOL ion energy analyzer (FY07) –divertor Thomson scattering (FY08)

22 Wall conditioning physics plan Wall conditioning technique assessment (FY04+) –how does boronization change wall physics? –how do those changes improve the core plasma? New Diagnostics –quartz crystal deposition monitors for real time flux (FY 03) –divertor SPRED for impurities (FY07) –divertor materials probes (like DiMES on DIII-D) (FY08)

23 Power Handling Fast CHERs power balance, heat flux scaling Divertor and center stack swept Langmuir probes Optimize X-point recipr. probe Helium Line ratio MPTS ch ST Edge Physics Improved TMB Divertor SPRED Particle Control and Fueling Li/B pellets and first Li evaporator system Cryopumps and baffles liquid Li module? Fast pressure gauges Additional visible, filtered cameras CT injector? fueling studies Supersonic gas injectors D  pellets: LFS divertor bolometer, upgrade add’l IR camera Fast IR camera MPTS divertor chans Ion Energy Analyzer-SOL DiMES probe Divertror Imaging Spectrometer Pedestal and ELM characterizationEdge Optimization Studies transient event studies Choose Cryopump(s) detachment studies D  pellet: HFS MPTS ch particle control studies Quartz crystal deposition monitor, upgrade IPPA: 10 yr IPPA: 5 year FY PFC upgrade? Tile material for Li film Lithium film studies particle balance 21 weeks/year

24 Boundary physics plan addresses NSTX program needs and contributes to ST physics Improved source and sink control to achieve ultra-low recycling limit Power balance studies for NSTX PFC needs and next step ST needs Dependence of H-mode, pedestal and ELM physics on R/a Edge, SOL, divertor and wall conditioning physics –nature of “classical” parallel transport and cross-field transport –ST kinetic effects in SOL

25 Backup

26 Self-contained deposition source is under development Electromagnetic version of commercial (permanent magnet) source now in use –Allows adjustment of power density by varying ratio of coil currents Beam power densities of 250 MW/m 2 attainable Shroud crucible or physically scan source to produce desired deposition pattern –Defocussed beam can heat/clean aperture Field coil E-beam source Externally fed lithium rod (source) Lithium crucible with aperture mask E-beam trajectory Shaped aperture Majeski, Kaita (PPPL)

27 NSTX implementation Replace one of the passive stabilizing plates with a new plate, faced with plasma sprayed tungsten or moly Install an insertable e-beam system which can be scanned over the stabilizing plate Deposit 1000Å of lithium and withdraw the e-beam system –Similar to the insertable getters used in PLT, PBX –But time scale is different Few 10’s of seconds for 1000Å coating Cycle time is dominated by insertion/removal of e-beam. Coat before every shot –1000 shots  0.1 mm accumulation Accumulation may be limited by evaporation Majeski, Kaita (PPPL)

28 Preliminary neutral transport studies show possible plenum pressure sensitivity to strike point Same model and n e, T e, P e profiles for DIII-D as in Maingi, et. al., Nucl. Fusion 39 (1999) 1190 Ion current = 5kA, used for normalization Leakage conductance = 20 m^3/sec Menon, ORNL

29 Density is intermittent Rate of bursts is 2E3 Poloidal field is much less intermittent Instantaneous particle flux ~10 19 m -2 s -1 Intermittent behavior observed in L and H-mode Boedo, UCSD L-mode # Time [msec] n e [10 19 m -3 ] H-mode # n e [10 19 m -3 ] Time [msec]

30 Progress made in 2-D modeling of L-modes Pigarov (UCSD) UEDGE with convective cross- field transport model Able to match L-mode well Concluded that main chamber recycling plays role in NSTX

31 High-Field Side Gas Injector Fueling Allows Early L-H Transition and Longer H-mode Duration

32 Flat T e will have profound effects on transport, MHD 1 keV m -3 PS&T seminar 7 March 2003 ICC-Seattle May 2003