TRANSPORT PROGRAM C-Mod C-MOD PAC FEBRUARY, 2005 PRESENTED BY MARTIN GREENWALD MIT PLASMA SCIENCE & FUSION CENTER
TRANSPORT IS A BROAD TOPIC WHERE DO WE FOCUS? We emphasize areas where C-Mod - Has unique capabilities - Is in unique parameter regimes - Observes unique or unusual phenomena - Can make important comparisons with other devices (esp. ITPA) Comparisons with theory and modeling form a critical part of the program - Theory plays critical role in motivation and design of experiments - Comparisons to include profiles, fluctuations and fluctuation dynamics need to develop synthetic diagnostics - C-Mod will continue the close collaboration with theory and modeling groups at MIT and elsewhere.
RELATION TO OUTSIDE RESEARCH PROGRAMS C-Mod is imbedded in a national and international transport program We do not propose to answer, by ourselves, all important transport questions discussed today. We do propose to make substantial contributions in each of them however RELATION OF TRANSPORT TO BALANCE OF C-MOD PROGRAM There is an obvious close connection to AT, BP thrusts Also couplings to Boundary, Stability and Wave/Particle programs Interesting physics at the interfaces between topical areas! o Examples L/H threshold, density limit, ELMs, EDA, Flow drive, etc.
TRANSPORT THEMES FOR 05-06 CAMPAIGNS Fluctuation studies electron transport Rotation and momentum transport Edge barriers thresholds and confinement, pedestals, EDA and QC mode ITBs threshold physics Particle transport Stress connection to reactor relevant regimes no core particle or momentum sources T i T e : τ ei <<τ E Balance of talk will outline goals, motivation, background and 05-06 plans for each
SELF GENERATED ROTATION AND MOMENTUM TRANSPORT Goals - Characterize momentum transport in torque-free discharges, especially in the outer regions of the plasma. - Begin investigations into underlying mechanisms of momentum transport. Momentum transport evaluated from analysis of profiles in source-free discharges
BACKGROUND - MOMENTUM TRANSPORT V//φ transport-driven parallel SOL flows: V//φ Ip B T SOL provides boundary condition Processes which carry this across separatrix unclear o Neutral collisions o Plasma collisions o Turbulence Toroidal Velocity (km s-1) -10-20 -30-40 Core Ar17+ Doppler Outer Probe ρ = 1 mm -10 0 10 Toroidal Projection of Parallel Velocity (km s-1) Momentum diffuses and convects from edge into core One might expect stronger turbulence effects near edge due to dissipation Despite significant theoretical interest (Catto, Chan, Chang, Coppi, Perkins, Rogister, Shaing) work on momentum transport is relatively immature
PLANS SELF GENERATED ROTATION AND MOMENTUM TRANSPORT Widen parameter range and investigate edge/core couplings Diagnostic enhancements for velocity CXR, Soft X-Rays (hydrogen-like neon) Transient experiments - SSEP step Dimensionless scaling DIII-D Poloidal rotation comparisons w/ neoclassical theory, role in barrier formation Will pursue flow drive by ICRF Try to motivate theory and -5 simulation work 0.75 0.80 0.85 0.90 0.95 1.00 I P (MA) V Tor (0) (10 4 m/s) 2 1 0-1 -2-3 -4 Topology combines with other effects to give net rotation. LSN n e = 1.7-1.9x10 20 /m 3 USN n e = 1.4-1.6x10 20 /m 3
EDGE BARRIERS H-MODES THRESHOLDS AND CONFINEMENT PEDESTALS EDA AND QC Goals - Compare L/H thresholds to emerging theories of transition including role of SOL/edge flows - Study mechanisms for regulating H-mode pedestal profiles - QC mode/eda, small ELMs including comparison with edge simulations - Contribute to international database for pedestal scaling - Characterize H-mode performance w/o BN tiles
1 2 3 4 1 4 BACKGROUND EDGE BARRIERS - THRESHOLD Topology dependent flow from resymmetrization of ballooning transport in SOL Couples across separatrix Pressure dependent rotation, Vϕ ~ W/I P independent of topology Net rotation is sum of these effects Plasma is farther from threshold condition for unfavorable drift direction Toroidal Velocity (km s -1 ) 40 0-40 20 0 Core Rotation SOL, near separatrix H(at transition) Upper Null Lower Null 1 2 3 4 Total Input Power (MW) L
BACKGROUND EDGE BARRIERS - THRESHOLD Normalized total input power 2.0 1.5 1.0 ING L-H thresholds vs topology INL RG LSN IWL LSN DN USN B drift effect explained by connection between topology, SOL flows and threshold Is momentum coupling from SOL to edge responsible for low density limit? Is I P dependence of rotation connected to lack of Ip scaling in L-H threshold? 0.5-20 -10 0 10 20, distance between primary and secondary separatrices or inner wall gap (mm) Connection to zonal flows (Drake, Rogers, Guzdar)? L-H threshold is identical for diverted and limited plasmas if flow topology is similar
PLANS EDGE BARRIERS - THRESHOLD Further parameter scans I P connection to threshold nonscaling? Density connection to low density limit? Transient experiments inward transport of momentum Check threshold at precisely balanced DN (MAST/AUG/NSTX) L-H thresholds and flows in helium discharges neutral physics effects T e /L n 1/2 (kev/m 1/2 ) 2.5 2.0 1.5 1.0 0.5 Theory Expt, USN Expt, LSN 0.0 0 2 4 6 8 10 B T,0 (T) Other H-mode threshold eg Guzdar theory Barrier and transition dynamics w/ Carreras
BACKGROUND EDGE BARRIERS PEDESTAL WIDTH Pedestal width scaling/physics has enormous leverage on ITER performance Relative importance of plasma and atomic physics probed via dimensionless identity experiments w/ DIII-D, ASDEX-U Role of neutrals investigated with more sophisticated neutral modeling (kinetic effects included) C-Mod
PLANS EDGE BARRIERS PEDESTAL WIDTH Continued parameter scans and contributions to international database Test neo-classical theory (C.S. Chang) scan RF power and B T Neutral studies Dimensionless identity experiments with JET and ASDEX-U Helium H-modes
BACKGROUND EDGE BARRIERS PEDESTAL RELAXATION EDA/ELMS Another critical issue for ITER (Large ELMs are very bad) 700 EDA H-mode combines good 600 energy confinement, relatively poor impurity confinement and no large ELMs collisionality? Reliable extrapolation depends on basic understanding Small ELM regimes have been T e ped (ev) 500 400 300 200 Unstable Stable ELMs EDA achieved but not fully understood. 100 1.0 1.5 2.0 2.5 3.0 3.5 4.0 α MHD
BACKGROUND EDGE BARRIERS QC MODE WIDTH Diagnostics not entirely in agreement (understandable?) Why do we care? Codes find that mode should fill pedestal Note high-frequency companion results Experiment/Code interactions
PLANS EDGE BARRIERS EDA/QC MODE QC mode Radial extent equal or less than pedestal width? Important comparison w/theory BOUT (Xu, Umansky) Modified probe Higher resolution BES JFT-2M comparisons EDA and other small ELM studies (with BP and MHD groups) NSTX joint experiments
FLUCTUATIONS AND TRANSPORT Goals - Identify fluctuations associated with anomalous electron transport, including any anisotropy in k spectrum - Characterize ion and electron transport as a function of magnetic shear (LHCD) - Further quantitative tests of marginal stability/critical gradient length paradigm
BACKGROUND - FLUCTUATIONS AND TRANSPORT Electron transport crucial but poorly understood If due to short wavelength fluctuations, need extended radial structures a ρ i c/ω pe ρ e Magnetic Flutter ITG TEM µ Tearing ETG ITB studies suggest magnetic shear is a critical parameter for suppressing electron transport Need to continue quantitative studies of ion channel The role of ETG in driving electron transport is the subject of much theoretical interest and dispute. (Lin, Dorland, Jenko, etc etc ) The existence and nature of radial streamers is at the heart of this debate
PLANS - FLUCTUATIONS AND TRANSPORT Electron transport use PCI spatial localization may allow determination of k space anisotropy Magnetic fluctuations (farther into future but polarimeter is first step) detailed comparisons of measured profiles and critical gradient lengths (L T ) from simulations. DNB diagnostics for j(r), Ti(r), V(r) GK simulations gs2 (Mikkelsen, Dorland, Ernst, Redi) and gyro (Bravenec) Control magnetic shear with LHCD
ITB PHYSICS Goals Evaluate the role of marginal stability and critical gradients in the creation of off-axis icrf ITBs Test model of barrier control via TEM Investigate role of magnetic shear in determining barrier foot location. Characterize access to ITBs via modification of magnetic shear (LHCD).
BACKGROUND - ITB PHYSICS (1) Hypothesis for off-axis barrier formation suppress ITG via reduction of temperature gradient relative critical value Barrier access is extremely sensitive to resonance location with little hysteresis Gyrokinetic analysis by Redi, Mikkelsen, Ernst
BACKGROUND - ITB PHYSICS (2) Hypothesis for barrier control mechanism (gyrokinetic analysis by Ernst). Fluctuations measured with PCI increase as barrier is controlled TEM? As ITG diminishes, Ware pinch causes density to peak. TEMs are destabilized Control is via temperature dependence of TEM turbulence. Non-linear upshift for critical L n for TEM predicted. GK analysis
BACKGROUND - ITB PHYSICS (3) Localized broadband fluctuations observed in barrier by HECE (UTA).
PLANS ITBS Threshold relation to marginal stability, - Hysteresis - Role of L-H transients Control of position and strength comparison with modeling - TEM and saturation - Localized turbulence measurements reflectometry, HECE Heat and density pulse propagation, barrier dynamics, turbulence spreading (Hahm, Diamond) Looking forward to additional capabilities from LHCD systems - Changes in transport/turbulence + ITBs via changing shear profile - Formation with weak or reversed shear
PARTICLE TRANSPORT Goals Evaluate particle transport in plasmas with no source and no Ware pinch Verify the existence and importance of anomalous pinch Explore the relation between particle and energy transport Plans Particle transport with no source and no Ware pinch (LHCD) Correlation with fluctuation measurements Transient transport experiments Comparison with emerging theories
C-MOD SUPPORT FOR ITPA HIGH-PRIORITY RESEARCH Transport Physics Improve experimental characterization and understanding of critical issues for reactor relevant regimes with enhanced confinement, by: - Obtaining physics documentation for transport modeling of ITER hybrid and steady-state demonstration discharges - Addressing reactor relevant conditions, e.g., electron heating, Te~Ti, impurities, density, edge-core interaction, low momentum input... Contribute to and utilize international experimental ITPA database for tests of the commonality of hybrid and steady state scenario transport physics across devices Encourage tests of simulation predictions via comparisons to measurements of turbulence characteristics, code-to-code comparisons and comparisons to transport scalings
C-MOD SUPPORT FOR ITPA HIGH-PRIORITY RESEARCH (CONT) Confinement Database and Modeling Assemble and manage multi-machine databases, analysis tools, and physics models Evaluate global and local models for plasma confinement by testing against the databases. Predict the performance of Burning Plasma Experiments using the models, and include an estimate of the uncertainty of the predictions. Pedestal and Edge Construct a Profile DB based on Inter machine experiment and perform tests of modeling using the profile DB as TG work. Improve predictive capability of pedestal structure through profile modelling. Construct physics-based and empirical scaling of pedestal parameters Improve predictive capability for ELM size and frequency and assess accessibility to regimes with small ELMs
ITPA JOINT TRANSPORT EXPERIMENTS Recently closed CDB-3 Improving the condition of H-mode and pedestal databases CDB-7 Ohmic identity scaling experiments PEP-11 Dimensionless comparison of L-H threshold and pedestals with C-Mod and ASDEX-U Current CDB-4 Confinement scaling in ELMy H-modes, nu* scans CDB-8 rho* scaling TP-1 Steady state plasma development TP-3.2 Investigation of transport mechanisms with Te~Ti TP-4.1 Similarity experiments with off-axis ICRF-generated density barriers TP-6 Obtain empirical scaling of spontaneous plasma rotations
ITPA JOINT TRANSPORT EXPERIMENTS (CONT) Current (cont) PEP-7 Pedestal width analysis via dimensionless identity experiments PEP-12 Comparison between C-Mod EDA and JFT-2M HRS regimes PEP-16 C-Mod/NSTX/MAST small ELM regimes C-Mod may contribute in 2006 CDB-2 beta confinement scaling in ELMy H-modes TP-2 Hybrid regime development TP-3.1 Sustained high performance operation with Ti ~ Te TP-4.2 Low momentum input operation of hybrid/at plasmas TP-4.3 Electron ITB similarity experiments with low momentum input
SUMMARY C-Mod experiment offers excellent opportunities to advance the state of transport science - Capable and unique facility - Strong diagnostic set - Wide collaborations with theory and modeling All three of these components will be improved and expanded. Good alignment with ITPA and US program goals (FESAC) Expect transport program to be dominated by close and careful comparisons with theory