Visions for Data Management and Remote Collaboration on ITER

C-Mod Core Transport Program Presented by Martin Greenwald C-Mod 5 Year Proposal Review May 7-9, 2008 MIT – Plasma Science & Fusion Center Practical Motivations for Transport Research • Overall plasma behavior must be robustly predictable – Could we design Demo based on empirical scaling of τE and PLH? – (These are still major uncertainties for ITER) – External controls are diminished - self heating, Bootstrap, CD dominate • All transport channels are important and must be understood – In a reactor electrons and ions are coupled – Density profile set by transport, not sources – Rotation profile mainly set by transport not sources • • Transport Barriers must be predictable and controlled – Impact on fusion gain and, through profiles, for stability and bootstrap current Note strong physics coupling to pedestal/edge and SOL transport including coupling via profiles, flows, turbulence (e.g. L-H threshold and density limit) ⇒ integrated studies stressed on C-Mod! C-Mod 5 Year Plan Review, May 2008, M. Greenwald 2 How Do We Take Advantage of C-Mod Characteristics to Best Address Critical Problems? • Exploit unique characteristics – Higher field, density, (ν*, νeiτE) coupled electrons and ions and Ti ~ Te – Standard operation with no core particle or momentum source – Decoupling between density profile and power deposition • Exploit facility capabilities – Efficient off-axis current drive for manipulation of magnetic shear – Diagnostic set: improvements in profile and fluctuation measurements – Upgraded computer cluster – for local nonlinear GK simulations • • Provide strong support for ITER: dimensionless scaling, etc… At the same time: C-Mod exploits multi-institutional strengths of transport program via formal and informal collaboration C-Mod 5 Year Plan Review, May 2008, M. Greenwald 3 Other Program Drivers (1) • • ITER needs, ITPA joint experiments – Compiled later in this presentation and in spreadsheets 2005 Priorities panel - address topical questions T4 and T5 – T4 How does turbulence cause heat particles and momentum to escape from plasmas?” – T5 How are electromagnetic fields and mass flows generated? • Priorities Panel recommendations for enhanced funding/activity – “Carry out additional science and technology activities supporting ITER…” – “Expand the effort to understand the transport of particles and momentum” – “Mount a focused enhanced effort to understand electron transport” – “Predict the formation, structure and transient evolution of edge transport barriers.” C-Mod 5 Year Plan Review, May 2008, M. Greenwald 4 Other Program Drivers (2) • 2007 Planning panel recommendations – issues to be resolved during “ITER era” – A1. Measurement: Make advances in sensor hardware, procedures and algorithms for measurements of all necessary plasma quantities with sufficient coverage and accuracy needed for the scientific mission, especially plasma control. – A2. Integration of high-performance, steady-state, burning plasmas: Create and conduct research, on a routine basis, of high performance core, edge and SOL plasmas in steady-state with the combined performance characteristics required for Demo. – A3. Validated Predictive Modeling: Through developments in theory and modeling and careful comparison with experiments, develop a set of computational models which are capable of predicting all important plasma behavior in the regimes and geometries relevant for practical fusion energy. (Turbulent transport stressed) C-Mod 5 Year Plan Review, May 2008, M. Greenwald 5 Proposed Major Themes For C-Mod Transport • Overarching - Model Testing and Code Validation – Systematic and quantitative comparisons with nonlinear turbulence codes – Quantitative where codes and models are more mature ◊ Role of magnetic shear ◊ Electron transport • • • Particle and Impurity Transport – How to predict fueling, density profile and impurity content? – Now within capabilities of gyrokinetic codes Self-Generated Flows and Momentum Transport – How to extrapolate to source-free, reactor-like conditions? Internal Transport Barriers – Access conditions and control, especially in absence of dominant ExB – Important element in advanced scenarios research C-Mod 5 Year Plan Review, May 2008, M. Greenwald 6 Model Testing/Validation • density fluctuation spectra[A.U.] Development of predictive model is a key goal for U.S. Fusion program – What are the critical elements of the models? – Requires careful thought about design of experiments, measurements 0.5 0.4 0.3 0.2 0.1 0.0 New GS 2 kR spectrum original GS 2 ky spectrum Measured P CI kR spectrum • Quantitative comparisons will stress more mature topics – drift-wave theories for ion and electron thermal transport – Deployment of fluctuation diagnostics – Development of synthetic diagnostics – Development of appropriate metrics – Significant priority for run time 0 2 4 6 8 Wavenumber [cm -1 ] Synthetic PCI spectrum shows agreement with experiment. (Ernst et al.) C-Mod 5 Year Plan Review, May 2008, M. Greenwald 7 Validation Experiments: Role of magnetic shear Exploit LHCD • • With Te ~ Ti , γ > ωExB , ZEFF << ZI, R/Ln < R/LT; choice of magnetic shear (Ŝ) regime can determine R/LT. We can exploit LHCD to allow direct manipulation of shear. – Test drift-wave models by evaluating change in R/LT, R/Ln and fluctuations as we modify Ŝ From linear ITG calculations – IFS-PPPL model Kotschenreuther et al, 1995 • There is additional work planned on effects of magnetic shear in pedestal and edge using other techniques C-Mod 5 Year Plan Review, May 2008, M. Greenwald 8 Validation Experiments: Test models for electron channel turbulence and transport in low-density regimes • Can we identify the fluctuations contributing to electron heat transport? – Diagnostics are critical here – Use PCI with kR up to 50-60 cm-1, spatial localization, separate kr, kθ – Compare with predictions for mixed scale turbulence – LH operation + cryopump will lead to more operation at low density, with strong electron heating • 0.04 0.03 0.02 0.01 Is there an important magnetic component in turbulence or transport? – Micro-tearing – Magnetic flutter – Measure B fluctuations with polarimeter τE (sec) 0.00 0.0 L. Lin (PhD Student) 0.5 1.0 (1020 ) 1.5 9 C-Mod 5 Year Plan Review, May 2008, M. Greenwald Self-Generated Flows and Momentum Transport • Strong, co-current self generated toroidal rotation in H-modes – Momentum transferred from edge to core – Significant rotation gradients in torque-free regions Toroidal Rotation Profile Evolution 100 Toroidal Rotation Velocity [km/s] 0.83 50 0.81 • • • • 0 0.79 0.77 0.73 0.71 0.75 Strong coupling in L-mode to SOL flows – Complex L-mode behavior Counter-current rotation driven by LHCD Similarity experiments with DIII-D Multi-machine database assembled and 0-d dimensionless scaling begun -50 0.70 A. Ince-Cushman (PhD Student) 0.75 0.80 Major Radius [m] [m 0.85 Evolution of velocity profiles following onset of ICRF heating. Changes begin in the edge and “propagate” into the core C-Mod 5 Year Plan Review, May 2008, M. Greenwald 10 Self-Generated Flows and Momentum Transport • Questions Raised by Observations – Can we understand momentum transport and origin of self-generated rotation? ◊ How is momentum transport driven by turbulence? ◊ Can we get at this at the level of fluctuations? – How does it extrapolate into reactor regime? (zero torque, low ρ*) – Will rotation be sufficient to affect micro- or macro-instabilities? – Can significant flows be driven with RF waves? • • Need for additional theory Comparisons will necessarily be qualitative in the near future C-Mod 5 Year Plan Review, May 2008, M. Greenwald 11 Plans: Self-Generated Flows and Momentum Transport • Major upgrade in profile diagnostic: unprecedented measurements in source-free discharges (PPPL collaboration) Near-term concentration of FES Joule milestone Compare measured selfgenerated flow profiles and crossfield fluxes with emerging theory and models. Compare fluctuation levels, spectra, correlation lengths and times Role of LHH and LHCD in modifying profiles Test feasibility of IC and IBW flow drive with mode converted ICRF Rotation data from 3rd generation high-resolution x-ray diagnostic Note VΦ gradient in torque free region 12 • • • • C-Mod 5 Year Plan Review, May 2008, M. Greenwald Highlights: Particle and Impurity Transport • • Peaked density profiles observed in low collisionality H-modes – Confirms results from AUG, JET – Breaks covariance between νEFF and ne/nG – Predicts moderate peaking for ITER ne(0)/ ~ 1.4-1.5 – Potential effects on fusion yield, MHD stability and divertor operation need to be explored. Density transport in ITBs – Fluctuations compared with ITG/TEM simulations – Mode spectrum and direction of propagation suggest TEM responsible for barrier “saturation” increase in particle diffusivity. (consistent with linear-gs2 but not nonlinear-gyro) Density fluctuations Ion direction electron direction C-Mod 5 Year Plan Review, May 2008, M. Greenwald L. Lin (PhD Student) 13 Particle and Impurity Transport • • • What is the interplay between various forms of drift-wave turbulence that determines particle transport? At the fluctuation level, what is the relation between ion energy, momentum and particle transport? What plasma conditions lead to a significant inward pinch and density peaking? – Collisionality is important controlling parameter – what is the physics? – What’s the role of magnetic shear? • What are the conditions in which impurity transport might lead to concentration of impurities and unacceptable radiation levels? – Connection to heat, momentum and particle transport – Z scaling of impurity transport, especially for peaked ne profiles C-Mod 5 Year Plan Review, May 2008, M. Greenwald 14 Plans: Particle and Impurity Transport • • Further exploration of peaked density regimes Key activity – model testing – Detailed comparisons of profiles and fluctuations with gk simulations – Comparisons with Thermodiffusion and Turbulence Equipartition models, mag. shear effects – Effects of TEM, ITG interplay, strong electron heating, ionelectron coupling • • New laser blow-off system for impurity transport Multi-pulse laser for multiple injections per discharge Impurity Injector Setup Optical Components (See Slide A) Optical Table (See Slide A) Laser Vacuum System And Measurement (See Slide C) Main Vacuum System Components. (See Slide B) Dell Horseshoe Shaped Supports to Reduce Vibration and Hold Main Vacuum System Computer for Operating The Control Software for Linear Translation and Mirror Movement Electronics Racks and Control Equipment On Two Shelves Ruffing Pump Support Arm For Ruffing Pump Shelf Hirex and Other Diagnostics Are Located Here Under the Rack To the Gate Valve and Plasma. Large Supports with Some Vibration Reduction • -This Diagram Provides a Side View Of the Impurity Injection System. -This Setup Goes roughly 2.5 feet Into the Page. LHCD: Experiments with Eφ = 0 4 feet C-Mod 5 Year Plan Review, May 2008, M. Greenwald N. Howard (PhD Student) 15 Highlights: Internal Transport Barrier Physics Investigations of barrier trigger Via BT scan, ICRF resonance location is varied. The ITB threshold can be correlated with a decrease in the normalized temperature gradient ICRF Resonance Location (m) 0.70 0.72 0.74 0.76 0.78 0.68 0.80 No ITB ITB Linear growth rates calculate by gs2 for the same set of shots The ITB threshold is seen to correspond to an expansion of the region of ITG stability C-Mod 5 Year Plan Review, May 2008, M. Greenwald non-ITB ITB K. Zhurovich (PhD Thesis) 16 Internal Transport Barrier Physics (2) • Barrier strength controlled by application of on-axis ICRF – Understood through interplay of ITG and TEM turbulence – Supported by turbulence measurements • • Width of barrier region found to be controlled via field and current: q Hysteresis in power deposition profile associated with transition has been characterized 17 C-Mod 5 Year Plan Review, May 2008, M. Greenwald Plans: Internal Transport Barrier Physics • • Investigate core barriers in reactor relevant regime: no core particle or momentum source, equilibrated ions/electrons & equilibrated current profile: Access/trigger conditions in terms of local physics variables – Focus on LS, LT, Ln mechanisms (rather than ExB shear) – Use LHCD, trigger via modification of magnetic shear – Exploit new core profile measurements – Quantitative comparisons with simulations – Change in fluctuation characteristics • What is the structure (width, height) of transport barriers? – Are these predictable from characteristic scales lengths? C-Mod 5 Year Plan Review, May 2008, M. Greenwald 18 Plans: Internal Transport Barrier Physics • • Control of barrier location via q profile – Magnetic Shear? – Effect of rational q surfaces? Measure transport within barrier – Magnetic shear and heating profile effects – Impurity and particle transport within barrier – Measurement of core fluctuations – in barrier zone – Heat and density pulse propagation across barrier • Integration with advanced scenarios program C-Mod 5 Year Plan Review, May 2008, M. Greenwald 19 Transport Research Objectives (1) Research Goal Improved understanding of self-generated rotation and momentum transport and extrapolation to future devices with low input torque Intermediate Objectives Role of electron heating and current drive in modifying self-generated rotation profiles Compare measured self-generated flows, and crossfield fluxes with emerging theories and models Compare fluctuation levels, spectra and correlations with emerging models Test feasibility of IC and IBW flow drive Identify the portion of k space important for anomalous electron heat transport in low density OH plasmas Extend studies to strongly heated (LHH) plasmas at low densities Test models for mixed scale (ion-electron) turbulence Better Understanding of electron transport in decoupled regimes C-Mod 5 Year Plan Review, May 2008, M. Greenwald 20 Transport Research Objectives (2) Research Goal Detailed comparisons with models with experimental measurements of particle transport Intermediate Objectives Compare profiles, fluxes, fluctuation levels and correlations with existing gyrokinetic simulation codes Study of particle transport in regimes without neoclassical pinch Quantitative assessment of the role of magnetic shear in setting density profiles Correlation of particle transport and ion thermal transport in a variety of confinement regimes Characterize anomalous and neoclassical impurity transport. Install impurity injection system and begin experiments Characterize impurity fluxes and their correlation with particle, energy and momentum transport in a variety of confinement regimes. Compare anomalous and neoclassical impurity fluxes Scaling of impurity fluxes with Z of impurity 21 C-Mod 5 Year Plan Review, May 2008, M. Greenwald Transport Research Objectives (3) Research Goal Better understanding of access conditions, transition dynamics and control of internal transport barriers Intermediate Objectives Validate modeling predictions for role of ion temperature gradient in ITB onset Test predictions for nature of density fluctuations during ITB, especially after addition of central ICRF Assess roles of magnetic and flow shear in C-Mod ITB Measure ITB transport behavior with respect to impurity diffusion and electron heat pulse propagation Detailed comparisons of ion Quantitative assessment of the role of magnetic thermal transport with shear in setting critical temperature gradients gyrokinetic models Comparison with particle and momentum transport channels A summary of our experimental approach, new diagnostics and modeling required to meet these objectives can be found in the proposal on pages 3-21 – 3-23 C-Mod 5 Year Plan Review, May 2008, M. Greenwald 22 Diagnostics Are The Key To Transport Research Important Upgrades • • • • • • • Polarimetry (including J(r), B fluctuations, improved ne profiles and R/Ln ) Better view for HECE Further upgrades to Reflectometry (higher frequency) Doppler reflectometry (Velocity fluctuations, zonal flows) Improved resolution for beam diagnostics Impurity injection system New scattering diagnostic for fluctuations, CO2 C-Mod 5 Year Plan Review, May 2008, M. Greenwald 23 We’re Well Aligned With ITER High-Priority Transport Issues (Shimada/ITPA) • “Utilize upgraded machine capabilities to obtain and test understanding of improved core transport regimes with reactor relevant conditions, specifically electron heating, Te~Ti and low momentum input, and provide extrapolation methodology” “Develop and demonstrate turbulence stabilization mechanisms compatible with reactor conditions, e.g. magnetic shear stabilization, shear flow generation, q-profile. Compare these mechanisms to theory.” “Study and characterize rotation sources, transport mechanisms and effects on confinement and barrier formation” “Quantitative tests of fundamental features of turbulent transport theory via comparisons to measurements of turbulence characteristics, code-to-code comparisons and comparisons to transport scalings” “Understand the collisionality dependence of density peaking” 24 • • • • C-Mod 5 Year Plan Review, May 2008, M. Greenwald Joint ITPA Experiments Currently Planned Description JOINT Experiments Notes on C-Mod Contributions Initial experiments performed, higher β operation required Will require further development of low density H-modes at high current. Initial data sets provided, parameter extension required Joint experiments under discussion by working group Exploit improved profile measurements 25 Confinement scaling, ν* scans CDB-4 at fixed n/nG ρ* scaling along ITER relevant CDB-8 path at both low and high β Density profiles at low collisionality Impurity transport in peaked density H-modes Scaling of spontaneous rotation with no momentum input CDB-9 Under discussion TP-6.1 C-Mod 5 Year Plan Review, May 2008, M. Greenwald Schedule HIREX Full Power LHCD Imp Injector Full Power LHCD C-Mod 5 Year Plan Review, May 2008, M. Greenwald 26 Summary • Prediction and control are the ultimate goals of transport studies – Experiments and theory have progressed to the point where meaningful, quantitative tests are being made. – Theory/experiment comparisons motivate the experimental program • • • C-Mod operates in unique regime in several important respects – crucial for validation of physics models Facility Upgrades - important tools for transport research: heating, current drive, particle control, power handling and impurity control. Diagnostics – the tokamak is a scientific instrument – Over the last 5 year period, previous investment in high resolution diagnostics enabled edge studies. – Lower Hybrid/AT/ program increases overall emphasis on core plasma – New and planned profile and fluctuation diagnostics will facilitate a wide range of core transport studies C-Mod 5 Year Plan Review, May 2008, M. Greenwald 27