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Turbulence Topics

Turbulence Topics. Radial fluxes, blobs and comparison to theory Turbulent flux scaling. Comparison to Lodestar code? Intermittency (aka Blobs) quantitative scaling and comparison to predictions (Myra, et al.) Velocity predictions with collisionality (scan density and power)

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Turbulence Topics

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  1. Turbulence Topics • Radial fluxes, blobs and comparison to theory • Turbulent flux scaling. Comparison to Lodestar code? • Intermittency (aka Blobs) quantitative scaling and comparison to predictions (Myra, et al.) • Velocity predictions with collisionality (scan density and power) • Aspect Ratio scaling (NSTX vs DIII-D) • Differences in H and L modes (scan power) • Detach divertor to increase blob Vr (increase density, lower power) • Basic Turbulence and L-H transition physics. Need low power H-mode or OH H-mode • Reynolds Stress (enter shear layer) • Bicoherency (enter shear layer) • Clarify GPI- Probe differences J. Boedo 2006 NSTX Forum

  2. Diagnostics • Key Diagnostics: • GPI • Scanning probe • Desirable diagnostics: • Reflectometry • High-k Scattering • TS (edge chords) • Other dignostics: • D-alpha chords • Machine diagnostics J. Boedo 2006 NSTX Forum

  3. Basic Plan with decision branches: • Start OH-OH mode (4 good shots) Ng~0.3 (shot list next page ) • if good, optional, 2 densities (Ng~0.1, 0.9 4 more good shots) • If we have problems getting predictable OH-H modes, quit and go to: • Low power H-mode then puff for L-mode (shot list next page ) • Density scan (16 good shots) • If there is enough time. Detachment: • puff gas to get detachment. Otherwise, try get detachment data during Vlad’s XP? J. Boedo 2006 NSTX Forum

  4. Present Shot Plan • Main goal is to assure probe penetration to shear layer • Go directly to H-mode discharge at 1 MW (Target discharge 124670-75; 75 in particular) • Start at 4 MW, drop power to 1 MW @ 0.3 s • Left with ~0.3 of quiescent plasma to plunge • Density scan. Ng~0.1, 0.3, 0.6, 0.9 if possible • If penetration insufficient, de-rate beams to 850 KW or so • If there is time (: o) • Decide to go to OH H-mode or to L-mode (see target shots next page) J. Boedo 2006 NSTX Forum

  5. Target shot list • Ohmic H-mode • 115523 (best) • 115516 • Plain OH • 120016 for 600 kA • 120032 for 500 kA • 120035 for 400 kA • Low Power H-Mode (70 kV beams, 1.2 MW per source) • 120019 Ip = 600 kA, source B (not the best) • 120020 Ip = 600 kA, source A • 120028 Ip = 500 kA, source B • 120029 Ip = 500 kA, source A • 120033 Ip = 400 kA, source A J. Boedo 2006 NSTX Forum

  6. Original Strategy: Power/Density Scan • Start at low power (OH) to try reach the shear layer (2 shots) • Void/peak creation, skewness • Go to OH H-mode to see changes. Also measure RS (2 shots) • Dito +++++ Reynolds Stress measurements+ Bicoherency • Move on to L-mode. Add NBI, pick reasonable power (1 -1.5 MW) to allow H_alpha spread and probe penetration. (8 shots). Blob creation, Skewness, voids, Velocity statistics • Density Scan in L-Mode. Ng~0.1, 0.3, 0.6, 0.9. • Move to H-mode by withdrawing puff. (8 shots). Dito++ H-mode regimes? • Repeat density scan. Ng~0.1, 0.3, 0.6, 0.9 • Try to detach (L mode best?) (2 shots) • Look for blob speeding and other changes? J. Boedo 2006 NSTX Forum

  7. Decision Branching • Good shot: • A shot that runs long enough and is close enough to the expected parameters (Ne, etc) to get the data required. • Start OH-OH mode (4 good shots) (shot list next page ) -if good, optional, 2 densities (Ng~0.1, 0.3, 0.6, 0.9 4 more good shots) If we have problems getting predictable OH-H modes, quit and go to: • Low power H-mode (Kessel’s) then puff for L-mode (shot list next page ) • Density scan (16 good shots) • If there is enough time. Detachment: • puff gas to get detachment. Otherwise, try get detachment data during Vlad’s XP? J. Boedo 2006 NSTX Forum

  8. Additional Slides J. Boedo 2006 NSTX Forum

  9. Radial fluxes, blobs and comparison to theory • Turbulent flux partially determine radial profiles. • They are speculated to also determine a type of high-density limit (Greenwald limit) • Dynamics theory (Myra, D’Ippolito, Krash., etc) has been developed. Needs testing. • Simulation of Intermittency origin is starting (BOUT, Lodestar). • NSTX features various Intermittency “regimes in H-mode J. Boedo 2006 NSTX Forum

  10. Testing Marginal Stability Theory: Study the Void (ITPA) • Voids found in NSTX in the pedestal • Voids and Peaks > Predicted by P. Diamond and T Hahm in 1995 in marginal stability theory w/ reflection symmetry • Velocity of voids and peaks opposite in a background gradient>> leads to separation. Observed! • Spread as they travel along the gradient. Observed in peaks! • Proposal: Test theory in more detail: • Get more data, statistics, PDFs • Change gradient drive • Low power L and H-mode Collaboration TS Hahm, P. Diamond J. Boedo 2006 NSTX Forum

  11. Fundamental Turbulence: Measuring Turbulent Stresses Across the L-H Transition (ITPA) • Goal: Directly measure electrostatic Reynolds stress (ERS) and parallel Reynolds stress (PRS) across L-H transition, and test against various theories/models • 5-tip high-bandwidth probe head is working • 3 tip measure floating potential, giving Er and Eq • 2 tips form Mach probe giving • Motivation: • Lack direct verification / testing of role of turbulent stresses in triggering and sustaining L-H transition • Very little information on role of parallel stress term • Experimental plan: 1/2 day of operations • First measure ERS and PRS terms in OH H-modes • Repeat with low-power NBI heating, Collaboration G. Tynan, C. Holland J. Boedo 2006 NSTX Forum

  12. L-H Comparison Critical for SOL (ITPA) • Intermittent plasma objects CAN decay radially in two ways: • Amplitude • Number of events per time • IN NSTX • Amplitude neat LCFS 5x that near wall • Amplitude in L and H mode nearly same • L-mode almost 2x H-mode frequency • There are various H-mode “regimes” J. Boedo 2006 NSTX Forum

  13. Blob Speed/Size Measurements and Theory (ITPA) • Intermittent plasma object velocity directly measured by probe vs R from core to wall • Velocity at LCFS ~ 400 m/s. Decays to ~100 m/s at ~6cm • Multi-machine comparison v* ~ cs (a*/R)^1/2 J. Boedo 2006 NSTX Forum

  14. Experiments to do: Explore Parameter Space • Intermittency radial velocity depends on geometry, collisionality and current loop • Vary Ne, Te • Dettach divertor (disconnect filaments) • Also R and a (compare NSTX, DIII-D) • Started doing that (IAEA) • Differences in L/H mode. Frequency only? • Similar H, L mode discharges • Proposal: • Run ne scan in L-mode, then detach plasma • Go to H-mode, detach plasma Collaboration w. R. Maqueda, S. Zweben J. Boedo 2006 NSTX Forum

  15. Searching for Off-Diagonal Toroidal Momentum Transport • Goal: examine toroidal Reynolds stress for “off-diagonal” terms such as pinches • Test whether is finite, and if so how it scales with and/or • Reynolds stress probe allows direct measurement of • Need to assume • Motivation: anomalous Vf transport key to understanding rotation profiles in absence of momentum input; directly relevant for ITER • Experimental plan: • setup similar to L-H experiment. Examine Vf scaling via momentum scan at fixed power (use coils for braking?) • ExB scaling by heating scan with fixed momentum (details TBD) (in collaboration w/ P. Diamond) J. Boedo 2006 NSTX Forum

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