Turbulence Topics

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

2
Diagnostics

• Key Diagnostics
• GPI
• Scanning probe
• Desirable diagnostics
• Reflectometry
• High-k Scattering
• TS (edge chords)
• Other dignostics
• D-alpha chords
• Machine diagnostics

3

• Basic Plan with decision branches
• Start OH-OH mode (4 good shots) Ng0.3 (shot list
  next page )
• if good, optional, 2 densities (Ng0.1, 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 Vlads XP?

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 _at_ 0.3 s
• Left with 0.3 of quiescent plasma to plunge
• Density scan. Ng0.1, 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)

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

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. Ng0.1, 0.3, 0.6, 0.9.
• Move to H-mode by withdrawing puff. (8 shots).
  Dito H-mode regimes?
• Repeat density scan. Ng0.1, 0.3, 0.6, 0.9
• Try to detach (L mode best?) (2 shots)
• Look for blob speeding and other changes?

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 (Ng0.1, 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 (Kessels) 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 Vlads XP?

8
Additional Slides
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, DIppolito, Krash., etc)
  has been developed. Needs testing.
• Simulation of Intermittency origin is starting
  (BOUT, Lodestar).
• NSTX features various Intermittency regimes in
  H-mode

10
Testing Marginal Stability Theory Study the Void
(ITPA)

• Voids found in NSTX in the pedestal
• Voids and Peaks gt 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 gradientgtgt 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
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
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

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

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
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)