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Integrated Scenarios

ITER H-mode BaselinePresented by:

Stephen M. Wolfe

Alcator C-Mod PAC MeetingMIT Plasma Science & Fusion CenterCambridge, MAJan 25, 2007

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C ModAlcator

−Definitions and Scope

• By “Integrated Scenarios”, we mean research aimed at reachingattractive operating points, generally cutting across multiple sciencetopics and often involving interaction and compatibility issues betweendifferent plasma processes or regions

• This year, we have separated our presentations between the H-modeQ = 10 “Baseline” Scenario and the Advanced Tokamak Scenarios(see next presentation)

• The ITER baseline scenario features� Positive shear, q0

<∼ 1� q95 ≈ 3, βN = 1.8, HH ∼ 1,fNI ∼ 0.5� Edge transport barrier

• Integrated Scenarios task has also hosted many (but not all)Cross-machine Scaling and targeted Joint Experiments

• New topics include support for resolution of ITER Design Review IssueCards

• Many ITER H-mode issues addressed under individual topical sciencetasks (see yesterday’s presentations)

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 1

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−Key issues for ITER H-mode baseline scenariocan be addressed in C-Mod

• Development and validation of models for Edge barrier,

pedestal physics

• Physics of Edge relaxation mechanisms, benign ELM

regimes; compatibility with good performance

• Validation of model for L/H threshold power (low density

limit)

• Development and validation of particle transport, fueling

models

• NTM stabilization (applicability of LHCD)

• Burn Control simulation

• Energetic particle transport by MHD instabilities

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 2

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���Relevance of C-Mod research for ITER

C-Mod physics regime, machine capabilities and control tools are uniquely ITER-relevant in many respects:

• Edge and Divertor: All metal walls. High divertor heat fluxes ~0.5 GW/m2. High SOL neutral opacity (similar fuelling to ITER). High Lyman opacity, radiation trapping (closest to ITER).

• Core Transport: Equilibrated ions and electrons. No core fuelling or momentum sources (will be very low on ITER).

• Macro-stability: Can access ITER β range, as well as same BT and absolute pressures (important for disruption mitigation).

• Wave Physics: Similar tools (ICRF and LHCD) to ITER. Same B, n => same ωp, ωc, similar ω (key for waves, LH feasibility).

• Pulse length: τpulse >> τCR (exceeds ITER). Adding non-inductive CD capability (important for Steady State scenarios).

Combination of these features is unique and is key to all integrated scenarios.

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−Addressing ITER H-mode (and Advanced)Scenario issues requires integration

Issues, Challenges are similar for C-Mod and ITER

• Divertor and wall materials and conditioning� High heat flux requirement

� Compatibility with low core radiation, Zeff

� Hydrogen retention and recovery

• ICRF Heating� Challenging RF power density

� Compatibility with H-mode edge, high ne operation

� Compatibility with wall conditioning requirements

• Control of pedestal parameters, Edge relaxation� Variation of edge parameters (ν∗,β)

� Particle and impurity control

• Disruptions� Large I ×B forces, halo currents, thermal loads

� Reliable, benign mitigation techniques must be demonstratedAlcator C-Mod PAC Meeting Jan 25, 2007 smw 4

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−H-mode Scenarios experiments in FY2006

All six run days charged to this topic in 2006 were devoted toexperiments supporting ITPA/IEA Joint Experiments

These experiments exploit the high leverage afforded by unique C-Modparameters for non-dimensional scaling studies

• MDC-6 Low beta error field experiments (Hender, Wolfe)

• CDB-8 C-Mod/JET ρ∗ Scan along an ITER-relevant path (Petty,Greenwald)

• PEP-7 Pedestal width analysis by dimensionless edge identityexperiments on JET, ASDEX-U, C-Mod (Maddison, Suttrop,Hubbard)

• PEP-16 C-Mod/NSTX/MAST small ELM regime comparison (Meyer,Maingi, Hubbard)

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 5

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−Non-dimensional scaling of locked modethreshold (MDC-6) completed in 2006

Validate ITER Error-field correction specification (low-density ohmic target)

• C-Mod/JET identityexperiments validatenon-dimensional scaling, andconfirm αn=1

• Projected ITER thresholdeBBT∼ (0.9± 0.5)× 10−4

(within design spec.)

• Lower-field (4T) C-Modthreshold in JET shape doesnot conform to same powerlaw; matching JET data notobtained (yet?)

Locked mode threshold

0 2 4 6 8 10BT (T)

0.00

0.05

0.10

0.15

0.20

0.25

B 21/n

e BT (

10-2

3 m-3)

JET ShapeBappl

11 /Bappl21 = 2.1

C-Mod dataJET data (scaled) αB

JET=-1.2

C-Mod Shapen/nG = 0.17Bappl

11 /Bappl21 =1.38

αBC-Mod=-1.06

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 6

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−Progress on PEP-7: Pedestal identityexperiments with JET, ASDEX-Upgrade

• C-Mod data at 7.8T obtainedat q95 = 5.2, 4.2, 3.2

• Identifies target parametersfor JET (1.3T) and ASDEX-U(2.5T)

• Range of pedestal parametersrestricted by available PRF

• Data contributed to extendedpedestal scaling data, andincorporated in APS InvitedTalk (Hubbard)

• Further C-Mod experimentson hold pending results fromJET and ASDEX-Upgrade

C-Mod Reference Parameters

           23/10/2006                                                                                                                                                                                                                                                                                                11

H­mode ranges in pedestal ρ∗ & βped relatively narrow and similar at 5.2 T & 8 T.

Range in pedestal ν∗ e is somewhat greater with 5.2 T reference tending to be higher. All instances are marginally to strongly collisional.

Collisional H­mode pedestals with relatively small spread in Collisional H­mode pedestals with relatively small spread in ρρ∗∗  , , ββpedped

•

•

Maddison (UKAEA)

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 7

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−C-Mod/MAST/NSTX small ELM regimecomparison (PEP-16)

• Establish dimensionless pedestalcomparison with small ELMs betweenMAST, NSTX, C-Mod

• Identify similarities and differencesbetween the regimes:� Is the type-V ELM regime (NSTX)

similar to EDA or HRS-mode onC-Mod and JFT-2M?

� To the C-Mod “small ELM” regimeat higher P?

� All 3 experiments have diagnosticsto measure edge fluctuations andpedestal profiles; may also help tounderstand pedestal width scaling

NSTX summary

• Only shape development done

• Good shape match achieved.

– Starting point for 2007 experiments.

• MAST so far only DN, but LSN shape developed.

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 8

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−All 3 machines made progress on small ELMcomparison in 2006

• C-Mod obtained brief periodof small ELMs� Achieved target pedestal

temperature

� Short of target density, βped

� More shots with high PRF

required

• MAST accessed Type-V ELMregime in DN configuration� Need data with matched

LSN shape, higher power

• NSTX shape developmentcompleted

C-Mod Small ELM case

Best shot from 1060407

• 3.7 MW RF

βN~1.25• Pe,ped~

1.2x1023

eVm-3.• Brief/weak

small ELMs?

0.7 0.8 0.9 1 1.1 1.2012345 RF Power (MW) 1060407033

0.7 0.8 0.9 1 1.1 1.25e+191e+201.5e+202e+20 Nel CH 4 (m-2) 1060407033

0.7 0.8 0.9 1 1.1 1.20

100W MHD (kJ) 1060407033

0.7 0.8 0.9 1 1.1 1.20

22Pi Foil 1060407033

0.7 0.8 0.9 1 1.1 1.202

4 D_alpha 1060407033

0.7 0.8 0.9 1 1.1 1.200.5

1BETAN

0.7 0.8 0.9 1 1.1 1.20

0.5Te 8 (r/a~0.89) (keV) 1060407033

0.7 0.8 0.9 1 1.1 1.20

1e+23

2e+23 Pe on 95% FS (eV m^-3)

All machines plan additional experiments in 2007

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 9

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−Experiments proposed for 2007 build on previousresults, exploit new C-Mod capabilities

• Continuation of small-ELM regime Joint Experiment with MAST,NSTX

• Improved compatibility of high-power ICRF heating and wallconditioning (boronization) for high performance H-mode experiments

• Joint studies on Intrinsic Toroidal Rotation using new HIREXdiagnostic (PPPL collaboration)� ITPA Rotation database

� Non-dimensional identity experiment with DIII-D (deGrassie)

• Access to low density, low collisionality regimes using newC-Mod cryopump provides research opportunities� H-mode Pedestal and core response to cryo-pumping

� Extension of pedestal scaling database

� Scaling of L→H threshold at low density

� Extension of ELM physics studies at low-collisionality in moreITER-relevant shapes

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 10

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−Scaling of the L→H transition at low density

• At low density, the powerrequired to accessH-mode increases rapidly

• Heating power in ITER ismarginal for H-mode ifminimum nearn̄e

<∼ 5× 1019m−3

• Problem acknowledged inITER Issue Cards LH-2,AUX-11 (ITPA)

• Goals of multi-machine experiments� Determine scaling of H-mode threshold with density at very low n̄e

� Correlate with edge parameters

� Determine correlation of local edge flows, Te, ne, fluctuations withincrease in threshold power

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 11

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−Developing pedestal (and core) particle controlusing cryopump

• Establish pumping control methods (SSEP controls, optimal magneticgeometry)

• Obtain H-mode in pumped and non-pumped discharges� Compare L-H threshold power, profiles, flows

� Assess impact on pedestal and core confinement

• Increase pumping rate after H-mode formation; examine pedestal responseand core pump-out rate

• Address open issues from pedestal fueling studies (Hughes, IAEA)� Relative contributions to neutral screening from SOL and pedestal

� Roles of critical gradients and neutral transport in determining pedestalprofiles at low density

� Can we regulate nped/nG with strong pumping?

Density profiles from H-mode

gas puffing experiments:

unpuffed and puffed

Base casePuffed with ~15 torr-L

n e (1

020m

-3)

IP = 0.4MAIP = 0.6MAIP = 0.8MAIP = 1.0MA0

0-5-10 0-5-100-5-100-5-10-15

1

2

3

0

1

2

3

R - RLCFS (mm) R - RLCFS (mm) R - RLCFS (mm) R - RLCFS (mm)Alcator C-Mod PAC Meeting Jan 25, 2007 smw 12

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−Continue exploration of pedestal structure,edge relaxation at lower collisionality

H-mode pedestal height is critical fordetermining core profiles, confinement inITER

• Recent work extended C-Mod H-modes tolower pedestal collisionality� High field (∼ 8T )

� Unfavorable ∇B drift direction

� Strong shaping

• Regimes characterized by higher Tpede ,

lower npede

• (Some) low ν∗ cases feature very steeppressure gradients (stability analysispending)

0 2 4 6 8 10ν*ped

0

5

10

15

20

α MHD

BT 4.5-6 T, EDA

BT~8T, weak QC BT~8T, ELM-free

In 2007 we will continue and extend our studies of these regimes,using the cryo-pump for additional particle control

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 13

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−Access to lower collisionality using the newCryo-pump facilitates studies of large ELMs

• Last year C-Mod accessed a regime oflow-density H-mode with large ELMsin “hi-δlower” shape

• With cryo-pump we should be able toinvestigate ELMs in ITER-like shape

• Study ELM stability (and type) asfunction of shape and collisionality

C-Mod Ideas ForumDec. 14, 2006 (1)

The Effects of Plasma Shape and Collisionality on ELMs

Proponents: J. Terry, I. Cziegler, A. Dominguez, A. Hubbard, M. Greenwald,

J.W. Hughes, B. LaBombard, R. Parker, P. Phillips (UT), J. Snipes, et al.

Area: Integrated Scenarios: H-mode baseline

Experimental Issues: Do we get H-Mode

and ELMs in low n* (cryo-pumped)

standard-shaped plasmas?

What is the ELM stability boundary in

the "hi-dlower shape"?

What is it about the "hi-dlower shape" that

allows H-mode at a n* significantly

lower than the threshold found for the

standard C-Mod shape?

10

50

62

80

14

@0

.9 s

Standard-Shape

Hi-dlower Shape

Signifcant differences

in H-mode behavior

between these shapes

- discrete ELMs- different profile

peaking

- different n* range

Movitation: C-Mod is the only device that has investigated the ELM stability

boundary in the so-calledÊ"hi-dlower shape". Plasmas in this shape exhibit other

interesting tranport properties, e.g. H-mode at low density. With cyro-pump

operation, we should have the capability to investigate ELMs in an ITER-like

shape. If so, we can study ELMs by varying the shape and collisionality in a

continuous controlled manner.

• Continue study of ELM structure, dynamics and energetics withimproved diagnostics� Related to ITPA task PEP-10

� Investigate hi-frequency magnetic oscillations observed at filamentejection

� Examine non-thermal electron generation at ELM crash

• Evaluate ELM mitigation using n=1 A-coil perturbation (as reportedon JET)

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 14

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−Extend high performance plasma studies atITER field, shape, I/aB, β, . . .

Integrated tests of confinement, heating, power handling

• Operate at ITER field (5.3T),maximum power(PICRF > 5MW )� f ≈ 80MHz, D(H) heating

� high single pass absorption

• High elongation (κ = 1.8)ITER shape fills C-Mod vessel

• Increase current toIp = 1.6MA with q95

>∼ 3

ITER Pressure

Assume W α Ip*

• Use cryo-pump for density control, lower collisionality

• Expanded parameter space for databases and extrapolation to ITER

• Demonstration of operation at ITER absolute pressure

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 15

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−C-Mod Research on Integrated Scenarios forITER H-mode Baseline

• H-mode baseline research program addresses cross-cutting physicsand technology issues

• Exploits ITER-relevant C-Mod parameters and tools

• Strongly coupled to ITPA tasks, Joint Experiments

• Experiments proposed for FY 2007 campaign exploit new C-Modcapabilities� Cryo-pump for density control, access to low collisionality

� New and improved diagnostics

• Many additional ITER-related experiments in Topical ScienceGroups

• Integrated Research in support of ITER Advanced Scenariosdescribed in Next Presentation

Alcator C-Mod PAC Meeting Jan 25, 2007 smw 16