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Integrated Scenarios: Advanced Regimes

C-Mod Program Five-year Plan Review

May 7-8, 2008

MIT PSFC

Presented by A. Hubbard, for the Advanced Scenarios thrust group

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���Outline

• Introduction: Scope and ‘niche’ of C-Mod Advanced Integrated Scenarios program.

• Research Highlights and Proposed Research Plan (by topic)

• Contributions to broader Fusion Program goals.

• Summary

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���Scope and ‘niche’ of C-Mod Integrated

Scenarios research

Overarching Goal:• Support development of ITER Advanced Scenarios by

demonstrating operating regimes with relevant plasma parameters and control tools.– Includes improving and testing predictive capability through

integrated scenario modeling.– Research is also relevant to DEMO and to proposed interim

devices which may be needed to fill ‘gaps’ before DEMO.

• We recognize that C-Mod research will add to an extensive body of advanced scenario research elsewhere (including DIII-D, AUG, JT60-U, JET), which has demonstrated attractive operating regimes (eg high βN, high bootstrap and non-inductive fraction, ‘hybrid’ scenario).

• We see the C-Mod role not so much as setting new parameter records, as extending the parameter space of these regimes in important ways, using different tools (all RF) and extending pulse lengths to many current relaxation times.

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���What do we mean by ‘Relevant

parameters and tools’?

• Coupled electrons and ions, no external momentum drive are potentially important features for scenarios with improved core confinement (eg, “hybrid”, ITBs). How will confinement scale to these ITER-like conditions?

• Heating and current drive tools (ICRH, LHCD) complement very well those on other US and world facilities. Together, can address relative advantages and limitations for ITER. Also most similar to projected tools for DEMO (eg, ARIES-RS, AT), at comparable power densities.Can non-inductive scenarios be produced and maintained?

NBIEBWHelicity inj.HHFW

ECCDNBIFWCD

LHCDMCCDFWCD

Current drive

NBIHigh Harm FW (~10 ωci)

NBIECHHHFW (4-8 ωci)

ICRH (Minority and Mode conv.)LH

Primary Heating

NSTXDIII-DC-Mod

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���C-Mod pulse lengths normally exceed

current relaxation times.

In core plasma physics terms, “Steady-state” current drive implies pulse lengths >> current relaxation time τCR.– This is needed to study fully

relaxed RF and bootstrap-driven current profiles.

• C-Mod τCR~ 0.2-1.4 s[Zeff=1.5; Te= 2-7.5 keV ]

• C-Mod has already run up to 3 s flat-top with ICRF, limited by V-s.

• Non-inductive operation, and divertor upgrade, should enable high power pulse extension to 4-5 secs (TF and LHCD limit).

(MajorRadius)-2

(m-2)

Puls

eLength

/ R

ela

xationT

ime

C-Mod (5s)

JT60-U (30s)

JET (50 s)

ITER (1000 s)

DIII-D (10s)

AUG (10s)

2 3 / 2

e

CR

eff

a1.4 T

Z

Te=6 keV (ITER 19 keV), Zeff=1.5

τ =

C-Mod (3s)

1050824007

time (s)0 1 2 3 4

Ip (MA)

Teo (keV)

PRF (MW)

nel

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���Research Plans for 2009-2013

Combine LHCD, minority ICRH, FWCD

Real-time j(r) control

Assess feasibility of hybrid scenario with LHCD

Documentpedestal and core contrib. to confinement

tions to coVary beta, study MHD instabilities

Assess effect of shear on ITBs with off-axis heating.

Barrier formationwith reversed shear.

2008 2009 2010 2011 2012 2013

Document heat loads in non-inductive scenarios

Participate in developing and benchmarking time-dependent ITER simulations

Comparison with experimental scenarios (hybrid, non-inductive, double-barrier….)

Integrated Plasma Simulator (w CQL3D-GENRAY, AORSA, TORIC)

TSC+LSC+TRANSP + TGLF Transport simulations

Higher n, H: fBS -60%, ITBs, fBS >60 %

Lower B, High β N scenarios

Assess non-inductive scenarios - fBS ~ 30 %

Benchmark RF CD models for ITER

LHCD in H-modes, double barriers Increase LH coupled power

2008 2009 2010 2011 2012 2013

Current profile control

Non-inductive Scenarios

IntegratedScenario Modeling

Core-edge H-mode density control

Integration

Core Transport

Control

Hybrid scenario

Divertor upgrades Extend pulses to 4-5 seconds

Compare with MHD, turbulence models to elucidate mechanisms

Explore real-time transport control with LH and ICRF.

ITBs with LHCD only

Integrate with radiative divertor

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���Key facility upgrades for Integrated

Scenarios programThe research program and schedule outlined will require timely

implementation and upgrade of several key tools, including: • LHCD upgrades:

– Improved, lower-loss launcher (FY09), plus second launcher. (FY11)– Upgrade to 4 MW source. (FY09) – Provides ~2.6 MW launched, possibility of compound N// spectra.

• j(r) measurements:– MSE upgrade + new polarimeter. (FY09)– Goal is routine measurements, eventually real-time inputs.

• ICRF upgrades:– Modify 4-strap launcher to reduce sheath effect on boron, wall

interactions. (FY09)– 2nd 4-strap launcher to preserve 8 MW source. (FY10/11)– FMIT 1&2 upgrade to variable frequency 50-80 MHz. (FY12)

• Divertor upgrades:– DEMO-like divertor upgrade for 4+ sec, 8 MW input. (FY11)

As can be seen, this research integrates hardware tools, as well as physics understanding, across the whole C-Mod program! The order of experiments, and this talk, reflects progression of capabilities, not priority.

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Hard x-ray emissivity profiles showing increasingly off-axis localization as N// is increased.

(Andrea Schmidt, MIT student)

Current profile control

• Active external current profile control is essential for C-Mod advanced scenarios (flip side of pulse lengths >> τCR. )– Cannot rely on tailoring of current rise and

heating as on many other experiments; without active current drive, this has very little influence on j(r).

• Key tool, implemented in past five-year period, is LHCD.– Aimed primarily at far off-axis current

drive, for which LH is known to be the most efficient technique.

– As shown in talk by Wilson, extensive results so far are very encouraging and in general agreement with expectations from LH modeling, though code development and detailed comparisons are ongoing.

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10

1

2

3

4

5

6

7

8

9x 10

4 Emissivity profiles for varied n||

r/a

40-6

0 k

eV

em

iss. (c

ounts

/(m

m3 s

tr s

))

n =1.6n||=2.3n||=3.1

||

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���LHCD successfully combined with ICRF

0.8 MA, 5.4 T, USN L-Mode

0

2

4PICRF (MW)

0.0

0.5

1.0PLH (MW)

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4time (s)

0

1

2n---e (1020m-3)

0

3

6Te0 (keV)

1070817021

LH

only

LH+

ICRF

• For integrated scenarios with high bootstrap fraction, it is necessary to combine LHCD with heating from ICRF, and in high confinement regimes.

• Good success combining LH and ICRF, except for adjacent antenna (D-port)– Will relocate ICRF antenna for next campaign.

• Simultaneous operation, and good LH coupling, have been demonstrated in both L and H-modes, and both current rise and flat top. – Note that density range, ne0~0.5-2.5x1020 m-3,

spans that of ITER and proposed reactors (ARIES-AT, RS)

– Alleviates concerns about steep edge gradients in H-mode.

• As expected, higher Te obtained with ICRF moves non-thermal deposition even further off axis.

0.8 11

2.

3.

4.

HXR spectra, energies 80 to 100 keV

sqrt(toroidal flux)

em

issiv

ity (

counts

/(m

m2 s

tr s

)

10

70

81

70

21

LH only (Te0 2.2 keV)

LH+ICRF(Te0 4 keV)

0.60.40.2

5.

(Andrea Schmidt, MIT student)

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TSC simulation of scenario with <ne> ~1020 m-3, adding 3 MW LH at N//=2.15. 3.5 MW ICRH5.4 T, 600 kA. Te0 6.1 keV, Ti0 4.1 keV

(C. Kessel, PPPL)

Current profile control: Plans

• Important steps in CD program are – Increasing LH power, for greater

shear modification over a wider density range.

– This should enable significant LHCD in H-mode and double barrier regimes.

– Exploring multiple N// spectra (with 2 launchers) for greater localization.

• Key diagnostic upgrades are MSE, polarimeter.

• We will also explore FWCD for small on-axis ‘seed current’.– First demonstrate alone, then use in

non-inductive scenarios.– First FWEH on C-Mod was seen in

recent experiments.• Real time control with DPCS ~ 2012.

1.0

0.6

0.2

0.2 0.6 1.0

sqrt( b)

<j.B

>/<

B2 >

, M

A/T

-m2 total

LHCDbootstrap

Itotal = 600 kAIBS = 205 kAILH = 456 kA (n|| = 2.15)

φ/φ

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���Density control

• Density control is key to maintaining strong LHCD.

– N//acc increases with ne.• A key new tool, the cryopump in upper

vacuum vessel, is now used routinely. – Meets expected pumping speed,

9600 liters/sec (D2).• Excellent density control in L-mode.

– Some ‘improved L-modes’ have H98~1, high edge and core Te, low ν*.

• Control of H-mode densities is more complex due to the strong and “stiff” edge particle transport barrier.

– Have found scenarios with reduced density, combining dynamic Ssep variation with cryopump. Scope for further optimization.

– Recent observation of further density reduction with LHCD is exciting, and will be explored further.

C-Mod shot 1080306013 0.6 MA, 5.4 T

0

1

2

PICRF (MW)PLH (MW)

0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5time (s)

0.5

1.5

2.5n---e (1020m-3)

ne,95

0.0

1.5

3.0Te,0 (keV)

0.0

0.3

0.6Te, r/a~0.85

* Te,95

0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.525

50

75WMHD (MJ)

e p2

LH //

n I R 1P N

η ≡ ∝

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���Hybrid Scenario

• “Hybrid Scenario” is one of 3 main scenarios planned for ITER operation. While there is not yet a universally accepted definition, features include low central shear, with q0 ~ 1, and improved confinement and stability over standard H-mode.

• On other experiments, flat q is typically produced using heating and/or current drive in Ip ramp, with strong NBI, and aided by NTMs.

• Several open issues for extrapolation to ITER (see ITPA priorities) can be addressed on C-Mod:– Can it be produced with coupled e-i, no particle or momentum input?– Can it be produced with j(r) control by RF (without relying on MHD)?– If so, how do confinement, and MHD, compare?

TSC simulation of scenario adding LHCD to 600 kA H-mode.

(C. Kessel, PPPL)

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���Recent experiments using LHCD to modify

j(r) prior to H-mode are promising.

• As a first step, very recent experiments (4/14/08) used LHCD to modify current profile before applying ICRH for H-mode.

• LHCD reproducibly delayed sawteeth until > 0.5 secs, and reduced li. Central ICRH leads to H-modes, sawteeth.

• Relative timing did induce changes in both L-H transition dynamics, and H-mode character and confinement.

• Influence of LHCD on H-modes promises to be a fruitful new area of research. Will extend to higher PLH, lower q95, examine transport and MHD in detail.

George Sips, IPP Garching and SSO-ITPA chair.

Ip(MA)

Te0(keV)

PLH(MW)PICRF(MW)

li(3)

ne(1020 m-3)

sawteeth start with LHno LH

10804140311080414033

no LH with LH

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���Non-inductive Scenarios

• As higher power becomes available, the integrated scenarios program will focus on non-inductive, quasi-steady, regimes.

• Progression from majority external CD (as on ITER) to majority bootstrap (as on ARIES RS) regimes.– Both dictated by available LH and ICRF powers, and useful in

understanding advantages and difficulties of these regimes for future machines.

<j.B

>/<

B2 >

, MA

/m2 -T

sqrt(norm tor flx)

totalBSLHFW

TSC simulation of scenario with H-mode ne profiles, <ne> ~1.5 x1020 m-3, adding 2.5 MW LH , 4 MW ICRH. 5.4 T, 600 kA, assumed H98y=1.44. βpol=1.95, fBS 60%.

Ip, k

A

time, s

totaltotal Non-ind

BootstrapLHCD

600

200

400

0

0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

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���Non-inductive Scenarios (cont)

• Scenarios will also progress from higher q, lower βN regimes to lower q and higher βN.

• This will likely need lower BT (4-4.5 T); there are tradeoffs with LH accessibility and efficiency.

• For full input power, and high beta, at reduced fields we need ICRF FMIT upgrade to tunable freq (f=50-80 MHz; FY12 proposal budget).

• Stability calculations indicate no-wall limit βN~3.• Approaching this regime would allow studies of MHD behaviour,

boundaries vs. shaping, profiles, and control methods to avoid limit.

ACCOME

• If we succeed in producing regimes limited by βN, would begin design studies for stabilization methods (in collaboration with other labs.)

• Implementation would be deferred to next five-year period.

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���Control of core transport

• Above scenarios assumed only modest increase in global confinement above standard H-modes (HH~1.4, vs HH~1.2 typical of our low n H-modes)

• If core transport barriers can be maintained and controlled, higher bootstrap fractions (~70%?) should be possible. Also needed for highest beta operation.

Ele

ctro

n P

ress

ure

(MP

asca

ls)

0.15

0.10

0.05

0

0.20

0.0 0.2 0.80.60.4 1.0r/a

1.5 MW central ICRFadded into fully formed ITB

ITB, 2.35 MW Off-axis ICRF

H-mode, No ITB

t=1.294 s

t=1.127s

t=0.894 s

• C-Mod has demonstrated control of core particle and energy transport by tailoring heating profiles, in discharges with ‘normal’ shear. Summary:

• OFF-axis heating alone causes strong density peaking.– Core thermal transport reduced to

ion neoclassical.• Addition of ON-axis heating tends to

increase transport (D and χeff), and can also peak Te.– Ratio can be used to control density

and impurity rise!

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���Control of core transport: Plans

• ITB research program will focus on effect of j(r) on barrier formation, location.

• Based on results elsewhere, we expect flat or reversed shear to lead to easier ITB formation (evidence of this in recent LHCD expts!)– This often affects just ion or electron channel. – C-Mod will be able to study in conditions of coupled e-I, as

expected on ITER. How will Te, Ti profiles respond?– Also in momentum-free conditions, allowing study of intrinsic core

rotation (seen to change in ITBs, and with LHCD). • We will explore active control of core particle & energy transport,

by varying both ICRH profile and j(r), in these new regimes. – If impurity buildup, and MHD instabilities, can be avoided, ITB

regimes become very attractive!• Would then use real-time control of Te, ne profile peaking, via DPCS,

with ICRH and LH powers, phases as actuators.

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���Core-edge integration

With a strong Boundary program, and record SOL heat fluxes (upstream q//exceeding ITER, approaching DEMO), C-Mod is very well placed to address the issues of integrating advanced scenarios with tolerable edge fluxes.

• For all scenarios explored, we will optimize and document H-mode pedestal and SOL/divertor parameters. (Note pedestal physics is already influencing our choice of plasma parameters).

• For high beta, we need both full ICRF power and clean, high confinement plasmas, so resolving RF-wall effects is critical. (Also true for ITER, could influence W vs C PFC decision.)

• Divertor heat fluxes will be a particular challenge for advanced scenarios due to lower density and longer pulses. – Motivates DEMO-like divertor upgrade 2011. Local T rises may

limit pulse duration at full power to 3-4 s (still several τCR). Will test materials (W tiles), techniques such as sweeping, to their limits.

• Will assess integrating with radiative divertor.– Is this compatible with LHCD (which needs reduced ne) and high

bootstrap fraction (which needs improved confinement)?

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���Integrated scenario modeling

• Integrated modeling is already being used to plan and interpretadvanced scenario experiments.

• Currently we chiefly use TSC-TRANSP (with LSC for LHCD) for our time-dependent simulations – several examples have been shown. Transport coefficients adjusted to match prior experimental profiles.

• Also using Fokker-Planck/ray tracing package CQL3D-GENRAY for more accurate analysis of LH deposition and current drive, for single time slices, with n, T profiles input. Synthetic diagnostics of x-rays, ECE have been added and compared to expt (examples in LH, theory talks).

• Looking ahead (~2009), plan to link these and other codes (eg TORIC) to exploit best features of each. Utilize Integrated Plasma Simulator, via strong MIT involvement in the SciDac, SWIM projects.– A key feature will be to also simulate transport, using TGLF or other

codes, to model profile evolution with changing j(r).• We anticipate this or similar packages will be used to simulate

ITER advanced scenarios.C-Mod team will help benchmark codes, develop operation scenarios.

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���Contributions to ITER

• The C-Mod integrated scenarios research programs are both primarily aimed at contributing to ITER scenarios – we feel our parameters and tools are extremely relevant.

• This is reflected in a long list of anticipated contributions to several ITPA/ITER high priority research needs, especially to SSO and Transport Physics.

• Some of the most important and unique contributions expected are:– To “obtain and test understanding of improved core transport

regimes with reactor relevant conditions, specifically electron heating, Te~Ti and low momentum input” (ITPA)

– To test LHCD as for non-inductive CD (volt-s reduction) and j(r) control tool, for Ip ramp and for both hybrid and steady state scenarios, at the ITER field and density. (Support development of a plan for Day 1 LHCD as per STAC recommendation, or earliest feasible H&CD upgrade; results so far are very positive.)

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���ITER High Priority Tasks: Present and

Planned C-Mod Contributions Steady State Operations• Joint experiments: Focus on qualifying candidates for ITER scenarios. Hybrid

experiments started, steady state later.• Continue the focussed modeling-benchmark activity on ITER Hybrid and steady state

scenarios, using standard/common input data. C-Mod team engaged, and C-Mod data will particularly enable LHCD benchmarking.

• Feedback control: Develop database of control tools. Continue development of profile control methods. Particular contributions in j(r) control with LHCD.

• Pedestal studies: Continue documentation and complete the analysis of pedestal in advanced scenarios. C-Mod will contribute for both hybrid and steady state scenarios.

• The breakdown and current rise of ITER, in particular requirements for advanced scenarios. Joint experiments and code simulations. Recommendations for ITER simulations. Experiments and modeling underway.

Transport Physics• 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. C-Mod uniquely features all of these conditions, and will study both hybrid and steady state scenarios.

• Develop and demonstrate turbulence stabilization mechanisms compatible with reactor conditions, e.g. shear-stabilization, shear flow generation, q-profile. Compare these mechanisms to theory. C-Mod will study core transport reduction in both normal and reversed shear.

• Study and characterize rotation sources, transport mechanisms and effects on confinement and barrier formation. Strong emphasis on momentum-free rotation.

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���ITER High Priority Tasks: Present and Planned C-Mod Contributions (con’t)

Confinement Database and Modelling• Develop a reference set of ITER scenarios for standard H-mode, steady-state, and

hybrid operation and submit cases from various transport code simulations to the Profile DB. This thrust will contribute steady-state and hybrid datasets, in ITER-relevant conditions to benchmark simulations.

• Develop common technologies for integrated modeling, e.g. frameworks, code interfaces, data structures.

Pedestal & Edge Physics• 1. Improve predictive capability of pedestal structure

1-3: Establish pedestal profile database for hybrid and advanced regimesC-Mod will extend its pedestal contributions to these regimes.

• 2-6: Assess applicability of low collisionality small ELM regimes. Advanced scenarios will extend C-Mod pedestals to lower ν*, seek to maintain small or no ELM regimes and assess their compatibility with these core regimes.

MHD• Study NTMs in Hybrid Scenarios, the effect of plasma rotation …. Hybrid scenarios

may access these modes, in momentum-free conditions.• For RWMs understand mode damping particularly at low rotation. High βN steady state

scenarios may access these modes, again in momentum-free conditions.

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���Contributions to ITPA Joint Experiments

• Now that our control tools are maturing, we plan increasing participation in ITPA joint experiments in next five years.

Transport dependence of high performance operation on low external momentum input.

TP-4

Determine transport dependence on Ti/Te ratio in hybrid and steady-state scenario plasmas.

TP-2

Simulation and validation of ITER startup to achieve advanced scenarios.

SSO-5

Documentation of the edge pedestal in advanced scenarios. SSO-PEP-1

Modulation of actuators to qualify real-time profile control methods for hybrid and steady state scenarios.

SSO-3

ρ* dependence of confinement and stability in hybrid scenarios. SSO-2.3

MHD in hybrid scenarios and effects on q-profile. SSO-2.2/CDB-8

Qualifying hybrid scenario at ITER-relevant parameters. (Experiments started in April 2008.)

SSO 2.1/TP-2

Document performance boundaries for steady state target q-profile.

SSO-1

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���Connection to US fusion (FESAC) priorities

• The C-Mod integrated scenarios research includes elements of several ‘campaigns’ identified by the 2005 FESAC “Priorities” panel, but aligns best with the Macroscopic Plasma Physics Campaign, in particularTopical area “T3: How can external control and plasma self-organization be used to improve fusion performance?”

• Recommended activities we plan to contribute strongly to include:– (T1) Test understanding of confinement in sustained high fBS tokamak for

pulse lengths much longer than τCR.– (T3) Understand and validate self-consistent steady state AT configurations

at high pressure and bootstrap fraction.– (T3) Explore use of external heating and control of q(r) and mass-flow

profiles to optimize transport and stability, and prospects for BP.– (T11) Understand how waves affect MHD and transport… and use these

effects to control profiles and develop attractive integrated BP scenarios.

• Addresses two of the ‘top 6’ recommended priority areas:– Integrated understanding of plasma self-organization and external

control, enabling high-pressure sustained plasmas.– Extend understanding and capability to control and manipulate

plasmas with external waves.These actually sum up nicely the goals of the C-Mod advanced scenarios program!

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���Connection to US Research for DEMO

• C-Mod program also will contribute to resolving some of the Issues in research for DEMO identified by the 2007 FESAC panel, especially– A2: Integration of high-performance, steady-state, burning

plasmas.While C-Mod is evidently not a burning plasma, research aims to combine a high pressure core with heat flux exceeding ITER's, for pulse lengths longer than τCR.

– A3. Validated theory and predictive modeling. Focus on developing and testing time-dependent, integrated “multiphysics”, models.

– A4: Control. Focus on current profile and transport control via RF. First preprogrammed demonstrations, later real-time.

• Should provide key information relevant to future steady state, high heat flux devices we feel may be needed to resolve Plasma Wall Interaction and Plasma Facing Component issues (“Gaps” G-9, G-10). Is a fully steady-state advanced tokamak feasible to test PFCs at reactor-relevant heat fluxes, but moderate scale, filling role of “Initiative 4”? What H&CD tools would be needed?

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���Summary

• C-Mod research program has made good progress on current profile, density and transport control needed for advanced scenarios.

• Over the next five years, we will be upgrading and exploiting these tools to demonstrate and assess integrated scenarios which are progressively more ambitious.– Hybrid scenarios– Non-inductive steady state– High bootstrap fractions– Reduced divertor heat flux.

• This research is motivated primarily by the needs of ITER and aims to extend results elsewhere by showing that such regimes can be obtained in high density, low momentum plasmas, using LHCD to tailor j(r).

• Ultimately we aim, in collaboration with the international fusion community, for a more complete understanding and predictive capability. This would be embodied in accurate integrated models which can be used to predict scenarios for ITER and devices beyond ITER.