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PPPL/C-Mod Collaboration

Presented to the C-Mod 5-year Program ReviewMay 13-14, 2003

Gerd Schilling

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Overview - C-Mod research schedule, with PPPL foci and participation in red

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Advanced Tokamak Recent Highlights

LHCD launcher development• Achievement of Advanced Tokamak parameters requires an off-axis driven current,

which together with high on-axis ICRF heating power modifies the current and pressure profiles.

• Bringing our experience from LH heating and current drive on PLT and PBX, PPPL has designed and fabricated a Lower Hybrid launcher for C-Mod.

First MSE measurements• Improvements to the MSE diagnostic have resulted in initial magnetic pitch angle

measurements.

ITB discharges• We have continued to participate in the production, measurements, and modeling of

Internal Transport Barriers induced through off-axis ICRF heating.

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Advanced Tokamak Proposed Research

Achieve AT parameters• Modify current profile with off-axis LHCD.• Modify pressure profile with high power ICRF.• Determine effect on transport and stability.• Produce, measure and model ICRF-induced ITB’s.

Determine current profile with MSE measurements• Continue to improve MSE optics and beam.• Participate in the analysis and physics of current profile modification.

Continue to study Internal Transport Barrier discharges• Extend the diagnosis and modeling of ITB discharges.

Input to:IPPA 3.1 - steady state, IPPA 3.2 - high performanceITPA - steady state non-inductive CD, steady state and energetic particlesITPA - transport & ITB, ITB operation with no external momentum input

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Burning Plasma Recent Highlights

Initial Single-null/double-null studies

• Comparison of single-null with double-null diverted discharges was started.

Input to:IPPA 3.2 - high performance, IPPA 3.3 - burning plasma

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Burning Plasma Proposed Research

Compare Single-null with Double-null Diverted Discharges• Study single-null diverted discharges for ITER.• Study double-null diverted discharges for FIRE.

ICRF Heating at High Power Levels• Extend ICRF heating power above 5 MW.

D(3He) Minority Heating• Extend the study of this heating scenario.

Transport Studies• Confinement scaling of H-mode with SN/DN and high triangularity.• Similarity discharge studies.• Transport scaling in ITBs.• Rotation with no momentum input.• Particle transport (peaked density profiles - fuel mix optimization).

Divertor and Plasma Boundary• Impact of SN/DN configuration on ELMs.

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Transport Recent Highlights

Marginal Stability and Turbulence• Temperature gradients measured on C-Mod exceed the estimates of the theoretical

critical gradient for ion-temperature-gradient (ITG) modes.• Nonlinear simulations using the gyrokinetic code GS2

show that the the discrepancy can be understood as asubstantial nonlinear upshift (Dimits shift) in the

‘effective’ critical gradient due to stabilization of ITG modes by zonal flows.

ITB Modeling• Linear and nonlinear calculations of gyrokinetic microturbulence have been carried out

using the GS2 code at the trigger time for formation of the ITB.• The simulations indicate that ITG modes are unstable outside the core plasma, that only

weak instabilities are present in the plasma core, and that in the barrier region the instabilities are quiescent at the trigger time.

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Con

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R/LT

IFS-PPPLmodel

Nonlinear GS2 simulations

Measured R/LTe

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Lower νe & ν

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Lower νi

Standardcollisionality

C-Mod EDA H-modermid

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Kinetic electrons and ions

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Transport Proposed Research

Marginal Stability and Turbulence• Continue to upgrade the reflectometer diagnostic, support operation, and measure

turbulent fluctuations.• Perform detailed comparisons of data from all the C-Mod fluctuation diagnostics with

nonlinear gyrokinetic simulations using GS2 and GYRO.

Electron Transport• Measure electron gradient scale length to high precision and compare experimental and

theoretical dependences of the electron temperature gradient on variation of important parameters such as the q profile.

ITB Modeling• Nonlinear ITG calculations will be processed with the Nevins’ GKV post-processor, and

heat and particle fluxes will be compared with transport analysis for off-axis ICRF.• Initial GYRO code simulations will be extended and compared with those from GS2.

Input to:IPPA 1.1 - turbulence and transportITPA - transport & ITB, pedestal and edge, divertor and SOLITPA - confinement scaling experiments extended over broader range ν*, ρ*

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Divertor and Plasma Boundary Recent Highlights

Gas Puff Imaging Edge Turbulence Visualization• The GPI diagnostic has been used to capture

both “snapshots” and “movies” of plasma edge turbulence.

• Initial comparisons with edge turbulencesimulations have been performed.

Edge Neutrals Modeling• The extensive C-Mod diagnostics have permitted the development of simple models of

plasma variation in the SOL and divertor.• As a result, the neutral gas behavior can be examined by a stand-alone code such as the

DEGAS 2 Monte Carlo neutral transport code.

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Divertor and Plasma Boundary Proposed Research

Edge Turbulence Visualization• Explore edge turbulence behavior under a wide variety of conditions using an improved

ultra-fast camera with >10 times the frame capacity.• Make detailed quantitative comparisons between the turbulence measurements and

theoretical simulation.• Extend 2-D imaging near the inner SOL and near the X-point.• Perform 2-D imaging with two wavelengths for ne/Te measurements.• Extend k-spectrum range to higher and/or lower k.

Edge Turbulence Control• Edge minority heating experiment for H-mode control.

Edge Neutrals Modeling• Represent C-Mod vacuum vessel and sub-divertor by an axisymmetric object with local

asymmetries.• Extend DEGAS 2 code to treat asymmetric objects and benchmark.

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RF (Wave-particle) Recent Highlights

Experiment Participation• Active participation in the D(H) minority heating experiments.• Active participation in the Mode Conversion experiments.

ICRF Modeling• METS 1-D all order kinetic wave solver has been used to explore minority heating and

mode conversion scenarios.• TRANSP time-dependent transport analysis code has been used to analyze ICRF

heating experiments and to simulate Lower Hybrid driven AT scenarios.• METS 1-D code has been used to detect errors in the TORIC 2-D FLR kinetic wave

code, leading to their correction.• A Lower Hybrid package, LSC, has been incorporated into TRANSP and has been

used to explore maintaining AT discharges with LHCD.

Input to:IPPA 1.3 - wave-particle interactions, 4.1 - plasma technologiesITPA - high performance with Te≈Ti

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RF (Wave-particle) Proposed Research

Active Participation in ICRF Experiments• D(3He) minority heating experiments (PPPL interest from PLT experiments).• FWCD experiments (PPPL interest from TFTR experiments).• MCCD experiments (PPPL interest from TFTR experiments).• Flow drive studies (PPPL interest from TFTR experiments).

Lower Hybrid Wave Physics• Study LH wave launching, propagation, damping and power deposition (PPPL interest

from PLT, PBX-M experiments).

Lower Hybrid Current Drive Physics• Study and determine current drive at desired radial position in plasma for AT

scenarios (PPPL interest from PLT, PBX-M experiments).

RF Modeling• Utilize the TRANSP/TORIC/LSC code package to analyze the transport properties of

the long-pulse AT discharges.• Modify METS and TORIC codes to include effects of non-Maxwellian species on

wave propagation and absorption (funded under the SciDAC initiative).

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Global Stability (MHD) Computational Tools

PPPL Theory Department Stability Code Development• Model development - two-fluid extended-MHD, kinetic extended-MHD.• Beta limiting MHD modes - sawtooth, classical and neoclassical tearing modes,

energetic particle modes.• Edge MHD stability and the behavior of ELMs - linear analysis, nonlinear physics of

ELMs and nonlinear evolution of free boundary modes.• Prediction of the cause and effect of disruptions - physics of the disruption, VDE

physics, non-axisymmetric disruption forces.• Control issues - profile and shape control, physics of pellet fueling, resistive wall

mode control, internal mode control.

Major Macrostability Codes Supported by PPPL Theory Department• TSC, JSOLVER, ESC, PIES, M3D, AMRMHD, PEST-I, PEST-II, BALLOON,

CAMINO, PEST-III, NOVA-K, HINST, VACUUM.

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Global Stability (MHD) Proposed Research

The Ultimate Goal of these Codes is to Provide Predictive Capability Toward a Burning Plasma

• Help to understand MHD on C-Mod.• Important to benchmark these codes on existing experiments.• Strong interest on part of PPPL theorists for benchmarking on C-Mod.

The following studies are especially relevant to C-Mod experiments:• Sawtooth - energetic particle stabilization, coupling to other modes.• Beta limiting MHD modes - classical and neoclassical tearing modes, energetic

particle modes.• Edge stability and the behavior of ELMs - nonlinear physics determining ELM

amplitude and period. • Physics of disruption - disruption mechanisms and non-axisymmetric VDE halo

currents.• Physics of pellet fueling.

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Facility Recent Highlights

Rework of all 4 ICRF Transmitters• Active PPPL participation, ongoing operations support.

Fabrication, Installation, Upgrading of 4-strap ICRF Antenna• Active PPPL participation, ongoing operations

support.

Design, fabrication of LHCD launcher at PPPL

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Facility Proposed Research

Active PPPL Participation in LHCD Launcher Installation and Commissioning• Checkout and testing, vacuum prep, installation.• RF power, controls hookup.• Commissioning.• Operation.

Fabricate LHCD Launcher #2• Modify design based on experience with LHCD launcher #1, if needed.• Fabricate launcher #2.• Install and commission launcher #2.

Participate in Design, Commissioning and Operation of ICRF 4-strap Antenna #2

Participate in Design and Fabrication of Tunable RF Cavities for ICRF Transmitters #1 and #2

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Budgets (latest DoE guidance)

• FY 2003 Baseline budget: Science + Ops + LH $2,771KIncremental: $ 0

• FY 2004 Baseline budget: $2,072KIncremental: Science + Ops $ 450K Faraday scr.

Lower Hybrid $ 630K LHCD#2

• FY 2005 Baseline budget: $2,072KIncremental: Science + Ops $ 450K RF cavities

Lower Hybrid $ 630K LHCD#2

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Research Manpower (FY 2004-2005)

FTE estimates, based on latest funding guidance:

Schilling 1.00 RF, managementScott 1.00 MSE diagnosticBernabei 0.70 LHMikkelsen 0.60 simulations and transport modelingZweben 0.35 GPI turbulence imaging diagnosticWilson 0.30 RFRedi 0.30 ITB modelingHosea 0.25 RFKramer 0.25 reflectometer diagnostic

Engineering and technical support: 0.7 FTEAdditional “free” research support from PPPL Theory, SciDAC, FIRE, NSTX (this run

campaign).

Priority has been given to the Lower Hybrid system startup and experiments.

Incremental budgets for Science + Ops can help by allowing us to increase our research participation on all fronts.

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PPPL Will Play an Important Role in the C-Mod Program

PPPL anticipates active research participation in:

1. AT Physics• LHCD current drive, current distribution measurement, ICRF heating and current drive.

2. Burning Plasma Issues• Study single- and double-null discharges for ITER and FIRE.

3. Transport• Model marginal stability and turbulence, ITBs; integrated modeling.

4. Plasma Boundary• Edge turbulence visualization and measurement, edge turbulence modification, turbulence and transport modeling.

5. RF (Wave-particle)• Heating experiments, current drive experiments, wave physics, RF modeling.

6. Global Stability (MHD)• Benchmark PPPL stability codes against C-Mod experiments.

7. Facility• ICRF antenna improvements/operation, LHCD launcher fabrication/operation.