novel aspects of iter plasma control

1Humphreys/55th APS-DPP/October 2012

D.A. Humphreys1, G.L. Jackson1,R. Hawryluk2, E. Kolemen2,D. Moreau3, A. Pironti4, G. Raupp5,O. Sauter6, J. Snipes7, W. Treutterer5,F. Turco8, M.L. Walker1, and A. Winter7

•General Atomics, San Diego•Princeton Plasma Physics Lab, Princeton•Commisariat a l’Energie Atomique, Cadarache•CREATE/Univ. of Naples, Naples•Max Planck Institut fur Plasmaphyzik, Garching•CRPP-EPFL, Lausanne•ITER International Organization, St. Paul lez Durance•Columbia Univ., New York

Presented at the55th Annual APS MeetingDivision of Plasma Physics Denver, Colorado

November 11–15, 2013

Novel Aspects of ITER Plasma Control

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Novel Challenges of ITER Control Require Novel Solutions

• ITER control is different from present devices in several important ways:– Highly robust control required– Model-based control designs– Simulations verify every discharge before execution– Exception Handling: fault responses for low disruptivity

• Progress has been made, but substantial control research remains to be done before ITER operates:– Control physics: specific physics knowledge for robust control – Control mathematics: specific algorithmic solutions to satisfy

ITER performance and robustness requirements

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Novel Elements in the ITER Plasma Control Development Process Include Model-Based Design and Shot Verification

Scenarios and Physics

Understanding

ControlSchemes

ActuatorEffects

Diagnostic

Responses

Models

AlgorithmsContinuo

us Control

Exception Handling

PCS Implementati

onVerification Simulations

Experiments/Validation

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The Plasma Control Development Process Includes Equal Measures of Physics Knowledge and Mathematics Solutions


Understanding

ControlSchemes

ActuatorEffects

Diagnostic

Responses

Models

AlgorithmsContinuo

us Control

Exception Handling

PCS Implementati



PhysiPhysicscs

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The Plasma Control Development Process Includes Equal Measures of Physics Knowledge and Mathematics Solutions


Understanding

ControlSchemes

ActuatorEffects

Diagnostic

Responses

Models

AlgorithmsContinuo

us Control

Exception Handling

PCS Implementati



PhysiPhysicscs

MathematiMathematicscs

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Axisymmetric Control is Well-Advanced But Requires Some Additional Research

Cu Vertical Stability

(VS) Coils

• Actuators and Scheme: – SC PF coils, Cu vertical

control coils– Boundary scheme:

plasma-wall gaps– Vertical stability

scheme: velocity control

– Used in continuous discharge control AND many exception handling scenarios

Superconducting PF Coils

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• Status/Research Gaps: – Many experiments done,

but ITER specific not demonstrated

– Need model-based algorithms for exception handling

– Need robust PF/VSsharing scheme, runaway control

Axisymmetric Control is Well-Advanced But Requires Some Additional Research

Cu Vertical Stability

(VS) Coils

• Actuators and Scheme: – SC PF coils, Cu vertical

control coils– Boundary scheme:

plasma-wall gaps– Vertical stability

scheme: velocity control

– Used in continuous discharge control AND many exception handling scenarios

Superconducting PF Coils

JET Model for Plasma Response to Coil

CurrentA. Pironti, CREATE

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Upper EC

Launchers

• Actuators and Scheme: – ECH, NBI, density,

loop voltage? – Multipoint q-profile

control– Share EC system with

MHD controlEquatorial

EC Launcher

NBI

Current Profile Control Has Been Studied on Several Devices But Remains Highly Experimental

• Status/Research Gaps: – Some experiments

done– ITER specific candidate

not identified and demonstrated

– Need robust actuator sharing scheme

– Need integrated goals: scenario/kinetic and stability control

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Upper EC

Launchers

• Actuators and Scheme: – ECH, NBI, density,

loop voltage? – Multipoint q-profile

control– Share EC system with

MHD controlEquatorial

EC Launcher

NBI

Current Profile Control Has Been Studied on Several Devices But Remains Highly Experimental

• Status/Research Gaps: – Some experiments

done– ITER specific candidate

not identified and demonstrated

– Need robust actuator sharing scheme

– Need integrated goals: scenario/kinetic and stability control

JET q-Profile ControlD. Moreau, CEA

• q-profile regulated using LHCD, NBI, ICRH

Safety factor

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Start of Control

End of Control


Divertor Ne gas puff

• Actuators and Scheme: – Fueling pellets and

local impurity gas injection (N, Ne, Ar?)

– Integrated regulation of core and divertor radiation to minimize target heat flux

– Maintain partial detachment

Fueling pellet

launcher

Divertor Control Experiments Have Been Performed But Research is Still Needed for ITER Solutions

• Status/Research Gaps: – Limited experiments– No ITER solution– Need model-based

exception handling– Need robust actuator

sharing scheme– Need integrated goals:

scenario/kinetic and divertor control

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Divertor Ne gas puff

• Actuators and Scheme: – Fueling pellets and

local impurity gas injection (N, Ne, Ar?)

– Integrated regulation of core and divertor radiation to minimize target heat flux

– Maintain partial detachment

Fueling pellet

launcher

Divertor Control Experiments Have Been Performed But Research is Still Needed for ITER Solutions

• Status/Research Gaps: – Limited experiments– No ITER solution– Need model-based

exception handling– Need robust actuator

sharing scheme– Need integrated goals:

scenario/kinetic and divertor control

DIII-D Divertor Detachment

ControlE. Kolemen, PPPL

No Detachment Control (#153814)

Detachment Control (#153815)

• Divertor Thomson measures detachment

• D2 gas injection to regulate partial detachment state084-13/DAH/jy


• Actuators and Scheme: – Fueling species

balance, transport control (RMP coils?)

– Integrated regulation of kinetic operating point and burn state

Fueling pellet

launcher

Burn Control Has Been Studied Minimally in Experiments and Requires Significant Research for ITER Solutions

• Status/Research Gaps: – Limited experiments– No ITER solution yet– Need model-based

exception handling– Need integrated goals:

scenario/kinetic and burn control

RMP Coils

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• Actuators and Scheme: – Fueling species

balance, transport control (RMP coils?)

– Integrated regulation of kinetic operating point and burn state

Fueling pellet

launcher

Burn Control Has Been Studied Minimally in Experiments and Requires Significant Research for ITER Solutions

• Status/Research Gaps: – Limited experiments– No ITER solution yet– Need model-based

exception handling– Need integrated goals:

scenario/kinetic and burn control

DIII-D Burn Control Experiment

R. Hawryluk, PPPLn

n=3 RMP coil current (kA)

Pinj (MW)

• n=3 RMP coils used to modify transport

• βN controlled during NBI power surge (red) emulating burn excursion

RMP Coils

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ITER Tearing Mode Control Involves Multiple Control Goals and Integrated Sharing of Many Actuators • ITER TM Control Scheme Includes:

– Profile/kinetic control to maintain distance from controllability boundary

– Continuous (periodic) sawtooth control– Continuous (periodic) TM suppression:

repeated “Catch and Subdue”– Exception handling response to off-

normal TM

• TM control involves complex sharing of actuators and integrated control goals:– 24 gyrotrons, 20 MW total: shareable

between upper/equatorial launchers– 33 MW NBI, 20 MW ICRF, transport

(burn) control for beta and profile regulation

– Active sawtooth and TM control with ECH/ECCD

Upper EC

Launchers

EquatorialEC

LauncherNBI

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Tearing Mode Continuous Control in ITER Enables Multiple Catch and Subdue Events

• Continuous active suppression scheme: “Catch and Subdue” – Maintain mirror alignment

near resonant surface…– As soon as mode grows

beyond noise threshold, align to island and turn on ECCD power before saturation (“Catch”)

– Fully suppress (“Subdue”) mode, turn off ECCD

– Repeat as necessary– Periodic, as-needed ECCD

minimizes average power

DIII-D Catch and Subdue

Simulated ITER 2/1 Catch and Subdue

ρEC

ρdiagρq

PECCD (MW)

wISLAND (cm)

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Continuous Tracking of Alignment Enables Rapid Suppression of Later Events and Low Average Power

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• Active tracking of alignment after mode suppressed

• Seed islands triggered by sawtooth, ELMs are immediately suppressed

• CW suppression 12 MW average

power

• Catch/Subdue 1 MW average

power


Degree of Novelty and Research Needed Varies Widely Among ITER Control Categories

Category Scheme Actuators Models Algorithms

Integration/Exceptions

Axisymmetric

Current profile

Divertor

Tearing Mode

Burn

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Mature, ITER-relevant

Candidate ITER solutionsLimited ITER-relevant

experiments

Limited ITER solutionsLimited ITER-relevant

experiments





Axisymmetric

- Gaps- VS3 for Z

- SC PF- Cu VS3

- Valid- Metrics

- Robust- Model-based

- Exception Handling- Disruptions

Current profile

- Multipoint- q profile?

- EC, NBI- Ohmic ψ- Density?

- Simple- Valid?- Metrics?

- Static?- Adaptive

- Actuator Sharing w/ MHD control

Divertor - Impurity inj for radiation- Integrated core/div ctrl

- Gas valves- Pellets

- Simple & heuristic- Metrics?

- Simple, not model-based orrobust

- Exception Handling - Actuator Sharing

Tearing Mode

- Sawtooth- Profile- Direct ctrl

- ECH/ECCD- Profile ctrl

- MRE- Metrics?- Profile params?

- Model-based, but not robust

- Exception Handling- Actuator Sharing

Burn - Fueling ctrl- Transport ctrl?

- Pellets- NTM ctrl?- RMP coil?

- ??? - ??? - ???

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Much Progress Has Been Made But Novel Aspects of ITER Control Require Ongoing Plasma Control Science Research

• Control Physics:– Good progress made in physics understanding needed for control– Further advances needed in highly novel areas including divertor,

burn, tearing mode, current profile control

• Control Mathematics:– Many candidate control algorithm solutions have been proposed – Quantified controllability and effective exception handling algorithms

needed to maximize physics productivity and prevent disruptions

• Integrated solutions and experimental demonstrations:– Methods for integrating control goals and robustly sharing actuators– Many specific solutions remain to be qualified on operating devices

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21Humphreys/55th APS-DPP/October 2012 084-13/DAH/jy

Additional Slides


Catch and Subdue Events Must Be Rapid Enough and Infrequent Enough to Maintain Fusion Gain

Q = PFUS/PEXT

O. Sauter, PPCF 52 (2010) 025002

Reduced Q due to confinement loss from unstabilized saturated islands

3/2

2/1

Q~7 for 2/1 stabilized with 20 MW CW at HH=1.0

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Accomplishment of ITER Control Requires a Sophisticated Exception Handling System

• Exceptions:– Off-normal event requiring a

change in control– Prediction by forecasting system– Direct detection

• Exception handling policy includes:– Relevant plasma/system context

(e.g. stored energy, saturation state of actuators)

– Specific signals to be predicted or detected

– Control modification response to exception: command waveforms, algorithm characteristics…

Exception Handling Will Use a Finite State Machine

Architecture

Research is Required to Prevent Explosion in Complexity

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ITER Exception Handling System Requires a Powerful Forecasting Capability for Sufficient Look-Ahead

• Forecasting Outputs:

– Controllability thresholds to trigger Exception Handling response

– Quantified Risk of disruption to trigger Disruption Mitigation System (> 10-20 ms before)

System Health

Projection

Faster Than

Realtime Simulati

on

Realtime Stability/ Control

Boundaries

ITER PCS Forecasting System Functional Block

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ITER Control Will Depend Critically on Full Pulse Schedule Verification and Validation via Simulation• Verification of pulse

schedule:– Pulse schedule = set of

program waveforms and control characteristics that define the pulse execution

– Verify consistent with administrative limits and requirements

– Verify consistent with experiment goals

• Validation of control performance:– Confirm sufficient nominal

control for scenario– Confirm sufficient

controllability in presence of “expected” exceptions

ITER Plasma Control System Simulation Platform Architecture

Likely Similar to Structure of Pulse Verifier PCSSP

ITER PCS

Simulator

ITER Plant

Simulator

PCS Development

084-13/DAH/jy


ITER Control will Depend Critically on Full Pulse Schedule Verification and Validation via Simulation• Verification of pulse

schedule:– Pulse schedule = set of

program waveforms and control characteristics that define the pulse execution

– Verify consistent with administrative limits and requirements

– Verify consistent with experiment goals

• Validation of control performance:– Confirm sufficient nominal

control for scenario– Confirm sufficient

controllability in presence of “expected” exceptions

ITER Plasma Control System Simulation Platform Architecture

Likely Similar to Structure of Pulse Verifier PCSSP

ITER PCS

ITER Plant

Simulator

Pulse Validation

084-13/DAH/jy

novel aspects of iter plasma control

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