The ITER Plasma Control Challenge

Alfredo PortoneFusion for Energy

Special thanks to: M Becoulet, DJ Campbell, JB Lister, A Loarte, G Saibene, H Zohm

Workshop ‘Control for Nuclear Fusion’May 7-8, 2008

Eindhoven University of Technology, The Netherlands

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Synopsis

1) What is ITER?• Objectives• Reference parameters• Operation modes

2) Which are the ITER plasma control challenges?• ITER plasma control• Magnetic and kinetic subsystems• Key features of magnetic and kinetic control

3) Conclusions and outlook

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ITER is ITER is the world’s largest S&T cooperation endeavor carried out under the auspices of carried out under the auspices of IAEA and involving EU, Japan, Russia, US IAEA and involving EU, Japan, Russia, US (founders Parties), China, South Korea & India(founders Parties), China, South Korea & India

ITER first plasma operation is expected in ITER first plasma operation is expected in 20182018

ITER is the experimental step between today’s machines (focused on ITER is the experimental step between today’s machines (focused on plasma physics studies) and tomorrow's fusion power plants. ITER is plasma physics studies) and tomorrow's fusion power plants. ITER is designed to achieve two key objectives:designed to achieve two key objectives:

confine DT plasmas for t > 300 s with α-particle heating >> aux. heatingconfine DT plasmas for t > 300 s with α-particle heating >> aux. heating (Q=Pfus/Paux~10, Paux~50 MW, Pfus~500 MW, P(Q=Pfus/Paux~10, Paux~50 MW, Pfus~500 MW, P~ 100 MW)~ 100 MW)

integrate all key technologies essential for a fusion reactor integrate all key technologies essential for a fusion reactor (superconducting magnets, remote (superconducting magnets, remote maintenancemaintenance, tritium breeding blanket,…), tritium breeding blanket,…)

Objectives

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Plasma current: 15 MA

Major radius: 6.2 m

Minor radius: 2.0 m

Plasma volume: 840 m3

Toroidal field: 5.3 T

Pulse length: > 300 s

Fusion power: 500 MW

Plasma energy: 350 MJ

n-wall load: 0.5 MW/ m2

n-fluence: 0.3 MW-a/m2

Heating power: 70-100 MW

TF coils #: 18

TFC energy: 41 GJ

TFC peak field: 11.8 T

Reference Parameters

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ELMy H-mode Advanced modeTypical operation scenario sequenceTypical operation scenario sequence

Operation Modes

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For each operation scenario the plasma control system (PCS) must:For each operation scenario the plasma control system (PCS) must:

1. Provide accurate control of the plasma position, current and shape

2. Control the (p,J)-profiles to form and control ITB and ETB

3. Stabilize the plasma column against the main MHD modes (RWMs, NTMs)

4. Control the fusion power (neutron flux) and the power flow to the divertor

5. Drive the emergency shut-down to mitigate disruption-induced loads

DIVIDE ET IMPERADIVIDE ET IMPERA

Magnetic controllerMagnetic controller: :

1. Regulate plasma magnetic configuration, MHD stabilization

2. PF coils current, Correction Coils currents,

Kinetic controllerKinetic controller: :

1. Regulate Pfus, T, n, q,…

2. Heating, Fuelling, Impurities injection, Pumping

It looks simple but everything is coupled!It looks simple but everything is coupled!

ITER Plasma Control

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Courtesy of J ListerCourtesy of J Lister

MAGNETIC CONTROL KINETIC CONTROL

ITER Plasma Control

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+

Reference Yref KFF

VFF

. .

-8

-6

-4

-2

0

2

4

6

8

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Z, m

R, m

CS

3UC

S2U

CS

1UC

S1L

CS

2LC

S3L

PF1PF2

PF3

PF4

PF5PF6

g1g2

g4

g3

g5

g6

Y VFBKFB

+

Diagnostics

+

-

Shape control requirements

Magnetic Control:Axi-symmetric (n=0) Control

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Stabilized plant!Stabilized plant!

Control design issuesControl design issues

• Kz and Ky are decoupled in the Kz and Ky are decoupled in the frequency domain (Kz~ 10-30 Hz, frequency domain (Kz~ 10-30 Hz, Ky ~ 0.1-1 Hz)Ky ~ 0.1-1 Hz)

• Strong non-linear nature of power Strong non-linear nature of power supply (e.g. thyristors)supply (e.g. thyristors)

• Open-loop system has 1 pole & 1 Open-loop system has 1 pole & 1 zero in RHP (L* has 1 negative zero in RHP (L* has 1 negative eigen-value) (non min. phase)eigen-value) (non min. phase)

• Current saturation in Kz + Current saturation in Kz + unstable open loop= problems!unstable open loop= problems!

• Avoid loss of control (Kz-loop Avoid loss of control (Kz-loop bullet proof!)… or be prepared for bullet proof!)… or be prepared for a Vertical Displacement Event a Vertical Displacement Event (VDE)!!!(VDE)!!!

VFB

z

* 1ˆ ( )

ˆˆ

ˆˆ

y

z

I sL R V

y C I

z C I

Kz(s)

+

Ky(s)

y

+

Kz(s): typically a lead controller (PD)Kz(s): typically a lead controller (PD)Ky(s): constant gain matrix or LQG Ky(s): constant gain matrix or LQG

Axi-symmetric (n=0) Control:Plasma Vertical Stabilization

disturbances

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Plasma vertical position is open-loop unstable!Plasma vertical position is open-loop unstable!

~ 7000 ton!~ 7000 ton!

2~z pF I z

The vertical de-stabilization force scales asThe vertical de-stabilization force scales as

ITER VDE ~ 10 worse that JET ones!ITER VDE ~ 10 worse that JET ones!

Vz

+

+

-

Vz

Vz

Vz

- If these currents saturate….If these currents saturate….

Vz

z

* 1ˆ ( )

ˆˆ

ˆˆ

y

z

I sL R V

y C I

z C I

Kz(s)

y

Plasma Vertical Instabilities

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CONTROL SPECSCONTROL SPECSStabilize as higher Stabilize as higher NN as possible as possible

Current limit ~ 200 kACurrent limit ~ 200 kA

CONTROL ACTUATORSCONTROL ACTUATORSOnly (brown) SIDE coils are used for feedback!Only (brown) SIDE coils are used for feedback!

Threshold level ~ 2 mTThreshold level ~ 2 mT

Magnetic Control: Resistive Wall Modes

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Key design issuesKey design issues

• Plasma models resemble n=0 formalism. However, several complications are present (e.g. accurate modeling of plasma rotation effects). Considerable modeling effort ongoing world-wide (active research)

• Non-linear nature of power supply complicates again closed-loop (see n=0 case)

• For each unstable n the open-loop system has 1 pole. If more than 1 n-mode is unstable (e.g. for n=1 & n=2), enough control knobs are necessary

• Lower plasma current (~ 9 MA) and minor coupling to VDE results in less critical problems in case of loss of control…

• RWMs call for prompt control (f ~ 50 Hz)… superconducting coils do not like AC operation! Minimize control voltage derived from magnetic noise amplification !

* 1ˆ ( )

ˆn n n n

pn n n

I sL R V

B C I

Vn

Bn

KRWM(s)

KRWM must provide strong phase lead!Lead network, or LQG are designed

Magnetic Control: Resistive Wall Modes

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Bp (mT)

ICC (MA)

VCC (V)

V. Amoskov et al., Plasma Devices and Operations, Vol. 12, No. 3, Sept. 04

Y. Liu et Al.: MARS-F simulation of n=1 RWM stabilization by CC & LQG control

Magnetic Control: Resistive Wall Modes

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NTM=Poor

confinement!

Kinetic/Magnetic Control: Neo-Classical Tearing Modes

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GOALShoot an island of ~ 10 cm rot. at f ~4 kHz~150 km/s

Upper Launcher

Midplane Launcher

Kinetic/Magnetic Control: Neo-Classical Tearing Modes

Main actuator: ECCD. Main actuator: ECCD. ITER:4 steerable launchers in upper ports injecting 20 MW of ECCD power localized current drive inside magnetic island to suppress NTM

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Courtesy of H ZohmCourtesy of H Zohm

( , ) (0,0), 0,02 2

1' '

1 1

( ) ( )

qress s other bs s p

s p

E m n Eq s m n

p s p s

LW r r a r

r L W

I IL r a a

I r I rW d

Modified Rutherford EquationPECCD

steer

W2,1 W3,2

KNTM

Kinetic/Magnetic Control: Neo-Classical Tearing Modes

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SOL/Divertornk, Tk, …

Core(ne,nDT, fAr, Te, Ti,j)

Fuelling

Heating

Impurities

Pumping

Pfus

PDIV

Prad

Coupling!

Coupling!

CommentsComments1. There is not a complete model of

the whole system! the coupling core+SOL is remarkably complicated!

2. 0D models are useful to get qualitatively analyses

3. 1.5 D models are based on computer codes such as ASTRA (core), B2 (SOL)

4. Sometime we try black/gray box approach (system identification)

Kinetic Control: Plasma Core & Divertor Control

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Divertor temperature control by impurity seeding following a power stepDivertor temperature control by impurity seeding following a power step

Kinetic Control: Divertor Control

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1. ITER demanding plasma performances (and costly consequences in case of failure!) call for an unprecedented level of sophistication in modeling and control techniques that MUST be both highly performing and fully reliable

2. Modern control competences are – especially at this point in time – of great help to the fusion community to improve the performances of tokamak “advanced mode” operation. The control problems that ITER face in this new physics realm are an outstanding challenge to modern control

3. Modern control areas that have been (and will be more and more) applied to ITER will likely include• Model-based, MIMO control (e.g. magnetic control)• Model reduction of large systems (e.g. eddy currents modeling)• MIMO, robust control (e.g. ITB control) • Non linear control (e.g. reactor kinetics)• System identification methods (e.g SOL modeling)

Conclusions and Outlook

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The ingenuity and synergy of Physicists andThe ingenuity and synergy of Physicists andControl Engineers is the key to success!Control Engineers is the key to success!

Conclusions and Outlook

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The ITER challengesITER will provide first test of major fusion technologies… many complex

systems & new problems to be solved in a nuclear environment

Superconducting magnetsUnprecedented size of super-conducting magnet and structures High field performance ~12TPower plant size and field 40GJ

Plasma facing componentsPlasma facing components>10 MW/m2 steady heat flux>10 MW/m2 steady heat flux>10000 cycles/ severe damage>10000 cycles/ severe damage

Diagnostic systemsDiagnostic systems40 different diagnostic systems40 different diagnostic systems

Heating and current drivesHeating and current drives>50 MW continuous>50 MW continuous~1 MeV neutral atoms~1 MeV neutral atomsIon cyclotron, electron cyclotronIon cyclotron, electron cyclotron

Tritium systemsTritium systemsActive recycling of tritiumActive recycling of tritiumTest of lithium blanketsTest of lithium blankets

MHD stability and plasma control -limitsControl of NTMs.Stabilization of RWMs.Disruptions control.

Plasma wall interactionsMinimise/mitigate disruptions & ELMs,

Control build-up of tritium inventory.

Control plasma purity

Extend the study of PWIs to much higher

power and much longer pulse duration

Heat confinementStudy strong heating by fusion products, innew regimes where multiple instabilities canoverlap.

TurbulencesExtend the study of turbulent plasmatransport to much larger plasmas.

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ITER plasma control

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Feed-forward controller

Feedback controller

PF power supply (12-pulse thyristor bridges)

+

-

+

+

Plasma reference

parameters

g, Ip, dzp/dt

wff

wfb

r

Magnetic control system

e-s1

2s+1

Magnetic diagnostics Plasma, PF coils & Metallic structures

*(s )

L R x Tv

C x

v

e-s3

4s+1

Magnetic controlMagnetic control Plasma position, current and shape Plasma position, current and shape

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JET: 1983 ITER: 2016

JETR=3 mIp=4 MA

ITERR=6.2mIp=15MA

What is ITER?What is ITER?

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TARGETTARGETPARAMETERPARAMETER

SPACESPACE

Kinetic control: Operating point controlKinetic control: Operating point control

Operating point Operating point is thermally stable!is thermally stable!

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ScenarioScenario 11 22 33 44 55 66 77

Plasma Current (MA) Plasma Current (MA) 1515 1515 13.813.8 99 1717 99 99

Fusion Power (MW) Fusion Power (MW) 500500 400400 400400 356356 700700 340340 352352

Power Amplification (i.e. Q)Power Amplification (i.e. Q) 1010 1010 5.45.4 66 2020 5.75.7 6.26.2

Burn flat top (s) Burn flat top (s) 400400 400400 10001000 30003000 100100 30003000 30003000

Normalized Normalized 2.02.0 1.81.8 1.91.9 3.03.0 2.22.2 2.92.9 2.92.9

Confinement Enhancement Factor Confinement Enhancement Factor 1.01.0 1.01.0 1.01.0 1.61.6 1.01.0 1.61.6 1.61.6

ITER shall operate in different modes characterized by different flattop current, burn length, burn power, n,T profiles, q etc…

ITER operation

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ITER Plant Systems

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• MHD Stability

• Heat Confinement

• Steady State Operation

• Control of Plasma Purity

• Exploration of the new physics with a dominant -particles plasma self heating

Plasma Physics Issues

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E IpR2P-2/3

EFusion Power

Fusion power amplification factor: Q ~ nTInput Power

BIG TOKAMAKS !!BIG TOKAMAKS !!

Temperature (T): 1-2 108 °C (10-20 keV) (~10 temperature of sun’s core)

Density (n): 1 1020 m-3 (~10-6 of atm. particle density)

Energy conf. time (E): 3-5 s (plasma pulse duration ~1000 s)

JETJET

PPfusfus~4 MW, ~4 MW, t t ~ 3.5 s,~ 3.5 s,

Q~0.20, (1997)Q~0.20, (1997)

ELMy H-modeELMy H-mode

ITERITER

PPfusfus~ 500 MW~ 500 MW

t ~ 300 st ~ 300 s

Q~10Q~10

(2020?)(2020?)

What is ITER?

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Fusion power:~500 MWFusion power:~500 MW

Machine mass:~ 23000 t!Machine mass:~ 23000 t!

Shield

Magnet System

Person

Divertor30 m

Vacuum Vessel

25 m

What is ITER?

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Kinetic/Magnetic Control: Resonant Mag. Perturbations

Lower RMP coil

Upper RMP coil

VS coilELMy H-modeELMy H-mode

plasmaplasma

RMP current

D, Tdiv …

Pellet injection

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J-K. Park

Kinetic/Magnetic Control: Resonant Mag. Perturbations