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
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