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The ITER Plasma Control Challenge Alfredo Portone Fusion for Energy Special thanks to:

The ITER Plasma Control Challenge Alfredo Portone Fusion 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. Synopsis. What is ITER?

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The ITER Plasma Control Challenge Alfredo Portone Fusion for Energy Special thanks to:

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  1. The ITER Plasma Control Challenge Alfredo Portone Fusion 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

  2. Synopsis • What is ITER? • Objectives • Reference parameters • Operation modes • Which are the ITER plasma control challenges? • ITER plasma control • Magnetic and kinetic subsystems • Key features of magnetic and kinetic control • Conclusions and outlook

  3. Objectives ITER is the experimental step between today’s machines (focused on plasma physics studies) and tomorrow's fusion power plants. ITER is designed to achieve two key objectives: confine DT plasmas for t > 300 s with α-particle heating >> aux. heating (Q=Pfus/Paux~10, Paux~50 MW, Pfus~500 MW, Pa~ 100 MW) integrate all key technologies essential for a fusion reactor (superconducting magnets, remote maintenance, tritium breeding blanket,…) ITER is the world’s largest S&T cooperation endeavor carried out under the auspices of IAEA and involving EU, Japan, Russia, US (founders Parties), China, South Korea & India ITER first plasma operation is expected in 2018

  4. Reference Parameters 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

  5. Operation Modes Typical operation scenario sequence ELMy H-mode Advanced mode

  6. ITER Plasma Control • For each operation scenario the plasma control system (PCS) must: • Provide accurate control of the plasma position, current and shape • Control the (p,J)-profiles to form and control ITB and ETB • Stabilize the plasma column against the main MHD modes (RWMs, NTMs) • Control the fusion power (neutron flux) and the power flow to the divertor • Drive the emergency shut-down to mitigate disruption-induced loads • DIVIDE ET IMPERA • Magnetic controller: • Regulate plasma magnetic configuration, MHD stabilization • PF coils current, Correction Coils currents, • Kinetic controller: • Regulate Pfus, T, n, q,… • Heating, Fuelling, Impurities injection, Pumping It looks simple but everything is coupled!

  7. ITER Plasma Control Courtesy of J Lister MAGNETIC CONTROL KINETIC CONTROL

  8. Reference Yref VFF KFF + Y + VFB + KFB - Diagnostics Magnetic Control:Axi-symmetric (n=0) Control Shape control requirements

  9. dy VFB + dz + Kz(s) Ky(s) Axi-symmetric (n=0) Control:Plasma Vertical Stabilization disturbances Control design issues • Kz and Ky are decoupled in the frequency domain (Kz~ 10-30 Hz, Ky ~ 0.1-1 Hz) Stabilized plant! • Strong non-linear nature of power supply (e.g. thyristors) • Open-loop system has 1 pole & 1 zero in RHP (L* has 1 negative eigen-value) (non min. phase) • Current saturation in Kz + unstable open loop= problems! • Avoid loss of control (Kz-loop bullet proof!)… or be prepared for a Vertical Displacement Event (VDE)!!! Kz(s): typically a lead controller (PD) Ky(s): constant gain matrix or LQG

  10. Plasma Vertical Instabilities dy dz dVz + dVz Kz(s) dVz + dVz - If these currents saturate…. - dVz Plasma vertical position is open-loop unstable! ~ 7000 ton! The vertical de-stabilization force scales as ITER VDE ~ 10 worse that JET ones!

  11. Magnetic Control: Resistive Wall Modes CONTROL ACTUATORS Only (brown) SIDE coils are used for feedback! CONTROL SPECS Stabilize as higher bN as possible Current limit ~ 200 kA Threshold level ~ 2 mT

  12. Magnetic Control: Resistive Wall Modes dBn dVn KRWM(s) Key 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) • 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 KRWM must provide strong phase lead! Lead network, or LQG are designed • Non-linear nature of power supply complicates again closed-loop (see n=0 case) • 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 !

  13. Magnetic Control: Resistive Wall Modes 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

  14. Kinetic/Magnetic Control: Neo-Classical Tearing Modes NTM=Poor confinement!

  15. Kinetic/Magnetic Control: Neo-Classical Tearing Modes Upper Launcher Midplane Launcher GOAL Shoot an island of ~ 10 cm rot. at f~4 kHz~150 km/s Main actuator: ECCD. ITER:4 steerable launchers in upper ports injecting 20 MW of ECCD powerlocalized current driveinside magnetic island to suppress NTM

  16. Kinetic/Magnetic Control: Neo-Classical Tearing Modes PECCD W2,1 W3,2 qsteer KNTM Modified Rutherford Equation Courtesy of H Zohm

  17. Kinetic Control: Plasma Core & Divertor Control Fuelling Pfus Core (ne,nDT, fAr, Te, Ti,j) Coupling! Heating PDIV Impurities SOL/Divertor nk, Tk, … Prad Coupling! Pumping • Comments • There is not a complete model of the whole system! the coupling core+SOL is remarkably complicated! • 0D models are useful to get qualitatively analyses • 1.5 D models are based on computer codes such as ASTRA (core), B2 (SOL) • Sometime we try black/gray box approach (system identification)

  18. Kinetic Control: Divertor Control Divertor temperature control by impurity seeding following a power step

  19. Conclusions and Outlook • 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 fullyreliable • 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 • 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)

  20. Conclusions and Outlook The ingenuity and synergy of Physicists and Control Engineers is the key to success!

  21. The ITER challenges MHD stability and plasma control b-limits Control of NTMs. Stabilization of RWMs. Disruptions control. Superconducting magnets Unprecedented size of super- conducting magnet and structures High field performance ~12T Power plant size and field 40GJ Plasma wall interactions Minimise/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 Plasma facing components >10 MW/m2 steady heat flux >10000 cycles/ severe damage Diagnostic systems 40 different diagnostic systems Heating and current drives >50 MW continuous ~1 MeV neutral atoms Ion cyclotron, electron cyclotron Heat confinement Study strong heating by fusion products, in new regimes where multiple instabilities can overlap. Tritium systems Active recycling of tritium Test of lithium blankets Turbulences Extend the study of turbulent plasma transport to much larger plasmas. ITER will provide first test of major fusion technologies… many complex systems & new problems to be solved in a nuclear environment

  22. ITER plasma control

  23. Magnetic control Plasma position, current and shape

  24. JET: 1983 ITER: 2016 JET R=3 m Ip=4 MA ITER R=6.2m Ip=15MA What is ITER?

  25. TARGET PARAMETER SPACE Operating point is thermally stable! Kinetic control: Operating point control

  26. ITER operation Scenario 1 2 3 4 5 6 7 Plasma Current (MA) 15 15 13.8 9 17 9 9 Fusion Power (MW) 500 400 400 356 700 340 352 Power Amplification (i.e. Q) 10 10 5.4 6 20 5.7 6.2 Burn flat top (s) 400 400 1000 3000 100 3000 3000 Normalized b 2.0 1.8 1.9 3.0 2.2 2.9 2.9 Confinement Enhancement Factor 1.0 1.0 1.0 1.6 1.0 1.6 1.6 ITER shall operate in different modes characterized by different flattop current, burn length, burn power, n,T profiles, q etc…

  27. ITER Plant Systems

  28. Plasma Physics Issues • MHD Stability • Heat Confinement • Steady State Operation • Control of Plasma Purity • Exploration of the new physics with a dominant a-particles plasma self heating

  29. What is ITER? 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) E IpR2P-2/3 ITER Pfus~ 500 MW Dt ~ 300 s Q~10 (2020?) BIG TOKAMAKS !! JET Pfus~4 MW, Dt ~ 3.5 s, Q~0.20, (1997) ELMy H-mode

  30. What is ITER? Vacuum Vessel Magnet System Shield 30 m Divertor Person Fusion power:~500 MW Machine mass:~ 23000 t! 25 m

  31. Kinetic/Magnetic Control: Resonant Mag. Perturbations ELMy H-mode plasma Da, Tdiv … Upper RMP coil RMP current VS coil Lower RMP coil Pellet injection

  32. Kinetic/Magnetic Control: Resonant Mag. Perturbations J-K. Park

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