1. Association Euratom-FOM Trilateral Euregio Cluster 1 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 In the control room: A customer’s perspective on the need and means for control Marco de Baar Tokamak Physics Group FOM institute for plasma physics

2. Association Euratom-FOM Trilateral Euregio Cluster 2 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 In present fusion experiments… Control is often used for a wide variety of applications in tokamaks –Operations control: Shape and position, density, machine integrity,.. –Physics control: Plasma scenarios, MHD, Dynamic fluxes Physics control (often) is not control in the strict sense. Feed-back loops that are used to –Improve the quality of experiments –Improve the reproducibility of experiments –Improve the discharge performance are often referred to as control

3. Association Euratom-FOM Trilateral Euregio Cluster 3 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Fusion Basics D + T  He (3.5 MeV) + n (14.1 MeV) This reaction requires –High T i –High n e –High energy confinement time  E –Moderate He confinement time  He In a reactor: –Neutron absorbed in Li mantle for T production –Energetic helium (  -particle) for  -heating –Collisional slowing down time 1 - 4 s! To achieve these conditions simultaneously: Confine a DT-plasma in a tokamak Control of a wide variety of parameters Observe requirements on power gain factor Q

4. Association Euratom-FOM Trilateral Euregio Cluster 4 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 ITER operating conditions ITER is expected to operate at: –I p ~ 15 MA, B  ~ 5 T –n D ~ n T = 5x10 19 m -3, –Ti ~ 20 keV Additional heating for (Core) Control required –Q = P FUS /P ADD = 5 – 10 –P  / P ADD = 1 - 2 –v  / v alfvén ~ 1.3

5. Association Euratom-FOM Trilateral Euregio Cluster 5 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Core control challenges Limited set of actuators P  ~ Padd Wide variety of processes and instabilities, most of which are inter connected To control the processes that are associated with –Operational limits: Avoidance and amelioration of MHD (examples JET and TEXTOR) –Performance: Turbulence and Transport (example JET) –Plasma self heating:  -particles confinement   ~  SD –Ash: Core helium concentration n He /(n D +n T ) < 0.15

6. Association Euratom-FOM Trilateral Euregio Cluster 6 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Island formation and suppression Magnetic island with m/n = 2/1 or 3/2 stable in normal conditions At high pressure non-linear interaction with sawtooth. This is an operational limit. In JET RTC is used to track the mode-onset in order to study in detail the mode-dynamics In TEXTOR this non-linearity can be mimicked at low pressure with the DED coils Non-linear islands can be stabilised with Electron Cyclotron Waves (ECRH). Dedicated actuator in ITER Upper Port Launcher

7. Association Euratom-FOM Trilateral Euregio Cluster 7 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Pressure gradient drives non-inductive current j bs Operational limit due to interaction of sawtooth with “seed island” and this current  w/  t [cm/s] W [cm] 0 10 -10 Pressure Sawtooth at q= 1/1 Magnetic ‘gong’ Seed-island w> w crit 8 cm

8. Association Euratom-FOM Trilateral Euregio Cluster 8 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Probing the operational boundary using Control I p = 2.0MA B t = 2.7T q 95 = 4.4 HH n=1 n=2 locked mode At high pressure, islands develop. These deteriorate the confinement. Power ramp-up to drive onset of 2/1 pressure limit Island onset  power (and hence pressure) ramp down Complicated mode dynamics: Locking and un- locking of modes Marginal pressure for onset of m/n=2/1 mode determined P marginal

9. Association Euratom-FOM Trilateral Euregio Cluster 9 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Marginal pressure determined

10. Association Euratom-FOM Trilateral Euregio Cluster 10 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Not control in the strict sense After detection of mode pre-programmed ramp down of the power was initiated This allowed for –high quality outcome of the experiment –At high reproducibility

11. Association Euratom-FOM Trilateral Euregio Cluster 11 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 In TEXTOR islands are induced with the Dynamic Ergodic Divertor 3/1 6/2 or 12/4 mode DC, AC to 10 kHz Our experiments: 3/1 mode Large 2/1 side band 1 kHz AC

12. Association Euratom-FOM Trilateral Euregio Cluster 12 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Island suppression with localised electron heating ECRH: Electron cyclotron resonant heating B T = 2.25 T; I p = 300 kA n e = 2.0 10 19 m -3 ECRH on “q=2” –140 GHz, 770 kW ECE sxr penetrationstabilisation resolution ~2cm

13. Association Euratom-FOM Trilateral Euregio Cluster 13 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Not control in the strict sense Real control requires Model of the non-linear behaviour of the island Model Electro-mechanical properties of ECHR Launcher RT-interpretation of island location –Egbert Westerhof and Sante Cirant (tomorrow)

14. Association Euratom-FOM Trilateral Euregio Cluster 14 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 ITER reference plasma scenario Control of Confinement Mode Local turbulence suppression Instabilities: Driven unstable by free energy Profiles of n e, T i,e, j, p, n Ep ITER workhorse: H-mode High confinement mode Dynamic heat fluxes Sawteeth: Repetitive modification of core profiles ‘Advanced modes:’ no sawteeth

15. Association Euratom-FOM Trilateral Euregio Cluster 15 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Controling Turbulent transport X.Garbet,CEA H-ModeAdvanced Mode Monotonic q profile (~inverse of current profile) Reversed q profile Off-axis current drive Turbulent vortices are ‘broken’ and transport reduced

16. Association Euratom-FOM Trilateral Euregio Cluster 16 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Shot 53521 (3.4T/2MA) 90% Non Inductive Current: Bootstrap current ~ 50% Neutral Beam Current Drive ~ 15% LH Current Drive ~ 25% (code CRONOS) Example advanced scenario

17. Association Euratom-FOM Trilateral Euregio Cluster 17 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Non-linear coupling between Current and Pressure Profiles in Advanced Modes Current Diffusion relaxes q(r) to monotonic profile Control of j(r) and p(r) required for advance modes Reversed shear by off-axis Current Drive (LHCD) Reduced turbulence: Steep p gradient Off-axis (bootstrap) current Off-axis current : q-profile modified

18. Association Euratom-FOM Trilateral Euregio Cluster 18 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08  -particles introduce new control issues Balance   vs  He Control of He recycling? Sawtooth control for   –Compatible with non-linear island formation? How to control   in discharges without sawteeth? Collective effect: Energetic particles drive instabilities

19. Association Euratom-FOM Trilateral Euregio Cluster 19 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Not control in the strict sense High degree of self organisation of the plasma and interaction between the profiles One-way only: Once the current density shaping is lost, almost impossible to re- achieve the target. Control can be used to coax the plasma in the desired self organised state

20. Association Euratom-FOM Trilateral Euregio Cluster 20 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Burning core Sawteeth NTMs A-birth and losses He accumulation Fast particle Instabilities: TAE Fishbone Performance Turbulent transport

21. Association Euratom-FOM Trilateral Euregio Cluster 21 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Observations For the burning plasma core control in the strict sense is required Need to be able to “move the working point around” Many interacting processes. Can we control a self organizing multi process system with a limited number actuators? This motivates setting-up an integrated model of the plasma core –Are the models that physicist are working on suited for this task?

22. Association Euratom-FOM Trilateral Euregio Cluster 22 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Conclusions Tokamak Plasma is a complex medium –Instability drive from gradients –P, j, n , Ti, … Wide variety of control issues: Turbulence, Transport, MHD, dynamic edge fluxes The control requirements are often conflicting. Limited number of actuators. Limited number of diagnostics Present experiments start to rely on RTC, but control if often used in a non-strict sense True Burn control will require control in the strict sense

23. Association Euratom-FOM Trilateral Euregio Cluster 23 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 07-05-08 Tokamak Functionality Divertor coils D1-4 Exhaust of heat and particles P4 UL For radial and vertical field P2 UL and P3 UL For plasma shaping Primary P1 For inductive current B  coils For toroidal field