Association Euratom-FOM Trilateral Euregio Cluster 1 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 2 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 3 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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 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

Association Euratom-FOM Trilateral Euregio Cluster 4 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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 = –v  / v alfvén ~ 1.3

Association Euratom-FOM Trilateral Euregio Cluster 5 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 6 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 7 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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] Pressure Sawtooth at q= 1/1 Magnetic ‘gong’ Seed-island w> w crit 8 cm

Association Euratom-FOM Trilateral Euregio Cluster 8 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

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

Association Euratom-FOM Trilateral Euregio Cluster 10 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 11 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

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

Association Euratom-FOM Trilateral Euregio Cluster 13 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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)

Association Euratom-FOM Trilateral Euregio Cluster 14 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 15 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

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

Association Euratom-FOM Trilateral Euregio Cluster 17 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 18 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands,  -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

Association Euratom-FOM Trilateral Euregio Cluster 19 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

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

Association Euratom-FOM Trilateral Euregio Cluster 21 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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?

Association Euratom-FOM Trilateral Euregio Cluster 22 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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

Association Euratom-FOM Trilateral Euregio Cluster 23 M.R. de Baar, Workshop Control for Nuclear Fusion, the Netherlands, 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