Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October CRONOS simulations of ITER AT scenarios F. Imbeaux, J.F. Artaud, V. Basiuk, L.G. Eriksson, G. Giruzzi, G. Huysmans, X. Litaudon, M. Schneider

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Main assumptions Hybrid scenario (presented at EPS 2005, joint with TP group) Projections using various models / scalings Current drive issues Steady-state scenario : demonstration of new feedback algorithm Database submission Outline

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Simulation parameters Hybrid (q 95 = 4) scenarios Thermal transport + current diffusion Density prescribed (flat Z eff profile, n e flat or peaked) f D = f T = 37.5 % (n D /n e ), f He = 2 %, f Be = 0.5 %, f C = 4.5 % 53 / 73 MW of additional power 33 MW 900 keV (SINBAD) 20 MW ICRH (PION, 2 nd harmonic of T, f = 55 MHz) 0 / 20 MW of LHCD (DELPHINE, f = 5 GHz, n // = 2.0)

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Transport model based on 2-terms scaling 1D model with a profile dependence : Most important point : C is a normalisation factor calculated at each time step so that the total energy content follows a global scaling law (IPB98(y,2) or DS03). If P in > P L-H, then a pedestal is added (fixed width). Constant  in the pedestal, pedestal energy content renormalised to a specific scaling law (2-terms approach, [Cordey et al NF 2003, 670]) P tot  max W0W0 W ped W core   ped   max   ped  core  neo  ped link

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Scaling expressions used Scaling set A (global IPB98 + core 96-L): Scaling set A’ with reduced pedestal (global IPB98 + enhanced 96-L), more consistent with official ITER reference H mode projections Scaling set B (DS03 + pedestal scaling), no  degradation H H = 1 One example using GLF23 for  < 0.8, with edge given by scaling set B

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Hybrid scenario for ITER, for various scalings / models I p = 13 MA only slightly lower than reference scenario (15 MA) (not lose too much on energy confinement). P aux = 53 MW (NBI + ICRH) Density peaking n e0 /n e,ped = 1.5 Greenwald fraction = 0.92 No enhancement w.r.t. scaling laws  NB : the GLF23 result uses same pedestal condition as DS03 [CRONOS]

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Off-axis current drive needed for high  N and extended duration ?  20 MW LHCD delay significantly the occurrence of q = 1 LH [CRONOS] Sustaining high  N ~ 3 requires no or small q = 1 surface In spite of reduced I p, q = 1 finally occurs … and might trigger deleterious NTMs ? DS03 scaling

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October The Hybrid scenario achieves Q = 10 at 13 MA (using DS03 scaling more favorable at high  N ) If only 33 MW NBI and 20 MW ICRH, q = 1 appears at ~ 650 s Additional off-axis current drive might be needed to reduce the size of the q = 1 surface and delay its occurrence 20 MW LHCD allow to delay the occurrence of the q = 1 surface until 1040 s 40 MW LHCD allows to get rid completely of q = 1 surface RWM stabilisation needed (  N > 4li) Conclusions for hybrid scenario

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Steady-state scenario

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Steady-state scenario Multi feedback control on the steady-state scenario (9 MA) : aim at sustaining internal transport barrier without going beyond operational limits A rather optimistic transport model is used : 2-terms scaling model, using scaling set B (DS03) Shear function to produce an ITB (improvement w.r.t. global scaling)

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October The « try, wait and see » feedback algorithm Philosophy : control a given parameter without a priori knowledge of the physics of the system Aim : maximize a given parameter (here : look for maximum P fus ) Try : modify one of the actuators (here, P NBI, P ICRH, n e ) (add or substract a given incremental value) Wait : let the plasma evolve during a given time scale (here : energy confinement time) See : has the modification of the actuator fullfilled the aim ? Yes  take another incremental step on the actuator No  if it was the first variation of actuator, try variation in the opposite direction; otherwise, step back and skip to next actuator

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Additional constraints The « try, wait and see » feedback algorithm is used with additional constraints, corresponding to physical limits and/or the desired operation space  N < 4.li : otherwise, reduce P NBI and P ICRH fr min  n/n G  fr max : otherwise : n/n G < fr min : increase density n/n G > fr max : increase P NBI and P ICRH (will increase Ip) Aim at V loop = 0 : Start at low I p (550 kA, fixed), and let I P vary as an actuator of the « try, wait and see » feedback algorithm As soon as full non-inductive current drive is reached (following the increase of the heating power), transition to constant edge flux  I p is left floating and removed from the list of TWS actuators

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Example Current, T e and T i are simulated, as well as heat sources and current drive Heat transport model : 2-terms scaling model, using scaling set B (DS03), with shear function (s,  ) The line-averaged density is considered directly as an actuator (no particle transport calculation). The whole density profile keeps a constant shape with peaking factor = 1.2 –Constraint on operational space : 0.55 < Greenwald fraction < 0.85 Injected Power –P LH fixed at 20 MW, with a fixed profile (center = 0.5, width = 0.2 and a fixed efficiency W/A/m² and scaling dependences) –P ICRH between 10 to 20 MW –P NBI between 0 to 32 MW « try, wait and see » feedback algorithm aiming at maximize P fus

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Currents Transition to constant edge flux Spikes are consequences of the TWS actuators dynamics

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October PP P LH P ICRH P NBI time (s) Transition to constant edge flux Heating powers P NBI drops because of operational limit

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Operational constraints NN 4li PP P LH P ICRH P NBI time (s) Transition to constant edge flux Constraint  N < 4li prevents from increasing PNBI As li slowly increases,  N is also allowed to increase slowly (via the density)  slow increase of fusion power time (s)

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October time (s) Bootstrap and Greenwald fractions Greenwald fraction increases slowly with  N limit, within the operational space : 0.55 < f GR < 0.85

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Until 400 s, the ITB shrinks owing to misalignment with bootstrap current To be continued … ITB dynamics

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October « Try, wait and see » feedback algorithm allows to maximise fusion power while keeping the system in a safe operational domain Does not require a priori knowledge of the system. Very useful for transient phases of the steady-state scenario (owing to the non-linearities due to the ITB) Can be applied too much more subtle optimisation problems Conclusions for steady-state scenario

Association Euratom-Cea ITPA CDBM group meeting, St Petersburg, October Conclusions and perspectives The Hybrid scenario achieves Q = 10 at 13 MA (using DS03 scaling more favorable at high  N ) If only 33 MW NBI and 20 MW ICRH, q = 1 appears at ~ 650 s Additional off-axis current drive might be needed to reduce the size of the q = 1 surface and delay its occurrence 20 MW LHCD allow to delay the occurrence of the q = 1 surface until 1040 s « Try, wait and see » feedback algorithm allows to maximise fusion power while keeping the system in a safe operational domain Very useful for transient phases of the steady-state scenario (owing to the non-linearities due to the ITB) CRONOS is now able to write ITER simulations in Profile DB  strategy to discuss