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CRONOS simulations of ITER AT scenarios

CRONOS simulations of ITER AT scenarios F. Imbeaux, J.F. Artaud, V. Basiuk, L.G. Eriksson, G. Giruzzi, G. Huysmans, X. Litaudon, M. Schneider. Outline. Main assumptions Hybrid scenario (presented at EPS 2005, joint with TP group) Projections using various models / scalings

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CRONOS simulations of ITER AT scenarios

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  1. CRONOS simulations of ITER AT scenarios F. Imbeaux, J.F. Artaud, V. Basiuk, L.G. Eriksson, G. Giruzzi, G. Huysmans, X. Litaudon, M. Schneider

  2. Outline • 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

  3. Simulation parameters • Hybrid (q95 = 4) scenarios • Thermal transport + current diffusion • Density prescribed (flat Zeff profile, ne flat or peaked) • fD = fT = 37.5 % (nD/ne), fHe = 2 %, fBe = 0.5 %, fC = 4.5 % • 53 / 73 MW of additional power • 33 MW NBI @ 900 keV (SINBAD) • 20 MW ICRH (PION, 2nd harmonic of T, f = 55 MHz) • 0 / 20 MW of LHCD (DELPHINE, f = 5 GHz, n// = 2.0)

  4. Ptot core link Wcore Wped ped neo W0   max max ped ped 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 Pin > PL-H, then a pedestal is added (fixed width). Constant c in the pedestal, pedestal energy content renormalised to a specific scaling law (2-terms approach, [Cordey et al NF 2003, 670])

  5. 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 b degradation • HH = 1 • One example using GLF23 for r < 0.8, with edge given by scaling set B

  6. Hybrid scenario for ITER, for various scalings / models r • Ip = 13 MA only slightly lower than reference scenario (15 MA) (not lose too much on energy confinement). Paux = 53 MW (NBI + ICRH) • Density peaking ne0/ne,ped = 1.5 • Greenwald fraction = 0.92 • No enhancement w.r.t. scaling laws [CRONOS] NB : the GLF23 result uses same pedestal condition as DS03

  7. Off-axis current drive needed for high bN and extended duration ? LH 20 MW LHCD delay significantly the occurrence of q = 1 [CRONOS] • Sustaining high bN ~ 3 requires no or small q = 1 surface • In spite of reduced Ip, q = 1 finally occurs … and might trigger deleterious NTMs ? DS03 scaling r

  8. Conclusions for hybrid scenario • The Hybrid scenario achieves Q = 10 at 13 MA (using DS03 scaling more favorable at high bN) • 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 (bN > 4li)

  9. Steady-state scenario

  10. 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)

  11. 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 Pfus) • Try : modify one of the actuators (here, PNBI, PICRH, ne) (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

  12. Additional constraints • The « try, wait and see » feedback algorithm is used with additional constraints, corresponding to physical limits and/or the desired operation space • bN < 4.li : otherwise, reducePNBI and PICRH • frmin n/nG frmax: otherwise : • n/nG < frmin: increase density • n/nG > frmax: increase PNBI and PICRH (will increase Ip) • Aim at Vloop= 0 : • Start at low Ip (550 kA, fixed), and let IPvary 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 toconstant edge flux  Ip is left floating and removed from the list of TWS actuators

  13. Example • Current, Te and Ti 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,a) • 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 • PLH fixed at 20 MW, with a fixed profile (center = 0.5, width = 0.2 and a fixed efficiency 2.5 1019 W/A/m² and scaling dependences) • PICRH between 10 to 20 MW • PNBI between 0 to 32 MW • « try, wait and see » feedback algorithm aiming at maximize Pfus

  14. Currents Transition to constant edge flux Spikes are consequences of the TWS actuators dynamics

  15. Transition to constant edge flux Pa PLH PICRH PNBI time (s) Heating powers PNBI drops because of operational limit

  16. Transition to constant edge flux Pa PLH PICRH PNBI time (s) Operational constraints • Constraint bN < 4li prevents from increasing PNBI • As li slowly increases, bN is also allowed to increase slowly (via the density)  slow increase of fusion power 4li bN time (s)

  17. Bootstrap and Greenwald fractions • Greenwald fraction increases slowly with bN limit, within the operational space : 0.55 < fGR < 0.85 time (s)

  18. ITB dynamics • Until 400 s, the ITB shrinks owing to misalignment with bootstrap current • To be continued …

  19. Conclusions for steady-state scenario • « 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

  20. Conclusions and perspectives • The Hybrid scenario achieves Q = 10 at 13 MA (using DS03 scaling more favorable at high bN) • 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

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