ITER scenarios with LHCD Status

1. ITER scenarios with LHCD Status F. Imbeaux, J. Citrin, J. Garcia, V. Basiuk, J. Decker, Y. Peysson, J. Hillairet

2. Integrated ITER scenario modelling with LHCD • Results obtained earlier this year : stand-alone LHCD modelling using fixed parameters (equilibrium, plasma profiles) • 4 situations analysed • H mode baseline scenario 2 • Hybrid scenario • Steady-state scenario 4 • Current ramp-up phase • Conclusion : n//0 ~ 2.0 is an optimum design for all scenarios • Now : analyse the effect of LHCD in ITER scenarios, using integrated modelling • Current profile control • Flux saving • Tools : CRONOS + C3PO/LUKE integrated simulations

3. H-mode baseline scenario 2 • From stand-alone studies : poor penetration of LH waves due to high density • Flux saving during the main heating phase to quantify • Detrimental impact on Q expected (stiff transport model / pedestal) • Main application of LHCD is during the pre-heating phase : control the shape of the target current profile  current ramp assisted by LHCD

4. Hybrid scenario • Hybrid scenario targets longer plasma duration ( > 400 s), is interested by flux saving • And by q-profile control : maintain no or small sawteeth to avoid triggering deleterious NTM  minimise the size of the q = 1 surface NB : scaling-based transport model, pure gyro-Bohm DS03, non-stiff pedestal  quite optimistic LH 20 MW LHCD delay significantly the occurrence of q = 1 [F. Imbeaux, PPCF 2005]

5. Hybrid scenario Non-inductive current drive profiles • Possible caveate : dependence of transport on magnetic shear • GLF23 : stiff model, pedestal fixed  reacts strongly to changes in the threshold, weakly on change of heating • LHCD far off-axis : decreases magnetic shear off axis  increases transport 33 NBI / 20 EC / 17 LHPfus= 273 MW, H98 = 1, Ip = 11.8 MAt(q=1) = 1220 s33 NBI / 37 ECPfus = 348 MW, H98 = 1.07t(q=1) = 1050 s [J. Citrin, EFTC 2009]

6. Steady-state scenario • Issue : the steady-state scenario is loosely defined on ITER: • Strong bootstrap current fraction required to reach full non-inductive current drive  operate at low current + • + assuming the establishement of a strong ITB  high uncertainties from the transport model • Baseline scenario 4 : original design uses hLH = 0.3.1020 A/W/m2 and PLH = 30 MW. Our stand-alone ALOHA/C3PO/LUKE calculations yield hLH = 0.15.1020 A/W/m2 (with optimal directivy 70 %) and used only PLH = 20 MW •  the baseline scenario 4 is based on unrealistic assumptions from the LHCD point of view

7. Steady-state scenario • Alternative example of an ITB scenario at Ip = 8 MA [J. Garcia PRL 2008] • ITB depends on magnetic shear  need to reverse the q-profile  do not drive current inside ITB  no NBI • LHCD drives current outside mid-radius + ECCD@mid-radius to lock the ITB position (current alignement)  ideal combination • Strong ITB can be avoided (improve MHD stability) by the cyclic scenario concept [J. Garcia et al, submitted] • Only PLH = 13 MW used, fboot = 70 % (quite optimistic confinement/ITB model) q-profile

8. Current ramp-up with LHCD • LHCD can be used to reach the desired target q-profile for any scenario + flux saving • Extensive simulations with DINA-CRONOS-DELPHINE [Kim PPCF 2009] • Flux savings (~ 43 Wb, of which 80 % are due to heating effect) • LH dynamics : absorption close to the center at the beginning, moves outwards as Te, Ip increase

9. Current ramp-up with LHCD • LHCD can be used to reach the desired target q-profile for any scenario + flux saving • To be repeated with C3PO/LUKE/ALOHA in fixed boundary mode, using additional transport models • (Start LHCD earlier ? With higher power ?)

10. Conclusions • During the main heating phase : • Flux savings / impact on Q : to be quantified for the inductive scenarios • Delay q-profile penetration / reduce size of q = 1 for hybrid scenario : ok, but impact on confinement may be deleterious (reducing magnetic shear off-axis). ECCD could also do a good job on controlling the q = 1 surface with higher shear and confinement • Ideal location of the power deposition for a steady-state scenario with ITB. LHCD is the only actuator with high CD efficiency off-axis, and is well located for ITB scenarios. However, in optimal coupling conditions, 20 MW of LHCD would drive less than 10 % of the total current. Only one scenario simulated where this is enough to sustain a steady-state ITB. The energy transport assumptions underlying such a pure steady-state scenario with Q ~ 5 are very optimistic  LHCD is more likely to play a role in advanced scenarios with some remaining ohmic current, but the installed power may be marginal to reach a significant target.These scenarios are not well defined (ITB model) • During the ramp-up phase : • LHCD achieves large flux saving + control of target q-profile • Since heating is the main player, ECCD could play a similar role ?

11. To complete the work • Flux savings calculations for ramp-up + inductive scenarios : depend on the transport model  try calculations with 2 different models (max. stiffness vs scaling based min. stiffness) • Q should be estimated for burning phases • Hybrid : evaluate the addition of 20 MW LHCD on baseline hybrid scenario (GLF23, 53 MW scenario vs 73 MW) • Ramp-up : repeat published simulations with C3PO/LUKE, use different transport models and spectrum assumption • Linear damping of LH waves of fast alpha particules in these scenarios