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Free boundary simulations of the ITER hybrid and steady-state scenarios

Free boundary simulations of the ITER hybrid and steady-state scenarios. J.Garcia 1 , J. F. Artaud 1 , K. Besseghir 2 , G. Giruzzi 1 , F. Imbeaux 1 , J.B. Lister 2 , P. Maget 1. 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.

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Free boundary simulations of the ITER hybrid and steady-state scenarios

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  1. Free boundary simulations of the ITER hybrid and steady-statescenarios J.Garcia1, J. F. Artaud1, K. Besseghir2, G. Giruzzi1, F. Imbeaux1, J.B. Lister2, P. Maget1 1 CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France. 2 Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, CH-1015 Lausanne, Switzerland

  2. Outline • Background: motivation • New ITER hybrid scenario • MHD analysis • Coils post processing analysis • Sensitivity analysis • Free boundary simulation • Steady-state scenario • Conclusions

  3. Hybrid scenario J. Citrin et al., Nucl. Fusion 50 (2010) 115007 • Hybrid scenario analyzed with GLF23 transport model and optimized in order avoid q=1 by still having Q=5 • For Tped=4 keV and flat density profile the q=1 surface can be strongly delayed. The q profile shape enhances fusion performance but... • ...βN=2 with H98=1, so roughly speaking it is an H mode at low current • What are the requirements for a hybrid scenario in ITER similar to those in present day machines? Could the device handle these scenarios? • In density peaking essential? Plasma shaping? High H98?

  4. Steady-State scenario J.Garcia et al., Nucl. Fusion 50 (2010) 025025 J.Garcia et al., Phys. Rev. Lett. 100, 255004 (2008) • Steady-state scenario with strong ITB developed • Simple core transport model: ce= ci= ci,neo + 0.4 (1+3r2) F(s) (m2/s) • F(s): shear function allowing an ITB formation for s < 0 • MHD problems quickly appear: oscillatory regimes can overcome them but require difficult time control • Steady-state scenarios with no ITB, low pedestal and good q profile properties are possible? What are the requirements?

  5. Simulations of new ITER hybrid scenario • Ip = 12 MA, BT = 5.3 T • dIp /dt= 0.18 MA/s, BT = 5.3 T, fG=0.4 during ramp-up. fG=0.85 flat-top phase • EC wave launch: top launchers, 8MW during ramp-up, 20MW flat-top (equatorial launchers) • ICRH: 20 MW, NBI: 33MW (off-axis and on-axis) • ne profile fixed, peaked profile, ne(0) ≈ 0.95 1020 m-3 • rped ≈ 0.95, nped≈ 0.55 1020 m-3, Tped 4.5 keV • Bohm-GyroBohm transport model during ramp-up • H98=1.3 with Bohm-GyroBohm shape for flat-top phase

  6. Simulations of new ITER hybrid scenario • The current configuration aims to have the bulk of the off-axis current inside ρ=0.5 • Only 16.5MW of off-axis NBI used • The on-axis NBI power helps to peak the pressure profile • Peaked density profile (peaking factor 1.4), checked with GLF23 • The ICRH power is on-axis for the electrons and off-axis for the ions • βN=2.65, βp=1.45, Q=8

  7. Simulations of new ITER hybrid scenario • Ini=8.65MA (fni=79.6%), Iboot=4.4MA (fboot=41.0%), Inbcd=3.5MA (fnbcd=31.8%), Ieccd=0.75MA (feccd=6.8%), • There is almost no evolution of q from 500s until t=1200s • q profile remains above 1 and almost stationary with a flat core profile • Ramp-down strategy: Avoid abrupt transition to low beta regime • Suppression of NBI and ICRH powers at the beginning of the ramp-down • Electron density ramped-down • H mode sustained with ECRH and alpha power • When alpha power is low, transition to L mode • No flux consumption during the H mode

  8. MHD analysis • Linear MHD analysis at the plasma edge done with MISHKA • The hybrid scenario is linearly stable. The pedestal assumptions seem reasonable • Core MHD analysis to be done

  9. Coils analysis • Post processing coils analysis done with the code Freebie • The scenario seems globally acceptable as it is in the CRONOS simulation, from the PF coils point of view (coils limits in green). • Some limits are approached or violated transiently, but there is margin to avoid it by slightly modifying the plasma shape evolution.

  10. Sensitivity analysis 1: Plasma shape t=850s t=850s • Alternative shape used for q95=3.5 • The plasma reaches q=1 at t=850s • Two different effects: • lower q with lower elongated plasma • lower bootstrap current due to lower q

  11. Sensitivity analysis 2: Density peaking • Different density peaking factors considered: 1.4, 1.25, 1.1 • The bootstrap current profiles changes especially in the region 0<ρ<0.5 • This change tailors the q profile which falls below 1 and becomes monotonic for the flat density case

  12. Sensitivity analysis 3: H98(y,2) factor • Sensitivity to H98(y,2) analyzed by repeating the simulation with H98(y,2)=1 • The bootstrap current profile drops in the full plasma column • This change tailors the q profile which falls below 1 and becomes monotonic • The situation is similar to the case with flat density

  13. Self consistent free boundary simulation with CRONOS-DINA-CH • The simulation is repeated in a self-consistent way with the free boundary code CRONOS-DINA-CH • Current and temperature profiles are simulated. Density is prescribed • The plasma is initiated in an inboard configuration • The shape can be controlled even at the transition to a high beta plasma at the L-H transition

  14. Self consistent free boundary simulation with CRONOS-DINA-CH • The coils are always within the limits, no transient saturation found • The evolution of q is very sensitive to the shape of the plasma and to the non-inductive currents. Real time control needed (not done yet)

  15. Simulations of ITER steady-state scenario • Ip = 10 MA (q95 = 4.85), BT = 5.3 T • dIp /dt= 0.18 MA/s, BT = 5.3 T, fG=0.4 during ramp-up. fG=0.9 flat-top phase • EC wave launch: top launchers, 8MW during ramp-up, equatorial launchers 20MW flat-top • ICRH: 20 MW, NBI: 33MW (off-axis and on-axis) • LHCD: 15 MW • ne profile fixed, peaked profile, ne(0) ≈ 0.9 1020 m-3 • rped ≈ 0.95, nped≈ 0.5 1020 m-3, Tped 3.7 keV • Bohm-GyroBohm transport model during ramp-up • H98(y,2)=1.4 with Bohm-GyroBohm shape for flat-top phase

  16. Simulations of ITER steady-state scenario • βN=2.60, βp=1.66, Q=5 • The scenario is similar to a hybrid one but with qmin≈1.5 • The inclusion of LH is essential to reach Vloop=0

  17. conclusions • A new ITER hybrid scenario is created with two goals: • Understanding the physical requirements in order to establish a hybrid scenario similar to present day machines • Analyze whether the ITER device can handle it • The q profile can be sustained above 1 with a flat profile for 1200s • The scenario is linearly MHD stable and feasible from the coil system point of view • The scenario is found to be very sensitive to the plasma shape, density peaking and H98(y,2) factor, through the bootstrap current • A free boundary simulation has been carried out with the full shape evolution for the scenario. No problems have been found for the coil system • A steady-state scenario similar to the hybrid one has been also developed. • Unlike in the hybrid case, the inclusion of a LH system is essential to reach Vloop=0

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