Free boundary simulations of the iter hybrid and steady state scenarios
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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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Free boundary simulations of the iter hybrid and steady state scenarios

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


Outline

Outline

  • Background: motivation

  • New ITER hybrid scenario

  • MHD analysis

  • Coils post processing analysis

  • Sensitivity analysis

  • Free boundary simulation

  • Steady-state scenario

  • Conclusions


Hybrid scenario

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?


Steady state scenario

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?


Simulations of new iter hybrid scenario

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


Simulations of new iter hybrid scenario1

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


Simulations of new iter hybrid scenario2

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


Mhd analysis

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


Coils analysis

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.


Sensitivity analysis 1 plasma shape

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


Sensitivity analysis 2 density peaking

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


Sensitivity analysis 3 h 98 y 2 factor

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


Self consistent free boundary simulation with cronos dina ch

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


Self consistent free boundary simulation with cronos dina ch1

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)


Simulations of iter steady state scenario

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


Simulations of iter steady state scenario1

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


Conclusions

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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