free boundary simulations of the iter hybrid and steady-state scenarios

1J. Garcia ITPA-IOS meeting Kyoto 18-21 October 2011

AssociationEuratom-CEA

Free boundary simulations of the ITER hybrid and steady-state

scenarios

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


AssociationEuratom-CEAOutline

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


AssociationEuratom-CEAHybrid scenario

•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?

J. Citrin et al., Nucl. Fusion 50 (2010) 115007


AssociationEuratom-CEASteady-State scenario

• Steady-state scenario with strong ITB developed• Simple core transport model: e = i = i,neo + 0.4 (1+32) 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?

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J.Garcia et al., Phys. Rev. Lett. 100, 255004 (2008)

J.Garcia et al., Nucl. Fusion 50 (2010) 025025


AssociationEuratom-CEASimulations 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

• ped ≈ 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



•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



•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


AssociationEuratom-CEAMHD 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


AssociationEuratom-CEACoils 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.


AssociationEuratom-CEASensitivity 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


AssociationEuratom-CEASensitivity 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


AssociationEuratom-CEASensitivity 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


AssociationEuratom-CEASelf 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


AssociationEuratom-CEASelf 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)


AssociationEuratom-CEASimulations 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

• ped ≈ 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


AssociationEuratom-CEASimulations 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


AssociationEuratom-CEAconclusions

• 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

free boundary simulations of the iter hybrid and steady-state scenarios

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