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Free boundary simulations of the ITER hybrid and steady-state scenariosPowerPoint Presentation

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

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### 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 steady-state

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

Hybrid scenario steady-state

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

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 steady-state

- 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 scenario steady-state

- 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 scenario steady-state

- 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 steady-state

- 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 steady-state

- 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 steady-state

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 steady-state

- 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 steady-state98(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 steady-state

- 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-CH steady-state

- 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 steady-state

- 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 scenario steady-state

- 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 steady-state

- 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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