Post on 05-Jan-2016
F. Koechl (1) IOS ITPA Meeting, Kyoto 19.10.2011
Free boundary simulationsof the ITER baseline scenario
and its variants
F. Koechl, M. Mattei, V. Parail, R. Ambrosino, M. Cavinato, G. Corrigan, L. Garzotti,C. Labate, D. C. McDonald, G. Saibene, R. Sartori
F. Koechl (2) IOS ITPA Meeting, Kyoto 19.10.2011
Objectives / Motivation:
Integrated simulations with the free boundary equilibrium code CREATE-NLand the JET suite of codes JINTRAC of the 15 MA ELMy H-mode scenarioin ITER and its variants have been done for the following purposes:
– exploration of the operational space and possibilities of scenario optimisation– assessment of the compatibility with machine constraints, in particular with
the poloidal field (PF) coil system– evaluation of plasma/control system reaction to transient events and
associated risks
F. Koechl (3) IOS ITPA Meeting, Kyoto 19.10.2011
CREATE-NL FBE solver
• Axial-symmetric free boundary code based on numerical solution of Grad-Shafranov equation.
• Determination of poloidal flux map by FEM discretisation and Newton based iterative method.
• Control of plasma shape (6 gaps) based on a feedforward+feedback control strategy (PF coil nominal current waveform calculated a-priori). Vertical stabilisation using in vessel coils (VS3).
• Includes eddy currents, limits in currents and voltages, calculation of forces and max. field in coils.
F. Koechl (4) IOS ITPA Meeting, Kyoto 19.10.2011
JINTRAC
• Weakly coupled mode: data exchange after each simulation run, iterative consistency check
• Strongly coupled mode: data exchange at every time step
F. Koechl (5) IOS ITPA Meeting, Kyoto 19.10.2011
• L-mode:– Bohm/gyroBohm
• H-mode, plasma core:– GLF23– Bohm/gyroBohm with “GLF23-like” pinch for fast transients– Kadomtsev model for sawtooth emulation
• H-mode, ETB:– Continuous ELM model with prescribed c
– Lower c prescription for type-III ELMy H-mode emulation
• L-H transition model:– L-H transition for Pnet > PL-H Martin
– Transition from type-III to type-I ELMs for Pnet > 1.4·PL-H Martin
• Source models:– PENCIL (NBI), PION / TOMCAT / CYRANO (ICRH),
SIMOD ( heating), NGPS / HPI2 (pellets), FRANTIC (neutrals), …
Transport / source models
F. Koechl (6) IOS ITPA Meeting, Kyoto 19.10.2011
Discharge configuration / shape evolution:
ITER Baseline Scenario
Central inboard breakdown with fast expansion to diverted shape
Flat-topRamp-down
Ramp-up
F. Koechl (7) IOS ITPA Meeting, Kyoto 19.10.2011
Plasma performance / flux consumption:
ITER Baseline Scenario (2)
F. Koechl (8) IOS ITPA Meeting, Kyoto 19.10.2011
PF coil voltages during current ramp-up in limiter phase:
Current ramp-up
Voltage saturationHigh load on PF coil converters to achieve fast plasma expansion
F. Koechl (9) IOS ITPA Meeting, Kyoto 19.10.2011
Early L-H transition:
Current ramp-up (2)
L-H @ 80s (15 MA)L-H @ 48s (10 MA)L-H @ 30s (7 MA)
same Pfus when steady-state jz is reached
sharp drop in li(3), because dIpl/dt 0
Confinement deterioration due to enhanced transport at lower s/q
F. Koechl (10) IOS ITPA Meeting, Kyoto 19.10.2011
Quasi-steady state profiles:
Flat-top
t = 400s
F. Koechl (11) IOS ITPA Meeting, Kyoto 19.10.2011
Comparison flat / prescribed vs. peaked / simulated density:
Flat-top (2)
ne ax/avg/ped
Te ax/avg/ped
Ti ax/avg/ped
ne
Te
Ti
t = 200s
F. Koechl (12) IOS ITPA Meeting, Kyoto 19.10.2011
Density / pedestal sensitivity scan:
Flat-top (3)
-- Simulation··· Qfus pped
2.0
··· Qfus pped1.3
Non-quadratic Pfus increase with pedestal pressure because of rise in bootstrap current causing lower s/q
Constant Pfus for higher ne because of pressure gradient maintenance, but higher flux losses
F. Koechl (13) IOS ITPA Meeting, Kyoto 19.10.2011
Flat-top (4)
Qfus ~ 10 cannot be reached due to back-transition to type-III ELMy H-mode and L-mode if PAUX is reduced
PL-H Martin
PL-H Green
Delayed transition from L-mode to type-I ELMy H-mode with increased flux losses
V. Parail, IOS-JA2
Consideration of type-III ELMs:
F. Koechl (14) IOS ITPA Meeting, Kyoto 19.10.2011
Flat-top (5)
dashed: PAUX = 40 MWsolid: PAUX = 0 MW
Pfus ~ 50 MW
Profile stiffness allows arbitrary increase in Qfus (provided that Pnet > PL-H)!
Scan in heating power:
F. Koechl (15) IOS ITPA Meeting, Kyoto 19.10.2011
Scan in possible abruptness of pedestal decay after H-L transition (depending on boundary conditions):
H-L transition
Inner plasma-wall gap safety margins can be temporarily violated for most extreme conceivable transition cases
F. Koechl (16) IOS ITPA Meeting, Kyoto 19.10.2011
PF coil currents / voltages during H-L transition
H-L transition (2)
PF6 voltage saturation leading to increasing loss of strike point control
Small margins left for required decrease in CS1 current, can only partly be compensated by different CS coil currents
F. Koechl (17) IOS ITPA Meeting, Kyoto 19.10.2011
Current ramp-down
li(3) / Vs consumption at ramp-down (L-mode only):
Solid: Vstot Dotted: Vsind
Dashed: Vsres Dash-dotted: Vssawt.
|dIpl/dt| ~ 250 kA/s, 60 s ramp-down|dIpl/dt| ~ 75 kA/s, 200 s ramp-down|dIpl/dt| ~ 38 kA/s, 400 s ramp-down
Strong increase in li(3) for high ramp rates affecting vertical stability control
F. Koechl (18) IOS ITPA Meeting, Kyoto 19.10.2011
Current ramp-down (2)
Comparison early vs. late H-L transition:Vs consumption (total: solid, inductive: dotted, sawtooth-induced: dash-dotted, resistive: dashed)
Psep (solid) / P (dash-dotted) / PAUX (dotted) / PL-H threshold (dashed):
H-L transition @ 15 MAH-L transition @ 7 MA
Drastic reduction in flux losses with prolonged H-mode phasePnet > PL-H achievable with
reduced P + PAUX
F. Koechl (19) IOS ITPA Meeting, Kyoto 19.10.2011
Ramp-down at constant loop voltage:
Current ramp-down (3)
prescr. IplVloop = -0.2VVloop = 0 VVloop = 0.6 V
li(3)
Ipl
Wth
Vloop Fast reduction in Ipl / inductive flux after the transition helps to increase headroom for PF coil control
li(3) kept at lower level in later phase due to decrease in |dIpl/dt|
F. Koechl (20) IOS ITPA Meeting, Kyoto 19.10.2011
Current ramp-down (4)
Non accessible region
Compatibility of flux at ramp-down with PF coil system:
450s flat-top scenarios:
ITER baselineFast ramp-up/downLate H-L transitionLate transition to
diverted phase at ramp-up
pol = 0.6 limits
pol = 0.1 limits
critical flux level reached at ramp-down for baseline scenario
F. Koechl (21) IOS ITPA Meeting, Kyoto 19.10.2011
Flat-top duration limited to 10-20s (up to ~50s with increased current ramp rate), as plasma stays in L-mode:
ITER 15 MA hydrogen scenario
Critical flux level is already reached because of increased Vsind (L-mode jz) and resistive flux losses (low Te) and strong sawtooth activity
F. Koechl (22) IOS ITPA Meeting, Kyoto 19.10.2011
General results
– According to simulation results, a slow ramp-up phase with late L-H transition gives the optimum fusion performance, whereas a fast ramp-up with early transition to high confinement is preferable in order to save Vs and extend the flat-top duration.
– Gap safety margins can be reached for H-L transition at 15 MA.– Trade-off between accumulation of resistive Vs losses for small dIpl/dt and limitations of
the PF coil and fuelling systems for high dIpl/dt for current ramp-down (optimum ramp-down period: ~200-250s). Late transition to L-mode during current ramp-down is feasible and advantageous. Constant loop voltage ramp-down is preferable.
– An optimisation of the ITER baseline scenario needs to be focused on the reduction of flux consumption to increase flux margins for the PF coil control system and / or increase the flat-top length, trying to avoid at the same time a drop in fusion power in the initial flat-top phase which could occur as a consequence of slowed down current penetration at ramp-up and which could increase the risk to remain in type-III ELMy H-mode conditions at flat-top.
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Complementary slides
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Current ramp-up scan:
Current ramp-up
F. Koechl (25) IOS ITPA Meeting, Kyoto 19.10.2011
Current ramp-up (3)Late transition between limiter / divertor configurationPsep in dependence of PAUX level in limited phase:
ITER baselineLate lim./div. transition,Paux: Ipl>7MALate lim./div. transition,Paux: Ipl>5.4MALate lim./div. transition,Paux: Ipl>4MAslowed down plasma expansion
Maximum allowed PAUX of 3 – 5 MW in limiter phase!
F. Koechl (26) IOS ITPA Meeting, Kyoto 19.10.2011
Flat-top (6)
Vertical force on P5 coil and CS separation force close to the limit
Forces on PF coils:
F. Koechl (27) IOS ITPA Meeting, Kyoto 19.10.2011
Transport dependence on s/q
Comparison of R/LTi predicted by GLF23 (solid) and by experimentally validated formula with s/q dependence (dotted) for t = 400 s:
L-H @ 7 MAL-H @ 10 MAL-H @ 15 MA
F. Koechl (28) IOS ITPA Meeting, Kyoto 19.10.2011
Long flat-top duration feasible due to small Vsind, plasma can access type-III/I Hmode due to low PL-H:
ITER 2.65 T / 7.5 MA H / He4 scenarios