F. Koechl (1) IOS ITPA Meeting, Kyoto Free boundary simulations of 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 Objectives / Motivation: Integrated simulations with the free boundary equilibrium code CREATE-NL and the JET suite of codes JINTRAC of the 15 MA ELMy H-mode scenario in 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 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 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 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 P net > P L-H Martin – Transition from type-III to type-I ELMs for P net > 1.4·P L-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 Discharge configuration / shape evolution: ITER Baseline Scenario Central inboard breakdown with fast expansion to diverted shape Flat-top Ramp-down Ramp-up

F. Koechl (7) IOS ITPA Meeting, Kyoto Plasma performance / flux consumption: ITER Baseline Scenario (2)

F. Koechl (8) IOS ITPA Meeting, Kyoto PF coil voltages during current ramp-up in limiter phase: Current ramp-up Voltage saturation High load on PF coil converters to achieve fast plasma expansion

F. Koechl (9) IOS ITPA Meeting, Kyoto Early L-H transition: Current ramp-up (2) 80s (15 MA) 48s (10 MA) 30s (7 MA) same P fus when steady-state j z is reached sharp drop in li(3), because dI pl /dt  0 Confinement deterioration due to enhanced transport at lower s/q

F. Koechl (10) IOS ITPA Meeting, Kyoto Quasi-steady state profiles: Flat-top t = 400s

F. Koechl (11) IOS ITPA Meeting, Kyoto Comparison flat / prescribed vs. peaked / simulated density: Flat-top (2) n e ax/avg/ped T e ax/avg/ped T i ax/avg/ped nene TeTe TiTi t = 200s

F. Koechl (12) IOS ITPA Meeting, Kyoto Density / pedestal sensitivity scan: Flat-top (3) -- Simulation ··· Q fus  p ped 2.0 ··· Q fus  p ped 1.3 Non-quadratic P fus increase with pedestal pressure because of rise in bootstrap current causing lower s/q Constant P fus for higher n e because of pressure gradient maintenance, but higher flux losses

F. Koechl (13) IOS ITPA Meeting, Kyoto Flat-top (4) Qfus ~ 10 cannot be reached due to back-transition to type-III ELMy H- mode and L-mode if P AUX is reduced P L-H Martin P L-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 Flat-top (5) dashed: P AUX = 40 MW solid: P AUX = 0 MW  Pfus ~ 50 MW Profile stiffness allows arbitrary increase in Q fus (provided that P net > P L-H )! Scan in heating power:

F. Koechl (15) IOS ITPA Meeting, Kyoto 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 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 Current ramp-down li(3) / Vs consumption at ramp-down (L-mode only): Solid: Vs tot Dotted: Vs ind Dashed: Vs res Dash-dotted: Vs sawt. |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 Current ramp-down (2) Comparison early vs. late H-L transition: Vs consumption (total: solid, inductive: dotted, sawtooth-induced: dash-dotted, resistive: dashed) P sep (solid) / P  (dash-dotted) / P AUX (dotted) / P L-H threshold (dashed): H-L 15 MA H-L 7 MA Drastic reduction in flux losses with prolonged H-mode phase P net > P L-H achievable with reduced P  + P AUX

F. Koechl (19) IOS ITPA Meeting, Kyoto Ramp-down at constant loop voltage: Current ramp-down (3) prescr. Ipl V loop = -0.2V V loop = 0 V V loop = 0.6 V li(3) Ipl W th V loop 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 Current ramp-down (4) Non accessible region Compatibility of flux at ramp-down with PF coil system: 450s flat-top scenarios: ITER baseline Fast ramp-up/down Late H-L transition Late 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 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 Vs ind (L-mode j z ) and resistive flux losses (low T e ) and strong sawtooth activity

F. Koechl (22) IOS ITPA Meeting, Kyoto 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 dI pl /dt and limitations of the PF coil and fuelling systems for high dI pl /dt for current ramp-down (optimum ramp- down period: ~ s). 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.

F. Koechl (23) IOS ITPA Meeting, Kyoto Complementary slides

F. Koechl (24) IOS ITPA Meeting, Kyoto Current ramp-up scan: Current ramp-up

F. Koechl (25) IOS ITPA Meeting, Kyoto Current ramp-up (3) Late transition between limiter / divertor configuration P sep in dependence of P AUX level in limited phase: ITER baseline Late lim./div. transition, Paux: Ipl>7MA Late lim./div. transition, Paux: Ipl>5.4MA Late lim./div. transition, Paux: Ipl>4MA slowed down plasma expansion Maximum allowed P AUX of 3 – 5 MW in limiter phase!

F. Koechl (26) IOS ITPA Meeting, Kyoto 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 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: 7 MA 10 MA 15 MA

F. Koechl (28) IOS ITPA Meeting, Kyoto Long flat-top duration feasible due to small Vs ind, plasma can access type-III/I Hmode due to low P L-H : ITER 2.65 T / 7.5 MA H / He4 scenarios