Some Physics Issues Related to ITER Plasma Performance Presented by V.Mukhovatov with contributions from M.Shimada, A.Polevoi, M.Sugihara, Y.Gribov and T.Oikawa ITPA Group Meeting 3-6 October 2005, St.Petersburg, Russia

Contents ITER design issues that need urgent ITPA input Major Transport Tasks Related to TP, CDBM and Pedestal Groups Major Physics Issues for ITER Operating Regimes Summary

ITER Design Issues that Need Urgent ITPA Input Relevant TG Issue Comment mhd/ pedestal Design of coils to mitigate / control ELMs and resistive wall modes Acceptable island size in the core plasma mhd Examinations of current quench time for the fastest disruptions Disruption mitigation scenarios and guidelines for design of mitigation systems Second circuit for plasma vertical stabilization Noise level AC losses during RWM stabilization by side correction coils Pellet injection for ELM control Inboard or outboard soldiv/ Heat load on first wall Especially due to ELM soldiv Carbon erosion/deposition/control of tritium inventory and material choice Especially tritium retention* and its removal Private region PFC and necessity of Dome To be discussed at TGM in July Physics guidelines for disruptions thermal load (update) * Understanding of large difference of fuel gas retention in different machines or in the same machine with different configuration/operation Summary Report of the Sixth Meeting of the ITPA Coordinating Committee (6-7 June 2005, Moscow, Russia) Appendix G: ITER Design Issues that need ITPA input (revised 14 June 2005)

Major Transport Tasks Related to TP, CDBM and Pedestal Groups Development and testing of theory-based models for heat transport in plasma core, edge pedestal and SOL particle transport including anomalous particle pinch toroidal momentum transport at NBI, RF and NBI + RF heating ITBs formation and control ELMs and ELM mitigation Projections of plasma performance in basic ITER regimes Checking compatibility of GLF23 and Multi-Mode transport models with experimental profile stiffness

ITPA High Priority Research Tasks for 2005-2006 TRANSPORT PHYSICS Understand and optimize transport properties of hybrid and steady-state demonstration discharges - Address reactor relevant conditions and dimensionless parameters e.g., electron heating, Te~Ti, low momentum input, He/impurity transport, edge-core interaction - Utilize international experimental databases in order to test commonality of transport physics in hybrid, steady state scenario and reactor relevant conditions - Test simulation predictions via comparisons to measurements of turbulence characteristics, code-to-code comparisons and comparisons to transport scalings CONFINEMENT DATABASE AND MODELING Resolve the differences in b scaling in H-mode confinement - Define a program to understand the density peaking - Develop a reference set of ITER scenarios for standard H-mode, steady-state, and hybrid operation and submit cases from various transport code simulations to the Profile DB - Resolve which is the most significant confinement parameter, n* or n/nG - Understand the aspect ratio dependence of the L-H power threshold PEDESTAL AND EDGE PHYSICS Improve predictive capability of pedestal structure through profile modeling of joint experimental comparisons Dimensionless cross machine comparisons to isolate physical processes; Rotation, Er, shape, etc Measurement and modeling of inter-ELM transport Establish profile database for modeling joint experiments Physics based empirical scaling Collaboration with CDBM to improve scalar database characteristics and utilization - Predict ELM characteristics and develop small ELM and quiescent H-mode regimes and ELM control techniques

2004 ITPA-IEA Joint Experiments TP-1 Steady state plasma development TP-2 Hybrid regime development TP-3 Assess performance with Te~Ti operation and/or dominant electron heating TP-3.1 and 3.3 Obtain and sustain high performance operation with Te~Ti, including in hybrid/AT discharges TP-3.2 Physics investigation of transport mechanisms with Te~Ti at high density TP-4 Investigation of high performance operation with low external momentum input TP-4.1 Similarity experiments with off-axis ICRF-generated density peaking TP-4.2/4.4 High performance operation with low momentum input in hybrid and AT plasmas TP-4.3 Electron ITB similarity experiments with low momentum input TP-5/PEP-14 QH/QDB plasma studies TP-8 ITB similarity experiments CDB-2 b confinement scaling in ELMy H-modes: b degradation CDB-3 CDB-3 Improving the condition of Global ELMy H-mode and pedestal Databases, in particular with H data CDB-4 Confinement scaling in ELMy H-modes: n* scans at fixed n/nG CDB-5 Inside and vertical pellet launch: ELM behaviour CDB-6 Improving the condition of Global DBs: Low A CDB-7 Ohmic identity experiments: test of scaling with dimensionless parameters PEP-1 &-3 Dimensionless identity experiments in JET and JT-60U PEP-2 JET/DIII-D Pedestal Comparison PEP-6 PEP-6 Edge transport barrier formation and confinement in exact double null configurations PEP-7 Dimensionless identity experiments on Alcator C-Mod and JET PEP-9 NSTX/MAST/DIII-D Pedestal Similarity PEP-10 The impact of the first wall on ELMs PEP-12 Comparison between C-Mod EDA and JFT-2M HRS regimes PEP-13 Comparison of Small ELM Regimes in JT-60U and AUG PEP-14 QH/QDB Comparison in JT-60U and DIII-D

Major Physics Issues for ITER Operating Regimes ALL REGIMES: Disruption avoidance/mitigation Type-I ELM avoidance/mitigation INDUCTIVE HIGH-Q REGIME: Type-I ELMy H-mode (15MA, Q 10, bN=1.8, HH=1) HYBRID REGIME: Type-I ELMy H-mode (13MA, Q 5, bN=2.0, HH=1) Energy confinement at high density - Density limit: Borrass, Greenwald, B2Eirene modelling [(0.45/1.0/1.4)  nG] Particle transport: core plasma fuelling, density peaking NTM suppression IMPROVED HYBRID REGIME: (10-12MA, Q~10, bN 2.5, HH1.2) - Accessibility of Improved H-mode: q(0)>1; Ploss/Pthr >2 Sustainment of Improved H-mode: prevention of sawteeth - NTM suppression Prevention of He and impurity accumulation STEADY STATE REGIME: (9MA, bN=3.0, Q 5, HH=1.4-1.6) ITB formation at large radius ITB sustainment at high bN, TeTi , low vtor: control of q and pressure profiles Compatibility of core and edge transport barriers RWM suppression: plasma rotation; feedback stabilization Prevention of He and impurity accumulation

Projection of H-Mode Power Threshold in ITER DIM = 8xn + 5xB - 4xL = 3 for scaling to be dimensionally correct PL-H = C nxn BxB LxL ITER Scenario 2: B=5.3T, n=1x1020m-3, R=6.2m, a=2m, M=2.5, Ploss=87MW, Psep=74MW PL-H xn xB xL DIM IPB (1999) 81 0.76 0.87 1.95 2.63 (averaged for 5 scalings) ITER Physics 48 0.58 0.82 1.81 1.50 J.Snipes,2000 Guidelines (2001) 43 0.49 0.85 1.69 1.45 J.Snipes,2000 ITER Physics 41 0.46 0.87 1.68 1.31 J.Snipes, 2002 Guidelines (2004) 69 0.73 0.74 1.96 1.70 F.Ryter, 2002 64 0.70 0.70 1.80 1.90 T.Takizuka, 2004 Threshold Group 39 0.67 0.62 1.72 1.58 Y.Martin [Vilamoura, 2004] recommendation 39 0.63 0.67 1.72 1.51 Y.Martin [Vilamoura, 2004] Threshold Group 69 0.73 0.74 1.96 1.70 Draft PIPB (2005) recommendation 64 0.70 0.70 1.80 1.90 What scaling is recommended by the Threshold Group?

Plasma Performance in ITER Inductive Scenario 2 The value of PL-H  70MW is in a dangerous proximity to projected Ploss in ITER Scenario 2, i.e., Ploss/PL-H 1.25 Low ratio of Ploss/PLH may result in Type III ELMy H-mode regime Log-linear fit for type III ELMy discharges results in scaling predicting E3s for ITER, i.e. H98y,2  0.85 and Q ~ 6 (O. Kardaun, July 2002 IPP-IR-2002/5 1.1) Type III ELMy H-mode could be a good candidate for an early phase of ITER DT operation: substantial Pfus and Q, acceptable ELMs

Effect of Particle Transport on Operational Space in ITER The operational space of inductive high Q regimes shrinks substantially if core particle transport is significantly lower that thermal transport (DHe=De=0.2e) This is caused mainly by increase of plasma dilution with helium up to the 1.5-2.2% in average A.Polevoi et al, 10th IAEA Technical Meeting on H–mode Physics and Transport Barriers, St.Petersburg, 28-30 Sep 2005

Possible Effect of Ripples on Edge Pedestal in ITER Ripple effect on the edge pedestal is studied by the Pedestal Group by comparing JT-60U configuration (B/B ~ 1.5-2%) with that reproduced in JET It is suggested to reproduce in JET the ITER-like configuration with B/B ~ 0.6-1% and compare it with original JET configuration (B/B ~ 0.1%) to evaluate possible effect of ripples in ITER

Accessibility of Improved Hybrid Regime in ITER Improved H-mode in AUG seems to require PL/Pthres=2-4 In the case of Pthres70MW, ITER will need PL=140-280MW to operate in Improved H-mode L.Gionnone et al PPCF 46 (2004) 835

Operational space of Improved Hybrid regime may be limited in ITER: (a) by divertor requirement Psep<140MW (100MW) (G.Pacher et al PPCF 46 (2004 A257), and (b) by capability of ITER blanket cooling system (maximum Pfus =700MW for 60-300s depending on season) (ITER Technical Basis, IAEA,Vienna,2002) B=5.3 I=12.5MA q95=3.6 R=6.2m a=2m x=1.85 x=0.48 <ne>=9x1019 m-3 <ne>/nG=0.9 PL-H = 64MW He*/E=2 fBe=0.02 fAr as required for Psep<140MW ASTRA Code with 1.2xScal.(9) from J.G.Cordey et al NF 45(2005)1078 Results of modelling of Improved Hybrid Regime in ITER PAUX (MW) 33(NB) 33(NB)+20(RF) 49.5(NB)+40(RF) Pfus (MW) 580 680 720 Q 17.5 12.8 8.1 Psep (MW) 124 140 Prad (MW) 25.4 49.4 94.4 Zeff 1.27 1.77 2.78 βN 2.66 3.03 3.28 4li(3) 3.5 3.59 3.67 fNON-IND 0.55 0.57 0.63 Psep/PL-H 1.9 2.2

Requirements on Rotation Speed in ITER SS Scenario and ASTRA Results Results from ASTRA Modelling Ref. 2 inj 3 inj Rotation speed ~2% of VA expected in ITER SS Scenario with 2NB(33MW) +EC(20MW) is sufficient to stabilize RWM with Cβ ~ 47% (βN ~ 3) A.Polevoi <polevoa@itergps.naka.jaeri.go.jp> RWM can be stabilized by saddle coils if w <10 Y. Liu et al Nucl. Fusion 45 (2005) 1131

Reduction of Toroidal Rotation Speed Driven by NBI in AUG at ICRH It is shown that observed reduction of plasma rotation in AUG is attributed to increasing momentum diffusivity connected with confinement degradation by additional ICRF power flux, and not to ICRF induced toroidal force related to radial non-ambipolar transport of resonant particles D Nishijima et al, PPCF 47 (2005) 89

Deficit of Off-Axis NB Current Density is Observed in AUG The disagreement in AUG between observations and code prediction is larger at high injection power and low triangularity Experiments on JT-60U at 4MW of NBI agree with code predictions The effect will be small in ITER if critical injection power scales as Pcr  plasma volume S.Günter 20th FEC OV / 1-5 Experiments on other tokamaks are needed to confirm the effect and find size scaling of critical injection power

Effect of TAE on NB Current Density Evaluated in JT-60U Redistribution of non-inductive current profiles in JT-60-U at burst of TAE activity Evaluation of TAE activity in ITER on NB current density profile is required PIPB Chapter 6, 2005

Summary-I: Major Physics Issues ALL REGIMES: Disruption avoidance/mitigation Type-I ELM avoidance/mitigation INDUCTIVE HIGH-Q REGIME: Type-I ELMy H-mode (15MA, Q 10, bN=1.8, HH=1) HYBRID REGIME: Type-I ELMy H-mode (13MA, Q 5, bN=2.0, HH=1) Good energy confinement at high density - Density limit: Borrass, Greenwald, B2Eirene modelling (0.45, 1.0, 1.4 x nG) Core plasma fuelling NTM suppression IMPROVED HYBRID REGIME: (10-12MA, Q~10, bN 2.5, HH1.2) - Accessibility of Improved H-mode: q(0)>1; Ploss/Pthr >2 Sustainment of Improved H-mode: prevention of sawteeth - NTM suppression Prevention of He and impurity accumulation STEADY STATE REGIME: (9MA, bN=3.0, Q 5, HH=1.4-1.6) ITB formation and sustainment at high bN, TeTi , low vtor Control of q and pressure profiles Compatibility of core and edge transport barriers RWM suppression: plasma rotation; feedback stabilization Prevention of He and impurity accumulation

Summary-II ITER design issues that need urgent input from the ITPA Edge Pedestal Group: Design of coils to mitigate / control ELMs (acceptable island size in the core plasma) Pellet injection for ELM control (inboard or outboard) Heat load on first wall (especially due to ELM) Major ITER Modelling tasks: Development and testing of theory-based transport models for core, pedestal and SOL, including ITBs and effects of ELMs Projections of ITER performance in three basic operating regimes Testing profile stiffness predicted by GLF23 and Multi-Mode transport models against experimental database

2005 ITPA-IEA Joint Experiments TP-1 Steady state plasma development (E) TP-2 Hybrid regime development (E) TP-3.1 Obtain and sustain high performance operation with Te~Ti, including in hybrid/AT discharge (P) TP-3.2 Physics investigation of transport mechanisms with Te~Ti at high density (D) TP-4.1 Similarity experiments with off-axis ICRF-generated density peaking (E) TP-4.2 Low momentum input operation of hybrid/AT plasmas (P/D) TP-4.3 Electron ITB similarity experiments with low momentum input (E) TP-5/PEP-14 QH/QDB plasma studies (E) TP-6 Obtain empirical scaling of spontaneous plasma rotation (NEW) (D/P?) TP-7 Measure ITG/TEM line splitting and compare to codes (NEW) (E) TP-8.1 ITB similarity experiments (E) TP-8.2 Investigation of rational q effects on ITB formation and expansion (E) TP-9 H-mode aspect ratio comparison (NEW) (E) CDB-2 b confinement scaling in ELMy H-modes: b degradation (E) CDB-4 Confinement scaling in ELMy H-modes: n* scans at fixed n/nG (E) CDB-6 Improving the condition of Global ELMy H-mode and pedestal DBs: Low A (NEW) (E) CDB-8 * scaling along an ITER relevant path at both high and low beta (NEW) (E) PEP-1/3 Dimensionless identity experiments in JET and JT-60U (E) PEP-2 Pedestal Comparison and r* scan (E) PEP-6 PEP-6 Pedestal Strucure and ELM stability in DN (MAST and AUG) (E) PEP-7 Pedestal width analysis by dimensionless edge identity experiments on JET, ASDEX Upgrade, Alcator C-Mod and DIII-D (E) PEP-9 NSTX/MAST/DIII-D Pedestal Similarity (E) PEP-10 The radial efflux at the mid-plane and the structure of ELMs (NEW) (E) PEP-12 Comparison between C-Mod EDA and JFT-2M HRS regimes (E) PEP-13 Comparison of Small ELM regimes in JT-60U, AUG and JET (E) PEP-14 QH/QDB Comparison in JT-60U and DIII-D (E) PEP-16 C-MOD/NSTX/MAST small ELM regime comparison (NEW) (E)

2004 ITPA-IEA Joint Experiments TP-1 Steady state plasma development TP-2 Hybrid regime development TP-3 Assess performance with Te~Ti operation and/or dominant electron heating TP-3.1 and 3.3 Obtain and sustain high performance operation with Te~Ti, including in hybrid/AT discharges TP-3.2 Physics investigation of transport mechanisms with Te~Ti at high density TP-4 Investigation of high performance operation with low external momentum input TP-4.1 Similarity experiments with off-axis ICRF-generated density peaking TP-4.2/4.4 High performance operation with low momentum input in hybrid and AT plasmas TP-4.3 Electron ITB similarity experiments with low momentum input TP-5/PEP-14 QH/QDB plasma studies TP-8 ITB similarity experiments CDB-2 b confinement scaling in ELMy H-modes: b degradation CDB-3 CDB-3 Improving the condition of Global ELMy H-mode and pedestal Databases, in particular with H data CDB-4 Confinement scaling in ELMy H-modes: n* scans at fixed n/nG CDB-5 Inside and vertical pellet launch: ELM behaviour CDB-6 Improving the condition of Global DBs: Low A CDB-7 Ohmic identity experiments: test of scaling with dimensionless parameters PEP-1 &-3 Dimensionless identity experiments in JET and JT-60U PEP-2 JET/DIII-D Pedestal Comparison PEP-6 PEP-6 Edge transport barrier formation and confinement in exact double null configurations PEP-7 Dimensionless identity experiments on Alcator C-Mod and JET PEP-9 NSTX/MAST/DIII-D Pedestal Similarity PEP-10 The impact of the first wall on ELMs PEP-12 Comparison between C-Mod EDA and JFT-2M HRS regimes PEP-13 Comparison of Small ELM Regimes in JT-60U and AUG PEP-14 QH/QDB Comparison in JT-60U and DIII-D