1. 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

2. 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

3. 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)

4. 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

5. 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

6. 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

7. 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= )
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

8. 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) (averaged for 5 scalings)
ITER Physics J.Snipes,2000
Guidelines (2001) J.Snipes,2000
ITER Physics J.Snipes, 2002
Guidelines (2004) F.Ryter, 2002
T.Takizuka, 2004
Threshold Group Y.Martin [Vilamoura, 2004]
recommendation Y.Martin [Vilamoura, 2004]
Threshold Group Draft PIPB (2005)
recommendation
What scaling is recommended by the Threshold Group?

9. 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

10. 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 % in average
A.Polevoi et al, 10th IAEA Technical Meeting on H–mode Physics and Transport Barriers, St.Petersburg, Sep 2005

11. 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

12. 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= MW to operate in Improved H-mode
L.Gionnone et al PPCF 46 (2004) 835

13. 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 s 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

14. 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
RWM can be stabilized by saddle coils if w <10
Y. Liu et al Nucl. Fusion 45 (2005) 1131

15. 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

16. 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

17. 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

18. 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= )
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

19. 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

20. 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)

21. 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