iter-feat physics pr/djc/oct00 · design basis and physics issues for iter • confinement and...
TRANSCRIPT
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EFDA ITER
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________________________________________________________________________________
THE PHYSICS OF ITER-FEATpresented by D J Campbell
EFDA, Close Support Unit - Garching
Acknowledgements:
Members of the ITER Joint Central Teamand Home Teams
42nd APS-DPP/ ICPP-2000, Québec City, 23-27 October 2000
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EFDA ITER
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________________________________________________________________________________
Synopsis
• ITER-FEAT Goals
• Physics design rules for ITER
• New ITER design
• Performance predictions:
• operating space for inductive operation• requirements for steady-state operation
• Design basis and physics issues:
• Confinement and transport• MHD stability and control• Divertor performance• Alpha-particle physics
• Conclusions
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EFDA ITER
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________________________________________________________________________________
ITER-FEAT GoalsPlasma Performance
• achieve extended burn in inductively drivenplasmas with the ratio of fusion power to auxiliaryheating power of at least 10:
• for a range of operating scenarios
• with a duration sufficient to achieve stationaryconditions on the time scales characteristic ofplasma processes.
• aim at demonstrating steady-state operation usingnon-inductive current drive with the ratio of fusionto current drive power of at least 5
• the possibility of controlled ignition should not beprecluded
Technology
• demonstration of integrated operation oftechnologies essential for a fusion reactor
• testing of components for a fusion reactor
• testing of concepts for a tritium breeding module
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EFDA ITER
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________________________________________________________________________________
Physics Design Rules
Confinement
• IPB98(y,2) ITER Physics Basis energyconfinement scaling (variations of scaling havealso been investigated):
τE,thELMy = 0.144 × I0.93B0.15P−0.69n
e,200.41M0.19R1.97ε0.58κ
eff0.78
• H-mode threshold scaling with isotope correction:
Pthr = 2.84 ×M−1B0.82n
e,200.58R1.0a0.81
MHD stability
• safety factor: q95 = 3
• elongation: determined essentially bytriangularity: control requirements
• density: ne ≤ nGW
• beta limit: βN ≤ 2.5
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EFDA ITER
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________________________________________________________________________________
Scrape-off layer/ Divertor
• peak target power: ≤10MWm-2
• helium content: simplified core/edge transportmodel
or: τHe∗ / τE ~ 5
• impurity content: nBe / ne = 0.02plus contribution from sputteredcarbon and seeded noble gasto limit peak target power
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
H-Mode ScalingsPower threshold Energy Confinement
ASDEX
AUG
C-MOD
DIII-D
JET
JFT-2M
JT60-U
PBX-MPDX
10.001.000.100.01τth (s)IPB98(y,2)
0.01
10.00
1.00
0.10
τ th
(s)
DB2P8=1
ER
99.1
.164
ITER-FEAT
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EFDA ITER
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________________________________________________________________________________
Device ParametersParameter ITER
κ95, κx 1.70, 1.85
δ95, δx 0.33, 0.49
R, a (m) 6.20, 2.0
R/a 3.1
Vol (m3) 828
B (T) 5.3
Ip (MA) 15.0
tburn (s) ≥300
<n>/nGW 0.85
<n> (1020m-3) 1.01
<Te>, <Ti> (keV) 8.8, 8.0
Zeff,axis 1.69
nHe,axis/ne (%) 4.3βN 1.8
β (%) 2.5
Pfus (MW) 400
Lwall (MWm-2) 0.47
Q 10
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EFDA ITER
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________________________________________________________________________________
ITER Poloidal Elevation
OperatingTemperature
20000 1000
PF5
PF4
PF3
PF2
PF1
TF Coil
CS
Blanket
VacuumVessel
Cassette
PF6
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
ITER: Main Design Features
Central Solenoid
Outer Intercoil
Structure
Toroidal Field Coil
Poloidal Field Coil
Machine Gravity
Support
Blanket Module
Vacuum Vessel
Cryostat
Port Plug
(EC Heating)
Divertor
Torus
Cryopump
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EFDA ITER
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________________________________________________________________________________
Heating and Current Drive
• Heating and current drive functions:
• heating plasmas through H-mode transition andto burn
• control of plasma burn point
• current drive for hybrid/ steady state operation
• localized current drive for mhd stability control
• plasma start-up assist, wall conditioning
• Proposed initial heating and current drivecapability: total power = 73MW
• 20MW of ECRF at 170GHz
• 20MW of ICRH in range 35-55MHz
• 33MW of 1MeV negative ion based NBI
• Additional capability for mhd control orsteady-state current drive foreseen, totalling>100MW
• this could include ~20MW of LHCD at 5GHz
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
ITER Plasma Equilibria
-5
-4
-3
-2
-1
0
1
2
3
4
5
3 4 5 6 7 8 9
Z, m
R, m
0.4MA
1.5MA
2.5MA
3.5MA4.5MA
5.5MA
SOH,SOB
XPF
11.5MA
6.5MA
-8
-6
-4
-2
0
2
4
6
8
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Z, m
R, mC
S3U
CS
2UC
S1U
CS
1LC
S2L
CS
3L
PF1PF2
PF3
PF4
PF5PF6
g1g2
g4
g3
g5
g6
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
Performance in Pulsed Operation
Q=10 at 15MA (q95=3) Q=50 at 17MA (q95=2.6)
0.7 0.8 0.9 1.0 1.1 1.2 1.3
1000
800
600
400
200
0
HH(y,2)
Fusi
on P
ower
(M
W) β
N = 3.0
βN = 2.0
βN = 2.5ne / nGW = 0.85
Ploss/PLH = 1
No
Solu
tion
n e / n GW
= 1.0
Ploss/PLH = 1.3
IP=15 MA, Q=10 (AN=0, AT=2.15, Ar=0.12%)
0.7 0.8 0.9 1.0 1.1 1.2 1.3
1000
800
600
400
200
0
Fusi
on P
ower
(M
W)
βN = 2.0
Ploss/PLH=1
No
Solu
tion
n e/nGW
= 1.
0
Ploss/PLH=1.3
βN = 2.5
ne/nGW = 0.85
IP=17 MA, Q=50 (AN=0, AT=2.15, Ar=0.12%)
HH(y,2)
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EFDA ITER
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________________________________________________________________________________
Q=10: Plasma Profiles
• Plasma profiles I=15MA, Paux=40MW, H98(y,2)=1
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EFDA ITER
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________________________________________________________________________________
ITER Performance
• At Q=10, fusion power is 200-700MW atH98(y,2)=1
• Neutron wall loading at H98(y,2)=1 variesbetween 0.23MWm-2 and 0.80MWm-2
• so there is still scope for technology studies
• Q=10 operational space has a margin indensity against the Greenwald value:
• at βN=1.5, H98(y,2)=1, Q=10 can be achieved atn/nGW~0.7
• ‘Controlled ignition’ (Q=50) can be attained inITER:
• in an inductive advanced scenario (H98(y,2)~1.2)
• if operation at n>nGW is possible
• if high confinement can be sustained at q95<3
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
Hybrid Operation: Q=5
100
1000
0 10 20 30 40 50
R/a= 6.35m / 1.85m, βN≤2.5
R/a= 6.20m / 2.00m, βN≤2.0
R/a= 6.20m / 2.00m, βN≤2.0, 1.5D
Bur
n T
ime
(s)
Fusion Gain Q
ne/n
G = 0.85
3000
500
IP≤17MA, 400MW ≤ P
f ≤ 700MW
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
Steady-State Operation: Q=5open - without impuritiesclosed - with impurities
1.0
1.2
1.4
1.6
1.8
2.0
8 9 10 11 12 13
HH
-fac
tor
IP (MA)
2.0
2.5
3.0
3.5
4.0
8 9 10 11 12 13β
N
IP (MA)
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
Hybrid and Steady-StateOperation
• Hybrid operation allows long pulses (~2000s)to be produced for technology testing
• Q=5 requires H98(y,2)~1 and βN=2.5
• this mode of operation should allow true steady-state to be developed gradually
• 1.5-D analysis of steady-state operation showsthat Q=5 requires:
• H98(y,2)≥1.5, βN≥3.5 for 9≤Ip≤12 and n/nGW≤1
• Ibs/Ip~40-50%
• These requirements imply that scenarios withactive profile control would be required
• βN values required imply that stabilization forresistive wall modes necessary
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
Design Basis and PhysicsIssues for ITER
• Confinement and transport
• MHD stability and control
• Divertor performance
• Alpha-particle physics
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EFDA ITER
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________________________________________________________________________________
J G Cordey et al, Plasma Phys Control Fusion 38 (1996) A67
H-Mode Confinement:Non-Dimensional Scaling
0.1��
0.1��
1��
10��
1��
10��B τITERH93–P�
�
Bτ t
h� �
(I) DIII–D��(I) JET��
(II) JET����
(II) DIII–D��
DIII–D βn = 2.0��
ρ* scans��
JET βn = 1.5��JET βn = 1.6��JET βn = 2.0��τ ITER��
JG97
.293
/5c�
�
• JET/ DIII-D comparisons (for example) showBτE scaling in an almost gyro-Bohm fashion
( B Eτ ρ~ *−3) - star shows ITER-1998
• independently derived global scalingexpressions have approximately gyro-Bohmdependence
• analysis of local transport coefficients confirmsgyro-Bohm form in ELMy H-modes
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EFDA ITER
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________________________________________________________________________________
Core-Edge Integration• At the reactor scale plasmas must
simultaneously:
• exhibit good core confinement• operate at high density (n~nGW)• possibly operate close to H-mode threshold• dissipate exhaust power (significant radiation)
• Core-edge integration issues
• core and pedestal confinement scale differentlyfrom existing experiments to ITER scale
• current experiments matching ITER coredimensionless parameters have ‘low density’edges, typically well above the H-modethreshold, and with low to moderate radiation
• only an ITER-scale device can maintain reactor-relevant core parameters with reactor-relevantedge
• operation at high density with low NBI fuellingwill necessitate application of reactor relevantfuelling techniques
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EFDA ITER
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________________________________________________________________________________
Triangularity Issues
• Wedged TF construction allows segmentedcentral solenoid, providing additional flexibilityin equilibrium control ⇒ higher triangularity
• limit in ITER is probably set by approach toDNX configuration - require ∆sep≥4cm fromdivertor modelling
• Although triangularity does not appearexplicitly in confinement scaling:
• increased triangularity increases currentcapability
• JET and ASDEX Upgrade have found highconfinement can be maintained at densitiescloser to nGW with increasing triangularity
• In contrast, with increasing triangularity, ELMfrequency decreases and heat pulses todivertor may cause increased erosion
• high density operation, pellet injection, oralternative access to alternative H-moderegimes may moderate ELM behaviour
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EFDA
ITER _________________________________________________________________________________________________________________________
_________________________________________________________________________________________________________________________
(J Paméla et al, 18th IAEA Conference, Sorrento, 2000) (O Gruber et al, 18th IAEA Conference, Sorrento, 2000)
Influence of Triangularity on ConfinementJET ASDEX Upgrade
density / empirical Greenwald density
HH-98PITER-FEAT
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EFDA ITER
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________________________________________________________________________________
(Y Murakami et al, Journal of Plasma and Fusion Research (to be published))
Sawtooth Simulation in ITER
• Sawteeth have small effect on fusion power
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EFDA ITER
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________________________________________________________________________________
Disruptions
There are 3 main issues arising from disruptionsand vertical displacement events:
• Thermal quench, involving ~300-500MJ:
• vapour shield formation expected to mitigatethermal quench effects (energy totarget<<10%)
• Current quench/ VDE involving ~0.5GJ ofenergy:
• eddy currents and halo currents give rise toelectromagnetic forces (up to ~104 tonnes)
• Runaway electrons might be produced byavalanche effect in cold, impure post-disruption plasma:
• calculations for the new ITER design indicatethat the total energy involved could be limited to~20MJ
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EFDA ITER
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________________________________________________________________________________
β-Limit - Neoclassical Modes
• Evidence from many tokamaks shows thatmost severe constraint on β is the growth ofneoclassical tearing modes:
• such modes are often observed in the regionβN~1.5-3
• extensive experimental evidence that critical βNdepends on (ρ*)µ, with 0.7≤µ≤1
• Experimentally (3,2) and (2,1) modes are mostcommon:
• (3,2) modes lead to degradation of confinement• (2,1) modes often cause disruption
• Theory of such modes is well-developed:
• however, predictive capability limited by needfor a ‘seed-island’ to trigger mode growth
• Expected mode growth time in ITER in range10-100s, allowing time for counter-measures:
• ECCD stabilization experiments now underway
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
R J LaHaye et al, Phys Plasmas 7 3349 (2000)
β-Limit - Neoclassical Modes
• Analysis of the critical βN for the onset of (3,2)NTMs has been carried out across severaldevices:• βN∝ρ*f(ν) is consistent with theory based on
(stabilizing) ‘polarization current’ theory
• Indicates neoclassical modes could beexpected in ITER operating region
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
G Gantenbein et al, Phys Rev Lett 85 1242 (2000)
Stabilization of NTMs
#12257
NBI Power (MW)
4.0
8.0
ECRH Power x 5 (MW)
0.0
4.0
8.0
Stored Energy (kJ)
400500600700
n=2 Amplitude (a.u.)
0.0
Scaled Energy (kJ)
2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.82.6time (s)
Shift of EC Resonance (cm)
02468
• Experiments with modulated ECCD in ASDEXUpgrade have successfully suppressed NTMs
• success achieved on several tokamaks• recovery of initial β remains a key issue• calculations predict that ~20-30MW of ECRF
power required for stabilization in ITER
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
MHD Stability
• Main influence of sawteeth is likely to be viageneration of seed islands for neoclassicaltearing modes (NTMs)
• however, test of m=1 theory is required atreactor scale to address role of α-particles insawtooth stabilization and fishbones
• Disruption thermal loads, forces, and halocurrents will allow investigation of reactor-relevant phenomena
• ITER will operate in range βN~1.5-2.5, whereNTMs might occur
• stabilization of NTMs by ECCD/ LHCD has beensuccessfully demonstrated on several devices - such a system is foreseen for ITER
• In steady-state scenarios, resistive wall modesare likely to determine β-limit - if theoreticallimit can be reached
• a system of external stabilization coils forlow-m, n=1 RWMs is in under design
• coil set also used for error field correction
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
Divertor Issues
• Long pulse capability of ITER makes divertorperformance critical - main issues:
• peak power load• helium fraction• control of density and fuel mixture• impurity content• transient power loads - ELMs, disruptions
• Divertor design developed from experience incurrent tokamaks
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
A S Kukushkin et al, 14th PSI Conference, Rosenheim, 2000
Divertor Modelling
0
4
8
12
16
qpk
[MW/m 2]
ns [10 20m-3]
0.24 0.26 0.28 0.3 0.32 0.34 0.36FEAT:
geometry variation
86MWstraight86MWold V86MWnew V100MWstraight100MWold V100MWnew V130MWnew V
• Modelling using B2-EIRENE for ITER showsthat under partially detached conditions, peakpower load on outer divertor remains below10MWm-2 over a range of separatrix densities
• V-shaped geometry used in target regionfavours development of partial detachment
• influence of impurity seeding investigated
• core Zeff lies below 1.6
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EFDA ITER
________________________________________________________________________________
________________________________________________________________________________
A S Kukushkin et al, 14th PSI Conference, Rosenheim, 2000
Helium Exhaust - Modelling
0.001
0.01
0.1
100 150 200 250Γ
DT [Pa-m 3s-1]
c He
limit
limit
OK
75 MW
86 MW
100 MW
FEAT: Power Variation (Straight, Sp=75, C)
• Predictions of core helium concentration as afunction of fuel throughput, ΓDT, for ITER
• an installed fuelling capacity of 200Pam3s-1
should ensure that the core heliumconcentration can be held below 6%.
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EFDA ITER
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A Loarte et al, 18th IAEA Conference, Sorrento 2000
ELM Power Loading
0
0.05
0.1
0.15
0.2
0.25
0.01 0.1 1 10
DIII-DJETASDEX-U
ν*
∆W
EL
M/W
ped
ν*ITER
• Recent analysis of ELM energy loss indicatesthat pedestal collisionality and paralleltransport time in the SOL are important
• extrapolation to ITER would imply type I ELMamplitude of ~10MJ
• this would pose problems for the divertorlifetime
• alternative H-mode operational regimes wouldbe desirable (eg type II ELMs, EDA)
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EFDA ITER
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Divertor Performance• Detailed modelling underway:
• steady-state peak power load on outer divertorcan be kept below 10MWm-2 design limit
• core helium concentration can be kept below6%, as required
• ∆sep≥4cm required to limit power load in vicinityof upper null to that of first wall generally
• Transient power loads due to ELMs anddisruptions might prove the most severe limiton target lifetime
• Use of inside pellet launch and hightriangularity plasmas can provide tools forachieving high confinement at high density
• Co-deposition and retention of tritium must beaddressed by development of appropriateconditioning techniques
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EFDA ITER
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Alpha Particle Physics• Key issue is that α-particles should slow down
classically and provide efficient heating
• extensive experience in experiments withenergetic particle populations produced byauxiliary power systems
• TFTR and JET DT experiments confirmα-heating as expected (within uncertainties)
• TF ripple losses must be within first wallpower loading constraints:
• theory well validated by experiments in severaltokamaks
• acceptable TF ripple losses in steady-stateconditions will require ferromagnetic inserts
• ITER will permit models of interaction withmhd instabilities to be tested:
• formalism exists for analyzing interaction withsawteeth, fishbones, kinetic ballooning modes,localized interchange modes
• interaction with NTMs and ELMs conjectural
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EFDA ITER
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• Alfvén eigenmodes:
• extensive validation of numerical codes againstexperimental observations
• ITER-1998 expected to differ from presentexperiments in that many modes with n>10could be excited
• many of critical parameters in ITER (βα(0),vα/vA, R∇βα) differ little from ITER-1998(~20%)
• certain parameters (ρα/a) differ by up to afactor of 1.5
• Analysis of α-particle behaviour for ITERplasma conditions is now being initiated
• it is expected that unless unstable modesoverlap and extend to wall, non-linearredistribution of α-particles may simply resultsin profile broadening
• complications arising from 1MeV beam ions willhave to be addressed in parallel
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EFDA ITER
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Conclusions• The new ITER design has been derived from:
• the ITER Physics Basis, which has beenvalidated in the experimental tokamakprogramme
• engineering methodologies and guidelineswhich have been established during the ITEREDA
• The design can fulfil the requirements of theITER programme:
• a significant margin for Q=10 inductiveoperation
• long pulse inductive operation appropriate forstudy of mhd stability and divertor operation(including helium exhaust)
• capability for studying steady-state scenarios atQ=5
• possibility of achieving ‘controlled ignition’ underfavourable conditions
• physics processes, including α-particle physics,will be characteristic of reactor scale plasmas
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EFDA ITER
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• Major physics issues:
• maintenance of high confinement at highdensity
• control of NTMs and their impact on the β-limit
• impact of ELMs on divertor target lifetime
• tritium inventory control
• development of steady-state scenarios