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Transcript of Key Issues in Plasma-Wall Interactions for ITER The European Approach V. Philipps, J. Roth, A....
Key Issues in Plasma-Wall Interactions for ITER
The European Approach
V. Philipps, J. Roth, A. Loarte
With Contributions
G.F Matthews H.G.Esser G. Federici
J.P.Coad U.Samm M. Mayer
J.Strachan P.Wienhold P.Andrew
M.Stamp A. Kirschner G. Pautasso
M. Rubel W. Jacob
Key Issues in Plasma-Wall Interactions for ITER
The European Approach
V. Philipps, J. Roth, A. Loarte
With Contributions
G.F Matthews H.G.Esser G. Federici
J.P.Coad U.Samm M. Mayer
J.Strachan P.Wienhold P.Andrew
M.Stamp A. Kirschner G. Pautasso
M. Rubel W. Jacob
EU-PWI-Task Force
EPS 2003, Petersburg
Magnetic Confinement Fusion is ready to build a first machine delivering 500 MW fusion power : ITER
Controlled Thermonuclear Fusion has the potential to open a new primary energy source to mankind
The fuel (deuterium and lithium) is cheap and worldwide accessible
– This is also a contribution to a peaceful world
EU-PWI-Task Force
EPS 2003, Petersburg
Magnetic Confinement Fusion
EU-PWI-Task Force
EPS 2003, Petersburg
ITER – a worldwide undertaking
Europe, Russia, Japan, Canada, USA, China, S.-Korea
goals• 500 MW fusion power, Q=10 with burn time 7 min
• Quasi-steady-state plasma operation,with Q=5 and 'Hybrid' scenarios with pulse length up to 30 min
• Integration of physics and technology (Tritium, breeder blanket, super conductors, heating)
Four ITER sites offered
Four ITER candidate sites
Magnetic Confinement Fusion
V. Mukhovatov, I.3.3, Wed
JET has achieved simultaneously the essential dimensionless ITER parameters
Confinement
Pressure
Density
Purity
RadiationShaping
Pulse duration
From JET to ITEREU-PWI-Task Force
EPS 2003, Petersburg
JET ITER
Scaling: Plasma performance
JET ITER
EU-PWI-Task Force
PULSE LENGTH (S)
STORED ENERGY (MJ)
INPUT ENERGY/ SHOT (MJ)
DIVERTOR PARTICLE FLUENCE/ SHOT
JET 40 10 40 1x 1024
ITER 400 350 50000 4 x 1027
x10 x35 x 1000 x 4000
Challenge to Technology and Plasma Wall Interaction
ELMs and disruptions
Lifetime and T-retention
From JET to ITER
EU-PWI-Task Force
EPS 2003, Petersburg
• Control of MHD modes (NTM)
high plasma pressure
-particle heating
• Current drive efficiencies
• Control of steady state heat load
• Control of transient heat loads (ELMs and Disruptions)
• Lifetime of plasma facing components
• Long term Tritium inventory limit (350g)
ITER is an experiment to analyse these questions.
Remaining crucial issues
• All present data from carbon devices indicate a long term fuel (T) retention which would be unacceptable for ITER
JET T experience
Long term fuel (T) retention
JET (T) 10%
TFTR (T) 13%
TEXTOR (D) 8%
Similar observations in Tore-Supra and various devices
Equivalent ITER T limit (350g) would be reached in less than 50 shots
10% long term retention
EU-PWI-Task Force
EPS 2003, Petersburg
Fuel retention: present database
Of injected fuel
T. Loarer P-1.161, Mon
EU-PWI-Task Force
EPS 2003, Petersburg
ITER
700m2 Be first wall Low Z Oxygen getter
100m2 Tungsten low erosion
50 m2 Graphite CFC no melting
ITER wall material Choice
A European Task Force on Plasma Wall Interaction has been formed to focus the EU- PWI research on the critical questions of Tritium retention and Wall Lifetime.
A European Task Force on Plasma Wall Interaction has been formed to focus the EU- PWI research on the critical questions of Tritium retention and Wall Lifetime.
ITER has different first wall materials
Simple extrapolation from present full carbon devices is not possible.
Must be based on physics understanding.
Long term tritium retention
EU PWI Task Force Strategies
Understand (better) the mechanism of fuel retention in present devices
• Improve predictions for ITER
• Develop Tritium control techniques
A
Develop Tritium removal techniques that are applicable for ITER
B
Develop a full metal Tokamak scenario
C
EU-PWI-Task Force
EPS 2003, Petersburg
EU PWI Strategies
EU-PWI TF structure
• Coordinated experiments and data analysis in JET (Task Force E & FT) and
EU Fusion associations
• Accompanying Technology Programme
• Contact persons in each association
EU-PWI-Task Force
EPS 2003, Petersburg
Diffusion along pores
Implantation(saturates)
D+ D+
C
Erosion area Deposition area
Remote area
• Tritium is retained by co-deposition with carbon, on the plasma facing sides or on remote areas
Understanding of T-codeposition is understanding of
where and how carbon is eroded and
how carbon migrates globally and locally
Fuel retention: Understanding
Co-ordinated research in Tokamaks and lab experiments in PWI-TF
EU-PWI-Task Force
EPS 2003, Petersburg
outer
Erosion and Deposition in Divertor (1)
P. Coad et al, PSI GIFUJET gas JET gas box, box, 5750 shots
Ero
-dep
osi
tio
n (m
)
JT-60 4300 shots
inner
Inner Divertor tileEro
-dep
osi
tio
n (m
)
Outer Divertor tile
Y. Gotoh et al , PSI GIFU
Inner Divertor is deposition dominated in all devices
The outer divertor can be erosion or deposition dominated
Depending on ?
In/out asymmetry of Divertor Conditions
Differences in SOL || Flows
Influence of temperature
Divertor Geometry
Adressed in PWI-TF
EU-PWI-Task Force
EPS 2003, Petersburg
ASDEX Upgrade, PSI 2002, V. Rohde
Inner Divertor
Outer
V.Rohde P-1.154, Mon
Erosion and Deposition in Divertor (2)
1
4
3
6
5
• Beryllium is deposited on the plasma facing areas, no transport to shadowed regions
• Carbon and deuterium is mainly transported to shadowed areas
Transport to remote areas is specific to carbon
EU-PWI-Task Force
3
4
C: Be = 10:1
CarbonBeryllium G. Matthews P-3.198, Thurs
Carbon
Erosion and Deposition in Divertor (3)
EU-PWI-Task Force
EPS 2003, Petersburg
Local geometry determines the C-deposition on the louver entrance
QMB and sticking monitors (M. Mayer O-2.6A, Tues) show that the
carbon deposition is mainly line of sight of the place of origin
Quartz monitor (QMB)
1 2 3
3
0,0
0,2
0,4
0,6
0,8
1,0
1,2
Configuration
C-d
epo
siti
on
(n
m/s
)
1
22
3
Erosion and Deposition in Divertor (4)
EU-PWI-Task Force
EPS 2003, Petersburg
13CH4 tracer injection in TEXTOR
LCFS13CH4
Plasma
P. Wienhold. A. Kirschner, PSI 2000
Modelling of erosion and redeposition
A. Kirschner et al
240230 250 260220
-170
-160
-150
-140
-130
-180
RC [cm]
ZC [cm]
C0 Density
• With standard assumptions (2% erosion yield, „TRIM“ sticking of redeposited species):
- modelled C-fluxes to the louvres much too low (JET) and - locally redeposited carbon (TEXTOR) much too low
• Good matching of Be transport
JET MKIIA
EU-PWI-Task Force
EPS 2003, Petersburg
Assumptions: carbon atoms eroded in a first step can be re-eroded with higher yields after re-deposition
Enhanced movement of carbon along surfaces to shadowed areas
Assumptions: carbon atoms eroded in a first step can be re-eroded with higher yields after re-deposition
Enhanced movement of carbon along surfaces to shadowed areas
Trim sticking for ions, zero sticking for CxHy
8% re-erosion of re-deposited carbon species
Understanding of carbon transport
Physics of sticking and re-erosion is the key to understand carbon long range transport
Substrate chemical erosion Yield 2 - 3%
D CH4
DCH4CH+
Shadowedareas
Graphite
Tungsten
Standard assumptions
Carbon deposition: 5% of C-erosion flux 0.7 gT retention / ITER shot
Enhanced re-erosion
Carbon deposition: 14% of C-erosion flux 2 gT retention / ITER shot
Eroded carbon can escape towards the dome and dome pumping ducts
T-removal should be considered there
EU-PWI-Task Force
EPS 2003, Petersburg
Modelling for ITER Divertor
A. Kirschner P-3.196, Thur
Modelling
EU-PWI-Task Force
EPS 2003, Petersburg
Erosion redeposition in divertor: summary
• Inner divertor deposition dominated always
• No unique behaviour of outer divertor
• Long range transport is specific of carbon
• Main chamber erosion dominated area in general (with local or global material redistribution)
• The material deposited in the divertor is mainly from main chamber erosion (mostly C at present, Be in ITER)
JET: material balance, divertor Be deposition
AUG: material balance and tungsten divertor experience
DIII: spectroscopic analysis
Main chamber ion PWI is significant and underestimated in the past
”long tails” in SOL ne & Te seen in many experiments
ASDEX Upgrade
Te
ne
• larger divertor closure moderate decrease of neutral pressure in main chamber
• minimum main chamber pressure set by main chamber ion plasma wall contact
• main chamber contact determined largely by ELMs?
J. Neuhauser et al.
SOL profilesNeutral Pressure measurements
EU-PWI-Task Force
EPS 2003, Petersburg
Main chamber Plasma Wall Interaction (1)
W.Fundamenski O-4.3C, Fri
A.Herrmann P-1.155, Mon
B. Lipschultz P-3.197, Thurs
A.Kallenbach P-1.159, Mon
Main chamber Plasma Interaction is main topic in TF work
EU-PWI-Task Force
EPS 2003, Petersburg
Main chamber erosion• Absolute main chamber PW interaction
Divertor / First Wall fluxes: 12 (JET), 10 (AUG), 50 (ITER modelling)
• Erosion Mechanisms Ions versus Neutrals
• Erosion Location HFS versus LFS
Material migration
• Measurements and understanding of SOL Flows Modelling based on ExB and Bxgrad B drifts
underestimates measured flows
Important to predict ITER outer divertor behaviour
Main chamber Plasma Wall Interaction (2)
EU-PWI-Task Force
EPS 2003, Petersburg
The ITER Be-first wall will reduce the Carbon deposition and associated T-retention
1. No C-flux into the divertor, but a similar Be-flux
[present modelling: 6 g Be/shot, better quantification needed]
2. Be is not transported to remote areas
3. Be-layers on the plasma facing sides of the divertor contain less T and are easier to access for cleaning
4. Chemical sputtering of the underlying C-substrate in the inner is reduced/suppressed
T-retention: Extrapolation to ITER
Be transport and influence of Be deposition on carbon erosion & transport are key questions for ITER ( PWI TF)
EU-PWI-Task Force
EPS 2003, Petersburg
Chemical erosion completely suppressed by adding 0.1 % Be to the plasma
Questions to address
• Thermal stability of Be layer during transient heat pulses
• Be erosion-deposition in the outer divertor
PISCES
R. Doerner P-2.162, Tues
Beryllium experiments in PISCES
EU-PWI-Task Force
EPS 2003, Petersburg
Fuel removal and control
Control of fuel retention and fuel removal will be essential in any wall material scenario and needs more attention in
present research (major topic of PWI-TF work)
Fuel Removal
• Isotope exchange on PFC side
• Thermal desorption on PFC side
• Oxygen venting remote areas?
• Scavenger techniques ??
and Fuel Control
• Temperature tailoring
• Carbon traps
• Divertor geometry …
Work in plasma simulators
+
Dedicated lab experiments
+
Tokamak research
Needs detailed understanding of the involved physics
EU-PWI-Task Force
EPS 2003, Petersburg
Full metal wall: wall lifetime
Steady state erosion
• Low erosion materials
• High local re-deposition
• Lost material replaced from main chamber
D+
99.8 0.002
Plasma
Divertor Strike zones
If the T-retention problem cannot be solved a full metal first wall concept is needed based on metals with low hydrogen retention
Plasma compatibilityWall Lifetime
Transient events
The main concern with metal walls is the lifetime due to melt layer erosion in transient heat loads (ELMs and Disruptions)
Particle flux
Stored energy
EU-PWI-Task ForceLifetime ELMs & Disruptions (1)
• In ELMs or disruptions part (<10%) or all of the plasma-stored-energy is lost on a short-time scale to the walls
Material limits T < 2300o (C), < 3400o (W)
T energy/ area/ sqrt(time)
Wetted area Duration of ELMsEnergy on target plates
20 (40) MJ m-2 s -1/2
Divertor wetted area during ELM similar to between ELMs
some ELM energy can reach the main chamber
T. Eich, A. Herrmann, this meeting
EU-PWI-Task Force
Duration of Divertor ELM Energy Pulse well correlated with II B Ion Transport 220s for ITER
Elm / in between Elm
Lifetime ELMs & Disruptions (2)
EU-PWI-Task Force
EPS 2003, Petersburg
number of ELMs for 1000 ITER pulses 4 x 105
Predictions for ITER divertor target lifetime
ITER Predictions
ELMs are marginally acceptable but behaviour for CFC and W not much different at moderate power densities
Lifetime: ELMS & Disruptions (3)
G. Federici et al.
Disruption Energy deposition
(Thermal Quench) occurs over a
large divertor area (AUG & JET)
Fraction of energy deposited in
Divertor: 1 (AUG), ~ 0.2 (JET)
ASDEX Upgrade
Poloidal Distance (m)
V. Riccardo, I.3.5. Wed
G. Pautasso P-1.135, Mon
P. Andrew P-1.54, Mon
EU-PWI-Task Force
EPS 2003, Petersburg
Disruptions: Present ITER specifications
All disruption energy is lost at the strike zones
with narrow deposition (broadening of 3)
half of the melt layer is lost per event
Lifetime: ELMS &Disruptions (4)
EU-PWI-Task ForceD
isru
pti
on
en
erg
y d
en
sit
y,
MJ
/m2
SOL broadening, lambdaplate
/lambdamid
Current ITER specifications
G. Federici, ITER JWS Garching, 7 Oct. 2002
Absence of melting for W
lambdamid
=5 mm
Dis
rup
tio
n e
ne
rgy
de
ns
ity
(M
J)
1
0.5
0.1
0.1
1
10
100
0 5 10 15 20 25 30
Fraction of energy to divertor
• Spatial and Time Evolution of thermal Energy Flux
• Dependence on Disruption Type
• Energy Balance during Current
Quench (Halo Currents)
PWI TF issues
Disruptions energy deposition and mitigation are key issues for the ITER material selection
SOL Broadening
Lifetime: ELMS &Disruptions (5)
• Development of disruption mitigation techniques
• Power exhaust on irregular, molten surfaces
EU-PWI-Task Force
Conclusions (1)
Predictions for long term tritium retention for ITER are critical, but are from full carbon machines. An integrated approach and understanding of
• Where and how impurities are produced in the main chamber
• How they are transported towards the divertor
• How the material is transported inside the divertor
• Influence of Be deposition on carbon erosion and transport
is necessary to predict the T retention under the ITER wall material conditions.
EU-PWI-Task Force
Conclusions (2)
In parallel co-ordinated work is necessary on
• In situ control of T retention
• Fuel (T) removal which can be employed under ITER conditions
• Disruption power deposition characteristics
• Disruption mitigation
More Tokamak experience is needed for metal wall conditions
• High Z first wall, tokamak behaviour under non- carbon wall conditions
• Be first wall with carbon and tungsten in the divertor
R.Neu P-1.123, Mon
EU-PWI-Task Force
Additional remarks
• A graphite and a tungsten divertor should be prepared in parallel.
• Possibilities to measure the fuel retention in the non activated phase of ITER are needed.
• The possibility to change ITER in a later state from a low to a high Z first wall should be evaluated.
• ITER needs flexibility to adopt Tritium control and removal techniques that have to be developed in parallel and tested in present devices.