ITER Design Review Activities on Steady State and Transient Power Loads in ITER

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ITER Design Review Activities on Steady State and
Transient Power Loads in ITER

• Alberto Loarte
• European Fusion Development Agreement
• Close Support Unit Garching

Acknowledgements EU-PWI TF, ITPA Divertor SOL
Group, ITER and many others
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Ramp-up/down Phase

• Requirement to maintain li lt during ramp-up/down
  ?Padd gt 10 MW
• Analysis of port limiter for ITER (Kobayashi NF
  2007) shows
• for Ip lt 6.5 MA ? qlimmax (MWm-2) PSOL(MW)
• Stable ramp-up Ptot/Prad 0.3 Ptot gt 11-14 MW
  ? PSOL gt 8-10 MW
• qlimmax gt 8-10 (MWm-2)

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New Proposed Ramp-up/down Phase

• New proposed scenario to full bore ramp-up with
  short ohmic phase (PSOL lt 3 MW) , early X-point
  formation heating
• Ramp-down in X-point configuration
• Full bore plasma large plasma near first wall
  but low PSOL

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QDT 10 steady plasma loads (I)

• All divertor tomakaks measure plasma particle
  fluxes (II B) to the main wall
• Extrapolated plasma flux to the main wall in
  ITER 1.0 - 5 .0 1023 s-1 (1-5 of Gdiv)

Lipschultz IAEA 2000
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QDT 10 steady plasma loads (II)

• Plasma fluxes predominantly on outer side of
  first wall
• Corresponding maximum IIB power densities up to
  5 MWm-2 (Upper X- point) to 1 MWm-2 near outer
  midplane and 0.4 MWm-2 near inner midplane

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QDT 10 steady C-X and radiation loads

• C-X particle fluxes vary along wall but C-X
  power fluxes change only by 2
• C-X particle flux 2 Ion flux ? 0.2-1.0 1024
  s-1 ? ltqC-Xgt 0.02-0.1 MWm-2

• Pedge gt 1.3 PL-H ? Prad lt 85 MW ? ltqradgt lt 0.12
  MW m-2

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Divertor ELM power fluxes
timescales
Time scale of divertor ELM energy flux rise
correlated with ion transport time
Eich JNM 2005 PIPB 2007
JET-Eich-JNM 2003
trise,ELM 200-500 ms
Plasma conditions affect tELMIR tII relation
(pre-ELM divertor plasma, DWELM, etc.)
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qELM(t)
Large proportion of DWELM arrives after tIR ?
smaller DTsurf for given DWELM
tdown,ELM 1-2 trise,ELM
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Divertor Area for ELM power Fluxes (I)
Ein,ELM/Eout,ELM 1-2
Eich, PIPB07
Adiv,ELM 3.5 m-2 Broadening 1
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Divertor Area for ELM power Fluxes (II)
Divertor ELM load near separatrix toroidally
symmetric but strong in/out asymmetries
TPFdiv,ELM 1.0
Loarte, PPCF03 from Leonard JNM97
DIII-D
Eich, PRL4
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Tolerable ELM size
QSPA experiments on NB31 targets show
Tolerable ELM energy density 0.5 MJm-2 no
broadening 21 in/out asymmetry ? DWELM 1MJ
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Fluxes to main wall during ELMs
Part of DWELM is reaches the main wall PFCs ?
energy flow along filaments
AUG- Herrmann PPCF06
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ELM fluxes to Main wall fluxes

• Model of II vs. I B transport during ELMs in
  agreement with experimental findings
• ELM Ti gt Te far from separatrix (Langmuir Probes
  Retarding Field Analyser)
• Deficit of divertor ELM energy for large ELMs
  (vr/cs (DWELM/DWped)0.5 Radiation)

R
JET- Pitts IAEA 2006 Fundamenski JNM 2007
Fundamenski - PPCF 2006
R
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ELM fluxes to Main wall in ITER (I)
ELM power fluxes to PFCs in ITER evaluated by
models/empirical extrapolation (input)
DWELMfilaments/DWELM , RELM, VrELM vs. DWELM
(nped, Tped), tIR (tII)

• Controlled ELM DWELM1MJ fELM20-40 Hz
• Uncontrolled ELM DWELM20MJ fELM1-2 Hz

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ELM fluxes to Main wall in ITER (II)
Average ELM power fluxes to PFCs require
knowledge of filament dynamics
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Energy Fluxes to main wall and divertor PFCs
during Marfes

• Pre-disruptive Marfes occur when plasma is
  already in L-mode
• In steady state Prad Pinp 70 -150 MW ? ltqradgt
  0.1-0.2 MWm-2
• Timescale for transient Marfes 0.01-0.1 s (no
  clear size dependence)
• Poloidal peaking lt 3

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Energy Fluxes during disruptions (I)

• Energy degradation before thermal quench for
  resistive MHD disruptions
• Large broadening of footprint for diverted
  discharges but small for limiter discharges

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Energy Fluxes during disruptions (II)

• Timescale ( R) but large variability (1.0-3.0 ms
  for ITER)
• Longer timescales in decay phase (gt 2 rise phase)

• Toroidal asymmetries (2) seen in some cases but
  poor documentation/statistics
• Systematic study of in/out asymmetries required

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Energy Fluxes during disruptions (III)
Proposed ITER specifications (M. Sugihara/M.
Shimada) Scenario 2 unit (MJ/m2)
?2.5 cm (left), 5 cm (right) Energy deposition
time duration 3-9 ms
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Energy Fluxes during disruptions (IV)
Proposed ITER specifications (M. Sugihara/M.
Shimada) Scenario 4 unit (MJ/m2)
?2.5 cm (left), 5 cm (right) Energy deposition
time duration 3-9 ms
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Energy Fluxes during disruptions (V)
Major disruptions during limiter phase (M.
Sugihara/M. Shimada)
(Kobayashi NF 07) 2 limiter case
Most severe assumption No broadening of
deposition width
If there is no broadening energy fluxes on
limiter for disruptions can be similar or larger
than for the divertor disruptions in scenario 2
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Energy Fluxes during disruptions (VI)
ITER
JET

• Presently proposed ITER specifications based on
  JET based extrapolations ? input from other
  tokamaks is required
• DW2 20-55 MJ
• t2 tJET/tL-modeJET (0.03-0.09)tL-modeITER
• DW3 W(t2)-dW/dtL-modet3

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Energy Fluxes during disruptions (VII)
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Confinement transients

• Fast H-L transition (b loss in 1-2 s? IW contact
  for up to 5s) can lead to large loads on the
  inner wall

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Runaway electron fluxes on PFCs (I)

• Predicted runaway current 10 (MA)
• Energy spectrum of electrons (E0 for
  exp(-E/E0)) 12.5 MeV
• Inclined angle 1 - 1.5?
• Total energy deposition due to runaway current 20
  MJ
• Average energy density deposition 1.5 MJ/m2
• Duration of the average energy density
  deposition 100 ms
• Maximum energy density deposition (end of the
• plasma termination) 25 MJ/m2
• Duration of the maximum energy deposition 10 ms
• Number of event Every major disruption

? These specifications are generally reasonable
but physics basis is weak (very poor experimental
input) ? Largest concern energy load by drifted
electrons due to formation of X-point
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Runaway electron fluxes on PFCs (I)
Runaway generation mechanisms for ITER like
disruptions conditions studied in detail but
runaway losses and dynamics are worse known
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Runaway electron fluxes on PFCs (II)
Current profile during runaway discharge peaks
(seen at JET) ? X-point formation in Scenario 2
Smith PoP 2006
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Runaway electron fluxes on PFCs (III)

• Significant drift of runaways near upper X-point
  due to poloidal field null f(E) 1/E0exp(-E/E0)
  with E0 12.5 MeV
• Angle of impact of runaways on drift orbits at
  upper X-point lt 1.5o but impact direction mainly
  toroidal

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Conclusions

• PID specifications for PFC loads in ITER
  considered for revision following ITER Design
  Review Process
• New specifications will be used for modification
  to existing design ? reasonable range and upper
  boundaries for loads have to be provided
• Input and constructive criticisms from EU-PWI TF
  and ITPA are gratefully acknowledged