Report on EUPWI SEWG on Transient Loads and Future Work

1
Report onEU-PWI SEWG on Transient Loads and
Future Work

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

Contributors to SEWG CEA F. Saint-Laurent, P.
Monier-Garbet, G. Arnoux CRPP R. Pitts ENEA
G. Maddaluno, B. Esposito IPP G. Pautasso, A.
Herrmann, T. Eich, B. Reiter, P.
Lang EFDA-Garching G. Federici, G.
Strohmayer FZJ M. Lehnen, S. Bozhenkov, J.
Linke, T. Hirai FZK I. Landman, S. Pestchanyi,
B. Bazylev UKAEA V. Riccardo, W. Fundamenski,
P. Andrew G. Counsell, A. Kirk
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Outline

• Summary of work
• Effects of transient loads on materials
  (Experiment/Modelling)
• Characterisation of ELM loads
• Characterisation of Disruption loads
• Disruption mitigation
• 2. Plans for 2008
• 3. Conclusions

3
Loads on Materials in ITER transients

• As guideline for experiments the following energy
  ranges and plasma impact energies have been
  defined
• Divertor target (CFC and W without/with Be
  coatings)
• Type I ELM 0.25 5 MJ/m2, Dt 200-500 ?s, Ee
  Ei 3 5 keV
• Thermal quench 3.0 20 MJ/m2, Dt 0.5-2.0
  ms, Ee Ei 3 5 keV
• Main wall (Be)
• Type I ELM 0.05 1 MJ/m2, Dt 200-500 ?s, Ee
  100 eV, Ei 3 keV
• Thermal quench 0.5 4 MJ/m2, Dt 0.5-2 ms,
  Ee Ei 3 5 keV
• Mitigated disruptions 0.1 2.0 MJ/m2, Dt
  0.2-1 ms, radiation

4
TRINITI facilities ? QSPA
QSPA facility provides adequate pulse durations
and energy densities. It is applied for erosion
measurement in conditions relevant to ITER ELMs
and disruptions
View of QSPA facility
The diagram of QSPA facility

• Conditions for ITER ELMs disruptions not
  easily reproducible in tokamaks
• QSPA reproduces
• Energy density Timescale
• with plasma pressure 10 too high
• nT3/2QSPAnT3/2ITER but TITER 10-100 x TQSPA

• Plasma parameters (ELMs Disruptions)
• Heat load 0.5 2 MJ/m2 / 8
  10MJ/m2
• Pulse duration 0.1 0.6 ms
• Plasma stream diameter 5 cm
• Magnetic field 0 T
• Ion impact energy 0.1 keV
• Electron temperature lt 10 eV
• Plasma density 1022 m-3/ 1022 m-3

5
CFC results

• Under ITER-like heat loads erosion of CFC was
  determined mainly by the erosion of PAN-fibers

CFC

• Noticeable mass losses of a sample took place at
  an energy density of 1.4 MJ/m2
• Severe crack formation was observed at energy
  densities 0.7 MJ/m2(cracking of pitch fibre
  bundles)
• Recommended threshold for damage 0.5 MJm-2 ?
  adopted by ITER

6
W results

• 1. Under ITER-like heat loads erosion of tungsten
  macrobrush was determined mainly by melt layer
  movement and droplets ejection

W

• Noticeable W erosion mainly due to droplet
  formation took place at wmax 1.6 MJ/m2. The
  average erosion was approx. 0.06 µm/shot (1
  µm/shot during the first shot, and then decreased
  to 0.03 µm/shot after 40th pulse).
• Cracks formation was observed at energy densities
  0.7 MJ/m2.Metallographic sections show crack
  depths ranging from 50 to 500 µm.
• Recommended threshold for damage 0.5 MJm-2 ?
  adopted by ITER
• W1La2O3 has a much lower damage threshold

7
ELM
energy loss and material effects (JET)
JET experiments at high Ip ITER-like controlled
ELMs of 1MJ

• Increase of radiation for these ELMs associated
  with ablation of surface layer deposits not bulk
  material ablation
• TOKES modelling of ITER plasma evolution
  (Landman) indicates that DWELM gt 4 MJ can lead
  to termination fo the discharge after few ELMs (1
  ELM for DWELM gt 15 MJ)

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Divertor ELM power
fluxes (I)
Progress in determination of divertor ELM power
flux time dependence
W. Fundamenski
JET-T. Eich
more than 60 of DWELM,div arrives after
qELM,divmax ? smaller DTsurfELM
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Divertor ELM power
fluxes (II)
Different scaling of tIR for inner and outer
divertor probably associated with energy
transport processes during ELMs
JET- T. Eich SEWG Meeting
PIBP
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ELM energy
fluxes to main chamber PFCs (I)
ELM energy deposition at main chamber given by
competition of parallel and perpendicular
transport and filament size detachment dynamics
T. Eich/W. Fundamenski/R. Pitts
JET data ? vELM/cs (DWELM/Wped)a with a 0.5-3
with 1-0.6 of DWELM in filaments
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ELM energy
fluxes to main chamber PFCs (II)
In MAST and ASDEX-Upgrade less clear correlation
of DWELM with vELM
MAST A. Kirk
AUG A. Kirk
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ELM energy
fluxes to main chamber PFCs (III)
Main energy flux spatial distribution linked to
filament physical size which is starting to be
studied in detail
A. Kirk H-mode workshop
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Pre-disruption energy confinement degradation (I)
Degradation of Wplasma before thermal quench
studied for H-modes and L-modes (not clear size
scaling in H-mode)
MAST G. Counsell
(c.q.)
(t.q.)
14

Pre-disruption energy confinement degradation (II)
Resistive-MHD caused disruption (JET-DL)
Low plasma energy by the time of the thermal
quench
15

Pre-disruption energy confinement degradation
(III)
Ideal-MHD caused disruption (JET-ITB-collapse, P.
Andrew EPS07)
Plasma energy kept until last stages of disruption
16

Pre-disruption energy confinement degradation (IV)
Ideal-MHD caused disruption (H-mode VDE)
L-mode transition vertical drift
Vertical drift in H-mode
thermal quench
Plasma energy kept until last stages of VDE
thermal quench
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Radiative Power during Marfes
JET (A. Huber)
Power deposited on the Wall
200
Pwall(kW/m2)
t57.1s
150
100
50
Poloidal distance along wall (m)
0
0
2
4
6
8
10
2.0
t57.1s
1.6
1.2
Radiation peaking
0,8
0.4
10
Poloidal distance along wall (m)
0.0
0
2
4
6
8
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Thermal
Quench Energy distribution (I)
conducted energy on upper X-point target for
lower X-point discharges JET-IR analysis by G.
Arnoux Density Limit Disruption (DLD),
Radiative Limit Disruption (RLD) and Upwards
Vertical Disruptive Event (VDE)

• Resistive-MHD disruptions consistent with large
  power foot broadening at thermal quench (10-50
  of Wdia found on upper X-point target DRt 2-3
  cm)
• VDE energy flows to upper target (broadening ?)

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Thermal
Quench Energy distribution (II)
Downwards VDE in ASDEX-Upgrade (A. Herrmann, SEWG
meeting)

• Wplasma lost within 2 ms
• No radiation correction ? 100 of Wplasma in
  lower divertor
• Radiation correction ?50 of Wplasma in lower
  divertor broad footprint

20
Radiation
during current quench (I)
JET (A. Huber)
69787
During current quench the radiation distribution
is poloidally asymmetric
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Radiation
during current quench (II)
Pwall(MW/m2)
Power deposited on the Wall
JET (A. Huber)
Radiation peaking
Poloidal distance along wall (m)
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Disruption mitigation (I)
Massive gas injection studies in TEXTOR
(M.Lehnen, S. Bozhenkov)
Thermal quench duration Ar mixtures 0.5 ms He 1
ms
Current quench duration dIp/dt with increasing Ar
amount
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Disruption mitigation (II)
Valve installed close to the plasma in
ASDEX-Upgrade (G. Pautasso)

• Faster effect on plasma
• Fastest current quench
• Better fuelling efficiency

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Disruption
mitigation (III)
Carbon plasma transport from the divertor to the
core in ITER (FOREV-2D, Petschanyi)
Radiation heat load to the first wall and to the
divertor

• Considerable amount of carbon plasma vaporized
  from divertor targets can penetrate into the core
  in the course of disruption
• This carbon plasma can irradiate up to 85 of the
  thermonuclear plasma energy to the first wall,
  thus reducing the divertor heat load

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Disruption mitigation (V)
Current quench avoidance by ECRH control of MHD
growth in FTU (B. Esposito, G. Maddaluno)
ECRH power injection can suppress current quench
if injected close to q2 surface, if not it slows
down the process but does not prevent it
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Disruption mitigation (VI)
Duration of disruptive phase vs ECRH power
deposition radius (lithium conditioned walls
narrower current profiles)
Deposition location is varied using steerable
ECRH mirrors

EC resonance
EC beam
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SEWG Workprogramme 2008 (I)

• ELM transient loads
• Measurements of main chamber and divertor Type I
  ELM power and particle fluxes (AUG. MAST, JET,
  TCV)
• Optimisation of measurements of ELM fluxes by
  interchange of diagnostics (IR, visible cameras,
  etc.) among collaborating groups and by sharing
  of analysis techniques/software
• Coordinated experiments with comparable plasma
  conditions dimensionless identical (pedestal
  parameters) Type I ELMy H-modes and ?/? scans
• First stage of comparison of ELM models with
  measurements from these experiments (UKAEA, CRPP,
  ÖAW, CEA, IPP-CR, TEKES, IPP)
• Validation of 1-D and 2-D fluid and kinetic
  models for ELM losses along and across B with
  results from coordinated experiments
• Physics-based extrapolation of
  experimental/modelling results to ITER

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SEWG Workprogramme 2008 (II)

• Disruption transient loads
• Measurements of power and particle fluxes on
  divertor and main chamber PFCs (including runaway
  fluxes) before and during the disruption for
  disruptions types expected in ITER (AUG. MAST,
  JET, TCV, TEXTOR, FTU)
• Optimisation of measurements of pre-disruption
  and disruption fluxes by interchange of
  diagnostics (IR, visible cameras, etc.) among
  collaborating groups and by sharing of analysis
• Coordinated experiments for disruptions expected
  during ITER high performance discharges
  disruption in limiter plasmas, Type I ELMy H-mode
  disruptions (density limit, radiative limit, NTM
  driven and pure VDE), ideal ?-limit disruptions
  (ITBs) and low q95 disruptions
• First stage of the evaluation of expected
  disruption fluxes in ITER for the disruption
  types examined
• Physics-based extrapolation of experimental
  results to ITER conditions
• Validation of available 2-D fluid models and
  modelling of ITER disruptions

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SEWG Workprogramme 2008 (III)

• Mitigation of transient loads during ELMs and
  disruptions
• First attempt at joint optimisation of MGI by
  coordinated experiments in conditions applicable
  to ITER (AUG, TS, TCV, TEXTOR, JET)
• Coordinated experiments for mitigation of
  disruptions in limiter plasmas (ohmic and
  L-mode), and Type I ELMy H-mode. Gas injection
  rates and composition to be explored
• Quantitative comparison of effectiveness of
  methods for comparable plasma conditions across
  devices ? initial evaluation of size scaling and
  requirements for ITER
• First attempt to optimisation of ECRH for
  disruption mitigation by coordinated experiments
  in conditions applicable to ITER (FTU and other
  limiter and divertor tokamaks with ECRH)
• Current quench avoidance in disruptive limiter
  plasmas (density limit, radiative limit and ideal
  limits (low q95)) and disruptive diverted plasmas
  in Type I ELMy H-mode
• Evaluation of required ECRH power/current drive
  for comparable plasma conditions across devices ?
  initial evaluation of size scaling and
  requirements for ITER

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SEWG Workprogramme 2008 (IV)

• Initial steps in optimisation of ELM loads
  controlby pellet injection by coordinated
  experiments in conditions applicable to ITER
  (AUG, JET, etc.)
• Coordinated experiments with comparable plasmas
  in Type I ELMy H-modes to determine optimum
  pellet characteristics as function of device size
  and plasma conditions ? minimisation of ELM
  energy loss and disturbance to plasma
• Optimise measurements of fluxes during mitigated
  ELMs by interchange of diagnostics (IR, visible
  cameras, etc.) among collaborating groups and by
  sharing of analysis techniques/software

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Conclusions

• Experiments and modelling of material damage
  under ITER-like transient loads are providing
  firm basis to determine maximum tolerable
  ELM/disruption loads for acceptable lifetime
• Coordinated experiments and data analysis on
  disruptions and ELMs are starting to provide a
  physics-based extrapolation of expected transient
  loads in ITER ? Further progress in 2008
  expected in by coordinated experiments, better
  measurements and data analysis and comparison
  with models
• Systematic application of MGI and ECRH for
  disruptions and pellet-pacing for ELM control
  should provide better physics basis for ITER ?
  use in comparable conditions will allow first
  estimate of applicability to ITER