Post on 27-Mar-2015
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 1
Report onEU-PWI SEWG on Transient Loads and
Future WorkAlberto Loarte
European Fusion Development Agreement
Close Support Unit - GarchingContributors to SEWG :
CEA : F. Saint-Laurent, P. Monier-Garbet, G. ArnouxCRPP : R. PittsENEA : G. Maddaluno, B. EspositoIPP : G. Pautasso, A. Herrmann, T. Eich, B. Reiter, P. LangEFDA-Garching : G. Federici, G. StrohmayerFZJ : M. Lehnen, S. Bozhenkov, J. Linke, T. HiraiFZK : I. Landman, S. Pestchanyi, B. BazylevUKAEA : V. Riccardo, W. Fundamenski, P. Andrew G. Counsell, A. Kirk
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 2
Outline
1. 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
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 3
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, t = 200-500 s, Ee ~ Ei ~ 3 – 5 keV Thermal quench : 3.0 – 20 MJ/m2, t = 0.5-2.0 ms, Ee ~ Ei ~ 3 – 5 keV
Main wall (Be) Type I ELM : 0.05 – 1 MJ/m2, t = 200-500 s, Ee ~ 100 eV, Ei ~ 3 keV Thermal quench : 0.5 – 4 MJ/m2, t = 0.5-2 ms, Ee ~ Ei ~ 3 – 5 keV Mitigated disruptions : 0.1 – 2.0 MJ/m2, t = 0.2-1 ms, radiation
Loads on Materials in ITER transients
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 4
QSPA facility provides adequate pulse durations and energy densities. It is applied for erosion measurement in conditions relevant to ITER ELMs and disruptions
Plasma flow
Target
Diagnostic windows
Vacuumchamber
600
The diagram of QSPA
facility
View of QSPA facility
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 < 10 eV• Plasma density ≤ 1022 m-3/≥ 1022
m-3
Conditions for ITER ELMs & disruptions not easily reproducible in tokamaks
QSPA reproduces :
Energy density & Timescale
with plasma pressure ~ 10 too highnT3/2|QSPA=nT3/2|ITER but T|ITER =10-100 x T|QSPA
TRINITI facilities QSPA
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 5
1. Under ITER-like heat loads erosion of CFC was determined mainly by the erosion of PAN-fibers:
2. Noticeable mass losses of a sample took place at an energy density of 1.4 MJ/m2
3. 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
energy density / MJm-2
0.5 1.0 1.5
neg
lig
ible
ero
sio
n
ero
sio
n s
tart
sat
PF
C c
orn
ers
PA
N f
ibre
ero
sio
n o
ffl
at s
urf
aces
afte
r 10
0 sh
ot
sig
nif
ican
tP
AN
fib
reer
osi
on
afte
r 50
sh
ots
PA
N f
ibre
ero
sio
naf
ter
10 s
ho
ts
CFC
CFC results
FZK-Pestchanyi
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 6
1. Under ITER-like heat loads erosion of tungsten macrobrush was determined mainly by melt layer movement and droplets ejection:
2. 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).
3. 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
W+1%La2O3 has a much lower damage threshold
energy density / MJm-2
0.5 1.0 1.5
neg
lig
ible
ero
sio
n
mel
tin
g o
f ti
le e
dg
es
mel
tin
g o
f t
he
fu
ll t
ile
surf
ace
(no
dro
ple
t e
ject
ion
)
dro
ple
t ej
ecti
on
and
bri
dg
ing
of
tile
s a
fter
50
sho
ts
W
W results
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 7
ELM energy loss and material effects (JET)
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 WELM > 4 MJ
can lead to termination fo the discharge after few ELMs (1 ELM for WELM > 15 MJ)
A. Huber/R. Pitts
JET experiments at high Ip ITER-like controlled ELMs of ~1MJ
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 8
Progress in determination of divertor ELM power flux time dependence
Divertor ELM power fluxes (I)
2
,
2
,
2
,,, exp1)(
tttAtP oioioioioi
more than 60% of WELM,div arrives after qELM,divmax smaller Tsurf
ELM
W. Fundamenski
AUG-Eich
T.Eich
JET-T. Eich
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 9
Different scaling of IR for inner and outer divertor probably associated with
energy transport processes during ELMs
Divertor ELM power fluxes (II)
IR (s
)
||,conv. (s)
PIBP
JET- T. Eich –SEWG Meeting
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 10
ELM energy deposition at main chamber given by competition of parallel and perpendicular transport and filament size + detachment dynamics
ELM energy fluxes to main chamber PFCs (I)
JET data vELM/cs ~ (WELM/Wped) with = 0.5-3 with 1-0.6 of WELM in filaments
T. Eich/W. Fundamenski/R. Pitts
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 11
In MAST and ASDEX-Upgrade less clear correlation of WELM with vELM
ELM energy fluxes to main chamber PFCs (II)
AUG – A. Kirk
MAST – A. Kirk
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 12
Main energy flux spatial distribution linked to filament physical size which is starting to be studied in detail
ELM energy fluxes to main chamber PFCs (III)
A. Kirk – H-mode workshop
0
2
4
6
8
10
12
14
0 0.1 0.2 0.3 0.4 0.5 0.6
W [MJ]
dJ [d
eg
]
68190 dJ1
68190 dJ2
68193 dJ1
68193 dJ2
68193 dJ3
68190 dJ3
JET – W. Fundamenski SEWG Meeting
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 13
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)
(t.q.)(c.q.)
MAST – G. Counsell
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 14
Pre-disruption energy confinement degradation (II)
Resistive-MHD caused disruption (JET-DL)
Low plasma energy by the time of the thermal quench
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 15
Pre-disruption energy confinement degradation (III)
Ideal-MHD caused disruption (JET-ITB-collapse, P. Andrew EPS’07)
R
Inner Gap
Wdia
1 msec
Plasma energy kept until last stages of disruption
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 16
Pre-disruption energy confinement degradation (IV)
Ideal-MHD caused disruption (H-mode VDE)
Wdia (MJ)
D(a.u.)
Plasma energy kept until last stages of VDE thermal quench
Vertical drift
in H-mode
L-mode
transition
+
vertical drift
thermal
quench
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 17
Radiative Power during Marfes
0
50
100
150
200
0 2 4 6 8 10
t=57.1sPwall(kW/m2)
Poloidal distance along wall (m)
Power deposited on the Wall
0.0
0.4
0,8
1.2
1.6
2.0
0 2 4 6 8
10
t=57.1s
Poloidal distance along wall (m)Rad
iati
on
pea
kin
g
JET (A. Huber)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 18
Stored energy in the plasma just before thermal quench
Energy loss during thermal quench/total
Max. power density
(conducted)Thermal MagneticRadiated Conducted
Wdia [MJ] Wmagn [MJ] Wrad [MJ] E [MJ] Qmax [MWm-2]
DLD 0.7 5.6 0.6/2.3 0.1 9
RLD 0.6 5.6 0.6/2.4 0.3 32
VDE 1.4 5.6 0.4/2.5 1.4 86
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)
Thermal Quench Energy distribution (I)
Resistive-MHD disruptions consistent with large power foot broadening at thermal
quench (10-50% of Wdia found on upper X-point target ~ Rt = 2-3 cm) VDE energy flows to upper target (broadening ?)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 19
• Wplasma lost within 2 ms• No radiation correction 100% of
Wplasma in lower divertor• Radiation correction 50% of Wplasma
in lower divertor & broad footprint
Thermal Quench Energy distribution (II)
Downwards VDE in ASDEX-Upgrade (A. Herrmann, SEWG meeting)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 20
#69787
During current quench the radiation distribution is poloidally asymmetric
Radiation during current quench (I)
JET (A. Huber)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 21
0.5
1.0
1.5
2.0
2.5
3.0
3.5t=66.861s
t=66.869s
t=66.872s
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 2 4 6 8 10
t=66.869s
t=66.872s
Pwall(MW/m2) Power deposited on the Wall
Poloidal distance along wall (m)
Rad
iati
on
pea
kin
g
Radiation during current quench (II)
JET (A. Huber)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 22
Massive gas injection studies in TEXTOR (M.Lehnen, S. Bozhenkov)
Disruption mitigation (I)
Thermal quench durationAr mixtures: 0.5 msHe: 1 ms
Current quench durationdIp/dt with increasing Ar amount
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 23
Disruption mitigation (II)
Valve installed close to the plasma in ASDEX-Upgrade (G. Pautasso)
Faster effect on plasma
Fastest current quench
Better fuelling efficiency
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 24
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
radiation from the core
radiation from the divertor
moderate disruption
strong disruption
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
“Disruption mitigation (III)”
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 25
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 q=2 surface, if
not it slows down the process but does not
prevent it
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 26
0
20
40
60
80
0 5 10 15 20 25
t dis-t
MH
D (
ms)
rdep
(cm)
q=3/2 q=2
˜̃q=1
q=3
SAVED
DELAYED
UNAFFECTED
EC resonance
Duration of disruptive phase vs ECRH power deposition radius (lithium conditioned walls: narrower current profiles)
EC beam
Deposition location is varied usingsteerable ECRH mirrors
Disruption mitigation (VI)
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 27
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
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 28
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
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 29
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
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 30
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
Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – CIEMAT 29-31 – 10 – 2007 31
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