alberto loarte eu plasma-wall interaction task force meeting – ciemat 29-31 – 10 – 2007 1...

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


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


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


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


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


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


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


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


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


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


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


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


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


Pre-disruption energy confinement degradation (II)

Resistive-MHD caused disruption (JET-DL)

Low plasma energy by the time of the thermal quench


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


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


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)


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 ?)


• 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)


#69787

During current quench the radiation distribution is poloidally asymmetric

Radiation during current quench (I)

JET (A. Huber)


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)


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


Disruption mitigation (II)

Valve installed close to the plasma in ASDEX-Upgrade (G. Pautasso)

Faster effect on plasma

Fastest current quench

Better fuelling efficiency


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)”


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


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)


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


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


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


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


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

alberto loarte eu plasma-wall interaction task force meeting – ciemat 29-31 – 10 – 2007 1...

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