alberto loarte eu plasma-wall interaction task force meeting – jozef stefan institute 13-15 – 11...

Alberto Loarte EU Plasma-Wall Interaction Task Force Meeting – Jozef Stefan Institute 13-15 – 11 – 2006 1

Report onEU-PWI SEWG on Transient Loads

Alberto Loarte

European Fusion Development Agreement

Close Support Unit - GarchingContributors to SEWG :

CEA : F. Saint-LaurentCRPP : R. PittsENEA : G. MaddalunoIPP : G. Pautasso, A. Herrmann, T. EichITER : G. Federici, G. StrohmayerFZJ : K.H. Finken, M. Lehnen, J. Linke, T. HiraiFZK : I. Landman, S. Pestchanyi, B. BazylevUKAEA : V. Riccardo, P. Andrew, W. Fundamenski, G. Counsell, A. Kirk


Outline

1. Summary of work in 2006

Effects of transient loads on materials

Characterisation of ELM loads

Characterisation of Disruption loads

Disruption mitigation

2. Plans for 2007

3. Conclusions


Expected transient loads at ITER divertor/first wall are uncertain but have strong implications for PFC lifetime

Expected loads in ITER transients (I)

0.0 0.5 1.0 1.5 2.00

50

100

150

Mol

ten

laye

r th

ickn

ess

(m

)Energy density (MJ/m2)

t = 0.1 ms t = 0.3 ms t = 1.0 ms

Raclette - G. Federici & G. Strohmayer

0.0 0.5 1.0 1.5 2.00

10

20

30

Eva

pora

ted

thic

knes

s (

m)

Energy density (MJ/m2)

t = 0.1 ms t = 0.3 ms t = 1.0 ms

Be

Be


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 : 0.5 – 4 MJ/m2, t = 300-600 s, Ee ~ Ei ~ 3 – 5 keV

Thermal quench : 2.0 – 13 MJ/m2, t = 1-3 ms, Ee ~ Ei ~ 3 – 5 keV

Main wall (Be) Type I ELM : 0.5 – 2 MJ/m2, t = 300-600 s, Ee ~ 100 eV, Ei ~ 3 keV Thermal quench : 0.5 – 5 MJ/m2, t = 1-3 ms, Ee ~ Ei ~ 3 – 5 keV

Mitigated disruptions : 0.1 – 2.0 MJ/m2, t = 0.2-1 ms, radiation

Expected loads in ITER transients (II)


FZJ e-beam Judith facilities

Forschungszentrum Jülichin der Helmholtz-Gemeinschaft

JUDITH II JUDITH I

electron beam power: 200 kW 60 kW

acceleration voltage: 30 - 60 kV 120 - 150 kV

electron beam diameter: ~ 5 mm ~1 mm

power density: < 10 GW/m² < 15 GW/m²

pulse duration: > 1 ms > 1 ms

scanning frequency: 10 kHz 100 kHz

max. scanning area: 500 x 500 mm² 100 x 100 mm²

combination of different loads: yes no

n-activated or toxic components: yes yes

installed components per test: 2 x 2 1

Status of JUDITH IIInstallation of:electron beam gun: Sep. 04vacuum chamber: Sep. 04heat exchanger: Aug. 04power supply: Dec. 04

start-up of JUDITH II: Feb. 05standard operation: Apr. 05

JUDITH II - October 2004

1. electron beam (EB) gun; 2. vacuum chamber; 3. cooling circuit; 4. test component; 5. diagnostics; 6. carrier system; 7. alternative flange for the EB-gun.

The new electron beamtest facility JUDITH II

J. Linke

T. Hirai


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 (I)


-6 -4 -2 0 2 4 6

-4

-3

-2

-1

0

1

2

3

4

X, cm

Y,

cm

10 20 30 40 50 60 70 80 90 100

-6 -4 -2 0 2 4 6

-4

-3

-2

-1

0

1

2

3

4

X, cm

Y,

cm

30 40 50 60 70 80 90 100

The energy density distribution on CFC surface,%

The energy density distribution on W surface,%

Typical energy density profile on CFC surface

X,Y, cm2

En

erg

y d

ensi

rt,

MJ/

m2

X,Y, cm2

En

erg

y d

ensi

rt, M

J/m

2

Typical energy density profile on W surface,%

TRINITI facilities QSPA (II)


Typical micrographs of the tungsten droplets tracks

Surface of th

e

sample

Plasma stream direction

3 ms after first shotMass loss 67 mg/shot

Surface of th

e

sample

Plasma stream direction

3 ms after 60th shotMass loss 2 mg/shot

During the first shot droplets ejected mainly from the edges of the tiles.

As a result of edge smoothing and bridging of gaps the droplet ejection was reduced and mass losses were decreased.

TRINITI facilities QSPA (III)


TRINITI facilities QSPA (IV)

W and CFC erosion at ~ 1.5 MJm-2

CFC4, L3, 0 exposures CFC4, L3, 100 exposures

1mm 1mm

CFC4, L3, 0 exposures CFC4, L3, 100 exposures

1mm 1mm

CFC4, L3, 0 exposuresCFC4, L3, 0 exposures CFC4, L3, 100 exposuresCFC4, L3, 100 exposures

1mm 1mm

QSPA can reproduce plasma-interaction

processes at ITER-like load levels :

Melt layer displacement under plasma pressure Vapour shielding formation and effects on damage developmentExtrapolation to ITER requires modelling (Pressure too high, no magnetic field, etc.)


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)

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


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.

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


ELMs in JET cause significant impurity influx (& deposition) particularly when ~ 1MJ ELMs is reached

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.2

0.4

0.6

WELM

radiation ~ 0.25 WELM

WE

LM

rad

iatio

n (M

J)

WELM

(MJ)

Impurity generation and deposition by ELMs can dominate in ITER even if target lifetime is OK 0.15 g-C/ELM 150 g-C per shot

Determination of impurity influx and C-deposition during ELMs (W & C comparison)

ELMs erosion/deposition and impurity influxes


Main plasma ELM energy loss

ELMELMpedpedELMpedpedELM VnTTnW )33( ,, WELM correlated with nped, Tped ( <n>, <T>) & transport loss mechanism

Conduction Convection

Convective ELMs obtained so far in regimes not compatible with ITER QDT= 10 scenario

i) q95 ~ 3 (Ip ~ 15 MA) but too high * (~ n/T2) or ii) low * but q95 > 4 (Ip ~ 11 MA)


During ELM event energy flows to divertor target and main chamber PFCs

e,i losses along B

to divertor

Inner divertor

Outer divertor

ASDEX Upgrade Herrmann

e,i losses along B

to divertor

i losses across B to main wall

vELM ~ km/s

ASDEX Upgrade Herrmann PPCF 2004

Kirk PPCF

ELM power fluxes to PFCs (I)


222

exp1)(ttt

tqELM

Eich JNM 2005Loarte PoP 2004

qELM,div (t) more than 60% of WELM,div arrives after qELM,divmax

smaller TsurfELM

Fundamenski PPCF 2006

Energy balance of ELM divertor power pulse

in agreement with PIC simulations


Eich PSI 2006

ELM energy deposition at divertor in/out asymmetric

asymmetry depends on B direction but extrapolation of observations to next

step devices remains unclear

In/out asymmetries of ELM divertor power fluxes


Formation and dynamics of ELM filaments and energy deposition at main chamber starts to be well diagnosed

ELM energy fluxes to main chamber PFCs (I)

Vtor ~ 0 before filament leaves LCFS

vr goes from 0 at LCFS to 1–3 km

Filaments leave LCFS at

different times

MAST-Kirk

Energy flux to the wall by individual filaments

Herrmann-AUG

Energy per filament < 2.5 % WELM (MAST)


JET-IR Eich

0.05 0.10 0.15 0.200.0

0.2

0.4

0.6

0.8

1.0

1.2DOC-L = 0.27 1.2MA q

95 = 3.1

2MA q95

= 3.7

2MA q95

= 4.6

3MA q95

= 3.1

WE

LM

IR/

WE

LM

WELM

/Wped

ELM energy deposition at main chamber given by competition of parallel and perpendicular transport (JET-Fundamenski + Pitts validated model)

larger VELM (MELM) larger WELMwall

ELM energy fluxes to main chamber PFCs (II)

AUG-Kirk

Correlation between vELM and WELM found experimentally :

vELM/cs ~ (WELM/Wped) with > 1 (deduced from DIII-D, Loarte IAEA 2006)

vELM/cs ~ (WELM/Wped) with = 1/2 (JET, Fundamenski PSI 2006)

vELM/cs ~ (WELM/Wped) with = 0 (Kirk, AUG)


Riccardo NF 2005 Riccardo NF 2005, Pautasso EPS 2004H-L

transitionthermal quench

Pre-disruption energy confinement degradation (I)

Wplasma at thermal quench usually much smaller than Wplasmafull-performance (except

for VDEs and ideal- limits) caused by E deterioration

Size scaling and/or disruption amelioration actions ?

VDEs-limits (ITBs)


Pre-disruption energy confinement degradation (II)

Does this hold across devices ?

Confinement deterioration takes place in timescales ~ E except for fast H-L transition

& growth/locking of modes but p does not change much

Most disruptions largest divertor surface temperature rise is caused by power fluxes

during thermal quench rather than pre-disruption events

T ~ qdiv 1/2


Timescale of thermal quench power fluxes

timescale of thermal quench fluxes increases with R but large disruption-to-disruption variability

222

.. exp1)(ttt

tq qt

qt.q,div (t) more than 75% of WELM,div arrives

after qt.q.,divmax

smaller Tsurft.q.


Footprint of thermal quench power fluxes

Power flux during thermal quench broadens significantly (even after radiation correction) & can develop toroidal asymmetries ( ~ 2-3)

A. Herrmann - ASDEX Upgrade

G. Counsell - MAST


Power fluxes on PFCs during ITER ELMs & disruptions

Extrapolation of power fluxes to PFCs based on experimental evidence & models

toroidal symmetry assumed

ITER PFCs’ lifetime can be evaluated from these loads tolerable WELM & Wt.q.


Material erosion by ELM/disruption transient loads - no vapour shielding & no redeposition (Raclette, Federici & Strohmayer)

CFC target lifetime requires qELMmax < 1.5-2.0 GWm-2

WELM/Wped < 0.05 (convective ELMs)

qUpper-BeELM < 50 MWm-2 No Be melting

Calculated ELM-driven/disruption erosion in ITER

0 2 4 6 8 10 121E-3

0.01

0.1

1

10

CFC Be W 250 s rectangular waveform 500 s rectangular waveform 250 s rise time experimental waveform 500 s rise time experimental waveform

Power Density (GWm -2)

Ero

ded

CF

C (m

)

106 ELMs CFC divertor lifetime

1

10

100

Depth of U

pper Be-m

odules and W divertor m

elt pool (m) 0 2 4 6 8 10 12

0

50

100

C Be W experimetal waveform t

t.q. = 1.0 ms

experimetal waveform tt.q.

= 3.0 ms

Ero

ded

CF

C (m

)

300 disruptions divertor lifetime

Power Density (GWm -2)

0

200

400

600

Depth of U

pper Be-m

odules and W divertor m

elt pool (m)

CFC target lifetime requires qdis,max < (2-4) GWm-2

Wped/Wplasmafull-performance < 0.4 (typical for JET ELMy H-modes)

qUpper-BeELM ~ 100-400 MWm-2 No Be melting for qexperimental(t)


Massive gas injection systems available in ASDEX-Upgrade, JET, TEXTOR and TORE-Supra

Disruption mitigation (I)

G. Counsell - MAST

F. Saint-Laurent – Tore Supra

He injection in Tore-Supra very effective in suppressing e runaway generation in disruptionsTime to t.q. depends on pressure but He penetration does not depend on pressure He injection does not suppress e runaways already produced

M. Lehnen – TEXTOR

no neutral penetration in MGI shots dynamics of disruption correlated with impurity mass Ar + D produces fast termination reduction of thermal

loads and runaway suppression (pure Ar produces runaways)


ECRH has been used to suppress disruption by affecting evolution of MHD

Disruption mitigation (II)

Density limitG. Maddaluno – FTU

Mo-injectionG. Maddaluno – FTU

ECRH power and localisation requires optimisation for different disruption type(central for DL and peripheral for Mo-injection)


Plans for 2007 (I)

Proposed joint activities

Comparison of models for material damage during ELMs and subsequent plasma

evolution with existing experimental data (mainly from JET) : FZK, FZJ, JET,

CSU Garching, IPP

Analysis of pre-disruptive thermal confinement deterioration and associated power

fluxes on PFCs for similar disruptive triggers (density limit, low q disruption,

ideal limits, etc.) and pre-disruptive regimes (L-mode, H-mode, ITBs, …) :

FZJ, CRPP, ENEA, UKAEA, CEA, IPP, JET, CRPP, CSU Garching

Determination of spatial and temporal characteristics of power fluxes during

disruption thermal quenches for comparable disruptions : FZJ, CRPP, ENEA,

UKAEA, CEA, IPP, JET, CSU Garching


Plans for 2007 (II)

Proposed joint activities

Comparative studies for the optimisation of disruption mitigation by massive gas

injection for runaway suppression and thermal load minimisation : FZJ, CEA,

IPP, JET, CRPP, HAS, CSU Garching

Determination of spatial and temporal characteristics of power/particle fluxes during

ELMs for comparable plasma conditions : CRPP, UKAEA, IPP, JET, CSU

Garching


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 2007 expected in by coordinated experiments and data analysis

Many EU devices are now equipped with systems for disruption mitigation by massive gas injection significant progress in 2007 expected in this area by inter-machine comparison

alberto loarte eu plasma-wall interaction task force meeting – jozef stefan institute 13-15 – 11...

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