evolution of tungsten degradation under combined high
TRANSCRIPT
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Th. Loewenhoff, A. Bürger, J. Linke, G. Pintsuk, A. Schmidt, C. ThomserL. Singheiser,
Forschungszentrum Jülich, EURATOM Association, 52425 Jülich, Germany
Introduction
� ELMs occur in normal operation at a rate of ≥ 1 Hz
more than 10 events during estimated ITER divertor lifetimeELMs deploy ~0.5 MJ/m² in 0.2 – 0.5 ms pulses
high power density and high number of events can cause surfaceroughening, cracking & melting of plasma facing components
heat loads during ELMs occur additionally to the steady state heat load of5 – 10 MW/m² that results in different surface temperatures
synergistic effects of steady state and transient heat loads
→
→
→
6
�
�
The importance of ( )edge localized modes ELMs
Experiment
Thermal loads on ITER wall / divertor
Thorsten Loewenhoff | Forschungszentrum Jülich | Institute of Energy and Climate Research IEK-2 | Association EURATOM - FZJ | [email protected]
Conclusions
Evolution of tungsten degradation under combinedhigh cycle ELM and steady state heat loads
10010-4 10-3 10310210110-2 10-1
105
104
103
102
101
100off-normal
normal
disruptions
VDEs
divertor: 5 MW/m², 450 s, n ~ 3000
ELMs: 1 GW/m², 0.5 ms, n > 106
po
we
r d
en
sity [
MW
/m²]
pulse duration [s]
Electron beam facility JUDITH 2
�
�
�
�
�
max. power 200 kWacceleration voltage 40 – 60 kVpulse duration 5 µs - CWEB diameter > 3 mm (FWHM)diagnostics: video & IR camera,
fast pyrometer ( t = 10 µs,
T = 350 °C, T = 3500 °C)
� min
min max
Layout data
�
�
�
EB is of Gaussian shape, while ELMs’ footprints occur on a wider scale
use of circular loading pattern to increase „homogeneously“ loadedarea around centre
pattern also increases stability with respect to beam width fluctuationstest components: W tiles brazed to actively cooled copper cooling block
→
EB power distribution at 44 kW*
*with 45 % reflection (tungsten surface)
t = 05 µs t = 10 µs t = 15 µs t = 20 µs
t = 25 µst = 30 µst = 35 µst = 40 µs
EB guidance – circular pattern
Tests with pure tungsten tiles
This work, supported by the European Communities under the contract of Association between EURATOM/Forschungszentrum Jülich, was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.
Surface condition after testing pure W at T 200 °C (0 MW/m² SSHL)≈
HF
F [
MW
/m²
]√
s 10
15
5
0
�t = 0.48 msf = 25 HzELM
abs. coeff.: 0.55
0.22
0.33
0.11
0103 104 105 106 107102
number of pulses
en
erg
y d
en
sity [
MJ/m
²]cr network
no damage
roughening
-10-5
05
10
y [mm]
-5
0
5
10
-10
x [mm]
700600500
400300
200
1000
Pow
er
density [M
W/m
²] 700
600
500
400
300
200
100
0
Pow
er
density [M
W/m
²]
Results
LM picture of undamaged surface
1,000 x HFF 9 MW/m2√s
1,000 x HFF 12 MW/m2√s 1,000,000 x HFF 6 MW/m
2√s
1,000 x HFF 9 M 10 MW/m² SSHLW/m +2√s
100,000 x HFF 6 MW/m + 10 MW/m² SSHL2√s
100,000 x HFF 6 MW/m2√s
Surface condition after testing pure W at T 700 °C (10 MW/m² SSHL)≈
HF
F [M
W/m
²]
√s
no damage
roughening
cr network
small cr
cr+melting0.22
0.33
0.11
0
energ
y d
ensity [M
J/m
²]
103 104 105 106 107102
number of pulses
10
15
5
0
�t = 0.48 msf = 25 HzELM
abs. coeff.: 0.55
�
�
�
�
material: sintered & double forged W elongated grains, oriented parallel to the loaded surface (aspect ratio ~0.4)sample size: W tiles of 12 x 12 x 5 mm³, loaded area: 3.5 – 12 mm² (depending on heat flux factor (HFF))active cooling: water with T = 100 °C (module starting/equilibrium temperature) at p = 3 MPa, tube Ø 8 mm
test mode: 400 s load (f = 25 Hz, pulse t = 0.48 ms) 10,000 pulses, 20 s break (back to equilibrium
temperature), tests done with and without additional steady state heat load (SSHL) of 10 MW/m²
→
→ELM �
he
at
loa
d
�
�
�
�
�
�
tests showed the feasibility of ELM-like loading in JUDITH 2 for up to 10 pulses and additional steady state heat load up to 10 MW/m²
results show a dependency of material degradation on the number of pulses, the power density and the steady state heat load (surface temperature)for higher temp. (700 °C, SSHL 10 MW/m²) the degradation appears earlier (in terms of number of pulses) and is more severe (e. g. additional melting)
the overall damage threshold is located between HFF 3 – 6 MW/m ( energy density 0.07 – 0.13 MJ/m²)roughening as precursor: roughening is always followed by cracking at higher number of pulseserosion of crack edges and/or melting takes place after cracking, depending on surface temperature
6
2√s →
simulation of heat loading conditions and temperatures as expected for the ITER divertor→
Test module
10 MW/m² SSHL
Surface temperature (HFF 3 )MW/m2√s
� = 0.2Tem
p. [°
C]
900
850
800
750
700
650
950
1000
20 30 40 50 60 70 80
t [ms]
10,000 x HFF 9 MW/m + 10 MW/m² SSHL2√s
100,000 x HFF 9 MW/m + 10 MW/m² SSHL2√s