Effects of transient heating events on W PFCs in a steady-state divertor-plasma environment
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Transcript of Effects of transient heating events on W PFCs in a steady-state divertor-plasma environment
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K.Umstadter –-Laser+D on W
PISCES
Effects of transient heating events on W PFCs in a steady-state divertor-plasma environment
Karl R. Umstadter,
R. Doerner, G.R.Tynan
PFC Annual Meeting
UCLA
August 5, 2010
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K.Umstadter –-Laser+D on W
PISCES
Overview
• Use of Laser Heat Pulse to Mimic ELMs
• Experiment & Apparatus
• Enhanced Mass Loss & Bulk Temperature
• Comparison with DIII-D Experiments
• Cause of Synergistic Effect
• Damage Threshold & Fluence Scaling
• Conclusion
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K.Umstadter –-Laser+D on W
PISCES
0
500
1000
1500
2000
2500
3000
35001.
0E-0
8
1.0E
-07
1.0E
-06
1.0E
-05
1.0E
-04
1.0E
-03
Depth in Target (m)
Te
mp
era
ture
(C
)
ELM (300usec)
ELM+60usec
YAG (5nsec)
YAG+1nsec
YAG Pulse Mimics ELM Surface Heating
Longer duration results in deeper
heat transport
May effect retention
Carslaw & Jaeger, “Conduction of Heat in Solids”, Oxford University Press, 1959
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K.Umstadter –-Laser+D on W
PISCESPISCES A & Beam Delivery
Laser PathQ-Switched
Nd:YAG Laser 1064nm
<850 mJ
~5 nsec
<1 mrad
PISCES A~1017 – 1019 D+/cm2 s-1
n ~ 1012 D+/cm3 Te ~ 5-10eV Vbias ~ up to 250V
Rp ~ 4cm
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K.Umstadter –-Laser+D on W
PISCES
Overview
• Use of Laser Heat Pulse to Mimic ELMs
• Experiment & Apparatus
• Enhanced Mass Loss & Bulk Temperature
Cause of Synergistic Effect
Comparison with DIII-D Experiments
• Damage Threshold & Fluence Scaling
• Conclusion
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K.Umstadter –-Laser+D on W
PISCES
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 30 60 90 120 150Ion Energy [eV] (Vbias-Vplasma)
Ma
ss L
oss
(m
g)
Laser + Plasma
Laser Only
Plasma Only
Erosion of W PFC under Simulated ELM Transients at High Repetition Rate
F~ 1026 D+/m2
Tsurf ~ 50ºC
3000 Transients withAbsorbed Energy Impact
~45 MJ/m2 s1/2
(low fluence between ELMs)
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K.Umstadter –-Laser+D on W
PISCES
Bursted Blisters
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K.Umstadter –-Laser+D on W
PISCES
D ionW atomW clusterW ion
Hypothetical Process
D+
Laser Pulse
W
W+
(C)(A) (B)
W
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K.Umstadter –-Laser+D on W
PISCES
Near surface location of D in samples exposed cold
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K.Umstadter –-Laser+D on W
PISCES
Near surface D decreases with increasing Temp
V.Kh. Alimov et al., JNM 375 (2008) 192–201
QSW Nd:YAGHeated Region
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K.Umstadter –-Laser+D on W
PISCES
0
0.1
0.2
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0.4
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40 60 80 100 120 140
Ion Energy (eV)
Dif
fere
nti
al
Ma
ss
Lo
ss (
mg
)
50C Bulk
630C Bulk
No Excess Mass Loss at Elevated Temperature
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K.Umstadter –-Laser+D on W
PISCES
Excess Mass Loss Not Limited to PISCES
DiMES samples of graphite and tungsten were “loaded” by
bombardment with deuterium ions (Eion~125eV) in the PISCES-A
Exposed on DiMES in DIII-D
He Exposures (VPS-W)Excess mass loss is 2-5x
D exposures (Plansee IG W)Excess mass loss is 3.5-8x
C:ATJ samples still under analysis
DIII-D with D.Rudakov & C.WongPresented at PSI-19, San Diego
ASIPP
Osaka C B1 D G
Tungsten
ATJ Graphite
A E
F
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K.Umstadter –-Laser+D on W
PISCES
Overview
• Use of Laser Heat Pulse to Mimic ELMs
• Experiment & Apparatus
• Enhanced Mass Loss & Bulk Temperature
• Comparison with DIII-D Experiments
• Cause of Synergistic Effect
• Damage Threshold & Fluence Scaling
• Conclusion
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K.Umstadter –-Laser+D on W
PISCES
Threshold for Damage Decreases
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1000 1500 2000 2500 3000 3500 4000 4500
Transient Surface Temperature (K)
W0 I
nten
sity
[10
10 p
hoto
ns/c
m2 ]
Deuterium Absorbed
No Deuterium
F=1E24 (below)
Linear (F=1E24(below))Linear (DeuteriumAbsorbed)Tbulk~325K
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K.Umstadter –-Laser+D on W
PISCES
Effects of D Loading on Damage
F = 5x1022/m2
F = 5x1023/m2
F = 2x1024/m2
Vbias=125V=2x1022/m2-sec
Te=11eVne=2x1024/m3
SA
MP
LE
Fluence to surfacebetween heating
transients
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K.Umstadter –-Laser+D on W
PISCES
Damage ~ Fluence1/3
0
1
2
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0 5 10 15 20
Fluence [1024 D+/m2]
W0 I
nten
sity
[10
11 p
hoto
ns/c
m2 ]
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K.Umstadter –-Laser+D on W
PISCESObservations
When fluence to PISCES-A targets between transients is increased synergistic effect between thermal transients & plasma exposure leads to enhanced material removal
Change in near surface material properties - TSurf a function of the energy density of deposition and thermal conduction to the bulk during and following the deposition
Operation above DBTT may alleviate excess mass loss mechanism and should prevent fracturing
Damage depends upon D fluence between transients and ion energy - more frequent ELMs may reduce damage by limiting fluence
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K.Umstadter –-Laser+D on W
PISCES
Conclusion
• Experiments with D-loaded samples in DIII-D on DiMES have shown that the enhanced erosion effect is not phenomena only witnessed in the laboratory PISCES device.
• Important to mimic ELM heat pulses in divertor-like plasma environment with ITER-relevant fluences
• Effects will be most apparent in high-performance steady-state tokamaks (EAST & KSTAR) as these experiments explore inter-ELM fluxes greater than operating tokamaks but in line with ITER
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K.Umstadter –-Laser+D on W
PISCES
Extra Slides
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K.Umstadter –-Laser+D on W
PISCES
Arcing during transient heating experiments
Early Focus On Avoiding These Phenomena
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K.Umstadter –-Laser+D on W
PISCES
Long Pulse Experiments
• 25J – 5msec - 1200 Laser Pulses @1/3 Hz 5 kW – 50MJ/m2s1/2
• 75V Bias – Total Fluence ~1026 D+/m2
Room Temperature >500ºC