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

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

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

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

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

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)

K.Umstadter –-Laser+D on W

PISCES

Bursted Blisters

K.Umstadter –-Laser+D on W

PISCES

D ionW atomW clusterW ion

Hypothetical Process

D+

Laser Pulse

W

W+

(C)(A) (B)

W

K.Umstadter –-Laser+D on W

PISCES

Near surface location of D in samples exposed cold

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

K.Umstadter –-Laser+D on W

PISCES

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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

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

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

K.Umstadter –-Laser+D on W

PISCES

Threshold for Damage Decreases

0

0.5

1

1.5

2

2.5

3

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

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

K.Umstadter –-Laser+D on W

PISCES

Damage ~ Fluence1/3

0

1

2

3

4

0 5 10 15 20

Fluence [1024 D+/m2]

W0 I

nten

sity

[10

11 p

hoto

ns/c

m2 ]

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

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

K.Umstadter –-Laser+D on W

PISCES

Extra Slides

K.Umstadter –-Laser+D on W

PISCES

Arcing during transient heating experiments

Early Focus On Avoiding These Phenomena

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