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 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 PISCES PISCES A & Beam Delivery Laser Path Q-Switched Nd:YAG Laser 1064nm <850 mJ ~5 nsec <1 mrad PISCES A  ~10 17 – D + /cm 2 s -1 n ~ D + /cm 3 Te ~ 5-10eV V bias ~ up to 250V R p ~ 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 Erosion of W PFC under Simulated ELM Transients at High Repetition Rate F~ D + /m 2 T surf ~ 50ºC 3000 Transients with Absorbed Energy Impact ~45 MJ/m 2 s 1/2 (low fluence between ELMs)

K.Umstadter –-Laser+D on W PISCES Bursted Blisters

K.Umstadter –-Laser+D on W PISCES D ion W atom W cluster W 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 Q SW Nd:YAG Heated Region

K.Umstadter –-Laser+D on W PISCES 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 (E ion ~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.Wong Presented 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 T bulk ~325K

K.Umstadter –-Laser+D on W PISCES Effects of D Loading on Damage F = 5 x /m 2 F = 5 x /m 2 F = 2 x /m 2 V bias =125V  =2x10 22 /m 2 -sec T e =11eV n e =2x10 24 /m 3 SAMPLE Fluence to surface between heating transients

K.Umstadter –-Laser+D on W PISCES Damage ~ Fluence 1/3

K.Umstadter –-Laser+D on W PISCES Observations 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 - T Surf 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 Laser Hz  5 kW – 50MJ/m 2 s 1/2 75V Bias – Total Fluence ~10 26 D + /m 2 Room Temperature >500ºC