1. PISCES AFOSR Materials and Processes Far From Equilibrium Workshop, Nov 2-4 2010 Arlington, VA. Some PMI Research Activities of the USDOE Fusion PFC Program M. J. Baldwin University of California - San Diego

2. PISCES Overview Brief description of the US-DOE PFC Program The UCSD PISCES PMI program. Examples of ‘far from equilibrium’ PMI observations on W Developing ties: An example of fruitful collaboration between Fusion and Propulsion PMI programs. Summary

3. PISCES ITER: First Burning Plasma Experiment Large System – (R~6m, a~2m) Expensive (~6 G$) 500 MW Fusion Power Energy Gain, Q=10

4. PISCES Plasma Facing Components (PFCs) must endure extreme conditions

5. PISCES D, T, He plasma ITER remote handling - divertor cassette mock-up http://www.alca-schio.com/nuclear_fusion_plants.htm W, liner/dome C strike points (start-up phase) W (DT phase) Hot surfaces T ~ 600-1000 K ~ few % Ar, Ne ext. radiator Be ‘rain’ from FW erosion ITER PMI is complicated

6. PISCES PFC program supports ‘next step’

7. PISCES PFC program members (Steering Committee) Task: Guide work, priorities, budgets Jeff Brooks (Purdue) – Chairman Gene Nardella, Barry Sullivan – DOE Stan Milora – VLT Members D. Buchenauer (SNL)R. Nygren (SNL) R. Doerner (UCSD)A. Hassanein (Purdue) G. Tynan (UCSD)T. Rognlien (LLNL) D. Ruzic (UIUC)N. Morley (UCLA) R. Maingi (ORNL) M. Ulrickson (SNL) R. Majeski (PPPL) C. Wong (GA) D. Whyte (MIT)

8. PISCES Major facility investment at UCSD PISCES-B: Be compatible PMI facility Diagnostics Probes, OES (absolute), YAG In-situ XPS, AES, SIMS Ex-situ SIMS, XPS, TDS, SEM, EDX, WDS PISCES-A: PMI & Supporting Research CSDX: Supporting Research

9. PISCES What do linear plasma devices offer? Toroidal PMI is complicated Open field line geometry in divertors can be simulated in linear plasma devices Steady state operation Flexibility / control Non toroidal geometry Can be well diagnosed PMI studies and code validation Not limited to fusion PMI. ITER PISCES Vert. Targets Target

10. PISCES PISCES linear plasmas simulate ITER edge

11. PISCES The Boundary Region of the Plasma Is Where Plasma Physics & Materials Science & Technology Meet Plasma Will Contact w/ Material Surfaces How Do Material Surfaces Respond to Plasma? How Does Plasma Respond to Materials?

12. PISCES UCSD PISCES Program Research Focus Perform Basic Plasma-Materials Interaction & Boundary Plasma Research Needed for ITER PFC Design Validation and Performance Predictions

13. PISCES Perform Controlled Be-C, Be-W, Be-C-W PMI Experiments Steady-state & Transient Thermal Loads Make Related Edge/SOL Plasma Transport Studies Develop and Validate Edge Plasma/PFC Models via Collaborations Mixed Mat’l Models (UCSD, EU) Eroded Mat’l Transport (Argonne) Time-averaged fluid codes (UEDGE, ERO,…) SOL Main Plasma & Impurity Transport (UCSD) Specifically …

14. PISCES W far from equilib.: Example 1. NAGDIS-II: He plasma D. Nishijima et al. JNM (2004) 329-333 1029 Surface morphology Shallow depth Micro-scale PISCES-A: D 2 -He plasma M. Miyamoto et al. NF (2009) (in press) 600 K, 1000 s, 2.0x10 24 He + /m 2, 55 eV He + Little morphology Occasional blisters PISCES-B: pure He plasma M.J. Baldwin et al, NF 48 3 (2008) 035001 1200 K, 4290 s, 2x10 26 He + /m 2, 25 eV He + NAGDIS-II: pure He plasma N. Ohno et al., in IAEA-TM, Vienna, 2006 1250 K, 36000 s, 3.5x10 27 He + /m 2, 11 eV He + 100 nm (VPS W on C) (TEM) ~ 600 - 700 K> 2000 K ~ 900 – 1900 K Surface morphology Evolving surface Nano-scale ‘fuzz’

15. PISCES How does ‘fuzz’ erode? W/ lower Y. Fuzz produced on W by He plasma exposure over 800 s at 1150 K, E i ~ 90 eV. Switch to He/Ar plasma at t = 0 s, & measure time evolution of W I emission in front of W target. Y smooth (Ar +  W) ~0.05 @ E i ~ 110 eV, by mass loss. (Agrees w/ TRIM). Y fuzzy = (0.05 / WI/ArII 110 eV, smooth ) x WI/ArII Why is the sputtering yield reduced? Porosity? Internal bubble? Not well understood.

16. PISCES Selected W samples exposed to the Magnetized Co-axial Plasma Gun (MCPG) at Univ. of Hyogo, Japan. Energy density: ~0.3-0.7 MJ/m 2 Pulse width: ~0.5 ms Ion energy for D + : ~30 eV n e ~10 21 m -3,  i ~ 1-2x10 25 m -2 s -1 Comparable to type I ELMs in ITER How does fuzz take power loads? Initial tests encouraging.

17. PISCES Ion fluence to surface varied before single ~45 MJ/m 2 s 1/2 laser pulse applied to W target V bias =125V  =2x10 22 /m 2 /s T e =11eV n e =2x10 24 /m 3 W far from equilib.: Example 2. 5 x 10 22 /m 2 5 x 10 23 /m 2 2 x 10 24 /m 2

18. PISCES Pathway for enhanced erosion  ~ 10 26 D + /m 2 T surf ~ 50ºC

19. PISCES Ties between plasma programs are mutually beneficial: Example 3. Enhanced high temperature erosion of Li by ion bombardment. Doerner, Baldwin et al. FED 61-62 (2002) 231. Also found for Be. At high temperature (Relevant to ITER). Doerner et al. JNM 1 (2005) 877. An ad-atom sublimation model explains the results.

20. PISCES Enhanced erosion of BaO impregnated W cathodes by Xe. Enhanced Ba loss is measured by biasing sample in Xe plasma At high temp., floating the material allows a direct measure of Ba sublimation.  t measurements (3 points – 10 minutes) show no surface depletion of BaO

21. PISCES The temp. dependent atom flux from a surface due to ion impact is: Where E eff = E ad - E D E ad is the adatom binding energy to the surface E D is the activation energy for surface diffusion of an adatom Y ad can be calculated with molecular dynamics code A is a material constant Independent of T Independent of J pl Dependent on both J pl and T  if adatom recombination dominates

22. PISCES Ad-atom model (UCSD data) and prediction for thruster cathode.

23. PISCES Summary Substantial capital investment by US-DOE in fusion PMI research and expertise spanning decades. There are 9 active PFC research groups incl. PISCES PMI studies PMI modeling / theory Technology Opportunities for developing ties and collaborations are welcome.