1. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Recent Results from PISCES Program R. P. Doerner, M. J. Baldwin, G. De Temmerman, J. Hanna, D. Nishijima, G. Tynan and K. Umstadter Center for Energy Research, University of California – San Diego, USA Work performed as part of: US-EU Collaboration on Mixed-Material PMI Effects for ITER TITAN US-Japan Collaboration UCSD – SNLL Collaboration on Be/W alloys

2. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Outline - Recent PISCES Results Erosion of Be layers Laser irradiation of plasma exposed targets –Preparation for ELM simulation studies Be/W formation conditions Mixed species (D/He) plasma studies W exposure to mixed species plasma –Impact of Be and C impurities on W surface evolution Codeposition studies (presented tomorrow) Summary

3. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 PISCES-B has been modified to allow exposure of samples to Be seeded plasma P-B experiments simulate Be erosion from ITER wall, subsequent sol transport and interaction with W baffles or C dump plates, as well as investigation of codeposited materials using witness plates

4. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Plasma deposited Be (from oven) erodes differently than other Be layers Erosion calibration measurements for JET ILW erosion marker tiles Plasma deposited Be is easily re-eroded from deposited locations (remember for tomorrow) Erosion of Be from Be 2 C are underway

5. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 ELM simulation experiments are beginning, using laser irradiation of plasma exposed targets Laser heating method allows use of background plasma as diagnostic tool High-speed diagnostics implemented using 750mJ YAG laser (0.5 nsec) –10000 fps, 10 msec camera, also single frame 2-100 nsec camera –Gated imaging spectrometer w/ ICCD (50 nsec gate) Hydrogen saturation of surface produces much different effects –Macroscopic material ejection observed both w&w/o plasma –10x more material lost from plasma exposed samples during laser shots –Laser irradiation of samples can induce plasma arcing (e - emission?) Acquired welding laser capable of simulating ELM conditions –1.5 – 50 J, 0.3 – 10 msec adjustable pulse, fiber delivery to P-B

6. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 2 Stable Be-W alloys are known and have melting points closer to that of Be than W. Stable Be-W alloys Stable Be-W inter- metallics are: ~2200°C (Be 2 W) ~1500°C (Be 12 W) ~1300°C (Be 22 W) What will happen if Be transport into the W bulk is rapid enough that alloy formation is not limited to the near surface?

7. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 XPS confirms Be-W alloy formation on W target surfaces exposed in range 850-1320 K. Be-W alloy line shifts are consistent with: Wiltner & Linsmeier, JNM 337–339 (2005) D ion fluence ~ 1.2x10 26 m -2 n Be+ /n e ~ 0.1 %,

8. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 The availability of surface Be is found to be critical for Be-W alloy formation ( t ~ 1 h). A 0.3 m Be 12 W layer forms at W-Be interface. Be 12 W nucleation on W rich surface. No Be sub-surface.

9. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Similar layered structure observed in SNLL vacuum deposition measurements

10. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007

11. Be re-erosion and evaporation reduce surface Be availability, reducing alloy formation rate. Surface composit- ion below stoichio- metry for Be 2 W. No Be sub-surface. Be 12 W surface nucleation over almost identical surface to (d).

12. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Simple particle transport model predicts Be overlayer formation (most efficient alloying). More detailed modeling needed. Values taken from: W. Eckstein, IPP Report 9/17, (1998) D. R. Lide, CRC Handbook of Chem. & Phys., Internet Version (2005)

13. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 Mixed D-Be/C-He on W experiments Effects of He and D-He plasma on W. Influence of plasma impurities Be and C on these effects.

14. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 PISCES-B: pure He plasma T s = 1200 K, t = 4290 s, Fluence = 2x10 26 He + /m 2, E i = 25 eV Plasma simulators observe morphology change on W surfaces exposed to pure He plasma. Transmission electron microscope (TEM) in Kyushu Univ. Scanning electron microscope (SEM) NAGDIS-II: pure He plasma T s = 1250 K, t = 36,000 s, Fluence = 3.5x10 27 He + /m 2, E i = 11 eV N. Ohno et al., in IAEA-TM, Vienna, 2006

15. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 D 2 -He plasma, E i = 60 eV n He+ /n e ~ 10 % t = 4200 s 1 0 25 He + /m 2 Effect of D 2 -He plasmas at T s = 1100-1200 K. Plasma exposure time, t, is a stronger influence than He ion flux or fluence He plasma, E i = 60 eV t = 420 s 1 0 25 He + /m 2 He plasma, E i = 25 eV t = 4290 s 2 x 10 26 He + /m 2

16. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 E i = 60 eV, T s = 1100 K, Fluence = 10 25 He + /m 2 D 2 -He plasmaD 2 -He plasma with Be n He+ /n e ~ 10 %, n Be+ /n e ~ 0.2 %, t = 4200 s D 2 -He mixture plasma w/wo Be induces morphology on W at T s = 1100 K & E i = 60 eV. Finger-like structures observed, similar to pure He plasma Ion bombardment at E i = 60 eV prevents Be layer growth. But, Be somewhat inhibits morphology. n He+ /n e ~ 10 %, t = 4200 s

17. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 RN01312007 Be 12 W layer RN01292007 95% C layer Be or C plasma impurities can inhibit morphology at T s = 1100 K & E i = 15 eV. E i = 15 eV, T s = 1100 K, Fluence = 10 25 He + /m 2 D 2 -He plasma with Be n He+ /n e ~ 10 %, n Be+ /n e ~ 0.5 %, t = 5000 s D 2 -He plasma with C n He+ /n e ~ 10 %, n C+ /n e < 0.1 %, t = 3600 s Surface layer composition determined by x-ray microanalysis (WDS). Be-W alloy and W-C layers inhibit He induced morphology. At E i = 15 eV, Be and C deposited on W are not sputtered away.

18. R. Doerner, EU SEWG meeting, JET. July 9-10, 2007 In conclusion Tungsten as PFM has unique issues for an all-W ITER, and beyond Mixed-material issues are critical, even in a device with only one element as a PFM –Helium ash, Argon/Neon radiator gas, Oxygen How will mixed-species plasmas effect Be mitigation of C chemical erosion Stay tuned for tomorrows discussion on codeposition (and the role of mixed species plasmas there)