Mixed Interactions of W, Be, C, D & He

1. Mixed Interactions of W, Be, C, D & He R. Doerner for the PISCES Team In collaboration with members of the US domestic fusion program, the EU & Japanese programs, and the ITPA DIV/SOL

2. W Temperature & PMI are coupled ~ 900 – 1900 K ~ 600 - 700 K > 2000 K PISCES-B: pure He plasmaM.J. Baldwin et al, NF 48 (2008) 035001 1200 K, 4290 s, 2x1026 He+/m2, 25 eV He+ NAGDIS-II: pure He plasmaN. Ohno et al., in IAEA-TM, Vienna, 2006 1250 K, 36000 s, 3.5x1027 He+/m2, 11 eV He+ • PISCES-A: D2-He plasma • M. Miyamoto et al. NF (2009) 065035600 K, 1000 s, 2.0x1024 He+/m2, 55 eV He+ • Little morphology • Occasional blisters • NAGDIS-II: He plasma • D. Nishijima et al. JNM (2004) 329-333 1029 • Surface morphology • Shallow depth • Micro-scale 100 nm (VPS W on C) (TEM) • Surface morphology • Evolving surface • Nano-scale ‘fuzz’

3. PISCES Mixed D/He reduces D retention in W at low temperature See more details in talk of D. Nishijima 1e21 D/m2 ~ 3 mg/m2 With He • Addition of He to the D plasma reduced D retention by about a factor of 35. • With He, D retention is mainly at the surface,whereas without He, D retention peaks ~ 1 micron beneath the surface.

4. PISCES At higher temperature, W ‘fuzz’ forms and is approx. 95% space • SEM used to profile ‘fuzz’ layer thickness over sample surface. • Geometric vol. of ‘fuzz’ layer est. (7.8 x10-10 m3 ±10%). • ‘Fuzz’ layer removed. Mass change (Dm=0.87 mg ±1%). Comp. w/ pure W, (r = 19.25 x103 kgm-3), ‘fuzz’ layer is 94 % porous.

5. ‘Fuzz’ growth is fastest at early times PISCES • If ‘fuzz’ is removed at equilibrium rate at 1120 K–500 nm length:1.4 mg.s-1m-2,0.62 g W per ITER shot 1600 shots to W dust limit.10 nm length, 69 mg.s-1m-2,0.3 kg W per ITER shot 320 shots to W dust limit. • Assuming ITER shot of 400 s and total strike point area w/ ‘fuzz’ growth to be 10 m2. • ITER W dust limit is 100 kg. • A TOKAMAK experiment to measure ‘fuzz’ erosion is NECESSARY.

6. PISCES Erosion rate of W fuzz • Measurements are underway to determine erosion yield and angular distribution of eroded W fuzz Sputtered Ar on W angular distribution from a smooth surface Integrated W atom surface loss rate from a nanostructured surface Smooth W W fuzz

7. PISCES What about effects of D + He plasma on other ITER materials • D +10% He plasma also reduces retention in Be targets and alters surface • D +10% He plasma on ATJ graphite has no effect on retention or surface Pure D Plasma on Be 200°C D+0.1He Plasma on Be 200°C Surface pits

8. PISCES Retention in Be codeposits resulting from mixed D/He plasma exposure is also being investigated • Co-deposits (from Be targetseroded by D2 and D2-He plasmas)is collected on W witness plates • TDS up to 800 C shows a smallrelease of He from mixed speciesD2-He-Be co-deposits • D2 release behavior is not significantly altered by thepresence of He • Total D2 retention is increased byin the D2-He plasma case,but D/Be ratio is more relevant • Be concentration is currently beingmeasured by NRA at IPP

9. PISCES High priority ITPA DIV/SOL R&D tasks The ITPA DIV/SOL group and ITER IO have identified 5 critical areas of R&D where community input is needed. While parts of the US PFC Program are included in the R&D effort, more involvement is encouraged. The next meeting of the ITPA DIV/SOL group will be at UCSD during Dec. 14-18, 2009. All are welcome to attend and contribute to this effort. The 5 primary R&D areas, along with the coordinators of those areas, are: 1) T retention – J. Roth and R. Doerner 2) Tungsten – A. Kallenbach and Y. Ueda 3) Dust – D. Rudakov and N. Ashikawa 4) Heat flux – A. Leonard and M. Lehnen 5) Erosion and Material Migration – P. Stangeby and V. Philipps

10. Proposed T retention and removal work plan • Refine ITER prediction (MIT mini-meeting) : High priority • • Participants (JAEA, FZJ, UCSD, IPP, Kyushu, CEA, MIT, UofT, Sandia, ITER, JET, FOM) • Fuel retention machine database : High priority • • Participants (FZJ, MIT, CEA, IPP, JET, GA, JAEA) • Ion cyclotron wall cleaning : High priority • • Participants (VR, FZJ, MIT, CEA, IPP, JET, EAST, NIFS) • Disruption flash heating : Med. priority • • Participants (CAE, UCSD, UKAEA, ITER, JET, MIT, GA) • Capability and risks of removing C : Med. priority • • Participants (UofT, VR, FZJ, CEA, IPP, JET, GA) • Isotope exchange : Med. priority • • Participants (JAEA, MIT, CEA, IPP, INL, Kyushu, FZJ, JET, GA) • T removal by heating to 350C : High priority • • Participants (MIT, CEA, UCSD, IPP, INL, Sandia, UKAEA, GA. FZJ) • Retention in gaps : Med. priority • • Participants (FZJ, IPP, INL, UKAEA, Kyushu, JET, GA, JAEA) • Influence of mixed species on retention : High priority • • Participant (UCSD, IPP, Kyushu, FZJ, JAEA, UofT, JET) DSOL (new) DSOL (new) Collabo- ration

11. PISCES 350C Different heating profiles and different implantation doses are being studied Six types of material – Be on W Be on CFC Be12W Be2C C on Be W on Be Four implantation doses - 3 E 16 D atoms (at room temp.) 3 E 17 D atoms 3 E 18 D atoms 3 E 19 D atoms

12. PISCES Be on CFC Be2C Be12W Be on W Retention and release from mixed material samples with Be-containing overlayers • 200 nm Be layers deposited on substrates at MEdC, Romania • Alloys formed and verified at IPP, Garching • Samples implanted at room temperature with 200 eV D ions at IPP, Garching to a fluence of 4-5 E22 D/m2 (~3 E18 D atoms) • TDS performed on samples at PISCES, UCSD • Assumes all D is released from samples by TDS at 800C (to be confirmed by post-TDS NRA at IPP, Garching) Total D released 1.3E17 1.3E17 7.4E16 5.2E16

13. PISCES 350 C Annealing to 350C is ineffective for release from C layersW layers retain very little implanted D

14. PISCES PISCES continues to contribute to ITER R&D • Mixed material/mixed plasma species effects on erosion, codeposition, retention and surface evolution • Impact of transient heating on fuel retention and surface loss rates • Plasma impurity transport, flow speed measurements and modeling comparison • Active collaborations continue with members of the US fusion program, EU, Japan, China and the ITER IO