CMS Multiscale modelling of D trapping in W Kalle Heinola, Tommy Ahlgren and Kai Nordlund Department of Physics and Helsinki Institute of Physics University of Helsinki, Finland
Contents Background Plasma-wall interactions in fusion reactors What is needed to model them? Methods Results on plasma-wall interactions D trapping in W Kai Nordlund, Department of Physics, University of Helsinki 2
Plasma-wall interactions: Plasma-wall interactions in fusion reactors D+T fusion reaction in ITER and future fusion power plants will produce lots of 14.4 MeV neutrons and 3.5 MeV alphas The alphas & other ions & neutrals leaking from the plasma bombard the main wall He energy ~ 1 MeV Others ~ 10 kev 1 MeV Flux high Divertor is bombarded by D, T and He leaking from the plasma Energies ~ 1 ev 1 KeV Flux very high, ~ 10 20 ions/cm 2 s Kai Nordlund, Department of Physics, University of Helsinki 3
Plasma-wall interactions: What happens physically? Length m mm μm nm Primary damage production (cascades) PLASMA Dislocation mobility and reactions Most relevant region for ITER Sputtering; Bubble formation; Point defect mobility and recombination Swelling Changes of macroscopic mechanical properties ps ns μs ms s hours years Time Kai Nordlund, Department of Physics, University of Helsinki 4
Plasma-wall interactions: What is needed to model it -> Multiscale modelling! m Rate equations, constitutive equations Length mm μm Discrete dislocation dynamics Most relevant region for ITER nm DFT Classical Molecular dynamics Kinetic Monte Carlo ps ns μs ms s hours years Time Kai Nordlund, Department of Physics, University of Helsinki 5
Bubble formation and blistering in W: Traps for D and T in W divertors Neutrons induce damage also in the W divertor This damage may bind T coming from the fusion plasma Retained T limits the usage lifetime of ITER (700 g limit) Hence it is important to know the nature of the damage in W, how much T it can retain, and how it can be taken out To this end, we are doing DFT and classical MD simulations of damage and T binding in W vs. W T Kai Nordlund, Department of Physics, University of Helsinki 6
Bubble formation and blistering in W: Structure of vacancy clusters in W DFT and classical MD results for vacancy clusters in W Binding energy [ev] 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 = vacancy = W atom 0.05 0.1 2 3 4 5 6 7 8 9 Distance between vacancies [Å] Binding energies (E bind ) and structures of vacancy clusters with different number of vacancies (N vac ).. => Small vacancy clusters more stable in W! => Large traps for T do not exist or are very rare!? Kai Nordlund, Department of Physics, University of Helsinki [Ahlgren, Heinola, et al. J. Appl. Phys., 107 (2010) ] 7
Bubble formation and blistering in W: D trapping in vacancy clusters in W DFT results for T binding and trapping energies in W Hydrogen detrapping energy E trap (and the attempt frequency to detrap) corresponds to specific release temperature T m In TDS experiments the T m is used for obtaining E trap Enables comparison with experiments via rate equation modelling Kai Nordlund, Department of Physics, University of Helsinki [Ahlgren, Heinola, et al. submitted (2010) ] 8
Bubble formation and blistering in W: Multiscale modelling of T trapping in W DFT: energetics: - point defect ground state configurations - E m, E bind, E trap, - 128 W atoms MD: defect properties in clusters: - clustering & annihilation radii - W in W projected ranges with low energies - thousands of W atoms BCA: Binary collision calculations: - initial damage profile with D implantation in W - SIA & vacancy clustering: I 1-5, V 1-10,(~90% V 1, ~99% V 1-3 ) - damage per implanted D after immediate clustering! Rate equations: final damage profile - ~95% of V 1 s annihilated with SIA s - annealing at RT for 1 hour Kai Nordlund, Department of Physics, University of Helsinki 9
Bubble formation and blistering in W: Comparison with experiments Experimental: NRA & SIMS K. Heinola, et al., PhD thesis (2010) Ahlgren, Heinola, et al., Nucl. Instr. Meth. B, 249, (2006) Kai Nordlund, Department of Physics, University of Helsinki Heinola, Ahlgren, et al.,phys. Scripta, T128 (2007) 10
Conclusions Fusion reactors involve numerous kinds of plasma ion irradiation of materials These can be studied theoretically using molecular dynamics methods developed for high-energy effects as well as kinetic Monte Carlo D trapping in W can now be well modelled with a multiscale modelling scheme Predictive modelling for ITER?! Kai Nordlund, Department of Physics, University of Helsinki 11