T. Wegener

Materials for DEMO and reactor applications-boundary conditions and new concepts

DEMO is the name for the first stage prototype fusion reactor considered to be the next step after ITER towards realizing fusion. For the realization of fusion energy especially, materials questions pose a significant challenge already today. Heat, particle and neutron loads are a significant problem to material lifetime when extrapolating to DEMO. For many of the issues faced, advanced materials solutions are under discussion or already under development. In particular, components such as the first wall and the divertor of the reactor can benefit from introducing new approaches such as composites or new alloys into the discussion. Cracking, oxidation as well as fuel management are driving issues when deciding for new materials. Here composites as well as strengthened CuCrZr components together with oxidation resilient tungsten alloys allow the step towards a fusion reactor. In addition, neutron induced effects such as transmutation, embrittlement and after-heat and activation are essential. Therefore, when designing a component an approach taking into account all aspects is required.

Dynamic outgassing of deuterium, helium and nitrogen from plasma-facing materials under DEMO relevant conditions

In confined plasma magnetic fusion devices significant amounts of the hydrogen isotopes used for the fusion reaction can be stored in the plasma-facing materials by implantation. The desorption of this retained hydrogen was seen to follow a t α law with α ≈ −0.7 in tokamaks. For a pulsed fusion reactor this outgassing can define the inter-pulse waiting time. This work presents new experimental data on the dynamic outgassing in ITER grade tungsten exposed under the well-defined conditions of PSI-2 to pure and mixed D2 plasmas. A peak ion flux of 1022 D+ m−2 s is applied for up to 6 h at sample temperatures of up to 900 K. Pure D2 and mixed D2 + He, D2 + N2 and D2 + He + N2 plasmas are applied to the sample at 68 V bias. The D2, He, N outgassing at 293 K and 580 k are observed via in-vacuo quadrupole mass spectrometry covering the range of 40 s–200 000 s after exposure. The outgassing decay follows a single power law with exponents α = −0.7 to −1.1 at 293 K, but at 580 K a drop from α = −0.25 to −2.35 is found. For DEMO a pump-down time to 0.5 mPa in the order of 1–5 h can be expected. The outgassing is in all cases dominated by D2.