• Energy Research

ITER will use beryllium as a plasma-facing material in the main chamber, covering a total surface area of about 620 m2. Given the importance of beryllium erosion and co-deposition for tritium retention in ITER, significant efforts have been made to understand the behaviour of beryllium under fusion-relevant conditions with high particle and heat loads. This paper provides a comprehensive report on the state of knowledge of beryllium behaviour under fusion-relevant conditions: the erosion mechanisms and their consequences, beryllium migration in JET, fuel retention and dust generation. The paper reviews basic laboratory studies, advanced computer simulations and experience from laboratory plasma experiments in linear simulators of plasma–wall interactions and in controlled fusion devices using beryllium plasma-facing components. A critical assessment of analytical methods and simulation codes used in beryllium studies is given. The overall objective is to review the existing set of data with a broad literature survey and to identify gaps and research needs to broaden the database for ITER.

We present a quasiclassical trajectory study of the photodissociation of CH3CHO to molecular and radical products, CH4 + CO and CH3 + HCO, respectively, using global ab initio-based potentials energy surfaces. The molecular products have a well-defined potential barrier transition state (TS) but the dynamics exhibit strong deviations from the TS pathway to these products. The radical products are formed via a variational TS. Calculations are reported at total energies corresponding to photolysis wavelengths of 308, 282, 264, 248 and 233 nm. The results at 308 nm focus on a comparison with experiment [Houston, P. L.; Kable, S. H. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 16079] and the elucidation of the nature and extent of non-TS reaction dynamics to form the molecular products, CH4 + CO. At the other wavelengths the focus is the branching ratio of these products and the radical products, CH3 + HCO.

Crossed molecular beam experiments and accurate quantum scattering calculations have been carried out for the polyatomic H + CD 4 → HD + CD 3 reaction. Unprecedented agreement has been achieved between theory and experiments on the energy dependence of the integral cross section in a wide collision energy region that first rises and then falls considerably as the collision energy increases far over the reaction barrier for this simple hydrogen abstraction reaction. Detailed theoretical analysis shows that at collision energies far above the barrier the incoming H-atom moves so quickly that the heavier D-atom on CD 4 cannot concertedly follow it to form the HD product, resulting in the decline of reactivity with the increase of collision energy. We propose that this is also the very mechanism, operating in many abstraction reactions, which causes the differential cross section in the backward direction to decrease substantially or even vanish at collision energies far above the barrier height.