In magnetically confined fusion plasmas the plasma core is separated from the first wall materials as far as possible. Highly energetic particles, however, can leave the confined plasma and collide with the surrounding walls. Due to the shape of the magnetic field, there is intensive plasma-wall interaction on the divertor wall. The plasma particles are collected, neutralized and extracted at the specially treated divertor surfaces. The same method is used to remove impurities from the plasma. Depending on operating conditions, however, high ion- and electron loads can cause considerable thermal stress and first-wall erosion. Developing suitable wall materials and understanding interactions between the plasma and the first wall are therefore central topics in fusion research.
In ITER beryllium will be used for the first wall and tungsten for the divertor. Recent molecular dynamic (MD) simulations of sputtering of BeD from pure Be surfaces by low-energy deuterium irradiation have shown that BeD and BeD+ are the most stable species, unlikely to further dissociate into their components. BeD2 and BeD2+are more likely to decompose into Be + D2 than into BeD + D. BeD3 and BeD3+ are metastable against their dissociation into BeD + D2. The analysis of the MD trajectories confirms that the formation of BeD occurs along the reaction pathways that have been suggested before.