Turbulence and transport in multi ion species fusion plasmas
Fusion energy research is entering into a new phase with the advent of the ITER device which is currently being constructed in Southern France. In parallel to the construction of the device an increased effort on the physics understanding and modelling with the aim of achieving an improved predictive capacity is undertaken. The main focus so far has been on the study of heat transport and relatively little effort has been devoted to the modelling of particle and impurity transport. Understanding the transport properties of impurities and He ash is important, since they are expected to significantly affect the performance of a fusion reactor by their contribution to radiation losses and main ion dilution. For example, high-Z impurity accumulation in the core region, predicted by neoclassical theory, would be devastating for fusion experiments. However, the presence of impurities at the edge of the reactor may be beneficial, and edge seeding of impurities is planned for future devices in order to create an edge-localized radiation belt for continuous heat exhaust. The behaviour of heavy impurities is of particular importance for ITER with a wall design with beryllium, carbon and tungsten, and for the JET ITER-like wall experimental programme where plasma performance is being tested to show that the level of tungsten reaching the core is acceptably low. On the other hand, main ion peaking in the plasma core is beneficial for a fusion device, leading to a strong increase in fusion energy output. Hence, for the optimisation of a fusion device, it is necessary to study the main ion peaking relative to the impurity peaking through a self-consistent treatment of multiple ion species plasmas. An extension with respect to previous years activities is that we are now starting to take into account rotational effects. The predicitive capability is established and assessed through validating simulations against experimental results on current devices such as JET.