Detailed magnetic structure and stochastic threshold

Non-linear evolution of reconnection is too slow to explain-by itself-fast phenomena such as internal disruptions in tokamaks or flares in the solar atmosphere. It has been proposed that the change in topology could lead to field line stochastization, and hence to highly increased transport. An important objection to this idea is that the increase of transport coefficients should smoothly follow the amplitude of the perturbation, while the observations show a catastrophic transition. We have shown 1) that the shape of the structures (and not only their size or amplitude) evolve during non-linear evolution 2) that the stochastic threshold can be strongly influenced by the detailed shape. Therefore, sharp transitions can appear during the evolution, due to the combination of these two effects. We will first consider an idealized situation, namely the two-waves problem in slab geometry, for which we will study the effect of the separatrix shape on the stochastic threshold. In the second part, we will present an application to the internal disruption in tokamaks, with anm=1 perturbation in a toroidal magnetic configuration. In the last part, we will discuss possible applications of the studies on shape effects to the behaviour of trapped particles in structures of the solar atmosphere.     

Some aspects of continuous flow electrophoresis in microgravity

Zone electrophoresis is a highly efficient method of separating biological products. It is based on the differences of mobilities of ionized particles in an electric field. During the separation complications arise due to electro-osmosis or thermal convection generated by Joule heating.This paper analyses the hydrodynamical running of a continuous flow zone electrophoresis cell and shows the influence of specific parameters on the separation.The modelling of the flow structure of the buffer solution is developed. The equations and the corresponding boundary conditions are solved by finite difference method. The model established provides knowledge of the hydrodynamical perturbations generated by electro-osmosis and thermal free convection. The case of microgravity is considered.