The particle flux structure and the search for a flux-expansion divertor in TJ-II

We explore the possibility of having a flux-expansion divertor in TJ-II. As a first step, the three-dimensional map of the particle flux has been obtained for two different plasma regimes using the code ISDEP, which computes the ion guiding-centre trajectories. We consider the particle trajectories rather than the field lines due to the fact that, in TJ-II, common ion orbits can separate from the field lines, and moreover the plasma electric field and the collisionality must be considered. We have chosen a configuration that presents flux expansion at given toroidal positions. We have estimated the heat and particle fluxes and checked that it is possible to reduce them strongly by intersecting the trajectories at a given zone of the space. Future studies, maybe including the creation of an ergodic zone, will determine the best strategy for intercepting the trajectories. (author)