Flux-expansion divertor studies in TJ-II

The flux-expansion divertor concept is theoretically explored in TJ-II. This concept seems to be most suitable for this flexible stellarator in which the positions and the order of the resonances can be varied. As a first step, a family of configurations that exhibit flux expansion is identified. Then, a three-dimensional map of the collisional particle flux has been obtained for two different plasma regimes using the full-f Monte Carlo code ISDEP (Integrator of Stochastic Differential Equations in Plasmas), which computes the ion guiding-centre trajectories. The particle trajectories rather than the field lines must be considered since ion orbits can drift from the field lines in TJ-II and the plasma electric field and the collisionality must be considered in such calculations. We have checked that it is possible to strongly reduce the heat and particle fluxes by intercepting the trajectories at a given zone of the space. These calculations are done for thermal ions and for fast particles coming from the neutral beam injection heating. Future studies, possibly including the creation of an ergodic zone, will determine the best strategy for intercepting the trajectories.