Transport studies with magnetic islands in fusion plasmas

3D physics studies are a main topic in the development of efficient operations for ITER and in the Roadmap extrapolation to DEMO. In this context, this paper aims at providing a new modelling capability to study the impact of spontaneous and RMP-induced islands on the plasma transport. This paper aims at filling the gap due to the fact that 1.5D transport codes, widely used to analyse transport in toroidal devices, are applicable only for flux surfaces nested around a single axis, hence their use is prevented when magnetic islands play an important role modifying heat and particle fluxes. The paper presents a 1.5D formulation, applicable to Tokamak, Stellarator and Reversed Field Pinch (RFP), able to treat multiple axis geometries. After describing the 1.5D formulation and the code where it has been implemented, we present some preliminary applications obtained in RFX-mod, LHD and TJ-II.