Evolution and consequences of orbit type distributions in FRCs

Field Reversed Configurations (FRCs) are characterized by particular electric and magnetic field geometries that are due to the presence of unique particle orbit types as so-called Betatron, Drift, Fig8 and Type1 orbits. Such a rich orbit type inventory includes a peculiarly significant fraction of large orbits that is of paramount relevance in terms of the global stability of the configuration. Different orbit types may have different toroidal drift velocities and consequently generate toroidal currents in opposite directions. Therefore a change in the orbit type distribution may lead to an important alteration at different scales of the original spatial structure of the plasma current and eventually to an alteration of the magnetic and electric fields geometries. Through simulations carried out with FPIC (TAE's 3D full hybrid PIC code) we investigate the evolution in time of both thermal and fast ion orbit distributions and examine a possible correlation between the observed changes and the onset of global instabilities.