Spontaneous development of toroidal magnetic field during formation of field-reversed theta pinch

Abstract

The formation of an FRC (Field-Reversed Configuration) is considered by using a hybrid simulation model that treats the electrons as a zero-inertia thermal fluid and the ions either kinetically or as a simple fluid. The unexpected spontaneous generation of a substantial toroidal magnetic field Bθ near magnetic reconnection points requires explanation. Although ion kinetic effects are responsible for some of the internal reconnection, simulations with a fluid ion representation also show similar self-generation of the toroidal field. Further investigation reveals that the origin of the toroidal field can be found in some of the terms that arise from retention of the Hall term – an automatic feature of the two-component model. Conceptually, the phenomena can be understood by noting that, if the magnetic field is ‘frozen into the electron fluid’, a sheared toroidal electron flow will stretch the poloidal field to make the toroidal field.