Kinetic simulations of collisionless magnetic reconnection in presence of a guide field

The results of kinetic simulations of magnetic reconnection in Harris current sheets are analyzed. A range of guide fields is considered to study reconnection in plasmas characterized by different $\beta$ values, $\beta > m_e/m_i$. Both an implicit Particle-in-Cell (PIC) simulation method and a parallel explicit PIC code are used. Simulations with mass ratios up to the physical value are performed. The simulations show that the reconnection rate decreases with the guide field and depends weakly on the mass ratio. The off-diagonal components of the electron pressure tensor break the frozen-in condition, even in low $\beta$ plasmas. In high $\beta$ plasmas, evidence is presented that whistler waves play a key role in the enhanced reconnection, while in low $\beta$ plasmas the kinetic Alfv\'en waves are important. The in-plane and the out-of-plane ion and electron motion are also considered, showing that they are influenced by the mass ratio and the plasma $\beta$.