The effect of the guide field on energy conversion during collisionless magnetic reconnection

Magnetic reconnection is well known as an efficient mechanism for transferring magnetic energy into plasma energy. However, how the energy conversion and partition between different species is influenced by the shear angle of the reconnecting magnetic component (i.e., the guide field strength) is not well understood. Using 2.5-dimensional particle-in-cell simulations, we investigated the energy conversion in reconnection with different guide fields. We found that the overall energy conversion first decreases steeply and then increases slowly when the guide field increases from B_g = 0 to B_g = 4. The increase in energy conversion in the large guide field regime is due to the electron energy gain through the perpendicular channel \boldsymbolJ_\perp \cdot \boldsymbolE_\perp . The overall energy conversion is predominantly contributed by \boldsymbolJ_\perp \cdot \boldsymbolE_\perp rather than J_\parallel E_\parallel . We further find that energy conversion mainly occurs within the reconnection front and the flux pileup region. However, the contribution from the fore reconnection front becomes important in large guide field regimes ( 3 < B_g\le 4 ) because of the enhanced electron energy gain.