Transition acceleration of electrons and reconnection of magnetic fields driven by two-beam relativistic laser pulses traversing a NCD plasma slab target

The self-generation and reconnection of magnetic fields and accompanying electron acceleration were studied when two ultrafast intense laser beams propagate synchronously through a thin plasma slab target with homogeneous near-critical density (NCD). The results show that the magnetic reconnection occurs behind the target and the electrons undergo three important accelerating stages, ponderomotive force acceleration in the plasma channels, transition (or transboundary) acceleration from the plasma medium to the vacuum, and acceleration by the reconnecting fields. In the reconnection process the hot electrons are compelled to be reverse-accelerated (generating refluxes) and consequently the double annular magnetic tube fields in channels are collapsed into one large-scale annular magnetic tube structure, in which a significant pinching effect is revealed. Meanwhile, two peculiar enclosed "field-free" zones were shown, which is suggested to be a combined effect of magnetic annihilation (MA) and longitudinal quasi-static electric field generated by separation of positive and negative charges.