Generation of Helical and Axial Magnetic Fields by the Relativistic Laser Pulses in Under—dense Plasma：Three—Dimensional Particle—in—Cell Simulation

The quasi-static magnetic fields created in the interaction of relativistic laser pulses with under-dense plasmas have been investigated by three-dimensional particle-in-cell simulation.The relativistic ponderomotive force can drive and intense electron current in the laser propagation direction,which is responsible for the generation of a helical magnetic field.The axial magnetic field results from a difference bean of wave-wave,which drives a solenoidal current.In particular,the physical significance of the kinetic model for the generation of the axial magnetic field is discussed.