Kinetic Theory for Spontaneous Magnetic Field in Laser Plasma Interaction

In our previous paper [Phys. Plasmas 10, 4166 (2003)], we pointed out that the experimental results on the axial spontaneous magnetic field given by Najmudin et al. [Phys. Rev. Lett. 10, 215004 (2001)] can be explained by our kinetic model [Phys. Plasmas 8, 329 (2001)]. We also found that the azimuthal magnetic field Bθ given by our kinetic model is much weaker than the axial spontaneous magnetic field, which is not consistent with particle-in-cell simulation results. In the present paper, we reinvestigate the generation mechanism of the spontaneous magnetic fields from relativistic Vlasov-Maxwell equations. It is found that the azimuthal spontaneous magnetic field Bθ can be same order as the axial spontaneous magnetic field if the laser beam self-focus effect is considered. It is also obtained that the magnitude of the spontaneous magnetic field is proportional to the plasma density for the case of low plasma density, but is independent of the plasma density for the case of high plasma density.