Generation of magnetic moment field due to resonant interaction of waves in laser induced relativistic plasma

One of the most important processes that accompany laser-matter interaction is the magnetic field generation. Magnetic fields could have a significant effect on the overall nonlinear plasma dynamics. Particularly, extremely high magnetic fields play an essential role in propagation of laser pulses, laser beam self-focusing, and penetration of laser radiation into over dense plasma. Among the various mechanisms the inverse Faraday effect is responsible for the magnetic field generation from the electron motion in the circularly polarized electromagnetic wave. The original trajectories of the electrons and ions are deviated when electromagnetic wave passes through plasma and there is some gain in angular momentum, consequently magnetic moment field is being generated. During interaction with a circularly polarized laser pulse, plasma electrons absorb not only the laser energy but also the amount of the total angular momentum of the laser pulse. This angular momentum transfer leads to the electron rotation and the generation of the axial magnetic field by the azimuthally electron current. In the present paper, the theoretical investigation is made to find the magnetic moment field generated due to resonant interaction of four waves, two (transverse) electromagnetic waves and two high frequency (longitudinal) electrostatic waves, in a laser induced relativistic plasma. The magnetic field excited in the plasma from a matching of frequencies of first harmonic part of four waves is obtained. The matching condition for the frequencies of electromagnetic and electrostatic waves for the excitation of moment field is satisfied in a small region compared to the largest of the wave length of the involved waves. It is shown that the inclusion of relativistic effect enhances the magnetic moment field in laser induced plasma. The moment field is numerically estimated for high intensity laser beams. This moment field may be of the order of a few mega gauss. This magnetic field may have considerable impact on transport phenomena in fusion plasma. (author)