Magnetic field generation in rotating plasma waves driven by co-propagating OAM lasers

We present a new magnetic field generation mechanism in underdense plasma due to rotating plasma waves driven by co-propagating Laguerre-Gaussian (LG) beating orbital angular momentum (OAM) laser beams with both a different frequency and also different twist index. In this plasma wave, particles oscillate elliptically in the transverse plane with an azimuthally dependent phase. We therefore call it a transverse rotating plasma wave (TRPW). The distribution and evolution of density and electric field in the transverse plane has some special characteristics. We present a linear fluid model of TRPW and also a high order analysis of the electrical current based on particle motion. To the second order, there is a net rotating current leading to the onset of an intense axial magnetic field (up to 0.4 MG), which persists over a long time in the plasma (ps scale). It is different from Inverse Faraday effects. Our analytical predictions are confirmed in three-dimensional particle-in-cell simulations using EPOCH. This new method of magnetic field creation may find applications in charged beam collimation and controlled fusion.