Magnetic field amplification by high power lasers in underdense plasma

The process by which an existing magnetic field of ∼102-103 T may be amplified by an order of magnitude along the axis of laser propagation in underdense plasma by an intense laser pulse is investigated. The mechanism underlying the effect is understood to be ponderomotive in nature, initiated by the drift motion of electrons displaced by the laser pulse as they relax towards the axis, and sustained by a combination of quasistatic magnetic field structures and electron Hall and diamagnetic currents. We employ two- and three-dimensional particle-in-cell simulations to numerically investigate the process and find qualitative agreement with the scaling relations found in our theory model. The lifetime of the process is considered, and we find the major factor limiting its growth and lifetime is ion motion, which disrupts the electron currents necessary to sustain the induced magnetic field. This field is found to be of sufficient strength, and is long-lived enough to be relevant for study in relation to applications in radiation production and laboratory astrophysics.