Magnetic field of a plasma wake driven by a laser pulse

The quasistatic magnetic field generated by a short laser pulse in a uniform rarefied plasma is found analytically and compared to two-dimensional particle-in-cell simulations. It is shown that in a frame moving with the pulse the magnetic field contains a component which is homogeneous in the longitudinal direction and a component which is oscillating at the wave number 2k(p), where k(p) is the wave number of the plasma wake. Particle simulations confirm the analytical results and are also used to treat the case of high intense laser pulses with upsilon(E)/c greater than or similar to 1. The resultant magnetic field has a focusing effect on relativistic electrons in the plasma wakefield accelerator context.