Ponderomotive force and dc magnetic field generation induced by laser absorption

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Abstract
A new expression for the ponderomotive force induced by high frequency electromagnetic and electrostatic waves propagating in plasma including the effects of dissipation is derived. Besides the usual irrotational leading term, a new simpler expression for the leading rotational term, which can contribute to the generation of mega‐Gauss dc magnetic fields is found. The leading irrotational term is proportional to the dissipation rate and vanishes for a standing wave. This expression is applied to the absorption of a planar electromagnetic wave, with polarization in (p) or out of (s) the plane of incidence, obliquely incident onto a half‐space of plasma with a linear density profile. The result for the dc magnetic field source term compares very well with the result from a two and one‐half dimensional particle simulation calculation for p polarization. Direct acceleration by the resonantly excited electrostatic waves is the dominant dissipation process in this case. At high power, the dominant dissipation process for s polarization is parametric decay into plasma waves which are Landau damped by the electrons. The magnetic field source term is found to be comparable to that of p polarization.