Nonlinear group velocity of an electron plasma wave

The nonlinear group velocity of an electron plasma wave is investigated numerically using a Vlasov code, and is found to assume values which agree very well with those predicted by a recently published theory [D. Benisti et al., Phys. Rev. Lett. 103, 155002 (2009)], which we further detail here. In particular we show that, once Landau damping has been substantially reduced due to trapping, the group velocity of an electron plasma wave is not the derivative of its frequency with respect to its wave number. This result is moreover discussed physically, together with its implications in the saturation of stimulated Raman scattering. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3464467]