We report on spatiotemporal evolution of relativistically intense longitudinal electron plasma waves in a cold homogeneous plasma, using the physically appealing Dawson sheet model. Calculations presented here in the weakly relativistic limit clearly show that under very general initial conditions, a relativistic wave will always phase mix and eventually break at arbitrarily low amplitudes, in a time scale omegapetaumix approximately {3/64(omegape2delta3/c2k2)|Deltak/k|(|1+Deltak/k|)](1+1|1+Deltak/k|)}(-1). We have verified this scaling with respect to amplitude of perturbation delta and width of the spectrum (Deltakk) using numerical simulations. This result may be of relevance to ultrashort, ultraintense laser pulse-plasma interaction experiments where relativistically intense waves are excited.

A numerical fluid simulation investigation of the temporal evolution of a special class of traveling wave solutions of the one dimensional relativistic cold plasma model is reported. The solutions consist of coupled electromagnetic and plasma waves in a solitary pulse shape (Phys. Rev. Lett. 68, 3172 (1992); Phys. Plasmas 9, 1820 (2002)). Issues pertaining to their stability, mutual collisional interactions and propagation in an inhomogeneous plasma medium are addressed. It is found that solitary pulses that consist of a single light peak trapped in a modulated density structure are long lived whereas structures with multiple peaks of trapped light develop an instability at the trailing edge. The interaction properties of two single peak structures show interesting dependencies on their relative amplitudes and propagation speeds and can be understood in terms of their propagation characteristics in an inhomogeneous plasma medium.

The occurrence of rogue waves (freak waves) associated with electromagnetic pulse propagation interacting with a plasma is investigated, from first principles. A multiscale technique is employed to solve the fluid-Maxwell equations describing a weakly nonlinear circularly polarized electromagnetic pulses in magnetized plasmas. A nonlinear Schrodinger (NLS) type equation is shown to govern the amplitude of the vector potential. A set of non-stationary envelope solutions of the NLS equation are considered, as potential candidates for modeling of rogue waves (freak waves) in beam-plasma interactions, namely in the form of the Peregrine soliton, the Akhmediev breather and the Kuznetsov-Ma breather. The variation of the structural properties of the latter structures with relevant plasma parameters is investigated, in particular focusing on the ratio between the (magnetic field dependent) cyclotron (gyro-) frequency and the plasma frequency.

We report on the kinetic Boltzmann approach adapted for simulations of highly ionized matter created from a solid by its x-ray irradiation. X rays can excite inner-shell electrons, which leads to the creation of deeply lying core holes. Their relaxation, especially in heavier elements, can take complicated paths, leading to a large number of active configurations. Their number can be so large that solving the set of respective evolution equations becomes computationally inefficient and another modeling approach should be used instead. To circumvent this complexity, the commonly used continuum models employ a superconfiguration scheme. Here, we propose an alternative approach which still uses "true" atomic configurations but limits their number by restricting the sample relaxation to the predominant relaxation paths. We test its reliability, performing respective calculations for a bulk material consisting of light atoms and comparing the results with a full calculation including all relaxation paths. Prospective application for heavy elements is discussed.