Envelope soliton solutions of a class of generalized nonlinear Schrödinger equations are investigated. If the quasiparticle number N is conserved, the evolution of solitons in the presence of perturbations can be discussed in terms of the functional behavior of N(η2), where η2 is the nonlinear frequency shift. For ∂η2N >0, the system is stable in the sense of Liapunov, whereas, in the opposite region, instability occurs. The theorem is applied to various types of envelope solitons such as spikons, relatons, and others.

No abstract

Nonlinear ion-acoustic waves in magnetized plasmas are investigated. In strong magnetic fields they can be described by a Korteweg-de Vries (KdV) type equation. It is shown here that these plane soliton solutions become unstable with respect to bending distortions. Variational principles are derived for the maximum growth rate γ as a function of the transverse wavenumber k of the perturbations. Since the variational principles are formulated in complementary form, the numerical evaluation yields upper and lower bounds for γ. Choosing appropriate test functions and increasing the accuracy of the computations we find very close upper and lower bounds for the γ(k) curve. The results show that the growth rate peaks at a certain value of k and a cut-off kc exists. In the region where the γ(k) curve was not predicted numerically with high accuracy, i.e. near the cut-off, we find very precise analytical estimates. These findings are compared with previous results. For k≥kc, stability with respect to transverse perturbations is proved.

Ultrashort-pulse laser intensities can reach 10(22) W/cm(2). In this case the electron motion becomes ultrarelativistic and significant bremsstrahlung occurs. The radiation causes a dissipative effect, which is called a radiation reaction. It has been shown in the literature that the radiation reaction force causes phase-space contraction when the motion of electrons in a laser field is considered. The effect of the radiation reaction force is smaller for electron propagation in the direction of a propagating plane wave compared to counterpropagation. In the case of two colliding laser beams with sufficiently large amplitudes, stochastic heating is an important process that will be influenced by the radiation reaction. It is shown here that the radiation reaction causes attractors and in certain parameter regimes electron motion converges to regular attractors. This causes a significant reduction of stochastic heating. The forms of the attractors are presented. The results confirm the general prediction of phase-space contraction and provide quantitative results for the speed of contraction as well as the type of attracted motion.

No abstract