Miloš M. Škorić

Stimulated photon cascade and condensate in a relativistic laser-plasma interaction

The propagation of a linearly polarized relativistic laser pulse in an underdense plasma is studied by fluid-Maxwell and particle-in-cell simulations. A nonlinear interplay between backward and forward stimulated Raman scattering instabilities produces a strong spatial modulation of the light pulse and the down cascade in its frequency spectrum. The Raman cascade saturates by a unique photon condensation at the bottom of the light spectra near the electron plasma frequency, related to strong depletion and possible break-up of the laser beam. In the final stage of the cascade-into-condensate mechanism, the depleted downshifted laser pulse is gradually transformed into a train of ultra-short relativistic light solitons.

Nonlinear physics of plasmas

Fundamentals of Plasma Physics.- Basic Properties of High Temperature Plasmas.- The Kinetic Theory of Plasmas.- The Fluid Theory of Plasmas.- Waves in Plasmas.- Nonlinear Theory of Plasmas.- Nonlinear Interactions in Plasmas.- Solitons in Plasmas.- Vortical Motions in Plasmas.- Chaos in Plasmas.- Ponderomotive Potential and Magnetization.- Structures in Strong Plasma Turbulence.- Strong Langmuir Turbulence.- Wave Collapse in Plasmas.- Spatiotemporal Complexity in Plasmas.- Relativistic Laser Plasma Interactions.- Multiscale Plasma Interactions.- Multifractal Characterization of Plasma Edge Turbulence.- Multi-Scale Modelling of Nonlinear Plasmas.

Stability of one-dimensional electromagnetic solitons in relativistic laser plasmas

Existence and stability of one-dimensional electromagnetic solitons formed in a relativistic interaction of a linearly polarized laser light with an underdense cold plasma are discussed. In a weakly relativistic model, the original equation of the nonlinear Schrodinger type, with local and nonlocal cubic nonlinearities, is derived. Standing electromagnetic soliton solutions are analytically shown to be stable in agreement with the model simulation. A difference in soliton stability for linear and circular polarization is discussed. Finally, by fully relativistic fluid–Maxwell simulations, a family of large relativistic solitons is revealed, while analytical estimates for the maximum amplitude and the soliton eigenfrequency come close to simulation results.

Spatiotemporal dynamics and transport reduction in helical magnetic configuration

Effects of multihelicity confinement magnetic fields on turbulent transport and zonal flows are investigated by means of spatiotemporal analysis of gyrokinetic Vlasov simulation results for the ion temperature gradient turbulence, where the standard and the inward-shifted configurations of the Large Helical Device are considered. The analysis of simulation results demonstrates that fluctuations of electrostatic potential for zonal flows exhibit spatiotemporal chaos in both configurations. However, the intensity of chaos found is considerably decreased in the inward-shifted configuration consistent with improved confinement. Enhanced zonal flow generation in the inward shifted case is accompanied by transport reduction which may be a direct consequence of chaos suppression.

On regimes of wave collapse in a magnetized plasma

Abstract We study the collapse dynamics of nonlinear upper-hybrid and lower-hybrid waves in a weakly magnetized plasma. We prove that, in these systems, three-dimensional soliton solutions do not exist and discuss necessary conditions for the wave collapse. Different collapse regimes, spanning from a strong to various weak types are shown to exist.

Stimulated Raman cascade and photon condensation in intense laser plasma interaction

Stimulated Raman scattering, stimulated Raman cascade, and the transition from Raman cascade into photon condensation, induced by linearly polarized intense laser interacting with an underdense uniform collisionless plasma, are studied by particle simulations. In addition to the stimulated Raman scattering process, the simulation results can reveal a clear physics picture on stimulated Raman cascade and cascade-into-condensation. It is found that, at appropriate laser amplitude and plasma conditions, a large amplitude relativistic electromagnetic soliton forms due to the strong photon condensation. The electromagnetic frequency of the soliton is about half of the unperturbed electron plasma frequency. The transverse electric field, magnetic field, and electrostatic field inside a soliton region have half-, one-, and one-cycle structure in space, respectively. Finally, the influence of the electron temperature and the ion dynamics are discussed briefly.

On transverse instability of large‐amplitude Langmuir solitons

The transverse instability of a large‐amplitude Langmuir soliton in a weakly magnetized plasma is examined in the framework of the generalized nonlinear Schrodinger type of equation with a nonadiabatic ion response. Making use of a numerical ‘‘shooting’’ method, the instability eigenfunctions and eigenvalues (growth rates) are calculated and depend on the magnetic field, soliton strength, and perturbation wave number. Results in small‐amplitude and curl‐free Zakharov equation limits are discussed.

Effects of time-varying E × B flow on slab ion-temperature-gradient turbulence

Effects of time-varying sheared E×B flow on turbulence driven by slab ion temperature gradient instabilities are investigated by means of Landau fluid simulation. Here, the E×B flow, which consists of stationary and time-periodic oscillatory parts, is externally imposed to the turbulence. The dependence on the amplitude and frequency of E×B flow is examined in the case that the amplitude of oscillatory part is the same or less than that of stationary part. The ion heat transport caused by turbulence oscillates with the same period as the E×B flow and the time-averaged transport coefficient is larger than the coefficient which is evaluated without the oscillatory part. The time-averaged coefficient is maximized when the amplitude of oscillatory part is equal to that of stationary part. As the frequency of E×B flow increases, the time-averaged coefficient decreases and is close to the coefficient which is evaluated without the oscillatory part. This mechanism is explained by introducing a kind of the logist...

Multi-scale simulation for plasma science

In order to perform a computer simulation of a large time and spatial scale system, such as a fusion plasma device and solar-terrestrial plasma, macro simulation model, where micro physics is modeled analytically or empirically, is usually used. However, kinetic effects such as wave-particle interaction play important roles in most of nonlinear plasma phenomena and result in anomalous behavior. This limits the applicability of macro simulation models. In a past few years several attempts have been performed to overcome this difficulty. Two types of multi-scale simulation method for nonlinear plasma science are presented. First one is the Micro-Macro Interconnected Simulation Method (MMIS), where micro model and macro model are connected dynamically through an interface and macro time and space simulation is performed. Second one is the Equation Free Projective Integration Method (EFPI), where macro space and time scale simulation is performed by using only a micro simulator and a sophisticated numerical algorithm.

Stimulated trapped electron acoustic wave scattering, electromagnetic soliton and ion vortices in intense laser interaction with subcritical plasmas

Stimulated trapped electron acoustic wave scattering by a linearly polarized intense laser in a subcritical plasma is studied by particle simulation. The scattering process is a three-wave parametric decay of the laser pump into a critical Stokes electromagnetic sideband wave and the trapped electron acoustic wave. As the ion acoustic wave grows in time, it breaks locally, followed by a large relativistic electromagnetic soliton. A new phenomenon, MeV ion vortex in ion phase space, forms by local electromagnetic and electrostatic fields inside the soliton. It is found that the electron acoustic wave mode is similar to the kinetic electrostatic electron nonlinear waves.