Electromagnetic rogue waves in beam-plasma interactions

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 weakly nonlinear circularly polarized electromagnetic pulses in magnetized plasmas. A nonlinear Schrödinger (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 the 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. © 2013 IOP Publishing Ltd.

Freak waves and electrostatic wavepacket modulation in a quantum electron-positron-ion plasma

The occurrence of rogue waves (freak waves) associated with electrostatic wavepacket propagation in a quantum electron-positron-ion plasma is investigated from first principles. Electrons and positrons follow a Fermi-Dirac distribution, while the ions are subject to a quantum (Fermi) pressure. A fluid model is proposed and analyzed via a multiscale technique. The evolution of the wave envelope is shown to be described by a nonlinear Schrödinger equation (NLSE). Criteria for modulational instability are obtained in terms of the intrinsic plasma parameters. Analytical solutions of the NLSE in the form of envelope solitons (of the bright or dark type) and localized breathers are reviewed. The characteristics of exact solutions in the form of the Peregrine soliton, the Akhmediev breather and the Kuznetsov-Ma breather are proposed as candidate functions for rogue waves (freak waves) within the model. The characteristics of the latter and their dependence on relevant parameters (positron concentration and temperature) are investigated. © 2014 IOP Publishing Ltd.

Effects of buried high-Z layers on fast electron propagation

By extending a prior model [A. R. Bell, J.R. Davies, S. M. Guerin, Phys. Rev. E 58, 2471 (1998)], the magnetic field generated during the transport of a fast electron beam driven by an ultraintense laser in a solid target is derived analytically and applied to estimate the effect of such field on fast electron propagation through a buried high-Z layer in a lower-Z target. It is found that the effect gets weaker with the increase of the depth of the buried layer, the divergence of the fast electrons, and the laser intensity, indicating that magnetic field effects on the fast electron divergence as measured from K-a X-ray emission may need to be considered for moderate laser intensities. On the basis of the calculations, some considerations are made on how one can mitigate the effect of the magnetic field generated at the interface.

The Influence of the User in Body-Centric Antennas and Propagation at 3–6 GHz—A Rician K-Factor Approach

We investigate whether the presence of a human body in wearable communications should be considered as part of the radiating structure or as part of the local radio environment. The Rician $K$ -factor was employed as a quantitative measure of the effect of the user's body for five environments and two mounting locations. Presented empirical results indicated that the environment had a greater impact on the $K$-factor values than the position of the transmit antenna for the ultrawideband signals used, confirming that the human body should be considered primarily as part of the overall radiating system when the antenna is worn on the body. Furthermore, independent variations also existed in the $K$-factor values for the differing antenna-body mounting positions, indicating that as the position changed, then the radiating effects and the contribution from the body changed. This is significant for ensuring body-antenna systems are accurately modeled in system-level simulations.

IMAGING OF SURFACE-PLASMON LAUNCH AND PROPAGATION USING A PHOTON SCANNING TUNNELING MICROSCOPE

The spectroscopic capability of the photon scanning tunneling microscope is exploited to study directly the launch and propagation of surface plasmons on thin silver films. Two input beams, of different wavelength, are incident through the prism in a prism-Ag film-air-fibre tip system. Both excite surface plasmons at the Ag-air interface and light of both wavelengths is coupled into the fibre probe via the respective surface plasmon evanescent fields. One laser beam is used for instrument control. The second, or probe beam is tightly focused on the sample, within the area of the unfocused or control beam, giving a well-defined and symmetrical, confined surface plasmon launch site. However, the image at the probe wavelength is highly asymmetrical in section with an exponential tail extending beyond one side of the launch site. This demonstrates in a very direct fashion;the propagation of surface plasmons; a propagation length of similar to 11.7 mu m is measured at a probe wavelength of 543.5 nm. On rough Ag films the excitation of localised scattering centres is also observed in addition to the launch of delocalised surface plasmons.

Propagation modelling and measurements in a populated indoor environment at 5.2 GHz

Human occupants within indoor environments are not always stationary and their movement will lead to temporal channel variations that strongly affect the quality of indoor wireless communication systems. This paper describes a statistical channel characterization, based on experimental measurements, of human body effects on line-of-sight indoor narrowband propagation at 5.2 GHz. The analysis shows that, as the number of pedestrians within the measurement location increases, the Ricean K-factor that best fits the empirical data tends to decrease proportionally, ranging from K=7 with 1 pedestrian to K=0 with 4 pedestrians. Level crossing rate results were Rice distributed, while average fade duration results were significantly higher than theoretically computed Rice and Rayleigh, due to the fades caused by pedestrians. A novel CDF that accurately characterizes the 5.2 GHz channel in the considered indoor environment is proposed. For the first time, the received envelope CDF is explicitly described in terms of a quantitative measurement of pedestrian traffic within the indoor environment.

Space-Constrained Massive MIMO: Hitting the Wall of Favorable Propagation

The recent development of the massive multiple-input multiple-output (MIMO) paradigm, has been extensively based on the pursuit of favorable propagation: in the asymptotic limit, the channel vectors become nearly orthogonal and interuser interference tends to zero [1]. In this context, previous studies
have considered fixed inter-antenna distance, which implies an increasing array aperture as the number of elements increases. Here, we focus on a practical, space-constrained topology, where an increase in the number of antenna elements in a fixed total space imposes an inversely proportional decrease in the inter-antenna distance. Our analysis shows that, contrary to existing studies, inter-user interference does not vanish in the massive MIMO regime, thereby creating a saturation effect on the achievable rate.

Polarization-dependent one-way surface wave propagation

We numerically study nonreciprocal regimes of surface plasmon-polariton at the interface between two gyrotropic media. We predict existence of isolated unidirectional TE and TM surface modes guided by the interface between gyroelectric and gyromagnetic media.

Modeling relativistic soliton interactions in overdense plasmas: A perturbed nonlinear Schrodinger equation framework

We investigate the dynamics of localized solutions of the relativistic cold-fluid plasma model in the small but finite amplitude limit, for slightly overcritical plasma density. Adopting a multiple scale analysis, we derive a perturbed nonlinear Schrodinger equation that describes the evolution of the envelope of circularly polarized electromagnetic field. Retaining terms up to fifth order in the small perturbation parameter, we derive a self-consistent framework for the description of the plasma response in the presence of localized electromagnetic field. The formalism is applied to standing electromagnetic soliton interactions and the results are validated by simulations of the full cold-fluid model. To lowest order, a cubic nonlinear Schrodinger equation with a focusing nonlinearity is recovered. Classical quasiparticle theory is used to obtain analytical estimates for the collision time and minimum distance of approach between solitons. For larger soliton amplitudes the inclusion of the fifth-order terms is essential for a qualitatively correct description of soliton interactions. The defocusing quintic nonlinearity leads to inelastic soliton collisions, while bound states of solitons do not persist under perturbations in the initial phase or amplitude

Pressure anisotropy effects on nonlinear electrostatic excitations in magnetized electron-positron-ion plasmas

The propagation of linear and nonlinear electrostatic waves is investigated in a magnetized anisotropic electron-positron-ion (e-p-i) plasma with superthermal electrons and positrons. A two-dimensional plasma geometry is assumed. The ions are assumed to be warm and anisotropic due to an external magnetic field. The anisotropic ion pressure is defined using the double adiabatic Chew-Golberger-Low (CGL) theory. In the linear regime, two normal modes are predicted, whose characteristics are investigated parametrically, focusing on the effect of superthermality of electrons and positrons, ion pressure anisotropy, positron concentration and magnetic field strength. A Zakharov-Kuznetsov (ZK) type equation is derived for the electrostatic potential (disturbance) via a reductive perturbation method. The parametric role of superthermality, positron content, ion pressure anisotropy and magnetic field strength on the characteristics of solitary wave structures is investigated. Following Allen and Rowlands [J. Plasma Phys. 53, 63 (1995)], we have shown that the pulse soliton solution of the ZK equation is unstable to oblique perturbations, and have analytically traced the dependence of the instability growth rate on superthermality and ion pressure anisotropy.