arXiv subjects

Y. Kominis

Publications and source records attributed to Y. Kominis.

5 recordsLinked to original sources

arXiv2024

Analytical calculation of the kinetic q factor and resonant response of toroidally confined plasmas

Symmetry-breaking perturbations in axisymmetric toroidal plasma configurations have a drastic impact on particle, energy, and momentum transport in fusion devices, thereby affecting their confinement properties. The perturbative modes strongly affect particles with specific kinetic characteristics through resonant mode-particle interactions. In this work we present an analytical calculation of the kinetic q factor enabling the identification of particles with kinetic properties that meet the resonant conditions. This allows us to predict the locations and structures of the corresponding resonant island-chains, as well as the existence of transport barriers in the particle phase space. The analytical results, derived for the case of a large aspect ratio configuration, are systematically compared to numerical simulations, and their domain of validity is thoroughly investigated and explained. Our findings demonstrate that calculating the kinetic q factor and its dependence on both particle and magnetic field characteristics, provides a valuable tool for understanding and predicting the resonant plasma response to non-axisymmetric perturbations. Moreover, this approach can be semi-analytically applied to generic realistic experimental equilibria, offering a low-computational-cost method for scenario investigations under various multiscale perturbative modes.

physics.plasm-ph↗

arXiv2021

Parametric control of self-sustained and self-modulated optomechanical oscillations

Optomechanical systems are known to exhibit a rich set of complex dynamical features including various types of chaotic behavior and multi-stability. Although this exotic behavior has attracted an intense research interest, the utilization of optomechanical systems in technological applications, in most cases necessitates a complex, yet predictable and controllable, oscillatory response. In fact, the various types of robust oscillations supported by optomechanical systems are nested in either the same or neighboring regions of the parameter space, where chaos exists. In this work we systematically dissect the parameter space of the fundamental optomechanical oscillator in order to identify regions where stable self-sustained and self-modulated oscillations exist, by utilizing bifurcation analysis and advanced numerical continuation techniques. Moreover,in cases where bistability occurs, we study the accessibility of these oscillatory states in terms of initial conditions and their location with respect to well-defined basins of attraction. The results provide specific knowledge for the parameter sets enabling the appropriate oscillatory response for different types of applications.

nlin.CD↗

arXiv2018

Presence of temporal dynamical instabilities in topological insulator lasers

Topological insulator lasers are a newly introduced kind of lasers in which light snakes around a cavity without scattering. Like for an electron current in a topological insulator material, a topologically protected lasing mode travels along the cavity edge, steering neatly around corners and imperfections without scattering or leaking out. In a recent experiment, topological insulator lasers have been demonstrated using a square lattice of coupled semiconductor microring resonators with a synthetic magnetic field. However, laser arrays with slow population dynamics are likely to show dynamical instabilities in a wide range of parameter space corresponding to realistic experimental conditions, thus preventing stable laser operation. While topological insulator lasers provide an interesting mean for combating disorder and help collective oscillation of lasers at the edge of the lattice, it is not clear whether chiral edge states are immune to dynamical instabilities. In this work we consider a realistic model of semiconductor class-B topological insulator laser and show that chiral edge states are not immune to dynamical instabilities.

physics.optics↗

arXiv2018

Nonlinear Beam Propagation in a Class of Complex Non-PT -Symmetric Potentials

The subject of PT-symmetry and its areas of application have been blossoming over the past decade. Here, we consider a nonlinear Schrödinger model with a complex potential that can be tuned controllably away from being PT-symmetric, as it might be the case in realistic applications. We utilize two parameters: the first one breaks PT-symmetry but retains a proportionality between the imaginary and the derivative of the real part of the potential; the second one, detunes from this latter proportionality. It is shown that the departure of the potential from the PT -symmetric form does not allow for the numerical identification of exact stationary solutions. Nevertheless, it is of crucial importance to consider the dynamical evolution of initial beam profiles. In that light, we define a suitable notion of optimization and find that even for non PT-symmetric cases, the beam dynamics, both in 1D and 2D -although prone to weak growth or decay- suggests that the optimized profiles do not change significantly under propagation for specific parameter regimes.

nlin.PS↗

arXiv2015

Orbital Spectrum Analysis of Non-Axisymmetric Perturbations of the Guiding-Center Particle Motion in Axisymmetric Equilibria

The presence of non-axisymmetric perturbations in an axisymmetric magnetic field equilibrium renders the Guiding Center (GC) particle motion non-integrable and may result in particle, energy and momentum redistribution, due to resonance mechanisms. We analyse these perturbations in terms of their spectrum, as observed by the particles in the frame of unperturbed GC motion. We calculate semi-analytically the exact locations and strength of resonant spectral components of multiple perturbations. The presented Orbital Spectrum Analysis (OSA) method is based on an exact Action-Angle transform that fully takes into account Finite Orbit Width (FOW) effects. The method provides insight into the particle dynamics and enables the prediction of the effect of any perturbation to all different types of particles and orbits in a given, analytically or numerically calculated, axisymmetric equilibrium.

physics.plasm-ph↗