arXiv subjects

M. Marklund

Publications and source records attributed to M. Marklund.

At least 55 records · Page 3Linked to original sources

arXiv2012

A Scalar Wigner Theory for Polarized Light in Nonlinear Kerr Media

A scalar Wigner distribution function for describing polarized light is proposed in analogy with the treatment of spin variables in quantum kinetic theory. The formalism is applied to the propagation of circularly polarized light in nonlinear Kerr media and an extended phase space evolution equation is derived along with invariant quantities. We further consider modulation instability as well as the extension to partially coherent fields.

physics.optics↗

arXiv2012

Laser Wakefield Acceleration Using Wire Produced Double Density Ramps

A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator (LWFA) is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection and acceleration in the second plasma wave period. Compared to self-injection by wavebreaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to one order of magnitude in the quasi-monoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by approximately 25 %, and the localized injection at the density downramps results in spectra with less than a few percent relative spread.

physics.plasm-ph↗

arXiv2012

Particle-in-Cell simulations of electron spin effects in plasmas

We have here developed a particle-in-cell code accounting for the magnetic dipole force and for the magnetization currents associated with the electron spin. The electrons is divided into spin-up and spin-down populations relative to the magnetic field, where the magnetic dipole force acts in opposite directions for the two species. To validate the code, we have studied the wakefield generation by an electromagnetic pulse propagating parallel to an external magnetic field. The properties of the generated wakefield is shown to be in good quantitative agreement with previous theoretical results. Generalizations of the code to account for more quantum effects is discussed

physics.plasm-ph↗

arXiv2012

Parametric resonance of capillary waves at the interface between two immiscible Bose-Einstein condensates

We study parametric resonance of capillary waves on the interface between two immiscible Bose-Einstein condensates pushed towards each other by an oscillating force. Guided by analytical models, we solve numerically the coupled Gross-Pitaevskii equations for two-component Bose-Einstein condensate at zero temperature. We show that, at moderate amplitudes of the driving force, the instability is stabilized due to non-linear modifications of the oscillation frequency. When the amplitude of the driving force is large enough, we observe detachment of droplets from the Bose-Einstein condensates, resulting in generation of quantum vortices (skyrmions). We analytically investigate the vortex dynamics, and conditions of quantized vortex generation.

cond-mat.quant-gas↗

arXiv2012

Proton acceleration by circularly polarized traveling electromagnetic wave

The acceleration of charged particles, producing collimated mono-energetic beams, over short distances holds the promise to offer new tools in medicine and diagnostics. Here, we consider a possible mechanism for accelerating protons to high energies by using a phase-modulated circularly polarized electromagnetic wave propagating along a constant magnetic field. It is observed that a plane wave with dimensionless amplitude of 0.1 is capable to accelerate a 1 KeV proton to 386 MeV under optimum conditions. Finally we discuss possible limitations of the acceleration scheme.

physics.acc-ph↗

arXiv2012

Doping front instabilities in organic semiconductors: a means for optimizing optoelectronic devices

Recently, it was demonstrated that electrochemical doping fronts in organic semiconductors ex- hibit a new fundamental instability growing from multidimensional perturbations [Phys. Rev. Lett. 107, 016103 (2011)]. In the instability development, linear growth of tiny perturbations goes over into a nonlinear stage of strongly distorted doping fronts. Here we develop the nonlinear theory of the doping front instability and predict the key parameters of a distorted doping front, such as its velocity, in close agreement with the experimental data. We show that the instability makes the electrochemical doping process considerably faster. We obtain the self-similar properties of the front shape corresponding to the maximal propagation velocity, which allows for a wide range of controlling the doping process in the experiments. The theory developed provides the guide for optimizing the performance of organic optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2011

Quantum swapping of immiscible Bose-Einstein condensates as an alternative to the Rayleigh-Taylor instability

We consider a two-component Bose-Einstein condensate in a quasi-one-dimensional harmonic trap, where the immiscible components are pressed against each other by an external magnetic force. The zero-temperature non-stationary Gross-Pitaevskii equations are solved numerically; analytical models are developed for the key steps in the process. We demonstrate that if the magnetic force is strong enough, then the condensates may swap their places in the trap due to dynamic quantum interpenetration of the nonlinear matter waves. The swapping is accompanied by development of a modulational instability leading to quasi-turbulent excitations. Unlike the multidimensional Rayleigh-Taylor instability in a similar geometry of two-component quantum fluid systems, quantum interpenetration has no classical analogue. A crossover between the Rayleigh-Taylor instability and the quantum interpenetration in a two-dimensional geometry is demonstrated.

cond-mat.quant-gas↗

arXiv2011

Signatures of Radiation Reaction in Ultra-Intense Laser Fields

We discuss radiation reaction effects on charges propagating in ultra-intense laser fields. Our analysis is based on an analytic solution of the Landau-Lifshitz equation. We suggest to measure radiation reaction in terms of a symmetry breaking parameter associated with the violation of null translation invariance in the direction opposite to the laser beam. As the Landau-Lifshitz equation is nonlinear the energy transfer within the pulse is rather sensitive to initial conditions. This is elucidated by comparing colliding and fixed target modes in electron laser collisions.

physics.class-ph↗

arXiv2011

Semi-relativistic effects in spin-1/2 quantum plasmas

Emerging possibilities for creating and studying novel plasma regimes, e.g. relativistic plasmas and dense systems, in a controlled laboratory environment also requires new modeling tools for such systems. This brings motivation for theoretical studies of the kinetic theory governing the dynamics of plasmas for which both relativistic and quantum effects occur simultaneously. Here, we investigate relativistic corrections to the Pauli Hamiltonian in the context of a scalar kinetic theory for spin-1/2 quantum plasmas. In particular, we formulate a quantum kinetic theory that takes such effects as spin-orbit coupling and Zitterbewegung into account for the collective motion of electrons. We discuss the implications and possible applications of our findings.

quant-ph↗

arXiv2011

Ultra-fast spin avalanches in crystals of molecular magnets in terms of magnetic detonation

Recent experiments (Decelle et al., Phys. Rev. Lett. 102, 027203 (2009)) discovered an ultra-fast regime of spin avalanches in crystals of magnetic magnets, which was three orders of magnitude faster than the traditionally studied magnetic deflagration. The new regime has been hypothetically identified as magnetic detonation. Here we demonstrate the possibility of magnetic detonation in the crystals, as a front consisting of a leading shock and a zone of Zeeman energy release. We study the dependence of the magnetic detonation parameters on the applied magnetic field. We find that the magnetic detonation speed only slightly exceeds the sound speed in agreement with the experimental observations.

cond-mat.mtrl-sci↗

arXiv2011

A pulsating regime of magnetic deflagration

The stability of a magnetic deflagration front in a collection of molecular magnets, such as Mn_12-acetate, is considered. It is demonstrated that stationary deflagration is unstable with respect to one-dimensional perturbations if the energy barrier of the magnets is sufficiently high in comparison with the release of Zeeman energy at the front; their ratio may be interpreted as an analogue to the Zeldovich number, as found in problems of combustion. When the Zeldovich number exceeds a certain critical value, a stationary deflagration front becomes unstable and propagates in a pulsating regime. Analytical estimates for the critical Zeldovich number are obtained. The linear stage of the instability is investigated numerically by solving the eigenvalue problem. The nonlinear stage is studied using direct numerical simulations. The parameter domain required for experimental observations of the pulsating regime is discussed.

cond-mat.other↗

arXiv2011

Wakefield generation in magnetized plasmas

We consider wakefield generation in plasmas by electromagnetic pulses propagating perpendicular to a strong magnetic field, in the regime where the electron cyclotron frequency is equal to or larger than the plasma frequency. PIC-simulations reveal that for moderate magnetic field strengths previous results are re-produced, and the wakefield wavenumber spectrum has a clear peak at the inverse skin depth. However, when the cyclotron frequency is significantly larger than the plasma frequency, the wakefield spectrum becomes broad-band, and simultaneously the loss rate of the driving pulse is much enhanced. A set of equations for the scalar and vector potentials reproducing these results are derived, using only the assumption of a weakly nonlinear interaction.

physics.plasm-ph↗

arXiv2011

Hollow microspheres as targets for staged laser-driven proton acceleration

A coated hollow core microsphere is introduced as a novel target in ultra-intense laser-matter interaction experiments. In particular, it facilitates staged laser-driven proton acceleration by combining conventional target normal sheath acceleration (TNSA), power recycling of hot laterally spreading electrons and staging in a very simple and cheap target geometry. During TNSA of protons from one area of the sphere surface, laterally spreading hot electrons form a charge wave. Due to the spherical geometry, this wave refocuses on the opposite side of the sphere, where an opening has been laser micromachined. This leads to a strong transient charge separation field being set up there, which can post-accelerate those TNSA protons passing through the hole at the right time. Experimentally, the feasibility of using such targets is demonstrated. A redistribution is encountered in the experimental proton energy spectra, as predicted by particle-in-cell simulations and attributed to transient fields set up by oscillating currents on the sphere surface.

physics.plasm-ph↗

arXiv2011

Interface dynamics of a two-component Bose-Einstein condensate driven by an external force

The dynamics of an interface in a two-component Bose-Einstein condensate driven by a spatially uniform time-dependent force is studied. Starting from the Gross-Pitaevskii Lagrangian, the dispersion relation for linear waves and instabilities at the interface is derived by means of a variational approach. A number of diverse dynamical effects for different types of the driving force is demonstrated, which includes the Rayleigh-Taylor instability for a constant force, the Richtmyer-Meshkov instability for a pulse force, dynamic stabilization of the Rayleigh-Taylor instability and onset of the parametric instability for an oscillating force. Gaussian Markovian and non-Markovian stochastic forces are also considered. It is found that the Markovian stochastic force does not produce any average effect on the dynamics of the interface, while the non-Markovian force leads to exponential perturbation growth.

cond-mat.quant-gas↗

arXiv2011

Gauge-Free Hamiltonian Structure of the Spin Maxwell-Vlasov Equations

We derive the gauge-free Hamiltonian structure of an extended kinetic theory, for which the intrinsic spin of the particles is taken into account. Such a semi-classical theory can be of interest for describing, e.g., strongly magnetized plasma systems. We find that it is possible to construct generalized brackets for the extended phase space, and discuss the implications of our findings.

physics.plasm-ph↗

arXiv2011

A model for the dynamics and internal structure of planar doping fronts in organic semiconductors

The dynamics and internal structure of doping fronts in organic semiconductors are investigated theoretically using an extended drift-diffusion model for ions, electrons and holes. The model also involves the injection barriers for electrons and holes in the partially doped regions in the form of the Nernst equation, together with a strong dependence of the electron and hole mobility on concentrations. Closed expressions for the front velocities and the ion concentrations in the doped regions are obtained. The analytical theory is employed to describe the acceleration of the p- and n-fronts towards each other. The analytical results show very good agreement with the experimental data. Furthermore, it is shown that the internal structure of the doping fronts is determined by the diffusion and mobility processes. The asymptotic behavior of the concentrations and the electric field is studied analytically inside the doping fronts. The numerical solution for the front structure confirms the most important predictions of the analytical theory: a sharp head of the front in the undoped region, a smooth relaxation tail in the doped region, and a plateau at the critical point of transition from doped to undoped regions.

cond-mat.mtrl-sci↗

arXiv2011

Fast electrochemical doping due to front instability in organic semiconductors

The electrochemical doping transformation in organic semiconductor devices is studied in application to light-emitting cells. It is shown that the device performance can be significantly improved by utilizing new fundamental properties of the doping process. We obtain an instability, which distorts the doping fronts and increases the doping rate considerably. We explain the physical mechanism of the instability, develop theory, provide experimental evidence, and perform numerical simulations. We further show how improved device design can amplify the instability thus leading to a much faster doping process and device kinetics.

cond-mat.mtrl-sci↗

arXiv2010

The ponderomotive force due to the intrinsic spin in extended fluid and kinetic models

In this paper we calculate the contribution to the ponderomotive force in a plasma from the electron spin using a recently developed model. The spin-fluid model used in the present paper contains spin-velocity correlations, in contrast to previous models used for the same purpose. Is its then found that previous terms for the spin-ponderomotive force are recovered, but also that additional terms appear. Furthermore, the results due to the spin-velocity correlations are confirmed using the spin-kinetic theory. The significance of our results is discussed.

physics.plasm-ph↗