arXiv subjects

Renaud Gueroult

Publications and source records attributed to Renaud Gueroult.

At least 19 recordsLinked to original sources

arXiv2026

Wave drag in moving plasmas: recent developments and prospects

Wave propagation in a medium differs depending on whether this medium is at rest or moving with respect to an observer. Motion can notably lead to modifications of the wave trajectory, of its polarization, or of its transverse structure. Although these effects are well documented in isotropic dielectrics, they remain largely unexplored and unaccounted for in plasmas, despite the fact that simple models suggest they could in fact be large under certain conditions, as well as recent experimental observations. Here we first review existing models for motion effects on plasma waves, then identify a number of basic challenges that lie in the way of using these models to quantify motion effects in realistic configurations, and finally discuss possible workarounds.

physics.plasm-ph↗

arXiv2026

Spin-redirection Berry phase with planar rays

Geometric or Berry phases are fundamental manifestations that appear in many areas of physics. They arise from the geometry of the space describing the properties of multi-component wave fields. An important example for electromagnetic waves is the spin-redirection Berry phase associated with the evolution of the spin direction. Because this effect has traditionally been studied in isotropic media where the spin is aligned with the ray trajectory, it has become commonly assumed that this spin-redirection Berry phase requires nonplanar rays. Here we show that a spin-redirection phase can in fact arise along a planar ray if the spin evolves along the ray. We expose this effect through the singular example of a moving unmagnetized plasma, and demonstrate how this behavior can more generally arise from a finite transverse spin. In identifying this new spin-redirection mechanism our work not only provides the tools to discover additional manifestations of SOIs in nature, but also uncovers supplemental degrees of freedom to harness SOIs to control light.

physics.optics↗

arXiv2025

Light drag in nonuniformly moving anisotropic media through the lens of gradient-index optics

The trajectory of light rays propagating through a nonuniformly moving anisotropic medium is determined by considering the Fresnel drag experienced by the wave at each point along the ray. By showing that symmetries in the velocity field manifest as symmetries in the effective wave index representing the moving medium, methods classically employed to model gradient index media are then used to obtain analytical forms for the ray trajectory. When applied to isotropic media, the results are verified to be consistent with those obtained using an optical (Gordon) metric. The potential of this method to model light rays in anisotropic media is finally demonstrated by considering waves in a nonuniformly moving magnetized plasma, exposing how nonuniform motion and anisotropy can compete with one another.

physics.plasm-ph↗

arXiv2025

Image rotation in plasmas

Because of the speed of light compared to material motion, the dragging of light is difficult to observe under laboratory conditions. Here we report on the first observation of image rotation, i. e. a dragging by the medium of the wave's transverse structure, of Alfv\'en waves in plasmas. Exploiting the naturally slow group velocity of these waves, significant wave rotation is achieved for modest angular frequency. Control over the rotation of the wave's structure is demonstrated through the plasma rotation imposed by biased electrodes. Remarkably, experimental results are well reproduced by light dragging theory derived for isotropic media, even if magnetized plasmas are anisotropic. In addition to offering new insights into the fundamental issue of angular momentum coupling between waves and media, these findings also open possibilities for new remote rotation sensing tools.

physics.plasm-ph↗

arXiv2025

Spin-orbit interactions induced by light drag in moving media

Spin-orbit interactions (SOIs) of light are manifestations of coupling between components of light's angular momentum. They are at play in most basic optical processes, offering opportunities both to understand their fundamental origin and to control light in novel ways. Because SOIs become significant at subwavelength scale, they have largely been explored in the context of inhomogeneous materials exhibiting wavelength-scale structures, and notably metamaterials. Here we demonstrate that spin-orbit interactions can in fact analogously emerge in moving matter through the well-known light-dragging effects. SOIs in moving media are shown to manifest through a Berry phase induced by vorticity, which then leads to a rotation of the wave's polarization. In bringing together electrodynamics of moving media and SOIs of light, our work not only paves the way for the discovery of new fundamental effects but also uncovers novel means to harness SOIs to control light.

physics.optics↗

arXiv2024

Ray tracing methods for wave propagation in moving anisotropic media : application to magnetized plasmas

The propagation of a wave in a medium is generally affected when the medium is moving with respect to the observer. Because plasma equilibria often involve plasma flows, for instance in astrophysics or in magnetic confinement nuclear fusion devices, understanding the effect of motion on plasma waves is important. Meanwhile, the presence of a background magnetic field in a plasma makes it anisotropic. To address this problem, we derive here ray tracing equations for the trajectory of rays propagating in a moving anisotropic medium. The proposed approach is to use an effective dispersion relation for the moving medium as seen from the laboratory, obtained by performing a Lorentz transformation of the dispersion relation known for the medium at rest. This formalism is illustrated by considering the standard ordinary and extraordinary modes in a magnetized plasma at rest. Although we work here at lowest order in the geometrical optics approximation, this method is a first step towards higher order expansions, as required for instance to capture polarization effects.

physics.plasm-ph↗

arXiv2024

Fresnel drag in a moving magnetized plasma

The change in direction of the wavevector and group velocity experienced by a wave refracted at the interface of an anisotropic medium in uniform linear motion are determined analytically. These transmission conditions, which are shown to be consistent with generalized Snell's law written in the laboratory frame, are then used to examine the effect of motion on waves incident on a magnetized plasma. For an incident wave in the plane perpendicular to the magnetic field the motion is observed to lead to non negligible deviation of the low-frequency X-mode, as well as to non-symmetrical total reflection angles. These effects are shown to be further complicated when the magnetic field is in the plane formed by the incident wavevector and the medium's velocity, as the anisotropy now competes with the motion-induced drag. Although obtained in simplified configurations, these results suggest that accounting for motion when modeling plasma waves trajectory could be important under certain conditions, calling for a more detailed quantification of the effect of motion in actual diagnostics and plasma control schemes.

physics.plasm-ph↗

arXiv2024

Signature of inertia on light dragging in rotating plasmas

The signature of light dragging in a rotating unmagnetized plasma is studied analytically. In contrast with previous work which focused exclusively on the drag effects arising from rigid rotation, we examine here the supplemental contribution of inertia to the rest-frame dielectric properties of a rotating medium. We reveal, for the first time, that these so far neglected contributions actually play a dominant role on light dragging in rotating unmagnetized plasmas. Besides birefringence and enhanced polarization drag, inertia is notably demonstrated to be the cause of a non-zero drag, pointing to fundamental differences between linear and angular momentum coupling. We finally discuss how, thanks to the more favourable scaling elicited here, it may be possible to observe these effects in recently proposed laser driven rotating plasmas, identifying new promising directions for experimental investigations.

physics.plasm-ph↗

arXiv2023

Contribution of fictitious forces to polarization drag in rotating media

Models for polarization drag - mechanical analog of the Faraday effect - are extended to include inertial corrections to the dielectrics properties of the rotating medium in its rest-frame. Instead of the Coriolis-Faraday term originally proposed by Baranova & Zel'dovich, inertia corrections due to the fictitious Coriolis and centrifugal forces are here derived by considering the effect of rotation on both the Lorentz and plasma dielectric models. These modified rest-frame properties are subsequently used to deduce laboratory properties. Although elegant and insightful, it is shown that the Coriolis-Faraday correction inferred from Larmor's theorem is limited in that it can only capture inertial corrections to polarization drag when the equivalent Faraday rotation is defined at the wave frequency of interest. This is notably not the case for low frequency polarization drag in a rotating magnetized plasma, although it is verified here using the more general phenomenological models that the impact of fictitious forces is in general negligible in these conditions.

physics.plasm-ph↗

arXiv2023

DC electric field generation and distribution in magnetized plasmas

Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines and usually providing the voltage drop feed between the field lines, impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity between the field lines then distribute this voltage drop. The global power balance and control parameters of wave and beam generated large DC electric fields in magnetized plasmas are identified, described and analyzed.

physics.plasm-ph↗

arXiv2022

Wave propagation in rotating magnetised plasmas

Wave propagation properties in a medium are fundamentally affected when this medium is moving instead of at rest. In isotropic dielectric media rotation has two noteworthy contributions: one is a mechanically induced circular birefringence which materialises as a rotation of the polarisation, the other is image rotation which corresponds to a rotation of the transverse structure of a wave. Here we review the effect of rotation in a magnetised plasma. We first show that the mechanical effect of rotation on polarisation is in a magnetised plasma superimposed onto the classical Faraday rotation, and that failing to account for this new contribution could lead to errors in the interpretation of polarimetry data. We also demonstrate that image rotation is recovered in plasmas for a number of low-frequency magnetised plasma waves carrying orbital angular momentum, and that this phenomenon holds promise for the development of new rotation diagnostic tools in plasmas.

physics.plasm-ph↗

arXiv2021

Faraday-Fresnel rotation and splitting of orbital angular momentum carrying waves in a rotating plasma

Rotational Fresnel drag - or orbital Faraday rotation - in a rotating magnetised plasma is uncovered and studied analytically for Trivelpiece-Gould and Whistler-Helicon waves carrying orbital angular momentum (OAM). Plasma rotation is shown to introduce a non-zero phase shift between OAM-carrying eigenmodes with opposite helicities, similarly to the phase-shift between spin angular momentum eigenmodes associated with the classical Faraday effect in a magnetised plasma at rest. By examining the dispersion relation for these two low-frequency modes in a Brillouin rotating plasma, this Faraday-Fresnel rotation effect is traced back to the combined effects of Doppler shift, centrifugal forces and Coriolis forces. In addition, rotation is further shown to lead to rotation- and azimuthal mode-dependent longitudinal group velocity, therefore predicting the Faraday-Fresnel splitting of the enveloppe of a wave packet containing a superposition of OAM-carrying eigenmodes with opposite helicities.

physics.plasm-ph↗

arXiv2021

Energy and momentum conservation upon reflection of a solitary pulse in a bounded magnetized plasma

When the nature of a magnetosonic pulse propagating in a bounded magnetized plasma slab is successively transformed from compression to rarefaction and vice-versa upon reflection at a plasma-vacuum interface, both the energy and the longitudinal electromagnetic (EM) momentum of the plasma-pulse system are found to oscillate between two states. Simple analytical models and particle-in-cell simulations show that these oscillations are associated with EM radiation to and from the surrounding magnetized vacuum. For partial reflection supplemental losses in total pulse energy and mechanical momentum are identified and shown to follow respectively Fresnel's transmission coefficients for the energy and the magnetic perturbation. This mechanical momentum loss upon partial reflection is traced to the momentarily non-zero volume integrated Lorentz force, which in turn supports that mechanical and EM momentum transfers are respectively associated with the magnetic and electric parts of the momentum flux density.

physics.plasm-ph↗

arXiv2020

Perspectives on Physics of ExB Discharges Relevant to Plasma Propulsion and Similar Technologies

This paper provides perspectives on recent progress in the understanding of the physics of devices where the external magnetic field is applied perpendicularly to the discharge current. This configuration generates a strong electric field, which acts to accelerates ions. The many applications of this set up include generation of thrust for spacecraft propulsion and the separation of species in plasma mass separation devices. These ExB plasmas are subject to plasma-wall interaction effects as well as various micro and macro instabilities, and in many devices, we observe the emergence of anomalous transport. This perspective presents the current understanding of the physics of these phenomena, state-of-the-art computational results, identifies critical questions, and suggests directions for future research

physics.plasm-ph↗

arXiv2019

A necessary condition for perpendicular electric field control in magnetized plasmas

The electrostatic model proposed by Poulos [Phys. Plasmas (2019), $\mathbf{26}$, 022104] to describe the electric potential distribution across and along a magnetized plasma column is used to shed light onto the ability to control perpendicular electric fields. The effective electrical connection between facing end-electrodes is shown to be conditioned upon the smallness of a dimensionless parameter $τ$ function of the plasma column aspect ratio and the square root of the conductivity ratio $σ_\perp/σ_{\parallel}$. The analysis of a selected set of past end-electrodes biasing experiments confirms that this parameter is small in experiments that have successfully demonstrated perpendicular electric field tailoring. On the other hand, this parameter is $\mathcal{O}(1)$ in experiments that failed to demonstrate control, pointing to an excessively large ion-neutral collision frequency. A better understanding of the various contributions to $σ_\perp$ is needed to gain further insights into end-biasing experimental results.

physics.plasm-ph↗

arXiv2019

Geometric phase in Brillouin flows

A geometric phase is found to arise from the cyclic adiabatic variation of the crossed magnetic and electric fields which sustain the Brillouin rotation of a plasma column. The expression of the gauge field associated with this geometric phase accumulation is explicited. The physical origin of this phase is shown to be the uncompensated inductive electric field drift that stems from magnetic field cyclic variations. Building on this result, the effect of a weak, periodic and adiabatic modulation of the axial magnetic field on the particle guiding center drift motion is demonstrated to be equivalent to that of a perpendicular electric field, allowing to study the gauge induced Brillouin flow through a geometrically equivalent linear radial electric field. This finding opens new perspectives to drive plasma rotation and hints at possible applications of this basic effect.

physics.plasm-ph↗

arXiv2019

Do pulsars rotate clockwise or counterclockwise?

Pulsars are rotating neutron stars which emit lighthouse-like beams. Owing to their unique properties, pulsars are a unique astrophysical tool to test general relativity, inform on matter at extreme densities, and probe galactic magnetic fields. Understanding pulsars physics and emission mechanisms is critical to these applications. Here we uncover that mechanical-optical rotation in the pulsars' magnetosphere affects polarisation in a way which is indiscernible from Faraday rotation in the interstellar medium for typical GHz observations frequency, but which can be distinguished in the sub-GHz band. Besides being essential to correct for possible systematic errors in interstellar magnetic field estimates, our novel interpretation of pulsar polarimetry data offers a unique means to determine whether pulsars rotate clockwise or counterclockwise, providing new constraints on magnetospheric physics and possible emission mechanisms. Combined with the ongoing development of sub-GHz observation capabilities, our finding promises new discoveries, such as the spatial distributions of clockwise rotating or counterclockwise rotating pulsars, which could exhibit potentially interesting, but presently invisible, correlations or features.

astro-ph.IM↗

arXiv2018

Cumulative displacement induced by a magnetosonic soliton bouncing in a bounded plasma slab

The passage of a magnetosonic (MS) soliton in a cold plasma leads to the displacement of charged particles in the direction of a compressive pulse and in the opposite direction of a rarefaction pulse. In the overdense plasma limit, the displacement induced by a weakly nonlinear MS soliton is derived analytically. This result is then used to derive an asymptotic expansion for the displacement resulting from the bouncing motion of a MS soliton reflected back and forth in a vacuum-bounded cold plasma slab. Particles' displacement after the pulse energy has been lost to the vacuum region is shown to scale as the ratio of light speed to Alfvén velocity. Results for the displacement after a few MS soliton reflections are corroborated by particle-in-cell simulations.

physics.plasm-ph↗