CE30 - Physique de la matière condensée et de la matière diluée

Wave Propagation in Rotating Plasmas – WaRP

Submission summary

The properties of wave propagation in moving media differ from those in non-moving media. The rotation of an isotropic dielectric medium is for instance known to lead to polarisation rotation, which corresponds to a phase shift between the spin angular momentum (SAM) components of the wave, and image rotation, which corresponds to a phase shift between the orbital angular momentum (OAM) components of the wave. Compared to typical dielectrics, a rotating magnetised plasma stands out in that polarisation rotation can arise from two different contributions: Faraday rotation, which stems from the intrinsic gyrotropy of plasmas, and mechanical polarisation rotation, which stems from the medium's rotation. A rotating magnetised plasma could also provide new means to transform SAM into OAM. Understanding the implications of rotation effects on propagation is anticipated to be of importance for basic plasma physics, but also for applications including pulsars physics and light manipulation.

The first part of this project will be mostly theoretical and fundamental. We will seek here to derive dispersion relations for electromagnetic wave propagation in a rotating plasma. Practically, we will build on our recent results, notably the simple case of propagation without OAM in an aligned rotator, and progressively add complexity with the goal of producing the most general model possible. We will in particular aim to include both SAM and OAM, as well as different geometrical effects. These fundamental results will then provide us with the necessary tools to examine two practical applications.

The first applied problem considered here will be to examine how these effects of rotation on wave propagation could be observed in laboratory experiments. Our preliminary results indeed suggest that the effect of mechanical rotation on wave polarisation in a plasma could in principle be separated from Faraday rotation in the presence of strong magnetic fields (tens to hundreds of Teslas). Such fields have recently been achieved using capacitor-coil targets in laser driven high energy density plasma (HEDP) experiments, and we will here seek to confirm in collaboration with HEDP specialists the possibility of using these unique conditions to measure polarisation drag.

Concurrently with this work on polarisation rotation in laboratory experiments, a second applied problem we will consider is the possible effects of the mechanical rotation of the magnetosphere surrounding pulsars on the polarisation of pulsars's signal received on Earth. We will notably study here, in collaboration with pulsar polarimetry specialists, how the inclusion of pulsars inclination - which is essential to pulsars' emission - in propagation model derived in the presence of rotation could explain certain experimental polarimetric observations, and in turn confirm our theoretical conjecture that polarisation could be uniquely used to determine the rotation direction in pulsars.

Project coordination

Renaud Gueroult (LABORATOIRE PLASMA ET CONVERSION D'ENERGIE)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LAPLACE LABORATOIRE PLASMA ET CONVERSION D'ENERGIE

Help of the ANR 289,182 euros
Beginning and duration of the scientific project: February 2022 - 42 Months

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