Wave drag in moving plasmas: theory, observation, and applications

The dynamics of wave propagating in moving media is affected by motion. Going back to the work of Fresnel and Fizeau, such wave-dragging phenomena have long been studied in isotropic dielectrics, demonstrating the effect of motion on both the wave trajectory and its polarization. For a rotating medium, this notably manifests as a mechanically induced circular birefringence [1] and a rotation of the wave transverse structure known as image rotation [2].

In contrast, wave drag in moving plasmas has received little attention, and that despite the fact the plasma flows are ubiquitous. A reason for that is that the anisotropic response of a magnetized plasma makes modelling wave drag effects comparatively more delicate. Looking at this problem, it has recently been predicted that mechanical effects on the wave’s polarization [3,4] and on the wave’s transverse structure [5,6] will manifest in plasmas, albeit with a more complex signature [7,8,9]. Predictions obtained in ideal configurations show that these effects could be important in a number of environments, notably astrophysics [3] or for light manipulation applications [4]. Given the wide range of applications of plasma waves and the ubiquity of plasma flows, these results suggest that wave drag in plasmas could play a wider role.

In this talk I will review what we have learned on the signature of wave drag in moving plasmas, present first experimental results obtained to demonstrate these effects in laboratory experiments [10], and discuss possible applications.

[1] M. Player (1976), Proc. R. Soc. A, 349, 441

[2] Franke-Arnold et al. (2011), Science, 333, 65

[3] R. Gueroult et al. (2019), Nat. Commun., 10, 3232

[4] R. Gueroult, J.-M. Rax and N. J. Fisch (2020), Phys. Rev. E, 102, 051202(R)

[5] J.-M. Rax and R. Gueroult (2021), J. Plasma Phys., 87, 905870507

[6] J.-M. Rax, R. Gueroult and N. J. Fisch (2023), J. Plasma Phys., 89, 905890613

[7] J. Langlois and R. Gueroult (2024), Proc. R. Soc. A, 480, 20240300

[8] J. Langlois, A. Braud and R. Gueroult (2025), J. Plasma Phys., 91, E47

[9] A. Braud, J. Langlois and R. Gueroult (2025), Comptes Rendus. Physique, 28, 7

[10] R. Gueroult et al. (2025), Phys. Rev. Lett., 134, 245101