The electron cyclotron maser instability in laser ionized plasmas

We propose the use of laser-ionized plasmas as a way to probe the electron cyclotron maser instability in the laboratory. Due to the conservation of canonical momentum, the laser imprints its polarization in the momentum distribution function of the electrons [1]: the distribution after the laser passes the region is closely connected to the laser vector potential at the ionization instant. Therefore, circularly polarized lasers can generate ring-shaped distribution functions [2]. Recent results have shown that these distributions may be much more common in astrophysical plasmas than previously thought [3].

Under the presence of external magnetic fields, these ring distributions can live over larger timescales. They present inverted Landau populations, so in a magnetized plasma, they are prone to kinetic instabilities such as the electron cyclotron maser [4]. Using theory and particle-in-cell simulations with the code OSIRIS [5], we investigate conditions for the unset of the maser and other competing instabilities using state-of-the-art laser systems. We show parameter regimes where the maser dominates and compare results for the radiation signature observed in simulation with results from kinetic theory.

[1] X. Xu et al., PRAB 25, 011302 (2022)

[2] C. Zhang et al., Sci. Adv. 5, eaax4545 (2019)

[3] P. J. Bilbao and L. O. Silva., PRL 130, 165101 (2023)

[4] K. R. Chu, Rev. Mod. Phys. 76, 489 (2004)

[5] R. A. Fonseca et al., in Computational Science — ICCS 2002, edited by P. M. A. Sloot, A. G. Hoekstra, C. J. K. Tan, and J. J. Dongarra (Springer Berlin Heidelberg, 2002) p. 342