The electron cyclotron maser instability in laser ionized plasmas

The electron cyclotron maser instability (ECMI) is a kinetic instability thought to be highly relevant to understanding radiation processes in a wide range of high-energy astrophysical phenomena. The ability to explore this instability in the laboratory can provide essential insights into astrophysics. However, generating plasmas with the required horseshoe or ring-like distribution functions in the laboratory can be highly challenging. Recent work [Zhang Sci. Adv., 2019] demonstrated that a circularly polarized laser that ionizes a neutral gas might generate ring-like distribution functions that quickly decay in other distributions. In this work, we use theory and particle-in-cell simulations (OSIRIS) to generalize previous studies in the presence of an external magnetic field, the condition relevant for the ECMI. We show that these rings in momentum stable have lower decay rates, and the plasma is unstable to the ECMI. We observe an excellent agreement between theory and simulations, not only for the growth rates but also for emitted radiation observed. Our proposed set-up opens a novel direction in laboratory astrophysics by enabling the observation of the maser radiation with the technology currently available in many laboratories worldwide.