Analysis of small scale fluctuations in Hall effect thrusters using virtual Thomson scattering on PIC simulations

Hall effect thrusters are yet not fully understood due to multiple open questions, among which the anomalous electron transport is the most challenging. Particle-In-Cell (PIC) simulations suggested that electron transport is strongly affected by small-scale instabilities which can be investigated experimentally using Collective Thomson Scattering (CTS). In this paper, we perform a virtual CTS diagnostic on PIC data in order to investigate these small scales and to relate simulation and experiments. The virtual diagnostic is performed on the electron density maps from a simplified 2D axial-azimuthal PIC simulation. Analysis along the channel axis showed two dominant modes at 8 and 3 rad mm-1. These modes exhibit ion-acoustic wave features and appear to be selectively affected by the acceleration of the ions when transitioning from the ionization zone to the acceleration zone. A numerical study of the electron density fluctuation rate from the virtual CTS is also performed and the obtained profiles are compared to PIC. This reveals that the virtual CTS integrates both axial and azimuthal fluctuations of the electron density due to the spatial extension of the scattering volume. Moreover, it also highlights the importance of a good estimation of the electron density in the scattering volume for an accurate estimation of the fluctuation rate.