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Accueil > A propos du LPP > Communication > Actualités archivées > 2022 > A virtual collective Thomson Scattering experiment to study electron drift instabilities in Hall thrusters
A virtual collective Thomson Scattering experiment to study electron drift instabilities in Hall thrusters
Toutes les versions de cet article : [English] [français]
Despite being a well-established technology in the aerospace industry, Hall thrusters are yet not fully understood due to multiple open questions, among which the underlying reason behind the high mobility of electrons in the thruster is the most challenging. Currently, the electron drift instability (EDI), characterized by a wavelength of about 1 mm and a frequency of the order of 5 MHz is considered to play a key role to explain this enhanced mobility and this has been well observed in 2D and 3D PIC simulations of Hall thrusters as well as in experiments using Collective Thomson Scattering (CTS).
Collective Thomson Scattering is a commonly used diagnostic tool in the fusion plasmas community and has become today a reference diagnostic in the low-temperature plasmas community when it comes to studying instabilities at millimetric scales. In the work recently published in Physics of Plasmas, Tarek Ben Slimane, Thomas Charoy, Anne Bourdon, and Pascal Chabert of the low-temperature plasma team at LPP have collaborated with Cyrille Honoré of the fusion plasma team at LPP to develop a virtual Thomson Scattering diagnostic that can be applied to PIC simulation data. The goal of this work was both to develop a new analysis method of simulation results and to carry out parametric studies that cannot be done easily experimentally (such as testing the influence of the beam waist or doing the diagnostic inside of the thruster).
On a 2D axial-azimuthal PIC simulation test case (Figure 1), the virtual CTS diagnostic allowed a better characterization of the modes present in the stationary state of the simulation, in both the plume and in the thruster channel. The virtual diagnostic permitted to resolve two millimetric modes at 3 and 8 rad/mm propagating all along the thruster axis, which is illustrated in Figure 2. Their direction is slightly oblique near the anode (x=3mm) and becomes almost azimuthal past the thruster exit plane (x=20mm) as ions are accelerated by the electric field.
Furthermore, a detailed parametric study on the impact of the laser beam waist was carried out to further clarify the discrepancies between PIC simulations and CTS experiments on the value of the electron density fluctuation rate. This provided an idea of how the spatial extension of the diagnostic volume might lead to higher estimations of the fluctuation rate especially when a strong axial electron density gradient is involved. Building on the findings of this comparison, this work concludes with the significant interest to perform virtual plasma diagnostics on either PIC or fluid simulations since they allow to relate simulations to experiments and foster common grounds for comparison and discussion.
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