Latest progress in Hall thrusters plasma modelling
Résumé
In the last thirty years, numerical models have revealed different physical mechanisms involved in the Hall thruster functioning leading to a bridge between analytical prediction / empirical intuition and experiments. For this reason, modeling effort is continuously increasing in the domain of Hall Thrusters. Two basic approaches exist: one based on fluid/hybrid simulation where the distribution of electrons is assumed Maxwellian and the plasma inside the thruster, considered as quasineutral, is described with macroscopic quantities (density, velocity and energy); the second approach is based on kinetic description for charged particles where no approximation is made for the distribution of particles. Fluid or hybrid approaches offer the advantage of demanding low run times and computational resources. They are very useful to perform parametric studies but actually the anomalous phenomena responsible for electron transport across the magnetic field barrier have not been self-consistently modeled. Kinetic approach is able to better capture phenomena originating on the Debye scale length like the lateral sheaths, ExB electron drift instability, important to explain the anomalous electron transport, but it requires very long run times. For this latter, the progress in computer science offers the advantage to describe conditions more and more close to the thruster operation. In this review, we will present the two approaches emphasizing on numerical schemes used with assumptions and approximations and on main results obtained. Future directions on the Hall thruster modeling will finally outlined.
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