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Gerjan Hagelaar

Publications and source records attributed to Gerjan Hagelaar.

3 recordsLinked to original sources

Branching Paths Statistics for confined Flows : Adressing Navier-Stokes Nonlinear Transport

Recent advances have allowed to tackle exact path-space probabilistic representations of macroscopic advection-diffusion models involving advection nonlinearities by step forward approaches in terms of continuous branching stochastic processes. Yet, the need of such paradigm shift is huge for the broad flied of fluid flows. In deed, wherever for climate dynamics, engeenering, geophysical and planetary formations, or biomedical applications, complex transport phenomena involving diffusion and advection in confined domains set the physics. In this work, we advance this framework by casting such branching representations within the class of Navier-Stokes strongly nonlinear transport. This yields novel propagator representations for fluid dynamics and opens new routes for efficient simulations of fluids in confined domains by use of new Backward Monte Carlo algorithms.

physics.flu-dyn

From Galactic Clusters to Plasmas in a Single Monte Carlo: Branching Paths Statistics for Poisson-Vlasov/Boltzmann

Recent advances have allowed to tackle path-space probabilistic representations of mesoscopic Boltzmann transport nonlinearly coupled to a sub-model of the force-field by step forward approaches in terms of continuous branching stochastic processes. In this work, path-space probabilistic representations of free-space Poisson-Vlasov and Poisson-Boltzmann systems are exhibited. This yields novel propagator representations and opens new routes for efficient and reference simulations by use of new branching backward Monte Carlo algorithms. Subsequent statistical estimator are benchmarked on gravitational clusters and plasmas dynamics.

physics.plasm-ph

Fluid and hybrid simulations of the ionization instabilities in Hall thruster

Low-frequency axial oscillations (5-50 kHz) stand out as a pervasive feature observed in many types of Hall thrusters. While it is widely recognized that the ionization effects play the central role in this mode, as manifested via the large scale oscillations of neutral and plasma density, the exact mechanism(s) of the instabilities remain unclear. To gain further insights into the physics of the breathing mode and evaluate the role of kinetic effects, a one-dimensional time-dependent full nonlinear low-frequency model describing neutral atoms, ions, and electrons, is developed in full fluid formulation and compared to the hybrid model in which the ions and neutrals are kinetic. Both models are quasineutral and share the same electron fluid equations that include the electron diffusion, mobility across the magnetic field, and the electron energy evolution. The ionization models are also similar in both approaches. The predictions of fluid and hybrid simulations are compared for different test cases. Two main regimes are identified in both models: one with pure low-frequency behaviour and the other one, where the low-frequency oscillations coexist with higher frequency oscillations (with the characteristic time scale of the ion channel flyby time, 100-200 kHz). The other test case demonstrate the effect of a finite temperature of injected atoms which is shown to have a substantial effect on the oscillation amplitude.

physics.plasm-ph