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Table of contents
1 Introduction
1.1 A new age for spacecraft propulsion
1.1.1 Electric propulsion
1.1.2 A broad range of needs
1.1.3 Working principles of the two main electric thrusters
1.2 Hall thrusters – General concepts
1.2.1 Basic concepts of Hall thruster plasma physics
1.2.2 Hall thruster instabilities
1.2.3 Why do we keep studying Hall thrusters?
1.3 Hall thrusters – Modeling
1.3.1 Multi-fluid models
1.3.2 Particle-In-Cell models
1.3.3 Hybrid and Direct-Kinetic models
1.4 Scope and outline of the thesis
2 Code development: from radial-azimuthal to axial-azimuthal geometry
2.1 A quick overview of LPPic, a 2D PIC-MCC code
2.1.1 Code main structure
2.1.2 A powerful numerical tool
2.2 Preliminary modifications towards axial-azimuthal simulations
2.2.1 Magnetic field
2.2.2 Ionization process
2.2.3 Code optimization
2.3 Neutral dynamics
2.3.1 Context
2.3.2 Model description
2.3.3 Solver verification and validation
2.4 Cathode model
2.4.1 Current Equality condition
2.4.2 Quasi-neutrality condition
2.4.3 Setting positions and energies
2.4.4 Which model should we choose?
2.5 Further improvements of the model
2.5.1 Fake radial dimension
2.5.2 Doubly-charged xenon ions
2.6 Conclusion
3 Code verification: 2D axial-azimuthal benchmark
3.1 Why do we need this benchmark?
3.2 Description of the model
3.2.1 Simulation domain
3.2.2 Imposed axial profiles
3.2.3 Boundary conditions
3.3 Code specificities
3.4 Results
3.4.1 Main plasma parameters
3.4.2 Azimuthal instabilities
3.5 Discussion
3.5.1 Numerical convergence
3.5.2 Case sensitivity
3.6 A tool to challenge numerical models – Example of the cathode injection
3.6.1 Studied cathode models
3.6.2 Main plasma parameters
3.6.3 Azimuthal instabilities
3.7 Conclusion
4 Instability-enhanced electron transport
4.1 Context
4.2 Theoretical models for enhanced electron transport
4.2.1 Electron-ion friction force
4.2.2 Theoretical models
4.2.3 Comparison with the nominal simulation case
4.3 2D PIC simulations
4.3.1 Model & Parametric studies
4.3.2 Comparison with parametric PIC results of the friction force derivation accounting for non-Maxwellian electrons
4.3.3 Ion-electron friction force
4.4 Influence of ion-neutral collisions
4.5 Discussion and Conclusion
5 Towards self-consistent simulations of Hall thrusters
5.1 Motivation
5.2 Numerical model
5.2.1 Case description
5.2.2 Importance of neutral dynamics and anode ion recombination
5.2.3 Cathode model
5.3 Axial electron transport during a breathing mode oscillation
5.3.1 Case closer to reality ( = 4)
5.3.2 Influence of vacuum permittivity scaling factor
5.3.3 VDF and plasma fluctuations
5.3.4 Azimuthal instabilities
5.4 Conclusion
6 Instabilities in Hall thrusters
6.1 Ion transit-time instabilities
6.1.1 Current understanding
6.1.2 Analysis of ITT: « 1D axial » simulations
6.1.3 Origin of the ITTI?
6.1.4 Evidence of ITTI in the self-consistent axial-azimuthal simulations
6.2 Influence of the azimuthal domain length Ly
6.2.1 Axial electron transport
6.2.2 Azimuthal instabilities
6.3 Interaction between ITTI & EDI
6.3.1 Preliminary analysis on the self-consistent simulations
6.3.2 Insights from the simplified benchmark case
6.4 Conclusion
7 Conclusion
7.1 Summary of the thesis
7.1.1 Importance of code verification
7.1.2 Origin of electron anomalous transport
7.2 Recommendations and prospects
7.2.1 Improvements of LPPic
7.2.2 Code validation with experiments
7.2.3 Towards an engineering tool?
A Sod test case
Bibliography
