Modelling of stationary plasma thrusters

2021

Technically, there are two types of propulsion systems namely chemical and electric depending on the sources of the fuel. Electrostatic thrusters are used for launching small satellites in low earth orbit which are capable to provide thrust for long time intervals. These thrusters consume less fuel compared to chemical propulsion systems. Therefore for the cost reduction interests, space scientists are interested to develop thrusters based on electric propulsion technology. This chapter is intended to serve as a general overview of the technology of electric propulsion (EP) and its applications. Plasma based electric propulsion technology used for space missions with regard to the spacecraft station keeping, rephrasing and orbit topping applications. Typical thrusters have a lifespan of 10,000 h and produce thrust of 0.1–1 N. These devices have E ! B ! configurations which is used to confine electrons, increasing the electron residence time and allowing more ionization in the channe...

This is the second and final yearly Report on Grant 91-0256, for the period 5/l/92-4/30/93. The Report describes two recently completed and highly successful models for the internal physics and the performance of hydrogen arcjets and Hall thrusters, respectively. These are thought to represent the state of the art in their respective topics. Also discussed is an equally significant theoretical model of MPD anode drops, which completes previously funded work. 93-24268 14. SUBJECT TERMS IS. NUMBER OF PAGES Electric Propulsion, Arcjets, Hall Thrusters 15 16. PRICE COOE 17. SECURITY CLASSIFICATION I18. SECURITY CLASSIFiCATION 19. SECURITY CLASSirCATION 20. LIMITATION OF ABSTRACT

Physics of Plasmas, 2012

In order to model the non-equilibrium plasma within the discharge region of a Hall thruster, the velocity distribution functions (VDFs) must be obtained accurately. A direct kinetic (DK) simulation method that directly solves the plasma Boltzmann equation can achieve better resolution of VDFs in comparison to particle simulations, such as the particle-in-cell (PIC) method that inherently include statistical noise. In this paper, a one-dimensional hybrid-DK simulation, which uses a DK simulation for heavy species and a fluid model for electrons, is developed and compared to a hybrid-PIC simulation. Time-averaged results obtained from the hybrid-DK simulation are in good agreement with hybrid-PIC results and experimental data. It is shown from a comparison of using a kinetic simulation and solving the continuity equation that modeling of the neutral atoms plays an important role for simulations of the Hall thruster discharge plasma. In addition, low and high frequency plasma oscillations are observed. Although the kinetic nature of electrons is not resolved due to the use of a fluid model, the hybrid-DK model provides spatially and temporally well-resolved plasma properties and an improved resolution of VDFs for heavy species with less statistical noise in comparison to the hybrid-PIC method. V

41st Aerospace Sciences Meeting and Exhibit, 2003

Among many reasons limiting the efficiency and lifetime of a Hall thruster, the most critical is the wear of the surface layer of the ceramic walls due to the plasma-wall interactions. The plasma-wall interaction is a function of wall potential, which in turn is determined by the secondary electron emission and sputtering yield. In this paper, we document the numerical result of the Hall thruster dynamics in the presence of plasma-wall interaction in one and twodimensional framework. A comparison is made with the two dimensional simulation. The changes in the plasma density, the potential and the azimuthal electron velocity due to the sputter yield are significant in the acceleration region. The plasma number density, temperature, velocity and potential decrease in the presence of the SEE and the sputter yield. However, the neutral number density and the velocity do not exhibit any significant change. The neutral velocity, which decreases initially, starts increasing toward the exit consistent with the computed neutral density profile. Numerical potential distribution shows a good agreement with experimental data reported in the literature.

JOURNAL OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES

To investigate a role of a hollow anode for discharge stabilization in anode-layer hall thrusters, plasma dynamics inside a thruster was computed using the fully kinetic 2D3 V Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) methods. The developed code successfully reproduced the measured discharge current waveform and threshold magnetic flux density for the oscillation onset. At the low magnetic flux density corresponding to the stable discharge case, ionization in the hollow anode was found vigorous and an ion sheath was created on the anode surface. This sheath contributed to the discharge stabilization. However, the amount of ionization in the anode decreased with the magnetic flux density, and the sheath structure changed to an electron sheath at the threshold magnetic flux density.

Physics of Plasmas, 2001

A macroscopic model which accounts for the complex interactions between electrostatic, thermal, and kinetic effects in a Hall thruster is presented. The analysis establishes the one-dimensional steady structure of the flow as consisting of an anode sheath, a long electron free-diffusion region, with reverse ion flow, a thin ionization layer, and the acceleration region, which extends into the plume. The ion flow presents a forward sonic point around the exit of the ionization layer, which can be either internal, with a smooth sonic transition, or localized at the channel exit. The supersonic plume is included via a simple expansion model, allowing closure of the formulation and calculation of thruster performance. The results indicate good agreement with experimental data for the case of an internal sonic point, and they delineate the existence and nonexistence regions in the space of externally controllable parameters. They also unveil the importance of the electron pressure, the reverse flow of ions, and the ionization rate in shaping the plasma structure, whereas, contrary to common perception, the details of the magnetic field profile influence weakly that structure.

Physics of Plasmas, 2006

The effect of the magnetic field configuration on the anode fall in an E ជ ϫ B ជ discharge of a Hall thruster is studied both experimentally and theoretically. Plasma potential, electron temperature, and plasma density in the near-anode region are measured with a biased probe in three configurations of the magnetic field. It is observed that the anode fall in a Hall thruster can be changed from negative to positive by creating a magnetic field configuration with a zero magnetic field region. Similar configurations are utilized in some advanced Hall thrusters, like an ATON thruster. Results of the measurements are employed to model a Hall thruster with different magnetic field configurations, including the one with a zero-field region. Different anode sheath regimes observed experimentally are used to set the boundary conditions for the quasineutral plasma. Numerical solutions obtained with a hydrodynamic quasi-one-dimensional model suggest that varying the magnetic field configuration affects the electron mobility both inside and outside the channel, as well as the plasma density distribution along the axis.

In Hall propulsion, the thrust is provided by the acceleration of ions in a plasma generated in a cross-field configuration. Standard thruster configurations have annular channels with an almost radial magnetic field at the channel exit. A potential difference is imposed in the axial direction and the intensity of the magnetic field is calibrated in order to hinder the electron motion, while leaving the ions non-magnetised. Magnetic field lines can be assumed, as a first approximation, as lines of constant electron temperature and of thermalized potential. In typical thruster configurations, the discharge occurs inside a ceramic channel and, due to plasma-wall interactions, the electron temperature is typically low, less than few tens of eV. Hence, the magnetic field lines can be effectively used to tailor the distribution of the electrostatic potential. However, the erosion of the ceramic walls caused by the ion bombardment represents the main limiting factor of the thruster lifetime and new thruster configurations are currently under development. For these configurations, classical first order models of the plasma dynamics fail to grasp the influence of the magnetic topology on the plasma flow. In the present paper, a novel approach to investigate the correlation between magnetic field topology and thruster performance is presented. Due to the anisotropy induced by the magnetic field, the gradients of the plasma properties are assumed to be mainly in the direction orthogonal to the local magnetic field, thus enabling a quasi-one-dimensional description in magnetic coordinates. Theoretical and experimental investigations performed on a 5 kW class Hall thruster with different magnetic field configurations are then presented and discussed.

Physics of Plasmas, 2002

The dynamics of the Hall thruster is investigated numerically in the framework of a one-dimensional, multifluid macroscopic description of a partially ionized xenon plasma using finite element formulation. The model includes neutral dynamics, inelastic processes, and plasma–wall interaction. Owing to disparate temporal scales, ions and neutrals have been described by set of time-dependent equations, while electrons are considered in steady state. Based on the experimental observations, a third order polynomial in electron temperature is used to calculate ionization rate. The results show that in the acceleration channel the increase in the ion number density is related to the decrease in the neutral number density. The electron and ion velocity profiles are consistent with the imposed electric field. The electron temperature remains uniform for nearly two-thirds of the channel; then sharply increases to a peak before dropping slightly at the exit. This is consistent with the predict...

2005

The electron-wall interaction and its dependence on the discharge voltage and channel width are studied through measurements of the electron temperature, plasma potential and density in a 2 kW Hall thruster. Experimental results are compared with theoretical predictions for different thruster configurations and operating conditions. The channel width is shown to have a more significant effect on the axial distribution of the plasma potential than the discharge voltage.

Plasma Sources Science & Technology, 2008

The modelling of the Hall thruster SPT-100 is a very important issue in view of the increasing importance of such propulsion devices in space applications. Only kinetic models can investigate the rich variety of physical mechanisms involved in the Hall discharge and in the plume emitted from the thruster. This paper collects a number of different particle-in-cell/Monte Carlo collision models which have been able to reveal different phenomena related to the peculiar physics of Hall thruster, such as sheath instability, azimuthal fluctuations and plume backflow.

2002

A quasi one-dimensional steady-state model of the Hall thruster is presented. For the same discharge voltage two operating regimes are possible-with and without the anode sheath. For given mass flow rate, magnetic field profile and discharge voltage the unique solution can be constructed, assuming that the thruster operates in one of the regimes. However, we show that for a given temperature profile the applied discharge voltage uniquely determines the operating regime: for discharge voltages greater than a certain value, the sheath disappears. That result is obtained over a wide range of incoming neutral velocities, channel lengths and widths and cathode plane locations. It is also shown that a good correlation between the quasi 1-D model and experimental results can be achieved by selecting an appropriate electron mobility and temperature profile.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001. Includes bibliographical references (p. 372-375). A Hall effect plasma thruster with conductive acceleration channel walls was numerically modeled using 2D3V Particle-in-Cell (PIC) and Monte-Carlo Collision (MCC) methodolo- gies. Electron, ion, and neutral dynamics were treated kinetically on the electron time scale to study transport, instabilities, and the electron energy distribution function. Axisymmet- ric R-Z coordinates were used with a non-orthogonal variable mesh to account for important small-scale plasma structures and a complex physical geometry. Electric field and sheath structures were treated self-consistently. Conductive channel walls were allowed to float electrically. The simulation included, via MCC, elastic and inelastic electron-neutral colli- sions, ion-neutral scattering and charge exchange collisions, and Coulomb collisions. The latter were also treated through...

The pulsed plasma thruster Add Simp-lex, developed at the IRS, was investigated at the University of Tokyo to further characterize the thruster's performance and discharge behavior. This was done by experimental investigation of configurations with a different amount of capacitors and discrete applied voltages. To do so, a measurement system for the discharge current and the optical properties was built up and successfully applied. Further, the numerical model for the prediction of the current-normalized magnetic flux density was improved and the convergence properties of the integration towards the change in inductance studied. From the discharge current waveforms and the pictures taken from the propagating plasma, information about the amount of plasma creations, their propagation velocity and the oscillation behavior was deducted. For further characterization, the energy transfer efficiency and the electrical efficiency was derived from these data, leading to a tool to compare different configurations. It was found, that a middle voltage yields higher electrical efficiencies of about 40% whereas the energy transfer efficiency is higher the lower the applied voltage.

Journal of Applied Physics, 2004

Plasmas 10, 3397 ͑2003͔͒ is used to carry out parametric investigations on the effects of ͑i͒ the discharge voltage, ͑ii͒ the gas flow rate, ͑iii͒ the axial gradient of the magnetic field, and ͑iv͒ the chamber length on the Hall thruster performances and the axial structure of the plasma discharge. The high-thrust and high-specific-impulse modes for dual-mode thrusters are compared too. The results of the simulations agree well with the main tendencies observed in different experiments. The interaction among the several physical phenomena is discussed and useful scaling laws are proposed. Special attention is paid to understand ͑i͒ the adjustment of the magnetic field strength with the discharge voltage for optimum operation, ͑ii͒ the effect of the magnetic field shape, ͑iii͒ the dimensions of the different regions of the discharge, and ͑iv͒ the parameter trends needed to increment the propulsive and ionization efficiencies ͑the product of which determines the thrust efficiency͒.