Academic Presentations

The Hall parameter (β), the ratio of azimuthal to axial current densities, governs transport and electron magnetization in Hall thrusters. Using a 0-D magnetoydrodynamic (MHD) model and RAIJIN66 experimental data, this study links β to thrust, mass flow rate, and magnetic field. Results show β is a key scaling factor connecting plasma behavior and performance, with high β essential for efficient, stable operation in high density plasma operation.

Hall thrusters are widely used for efficient in-space propulsion, but their reliance on xenon presents challenges in terms of cost and availability. Alternative propellants such as argon or krypton exhibit lower propellant utilization efficiency, motivating thruster designs that increase plasma density within the ionization region. This work investigates such a scaling method using an analytical magnetohydrodynamic (MHD) framework to examine the effects of higher plasma density and magnetic field adjustments. Experimental Hall parameters and anomalous diffusion coefficients of existing thruster designs were estimated using the J × B force, highlighting differences between SPT and TAL configurations. A fluid-based MHD approach was then applied to identify the principal scaling parameters: mass flow density and magnetic flux density. The framework was demonstrated on the reference TAL-type thruster RAIJIN66. Reducing the anode cross-sectional area increased propellant utilization efficiency but also raised the discharge current and thermal load, which were mitigated by increasing the magnetic flux density. Importantly, while thrust remained essentially constant, the electron current was significantly reduced, illustrating the role of the magnetic field in controlling currents and thermal loads in high-density operation. These results highlight the importance of magnetic field adjustment in maintaining efficient thruster operation under high-density conditions and establish a first-order analytical tool for guiding the design of Hall thrusters using alternative propellants, with potential applications to future high-density, ion-magnetized regimes.

Hall thrusters are widely used in the field of electric propulsion due to their high efficiency and specific impulse. However, the reliance on xenon as a propellant is challenging due to its scarcity and cost, leading to interest in alternatives such as argon and krypton. A key limitation of these alternative propellants is their lower propellant utilization efficiency, which can be addressed by increasing the neutral density within the ionization region. This study investigates a high-density plasma Hall thruster design by scaling down the anode cross-sectional area of the RAIJIN66 thruster while maintaining the same mass flow rate and power. This geometric modification increases neutral density, enhancing ionization but also decreasing the Hall parameter due to higher electron-neutral collision frequencies. To compensate for this effect and sustain efficient thruster operation, the magnetic flux density must be increased by a factor of four using a permanent magnet. A magnetohydrodynamic (MHD) framework is employed to analyze electron behavior under these high-density conditions, utilizing a two-fluid model for ions and electrons. To study the thrust generation at high plasma densities, electromagnetic acceleration is analyzed, which is quantitatively equivalent to conventional electrostatic acceleration. This research shows how increased neutral density enhances performance and mitigates negative effects through magnetic field adjustments, contributing to the development of Hall thrusters optimized for alternative propellants and scalable space applications.

Space missions in very low Earth orbit (VLEO) offer advanced capabilities for Earth observation, telecommunications, and security but are challenged by continuous orbit decay. Atmosphere-Breathing Electric Propulsion (ABEP), which uses atmospheric particles as propellant, provides a potential solution. Within the H2020 DISCOVERER, ESA ram-CLEP, and ATLAS projects, IRS is developing a specular intake and helicon plasma thruster to advance ABEP systems. This study uses Direct Simulation Monte Carlo (DSMC) simulations to evaluate specular intake geometries, analyzing particle density, pressure, mass flow rate, and collection efficiency. The results indicate that reducing the focal length of the parabolic intake significantly improves efficiency and mass flow rate, while increasing the discharge channel diameter proves more effective for achieving these high values as well. As pressure follows an opposing trend to efficiency, and reaching the ignition pressure is crucial, the optimal configuration among the investigated for balancing efficiency and pressure is a discharge channel diameter of 25 mm with a focal length of 3 mm.

Challenging space missions at very low altitudes face significant atmospheric drag, requiring efficient propulsion methods such as Atmosphere-Breathing Electric Propulsion (ABEP) to extend mission lifetimes. ABEP captures atmospheric particles and uses them as propellant for an electric thruster, reducing dependence on limited on-board propellant. This could extend missions in Very Low Earth Orbit (VLEO) and on celestial bodies with an atmosphere, such as Mars. The Institute of Space Systems (IRS), under the EU H2020 DISCOVERER, ESA Ram-CLEP, and CRC ATLAS projects, is developing a high-efficiency specular intake and a RF Helicon-based plasma thruster (IPT) for ABEP. This study uses the numerical tool PICLas and its Direct Simulation Monte Carlo Method (DSMC) to analyse the effect of solar activity and evaluate the validity of the hyperthermal assumption in VLEO for ABEP intake designs. Additionally, the effect of changing intake lengths on important key parameters, such as intake efficiency, mass flow rate, and pressure, is examined. The results show that efficiency decreases with higher solar activity, longer intakes, and higher altitudes, with particle temperature having the greatest effect on efficiency, due to its influence on thermal velocity and the molecular speed ratio. An almost linear relationship between efficiency and molecular speed ratio is shown, revealing that the hyperthermal assumption may not be valid for VLEO applications. To achieve the required pressure level for ignition, flexible ABEP operation is recommended to accommodate varying solar activity, suggesting lower altitude operation during low solar activity and higher altitude operation during high solar activity.