We report here on initial studies of a pulsed hydromagnetic plasma gun that can operate in either a pre-filled or a gas-puff mode on demand. These modes enable agile and responsive performance through tunable thrust and specific impulse. Operation with a molecular nitrogen propellant is demonstrated to show that the hydromagnetic thruster is a candidate technology for air-harvesting and drag compensation in very low Earth orbit. Dual mode operation is achieved by leveraging propellant gas dynamics to change the fill fraction and flow collisionality within the thruster. This results in the formation of distinct modes that are characterized by the current-driven hydromagnetic waves that they allow, namely a magneto-deflagration and magneto-detonation respectively. These modes can be chosen by changing the time propellant is allowed to diffuse into the thruster based on the desired performance. Using time-of-flight emission diagnostics to characterize near-field flow velocities, we find that a relatively dramatic transition occurs between modes, with exhaust velocities ranging from 10 km/s to 55 km/s in deflagration and detonation regimes, respectively. Simulations of the processed mass bit offers a first glimpse into possible thruster performance confirming a broad range and tradeoff between specific impulse (2600 - 5600 sec) and thrust (up to 31 mN) when operating in a burst mode.
Hall Thrusters typically operate at thrust densities on the order of 10 N/m2, which is well below the thrust density limits discussed in previous literature. These limits have been considered here and each component of thrust density is analyzed to demonstrate the relative contribution to the total thrust density. Dependencies of the thrust density limits upon the thruster geometry, electron mobility, and the applied magnetic field are revealed and compared with experimental data.
The following paper includes a physical microscopic particle-description of the phenomena and mechanisms that lead to the extraction of ions with the aim to generate thrust. This theoretical treatise arose from the intention to visualize the behavior of the involved particles under effect of the involved electrical fields. By this way, an underlying basis for experimental investigations of the work of an ion thruster should be formed. So a foundation was created, which explains the ion extracting and so thrust generating function of an ion thruster. The theoretical work was related to the Radi…
Large-payload deep space missions are impractical with current rocket propulsion technologies in use. Chemical thrusters yield a high thrust but low efficiency while ion thrusters are efficient but provide too little thrust for large satellites and manned spacecraft. Plasma propulsion is a viable alternative with a higher thrust than electric ion thrusters and specific impulse far exceeding those of chemical rocket engines. In this paper, a hybrid thruster is explored which affords the high mass flow rate of plasma thrusters while maximizing the specific impulse. The two primary processes of t…
Along with crossed electric and magnetic fields in a Hall thruster, a radial component of electric field is generated that takes ions toward the walls, which causes sputtering and produces dust contamination in the thruster plasma. Considering negatively charged dust particles in the Hall thruster, we approach analytically the resistive instability by taking into account the oscillations of dust particles, ions and electrons along with finite temperatures of ions and electrons. In typical Hall thruster regimes, the resistive instability growth rate increases with higher collision rates in the …
Energy losses in a magnetic nozzle radiofrequency plasma thruster are investigated to improve the thruster efficiency, which are calculated from particle energy losses in fully kinetic simulations. The simulations calculate particle energy fluxes with a vector resolution including the plasma energy lost to the dielectric wall, the plasma beam energy, and the divergent plasma energy in addition to collisional energy losses. As a result, distributions of energy losses in the thruster and the ratios of the energy losses to the input power are obtained. The simulation results show that the plasma …
Consuming long-range interplanetary medium with fuel for driving plasma thrust is vital. Methods of capturing the space environment depending on its density and the ship velocity are indispensable issues to extract the space environment as a propellant. This matter of neutral fluxes would use solar radiation to create ionization in a plasma thruster. Extracting propellant at certain ranges look extremely promising where a low thrust device operates continuously to deliver a celestial target close at the speed of light. However, at longer distances, the density of space rapidly diminishes and i…
Traditional expressions and definitions describing performance of plasma thrusters, including the thrust, specific impulse, and the thruster efficiency, assume a steady state plasma flow with a constant flow velocity. However, it is very common for these thrusters that the plasma exhibits unstable behavior resulting in time-variations of the thrust and the exhaust velocity. For example, in Hall thrusters, the ionization instability leads to strong oscillations of the discharge current (so-called breathing oscillations), plasma density, ion energy, and as a result the ion flow. In this paper, w…
In a grid-less Electron Cyclotron Resonance (ECR) plasma thruster with a diverging magnetic nozzle, the magnitude of the ambipolar field accelerating the positive ions depends of the perpendicular energy gained by the electrons. This work investigates the heating of the electrons by electromagnetic waves, taking their bouncing motion into account in a confining well formed by the magnetic mirror force and the electrostatic potential of the thruster. An electromagnetic Particle-In-Cell (PIC) code is used to simulate the plasma in a magnetic field tube. The code's Maxwell solver is based on a se…
A two-dimensional simulation is conducted to investigate the effect of cross-field electron transport enhancement in the Hall thruster discharge caused by the nonuniform propellant supply in azimuth. The Hall thruster operation with azimuthally nonuniform propellant supply is expected to be a good test case to understand the influences of azimuthal plasma property distributions on the axial electron transport. A particle-fluid hybrid model is developed with a two-dimensional magnetized electron fluid model incorporated with an empirical anomalous electron mobility model. The calculation result…
Azimuthal spoke-like modes commonly occur in ExB discharges. The natural occurrence of the spoke mode is correlated with changes of plasma parameters. Here, instead of allowing these changes to occur naturally, we report a technique for actively controlling the spoke by adjusting the boundary condition at the anode. The technique is demonstrated using a cylindrical Hall thruster equipped with a segmented anode. By varying the voltage and the relative phases of the anode segments, properties of the azimuthal mode can be altered substantially, as shown by fast camera images and probe diagnostics…
The Particle-in-Cell (PIC) method was used to study two different ion thruster concepts - Stationary Plasma Thrusters (SPT) and High Efficiency Multistage Plasma Thrusters (HEMP-T), in particular the plasma properties in the discharge chamber due to the different magnetic field configurations. Special attention was paid to the simulation of plasma particle fluxes on the thrusters channel surfaces. In both cases, PIC proved itself as a powerful tool, delivering important insight into the basic physics of the different thruster concepts. The simulations demonstrated that the new HEMP thruster co…
Conventional snowplow/1-D models assume the existence of single completely ionized plasma sheet in the discharge chamber of pulsed plasma thrusters (PPTs). However, extensive experimental analysis and observations suggest the presence of multiple plasma streams and partial ionization of the propellant gas. A multi-layered plasma-neutral mass sheet one-dimensional numerical model is developed for PPTs in the present paper. The model accounts for the secondary plasma sheets generated due to the crowbar breakdowns as well as the neutral gas generated after the main discharge. The model accurately…
An axial-azimuthal two-dimensional Hall thruster discharge model was developed for analyzing gradient drift instability (GDI) and cross-field electron transport enhancement induced solely by the GDI. A hybrid particle-fluid model was used for the partially ionized plasma, where the inertialess electron fluid in the quasineutral plasma was assumed. A nonoscillatory numerical method was proposed for the potential solver in the electron fluid model to avoid numerical instability and analyze the physics of GDI accurately. A simulation is performed for a 1 kW-class anode-layer-type Hall thruster, a…
The performance gain of co-axial vacuum arc thruster in external axial magnetic field is analyzed by power and direct thrust measurements. Thruster geometry is actively controlled and inspected using laser profilometry. Peak performance is shown to be obtained in magnetic induction of 0.1 - 0.2 T, with measured thrust of 21 uN at arc power of 2.7 W, and thruster efficiency of ~ 4 %. The performance gain is attributed to ion beam focusing, increased erosion rate, and ion acceleration due to the axial magnetic field.
In this paper, a coaxial pulsed plasma thruster was designed, built, and tested. This design confirmed PPT operation at substantially reduced discharge voltages of 100 to 200 V across the discharge plasma at a discharge current level of 10.4 kA similar to magnetoplasmadynamic arcs. The PPT cathode was imaged with an ICCD camera over a wide range of pressures, and the photos indicated "spotless" diffuse arc attachment to the cathode at higher pressures, and the appearance of conventional cathode spots at lower pressures. Cathode erosion rate measurements support the conclusion of "spotless" ope…
A new concept for generation of thrust for space propulsion is introduced. Energetic thrust is generated in the form of plasmoids (confined plasma in closed magnetic loops) when magnetic helicity (linked magnetic field lines) is injected into an annular channel. Using a novel configuration of static electric and magnetic fields, the concept utilizes a current-sheet instability to spontaneously and continuously create plasmoids via magnetic reconnection. The generated low-temperature plasma is simulated in a global annular geometry using the extended magnetohydrodynamic model. Because the syste…
The electron cross-field transport by the induced azimuthal electric field in a Hall thruster exhibits the mobility scaled by $1/B$. This study investigates parameters affecting this transport over a Hall thruster's distinct regions, such as the ionization, acceleration, and plume region. The main focus is on the nonzero equilibrium azimuthal electric field induced by an azimuthally inhomogeneous neutral supply. A fast Fourier transform analysis of the plasma structure reveals that the wavenumber $k$ of the azimuthal plasma structure increases from $k=2$, which is the input condition, to $k=4$…
A two-fluid flowing plasma model is applied to describe the plasma rotation and resulted instability evolution in magnetically enhanced vacuum arc thruster (MEVAT). Typical experimental parameters are employed, including plasma density, equilibrium magnetic field, ion and electron temperatures, cathode materials, axial streaming velocity, and azimuthal rotation frequency. It is found that the growth rate of plasma instability increases with growing rotation frequency and field strength, and with descending electron temperature and atomic weight, for which the underlying physics are explained. …
In this work we are going to perform a simulation of a positive corona discharge in nitrogen gas, using two different asymmetric capacitor geometries. This work represents an improvement over previous work in order to accomplish higher ion wind velocities as well as stronger electrostatic propulsion forces on all the involved electrodes. In our model, the used positive ion source is a small diameter wire, which generates a positive corona discharge in nitrogen gas directed to the ground (or negatively charged) electrodes. By applying the fluid dynamic and electrostatic theories, all hydrodynam…
Hall-effect thrusters (HETs) operated with xenon are one of the most commonly used electric propulsion technologies for a wide range of space missions, including drag compensation in low Earth orbit, station-keeping, and orbital insertion, as access to space becomes more affordable. Although anomalous electron transport, the electron drift instability (EDI), and secondary electron emission (SEE) have been studied experimentally and numerically in xenon-based HETs, the impact of alternative propellants is still poorly characterized. In this work, a two-dimensional particle-in-cell/Monte Carlo c…
This paper presents a novel micropropulsion system for nanosatellite applications - a liquid fed pulsed-plasma thruster (LF-PPT) comprised of a Lorentz-force pulsed plasma accelerator (PPA) and a low-energy surface flashover (LESF) igniter. A 3 μF / 2 kV capacitor bank, offering shot energies of < 6 J, supported PPA current pulsed durations of ~ 16 μs with observed peaks of 7.42 kA. Plasma jet exhaust velocity was measured at ~ 32 km/s using a time-of-flight technique via a set of double probes located along the jet's path. Intensified charge coupled device (ICCD) photography was concurrently …
Electromagnetic propulsion technology has been thought to provide a potential form of future spacecraft propulsion for some time. In contrast to ion thrusters, which utilize the Coulomb force to accelerate positively charged species, electromagnetic propulsion systems utilize the Lorentz force to accelerate all species in a quasi-neutral state, providing significant technological benefits over ion thrusters. Several forms of electromagnetic propulsion have been researched and developed, such as the Variable Specific Impulse Magnetoplasma Rocket, pulsed inductive thrusters, and the electrodeles…
We examine the use of the interplanetary substance as a possible fuel for spacecraft plasma thrusters for interplanetary flights. The solar radiation is considered as an energy source for the ionization and the acceleration of particles of captured space environment that is used as drop weight. The method of capturing the space environment, which is dependent on its density, the velocity of the spacecraft, and the power of solar radiation, defines the technical feasibility of this scheme. Both pulsed and continuous operations of the plasma accelerator are possible under some conditions as show…
Hall thrusters are susceptible to large-amplitude plasma oscillations that impact thruster performance and lifetime and are also difficult to model. High-speed cameras are a popular tool to study these dynamics due to their spatial resolution and are a popular, nonintrusive complement to in-situ probes. High-speed video of thruster oscillations can be isolated (decomposed) into coherent structures (modes) with algorithms that help us better understand the evolution and interactions of each. This work provides an introduction, comparison, and step-by-step tutorial on established Fourier and new…
Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft. To extend such missions lifetime, an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP). It collects atmospheric particles to be used as propellant for an electric thruster. The system would minimize the requirement of limited propellant availability and can also be applied to any planet with atmosphere, enabling new mission at low altitude ranges for longer times. Challenging is also the presence of reactive…
A reversed gas feed configuration for Hall thrusters is proposed and studied numerically. As an alternative to standard direct injection, we investigate the effect of injecting the propellant near the channel exit and directing it backwards, towards the anode. The resulting neutral density and average velocity fields are studied with the Direct Simulation Monte Carlo method for both cold and warm anode conditions. The residence time of neutral particles inside the channel and in the ionization region is computed using a test-particle Monte Carlo method. The computations indicate that the rever…
Challenging space missions include those at very low altitudes, where the atmosphere is source of aerodynamic drag on the spacecraft that finally defines the missions lifetime unless way to compensate for it is provided. This environment is named Very Low Earth Orbit (VLEO) and is defined for $h<450~km$. In addition to the satellite's aerodynamic design, to extend the lifetime of such missions an efficient propulsion system is required. One solution is Atmosphere-Breathing Electric Propulsion (ABEP) that collects atmospheric particles to be used as propellant for an electric thruster. The syst…
Laser ablation plasma thrusters are an emerging space propulsion concept that provides promise for lightweight payload delivery. Predicting the lifetime and performance of these thrusters hinges on a comprehensive characterization of the expansion dynamics of the ablated plasma plume. While state-of-the-art techniques for simulating plasmas are often particle-based, a grid-based direct kinetic solver confers advantages in such a transient and inhomogeneous problem by eliminating statistical noise. A direct kinetic solver including interparticle collisions is employed on a plume expansion model…
Low frequency ionization oscillations involving plasma and neutral density (breathing modes) are the most violent perturbations in Hall thrusters for electric propulsion. Because of its simplicity, the zero-dimensional (0-D) predator-prey model of two nonlinearly coupled ordinary differential equations for plasma and neutral density has been often used for the characterization of such oscillations and scaling estimates. We investigate the properties of its continuum analog, the one-dimensional (1-D) system of two nonlinearly coupled equations in partial derivatives (PDE) for plasma and neutral…
The coupling physics between multiple antennas separated axially along a plasma cylinder is investigated. Experiments are carried out on a recently built device: Physics ANd Thruster oriented HElicon Research (PANTHER), with an upgrade of second-stage antennas. Mutual induction currents are measured in detail. It is found that the existence of plasma column going through these antennas increase the coupling effects among them significantly. Theoretical analyses from the perspectives of transformer and magnetic permeability and moment confirm the reasonability of this phenomenon. This work is o…
The creation and design of a plasma thruster are considered using a rotating cylindrical plasma flow in crossed magnetic fields. The thruster scheme uses this plasma guided by a permanent, radial and a time-dependent axial magnetic field. Namely, the acceleration effect is formed by the azimuthal electric field which comes about as a variation of an external, axial magnetic flux. Besides, it is possible to go beyond the approach of quasi-neutrality. These processes can lead to the generation of a local azimuthal time-dependent electric field which may also accelerate the rotation of the electr…
Two-dimensional fully kinetic particle-in-cell simulations of an electrodeless plasma thruster, which uses a magnetic nozzle, were conducted to investigate the thrust generation induced by the internal plasma current. The results clearly show that the $\bf{E} \times \bf{B}$ and diamagnetic current densities are the major components of the internal plasma current. The simulated pressure structures reproduced the experimentally observed structures well. The results for various magnetic field strengths reveal that the $\bf{E} \times \bf{B}$ effect decreases and the diamagnetic effect becomes domi…
