Electrodeless Plasma Thruster Research Articles

Numerical Investigation of Electrodeless Plasma Thruster with Rotating Electric Field

Two-dimensional simulations of various cross-sections under different magnetic field strengths in an electrodeless plasma thruster acceleration part using rotating electric field were conducted. The Particle-In-Cell and Monte Carlo Collision method was used to better understand plasma movement and find the ideal condition for the azimuthal current formation. The findings suggest that raising the voltage amplitude can improve the electric field’s penetration into the plasma, diminish the disparity between the azimuthal current’s maximum and minimum values, and consequently generate a more uniform size and distribution. Peak azimuthal current values are directly proportional to the ac frequency at frequencies above 100 MHz and inversely proportional to the frequency below 100 MHz. A rotating electric field that matches the background magnetic field could be produced by adjusting the phase difference among the two sets of antennas. And then the plasma is accelerated by the effect of E×B to achieve a more favorable azimuthal current. The results also demonstrate that an appropriately sized and distributed azimuthal current benefits more from a magnetic field with a strength between 200 and 1000 G and a value that declines from the cross-section center to its periphery.

Starting Modes of Bi-Directional Plasma Thruster Utilizing Krypton

Multidirectional plasma thrusters are of particular interest for dynamic space missions due to the adjustability of their integral characteristics. One type of multidirectional plasma thrusters is -directional, consisting of a symmetric electromagnetic system surrounding the gas discharge chamber, capable of generating a propulsion minimum in two directions. The experimental results of this study of the starting modes of a multidirectional plasma thruster utilizing krypton as propellant are reported. The thruster is placed in a vacuum chamber. The magnetic field strength is adjusted in the range of 35 to 400 G in peaks. The current of 13.56 MHz frequency applied to the antenna is regulated in the range of 0 to 25 A. The diameter of the orifices is varied in the range of 3 to 10 mm. In contrast to the unidirectional electrodeless plasma thruster, the radiofrequency breakdown threshold of the multidirectional plasma thruster decreases with increasing static magnetic field due to the symmetry of the magnetic system and the gas discharge chamber. The influence of the magnetic field on the radiofrequency breakdown threshold in the multidirectional plasma thruster is shown theoretically by the classical diffusion theory and ponderomotive effects, and discussed in the electron circulation hypothesis.

Nature-Inspired Concepts for High-Power Electric Propulsion Systems

The development of new space missions and the growing interest in space exploration have created an urgent need to develop high-thrust propulsion systems capable of propelling spacecraft far beyond the Earth and the solar system for long periods. Electric propulsion can potentially enable space missions to reach speeds thousands of times greater than conventional high-thrust chemical rockets. However, high speed comes at the cost of low power-to-thrust efficiency when considering propulsion systems as a whole, including the power generation system, transmission lines, and thrusters, which prevents high thrust from being achieved with any conceivable power system, resulting in long acceleration times. In addition, modern electric propulsion systems rely on external power sources that suffer significant power transfer losses at the high power levels required for high thrust levels. In addition, modern electric propulsion systems suffer from a number of critical physical and engineering problems that affect thrust levels and longevity. In addition, modern electric propulsion systems do not follow the principles of generation and acceleration of plasma flow that can be observed in space and potentially borrowed for artificial applications. This paper discusses several promising electrodeless plasma thruster concepts for high-power, high-thrust electric propulsion systems based on a combined power source/power converter/thruster architecture. These concepts have the potential to overcome modern limitations of high-power electric propulsion systems and enable new outer space missions that would not be possible with conventional thrusters.

Plasma acceleration in a magnetic arch

When two magnetic nozzles with opposite polarity are placed side by side, a ‘magnetic arch’ (MA) is formed, which connects the field lines of each nozzle into a closed-line configuration. The plasma expansion and acceleration in this magnetic topology are relevant for clusters of electrodeless plasma thrusters, as well as novel, non-cylindrical thruster architectures. A collisionless, quasineutral, two-fluid model of the plasma expansion in a MA, is introduced. The plasma properties (density, electron temperature, electrostatic potential, ion velocity, electric currents) in the 2D planar and zero plasma-beta limit are analyzed, and the magnetic thrust density is discussed. It is shown that the ions coming out of the two nozzles meet on a shock-like structure to form a single beam that propagates beyond the closed lines of the applied magnetic field, generating magnetic thrust. A small magnetic drag contribution comes from the final part of the expansion. The plasma-induced magnetic field is then computed self-consistently for non-zero plasma-beta expansions, showing that it stretches the MA in the downstream direction and helps reduce that drag contribution. Finally, the limitations of the present model are discussed.

Energy Coupling Mechanism of Electrodeless Plasma Thruster with Rotating Electric Field

The energy coupling process indicated by particle density, speed, current density, and power absorption in a thruster using a rotating electric field was simulated using a one dimension, three velocities electrostatic particle-in-cell (PIC) code under different external magnetic field strengths varying from 0 to 80 G. The longer interaction between electrons and the sheath layer due to the increased magnetic field results in a significant decrease in electron speed from at 0 G to at 80 G; a reduction in electron power absorption from at 0 G to at 80 G; and an increase in electron density, current density, and total current density about 69.48, 21.11, and 5.4%, respectively. While ions cannot respond to the changes in time because of their large mass. Three types of currents, namely, electron, ion, and displacement, are primarily present throughout the discharge process. Ion current is significantly less than the other two. The characteristics of plasma described exhibit a nonlinear change, dropping at first and then rising when the magnetic field is strengthened. The results have implications for both choosing the magnetic field for the thruster and thoroughly investigating the energy coupling inside the plasma.

Coupling between multiple coaxial antennas surrounding a plasma column produced by helicon antenna

AbstractThe coupling physics between multiple coaxial antennas separated axially along plasma column produced by helicon antenna are investigated. Experiments are carried out on a recently built device, named Physics ANd Thruster oriented HElicon Research (PANTHER) with the upgrade of second‐stage antennas. Mutual induction currents on these antennas are measured for two cases: without plasma discharge and with plasma discharge, respectively. It is found that the existence of a plasma column going through these antennas increases the coupling effects among them significantly. Theoretical analyses from the perspectives of transformer and magnetic permeability and moment confirm the reasonability of this phenomenon. Equivalent circuit models and governing equations are provided for preliminary analyses, covering both single‐antenna‐driven cases and dual‐antenna‐driven cases. The effects of confining magnetic field and background pressure on the mutual coupling are shown as well. This work is of particular interest for electrodeless plasma source or thruster which employs multiple coaxial antennas for ionization and acceleration. The analogy of a plasma column going through multiple antennas to a magnetic core for a transformer is an innovative attempt.

Design of an intake and a thruster for an atmosphere-breathing electric propulsion system

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 system would minimize the requirement of limited propellant availability and can also be applied to any planetary body with atmosphere, enabling new missions at low altitude ranges for longer times. One of the objectives of the H2020 DISCOVERER project, is the development of an intake and an electrode-less plasma thruster for an ABEP system. The article describes the characteristics of intake design and the respective final deigns providing collection efficiencies up to $94\%$. On the other side, the radio frequency (RF) Helicon-based plasma thruster (IPT) developed at IRS, is hereby presented as well, while its performances are being evaluated, the thruster has been operated with single atmospheric species as propellant, and has highlighted very low input power requirement for operation at comparable mass flow rates $P\sim 60~W$.

Magnetic Nozzle and RPA Simulations vs. Experiments for a Helicon Plasma Thruster Plume

The experimental characterization of electrodeless plasma thrusters with a magnetic nozzle is fundamental in the process of increasing their maturity to reach the industrialization level. Moreover, it offers the unique opportunity of validating existing numerical models for the expansion of a magnetized plasma plume, and for the synthetic simulation of diagnostics measurements, like those of a retarding potential analyzer, which provides essential information regarding the ion beam energy distribution function. Simulations to experiments comparison ultimately enables a better understanding of the physical processes behind the observed experimental curves. In this work, input experimental data of a Helicon plasma plume is used to simulate both a magnetic nozzle expansion in the divergent field region, and the corresponding measurements of a retarding potential analyzer, through dedicated small-scale simulations of this diagnostics tool. Magnetic nozzle simulation and experimental results agree well in terms of the angular distribution of the ion current at 40 cm distance from the source, and also in the prediction of the energies of the two main peaks of the ion energy distribution function: a first one at 45 eV due to source ions, and a second one, at 15–20 eV, due to ions from charge-exchange and ionization collisions in the plume. Finally, the small-scale simulation of the retarding potential analyzer permits to assess the parasitic effects caused by the ion current collected by the different analyzer grids. The inclusion of the retarding and electron suppression grids currents in the overall I-V characteristic is shown to correct almost entirely these effects on the obtained ion velocity distribution.

Magnetized fluid electron model within a two-dimensional hybrid simulation code for electrodeless plasma thrusters

An axisymmetric fluid model for weakly-collisional, magnetized electrons is introduced and coupled to a particle-in-cell model for heavy species to simulate electrodeless plasma thrusters. The numerical treatment of the model is based on a semi-implicit time scheme, and specific algorithms for solving on a magnetic field aligned mesh. Simulation results of the plasma transport are obtained for a virtual electrodeless thruster. The particle and energy fluxes of electrons are discussed. A first phenomenological model is included for the anomalous cross-field electron transport, and a second one for the anomalous parallel-field electron cooling in the plume. The balances of the plasma properties reveal that wall losses are the crucial reason for the poor thrust efficiency of these thrusters. The magnetic thrust inside the source could be negative and largely depending on the location of the magnetic throat, which is found uncoupled from the location of the plasma beam sonic surface. Furthermore, a sensitivity analysis of the results against the simulated plume extension shows that finite plumes imply an incomplete electron expansion, which leads to underestimating the performances.

Development of a novel wave plasma propulsion module with six-directional thrust vectoring capability

Nowadays, the development of low Earth orbits’ (LEO) - up to 2000 km - small satellites (SSs) is of particular interest. Such SSs are supposed to use for effective telecommunication systems and advanced Earth research missions. When developing space missions of LEO SSs, designers and operators encounter a number of the following technical problems: an inability to use a single propulsion system for all flight operations, such as transfer from parking orbit to the target one, maneuvers between orbits, altitude control, orbit maintenance, attitude control, de-orbiting; a limited lifetime of conventional (Hall-Effect and Ion type) Electric Propulsion Systems (EPs) in low Earth orbits; high energy consumption of existing EPs; unloading of SSs' attitude control systems; de-orbiting of the SSs from the target orbit at the end of the active life to reduce contamination of LEO. The multidirectional electrodeless plasma thrusters could be the solution to overcome these problems. For example, such propulsion systems (PSs) can generate thrust in two directions. Using three bi-directional plasma thrusters in one PS, it is possible to create a plasma propulsion module with six thrust vectors that allows performing all of the SSs' space mission tasks where propulsion systems are needed while having a long-term service life in the upper atmosphere, low energy consumption – from 100 W, - and compact size – from 1U - which allows using this module on board of the SSs. This paper describes the first prototype of the six-directional plasma propulsion module. The focus of this paper is the study of the bi-directional wave plasma source with an open-ended gas discharge chamber and magnetic nozzles for plasma flow control – plasma flows acceleration and locking. The example of this source demonstrates the possibility of creating two thrust vectors using the single bi-directional wave plasma source and allows suggesting the creation of the six-directional wave plasma propulsion module for SSs.

Compositions and distributions of the azimuthal currents in the magnetic nozzle

The azimuthal currents in the divergent magnetic nozzle of the electrodeless plasma thrusters are investigated using a two-dimensional axisymmetric particle-in-cell code. In this paper, the azimuthal currents are decomposed into four components—the diamagnetic drift current, the E × B drift current, the viscous-stress-induced current and the inertia-induced current. The azimuthal current and its four components are analyzed under three magnetization levels of 0.25 T, 0.75 T and 2.15 T. In the absence of inlet ion temperature, the azimuthal currents mainly consist of electron currents resulted from ∇p e, E × B drift and electron viscosity, while the azimuthal currents caused by the inertia can generally be neglected. The azimuthal ion currents considered negligible in previous studies are shown to be non-negligible in the highly-magnetized and collisionless magnetic nozzle, where the dominant mechanism for its formation is E × B drift and drift from the centrifugal force. In the upstream and midstream, the compositions and distributions of the azimuthal currents can vary at different radial positions and magnetization conditions because of the influence of the electric potential barrier and the high density conic. In the downstream, a vast range of paramagnetic currents are produced by the E × B drift due to ion inward detachment. And the paramagnetic stress-induced current begins to prevail due to the FELR effect. Superimposed with the paramagnetic part of the diamagnetic drift current under a high magnetic field, they can undermine the thrust gain coefficient of the magnetic nozzle.

Numerical investigation of internal plasma currents in a magnetic nozzle

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 E×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 E×B effect decreases, and the diamagnetic effect becomes dominant with an increase in the magnetic field strength; this demonstrates the significant contribution of the diamagnetic effect in thrust generation.

The curling probe: A numerical and experimental study. Application to the electron density measurements in an ECR plasma thruster

The measurement of electron density is a key issue in understanding and controlling plasma applications. To date, plasma density in electric thrusters has been mainly evaluated with electrostatic techniques, such as the Langmuir probe, which could be quite invasive. In this paper, we propose the application of a microwave resonant probe, the curling probe, to the diagnostic of an electrodeless plasma thruster. The measurable electron density range and the probe accuracy are found to be limited by the probe natural frequency. We present the numerical study and the experimental characterization of three curling probes with different natural frequencies (700, 1400, and 3000 MHz, approximately). First, an analytical equation of the natural frequency as a function of geometrical parameters is drawn from 2D numerical simulations. Then, a procedure based on solid dielectric etalons is proposed for the absolute calibration of the probe. Finally, measurements are performed in the plume of an electron cyclotron resonance plasma thruster. Electron densities from 108 to 1011 cm-3 have been obtained in agreement with hairpin and Langmuir probes results. A wall-embedded probe has enabled measurements inside the thruster source with minimal plasma perturbation. A possible curling probe configuration, embedded in a reactor wall, is proposed as a fully non-invasive diagnostic for plasma sources.

Measurement and identification of azimuthal current in an RF plasma thruster employing a time-varying magnetic field

We report two-dimensional temporally resolved measurements of the magnetic field and the azimuthal current in a radio-frequency plasma thruster with a time-varying magnetic field. The measured azimuthal current cannot be explained by the classical cross-field transport theory, which has been used in modeling of inductive electrodeless plasma thrusters; rather, it is fairly close to the estimated current using parallel electrical conductivity. In the analysis in the collisionless limit, the comparison of the measured azimuthal current and the diamagnetic current implies the non-negligible contribution of the azimuthal electron E × B drift current in the azimuthal current, in contrast with the case of conventional helicon plasma thrusters. This result indicates the establishment of the strong in-plane perpendicular electric field, as observed in the previous experiment [H. Sekine, H. Koizumi, and K. Komurasaki, Phys. Plasmas 27, 103513 (2020)]. Based on the experimental results, we build a hypothesis on the wall-charging-induced in-plane perpendicular electric field and the in-plane current-free condition. By analyzing the electron momentum equation under this condition, the electrical conductivity in the azimuthal direction agrees to the parallel conductivity, explaining the present result well.

Mechanically Amplified Milli-Newton Thrust Balance for Direct Thrust Measurements of Electric Thrusters for Space Propulsion

Direct thrust measurements by means of a thrust balance (TB) are the golden standard for measuring thrust and, concurrently, the specific impulse in electric thrusters. To measure these properties in the novel class of electrodeless plasma thrusters, a new TB based on the Variable Amplitude Hanging Pendulum with Extended Range (VAHPER) concept has been developed. The TB has a mechanical amplification mechanism with an angular magnification of $31^\circ /^\circ $ . Using Lagrangian mechanics, we show that the TB loaded with a 5.2-kg thruster prototype behaves like a damped harmonic oscillator with a natural frequency of 0.37 Hz. A variable damping system provides damping with an optimal damping ratio of 0.78, which corresponds to a settling time of only 1.8 s. Both the model and the damping and calibration system have been validated. To accommodate the particularities of medium power electrodeless plasma thrusters, the TB design includes the following features: an optical displacement sensor, water cooling, liquid metal connectors, and dedicated vacuum-rated electronics for autoleveling, remote (in-vacuum) calibration, and temperature monitoring. To test the TB, measurements were performed on a 500-W Helicon Plasma Thruster breadboard model. When loaded with this thruster, the measured stiffness of the system was 12.67 ± 0.01 mN/mm. For this stiffness, the thrust range is 150 mN with a 0.1-mN resolution. The relative uncertainty on the thrust measurements is found to be on the order of 2%.

Extremely small-diameter, high-density, radio frequency, plasma sources and central gas feeding for next-generation electrodeless plasma thrusters.

Radio frequency (RF) waves including helicon waves can readily produce high-electron-density (ne up to 1013 cm-3) plasmas with a broad range of external operating parameters. Various featured RF and helicon sources in a wide range of scales are suitable for plasma propulsion schemes. Electrodeless RF plasmas have no direct contact between electrodes and antennas, which enables long-life operation. However, one of the crucial problems is to reduce the plasma size for future applications in nano- and pico-satellites. Diagnostics of the plasma parameters in a small area should also be improved. Furthermore, to increase plasma performance, it is important to consider the radial electron density (ne) profile with an increasing upper limit, observed in high-density helicon sources due to the depletion of neutrals. This problem may be controlled by the location of neutral gas feeding and knowledge of the gas pressure distribution. Here, production of RF plasmas, with extremely small diameters from 3-mm down to 0.5-mm including 1-mm, was demonstrated, and characterization of ne and the electron temperature was performed with a collisional radiative model. Finally, to improve plasma performance such as ne and the thrust force, internal gas feeding was demonstrated using a developed Pirani gauge to measure neutral density.

Experimental Evaluation of Steady-State Electromagnetically Inductive Acceleration for Electrodeless Plasma Thruster and Fundamental Measurement of the Correlation between the Effective Current of Acceleration Coil and Thrust

Experimental Evaluation of Steady-State Electromagnetically Inductive Acceleration for Electrodeless Plasma Thruster and Fundamental Measurement of the Correlation between the Effective Current of Acceleration Coil and Thrust

Development of featured high-density helicon sources and their application to electrodeless plasma thruster

Helicon plasma sources using radio frequency (rf) waves are very useful, as they can produce high-density (∼1013 cm−3) plasma easily with a broad range of external operating parameters. Various kinds of featured helicon sources in a wide range of geometrical scales have been developed and characterized to control plasmas as required. Furthermore, particle production efficiency has demonstrated excellent performance over a very wide range of plasma sizes. High-beta (∼1) plasmas can also be easily achieved, showing the importance of the neutrals effect. As one of the many applications in areas ranging from fundamental to application fields, a space propulsion system with an advanced concept of an electrodeless condition (no direct contact between the plasma and electrodes/antennas) has been developed, owing to the expectation of a longer life operation. Among many proposals, two trials of electrodeless, additional acceleration methods are introduced, emphasizing the importance of some diagnostics. Here, we will review and describe the present status of our high-density rf plasma production with additional acceleration in an advanced propulsion field.

Radio Frequency Excited Plasma Discharge Simulation for Potential Helicon Plasma Thruster

The development of advanced propulsion is the key element in the implementation of a robust space exploration program. Advance thruster concepts such as the development of electrodeless Plasma thrusters with high-density helicon plasma sources expected to mitigate the existing problems of the finite lifetimes inherent in electric propulsion. Electrodeless plasma thrusters are potentially more durable than conventional thrusters that use electrodes such as a gridded ion, Hall thrusters, arcjets, and resistojets. The goal of the research is to simulate a compact high-power-density helicon plasma source operating, which is under examination for a potential electric propulsion application. Plasma modeling is performed in COMSOL Multiphysics plasma module. A Nagoya type III antenna is placed on the surround of a dielectric tube and electrically excited at 13.56 MHz. Plasma is formed in the ionization chamber, which contains argon gas at low pressure. The plasma is sustained utilizing electromagnetic induction.

Effects of neutral distribution and external magnetic field on plasma momentum in electrodeless plasma thrusters

The effects of neutral distribution and an external magnetic field on plasma distribution and thruster performance are numerically investigated using a particle-in-cell simulation with Monte Carlo collisions (PIC-MCC) and the direct simulation Monte Carlo (DSMC) method. The modeled thruster consists of a quartz tube 1 cm in diameter and 3 cm in length, where a double-turn rf loop antenna is wound at the center of the tube and a solenoid is placed between the loop antenna and the downstream tube exit. A xenon propellant is introduced from both the upstream and downstream sides of the thruster, and the flow rates are varied while maintaining the total gas flow rate of 30 μg/s. The PIC-MCC calculations have been conducted using the neutral distribution obtained from the DSMC calculations, which were applied with different strengths of the magnetic field. The numerical results show that both the downstream gas injection and the external magnetic field with a maximum strength near the thruster exit lead to a shift of the plasma density peak from the upstream to the downstream side. Consequently, a larger total thrust is obtained when increasing the downstream gas injection and the magnetic field strength, which qualitatively agrees with a previous experiment using a helicon plasma source.