Kan Xie

Study of breakdown in an ablative pulsed plasma thruster

Breakdown in ablative pulsed plasma thrusters (APPTs) must be studied in order to design new types of APPTs and measure particular parameters. In this paper, we studied a parallel-plate ablative pulsed plasma thruster that used a coaxial semiconductor spark plug. By operating the APPT about 500 times with various capacitor voltages and electrode gaps, we measured and analyzed the voltage of the spark plug, the voltage between the electrodes, and the discharge current. These experiments revealed a time delay (∼1–10 μs) between spark plug ignition and capacitor discharge, which may affect the performance of high-pulsing-rate (>10 kHz) and double-discharge APPTs, and the measurements of some of the APPT parameters. The delay time decreased as the capacitor voltage increased, and it increased with an increasing electrode gap and increasing number of ignitions. We explain our results through a simple theoretical analysis.

Self-pulsing of hollow cathode discharge in various gases

In this paper, we investigate the self-pulsing phenomenon of cavity discharge in a cylindrical hollow cathode in various gases including argon, helium, nitrogen, oxygen, and air. The current-voltage characteristics of the cavity discharge, the waveforms of the self-pulsing current and voltage as well as the repetition frequency were measured. The results show that the pulsing frequency ranges from a few to tens kilohertz and depends on the averaged current and the pressure in all gases. The pulsing frequency will increase with the averaged current and decrease with the pressure. The rising time of the current pulse is nearly constant in a given gas or mixture. The self-pulsing does not depend on the external ballast but is affected significantly by the external capacitor in parallel with the discharge cell. The low-current self-pulsing in hollow cathode discharge is the mode transition between Townsend and glow discharges. It can be described by the charging-discharging process of an equivalent circuit consisting of capacitors and resistors.

Self-pulsing in a low-current hollow cathode discharge: From Townsend to glow discharge

We investigate the self-pulsing phenomenon of a low current cavity discharge in a cylindrical hollow cathode in pure argon. The waveforms of pulsed current and voltage are measured, and the time-averaged and time-resolved images of hollow cathode discharge are recorded by using high-speed intensified charge coupled device camera. The results show that the self-pulsing is a mode transition between low-current stage of Townsend discharge and high-current stage of glow discharge. During the self-pulsing, the current rising time relates to the dissipation of space charges, and the decay time relates to the reconstruction of the virtual anode by the accumulation of positive ions. Whether or not space charges can form and keep the virtual anode is responsible for the discharge mode and hence plays an important role in the self-pulsing phenomenon in low current hollow cathode discharge.

Current?voltage characteristics of a cathodic plasma contactor with discharge chamber for application in electrodynamic tether propulsion

This paper focuses on the net electron-emission current as a function of bias voltage of a plasma source that is being used as the cathodic element in a bare electrodynamic tether system. An analysis is made that enables an understanding of the basic issues determining the current?voltage (C?V) behaviour. This is important for the efficiency of the electrodynamic tether and for low impedance performance without relying on the properties of space plasma for varying orbital altitudes, inclinations, day?night cycles or the position of the plasma contactor relative to the wake of the spacecraft. The cathodic plasma contactor considered has a cylindrical discharge chamber (10?cm in diameter and ?11?cm in length) and is driven by a hollow cathode. Experiments and a 1D spherical model are both used to study the contactors C?V curves. The experiments demonstrate how the cathodic contactor would emit electrons into space for anode voltages in the range of 25?40?V, discharge currents in the range of 1?2.5?A, and low xenon gas flows of 2?4?sccm. Plasma properties are measured and compared with (3?A) and without net electron emission. A study of the dependence of relevant parameters found that the C?V behaviour strongly depends on electron temperature, initial ion energy and ion emission current at the contactor exit. However, it depended only weakly on ambient plasma density. The error in the developed model compared with the experimental C?V curves is within 5% at low electron-emission currents (0?2?A). The external ionization processes and high ion production rate caused by the discharge chamber, which dominate the C?V behaviour at electron-emission currents over 2?A, are further highlighted and discussed.

Influence of the Magnetic Field Topology on Hall Thruster Discharge Channel Wall Erosion

A 2D3V Particle-In-Cell (PIC) and Monte-Carlo Collision (MCC) model is adopted to simulate the plasma parameters and the channel wall erosion depth of a Hall thruster. Ions and electrons are modeled as particles. Artificial mass ratio and permittivity are employed to simulate the electrons and ions simultaneously. The influence of the magnetic topology on the erosion of the channel walls is discussed. The erosion model is based on the distributions of ion energy and incidence angle and the sputtering yield function at the channel wall. Simulation results are compared with experimental data.

Characteristics of plasma properties in double discharge ablative pulsed plasma thrusters

Ablative pulsed plasma thrusters, the earliest electric space propulsion devices, create highly transient plasmas in short discharges that are expelled to create thrust. In recent years, the double-discharge ablative pulsed plasma thruster design has been proposed to improve the low-thrust efficiency. In this study, optical emission spectroscopy was applied to investigate the plasma properties in different regions and energy distributions. The electron temperature and electron density of the plasmas are derived and discussed. This study provides a physical mechanism for double-discharge pulsed plasma thrusters.

Thrust Control by Fluidic Injection in Solid Rocket Motors

Cold-flow tests, thermal tests, and numerical simulation were performed to study the thrust-adjustment characteristics, and the thrust-vector-control characteristics, of a fluidic nozzle throat com...

Extracted Current, Bias Voltage, and Ion Production of Cathodic Hollow-Cathode-Driven Plasma Contactors

Plasma properties on extracted electron current–bias voltage characteristics are presented for three selected plasma contactor configurations: a hollow-cathode-only concept, a motive discharge chamber concept, and a passive discharge chamber concept. Measurements were used to demonstrate how one could achieve low impedance performance without being affected by space plasma properties or by consuming significant propellant mass and power. A one-dimensional model was applied to describe the plasma expansion process that occurs downstream of a cathodic contactor. The model matched well with experimental trends and indicated that the plasma ion production rate within and nearby the plasma contactor dominated the emission-bias behavior of the devices. High ion production rate at a given total mass flow resulted in high propellant utilization and low discharge loss. However, plasma potential measurements showed that an anode sheath limited the maximum propellant unitization to less than ∼75% and led to a foldba...

The plasma properties and electron emission characteristics of near-zero differential resistance of hollow cathode-based plasma contactors with a discharge chamber

The formation of electron emission-bias voltage (I-V) characteristics of near-zero differential resistance in the cathodic plasma contactor for bare electrodynamic tether applications, based on a hollow cathode embedded in a ring-cusp ionization stage, is studied. The existence of such an I-V regime is important to achieve low impedance performance without being affected by the space plasma properties for a cathodic plasma contactor. Experimental data on the plasma structure and properties downstream from the ionization stage are presented as functions of the xenon flow rate and the electron emission current. The electrons were emitted from the cathode to the cylindrical vacuum chamber wall (r = 0.9 m) under ≈10−5 Torr of vacuum pressure. The ring-cusp configuration selected for the plasma contactor created a 125-Gauss axial field near the cathode orifice, along with a large-volume 50-Gauss magnitude pocket in the stage. A baseline ion energy cost of ≈300 eV/ion was measured in the ionization stage when n...

Parametric Study of an Air-Breathing Electric Propulsion for Near-Space Vehicles

An air-breathing electric propulsion system is regarded as a potential alternative propulsion system to the propeller system for near-space vehicles. The goal of this paper is to study the performa...