Performance of pulsed plasma thruster at low discharge energy

As the size of satellites scales down, low-power and compact propulsion systems such as the pulsed plasma thruster(PPT) are needed for stabilizing these miniature satellites in orbit. Most PPT systems are operated at 2 J or more of discharge energy. In this work, the performance of a PPT with a side-fed, tongue-flared electrode configuration operated within a lower discharge energy range of 0.5-2.5 J has been investigated. Ablation and charring of the polytetrafluoroethylene propellant surface were analyzed through field-effect scanning electron microscopy imaging and energy-dispersive X-ray spectroscopy. When the discharge energy fell below 2 J, inconsistencies occurred in the specific impulse and the thrust efficiency due to the measurement of the low mass bit. At energy ≥2 J, the performance parameters are compared with other PPT systems of similar configuration and discussed in depth.

Application and development of the pulsed plasma thruster

The application and development of pulsed plasma thrusters(PPTs)in recent years are reviewed in this paper.The advantages of PPTs are discussed.The schematics,propulsion performance parameters and key physical processes of PPTs are described.Some representative PPT products and flight systems developed in recent years are presented to show the performance of the PPT.Studies about how electrode structures,discharge circuits,propellant materials,energy discharge method,propellant feed method,ignition method and number of thruster heads influence the PPT performance are presented and analyzed.The ignitor design method,ignition process and propellant carbonization are introduced to discuss the reliability and lifetime issues in PPTs.The modeling methods of the discharge circuit,as well as ablation,ionization and acceleration in PPTs are presented.Finally,the application of PPTs in the future is analyzed and some suggestions for PPT development are proposed.

Comprehensive analysis of pulsed plasma nitriding preconditions on the fatigue behavior of AISI 304 austenitic stainless steel

This study aims to draw an exact boundary for microstructural and mechanical behaviors in terms of pulsed plasma nitriding conditions.The pulsed plasma nitriding treatment was applied to AISI 304 austenitic stainless steel at different temperatures and durations.Results reveal that nitriding depth increased as process temperature and duration increase.The nitriding depth remarkably increased at 475℃for 8 h and at 550℃for 4 h.An austenite structure was transformed into a metastable nitrogen-oversaturated body-centered tetragonal expanded austenite(S-phase)during low-temperature plasma nitriding.The S-phase was converted to CrN precipitation at 475℃for 8 h and at 550℃for 4 h.Surface hardness and fatigue limit increased through plasma nitriding regardless of process conditions.The best surface hardness and fatigue limit were obtained at 550℃for 4 h because of the occurrence of CrN precipitation.

Volumetric Langmuir probe mapping of a transient pulsed plasma thruster plume

The triple Langmuir probe enables measurements of the transient plasma parameters over time at a point of interest.We demonstrate how these measurements can be easily combined to obtain a visualization of the overall plasma behavior of a pulsed plasma thruster.Through this,it is possible to identify features in the expansion of the plasma such as the canting angle of the plume.We also identified the early arrival of a negatively canted low-density plasma plume.The 2D profiles also reveal data that would otherwise be obscured by other planes in optical measurements.

Study on the Discharge Characteristics of a Coaxial Pulsed Plasma Thruster

A new coaxial pulsed plasma thruster （PPT） laboratory model is designed and employed in this study. A Teflon sleeve is connected with the anode, which is shaped as a nozzle, and a cathode is mounted in the cavity of the Teflon sleeve and kept in close contact with it. A thread is then designed in the internal surface of the Teflon sleeve, and because of the strong field strength of the cathode triple junction （CTJ）, vacuum flashover occurs and a plasma jet is acquired behind the anode. The electric field distribution of the designed coaxial PPT laboratory model is simulated by MAXWELL 3D simulation software, and the plasma density and thrust are measured by a Langnmir probe and a piezoelectric thin-film sensor, respectively. Through a series of comparative experiments, we discuss the impact of optimal designs, such as the thread and the nozzle-shaped anode, on the discharge characteristics of the coaxial PPT. The experimental and simulation results indicate that the designed coaxial PPT laboratory model presents better discharge characteristics in view of its higher plasma density and greater thrust.

Characteristics of plasma in a novel laser-assisted pulsed plasma thruster

A novel laser-assisted pulsed plasma thruster(LA-PPT)is proposed as an electric propulsion thruster,which separates laser ablation and electromagnetic acceleration.It aims for a higher specific impulse than that achieved with conventional LA-PPTs.Owing to the short-time discharge and the novel configuration,the physical mechanism of the discharge is unclear.Time and spatial-resolved optical emission spectroscopy was applied to investigate the variation in the plasma properties in the thruster discharge channel.The plasma species,electron temperature,and electron density were obtained and discussed.Our investigation revealed that there were H_(α),H_(β),H_(γ),H_(ε) atoms,CⅠ,CⅡ,CⅢ,CⅣ,ClⅠ,ClⅡparticles,and a small amount of CH,C_(3),C_(2),H_(2) neutral molecular groups in the plasma.The electron temperature of the discharge channel of the thruster was within 0.6–4.9 e V,and the electron density was within(1.1–3.0)×10^(18)cm^(-3),which shows that the optical emission spectroscopy method is to measure the electron excitation temperature and electron density in heavy particles.But the Langmuir probe method is to measure the temperature and density of free electrons.The use of laser instead of spark plug as the ignition mode significantly changed the plasma distribution in the discharge channel.Unlike the conventional PPT,which has high electron density near the thruster surface,LAPPT showed relatively large electron density at the thruster outlet,which increased the thruster specific impulse.In addition,the change in the ignition mode enabled the electron density in the LA-PPT discharge channel to be higher than that in the conventional PPT.This proves that the ignition mode with laser replacing the spark plug effectively optimised the PPT performance.

Study of the expansion characteristics of a pulsed plasma jet in air

In the background of electrothermal-chemical （ETC） emission,an investigation has been conducted on the characteristics of a freely expanding pulsed plasma jet in air.The evolutionary process of the plasma jet is experimentally investigated using a piezoelectric pressure sensor and a digital high-speed video system.The variation relation in the extended volume,axial displacement and radial displacement of the pulsed plasma jet in atmosphere with time under different discharge voltages and jet breaking pressures is obtained.Based on experiments,a two-dimensional axisymmetric unsteady model is established to analyze the characteristics of the two-phase interface and the variation of flow-field parameters resulting from a pulsed plasma jet into air at a pressure of 1.5-3.5 MPa under three nozzle diameters （3 mm,4 mm and 5 ram,respectively）.The images of the plasma jet reveal a changing shape process,from a quasiellipsoid to a conical head and an elongated cylindrical tail.The axial displacement of the jet is always larger than that along the radial direction.The extended volume reveals a single peak distribution with time.Compared to the experiment,the numerical simulation agrees well with the experimental data.The parameters of the jet field mutate at the nozzle exit with a decrease in the parameter pulse near the nozzle,and become more and more gradual and close to environmental parameters.Increasing the injection pressure and nozzle diameter can increase the parameters of the flow field such as the expansion volume of the pulsed plasma jet,the size of the Mach disk and the pressure.In addition,the turbulent mixing in the expansion process is also enhanced.

Investigation of self-generated magnetic field and dynamics of a pulsed plasma flow

Due to the growing interest in studying the compression and disruption of the plasma filament in magnetic fusion devices and Z-pinches, this work may be important for new developments in the field of controlled thermonuclear fusion. Recently, on a coaxial plasma accelerator, we managed to obtain the relatively long-lived(~300 μs) plasma filaments with its self-magnetic field. This was achieved after modification of the experimental setup by using high-capacitive and lowinductive energy storage capacitor banks, as well as electrical cables with low reactive impedance. Furthermore, we were able to avoid the reverse reflection of the plasma flux from the end of the plasma accelerator by installing a special plasma-absorbing target. Thus, these constructive changes of the experimental setup allowed us to investigate the physical properties of the plasma filament by using the comprehensive diagnostics including Rogowski coil,magnetic probes, and Faraday cup. As a result, such important plasma parameters as density of ions and temperature of electrons in plasma flux, time dependent plasma filament’s azimuthal magnetic field were measured in discharge gap and at a distance of 23.5 cm from the tip of the cathode. In addition, the current oscillograms and Ⅰ–Ⅴ characteristics of the plasma accelerator were obtained. In the experiments, we also observed the charge separation during the acceleration of plasma flow via oscillograms of electron and ion beam currents.

Experimental investigation on the plasma morphology of ablative pulsed plasma thruster with tongue-shaped and flared electrodes

Ablative pulsed plasma thrusters(APPTs)are considered as an attractive propulsion option for station-keeping and drag makeup purposes for mass-and power-limited satellites.In order to understand the physical mechanism of APPTs,high-speed camera and optical emission spectroscopy are utilized to investigate the plasma characteristics including the spatial distribution and composition between the electrodes.The plume images and spectra at different times and positions are experimentally recorded,and the spatial distribution,composition,and trajectory of plasmas can be concluded through analyzing them.With the increase of the distance from the ablation surface,two clusters of plasmas near the anode and cathode meet downstream,and the species and density of plasmas tend to be uniform.

Experimental investigation on the evolution of plasma properties in the discharge channel of a pulsed plasma thruster

Pulsed plasma thrusters(PPTs)are an attractive form of micro-thrusters due to advantages such as their compactness and lightweight design compared to other electric propulsion systems.Experimental investigations on their plasma properties are beneficial in clarifying the complex process of plasma evolution during the micro-second pulse discharge of a PPT.In this work,the multi-dimensional evolutions of the light intensity of the PPT plasma with wavelength,time,and position were identified.The plasma pressure was obtained using an iterative process with composition calculations.The results show that significant ion recombination occurred in the discharge channel since the line intensities of CII,CIII,CIV,and FII decreased and those of CI and FI increased as the plasma moved downstream.At the center of the discharge channel,the electron temperature and electron density were in the order of 10000 K and 1017 cm-3,respectively.These had maximum values of 13750 K and 2.3?×?1017 cm-3 and the maximum temperature occurred during the first half-cycle while the maximum number density was measured during the second half-cycle.The estimated plasma pressure was in the order of 105 Pa and exhibited a maximum value of 2.69?×?105 Pa.

Pulsed plasma arc cladding

A prototype of Pulsed Plasma Arc Cladding system was developed, in which single power source supplies both transferred plasma arc (TPA) and non-transferred plasma arc (N-TPA). Both plasmas work in turn in a high frequency controlled by an IGBT connecting nozzle and workpiece. The working frequency of IGBT ranges from 50 ～ 7 000 Hz, in which the plasmas can work in turn smoothly. Higher than 500 Hz of working frequency is suggested for promotion of cladding quality and protection of IGBT. Drag phenomenon of TPA intensifies as the frequency goes up, which tends to increase the current proportion of TPA and suppress N-TPA. The occupation ratio of IGBT can be regulated from 5% ～ 95%, which balances the power supplies of both plasmas. An occupation ratio higher than 50% gives adequate proportion of arc current for N-TPA to preheat powder.

The ablation characteristics of laser-assisted pulsed plasma thruster with metal propellant

In this study,a laser-assisted pulsed plasma thruster(LA-PPT)with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration.Owing to the unique structure of the thruster,metals can also be used as propellants,and a higher specific impulse is expected.The ablation quality,morphology,and plume distribution of various metals(aluminium alloy,red copper,and carbon steel)with different laser energies were studied experimentally.The ablation morphology and plume distribution of red copper were more uniform,as compared to those of other metals,and the ablation quality was higher,indicating its greater suitability for LA-PPT.The plume generated by nanosecond laser ablation of aluminium alloy expanded faster,which indicated that the response time of the thruster with aluminium alloy as the propellant was shorter.In addition,when the background pressure was 0.005 Pa,an obvious plume splitting phenomenon was observed in the ablation plume of the pulsed laser irradiating aluminium alloy,which may significantly reduce the utilisation rate of the propellant.

Study on the plasma generation characteristics of an induction-triggered coaxial pulsed plasma thruster

At present,spark plugs are used to trigger discharge in pulsed plasma thrusters（PPT）,which are known to be life-limiting components due to plasma corrosion and carbon deposition.A strong electric field could be formed in a cathode triple junction（CTJ） to achieve a trigger function under vacuum conditions.We propose an induction-triggered electrode structure on the basis of the CTJ trigger principle.The induction-triggered electrode structure could increase the electric field strength of the CTJ without changing the voltage between electrodes,contributing to a reduction in the electrode breakdown voltage.Additionally,it can maintain the plasma generation effect when the breakdown voltage is reduced in the discharge experiments.The induction-triggered electrode structure could ensure an effective trigger when the ablation distance of Teflon increases,and the magnetic field produced by the discharge current could further improve the plasma density and propagation velocity.The induction-triggered coaxial PPT we propose has a simplified trigger structure,and it is an effective attempt to optimize the micro-satellite thruster.

A comparative study on the activity of TiO_2 in pulsed plasma under different discharge conditions

In the present study,a combination of pulsed discharge plasma and TiO2（plasma/TiO2）has been developed in order to study the activity of TiO2by varying the discharge conditions of pulsed voltage,discharge mode,air flow rate and solution conductivity.Phenol was used as the chemical probe to characterize the activity of TiO2in a pulsed discharge system.The experimental results showed that the phenol removal efficiency could be improved by about 10%by increasing the applied voltage.The phenol removal efficiency for three discharge modes in the plasma-discharge-alone system was found to be highest in the spark mode,followed by the spark–streamer mode and finally the streamer mode.In the plasma/TiO2system,the highest catalytic effect of TiO2was observed in the spark–streamer discharge mode,which may be attributed to the favorable chemical and physical effects from the spark–streamer discharge mode,such as ultraviolet light,O3,H2O2,pyrolysis,shockwaves and high-energy electrons.Meanwhile,the optimal flow rate and conductivity were 0.05 m^3l^（-1）and 10μS cm^（-1）,respectively.The main phenolic intermediates were hydroquinone,catechol,and p-benzoquinone during the discharge treatment process.A different phenol degradation pathway was observed in the plasma/TiO2system as compared to plasma alone.Analysis of the reaction intermediates demonstrated that p-benzoquinone reduction was selectively catalyzed on the TiO2surface.The effective decomposition of phenol constant（De）increased from 74.11%to 79.16%when TiO2was added,indicating that higher phenol mineralization was achieved in the plasma/TiO2system.

Electrical and aerodynamic characteristics of sliding discharge based on a microsecond pulsed plasma supply

Plasma flow control technology has broad prospects for application.Compared with conventional dielectric barrier discharge plasma actuators(DBD-PA),the sliding discharge plasma actuator(SD-PA)has the advantages of a large discharge area and a deflectable induced jet.To achieve the basic performance requirements of light weight,low cost,and high reliability required for UAV(Unmanned Aerial Vehicle)plasma flight experiments,this work designed a microsecond pulse plasma supply that can be used for sliding discharge plasma actuators.In this study,the topology of the primary circuit of the microsecond pulse supply is determined,the waveform of the output terminal of the microsecond pulse plasma supply is detected using the Simulink simulation platform,and the design of the actuation voltage,the pulse frequency modulation function and the construction of the hardware circuit are achieved.Using electrical diagnosis and flow field analysis,the actuation characteristics and flow characteristics of sliding discharge plasma under microsecond pulse actuation are studied,the optimal electrical actuation parameters and flow field characteristics are described.

Microstructural Evolution and Mechanical Properties of Inconel 625 Alloy during Pulsed Plasma Arc Deposition Process

Pulsed plasma arc deposition （PPAD）, which combines pulsed plasma cladding with rapid prototyping, is a promising technology for manufacturing near net shape components due to its superiority in cost and convenience of processing. In the present research, PPAD was successfully used to fabricate the Ni-based superalloy Inconel 625 components. The microstructures and mechanical properties of deposits were investigated by scanning electron microscopy （SEM）, optical microscopy （OM）, transmission electron microscopy （TEM） with energy dispersive spectrometer （EDS）, microhardness and tensile testers. It was found that the as-deposited structure exhibited homogenous columnar dendrite structure, which grew epitaxially along the deposition direction. Moreover, some intermetallic phases such as Laves phase, minor MC （NbC, TiC） carbides and needle-like δ-Ni3Nb were observed in y-Ni matrix. Precipitation mechanism and distribution characteristics of these intermetallic phases in the as-deposited 625 alloy sample were analyzed. In order to evaluate the mechanical properties of the deposits, microhardness was measured at various location （including transverse plane and longitudinal plane）. The results revealed hardness was in the range of 260- 285 HVo.2. In particular, microhardness at the interface region between two adjacent deposited layers was slightly higher than that at other regions due to highly refined structure and the disperse distribution of Laves particles. Finally, the influence of precipitation phases and fabrication strategies on the tensile properties of the as-deposited samples was investigated. The failure modes of the tensile specimens were analyzed with fractography.

A brief review of alternative propellants and requirements for pulsed plasma thrusters in micropropulsion applications

Technological miniaturization has enabled the development of small satellites weighing as little as 1 kg.Unfortunately,there is still a lack of suitable efficient micropropulsion systems at these scales.The pulsed plasma thruster is a structurally simple form of electric propulsion.This simplicity also makes it ideally suited for miniaturization.Its history can be traced back to applications in satellites that are much larger than micro/nano-satellites.The vast majority of modern pulsed plasma thrusters use solid polytetrafluoroethylene(PTFE)as a propellant.Unfortunately,at lower discharge energy levels such as those necessitated by the power limitations of micro/nano-satellites,PTFE has a tendency to exhibit carbon deposition,which can ultimately lead to thruster failure.In this new era of small satellites,it is important to consider alternative propellants in the miniaturization of pulsed plasma thrusters.This brief review discusses the needs and limitations of small satellites and alternative propellants that may be able to meet these needs.Such propellants may be able to offer advantages such as a longer thruster lifetime,a higher specific impulse,or a higher thrust-topower ratio.This would enable the development of different types of pulsed plasma thrusters that can be tailored towards specific mission requirements.

Treatment of Dye Wastewater by Using a Hybrid Gas/Liquid Pulsed Discharge Plasma Reactor

A hybrid gas/liquid pulsed discharge plasma reactor using a porous ceramic tube is proposed for dye wastewater treatment. High voltage pulsed discharge plasma was generated in the gas phase and simultaneously the plasma channel was permeated through the tiny holes of the ceramic tube into the water phase accompanied by gas bubbles. The porous ceramic tube not only separated the gas phase and liquid phase but also offered an effective plasma spreading channel. The effects of the peak pulse voltage, additive gas varieties, gas bubbling rate, solution conductivity and TiO2 addition were investigated. The results showed that this reactor was effective for dye wastewater treatment. The decoloration efficiency of Acid Orange II was enhanced with an increase in the power supplied. Under the studied conditions, 97% of Acid Orange II in aqueous solution was effectively decolored with additive oxygen gas, which was 51% higher than that with argon gas, and the increasing 02 bubbling rate also benefited the decoloration of dye wastewater. Water conductivity had a small effect on the level of decoloration. Catalysis of TiO2 could be induced by the pulsed discharge plasma and addition of TiO2 aided the decoloration of Acid Orange II.

Electrical Characteristics of Pulsed Corona Discharge Plasmas in Chitosan Solution

Pulsed discharge plasma has exhibited active potential to prepare low molecular weight chitosan. In the present study, the viscosity of ehitosan solution was decreased noticeably after treated with pulsed corona discharge plasma. An experimental investigation on electrical characteristics of pulsed corona discharge plasma in chitosan solution was conducted with a view toward getting insight into discharge process. Factors affecting I-V curve, single pulse injec- tion energy and pulse width were studied. Experimental results showed positive effect of pulsed peak voltage on discharge plasma in chitosan solution. Pulse-forming capacitor greatly influenced the discharge form, and 4 nF was observed as a suitable value for efficiently generating stable discharge plasmas. As the electrode distance was larger than 10 ram, it had slight impact on dis- charge plasma due to the excellent conductive-property of chitosan solution. The injection energy significantly increased with air flow rate, while the pulse width hardly changed as the air flow rate increased from 0.5 m^3/h to 1.0 m^3/h. This study is expected to provide reference for promoting the application of pulsed corona discharge plasma to ehitosan solution treatment.

Regeneration of Acid Orange 7 Exhausted Granular Activated Carbon Using Pulsed Discharge Plasmas

In this paper, a pulsed discharge plasma （PDP） system with a multi-needle-to-plate electrodes geometry was set up to investigate the regeneration of acid orange 7 （AO7） exhausted granular activated carbon （GAC）. Regeneration of GAC was studied under different conditions of peak pulse discharge voltage and water pH, as well as the modification effect of GAC by the pulse discharge process, to figure out the regeneration efficiency and the change of the GAC structure by the PDP treatment. The obtained results showed that there was an appropriate peak pulse voltage and an optimal initial pH value of the solution for GAC regeneration. Analyses of scanning electron microscope （SEM）, Boehm titration, Brunauer-Emmett-Teller （BET）, Horvath-Kawazoe （HK）, and X-ray Diffraction （XRD） showed that there were more mesopore and macropore in the regenerated GAC and the structure turned smoother with the increase of discharge voltage; the amount of acidic functional groups on the GAC surface increased while the amount of basic functional groups decreased after the regeneration process. From the result of the XRD analysis, there were no new substances produced on the GAC after PDP treatment.