查看更多>>摘要：Coaxial plasma guns are a type of plasma source that produces plasma which propagates radially and axially controlled by the shape of the ground electrode,which has attracted much interest in several applications.In this work,a 120° opening angle of CPG nozzle is used as a plasma gun configuration that operates at the energy of 150 J.The ionization of polyethylene insulator between the electrodes of the gun produces a cloud of hydrogen and carbon plasma.The triple Langmuir probe and Faraday cup are used to measure plasma density and plasma temperature.These methods are used to measure the on-axis and off-axis plasma divergence of the coaxial plasma gun.The peak values of ion densities measured at a distance of 25 mm on-axis from the plasma gun are(1.6±0.5)×1019 m-3 and(2.8±0.6)×1019 m-3 for hydrogen and carbon plasma respectively and the peak temperature is 3.02±0.5 eV.The mean propagation velocity of plasma is calculated using the transit times of plasma at different distances from the plasma gun and is found to be 4.54±0.25 cm/μs and 1.81±0.18 cm/μs for hydrogen and carbon plasma respectively.The Debye radius is obtained from the measured experimental data that satisfies the thin sheath approximation.The shot-to-shot stability of plasma parameters facilitates the use of plasma guns in laboratory experiments.These types of plasma sources can be used in many applications like plasma opening switches,plasma devices,and as plasma sources.
查看更多>>摘要：The discharge morphology of pulsed dielectric barrier discharge(PDBD)plays important roles in its applications.Here,we systematically investigated the effects of the voltage amplitude,discharge gap,and O2 content on the PDBD morphology,and revealed the possible underlying mechanism of the U-shaped formation.First,the morphological evolution under different conditions was recorded.A unique U-shaped region appears in the middle edge region when the gap is larger than 2 mm,while the entire discharge region remains columnar under a 2 mm gap in He PDBD.The width of the discharge and the U-shaped region increase with the increase in voltage,and decrease with the increase of the gap and O2 content.To explain this phenomenon,a two-dimensional symmetric model was developed to simulate the spatiotemporal evolution of different species and calculate the electric thrust.The discharge morphology evolution directly corresponds to the excited-state atomic reduction process.The electric thrust on the charged particles mainly determines the reaction region and strongly influences the U-shaped formation.When the gap is less than 2 mm,the electric thrust is homogeneous throughout the entire region,resulting in a columnar shape.However,when the gap is larger than 2 mm or O2 is added,the electric thrust in the edge region becomes greater than that in the middle,leading to the U-shaped formation.Furthermore,in He PDBD,the charged particles generating electric thrust are mainly electrons and helium ions,while in He/O2 PDBD those that generate electric thrust at the outer edge of the electrode surface are mainly various oxygen-containing ions.
查看更多>>摘要：Streamers represent an important stage in the initiation of gap discharge.In this work,we used an eight-frame intensified charge-coupled device camera to capture the streamer development process when a lightning impulse voltage of 95％-100％U50％was applied in a 3 m rod-plate gap and the streamer velocity was analyzed.Analysis of the observations shows that streamer velocity can be defined by three stages:rapid velocity decline(stage 1),rapid velocity rise(stage 2)and slow velocity decline(stage 3).The effects of electrode shape,applied voltage and gap breakdown or withstanding on streamer velocity were analyzed.The electrode with a larger radius of curvature will result in a higher initial velocity,and a higher voltage amplitude will cause the streamer to propagate faster at stage 3.Gap withstanding or breakdown has no obvious effect on streamer velocity.In addition,the experimental results are compared with previous results and the statistical characteristics of the primary streamer discharge are discussed.
查看更多>>摘要：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.
查看更多>>摘要：It is difficult to determine the discharge stages in a fixed time of repetitive discharge underwater due to the arc formation process being susceptible to external environmental influences.This paper proposes a novel underwater discharge stage identification method based on the Strong Tracking Filter(STF)and impedance change characteristics.The time-varying equivalent circuit model of the discharge underwater is established based on the plasma theory analysis of the impedance change characteristics and mechanism of the discharge process.The STF is used to reduce the randomness of the impedance of repeated discharges underwater,and then the universal identification resistance data is obtained.Based on the resistance variation characteristics of the discriminating resistance of the pre-breakdown,main,and oscillatory discharge stages,the threshold values for determining the discharge stage are obtained.These include the threshold values for the resistance variation rate(K)and the moment(t).Experimental and error analysis results demonstrate the efficacy of this innovative method in discharge stage determination,with a maximum mean square deviation of Scr less than 1.761.
查看更多>>摘要：Field emission electric propulsion(FEEP)thrusters possess excellent characteristics,such as high specific impulse,low power requirements,compact size and precise pointing capabilities,making them ideal propulsion devices for micro-nano satellites.However,the detection of certain aspects,such as the evolution process of the liquid cone and the physical quantities at the cone apex,proves challenging due to the minute size of the needle tip and the vacuum environment in which they operate.Consequently,this paper introduces a computational fluid dynamics(CFD)model to gain insight into the formation process of the liquid cone on the tip apex of indium FEEP.The CFD model is based on electrohydrodynamic(EHD)equations and the volume of fluid(VOF)method.The entire cone formation process can be divided into three stages,and the time-dependent characteristics of the physical quantities at the cone apex are investigated.The influences of film thickness,apex radius size and applied voltage are compared.The results indicate a gradual increase in the values of electrostatic stress and surface tension stress at the cone apex over an initial period,followed by a rapid escalation within a short duration.Apex configurations featuring a small radius,thick film and high voltage exhibit a propensity for liquid cone formation,and the cone growth time decreases as the film thickness increases.Moreover,some unstable behavior is observed during the cone formation process.
查看更多>>摘要：Electron density in fusion plasma is usually diagnosed using laser-aided interferometers.The phase difference signal obtained after phase demodulation is wrapped,which is also called a fringe jump.A method has been developed to unwrap the phase difference signal in real time using FPGA,specifically designed to handle fringe jumps in the hydrogen cyanide(HCN)laser interferometer on the EAST superconducting tokamak.This method is designed for a phase demodulator using the fast Fourier transform(FFT)method at the front end.The method is better adapted for hardware implementation compared to complex mathematical analysis algorithms,such as field programmable gate array(FPGA).It has been applied to process the phase measurement results of the HCN laser interferometer on EAST in real time.Electron density results show good confidence in the fringe jump unwrapping method.Further possible application in other laser interferometers,such as the POlarimeter-INTerferometer(POINT)system on EAST tokamak is also discussed.
查看更多>>摘要：A magnetic field produced by a current flowing through the plasma grid(PG)is one of the solutions to reduce the collisional loss of negative ions in a negative ion source,which reduces the electron temperature in front of the PG.However,the magnetic field diffused into the driver has some influence on the plasma outflowing.In order to investigate the effect of changing this magnetic field on the outflowing of plasma from the driver,a circular ring(absorber)of high permeability iron has been introduced at the driver exit,which can reduce the magnetic field around it and improve plasma outflowing.With the application of the absorber,the electron density is increased by about 35％,and the extraction current measured from the extraction grid is increased from 1.02 A to 1.29 A.The results of the extraction experiment with cesium injection show that both the extraction grid(EG)current and H-current are increased when the absorber is introduced.
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