Jiaqi Yan

A platform for exploding wires in different media

A platform SWE-2 used for single wire explosion experiments has been designed, established, and commissioned. This paper describes the design and initial experiments of SWE-2. In summary, two pulsed current sources based on pulse capacitors and spark gaps are adopted to drive sub-microsecond and microsecond time scale wire explosions in a gaseous/liquid medium, respectively. In the initial experiments, a single copper wire was exploded in air, helium, and argon with a 0.1-0.3 MPa ambient pressure as well as tap water with a 283-323 K temperature, 184-11 000 μS/cm conductivity, or 0.1-0.9 MPa hydrostatic pressure. In addition, the diagnostic system is introduced in detail. Energy deposition, optical emission, and shock wave characteristics are briefly discussed based on experimental results. The platform was demonstrated to operate successfully with a single wire load. These results provide the potential for further applications of this platform, such as plasma-matter interactions, shock wave effects, and reservoir simulations.

Relaxation processes and conduction mechanism of epoxy resin filled with graphene oxide

In this work, mono-layer and multi-layer graphene oxide were used as fillers to be mixed with epoxy resin, where water solution, ultrasonication and magnetic stirring were used to achieve an optimal dispersion. The dispersion state of graphene oxide was observed by both scanning electron microscope (short as SEM) and transmission electron microscope (short as TEM). Different relaxation processes were studied over a wide range of temperature and frequency by an impendence analyzer. The observed nonlinear relationship between the electrical conductivity and the applied electric field strength potentially can be applied for field grading. This was verified by electric field simulations. Based on the experimental results, the nature of the interface interaction between epoxy resin and graphene oxide, the relaxation processes and the conduction mechanism of the studied epoxy-based nanocomposites were discussed.

An Investigation of Discharge Characteristics of an Electrothermal Pulsed Plasma Thruster

The capillary-based pulsed plasma thruster (PPT) has high-energy transfer efficiency, which provides potential to improve traditional PPT performance. In this paper, the discharge characteristics of a capillary-based PPT have been investigated. First, the typical process of voltage and current waveform is recognized. It is featured with a fast voltage drop (~25 ns) and a consequent damped sine wave oscillation discharge. Then based on the circuit analysis, the equivalent plasma resistance has been calculated. The current waveform is well fit with a linearly increasing resistance model. The influence of charging voltage has also been studied. The deposited energy increases while the transfer efficiency decreases with the increasing applied voltage. The cavity dimension has effects on the equivalent circuit parameters. The results show that longer cavity and smaller diameter lead to more deposited energy and higher transfer efficiency. The influence of voltage and capillary dimension on the mass shot characteristic has been discussed. Finally, the estimated impulse bit has been calculated and the impulse bit characteristics have been discussed. These results can contribute to the further optimization of PPT.

A novel trigger for pseudospark switch with high repetition rate, low jitter, and compact structure

This paper presents the design and development of a trigger with a high repetition rate, low jitter, and compact structure for the pseudospark switch (PSS), which includes an improved Marx generator based on avalanche transistors and a corona-plasma trigger unit. The generator adopted a novel 3 × 12-stage Marx circuit based on avalanche transistors in which the failure rate of transistors in the first and second stages was significantly reduced by connecting the parallel capacitors compared to the previous similar generator. The reason for the improved performance was also discussed. The main parameters of output pulses were an amplitude of -7 kV, rise time of 6 ns, jitter of 0.2 ns, and repetition rate of 2 kHz. The corona-plasma trigger unit adopted BaTiO3 ceramics with high εr as the dielectric and was arranged in the hollow cathode of the PSS. The experiments of triggering a PSS prototype were conducted. The influence of anode voltage and pressure on the trigger delay and jitter was studied, and the minimum trigger jitter achieved <1 ns. This trigger worked for 107 shots at the repetition rate of 2 kHz continuously without obvious performance degradation and any failure of the generator. The main advantage of this trigger is the simultaneous combination of the high repetition rate, low jitter, long lifetime, and great simplicity in a compact structure.

Development and analysis of a novel printed circuit board electrostatic comb system for micro-newton thrust stand calibration

An electrostatic calibration technique is highly flexible in producing a wide range of force and it is widely applied for nano-newton to micro-newton thrust stand calibration. This paper proposes a novel method for electrostatic comb implementation and related experiments have been carried out. Based on the printed circuit board and commercial fins, the comb can be realized flexibly with the output force conveniently extended. The force generated by this kind of comb is theoretically analyzed. Different from the traditional comb structure, the conductive area of the comb fixed plate is minimized to improve the force consistency over engagement. The influence of fin length, fin number, applied voltage, and engagement on the output force has been studied experimentally. The final comb system is capable of producing steady force in the range 13-5040 μN with the relative error within 5%. With a high voltage pulse generator, this system could produce calibration impulse bit in the range 1-1000 μN s for which the lowest level can be far more extended to the nanonewton range with a shorter pulse width, a lower voltage, and a reduced number of fins. Moreover, the calibrator has a rather flat force-engagement characteristic when the engagement is in the range of 6 mm-16 mm, while the variation of electrostatic force is within 5%. This calibrator has a wide output range and great consistency, and it is beneficial for the thrust stand calibration.

Experimental study on the discharge ignition in a capillary discharge based pulsed plasma thruster

Low power capillary discharge based pulsed plasma thrusters (CDPPTs) are electrothermally dominated thrusters and they have aroused renewed interest in the investigation and enhancement of the basic performance for the application of micro/nano satellites recently. Research on the ignition mechanism of a CDPPT has been conducted to provide insight into the optimization of the structure design and promotion of the lifetime performance. It has been found that the electrical parameters, the geometry parameters, and the cumulative effect of discharge jointly determine the discharge ignition characteristics. A single ignition process is divided into the breakdown of igniter and the development of the main discharge, while the results show that the jitter of the ignition delay time is mainly introduced from the former. Shorter ignition delay time and lower jitter can be obtained with a higher ignition energy and main charging voltage or a shorter and narrower cavity, which is positively correlated to the electric field distribution along the propellant surface. Moreover, with long duration experiments, it reveals that the surface deposits and morphology of propellant and igniter are the dominant factors that cause the dispersity of the ignition effect and main discharge characteristics.Low power capillary discharge based pulsed plasma thrusters (CDPPTs) are electrothermally dominated thrusters and they have aroused renewed interest in the investigation and enhancement of the basic performance for the application of micro/nano satellites recently. Research on the ignition mechanism of a CDPPT has been conducted to provide insight into the optimization of the structure design and promotion of the lifetime performance. It has been found that the electrical parameters, the geometry parameters, and the cumulative effect of discharge jointly determine the discharge ignition characteristics. A single ignition process is divided into the breakdown of igniter and the development of the main discharge, while the results show that the jitter of the ignition delay time is mainly introduced from the former. Shorter ignition delay time and lower jitter can be obtained with a higher ignition energy and main charging voltage or a shorter and narrower cavity, which is positively correlated to the electr...

The investigation and improvement of the lifetime of high voltage ceramic capacitor under repetitive frequency operation

The lifetime tests for High Voltage Ceramic Capacitors (HVCC) were investigated under repetitive frequency operation at 25 Hz and three kinds of failure modes were summarized. The significant innovation of this paper is testing HVCC, made in the laboratory, under repetitive pulses and proposing several effective improvement methods. The results show that the lifetime of HVCC meets inverse power-law with the applied voltage and the voltage acceleration factor is about 5.8. Failure modes of HVCC are inner breakdown of ceramic dielectric, interface breakdown of ceramic-epoxy and abscission of brass terminals. The inner breakdown is in connection with abrupt destructive discharge under much higher stress while the interface breakdown is related to interface delamination and development of electrical trees in relatively low strength. The third failure mode is always caused by high current density. Based on the failure modes, several methods were taken to improve the performance of HVCC, which included coating semiconductor at the edge of silver layers, adding coupling agent to ceramic-epoxy interface and improving the structure of brass terminals. The lifetime of HVCC under repetitive frequency operation has been extended greatly from 103 shots to more than 105 shots after the investigation and improvement.

The diffusion effect of transverse magnetic field on filamentary atmospheric pressure glow discharge sustained by a resonant power supply

Summary form only given. In our previous study, stable and long-interelectrode gap and large-volume atmospheric pressure glow discharge (APGD) in ambient air has been obtained by using a resonant power supply which can successfully and effectively restrict the development of glow to arc transition. However, the APGD is centimeter-level in the length but only several millimeters in diameter, the energy in the discharge channel is very concentrated, which does not benefit industrial applications. The purpose of this study is to make the plasma channel of the stable but filamentary APGD more diffusive by using a transverse magnetic field. In experiment, the transverse magnetic field which was produced by using the dc power supply electromagnet was perpendicular to the plasma channel. The resonant frequency of discharge power supply can adjust from 10 kHz to 60 kHz. By keeping the distance of interelectrode gap, and input voltage amplitude and frequency of resonant power supply constant, with the increase of the current of electromagnet, the discharge channel did not change in the inceptive certain range, which showed that the diffusion effect was not apparent when the magnetic field intensity was weak. When the current of electromagnet increased to a certain value and the transverse magnetic field was strong enough, the diameter of discharge channel gradually increased and the bright area, which was focused near the channel center before, becomed more uniform. Therefore, the diffusion effect of transverse magnetic field on filamentary APGD obtained by resonant power supply presented to be very effective. When the current of the electromagnet was fixed to a value which was efficient enough to diffuse the discharge channel apparently, then the resonant frequency was adjusted from 10kHz to 60 kHz. With the increase of the resonant frequency, the plasma channel diffuses obviously. Accordingly, a transverse magnetic field can enhance the diffusion effect of resonant frequency on plasma channel. It is very meaningful to study how to obtain stable and long-interelectrode gap and largevolume and uniform APGD by matching up the transverse magnetic and resonant power supply.

The influence of air pressure on glow discharge in a pin-to-plate gap sustained by a resonant power supply

Summary form only given. Different from glow discharge (GD) in vacuum or at low pressure environment, it is difficult to obtain stable and uniform GD at high pressure, especially atmospheric pressure, because the GD easily transforms to arc discharge. In our previous research, stable filamentary APGD between pin-to-plate electrodes has been successfully obtained by using a resonant power supply to limit the peak value of discharge current through a series-wound resonance principle1. In order to find out the influence of different pressure on the filamentary glow discharge, filamentary APGD between 15 mm pin-to-plate interelectrode gap at respectively 0.02 MPa, 0.04 MPa to 0.06 MPa, 0.08 MPa, 0.1 MPa air pressure was studied.By comparing with discharge photos and data of discharge voltage and current, changes of extension length of discharge coverage on tungsten pin-electrode surface, the diameter of plasma channel, the average discharge current, the average discharge voltage and the average discharge power under different pressure were found. With the increase of air pressure, electrode coverage area was significantly reduced, and discharge current was nearly constant, and average discharge voltage and average discharge power and channel significantly increased. It was interesting that plasma channel diameter decreased in the beginning but increased at 0.08 MPa and 0.( MPa air pressure. When the air pressure changed from 0.02 MPa to 0.06 MPa, the rising of the pressure led the decrease of the charged particles mean free path and the ions in the plasma channel spacing was compressed, it presented that the channel diameter decreased. When pressure changed from 0.06 MPa to 0.( MPa, while the ions spacing was compressed, but the increase of the discharge power seemed to be the main influence factor, which means that the increase of the power generates more residual charged particles and excited particles in the channel, the diffusion of these residual charged particles and excited particles is helpful to form a large uniform glow discharge.

The diffusion effect of input voltage on filamentary atmospheric pressure glow discharge sustained by a resonant power supply

Summary form only given. Atmospheric pressure glow discharge (APGD) has attracted more and more attentions of the researchers in the world, because its typical atmospheric pressure using environment offers a low cost and chamber-free route for the applications in numerous industrial areas. It is well known that APGD in air is easy to transform to arc discharge. In our previous research, we have successfully obtained the stable APGD in air by using of resonant power supply. However, the discharge form is a narrow and filamentary APGD plasma channel1. In this work, the effect of increase of input voltage of resonant power supply on the diffusion of the filamentary APGD plasma channel was studied. Experiment was done at atmospheric pressure, with resonant power supply working at frequency of 5 kHz and the 8 mm brass pin-plate interelectode gap. The current waveform presented current pulse phenomenon, when the input voltage was ,0V because there were only a few charged particles in the interelectode gap so that insulation of air gap recovered quickly according to the characteristics of resonant power supply. When the input voltage reached 50V or the value more than 50V, there were plenty of charged particles in the interelectode gap, air gap kept to be conducting state after the air breakdown, so there was no obvious current pulse. The area of discharge point on the surface of the brass-pin-electrode gradually increased with the increase of input voltage. Moreover, the thickness of plasma channel halo, light intensity and plasma channel diameter also increased. The phnomenons could be explained by that charged particles and excited particles in the channel were increased with the increase input voltage and the 45 kHz ac frequency of resonant power supply is helpful to the diffusion of the charged particles and excited particles in the discharge channel2. Therefore, with the increase of input voltage of resonant power supply, it is significantly found that the diameter of the plasma channel of the filamentary APGD increases.