Guangsheng Sun

Experimental investigation of surface flashover in vacuum using nanosecond pulses

Based on a Marx generator and a coaxial pulse forming line, an experimental investigation of surface flashover characteristics in vacuum is conducted by using nanosecond pulses of 10 ns rise time and 30 ns full width at half maximum (FWHM). Insulator dielectrics chosen for this investigation are Teflon, PMMA and Nylon. The tested factors include gas pressure, cone angle of conical frustum, diameter and length of cylindrical insulator, material and shape of electrode, and contact style between insulator and electrodes. The effects of these parameters on the surface flashover characteristics are described and analyzed in this paper. In addition, the character of flashover time lag in the nanosecond range, and surface flashover theory in vacuum charged by nanosecond pulses are also discussed.

Breakdown Phenomena in Nitrogen Due to Repetitive Nanosecond-pulses

Nanosecond-pulse breakdown indicates special characteristics depending on the pulse rise-time and duration. Based on a repetitive nanosecond-pulse generator, breakdown phenomena of parallel-plane gaps in nitrogen were investigated with single pulse and repetitive bursts under different gap conditions. The relationships between applied voltage, pulse repetition frequency, breakdown time lag, repetitive pulse stress time and the number of applied pulses are presented. The curves regarding E-field strength, breakdown time lag and gas pressure are also obtained. The experimental results show that breakdown characteristics with repetitive nanosecond-pulses are different from that with single pulse. Repetitive nanosecond-pulse breakdown is concerned with the accumulation effect that is attributed to residual ions and metastable species survived from previous pulses. In addition, a modified empirical formula about E-field strength, breakdown time lag and gas density is given for the breakdown data.

Repetitive Nanosecond-Pulse Breakdown in Tip–Plane Gaps of Air

Repetitive pulsed power is becoming an important area of high-power technology. Dielectric failure data concerning electrical insulation play a basic role, but breakdown has been inadequately studied for the repetitive nanosecond-pulse conditions. This paper is concerned with the breakdown characteristics of tip-plane gas gaps under repetitive burst conditions at variant repetition rates (rep-rates) and diverse gap distances. The relationship among applied voltage, breakdown time lag, number of applied pulses to breakdown, repetitive pulse stress time, and rep-rates is presented. The experimental results presented show that breakdown polarity dependence is not distinct. The data also indicate that significant concentrations of excited particles and residual charges would be formed during the consecutive nanosecond pulses and would present a memory effect that affects the development of gas breakdown. In addition, the detachment of negative ions, cathode collision of positive ions, and deexcitation of metastable species can provide the source of avalanche-initiating electrons

Experimental Study of Similarity Laws in Gas Breakdown with Repetitive Nanosecond Pulses

It has been known that breakdown voltage has a functional dependence on the product of gas pressure and gap distance. Furthermore, the product of gas pressure and breakdown time lag is related to electric field divided by gas pressure. In this paper, both these similarity laws were investigated in repetitive nanosecond-pulse breakdown of dry air and nitrogen. The experimental results indicated that breakdown voltage was close to DC value when repetition rate was up to 1 kHz, and the product of gas pressure and breakdown time lag is unambiguously associated with E-field strength divided by gas pressure under repetitive nanosecond-pulse conditions.

Experimental research on microdischarge characteristics of DBD

Summary form only given. Dielectric barrier discharge (DBD) consists of filamentary micro-discharges under nonequilibrium, atmospheric pressure plasma condition. The size and spatial distribution of microdischarge spots are of great importance to surface processing. In our experiment, water electrodes were used for visualization. Charge-coupled device and highspeed photography technology were used to capture the quasi-stationary and transient image of microdischarge spots. The microdischarge current and voltage waveforms were recorded by digital oscilloscope. A special circuit synchronized both optical device and oscilloscope. The experiments were done under different voltages, frequencies, gaps and dielectrics with nitrogen mixture flowing through the discharge chamber. By comparisons of visualization images and electrical waveforms, some interesting conclusions were drawn.

Research on power supply used in dielectric barrier discharge

Summary form only given. A 20 kW, 50 kV power supply with the frequency ranging from 50 Hz to 50 kHz used in dielectric barrier discharge (DBD) is introduced in this paper. The power supply consisted of commuting module, high frequency inverter, high frequency and high voltage transformer and feedback control circuit. More considerations were put on electrical efficiency to increase work frequency. An advanced quasi-resonant zero current switching technology had been used in this device. The inductor of high voltage transformer was designed to construct the quasi-resonant circuit with a resonant capacitor to reduce the transformers energy dissipation that would be serious as the frequency rises. The inverter was mainly constituted of four IGBTs and four crowbars. Each IGBT would be spontaneously closed when the current was zero and was opened by control on its grid. By utilizing of quick reverse diodes, the inverter absorbed less energy than traditional IGBT inverter. By those means the energy dissipated in switch and transformer was greatly reduced and the work frequency reached 50 kHz. The power supply for DBD also had advantages of low cost, little volume and convenient control. The power supply had been used in DBD research and worked stably.

Study of dielectric barrier discharge under atmospheric condition

Summary form only given, as follows. The dielectric barrier discharge (DBD) possesses potential advantages in surface processing and plasma chemistry under atmospheric condition. The most common case of DBD shows a filamentary form between electrodes. To obtain a homogeneous i.e. non-filamentary DBD, so called atmospheric pressure glow discharge (APGD), is the point of special interest in achieving better results of surface treatment. In this paper, in order to obtain the homogeneous form investigation on DBD is carried out with different voltages, frequencies and dielectrics. Optical properties and power consumption measurements were made in different gas mixtures with and without the presence of gas flow through the discharge chamber.