钪酸盐阴极电子枪双短脉冲发射实验研究

本工作研究在ns量级双脉冲高压下钪酸盐阴极电子枪电流发射。实验中采用Blumlein线形成ns量级脉冲高压作为电子枪馈入高压,脉冲宽度约为80ns,双脉冲间隔约为300ns。实验结果表明:在消除了空间高频干扰后,法拉第筒测量到的电子枪发射电流脉冲形状与馈入的ns量级双脉冲高压形状非常吻合。由此验证了钪酸盐阴极电子枪对ns级脉冲高压发射响应能力能满足双短脉冲高压工作状态要求,可以作为ns量级多脉冲电子束注入器。     

Dynamics of plasma bullets by nanosecond pulsed micro-hollow cathode discharge within air

In this paper, the air plasma jet produced by micro-hollow cathode discharge(MHCD) is investigated. The discharge is powered by a positive nanosecond pulse high voltage supply. The waveforms of the discharge, the images of the jet, the evolution of the plasma bullet and the reactive species are obtained to analyze the characteristics of the MHCD plasma jet. It is found that the length of the plasma jet is almost proportional to the air flow rate of 2–6 slm. Two plasma bullets appear one after another during a single period of the voltage waveform, and both of the two plasma bullets are formed during the positive pulse voltage off. The propagation velocity of the two plasma bullets is on the order of several hundred m/s, which is approximate to that of the air flow. These results indicate that the gas flow has an important influence on the formation of this MHCD plasma jet.     

Spectroscopic study of bipolar nanosecond pulse gas-liquid discharge in atmospheric argon

Atmospheric gas-liquid discharge with argon as a working gas is presented by employed nanosecond pulse power. The discharge is presented in a glow-like mode. The discharge powers are determined to be less than 1 W, and remains almost constant when the discharge duration time increases. Bountiful active species are determined by capturing optical emission spectra,and their main generation processes are also discussed. The plasma gas temperature is calculated as 350 K by comparing the experimental spectra and the simulated ones of N_2(C~3Ⅱ_g→B~3Ⅱ_g, Δv =-2). The time resolved vibrational and rotational temperature is researched to present the stability of discharge when pulse voltage and discharge duration vary.The electron density is determined to be 10~(16) cm~(-3) according to the Stark broadening effect of the H_α line.     

Simulations and Measurement of Electron Energy and Effective Electron Temperature of Nanosecond Pulsed Argon Plasma

The behavior of argon plasma driven by nanosecond pulsed plasma in a low-pressure plasma reactor is investigated using a global model, and the results are compared with the experimental measurements. The time evolution of plasma density and the electron energy probability function are calculated by solving the energy balance and Boltzmann equations. During and shortly after the discharge pulse, the electron energy probability function can be represented by a bi-Maxwellian distribution, indicating two energy groups of electrons. According to the effective electron temperature calculation, we find that there are more high-energy electrons that play an important role in the excitation and ionization processes than low-energy electrons. The effective electron temperature is also measured via optical emission spectroscopy to evaluate the simulation model. In the comparison, the simulation results are found to be in agreement with the measure- ments. Furthermore, variations of the effective electron temperature are presented versus other discharge parameters, such as pulse width time, pulse rise time and gas pressure.     

Ir—Ce合金阴极及其应用研究

重点研究了粉末冶金法制备Ｉｒ－Ｃｅ（铱－铈）合金阴极过程中压制压力和烧结温度对发射性能的影响，建立起了一套稳定的制备工艺。试验得到Ｉｒ－Ｃｅ掺Ｗ阴极在１７５３Ｋ时的发射电流密度达１２．４Ａ／ｃｍ２，电流密度保持为１．７Ａ／ｃｍ２，发射试验稳定达１５０ｈ。从机理上验证了它是一种高温大发射电流的发射体。试验还表明Ｉｒ－Ｃｅ阴极具有良好的抗中毒能力。作为应用研究，测量了该阴极在热阴极微波电子枪中的发射性能，微波腔场强约１０ＭＶ／ｍ，工作温度１９１３Ｋ，零场发射电流密度为１０Ａ／ｃｍ２，最大发射电流密度达２１Ａ／ｃｍ２，在２０２０Ｋ时计算零场发射电流密度可达４２Ａ／ｃｍ２。     

Experimental investigations of enhanced glow based on a pulsed hollow-cathode discharge

In this work, the pulsed hollow cathode discharges at low pressure argon with an axial magnetic field were studied. The results indicate that the pulsed discharge is operated in an enhanced glow(EG) mode. Under the same conditions, the discharge current of the pulsed discharge is two or three orders higher than that of the direct current discharge. The spatial and temporal evolution of the light emission shows that, the current fluctuation at the rising edge of the pulse plays an important role for the EG discharge of pulsed hollow cathode, which forms a high-density, highcurrent and long-distance plasma column outside the cavity.     

Research on Nanosecond Pulse Corona Discharge Attenuation

A line-to-plate reactor was set-up in the experimental study on the application of nanosecond pulsed corona discharge plasma technology in environmental pollution control. Investigation on the attenuation and distortion of the amplitude of the pulse wave front and the discharge image as well as the waveform along the corona wire was conducted. The results show that the wave front decreases sharply during the corona discharge along the corona wire. The higher the amplitude of the applied pulse is, the more the amplitude of the wave front decreased. The wave attenuation responds in a lower corona discharge inversely. To get a higher efficiency of the line-to-plate reactor a sharp attenuation of the corona has to be considered in practical design.     

Research on Nanosecond Pulse Corona Discharge with Cross Magnetic Field Applied

An application of magnetic field to the nanosecond pulse corona discharge is investigated. A cylinder reactor with different corona electrodes is set up for experimental study. A magnetic field with its direction perpendicular to the corona discharge is applied. Different discharge images are taken under single nanosecond pulse with a high sensitive UV-visible light imagine recorder. Experimental results show that with a cross magnetic field the nanosecond corona discharge both generates paths and develops homogeneously in space more than that without the magnetic field. The results may lead to a possibility to apply a cross magnetic field on nanosecond pulse corona discharge for getting higher desulfurization efficiency.     

Investigation on discharge characteristics of a coaxial dielectric barrier discharge reactor driven by AC and ns power sources

A coaxial dielectric barrier discharge(DBD) reactor with double layer dielectric barriers has been developed for exhaust gas treatment and excited either by AC power or nanosecond(ns)pulse to generate atmospheric pressure plasma. The comparative study on the discharge characteristics of the discharge uniformity, power deposition, energy efficiency, and operation temperature between AC and ns pulsed coaxial DBD is carried out in terms of optical and electrical characteristics and operation temperature for optimizing the coaxial DBD reactor performance. The voltages across the air gap and dielectric layer and the conduction and displacement currents are extracted from the applied voltages and measured currents of AC and ns pulsed coaxial DBDs for the calculation of the power depositions and energy efficiencies through an equivalent electrical model. The discharge uniformity and operating temperature of the coaxial DBD reactor are monitored and analyzed by optical images and infrared camera. A heat conduction model is used to calculate the temperature of the internal quartz tube. It is found that the ns pulsed coaxial DBD has a much higher instantaneous power deposition in plasma, a lower total power consumption, and a higher energy efficiency compared with that excited by AC power and is more homogeneous and stable. The temperature of the outside wall of the AC and ns pulse excited coaxial DBD reaches 158 ℃ and 64.3 ℃ after 900 s operation, respectively.The experimental results on the comparison of the discharge characteristics of coaxial DBDs excited by different powers are significant for understanding of the mechanism of DBDs,reducing energy loss, and optimizing the performance of coaxial DBD in industrial applications.     

Study of Preionization XeCl Excimer Laser and Ultraviolet Spectrum Characteristic

The pumped system of the XeCl excimer laser has been designed and applied to analyze UV XeC1 laser spectroscopy characteristics. Under the proportion of mixed gas of HCI：Xe：He = 0.1%： 1% ：98.9%, excimer laser light was generated by stable glow discharge process. The laser spectrum, pulse duration, and laser power properties were obtained. The result shows that this XeCI excimer laser exhibits unique spectral properties, with two peaks between 307.7 nm and 308.5 nm at high pressure with a pumped power of 1.3959 MW/cm^3. The transition relies on the strongest transitions between B-X and C-X. The maximum-intensity transition of spectroscopy is B to X energy levels. The laser parameters are as follows： minimal duration of 15.42 ns, a repetition rate from 0.5 Hz to 5 Hz, single pulse stable power of 400 m J, and beam divergence angle of 3 mrad. The laser can be used to study UV spectroscopy, laser ablation sampling and sputtered pinnate form.     

Effects of O2 addition on the plasma uniformity and reactivity of Ar DBD excited by ns pulsed and AC power supplies

Dielectric barrier discharges (DBDs) have been widely used in ozone synthesis, materials surface treatment, and plasma medicine for their advantages of uniform discharge and high plasma-chemical reactivity. To improve the reactivity of DBDs, in this work, the O₂ is added into Ar nanosecond (ns) pulsed and AC DBDs. The uniformity and discharge characteristics of Ar ns pulsed and AC DBDs with different O₂ contents are investigated with optical and electrical diagnosis methods. The DBD uniformity is quantitatively analyzed by gray value standard deviation method. The electrical parameters are extracted from voltage and current waveforms separation to characterize the discharge processes and calculate electron density n_e. The optical emission spectroscopy is measured to show the plasma reactivity and calculate the trend of electron temperature T_e with the ratio of two emission lines. It is found that the ns pulsed DBD has a much better uniformity than AC DBD for the fast rising and falling time. With the addition of O₂, the uniformity of ns pulsed DBD gets worse for the space electric field distortion by O₂⁻, which promotes the filamentary formation. While, in AC DBD, the added O₂ can reduce the intensity of filaments, which enhances the discharge uniformity. The ns pulsed DBD has a much higher instantaneous power and energy efficiency than AC DBD. The ratio of Ar emission intensities indicates that the T_e drops quickly with the addition of O₂ both ns pulsed and AC DBDs and the ns pulsed DBD has an obvious higher T_e and n_e than AC DBD. The results are helpful for the realization of the reactive and uniform low temperature plasma sources.     

Influence of high-voltage pulse parameters on the propagation of a plasma synthetic jet

In this work, a typical pin-to-pin plasma synthetic jet in static air is excited by a pulsed DC power supply. The influences of the pulse rising time, the amplitude and the repetition frequency of the pulse voltage on the jet flow have been investigated. First, using a high-speed Schlieren imaging technique, the induced shock waves and the fast jet flow generated by the plasma synthetic jet are characterized. With a deposited energy of 44 mJ per pulse, the velocity of the shock wave and the maximum velocity of the jet flow reach 320 m s⁻¹ and 100 m s⁻¹, respectively. Second, when the applied voltage increases from 12.8 kV to 16 kV, the maximum jet velocity increases from 66 m s⁻¹ to 93 m s⁻¹. On the other hand, as the pulse rising time varies from 50 ns to 500 ns, or the pulse repetition frequency increases from 5 Hz to 40 Hz, the jet velocity induced by the plasma synthetic jet is weakly dependent. In addition, a comparative study of the plasma synthetic jets using three commercial pulsed power supplies (XJ-15, NPG- 18, and PG-30) is implemented. It reveals that the maximum jet velocity of 120 m s⁻¹ is obtained in the case of PG-30, with the longest pulse rising time and the lowest breakdown voltage, while the maximum velocity of 33 m s⁻¹ is detected in the case of NPG-18, even though it has the shortest pulse rising time and the highest breakdown voltage.     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas-liquid discharge generated in atmospheric

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas-liquid discharge in atmospheric N2 with a trumpet-shaped quartz tube.The current-voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H2O2,NO2-,and NO3-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min-1 of gas flow rate.The absorbance intensities of NO2 and N2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N2(C),OH(A),and O(3p)),nitrogen oxides (NO2,NO,and N2O),and higher production of aqueous H2O2,NO2-,and NO3-compared with both unipolar positive and negative discharges.     

High Pressure Micro-Slot Hollow Cathode Discharge

A direct current glow discharge source structure operating at high pressure based on the micro-slot hollow cathode is presented in this article. A 100 μm width slot cathode was fabricated of copper, and a stable DC glow discharge with an area of 0.5 mm^2 was produced in noble gases （He, Ne） and air over a wide pressure range （kPa - 10 kPa）. The current-voltage characteristics and the near UV radiation emission of the discharge were studied.