Development of an atmospheric fluorocarbon plasma jet generated by pulse modulated microwave discharge

Atmospheric fluorocarbon plasma plays an important role in the surface modification of insulating materials like polymers.The existing fluorocarbon plasma is usually generated by dielectric barrier discharge,which has a low concentration of reactive species and may cause insufficient surface fluorination.This work attempts to develop an atmospheric fluorocarbon plasma jet using a coaxial transmission line resonator by microwave discharge with locally enhanced electric field and high density.The gas temperature is reduced by pulse modulation technology.Three kinds of working gases,pure CF_(4),Ar/CF_(4)and He/CF_(4),are utilized to generate the atmospheric microwave fluorocarbon plasma jet.The discharge images,optical emission spectra,electron densities and gas temperatures are studied experimentally.The results show that the Ar/CF_(4)plasma jet has the best comprehensive performance,such as strong discharge intensity and controllable gas temperature.The electron density of the Ar/CF_4plasma jet has a magnitude of 10~(20)m^(-3),indicating a higher density than that of the frequently used dielectric barrier discharge.With the other conditions unchanged,the gas temperature at the end of the Ar/CF_(4)plasma jet can be reduced from 410.2 to 347.3 K by decreasing the duty cycle of the modulated pulse from 0.5 to 0.1.Thence,the microwave Ar/CF_(4)plasma jet is considered to be a promising fluorocarbon plasma source for surface fluorination of polymers.

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study,a coaxial transmission line resonator is constructed,which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon,nitrogen,or even air,respectively.Although the different kinds of working gas induce the different discharge performance,their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods,and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 10^(18)m^(-3).The tail region of plasma jets all contain a large number of active particles,like NO,O,emitted photons,etc,but without O_(3).The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields,the ionization wave propulsion,and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets.The parameters of plasma jet could be modulated by adjusting microwave power,modulation pulse parameters(modulation frequency and duty ratio),gas type and its flow rate,according to the requirements of application scenarios.

Development of a portable cold air plasma jet device and observation of its photo ionization process

Photo ionization plays a critical role in the formation and propagation of atmospheric pressure plasma jet plumes.But in experiments,it is very difficult to observe the photo ionization due to its relative lower density of photo electrons.In the present study,we develop a portable cold air plasma jet device and observe the ionization wave in adc spark air plasma jet.The discharge images acquired by an ICCD camera show that the ionization wave front performs as a quickly moving bright ball.Breakdown could take place at another side of the quartz plate or pork tissue layer(6 mm thick),which suggests that the ionization should be attributed to photo ionization.The laser schlieren images indicate there is propagation of a shock wave along with the plasma bullet.Based on the photo ionization theory and the photo-electric measurement,the direct photo ionization and multistage photo ionization are the main factors in charge of generating the cold air plasma jet.In addition,the plasma jet outside of the cathode nozzle is colder than 320 K and can be touched safely by a human.In view of the plasma jet including a large amount of active particles,such as NO,O,OH,emitted photons,etc,the proposed portable cold air plasma jet device could be qualified for plasma bio-medicine applications.

云南普洱季风常绿阔叶林不同种子扩散方式的优势种空间点格局分析

物种的空间分布格局和种群结构受生境过滤、扩散限制、种内和种间相互作用等多重过程的影响。研究物种的空间分布格局、物种关联及其与环境因子的关系,有利于揭示生物多样性维持机制,探索群落稳定演替的生态过程。季风常绿阔叶林作为我国热带-亚热带交错区典型的地带性植被类型,是研究交错区物种空间分布格局的重要平台。本研究基于普洱30ha季风常绿阔叶林动态监测样地的调查资料,采用点格局分析的方法,对3种不同种子扩散方式的优势种即短刺锥(Castanopsis echidnocarpa)、茶梨(Anneslea fragrans)、西南桦(Betula alnoides)的空间分布格局及其随尺度的变化进行研究,分析了生境过滤和扩散限制对物种空间分布格局的影响以及不同生活史阶段间的种内和种间关联。结果显示:短刺锥和茶梨在山脊和山坡分布居多,而在沟谷较少,西南桦则主要分布于山坡。3种优势种在完全随机模型下所有尺度上均表现为聚集分布,且聚集强度随空间尺度的增大而减小。排除生境异质性后,所有优势种只在小尺度上表现为聚集分布,大尺度上为随机分布或规则分布。扩散限制对短刺锥和茶梨的分布格局影响较小,而对西南桦的分布格局影响较为显著。在种内不同径级的空间关联上,短刺锥和茶梨种内不同生长阶段树木之间存在相关性,但西南桦则相关性不明显;在种间关联上,短刺锥和茶梨为正相关,和西南桦为负相关,茶梨和西南桦则正、负相关都存在。本研究表明,物种的空间分布格局是物种本身属性和环境条件的综合反映,其中生境过滤和扩散限制的关联效应是影响物种空间分布的主要原因。

Mechanism on improved surface flashover performances in vacuum of epoxy resin using fluorocarbon plasma treatment

To improve the insulation,strength of materials is a permanent topic in the fields of high voltage and insulation,and surface insulation is one of the difficulties.Research shows that the surface fluorination by a non-equilibrium plasma is a promising method to enhance the surface flashover characteristics of insulating materials.However,the de-terminants of flashover characteristics are so many that the mechanism is not well known.This paper aims to find out the reasons for the surface insulation improvement and optimise the plasma process parameters.The epoxy resin surfaces are modified by a fluorocarbon plasma,and the flashover voltages in vacuum and secondary electron emission yield are tested experimentally.Combined with the state of the art and the authors'previous work,the mechanism of improved surface flashover performances is investigated in depth from three aspects:the plasma process parameters,the surface physical and chemical properties and the surface electrical performances.A compre-hensive understanding of the mechanism is concluded,of which the whole processes from the plasma surface modification of materials to the surface insulation performances are taken into account.It is hopeful to promote the practical applications of plasma fluorination in electrical engineering through the findings of this paper.