Study of the influence of discharge loop parameters on anode side on generation characteristics of metal plasma jet in a pulsed vacuum discharge

In a pulsed vacuum discharge, the ejection performance of a metal plasma jet can be effectively improved by preventing charged particles from moving to the anode. In this paper, the effects of resistance and capacitance on the anode side on the discharge characteristics and the generation characteristics of plasma jet are investigated. Results show that the existence of a resistor on the anode side can increase the anode potential, thereby preventing charged particles from entering the anode and promoting the ejection of charged particles along the axis of the insulating sleeve nozzle. The application of a capacitor on the anode side can not only absorb electrons at the initial stage of discharge, increasing the peak value of the cathode hump potential, but also prevent charged particles from moving to the anode, thereby improving the ejection performance of the plasma jet. In addition, the use of a larger resistance and a smaller capacitance can improve the blocking effect on charged particles and further improve the ejection performance of the plasma jet. Results of this study will provide a reference for the improvement of the ejection performance of plasma jets and their applications.     

Development and experimental study of large size composite plasma immersion ion implantation device

Plasma immersion ion implantation(PⅢ) overcomes the direct exposure limit of traditional beamline ion implantation, and is suitable for the treatment of complex work-piece with large size. PⅢ technology is often used for surface modification of metal, plastics and ceramics. Based on the requirement of surface modification of large size insulating material, a composite full-directional PⅢ device based on RF plasma source and metal plasma source is developed in this paper. This device can not only realize gas ion implantation, but also can realize metal ion implantation, and can also realize gas ion mixing with metal ions injection. This device has two metal plasma sources and each metal source contains three cathodes. Under the condition of keeping the vacuum unchanged, the cathode can be switched freely. The volume of the vacuum chamber is about 0.94 m~3, and maximum vacuum degree is about 5?×?10~(-4) Pa. The density of RF plasma in homogeneous region is about 10~9 cm~(-3), and plasma density in the ion implantation region is about 10~(10) cm~(-3). This device can be used for large-size sample material PⅢ treatment, the maximum size of the sample diameter up to 400 mm. The experimental results show that the plasma discharge in the device is stable and can run for a long time. It is suitable for surface treatment of insulating materials.     

真空弧离子源脉冲工作瞬间的放电行为

采用高速摄影和光谱诊断的方法研究了真空弧离子源脉冲工作瞬间的放电行为。拍摄了离子源放电瞬间吸氢电极上阴极斑的形成过程，分析了不同放电电流时阴极斑的发射光谱。实验结果表明，当脉冲工作电流为10^1—10^2A时，真空弧离子源放电区一般只有单个阴极斑，阴极斑的位置在同一次放电中的变化很小；较大的脉冲工作电流有利于提高阴极斑的温度，并最终导致氢离子浓度的增加，但也会使阴极材料的溅射更加严重，造成离子源等离子体品质下降。     

磁过滤等离子体沉积和注入技术

利用阴极真空弧放电技术能够产生高密度的金属等离子体。经过90度的磁过滤器，可以除去金属等离子体中的大颗粒微粒，从而为制备高质量的、致密的各种薄膜提供了一种全新的技术。利用该技术制备薄膜具有非常广泛的应用。本文介绍了阴极真空弧放电技术的应用，以及磁过滤等离子体沉积和注入装置及其应用。     

Effect of insulating oil covering electrodes on the characteristics of a dielectric barrier discharge

In this study, the effects of the fluid cooling and electric field line deformation were investigated in a dielectric barrier discharge (DBD) plasma source. The DBD plasma jet is improved by covering the ground electrode and a power electrode with insulating oil. We obtained positive results as insulating oil prevents arc formation, while it improved the supplied power and plasma jet length, and increased radical production. Radical production of this nonthermal plasma jet is studied with polyvinyl alcohol–potassium iodide liquid.     

Investigation of cathode spot characteristics in vacuum under transverse magnetic field (TMF) contacts

With the continuous improvement of current levels in power systems,the demands on the breaking capacity requirements of vacuum circuit breakers are getting higher and higher.The breaking capacity of vacuum breakers is determined by cathode spots,which provide electrons and metal vapor to maintain the arc.In this paper,experiments were carried out on two kinds of transverse magnetic field (TMF) contacts in a demountable vacuum chamber,the behavior of the cathode spots was recorded by a high-speed charge-coupled device (CCD) video camera,and the characteristics of the cathode spots were analyzed through the image processing method.The phenomenon of cathode spot groups and the star-shaped pattern of the spots were both discovered in the experiment.The experimental results show that with the condition of TMF contacts the initial expansion speed of cathode spots is influenced by some parameters,such as the tested current,contact gap,the structure of the contact,the contact diameter,the number of slots,etc.In addition,the influence of the magnetic field on the formation of the cathode spot groups,the distribution,and the dynamic characteristics of the cathode spots were analyzed.It is concluded that the characteristics of the cathode spots are due to the effect of the magnetic field on the near-cathode plasma.The study of the characteristics of cathode spots in this paper would be helpful in the exploration of the physical process of vacuum arcs,and would be of guiding significance in optimizing the design of vacuum circuit breakers.     

The Effect of Gas Flow Rate on Radio-Frequency Hollow Cathode Discharge Characteristics

It is known that gas flow rate is a key factor in controlling industrial plasma processing. In this paper, a 2D PIC/MCC model is developed for an rf hollow cathode discharge with an axial nitrogen gas flow. The effects of the gas flow rate on the plasma parameters are calculated and the results show that： with an increasing flow rate, the total ion（N＋2, N＋） density decreases, the mean sheath thickness becomes wider, the radial electric field in the sheath and the axial electric field show an increase, and the energies of both kinds of nitrogen ions increase;and, as the axial ion current density that is moving toward the ground electrode increases, the ion current density near the ground electrode increases. The simulation results will provide a useful reference for plasma jet technology involving rf hollow cathode discharges in N2.     

Impact of the Insulator on the Electric Field and Generation Characteristics of Vacuum Arc Metal Plasmas

The field electron emission plays a vital role in the process of vacuum discharge breakdown. The electric field strength at the cathode tip is significant to the generation char- acteristics of vacuum arc metal plasmas. To increase the field strength at the cathode tip, a coaxial electrode plasma source was employed with an insulator settled between the electrodes. The math expression of the field strength is derived based on the Gauss theory. The impact of the insulator on the electric field and parameters of plasmas were investigated by MAXWELL 3D simulation software and the Langmuir probe. In addition, a composite insulator was adopted to further strengthen the field strength. A series of experiments were performed to focus on the role of the composite insulator in detail. The experimental and simulation results indicate that, a reasonable layout of the insulator, especially the composite insulator, can effectively increase the field strength at the cathode tip and the plasma density.     

Numerical simulation of low-current vacuumarc jet considering anode evaporation in different axial magnetic fields

As the main source of the vacuum arc plasma, cathode spots (CSs) play an important role on the behaviors of the vacuum arc. Their characteristics are affected by many factors, especially by the magnetic field. In this paper, the characteristics of the plasma jet from a single CS in vacuum arc under external axial magnetic field (AMF) are studied. A multi-species magneto-hydro-dynamic (MHD) model is established to describe the vacuum arc. The anode temperature is calculated by the anode activity model based on the energy flux obtained from the MHD model. The simulation results indicate that the external AMF has a significant effect on the characteristic of the plasma jet. When the external AMF is high enough, a bright spot appears on the anode surface. This is because with a higher AMF, the contraction of the diffused arc becomes more obvious, leading to a higher energy flux to the anode and thus a higher anode temperature. Then more secondary plasma can be generated near the anode, and the brightness of the ‘anode spot’ increases. During this process, the arc appearance gradually changes from a cone to a dumbbell shape. In this condition, the arc is in the diffuse mode. The appearance of the plasma jet calculated in the model is consistent with the experimental results.     

Measurements of Plasma Jets and Collimated Flux Tubes that are the Precursors of Spheromak Self-organization

A magnetized planar coaxial plasma gun is used to study the physics of spheromak formation. Eight magnetic flux tubes spanning from the cathode to the anode electrode are first filled with plasma by a rapid MHD pumping mechanism which ingests plasma from nozzles at the wall. The ingested plasma convects toroidal flux and the pile-up of this flux in the flux tube causes the flux tube to become collimated. The eight collimated flux tubes first have the shape of spider legs, but then merge to form a central column jet. This jet lengthens, continuing to ingest plasma from the wall sources, and becomes kink unstable. At a later stage the root of the jet can break off from the electrode and this detachment has been identified as being associated with a sausage instability. The sausage instability takes place during the nonlinear stage of the kinking. The above statements are based on experimental observations and have been reconciled with MHD models.     

CSNS四极陶瓷真空盒磁控溅射镀TiN膜研究

介绍了中国散裂中子源（CSNS）快循环同步加速器（RCS）中四极陶瓷真空盒内表面镀TiN膜技术与成膜系统装置。采用磁控溅射法,通过在绝缘体长直管道外表面安装金属屏幕罩来提供同轴电场的方法,解决了镀膜均匀性的问题。镀膜样品Ti、N比在0.9~1.1范围内,膜厚为100nm左右,附着力达到要求,总体满足设计指标,完成了CSNS四极陶瓷真空盒样机的镀膜。     

Simulation of the Effect of a Metal Vapor Arc on Electrode Erosion in Liquid Metal Current Limiting Device

The effect of arc plasma on electrode erosion in a liquid metal current limiter(LMCL)is studied.Based on a simplified two-dimensional magnetohydrodynamic model,the elongated GaInSn metal vapor arc and its contraction process in a liquid metal current limiter are simulated.The distributions of temperature,pressure and velocity of the arc plasma are calculated.The simulation results indicate that the electrode erosion is mainly caused by two high temperature gas jet flows arising from the pressure gradient,which is a result of the non-uniform arc temperature distribution.The gas flows,which act as jets onto the electrode surface,lead to the evaporation of the electrode material form the surface.A redesign structure of the electrode is proposed and implemented according to the analysis,which greatly increased the service life of the electrode.     

Measurements of plasma parameters in a hollow electrode AC glow discharge in helium

Measurements of the plasma parameters of coaxial gridded hollow electrode alternating current(AC)discharge helium plasma were carried out using an improved probe diagnostic technology.The measurements were performed under well-defined discharge conditions(chamber geometry,input power,AC power frequency,and external electrical characteristics).The problems encountered in describing the characteristics of AC discharge in many probe diagnostic methods were addressed by using an improved probe diagnostics design.This design can also be applied to the measurement of plasma parameters in many kinds of plasma sources in which the probe potential fluctuates with the discharge current.Several parameters of the hollow electrode AC helium discharge plasma were measured,including the plasma density,electron temperature,plasma density profiles,and changes in plasma density at different input power values and helium pressures.The characteristics of the coaxial gridded hollow electrode plasma determined by the experiments are suitable for comparison with plasma simulations,and for use in many applications of hollow cathode plasma.     

Study on the plasma generation characteristics of an induction-triggered coaxial pulsed plasma thruster

At present,spark plugs are used to trigger discharge in pulsed plasma thrusters (PPT),which are known to be life-limiting components due to plasma corrosion and carbon deposition.A strong electric field could be formed in a cathode triple junction (CTJ) to achieve a trigger function under vacuum conditions.We propose an induction-triggered electrode structure on the basis of the CTJ trigger principle.The induction-triggered electrode structure could increase the electric field strength of the CTJ without changing the voltage between electrodes,contributing to a reduction in the electrode breakdown voltage.Additionally,it can maintain the plasma generation effect when the breakdown voltage is reduced in the discharge experiments.The induction-triggered electrode structure could ensure an effective trigger when the ablation distance of Teflon increases,and the magnetic field produced by the discharge current could further improve the plasma density and propagation velocity.The induction-triggered coaxial PPT we propose has a simplified trigger structure,and it is an effective attempt to optimize the micro-satellite thruster.     

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.     

The influence of grounded electrode positions on the evolution and characteristics of an atmospheric pressure argon plasma jet

An atmospheric pressure plasma jet (APPJ) in Ar with various grounded electrode arrangements is employed to investigate the effects of electrode arrangement on the characteristics of the APPJ.Electrical and optical methods are used to characterize the plasma properties.The discharge modes of the APPJ with respect to applied voltage are studied for grounded electrodepositions of 10 mm,40 mm and 80 mm,respectively,and the main discharge and plasma parameters are investigated.It is shown that an increase in the distance between the grounded electrode and high-voltage electrode results in a change in the discharge modes and discharge parameters.The discharges transit from having two discharge modes,dielectric barrier discharge (DBD) and jet,to having three,corona,DBD and jet,with increase in the distance from the grounded to the high-voltage electrodes.The maximum length of the APPJ reaches 3.8 cm at an applied voltage of 8 kV.The discharge power and transferred charges and spectral line intensities for species in the APPJ are influenced by the positions of the grounded electrode,while there is no obvious difference in the values of the electron excited temperature (EET) for the three grounded electrode positions.     

Study on plasma sheath and plasma transport properties in the azimuthator

A physical model of transport in an azimuthator channel with the sheath effect resulting from the interaction between the plasma and insulation wall is established in this paper.Particle in cell simulation is carded out by the model and results show that,besides the transport due to classical and Bohm diffusions,the sheath effect can significantly influences the transport in the channel.As a result,the ion density is larger than the electron density at the exit of azimuthator,and the non-neutral plasma jet is divergent,which is unfavorable for mass separation.Then,in order to improve performance of the azimuthator,a cathode is designed to emit electrons.Experiment results have demonstrated that the auxiliary cathode can obviously compensate the space charge in the plasma.     

Measurement ofHe2* density with an auxiliary measuring electrode in atmospheric pressure plasma jet

In this study, the density of metastable He₂* in an atmospheric-pressure plasma jet operating in helium with 0.001% nitrogen has been measured using an auxiliary measuring electrode technique. In the glow discharge mode, waveforms from two grounding electrodes, including one main discharge electrode and one auxiliary electrode, are captured. The isolated current peak formed by Penning ionization in waveforms from the auxiliary measuring electrode is identified to calculate the density of metastable He₂*. In our discharge environment, the helium metastable densities along the jet axis direction are between 2.26× 10¹³ and 1.74× 10¹³ cm^-3, which is in good agreement with the results measured by other techniques. This measurement technique can be conveniently applied to the diagnosis of metastableHe₂* in an atmospheric-pressure plasma jet array.     

Characteristics of a radio-frequency cold atmospheric plasma jet produced with a hybrid cross-linear-field electrode configuration

Cold atmospheric plasma (CAP) jet has wide applications in various fields including advanced materials synthesis and modifications, biomedicine, environmental protection and energy saving, etc. Appropriate control on the volume, temperature and chemically reactive species concentrations of the CAP jet is of great importance in actual applications. In this paper, an radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma generator with a hybrid cross-linear-field electrode configuration is proposed. The experimental results show that, with the aid of the copper mesh located at the downstream of the traditional co-axial-type plasma generator with a cross-field electrode configuration, a linear field between the inner powered electrode of the traditional plasma generator and the copper mesh can be established. This liner- field can, to some extent, enhance the discharges at the upstream of the copper mesh, resulting in small increments (all less than 12.5%) of the species emission intensities, electron excitation temperatures and gas temperatures by keeping other parameters being unchanged. And due to the intrinsic transparent and conducting features of the grounded copper mesh to the gas flowing, electric current and heat flux of the plasma plumes, a plasma region with higher concentrations of chemically reactive species and larger plasma plume diameters is obtained at the downstream of the grounded copper mesh on the same level of the gas temperature and electron excitation temperature compared to those of the plasma free jet. In addition, the charged particle number densities at the same downstream axial location of the grounded copper mesh decrease significantly compared to those of the plasma free jet. This means that the copper mesh is also, to some extent, helpful for separating the chemically reactive neutral species from the charged particles inside a plasma environment. The preceding results indicate that the cross-linear-field electrode configuration of the plasma generator is an effective approach for tuning the characteristics of the RF-APGD plasma jet in order to obtain an appropriate combination of the plasma jet properties with higher chemically reactive species concentrations, especially relative higher number densities of neutral species, larger plasma volumes and lower gas temperatures.     

Low energy nuclear reaction polyplasmon postulate

An explanation is proposed for the nuclear reactions that occur in the electrolysis class of LENR processes. The proposed explanation postulates that a proton, or deuteron, dissolved in the hydrogen bearing metal cathode, absorbs its associated atomic electron to become a short lived state of the neutron with the resulting neutrino in a singular wave function centered on the neutron. The energy required to initiate this endothermic reaction is supplied either by the ion current during electrolysis type experiments, or by ion bombardment in plasma type experiments. It is the energy of this bombardment of the cathode with heavy ions that creates a coherent polyplasmon field within crystalline metallic grains that are present in the metal cathode of typical active electrolysis cells. The LENR process consists of a second order reaction mediated by a coherent plasmon field excited in the conduction electrons in a hydrogen bearing metal that is in the form of crystalline grains of the order of a few microns in dimension. The coherent plasmon field in each grain is called a polyplasmon. The metallic grains typically form during solidification of a metal, the impurities being forced to the grain surfaces. The resulting grain thus forms a resonant structure that can be filled with a number of coherent plasmons, i.e., a polyplasmon.