Millimeter-Scale PIG Source for Miniature Mass Spectrometers

A new millimeter-scale penning ion generator (PIG) ion source has been developed for miniature mass spectrometers. The cathode is a 40?mm diameter?×?2?mm long stainless steel cylinder with a hole of 4?mm, the anode with a hole of 12.6?mm and a length of 6.4?mm is made in stainless steel, and the ion emission hole size on the anticathode is 5?mm. Several microamperes of H⁺ ions can be extracted with less than 10?W discharge power consumption. The PIG ion source is shown to have advantages of long lifetime under high-pressure operation and low power consumption. The ion source is being designed and investigated for use in miniature mass spectrometer; however this ion source is thoroughly described so that it can be easily implemented by other researchers for other applications.     

Cathode erosion site distributions in an applied-field magnetoplasmadynamic thruster

Erosion can influence cathode life, and is thus considered to be one of the main factors limiting the application of applied-field magnetoplasmadynamic thrusters. In this paper, erosion sites on graphite cathodes are studied so as to identify the influence of applied magnetic field and the ratio of propellant mass flow rate supplied from cathode and anode. The experiment results show that the application of applied magnetic field can significantly reduce the erosion rate of the cathode compared to that without magnetic field. The erosion sites on the cathode vary with the relative position of the convergent-divergent magnetic field, and are mainly distributed in the divergent part of the field. The erosion sites on the cathodes are found to be related to the propellant supply. The decreasing anode mass flow rate enlarges the range of erosion. These results are much helpful for the analysis of cathode erosion site location since they provide evidences of erosion mechanisms and point out the directions for further research.     

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。     

Generation scenarios of anodic structures and experimental realization of turbulence in unmagnetized plasma

In the present work, we report development of a DC glow discharge plasma(GDP) set-up to study controlled evolution of anodic structures having distinctive geometry, size and layers,generated in front of a positively biased electrode, submerged in unmagnetized plasma. For such an anodic structure, we have also investigated the condition under which the turbulence is triggered. Characteristic of these structures, generated in front of a positively biased electrode,depends on multiple parameters such as the ratio of anode to cathode size, electrode separation,gas pressure, biasing configuration such as anode bias, cathode bias and grounding schemes. We attempted to classify different anodic structures observed experimentally, as anode glow, fireball,anode spot, double layer and multiple double layers(MDLs) based on its physical characteristics.Among these structures the present investigation is focused on MDLs. The number of layers,observed in MDLs varied from as high as six to as low as zero, by controlling the operating discharge parameters, externally. Diagnostics were carried out using Langmuir probe. The analysis of floating potential fluctuations corresponds to a multiple anodic structure showed emergence of turbulence, at its critical stage, satisfying condition for self-organized criticality(SOC). This was identified with three slopes observed in the power spectrum, resembling the sand-pile model. Though, the GDP is completely different from that of the magnetically confined plasma, the nature of turbulence observed with SOC, is very similar to that observed in the scrape of layer of fusion devices. Therefore, the present investigation could provide new approach to study turbulence of similar nature, under an experimental condition that is free from the complexities of complicated field geometries used in confinement devices.     

Particle-in-cell simulation for effect of anode temperature on discharge characteristics of a Hall effect thruster

Propellant gas flow has an important impact on the ionization and acceleration process of Hall effect thrusters (HETs). In this paper, a particle-in-cell numerical method is used to study the effect of the anode temperature, i.e., the flow speed of the propellant gas, on the discharge characteristics of a HET. The simulation results show that, no matter the magnitude of the discharge voltage, the calculated variation trends of performance parameters with the anode temperature are in good agreement with the experimental ones presented in the literature. Further mechanism analysis indicates that the magnitude of the electron temperature is responsible for the two opposing variation laws found under different discharge voltages. When the discharge voltage is low, the electron temperature is low, and so is the intensity of the propellant ionization; the variation of the thruster performance with the anode temperature is thereby determined by the variation of the neutral density that affects the propellant utilization efficiency. When the discharge voltage is high, the electron temperature is large enough to guarantee a high degree of the propellant utilization no matter the magnitude of the anode temperature. The change of the thruster performance with the anode temperature is thus dominated by the change of the electron temperature and consequently the electron-neutral collisions as well as the electron cross-field mobility that affect the current utilization efficiency.     

Effect of the Discharge Voltage on the Performance of the Hall Thruster

In this paper,a two-dimensional physical model is established according to the discharging process in the Hall thruster discharge channel using the particle-in-cell method.The influences of discharge voltage on the distributions of potential,ion radial flow,and discharge current are investigated in a fixed magnetic field configuration.It is found that,with the increase of discharge voltage,especially during 250-650 V,the ion radial flow and the collision frequency between ions and the wall are decreased,but the discharge current is increased.The electron temperature saturation is observed between 400-450 V and the maximal value decreases during this region.When the discharge voltage reaches 700 V,the potential distribution in the axis direction expands to the anode significantly,the ionization region becomes close to the anode,and the acceleration region grows longer.Besides,ion radial flow and the collision frequency between ions and the wall are also increased when the discharge voltage exceeds 650 V.     

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.     

Effects of discharge parameters on the micro-hollow cathode sustained glow discharge

The effects of parameters such as pressure, first anode radius, and the cavity diameter on the micro-hollow cathode sustained glow discharge are investigated by using a two-dimensional self-consistent fluid model in pure argon. The results indicate that the three parameters influence the discharge in the regions inside and outside of the cavity. Under a fixed voltage on each electrode, a larger volume of high density plasma can be produced in the region between the first and the second anodes by selecting the appropriate pressure, the higher first anode, and the appropriate cavity diameter. As the pressure increases, the electron density inside the hollow cathode, the high density plasma volume between the first anode and second anodes, and the radial electric field in the cathode cavity initially increase and subsequently decrease. As the cavity diameter increases, the high-density plasma volume between the first and second anodes initially increases and subsequently decreases; whereas the electron density inside the hollow cathode decreases. As the first anode radius increases, the electron density increases both inside and outside of the cavity. Moreover, the increase of the electron density is more obvious in the microcathode sustained region than in the micro cavity region. The results reveal that the discharge inside the cavity interacts with that outside the cavity. The strong hollow cathode effect and the high-density plasma inside the cavity favor the formation of a sustained discharge between the first anode and the second anodes. Results also show that the radial boundary conditions exert a considerably weaker influence on the discharge except for a little change in the region close to the radial boundary.     

Study of electron-extraction characteristics of an inductively coupled radio-frequency plasma neutralizer

Inductively coupled radio-frequency (RF) plasma neutralizer (RPN) is an insert-free device that can be employed as an electron source in electric propulsion applications.Electron-extraction characteristics of the RPN are related to the bulk plasma parameters and the device's geometry.Therefore,the effects of different electron-extraction apertures and operational parameters upon the electron-extraction characteristics are investigated according to the global nonambipolar flow and sheath model.Moreover,these models can also be used to explain why the electron-extraction characteristics of the RPN strongly depend upon the formation of the anode spot.During the experimental study,two types of anode spots are observed.Each of them has unique characteristics of electron extraction.Moreover,the hysteresis of an anode spot is observed by changing the xenon volume-flow rates or the bias voltages.In addition,the rapid ignited method,gas-utilization factor,electron-extraction cost and other factors that need to be considered in the design of the RPN are also discussed.     

乏燃料干法后处理中铀电沉积行为模拟研究

基于多物理场耦合软件COMSOL,在LiCl-KCl熔盐体系中建立以电解槽为阳极、双石墨棒为阴极的氯化铀电沉积行为三维数值模型。通过研究熔盐中铀离子的运动情况以及对阴极几何形状的实时计算,得到了铀电沉积的沉积层厚度随时间的变化情况,得到了铀离子阴极沉积行为与阴极表面的位置、熔盐铀离子浓度、反应温度、平均电流密度之间的关系。研究中,还将模拟结果与氯化铀熔盐电解实验数据进行对比,计算与实验结果拟合良好,证明铀电沉积行为模拟的可靠性,模拟结果可为乏燃料干法后处理中铀的提取提供设计参考。      

Effects of Gas Flow Rate on the Discharge Characteristics of a DC Excited Plasma Jet

A direct current(DC) source excited plasma jet consisting of a hollow needle anode and a plate cathode has been developed to form a diffuse discharge plume in ambient air with flowing argon as the working gas.Using optical and electrical methods,the discharge characteristics are investigated for the diffuse plasma plume.Results indicate that the discharge has a pulse characteristic,under the excitation of a DC voltage.The discharge pulse corresponds to the propagation process of a plasma bullet travelling from the anode to the cathode.It is found that,with an increment of the gas flow rate,both the discharge plume length and the current peak value of the pulsed discharge decrease in the laminar flow mode,reach their minima at about1.5 L/min,and then slightly increase in the turbulent mode.However,the frequency of the pulsed discharge increases in the laminar mode with increasing the argon flow rate until the argon flow rate equals to about 1.5 L/min,and then slightly decreases in the turbulent mode.     

Comparison of pulse-modulated and continuous operation modes of a radio-frequency inductive ion source

The paper describes an experimental study of the characteristics of a pulse-modulated radiofrequency(RF) discharge sustained at low pressures, typical of the operating modes of RF gridded ion sources. The motivation for the study is the question of whether the RF pulsemodulated mode can increase the efficiency of the ion source. The ion current values extracted from an RF inductive ion source operating in continuous and pulse-modulated modes were compared. The experimental data were also compare...     

大束流场发射阴极X射线管的阳极设计

采用蒙特卡罗软件和有限元分析软件分析了固定阳极X射线管中电子轰击阳极靶的能量沉积和热量传输过程,固定阳极由铜棒和钨片组成。研究了在不同形状、尺寸和占空比的电子束脉冲轰击下,阳极靶面不同厚度的钨片和相邻铜棒的温度上升过程。结果表明,钨片厚度存在最优值,但最优值与具体使用条件相关;在脉冲成像方式下,固定阳极靶能承受更强束流强度的轰击。因此,采用固定阳极靶方案,研制140 kV高压、10 mA以上电流、直径1 mm以下有效焦点的场发射阴极X射线管是可行的。     

Influence of heating on the discharge characteristics of a hollow cathode

Hollow cathodes are widely used as electron sources and neutralizers in ion and Hall electric propulsion. Special applications such as commercial aerospace and gravitational wave detection require hollow cathodes with a very wide discharge current range. In this paper, a heater is used to compensate for the temperature drop of the emitter at low current. The self-sustained current can be extended from 0.6 to 0.1 A with a small discharge oscillation and ion energy when the flow rate is constant. This is also beneficial for long-life operation. However, when the discharge current is high(1 A), heating can cause discharge oscillation, discharge voltage and ion energy to increase. Further, combined with a rapid decline of pressure inside the cathode and an increase in the temperature in the cathode orifice plate, electron emission in the orifice and outside the orifice increases and the plasma density in the orifice decreases. This leads to a change in the cathode discharge mode.     

Electrodeless plasma thrusters for spacecraft: a review

The physics of electrodeless electric thrusters that use directed plasma to propel spacecraft without employing electrodes subject to plasma erosion is reviewed.Electrodeless plasma thrusters are potentially more durable than presently deployed thrusters that use electrodes such as gfidded ion,Hall thrusters,arcjets and resistojets.Like other plasma thrusters,electrodeless thrusters have the advantage of reduced fuel mass compared to chemical thrusters that produce the same thrust.The status of electrodeless plasma thrusters that could be used in communications satellites and in spacecraft for interplanetary missions is examined.Electrodeless thrusters under development or planned for deployment include devices that use a rotating magnetic field;devices that use a rotating electric field;pulsed inductive devices that exploit the Lorentz force on an induced current loop in a plasma;devices that use radiofrequency fields to heat plasmas and have magnetic nozzles to accelerate the hot plasma and other devices that exploit the Lorentz force.Using metrics of specific impulse and thrust efficiency,we find that the most promising designs are those that use Lorentz forces directly to expel plasma and those that use magnetic nozzles to accelerate plasma.     

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.     

Investigation of short-channel design on performance optimization effect of Hall thruster with large height–radius ratio

In this study, the neutral gas distribution and steady-state discharge under different discharge channel lengths were studied via numerical simulations. The results show that the channel with a length of 22 mm has the advantage of comprehensive discharge performance. At this time, the magnetic field intensity at the anode surface is 10% of the peak magnetic field intensity. Further analysis shows that the high-gas-density zone moves outward due to the shortening of the channel length, which optimizes the matching between the gas flow field and the magnetic field, and thus increases the ionization rate. The outward movement of the main ionization zone also reduces the ion loss on the wall surface. Thus, the propellant utilization efficiency can reach a maximum of 96.8%. Moreover, the plasma potential in the main ionization zone will decrease with the shortening of the channel. The excessively short-channel will greatly reduce the voltage utilization efficiency. The thrust is reduced to a minimum of 46.1 mN. Meanwhile, because the anode surface is excessively close to the main ionization zone, the discharge reliability is also difficult to guarantee. It was proved that the performance of Hall thrusters can be optimized by shortening the discharge channel appropriately, and the specific design scheme of short-channel of HEP-1350PM was defined, which serves as a reference for the optimization design of Hall thruster with large height–radius ratio. The short-channel design also helps to reduce the thruster axial dimension, further consolidating the advantages of lightweight and large thrust-to-weight ratio of the Hall thruster with large height–radius ratio.     

Temperature dependence of pattern transitions on water surface in contact with DC microplasmas

The DC-driven atmospheric-pressure microplasma is generated in a helium gas flowing through the metal tube cathode and is brought into contact with the surface of the water with the immersed Pt anode. By adjusting the gas flow, discharge current and gap distance, self-organized patterns are observed and varied sequentially from the homogeneous spot to the ring-like shape,distinct spot shape and the gearwheel shape on the water surface. The electrode temperature is measured and the gas temperature of the plasma discharge is calculated through the numericalfitting of the second positive system of the spectrum of N2 molecules. It is shown that the pattern transition is related to the electrode and gas temperatures of the plasma. Moreover, specific discretization features of the patterns are shown to appear at certain gas temperatures.     

Discharge instability in a plasma contactor

Like the hollow cathode, discharge instability also occurs during the operation of a plasma contactor.Voltage and current probes were employed to test the change of keeper voltage, keeper current,anode voltage, and anode current parameters with time under different working conditions. The anode current range corresponding to the discharge instability phenomenon is about 0.4 A to 1.2 A,and the emission characteristic curve in this area appears to bulge wherein the four parameters all produce different degrees of oscillation, the anode current oscillation being the greatest. Its waveform is considered to consist of a small-amplitude, high-frequency triangular wave and a large-amplitude,low-frequency sawtooth wave, and we have explained the shape of the wave. Each parameter shows hundreds of Hz in oscillation frequency and the phases of the four parameters appear to be regular.After fast Fourier transform processing, the frequency and amplitude of the main peak of the anode current oscillation tend to change with changes of the anode current, and there are differences in the trends under different keeper currents and xenon flows.