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.     

Experimental investigation on the evolution of plasma properties in the discharge channel of a pulsed plasma thruster

Pulsed plasma thrusters(PPTs) are an attractive form of micro-thrusters due to advantages such as their compactness and lightweight design compared to other electric propulsion systems.Experimental investigations on their plasma properties are beneficial in clarifying the complex process of plasma evolution during the micro-second pulse discharge of a PPT. In this work, the multi-dimensional evolutions of the light intensity of the PPT plasma with wavelength, time, and position were identified. The plasma pressure was obtained using an iterative process with composition calculations. The results show that significant ion recombination occurred in the discharge channel since the line intensities of CII, CIII, CIV, and FII decreased and those of CI and FI increased as the plasma moved downstream. At the center of the discharge channel, the electron temperature and electron density were in the order of 10 000 K and 10~(17) cm~(-3),respectively. These had maximum values of 13 750 K and 2.3?×?10~(17) cm~(-3) and the maximum temperature occurred during the first half-cycle while the maximum number density was measured during the second half-cycle. The estimated plasma pressure was in the order of 10~5 Pa and exhibited a maximum value of 2.69?×?10~5 Pa.     

Investigation of the self-induced magneticfield characteristics in a pulsed plasma thruster with flared electrodes

The self-induced magnetic field in a pulsed plasma thruster(PPT)with flared electrodes is investigated for a better understanding of the working process and the structural design of the thruster.A two-dimensional model of the magnetic field is built and is validated by comparing the simulated results with the experimental results in literature.The magnetic flux density in the discharge channel during the working process is presented and analyzed regarding the electrode structures.The calculated magnetic field flux density decreases from 0.8 T at the upstream to 0.1 T and below at the downstream in the discharge channel(68 J).The peak of the magnetic flux density over time lags behind the current peak,which provides evidence for the existence of a moving plasma sheet in the discharge process.The magnetic field induced by the current in the extra bending part of the anode enhances the Lorentz force,which acts on the charged particles near the propellant.Finally,the geometric study indicates that the electromagnetic impulse bit does not monotonically increase with the flared angle of the electrodes.Instead,it reaches a maximum at a certain flared angle,which could provide significant suggestions for structural optimization.     

PIC simulation of plasma properties in the discharge channel of a pulsed plasma thruster with flared electrodes

Plasma in the discharge channel of a pulsed plasma thruster (PPT) with flared electrodes is simulated by a self-developed two-dimensional code. The fully particle-in-cell method with Monte Carlo collision is employed to model the particle movement and collisions and investigate the plasma properties and acceleration process. Temporal and spatial variations of the electron density distribution and the ion velocity between electrodes are calculated and analyzed in detail. The computational results of the electron number density, which is in the order of 10²³ m⁻³, show good agreements with experimental results of a PPT named ADD SIMP-LEX. The ion velocity distributions along the center line of the channel lead to a comprehensive understanding of ions accelerated by electromagnetic field. The electron distributions of PPT with discharge voltages varying from 1300 to 2000 V are compared. The diffusion of electrons presents strong dependency on discharge voltage and implies higher degree of ionization for higher voltage.     

The implementation of magnetics verification in EAST plasma control system

Experimental advanced superconducting tokamak (EAST) is an experimental device aiming at steady state plasma operation for fusion research. The values of many discharge parameters, such as plasma shape, position and current must be directly acquired or indirectly evaluated from the magnetic measurements, so the accuracy of magnetic measurements plays an important role in reliable plasma control performance. A method for verifying the key magnetic measurements in real time for each shot is described in this paper. Such magnetics verification will prevent the discharge from a key magnetic signal failure and ensure the quality of a successful discharge. The diagnostics verification algorithm has been implemented in the plasma control system for the EAST. The implementation details and its application in the recent experiment are presented in this paper.     

Characteristics of plasma in a novel laser-assisted pulsed plasma thruster

A novel laser-assisted pulsed plasma thruster (LA-PPT) is proposed as an electric propulsion thruster, which separates laser ablation and electromagnetic acceleration. It aims for a higher specific impulse than that achieved with conventional LA-PPTs. Owing to the short-time discharge and the novel configuration, the physical mechanism of the discharge is unclear. Time and spatial-resolved optical emission spectroscopy was applied to investigate the variation in the plasma properties in the thruster discharge channel. The plasma species, electron temperature, and electron density were obtained and discussed. Our investigation revealed that there were H_α, H_β, H_γ, H_ε atoms, C I, C II, C III, C IV, Cl I, Cl II particles, and a small amount of CH, C₃, C₂, H₂ neutral molecular groups in the plasma. The electron temperature of the discharge channel of the thruster was within 0.6–4.9 eV, and the electron density was within (1.1–3.0) $\times $ 10¹⁸ cm⁻³, which shows that the optical emission spectroscopy method is to measure the electron excitation temperature and electron density in heavy particles. But the Langmuir probe method is to measure the temperature and density of free electrons. The use of laser instead of spark plug as the ignition mode significantly changed the plasma distribution in the discharge channel. Unlike the conventional PPT, which has high electron density near the thruster surface, LA-PPT showed relatively large electron density at the thruster outlet, which increased the thruster specific impulse. In addition, the change in the ignition mode enabled the electron density in the LA-PPT discharge channel to be higher than that in the conventional PPT. This proves that the ignition mode with laser replacing the spark plug effectively optimised the PPT performance.     

Special issue on selected papers from HVDP 2020

正High-voltage and discharge plasma technology is playing an increasingly important role in the construction of national economy and social development,and has attracted extensive attention from both academia and industry. As a novel molecular activation method, discharge plasma can enable thermodynamically difficult reactions to occur under relatively mild conditions, and its effectiveness has successfully been demonstrated in gas cleaning and material surface treatment.     

Effect of shock wave formation on propellant ignition in capillary discharge

In order to study the effect of shock wave formation on propellant ignition in capillary discharge, the shock wave formation process was analyzed using experimental and theoretical methods; the plasma jet temperature was measured, and closed bomb and 30 mm gun experiments were carried out. The results show that the first shock wave has a smaller value and larger range of influence, while the second shock wave has a larger value and smaller range of influence. A plasma jet can generate a shock wave at the nozzle according to the calculated plasma pressure and velocity, which is well confirmed by experiments and calculations. The plasma jet temperature is high during the formation of a shock wave and then decreases sharply. Plasma ignition can increase the burning rate of a propellant by about 30% by increasing the burning surface area of the propellant. Compared to conventional ignition, the average maximum chamber pressure and average muzzle velocity of plasma ignition are increased by 9.1 MPa and 29.3 m·s−1(∼3%), respectively, in a 30 mm gun. Plasma ignition has strong ignition ability and short ignition delay time due to the generation of a shock wave. By increasing the burning rate of the propellant, the muzzle velocity can be greatly improved when the maximum chamber pressure increases a little. The characteristics of the shock wave can be applied in the application of the capillary discharge plasma. For example, it can be applied in fusion, launching and combustion.     

Effect of low-frequency oscillation on performance of Hall thrusters

In this paper,a direct connection between the discharge current amplitude and the thruster performance is established by varying solely the capacitance of the filter unit of the Hall thrusters.To be precise,the variation characteristics of ion current,propellant utilization efficiency,and divergence angle of plume at different low-frequency oscillation amplitudes are measured.The findings demonstrate that in the case of the propellant in the discharge channel just meets or falls below the full ionization condition,the increase of low-frequency oscillation amplitude can significantly enhance the ionization degree of the neutral gas in the channel and increase the thrust and anode efficiency of thruster.On the contrary,the increase in the amplitude of low-frequency oscillation will lead to increase the loss of plume divergence,therefore the thrust and anode efficiency of thruster decrease.     

Investigation on plasma characteristics in a laser ablation pulsed plasma thruster by optical emission spectroscopy

In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion, a novel laser ablation pulsed plasma thruster is proposed, which separated the laser ablation and electromagnetic acceleration. Optical emission spectroscopy is utilized to investigate the plasma characteristics in the thruster. The spectral lines at different times,positions and discharge intensities are experimentally recorded, and the plasma characteristics in the discharge channel are concluded through analyzing the variation of spectral lines. With the discharge energy of 24 J, laser energy of 0.6 J and the use of aluminum propellant, the specific impulse and thrust efficiency reach 6808 s and 70.6%, respectively.     

电子探针化学测年法在晶质铀矿/沥青铀矿定年研究中的应用现状

简要介绍近年发展起来的各种微区测年方法及其优缺点,重点介绍不同时期电子探针化学测年法在晶质铀矿/沥青铀矿定年研究中的发展状况及前人使用的分析测试条件,并展望了该方法在晶质铀矿/沥青铀矿定年研究中的应用前景及可能存在的问题。通过系统研究,认为该方法在铀矿物定年研究中将大有作为,尤其是在微小铀矿物(<10μm)和多期次、多阶段铀矿体的微区定年研究中更能显示其优越性。     

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.     

The effect of anode axial position on the performance of a miniaturized cylindrical Hall thruster with a cusp-type magnetic field

A 200 W cylindrical Hall thruster with a cusp-type magnetic field was proposed, manifesting convergent plume and high specific impulse. In this paper, a series of ring-shaped anodes are designed and the influence of anode axial position on the performance of CHT with a cusp-type magnetic field is studied. The experimental results indicate that the thruster keeps stable operation at the condition of 140–270 W discharge power. When the anode moves axially towards the upstream cusp field, the thrust enhances from 6.5 mN to 7.6 mN and specific impulse enhances from 1658 s to 1939 s significantly. These improvements of thruster performance should be attributed to the enhancement of current utilization, propellant utilization and acceleration efficiency. According to the analyses on the discharge characteristics, it is revealed that as the anode moves upstream, the electron transport path could be extended, the magnetic field in this extended path could impede electron cross-field transport and facilitate the ionization intensity, yielding to the enhancement of current utilization and propellant utilization efficiency. Moreover, along with this enhancement of upstream ionization at the given anode flow rate, the main ionization region is thought to move upstream and then separate more apparently from the acceleration region, which has been demonstrated by the narrowing of ion energy distribution function shape. This change in acceleration region could decrease the ion energy loss and enhance acceleration efficiency. This work is beneficial for optimizing the electrode structure of thruster and recognize the ionization and acceleration process under the cusp magnetic field.     

同行评估在我国核电行业的应用与发展

对国内外各种不同的评估方法进行对比分析,以中国核工业集团公司（以下简称＂中核集团＂）的相关实践为主线,对现有的核电同行评估进行了简要的对比分析,描述了同行评估在中国核电行业的应用与发展,并提出了若干改进建议与同行分享。     

中国粒子加速器的发展现状和趋势

我国的粒子加速器近20年来发展迅速,在加速器不同的类型、规模和应用方向上全面向世界先进水平靠近。本文以几个主要加速器研究或应用方向如先进光源、强流质子-重离子加速器、粒子对撞机、民生应用型加速器为主线,介绍其中几台典型装置的建设和发展,以及它们在国际上的地位和在相应学科研究中所发挥的作用。同时,也介绍我国在加速器物理和技术方面的快速进步,这些进步不仅对已经建造和正在建造的大型加速器装置是个极为重要的支持,也是加速器学科的自身发展,并为未来更先进的加速器装置的发展提供了可能性。本文对我国未来若干年的加速器事业发展作了展望,期望我国的加速器在10年后将全面处于国际先进水平,同时也对我国在激光等离子体尾场加速领域近些年来的飞速发展作一个简单评述。     

有机荧光探针在铀酰离子检测方面的研究进展

荧光分析法是检测铀酰离子最主要的方法之一,它具有设备简单、高灵敏度和高选择性等优点。本文主要阐述了近几年来有机荧光分子在铀酰离子检测领域的研究进展,主要包括有机荧光染料、含氧酸等天然荧光/药物分子,以及利用席夫碱、卟啉、偕氨肟等官能团构筑的有机荧光分子和AIE型荧光分子等。这为后续性能优异的有机荧光探针的分子设计和铀酰离子检测等研究工作提供了借鉴。     

拖曳式水槽模拟实验系统及实验验证

对大气环境进行研究时主要有三种手段:物理模拟、数值模拟和现场实测。其中,物理模拟的方法除了风洞实验之外,近年来不断发展的还有水槽模拟实验。为了完善水槽模拟实验方法,中国辐射防护研究院建成了国内大型环境模拟拖曳水槽及配套测试设备。本文介绍该实验装置的结构、性能与特点,并通过初步实验,证明该实验装置在对污染物在大气环境中迁移扩散的模拟具有一定的有效性。     

钴-60数字辐射成像检测技术回顾与展望

本文对近二十年来清华大学核能与新能源技术研究院主导研究开发⁶⁰Co辐射成像检测技术并实现产业化工作进行了回顾与展望。从国家需求出发,系统说明此技术的研发目标、创新思路和主要研究成果,并介绍实现产业化的装备品种、性能、运行情况和应用效益,总结此项技术的突出优点和发展前景。文中对推广应用时一些认识障碍做了梳理和解释,希望有助于新技术的改进与发展。     

Performance of a 4 cm iodine-fueled radio frequency ion thruster

The performance of an iodine radio ion thruster with a 4 cm diameter(IRIT4) was studied experimentally in this paper. Regulation of the mass flow rates of the iodine propellant is achieved by using a temperature control method of the iodine reservoir. Performance of the thruster using iodine as propellants is obtained at different total thruster powers of 40.6–128.8 W,different grid voltages of 1000–1800 V and the iodine flow rate of 100 μgs~(-1). Results show that thrust and specific impulse increase approximately linearly with the increasing total thruster power and the screen grid voltage. The thrust of 2.32 mN and the specific impulse of 2361 s are obtained at the nominal total thruster power of 95.8 W and the screen grid voltage of 1800 V. It is also indicated that performance of the iodine propellant is comparable to that of the xenon propellant; and a difference between them is that the iodine thrust is slightly higher than xenon when the total thruster power is more than 62 W. At the nominal 95.8 W total thruster power, the thrust values of them are 2.32 m N and 2.15 mN respectively, and the thrust-to-power ratios of them are 24.2 mN kW~(-1) and 23.5 mN kW~(-1), respectively.     

Characteristics of Electrode-Water-Electrode Discharge and its Application to Water Treatment

Atmospheric air discharge above the surface of water is an effective method for water treatment.The leakage current and Joule heating of water are reduced by the air gap,which raises the energy efficiency of the water treatment.However,the application of this kind of discharge is limited by a pair of conflicting factors：the chemical efficiency grows as the discharge gap distance decreases,while the spark breakdown voltage decreases as the gap distance decreases.To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge,both the high-voltage electrode and the ground electrode are suspended above the water surface to form an electrode-water-electrode discharge system.For this system,there are two potential discharge directions：from one electrode to another directly,and from the electrodes to the water surface.The first step in utilizing the electrode-water-electrode discharge is to find out the discharge direction transition criterion.In this paper,the discharge direction transition criterions of spark discharge and streamer discharge are presented.By comparing the discharge characteristics and the chemical efficiencies,the discharge propagating from the electrodes to the water surface is proved to be more suitable for water treatment than that propagating directly between the electrodes.