The plume diagnostics of 30 cm ion thruster with an advanced plasma diagnostics system

In order to achieve a better understanding of plume characteristics of LIPS-300 ion thruster,the beam current density,ion energy and electron number density of LIPS-300 ion thruster plume are studied with an Advanced Plasma Diagnostics System(APDS)which allows for simultaneous in situ measurements of various properties characterizing ion thruster,such as plasma density,plasma potential,plasma temperature and ion beam current densities,ion energy distribution and so on.The results show that the beam current density distribution has a double‘wing'shape.The high energy ions were found in small scan angle,while low energy ions were found in greater scan angle.Electron number density has a similar shape with the beam current density distribution.

Diagnostics of electron temperature and ions distribution in expanding Al plasmas pumped by a ns-pulsed 1.06μm laser

Resonance lines are extensively used to diagnose electronic temperature Te and ions distribution. However, the analysis of the x-ray spectroscopy emitted from plasmas produced by a ns laser Jsually needs the help of a code or some assumptions. In this paper, a diagnostic idea of using line-pairs emitted from a doubly-excited state is proposed. By using the method presented in this paper, Te and the fractional population ratio of bare nuclei and H-like ions are directly obtained from the emission intensity ratios.

Energy loss of an energetic Ga ion in hot Au plasmas

Self-consistent calculations of energy loss for a Ga ion moving in hot Au plasmas are made under the assumption of wide ranges of the projectile energy and the plasma temperature with all important mechanisms considered in detail.The relevant results are found to be quite different from those of an a particle or a proton.One important reason for this is the rapid increasing of the charge state of a Ga ion at plasma temperature.This reason also leads to the inelastic stopping which does not always decrease with the increase of plasma temperature,unlike the case of an a particle.The nuclear stopping becomes very important at high enough plasma temperature due to the heavy reduced mass of a Ga and an Au ion and the above-mentioned reason.The well-known binary collision model[Phys.Rev.126(1962)1]and its revised one[Phys.Rev.A 29(1984)2145]are not working or unsatisfactory in this case.

Control of Beam Energy and Flux Ratio in an Ion-Beam-Background Plasma System Produced in a Double Plasma Device

Plasmas containing ion beams have various applications both in plasma technology and in fundamental research. The ion beam energy and flux are the two factors characterizing the beam properties. Previous studies have not achieved the independent adjustment of these two parameters. In this paper, an ion-beam-background-plasma system was produced with hotcathode discharge in a double plasma device separated by two adjacent grids, with which the beam energy and flux ratio （the ratio between the beam flux and total ion flux） can be controlled independently. It is shown that the discharge voltage （i.e., voltage across the hot-cathode and anode） and the voltage drop between the two separation grids can be used to effectively control the beam energy while the flux ratio is not affected by these voltages. The flux ratio depends sensitively on hot-filaments heating current whose influence on the beam energy is relatively weak, and thus enabling approximate control of the flux ratio

Phase shift effects of radio-frequency bias on ion energy distribution in continuous wave and pulse modulated inductively coupled plasmas

A retarding field energy analyzer（RFEA） is used to measure the time-averaged ion energy distributions（IEDs） on the substrate in both continuous wave（CW） and synchronous pulse modulated radio-frequency（RF） inductively coupled Ar plasmas（ICPs）.The effects of the phase shift θ between the RF bias voltage and the RF source on the IED is investigated under various discharge conditions.It is found that as θ increases from 0 to π,the IED moves towards the low-energy side,and its energy width becomes narrower.In order to figure out the physical mechanism,the voltage waveforms on the substrate are also measured.The results show that as θ increases from 0 to π,the amplitude of the voltage waveform decreases and,meanwhile,the average sheath potential decreases as well.Specifically,the potential drop in the sheath on the substrate exhibits a maximum value at the same phase（i.e.,θ = 0） and a minimum value at the opposite phase（i.e.,θ = π）.Therefore,when ions traverse across the sheath region above the substrate,they obtain less energies at lower sheath potential drop,leading to lower ion energy.Besides,as θ increases from π to 2π,the IEDs and their energy widths change reversely.

Computer-Controlled System for Plasma Ion Energy Auto-Analyzer

A computer-controlled system for plasma ion energy auto-analyzer was technically studied for rapid and online measurement of plasma ion energy distribution. The system intelligently controls all the equipments via a RS-232 port, a printer port and a home-built circuit. The software designed by LabVIEW G language automatically fulfils all of the tasks such as system initializing, adjustment of scanning-voltage, measurement of weak-current, data processing, graphic export, etc. By using the system, a few minutes are taken to acquire the whole ion energy distribution, which rapidly provides important parameters of plasma process techniques based on semiconductor devices and microelectronics.

Electron population properties with different energies in a helicon plasma source

The characteristics of electrons play a dominant role in determining the ionization and acceleration processes of plasmas.Compared with electrostatic diagnostics,the optical method is independent of the radio frequency(RF)noise,magnetic field,and electric field.In this paper,an optical emission spectroscope was used to determine the plasma emission spectra,electron excitation energy population distributions(EEEPDs),growth rates of low-energy and highenergy electrons,and their intensity jumps with input powers.The 56 emission lines with the highest signal-to-noise ratio and their corresponding electron excitation energy were used for the translation of the spectrum into EEEPD.One discrete EEEPD has two clear different regions,namely the low-energy electron excitation region(neutral lines with threshold energy of13–15 eV)and the high-energy electron excitation region(ionic lines with threshold energy?19 e V).The EEEPD variations with different diameters of discharge tubes(20 mm,40 mm,and 60 mm)and different input RF powers(200–1800 W)were investigated.By normalized intensity comparison of the ionic and neutral lines,the growth rate of the ionic population was higher than the neutral one,especially when the tube diameter was less than 40 mm and the input power was higher than 1000 W.Moreover,we found that the intensities of low-energy electrons and high-energy electrons jump at different input powers from inductively coupled(H)mode to helicon(W)mode;therefore,the determination of W mode needs to be carefully considered.

Modeling of Inner Surface Modification of a Cylindrical Tube by Plasma-Based Low-Energy Ion Implantation

The inner surface modification process by plasma-based low-energy ion implantation（PBLEII）with an electron cyclotron resonance（ECR）microwave plasma source located at the central axis of a cylindrical tube is modeled to optimize the low-energy ion implantation parameters for industrial applications.In this paper,a magnetized plasma diffusion fluid model has been established to describe the plasma nonuniformity caused by plasma diffusion under an axial magnetic field during the pulse-off time of low pulsed negative bias.Using this plasma density distribution as the initial condition,a sheath collisional fluid model is built up to describe the sheath evolution and ion implantation during the pulse-on time.The plasma nonuniformity at the end of the pulse-off time is more apparent along the radial direction compared with that in the axial direction due to the geometry of the linear plasma source in the center and the difference between perpendicular and parallel plasma diffusion coefficients with respect to the magnetic field.The normalized nitrogen plasma densities on the inner and outer surfaces of the tube are observed to be about 0.39 and 0.24,respectively,of which the value is 1 at the central plasma source.After a 5μs pulse-on time,in the area less than 2 cm from the end of the tube,the nitrogen ion implantation energy decreases from 1.5 keV to 1.3 keV and the ion implantation angle increases from several degrees to more than 40°;both variations reduce the nitrogen ion implantation depth.However,the nitrogen ion implantation dose peaks of about 2×10^（10）-7×10^（10）ions/cm^2 in this area are 2-4 times higher than that of 1.18×10^（10）ions/cm^2 and 1.63×10^（10）ions/cm^2 on the inner and outer surfaces of the tube.The sufficient ion implantation dose ensures an acceptable modification effect near the end of the tube under the low energy and large angle conditions for nitrogen ion implantation,because the modification effect is mainly determined by the ion implantation dose,just as the mass transfer process in PBLEII is dominated by low-energy ion implantation and thermal diffusion.Therefore,a comparatively uniform surface modification by the low-energy nitrogen ion implantation is achieved along the cylindrical tube on both the inner and outer surfaces.

Experimental Study of the Influence of Process Pressure and Gas Composition on GaAs Etching Characteristics in Cl_2/BCl_3-Based Inductively Coupled Plasma

A study of Cl2/BCl3-based inductively coupled plasma （ICP） was conducted using thick photoresist mask for anisotropic etching of 50μm diameter holes in a GaAs wafer at a relatively high average etching rate for etching depths of more than 150μm. Plasma etch characteristics with ICP process pressure and the percentage of BCI3 were studied in greater detail at a constant ICP coil/bias power. The measured peak-to-peak voltage as a function of pressure was used to estimate the minimum energy of the ions bombarding the substrate. The process pressure was found to have a substantial influence on the energy of heavy ions. Various ion species in plasma showed minimum energy variation from 1.85 eV to 7.5 eV in the pressure range of 20 mTorr to 50 mTorr. The effect of pressure and the percentage of BCl3 on the etching rate and surface smoothness of the bottom surface of the etched hole were studied for a fixed total flow rate. The etching rate was found to decrease with the percentage of BCl3, whereas the addition of BCl3 resulted in anisotropic holes with a smooth veil free bottom surface at a pressure of 30 mTorr and 42% BC13. In addition, variation of the etching yield with pressure and etching depth were also investigated.

Diagnosing the Fine Structure of Electron Energy Within the ECRIT Ion Source

The ion source of the electron cyclotron resonance ion thruster （ECRIT） extracts ions from its ECR plasma to generate thrust, and has the property of low gas consumption （2 seem, standard-state cubic centimeter per minute） and high durability. Due to the indispensable effects of the primary electron in gas discharge, it is important to experimentally clarify the electron energy structure within the ion source of the ECRIT through analyzing the electron energy distribution function （EEDF） of the plasma inside the thruster. In this article the Langmuir probe diagnosing method was used to diagnose the EEDF, from which the effective electron temperature, plasma density and the electron energy probability function （EEPF） were deduced. The experimental results show that the magnetic field influences the curves of EEDF and EEPF and make the effective plasma parameter nonuniform. The diagnosed electron temperature and density from sample points increased from 4 eV/2 ×10^16 m-3 to 10 eV/4×10^16 m-3 with increasing distances from both the axis and the screen grid of the ion source. Electron temperature and density peaking near the wall coincided with the discharge process. However, a double Maxwellian electron distribution was unexpectedly observed at the position near the axis of the ion source and about 30 mm from the screen grid. Besides, the double Maxwellian electron distribution was more likely to emerge at high power and a low gas flow rate. These phenomena were believed to relate to the arrangements of the gas inlets and the magnetic field where the double Maxwellian electron distribution exits. The results of this research may enhance the understanding of the plasma generation process in the ion source of this type and help to improve its performance.

Effectiveness of Radiofrequency Inductively Coupled Plasma Sources for Space Propulsion

Evolution of geometric forms of antenna coils for radiofrequency(RF)inductively coupled plasma(ICP)sources is analyzed.Top effectiveness of flat ICPSs generating plasma"tablet"is shown.Especially effective are ICPSs using antenna coils enhanced with ferromagnetic cores(FMICPS).It is found that the design of flat ICPSs is simpler and more convenient for the arrangement of plasma diagnostics in comparison with ICPSs of other geometries.Effective flat FMICPS models of different diameters ranging from 10 cm to 100cm are considered.Recommendations are given for development engineers dealing with ICPS devices in general and with radio frequency ion thrusters(RITs)in particular.

Impact of Initial Electron Development on Sodium Plasma Generation Using LIBORS Technique: Numerical Modeling

The present work reports an investigation on the role played by Na3+ ions formed through triatomic associative ionization collision of Na(4d) atoms with Na2 ground state molecules during the early phase of sodium plasma generation by laser ionization based on resonance saturation (LIBORS). Such ionization mechanism is observed experimentally for the first time by Tapalian and Smith (1993) [1]. In their experiment, stepwise atomic excitations are created using two CW dye lasers;one laser is tuned to 589 nm to excite the Na(3s) to Na(3p) D2 transition of sodium and the other laser is tuned 569 nm to excite the Na(3p) to Na(4d) transition. The analysis is grounded on a numerical study of the role of seed electron processes on the temporal evolution of sodium plasma formation by laser irradiation. A previously developed numerical model based on LIBORS technique is modified and adopted. In the present study, the sodium atom is treated as an atom comprises 22 levels namely: a ground state, 18 excited states and three ionic states (atomic, molecular and tri-atomic). The model tackled various collisional and radiative processes that act to enhance and deplete the free electrons generated in the interaction region. The contribution of these processes is signified by solving numerically a system of time-dependent rate equations, which couple the generated atomic and ionic species with the laser fields. Meanwhile, it solves the time-dependent Boltzmann equation for the electron energy distribution function (EEDF) of the generated electrons. The computed values of the EEDF, time evolution of both excited states population and the formed ionic species considering the individual effect of associative ionization, Penning, and photo-ionization and triatomic associative ionization justified the important effect of each of these ionizing processes in creating the early stage electrons. These seed electrons are assumed to rapidly gain energy through superelastic collisions leading eventually to plasma development.

Cold Fusion Based on Matter-Antimatter Plasma Formed in Molecular Crystals

The main purpose of this work is to shed light on the possibility of producing huge amount of energy based on the construction matter-antimatter plasma in a molecular crystal. It is assumed that two beams of isothermal hydrogen and antihydrogen are injected into a palladium crystal leading to a plasma state composed of particles and antiparticles. The collapse of this state releases a huge amount of energy which can be used as fuel for space shuttles. Thus, the novel system of isothermal pressure interaction enhances the energy power carried out by the quantum ion acoustic soliton (QIAS). In addition to the energy power released from the particle-antiparticle annihilation. The probability of merging the energy from these two cases is available at certain condition. The released energy may be a significant step in solving the energy scape of Tokomak to produce fusion energy. The study starting from the one-dimensional quantum hydrodynamic model (in which the term of electron-positron and proton-antiproton for hydrogen-antihydrogen is included), a Korteweg de Vries equation (kdv) is derived, the QIAS energy experiences and the annihilation energy power are calculated. It is found that the total energy of QIAS and the energy resulting from hydrogen-antihydrogen annihilation are important step towards the establishment of a cold fusion power station.

带有射频偏压源的感性耦合Ar/O_(2)/Cl_(2)等离子体放电的混合模拟研究

在刻蚀工艺中,通常会在感性耦合等离子体源的下极板上施加偏压源,以实现对离子能量和离子通量的独立调控.本文采用整体模型双向耦合一维流体鞘层模型,在Ar/O_(2)/Cl_(2)放电中,研究了偏压幅值和频率对等离子体特性及离子能量角度分布的影响.研究结果表明:当偏压频率为2.26 MHz时,随着偏压的增加,除了Cl^(–)离子和ClO^(+)离子的密度先增加后降低最后再增加外,其余带电粒子、O原子和Cl原子的密度都是先增加后基本保持不变最后再增加.当偏压频率为13.56和27.12 MHz时,除了Cl^(–)离子和Cl^(+)_(2)离子外,其余粒子密度随偏压的演化趋势与低频结果相似.随着偏压频率的提高,在低偏压范围内(<200 V),由于偏压源对等离子体加热显著增加,导致了带电粒子、O原子和Cl原子的密度增加;而在高偏压范围内(>300 V),由于偏压源对等离子体加热先减弱后增强,导致除了Cl^(+)_(2)离子和Cl^(–)离子外,其余带电粒子、O原子和Cl原子的密度都是先下降后增加的.此外,随着偏压频率的增加,离子能量分布中的高能峰和低能峰彼此靠近,离子能峰间距变窄,并最终变成单峰结构.本文的结论对于优化等离子体刻蚀工艺具有重要意义.

Electron beam ion traps and their applications

A brief introduction to the historical background and current status of electron beam ion traps (EBITs)is presented. The structure and principles of an EBIT for producing highly charged ions are described. Finally,EBITs as a potential tool in hot-plasma diagnostics and in studying frontier problems of highly charged ion physicsare discussed.

Numerical Investigation of the Tri-Atomic Ions Formation during Laser Ionization Based on Resonance Saturation

We present a theoretical investigation of plasma generation in sodium vapor induced by laser radiation tuned to the first resonance line (3S-3P) at λ = 589 ns. A set of rate equations that describe the rate of change of the ground and excited states population as well as the temporal variation of the electron energy distribution function (EEDF), beside the formed atomic ion Na+, molecular ion ?and tri-atomic ions are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities under the experimental conditions of Tapalian and Smith (1993) to test the existence of the formed tri-atomic ions. The numerical calculations of the electron energy distribution function (EEDF) show that a deviation from the Maxwellian distribution due to the super elastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Horn- beck ionization processes for producing , the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

DC放电Plasma动态扫描三探针系统

本文介绍了静电三探针的诊断原理,发展了一套用于等离子体诊断的动态扫描三探针实验系统。该系统可记录探针的伏安特性曲线及其二阶导数,测量等离子体的电子密度,电子温度和电子能量分布函数。分析了该系统的实验精度,给出了三探针诊断系统应用于HLD-30型辉光放电离子源内等离子体特性测量的实验结果。

极化效应对Bohr速度能区O^(5+)离子在低密度氢等离子体中的能损影响

基于HIRFL加速器装置的低能束实验平台,实验测量了1.07 MeV(~66.9 keV/u)高电荷态O^(5+)离子穿过中性氢气和部分电离的低密度氢等离子体靶后的能量损失,观测到等离子体中离子能损减小的新实验现象.分别考虑部分电离等离子体对炮弹离子的电荷屏蔽效应以及靶区原子的极化效应(Barkas修正),重新计算了离子能损,讨论了离子能损减小的可能物理机制.研究结果表明:在部分电离的低密度等离子体中,靶区的原子极化效应将显著影响Bohr速度能区离子的能量损失过程.

近玻尔速度能区高电荷态离子与激光等离子体相互作用实验研究装置

近玻尔速度能区高电荷态离子在稠密等离子体中的能量损失是强流重离子束驱动的高能量密度物理等前沿研究中的核心物理问题之一.基于中国科学院近代物理研究所的320 kV实验平台,新建立了一套近玻尔速度能区离子束与激光等离子体相互作用的实验研究装置,用于开展高精度的离子能量损失和电荷态研究.本文将详细介绍该装置的特点,包括脉冲离子束(≥200 ns)的产生与调控、高密度(10^(17)—10^(21)cm^(–3))激光等离子体靶的制备、等离子体参数诊断与离子的高精度测量(<1%)等.基于该装置已开展了百keV的质子束和4 MeV的Xe^(15+)离子束与激光Al等离子体靶相互作用的实验,并取得了相应的结果.本实验装置能够为中国在近玻尔速度能区高电荷离子与稠密激光等离子体相互作用研究提供高精度的实验数据,以促进理论工作的发展.

亚波长多功能微纳米结构制造及性能分析

利用等效介质理论计算出区熔硅微纳米结构的几何尺寸,然后在有限元模拟的基础上建立了光学模型。研究了在长波红外(8~12μm)范围内的抗反射效果,并分别分析了表面形貌和结构特征尺寸对透射率的影响。通过自由基等离子源刻蚀技术和低能量离子束刻蚀技术联合制备的方式,在硅表面形成了具有抗反射自清洁功能的微纳米复合结构。测得其透射率为78%,静态接触角为125.77°,并对所得结构进一步分析,实验结果表明:在长波红外范围微纳米复合结构的抗反射性能优于仅存在单一微米结构时,且纳米级别的微结构对红外波段减反射作用并不明显,微米结构是提升硅材料表面长波红外范围透射率的主要因素;具有微纳复合结构的材料表面张力大于单一微/纳米结构,与理论模拟结果一致,表明微纳米结构的存在能够有效改善硅表面的疏水能力。