Preliminary results of optical emission spectroscopy by line ratio method in the RF negative ion source at ASIPP

Optical emission spectroscopy (OES) using the trace rare gases of Ar and Xe have been carried out in a radio frequency (RF) driven negative ion source at Institute of Plasma Physics, Chinese Academy of Science (ASIPP), in order to determine the electron temperature and density of the hydrogen plasma. The line-ratio methods based on population models are applied to describe the radiation process of the excited state particles and establish their relations with the plasma parameters. The spectral lines from the argon and xenon excited state atoms with the wavelength of 750.4 and 828.0 nm are used to calculate the electron temperature based on the corona model. The argon ions emission lines with the wavelength of 480 and 488 nm are selected to calculate the electron density based on the collisional radiative model. OES has given the preliminary results of the electron temperature and density by varying the discharge gas pressure and RF power. According to the experimental results, the typical plasma parameters is T_e ≈ 2–4 eV and n_e ≈ 1×10 ¹⁷– 8×10¹⁷ m⁻³ in front of plasma grid.     

Experimental study of density pump-out on EAST

In the experimental advanced superconducting tokamak,density pump-out phenomena were observed by using a multi-channel polarimeter-interferometer system under different heating schemes of ion cyclotron resonant heating,electron cyclotron resonance heating,and neutral beam injection.The density pump-out was also induced with application of resonant magnetic perturbation,accompanied with a degradation of particle confinement.For the comparison analysis in all heating schemes,the typical plasma parameters are plasma current 400 k A,toroidal field 2 T,and line average density 2?×?10~(19)m~(-3).The experimental results show that the degree of pump-out is concerned with electron density and heating power.Low density deuterium low confinement(L-mode) plasmas(3.5?×?10~(19)m~(-3)) show strong pump-out effects.The density pump-out correlated with a significant drop of particle confinement.     

Plasma effects on the bacteria Escherichia coli via two evaluation methods

The degradation of?Escherichia coli?bacteria?by treatment with?cold,?weakly ionised, highly dissociated oxygen plasma,?with?an?electron temperature of 3 e V, a?plasma density of 8?×?10~(15)m~(-3) and a?neutral oxygen atom density of 3.5?×?1021m~(-3) was studied. To determine the ‘real' plasma effects,?two methods were used for evaluation and determination, as well as a comparison of the number of?bacteria that had?survived: the standard plate count technique(PCT) and?advanced fluorescence-activated cell sorting(FACS). Bacteria were deposited onto glass substrates and kept below 50 °C during the experiments with oxygen plasma. The results showed that the?bacteria had?fully degraded after about 2 min of plasma treatment, depending slightly on the amount of bacteria that had been?deposited on the substrates. The very?precise determination of the O flux on?the substrates and the two-method comparison allowed for the determination of the critical dose of oxygen atoms required for the destruction of a bacterial cell wall—about 6?×?10~(24)m~(-2)—as well as deactivation of the substrates—about 8?×?1025m~(-2).These results were taken in order to discuss other results obtained by comparable studies and scientific method?evaluations in the determination of plasma effects on bacteria.     

Investigation on the characteristics of an atmospheric-pressure microplasma plume confined inside a long capillary tube

An atmospheric-pressure microplasma plume of diameter 10 μm is generated inside a long tube. The length of the microplasma plume reaches as much as 2 cm. First, with the assistance of an air dielectric barrier discharge (DBD), the ignition voltage of the microplasma decreases from 40 kV to 23.6 kV. Second, although the current density reaches as high as (1.2−7.6)×10⁴ A cm ⁻² , comparable to the current density in transient spark discharge, the microplasma plume is non- thermal. Third, it is interesting to observe that the amplitude of the discharge current in a positive cycle of applied voltage is much lower than that in a negative cycle of applied voltage. Fourth, the electron density measured by the Stark broadening of Ar spectral line 696.5nm reaches as high as 3×10¹⁶ cm⁻³ , which yields a conductivity of the microplasma column of around 48 S m⁻¹ . In addition, the propagation velocity of the microplasma plume, obtained from light signals at different axial positions, ranges from 1×10⁵ m s ⁻¹ to 5×10 ⁵ m s⁻¹ . A detailed analysis reveals that the surface charges deposited on the inner wall exert significant influence on the discharge behavior of the microplasma.     

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 sccm,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.     

Time-Resolved Optical Emission Spectroscopy Diagnosis of CO2 Laser-Produced SnO2 Plasma

The spectral emission and plasma parameters of SnO_2 plasmas have been investigated.A planar ceramic SnO_2 target was irradiated by a CO2 laser with a full width at half maximum of 80 ns.The temporal behavior of the specific emission lines from the SnO_2 plasma was characterized.The intensities of Sn I and Sn II lines first increased,and then decreased with the delay time.The results also showed a faster decay of Sn I atoms than that of Sn II ionic species.The temporal evolutions of the SnO_2 plasma parameters(electron temperature and density) were deduced.The measured temperature and density of SnO_2 plasma are 4.38 eV to0.5 eV and 11.38×10~(17) cm~(-3) to 1.1×10~(17) cm~(-3),for delay times between 0.1 μs and 2.2 μs.We also investigated the effect of the laser pulse energy on SnO_2 plasma.     

Release of tritium from boron carbide irradiated with reactor neutrons

The release of tritium from irradiated boron carbide in a pure Ar atmosphere was investigated between 500 and 900°C. The sintered B₄C samples with densities between 75 and 95% of the theoretical density were irradiated with reactor neutrons with total neutron doses up to 5 × 10²⁰/cm². Effective diffusion coefficients, D_eff, were derived from the release data using the model “diffusion out of a sphere”. D_eff decreases by about 3 orders of magnitude with increasing total neutron dose, levels off at about 10¹⁸n/cm² and increases at very high doses ( > 10²⁰ n/cm²). The decrease in the tritium mobility is attributed to the radiation defects formed in the B₄C. The activation energy of 210 ± 30 kJ/mol for the tritium diffusion in the irradiated B₄C is much higher than the value found for unirradiated material. D_eff depends also very strongly on the density of the sintered material.     

Design of Q-band FMCW reflectometry for electron density profile measurement on the Joint TEXT tokamak

The Q-band(33-50 GHz) fast sweep frequency modulated continuous wave(FMCW)reflectometry has been recently developed for electron density profile measurement on the Joint TEXT tokamak.It operates in ordinary mode(O-mode) with a 20 μs sweeping period,covering the density range from 1 × 10~(19) m~(-3) to 3 × 10~(19) m~(-3).On the bench test,a Yttrium Iron Garnet(YIG) filter is used for the dynamic calibration of the voltage controlled oscillator(VCO) to obtain a linear frequency sweep.Besides,the use of a power combiner helps to improve the sideband suppression level of the single side-band modulator(SSBM).The reconstructed density profiles are presented,which demonstrate the capability of the reflectometry.     

Plasma density measurement and downstream etching of silicon and silicon oxide in Ar/NF3 mixture remote plasma source

In this study, plasma density measurements were performed near the plume region of the remote plasma source (RPS) in Ar/ NF₃ gas mixtures using a microwave cutoff probe. The measured plasma density is in the range of 10 ¹⁰ –10 ¹¹ cm ⁻³ in the discharge conditions with RPS powers of 2–4 kW and gas pressures of 0.87–4 Torr. The plasma density decreased with increasing gas pressures and RPS powers under various Ar/ NF₃ mixing ratios. This decrease in the plasma density measured at the fixed measurement position (plume region) can be understood by the reduction of the electron energy relaxation length with increases in the gas pressures and mixing ratio of NF₃/(Ar / NF₃). We also performed downstream etching of silicon and silicon oxide films in this system. The etch rate of the silicon films significantly increases while the silicon oxide is slightly etched with the gas pressures and powers. It was also found that the etch rate strongly depends on the wafer position on the processing chamber electrode, and that the etch selectivity reached 96–131 in the discharge conditions of RF powers (3730–4180 W) and gas pressures (3.6–4 Torr).     

Preparation of High Specific Activity Strontium-89 Solution in High Flux Engineering Test Reactor

⁸⁹SrCl₂ is an important radioactive drug for the bone metastasis. It is included in the new pharmacopoeia in 2015 and has a promising future in the market. Depending on the high flux engineering test reactor(HFETR), the process of preparation of high specific activity⁸⁹SrCl₂ solution by nuclear reaction ⁸⁸Sr(n, γ)⁸⁹Sr was studied. High purity enriched⁸⁸SrCO₃ was used as target material and irradiated for 56 days under the condition of thermal neutron fluence rate about 2×10¹⁴ n•cm^-2•s^-1. After dissolution and filtration, the colorless⁸⁹SrCl2 solution was obtained. The specific activity of⁸⁹SrCl₂ solution was 7.77×10⁹-1.08×10¹⁰ Bq•g^-1, the activity concentration was 3.59×10⁸-1.21×10⁹ Bq•mL^-1, the gamma impurity content was 0.11%-0.14%, the Al impurity content was much lower than 2 μg•mL^-1(activity concentration 7.4×10⁷ Bq• mL^-1).⁸⁹SrCl₂ solution had been tested to meet the requirements of the industry and could be used as raw material for the production of injection. The development of single 7.4×10¹⁰ Bq level preparation device of high purity and high specific activity of ⁸⁹Sr had been finished. This research is important for localization of isotope products.     

A comparison of emissive and cold floating probe techniques for electric potential measurements in rf inductive discharge

A cold floating probe method was compared with the emissive floating probe method in terms of a low-pressure radio-frequency inductive discharge. The dependences of difference between the plasma potential and the floating potential on the electron temperature 1–8 eV, plasma density 10⁹ –10¹² cm⁻³ and magnetic field 100–650 G were obtained. It was demonstrated that the difference between the potentials that obtained by these two methods can differ significantly from the expected value of 5.2 kT_e/e for argon.     

Ion beam induced nucleation in amorphous GaAs layers during MeV implantation

To investigate the nonlinear dose dependence of the thickness of the recrystallized layer during ion beam induced epitaxial recrystallization at amorphous/crystalline interfaces GaAs samples were irradiated with 1.0 MeV Ar⁺, 1.6 MeV Ar⁺ or 2.5 MeV Kr⁺ ions using a dose rate of 1.4 × 10¹² cm⁻² s⁻¹ at temperatures between 50°C and 180°C. It has been found that the thickness of the recrystallized layer reaches a maximum value at T_max = 90°C and 135°C for the Ar⁺ and Kr⁺ implantations, respectively. This means that the crystallization rate deviates from an Arrhenius dependence due to ion beam induced nucleation and growth within the remaining amorphous layer. The size of the crystallites depends on the implantation dose. This nucleation and growth of the crystallites disturbes and at least blocks the interface movement because the remaining surface layer becomes polycrystalline. Choosing temperatures sufficiently below T_max the thickness of the recrystallized layer increases linearly with the implantation dose indicating that the irradiation temperature is too low for ion induced nucleation.     

Study of the key factors affecting the triple grid lifetime of the LIPS-300 ion thruster

In order to ascertain the key factors affecting the lifetime of the triple grids in the LIPS-300 ion thruster,the thermal deformation,upstream ion density and component lifetime of the grids are simulated with finite element analysis,fluid simulation and charged-particle tracing simulation methods on the basis of a 1500 h short lifetime test.The key factor affecting the lifetime of the triple grids in the LIPS-300 ion thruster is obtained and analyzed through the test results.The results show that ion sputtering erosion of the grids in 5 kW operation mode is greater than in the case of 3 kW.In 5 kW mode,the decelerator grid shows the most serious corrosion,the accelerator grid shows moderate corrosion,and the screen grid shows the least amount of corrosion.With the serious corrosion of the grids in 5 kW operation mode,the intercept current of the acceleration and deceleration grids increases substantially.Meanwhile,the cold gap between the accelerator grid and the screen grid decreases from 1 mm to 0.7 mm,while the cold gap between the accelerator grid and the decelerator grid increases from 1 mm to 1.25 mm after 1500 h of thruster operation.At equilibrium temperature with 5 k W power,the finite element method(FEM)simulation results show that the hot gap between the screen grid and the accelerator grid reduces to 0.2 mm.Accordingly,the hot gap between the accelerator grid and the decelerator grid increases to 1.5 mm.According to the fluid method,the plasma density simulated in most regions of the discharge chamber is 1?×?10~(18)-8?×?10~(18)m~(-3).The upstream plasma density of the screen grid is in the range 6?×?10~(17)-6?×?10~(18)m~(-3)and displays a parabolic characteristic.The charged particle tracing simulation method results show that the ion beam current without the thermal deformation of triple grids has optimal perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 5.5?×?10~(-14)kg s~(-1)and 4.28?×?10~(-14)kg s~(-1),respectively,while after the thermal deformation of the triple grids,the ion beam current has over-perveance status.The ion sputtering rates of the accelerator grid hole and the decelerator hole are 1.41?×?10~(-13)kg s~(-1)and 4.1?×?10~(-13)kg s~(-1),respectively.The anode current is a key factor for the triple grid lifetime in situations where the structural strength of the grids does not change with temperature variation.The average sputtering rates of the accelerator grid and the decelerator grid,which were measured during the 1500 h lifetime test in5 k W operating conditions,are 2.2?×?10~(-13)kg s~(-1)and 7.3?×?10~(-13)kg s~(-1),respectively.These results are in accordance with the simulation,and the error comes mainly from the calculation distribution of the upstream plasma density of the grids.     

Ion implantation doping and electrical conductivity enhancement of C60 films

Pristine C₆₀ films sublimed onto sheet mica were implanted with 20 keV K⁺ ions and I⁺ ions at doses of 1.0 × 10¹⁶/cm², 3.0 × 10¹⁶/cm² and 5.0 × 10¹⁶/cm², and with 20 keV Ar⁺ ions at a dose of 5.0 × 10¹⁶/cm². The distributions of dopants were studied using Rutherford backscattering spectrometry (RBS). The temperature dependence of sheet resistivity of the films was investigated applying a four-probe system. It was proposed that the conductivity enhancement of K⁺ implanted C₆₀ films was due to the implanted ions in the films, while for I⁺ implanted C₆₀ films, both implanted I⁺ ions and irradiation effects of the ions contributed to the enhancement of conductivity.     

Ion beam enhanced etching of LiNbO3

Single crystals of z- and x-cut LiNbO₃ were irradiated at room temperature and 15 K using He⁺- and Ar⁺-ions with energies of 40 and 350 keV and ion fluences between 5 × 10¹² and 5 × 10¹⁶ cm⁻². The damage formation investigated with Rutherford backscattering spectrometry (RBS) channeling analysis depends on the irradiation temperature as well as the ion species. For instance, He⁺-irradiation of z-cut material at 300 K provokes complete amorphization at 2.0 dpa (displacements per target atom). In contrast, 0.4 dpa is sufficient to amorphize the LiNbO₃ in the case of Ar⁺-irradiation. Irradiation at 15 K reduces the number of displacements per atom necessary for amorphization. To study the etching behavior, 400 nm thick amorphous layers were generated via multiple irradiation with He⁺- and Ar⁺-ions of different energies and fluences. Etching was performed in a 3.6% hydrofluoric (HF) solution at 40 °C. Although the etching rate of the perfect crystal is negligible, that of the amorphized regions amounts to 80 nm min⁻¹. The influence of the ion species, the fluence, the irradiation temperature and subsequent thermal treatment on damage and etching of LiNbO₃ are discussed.     

Effect of N_2 and O_2 on OH radical production in an atmospheric helium microwave plasma jet

UV-pulsed laser cavity ringdown spectroscopy of the hydroxyl radical OH(A–X)(0–0)band in the wavelength range of 306–310 nm was employed to determine absolute number densities of OH in the atmospheric helium plasma jets generated by a 2.45 GHz microwave plasma source.The effect of the addition of molecular gases N_2 and O_2 to He plasma jets on OH generation was studied.Optical emission spectroscopy was simultaneously employed to monitor reactive plasma species.Stark broadening of the hydrogen Balmer emission line(H_β)was used to estimate the electron density nein the jets.For both He/N_2 and He/O_2 jets, newas estimated to be on the order of 10~(15)cm~(-3).The effects of plasma power and gas flow rate were also studied.With increase in N_2 and O_2 flow rates, netended to decrease.Gas temperature in the He/O_2 plasma jets was elevated compared to the temperatures in the pure He and He/N_2 plasma jets.The highest OH densities in the He/N_2 and He/O_2 plasma jets were determined to be 1.0?×10~(16)molecules/cm~3 at x?=?4 mm(from the jet orifice)and 1.8?×?10~(16)molecules/cm~3 at x=3 mm, respectively.Electron impact dissociation of water and water ion dissociative recombination were the dominant reaction pathways, respectively, for OH formation within the jet column and in the downstream and far downstream regions.The presence of strong emissions of the N_2~+ bands in both He/N_2 and He/O_2 plasma jets, as against the absence of the N_2~+ emissions in the Ar plasma jets, suggests that the Penning ionization process is a key reaction channel leading to the formation of N_2~+ in these He plasma jets.     

Mechanism of high growth rate for diamond-like carbon films synthesized by helicon wave plasma chemical vapor deposition

A high growth rate fabrication of diamond-like carbon(DLC)films at room temperature was achieved by helicon wave plasma chemical vapor deposition(HWP-CVD)using Ar/CH_4gas mixtures.The microstructure and morphology of the films were characterized by Raman spectroscopy and scanning electron microscopy.The diagnosis of plasma excited by a helicon wave was measured by optical emission spectroscopy and a Langmuir probe.The mechanism of high growth rate fabrication for DLC films by HWP-CVD has been discussed.The growth rate of the DLC films reaches a maximum value of 54μm h~(-1)at the CH_4flow rate of 85 sccm,which is attributed to the higher plasma density during the helicon wave plasma discharge.The CH and H_αradicals play an important role in the growth of DLC films.The results show that the H_αradicals are beneficial to the formation and stabilization of C=C bond from sp~2to sp~3.     

Argon irradiation damage at a Cu/Al2O3 interface for different alumina structures

The evolution of damages at a Cu/Al₂O₃ device interface after Ar⁺ irradiation, depending on alumina structure, and the effect of surface roughness on sputtering have been studied. A polycrystalline Cu/Al₂O₃ bilayer and polycrystalline Cu on amorphous alumina were irradiated with 400 keV Ar⁺ ion beam at doses ranging from 5 × 10¹⁶ to 10¹⁷ Ar⁺/cm² at room temperature. The copper layer thicknesses were between 100 and 200 nm. RBS analysis was used to characterize the interface modification and to deduce the sputtering yield of copper. The SEM technique was used to control the surface topography. A RBS computer simulation program was used to reproduce experimental spectra and to follow the concentration profile evolutions of different elements before and after ion irradiation. A modified TRIM calculation program which takes into account the sputtering yield evolution as well as the concentration variation versus dose gives a satisfactory reproduction of the experimental argon distribution. The surface roughness effect on sputtering and the alumina structure influence at the interface on mixing mechanisms are discussed.     

LiH和LiT与H2O反应机理研究

氢材料在微量H₂O、CO₂、O₂和N₂存在下可能发生物理化学反应,使材料的物理品位下降。由于反应过程十分复杂,很难从实验上准确获取这类反应的最佳通道和具体产物信息,因此,从理论上研究氢材料分子的物理化学性质及其化学反应机制,了解化学反应过程具有十分重要的意义。本文使用Gaussian03软件包和Gaussview工具软件,在6-311G(d)全电子基函数水平上,应用二阶微扰理论优化得到了⁶LiH、⁶LiT与H₂O反应的中间体、过渡态及产物的结构,总能量,振动频率和零点能等。通过计算发现⁶LiH、⁶LiT均只有1个反应通道,⁶LiH与H₂O反应的焓变、活化能和反应速率常数分别为-156.99 kJ/mol、8.95 kJ/mol和3.75×10¹⁰(mol•dm^-3)^-1/s,⁶LiT与H₂O反应的焓变、活化能和反应速率常数分别为-159.02 kJ/mol、9.92 kJ/mol和1.72×10¹⁰ (mol•dm^-3)^-1/s。     

Surface morphology of the Ar ion-irradiated Ag/Si(1 1 1) system

In the present study, a 500 Å thin Ag film was deposited by thermal evaporation on 5% HF etched Si(1 1 1) substrate at a chamber pressure of 8×10⁻⁶ mbar. The films were irradiated with 100 keV Ar⁺ ions at room temperature (RT) and at elevated temperatures to a fluence of 1×10¹⁶ cm⁻² at a flux of 5.55×10¹² ions/cm²/s. Surface morphology of the Ar ion-irradiated Ag/Si(1 1 1) system was investigated using scanning electron microscopy (SEM). A percolation network pattern was observed when the film was irradiated at 200°C and 400°C. The fractal dimension of the percolated pattern was higher in the sample irradiated at 400°C compared to the one irradiated at 200°C. The percolation network is still observed in the film thermally annealed at 600°C with and without prior ion irradiation. The fractal dimension of the percolated pattern in the sample annealed at 600°C was lower than in the sample post-annealed (irradiated and then annealed) at 600°C. All these observations are explained in terms of self-diffusion of Ag atoms on the Si(1 1 1) substrate, inter-diffusion of Ag and Si and phase formations in Ag and Si due to Ar ion irradiation.