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.     

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.     

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma(HWP)source device in a high axial magnetic field(B_0)developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure(5?×?10~(-3)?-?10 Pa)and a RF(radio frequency,13.56 MHz)power(maximum power of 2 k W)using an internal right helical antenna(5 cm in diameter by 18 cm long)with a maximum B_0of 6300 G.Ar HWP with electron density~10~(18)–10~(20)m~(-3)and electron temperature~4–7 e V was produced at high B_0 of 5100 G,with an RF power of 1500 W.Maximum Ar~+ion flux of 7.8?×?10~(23)m~(-2)s~(-1)with a bright blue core plasma was obtained at a high B_0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar~+ion-beams of 40.1 eV are formed,which are supersonic(~3.1c_s).The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1?×?10~(24)N_2/m~2 h.     

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.     

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.     

Exposure of Equal-Channel Angular Extruded Tungsten to Deuterium Plasma

Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing(ECAP) have been examined after exposure to a low energy,high-flux deuterium(D) plasma at fluences of 3×10~(24) D/m~2 and 1×10~(25) D/m~2 in a temperature range of 100 ℃-150 ℃.The methods used were scanning electron microscopy(SEM) and thermal desorption spectroscopy(TDS).Sparse and small blisters(~0.1 μm) were observed by SEM after D plasma irradiation on every irradiated surface;yet they did not exhibit significant structure or plasma fluence dependence.Larger blisters or protrusions appeared after subsequent TDS heating up to 1000 ℃.The TDS results showed a single D desorption peak at ~220℃ for all samples and the D retention increased with increasing numbers of extrusion passes,i.e.,the decrease of grain sizes.The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.     

Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity

Two experimental techniques have been used to quantify the atomic oxygen density in the case of hot air plasma generated by a microwave (MW) resonant cavity. The latter operates at a frequency of 2.45 GHz inside a cell of gas conditioning at a pressure of 600 mbar, an injected air flow of 12 L/min and an input MW power of 1 kW. The first technique is based on the standard two photon absorption laser induced fluorescence (TALIF) using xenon for calibration but applied for the first time in the present post discharge hot air plasma column having a temperature of about 4500 K near the axis of the nozzle. The second diagnostic technique is an actinometry method based on optical emission spectroscopy (OES). In this case, we compared the spectra intensities of a specific atomic oxygen line (844 nm) and the closest wavelength xenon line (823 nm). The two lines need to be collected under absolutely the same spectroscopic parameters. The xenon emission is due to the addition of a small proportion of xenon (1% Xe) of this chemically inert gas inside the air while a further small quantity of H₂ (2%) is also added in the mixture in order to collect OH(A¬X) and NH(A-X) spectra without noise. The latter molecular spectra are required to estimate gas and excitation temperatures. Optical emission spectroscopy measurements, at for instance the position z=12 mm on the axis plasma column that leads to a gas measured temperature equal to 3500 K, an excitation temperature of about 9500 K and an atomic oxygen density 2.09×1017± 0.2×10¹⁷ cm ⁻³ . This is in very good agreement with the TALIF measurement, which is equal to 2.0×10¹⁷ cm ⁻³ .     

Oxide Coated Cathode Plasma Source of Linear Magnetized Plasma Device

Plasma source is the most important part of the laboratory plasma platform for fundamental plasma experimental research. Barium oxide coated cathode plasma source is well recognized as an effective technique due to its high electron emission current. An indirectly heated oxide coated cathode plasma source has been constructed on a linear magnetized plasma device. The electron emission current density can reach 2 A/cm 2 to 6 A/cm ² in pulsed mode within pulse length 5–20 ms. A 10 cm diameter, 2 m long plasma column with density 10 ¹⁸ m ⁻³ to 10 ¹⁹ m ³ and electron temperature T_e ≈ 3–7 eV is produced. The spatial uniformity of the emission ability is less than 4% and the discharge reproducibility is better than 97%. With a wide range of the plasma parameters, this kind of plasma source provides great flexibility for many basic plasma investigations. The detail of construction and initial characterization of oxide coated cathode are described in this paper.     

High-energy-density electron beam generation in ultra intense laser-plasma interaction

By using a two-dimensional particle-in-cell simulation,we demonstrate a scheme for highenergy-density electron beam generation by irradiating an ultra intense laser pulse onto an aluminum(Al) target.With the laser having a peak intensity of 4?×?1023W cm~(-2),a high quality electron beam with a maximum density of 117 ncand a kinetic energy density up to8.79?×?1018J m~(-3) is generated.The temperature of the electron beam can be 416 Me V,and the beam divergence is only 7.25°.As the laser peak intensity increases(e.g.,1024 W cm~(-2)),both the beam energy density(3.56?×?1019J m~(-3)) and the temperature(545 Me V) are increased,and the beam collimation is well controlled.The maximum density of the electron beam can even reach 180 nc.Such beams should have potential applications in the areas of antiparticle generation,laboratory astrophysics,etc.     

Insulation characteristics of triple mixtures of c-C4F8/N2/CO2 under lightning impulse voltage

This paper has researched the insulation characteristics of 10%c-C₄F₈/N₂/CO₂ mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C₄F₈/N₂/CO₂ gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF₆ and the comprehensive GWP is about 5% of SF₆ , and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF₆ , 10%c-C₄F₈/N₂/CO₂ gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.     

The effect of gas additives on reactive species and bacterial inactivation by a helium plasma jet

In this paper,the influences of gas doping(O_2,N_2,Air)on the concentrations of reactive species and bactericidal effects induced by a He plasma jet are studied.Firstly,results show that gas doping causes an increase in voltage and a decrease in current compared with the pure He discharge under the same discharge power,which might be attributed to the different chemical characteristics of O_2 and N_2 and verified by the changes in the gaseous reactive species shown in the optical emission spectroscopy(OES) and Fourier transform infrared(FTIR)spectroscopy.Secondly,the concentrations of aqueous reactive oxygen species(ROS) and reactive nitrogen species(RNS) are tightly related to the addition of O_2 and N_2 into the working gas.The concentrations of aqueous NO_2~- and NO_3~- significantly increase while the concentrations of aqueous ROS decrease with the admixture of N_2.The addition of O_2 has little effect on the concentrations of NO_2~- and NO_3~- and pH values; however,the addition of O_2 increases the concentration of O_2~- and deceases the concentrations of H_2O_2 and OH.Finally,the results of bactericidal experiments demonstrate that the inactivation efficiency of the four types of plasma jets is He?+?O_2??He+AirHeHe+N_2,which is in accordance with the changing trend of the concentration of aqueous O_2~-.Simultaneously to the better understanding of the formation and removal mechanisms of reactive species in the plasma–liquid interaction,these results also prove the effectiveness of regulating the concentrations of aqueous reactive species and the bacteria inactivation effects by gas doping.     

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.     

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).     

Fast and low-temperature elimination of organic templates from SBA-15 using dielectric barrier discharge plasma

Organic templates P-123 of mesoporous SBA-15 can be effectively removed in a few minutes (4min) by using the dielectric-barrier discharge (DBD) plasma technique at ambient pressure and low gas temperature (around 130°C). The mesoporous SBA-15 was characterized by FT-IR, ²⁹ Si solid sate NMR, TEM, XRD, TGA and N₂ adsorption/desorption isotherms. The as-made SBA-15 treated with DBD plasma exhibited a larger surface area of 790 m ²·g ⁻¹ with larger pores and microspore volume than samples prepared by using the conventional thermal calcination method (550 °C and 5h, 660 m ²·g ⁻¹ ). In addition to less shrinkage of the silica framework, the DBD-prepared SBA-15 showed significantly increased weight loss of 8.3% about 200 °C as compared with that of conventional calcination (5.5%), which is attributed mainly to the dehydroxylation by condensation of silanol groups.     

Scintillation properties of RbGd2Br7:Ce.Advantages and limitations

The scintillation properties of RbGd₂Br₇ crystals, doped with Ce³⁺ concentrations of 0.02, 0.11, 0.88, 2.05, 4.1, and 9.8%, are studied under X-ray and γ-quanta excitations. For the RbGd₂Br₇ sample doped with 9.8% Ce, the authors measured a light yield of 56000±6000 photons per MeV of absorbed γ-ray energy with a main decay time of 43±1 ns, using a Hamamatsu R1791 photomultiplier (PMT), a ¹³⁷Cs radioactive source, and a shaping time of 10 μs. A time resolution of 790±10 ps was measured for the RbGd₂Br₇:9.8% Ce compound, using BaF₂ as second scintillator, two XP2020Q PMTs, a ²²Na source, and an energy threshold set at E⩾511 keV. With the R1791 PMT, an energy resolution of 4.1% (FWHM over peak position) for the 662-keV full absorption peak has been observed for two crystals of 7×4×2 mm³ and 15×5×1 mm³ with 4.1 and 9.8% Ce content, respectively. Moreover, the nonproportional responses of three RbGd₂Br₇:Ce compounds with different concentrations (0.11, 2.05, and 9.8%) were studied revealing an almost-constant light output response from 17.4 keV to 1 MeV. These properties are compared to three other well-known scintillators: NaI:Tl, CsI:Tl, and Lu₂SiO₅:Ce     

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N_2

In this paper,unipolar pulse (including positive pulse and negative pulse) and bipolar pulse voltage are employed to generate diffuse gas–liquid discharge in atmospheric N_2with a rumpetshaped quartz tube.The current–voltage waveforms,optical emission spectra of excited state active species,FTIR spectra of exhaust gas components,plasma gas temperature,and aqueous H_2O_2,NO_2~-,andNO_3~-production are compared in three pulse modes,meanwhile,the effects of pulse peak voltage and gas flow rate on the production of reactive species are studied.The results show that two obvious discharges occur in each voltage pulse in unipolar pulse driven discharge,differently,in bipolar pulse driven discharge,only one main discharge appears in a single voltage pulse time.The intensities of active species (OH(A),and O(3p)) in all three pulsed discharge increase with the rise of pulse peak voltage and have the highest value at 200 ml min~(-1)of gas flow rate.The absorbance intensities of NO_2and N_2O increase with the increase of pulse peak voltage and decrease with the increase of gas flow rate.Under the same discharge conditions,the bipolar pulse driven discharge shows lower breakdown voltage,and higher intensities of excited species (N_2(C),OH(A),and O(3p)),nitrogen oxides (NO_2,NO,and N_2O),and higher production of aqueous H_2O_2,NO_2~-,andNO_3~-compared with both unipolar positive and negative discharges.     

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。     

Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234ze(E)(trans-1,3,3,3-tetrafluoropropene, chemical formula: C₃H₂F₄) is an extremely environmentally friendly SF₆ alternative gas with high electrical strength. In this paper, the partial discharge (PD) characteristics of HFO-1234ze(E)/N₂ mixtures were studied using the gas insulation test platform. The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested. Using SF₆/N₂ mixtures as a control group, the effects of electrode spacing, mixing ratio and pressure on the insulation performance of HFO-1234ze(E)/N₂ mixtures were explored. The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234ze(E) under short electrode spacing can reach 0.96–1.04 times of pure SF₆ under different pressures; the PD inception voltage of 40%HFO-1234ze(E)/60%N₂ mixtures at 0.3 MPa is 0.67–0.89 times that of SF₆/N₂ mixtures under the same conditions, which has great application prospect.     

On the green aurora emission of Ar atmospheric pressure plasma

The Ar atmospheric pressure plasma was found to be an excellent laboratorial source for green aurora emission. However, the characteristic and production mechanism of the green aurora emission of the Ar atmospheric pressure plasma are still not clear. In this work, an Ar plasma in a long glass tube which emits intense green aurora light is investigated. With the long glass tube, it can be concluded that the green aurora emission in the Ar plasma is not owing to the mixture of Ar plasma plume with the surrounding air. It is also found that the green aurora emission often appeared beyond the active electrode when the active electrode is placed at the downstream of the gas flow. The green emission disappears when the traces amount of O₂ or N₂ (about 0.05%–0.07%) is added to Ar. This is because the O₂ molecules deactivate the upper state O(1S), which results in the decrease of the green emission. On the other hand, when N₂ is added, Ar metastable atoms are quenched by N₂, which results in the decrease of O atoms and eventually leads to the decrease of the green emission intensity. The intensity of the green aurora emission increases when the driving voltage frequency increases from 1 to 10 kHz. More importantly, it is found that the green aurora emission is not affected when a grounded stainless steel needle is in contact with the plasma plume. Thus, the green emission is not driven electrically. All these findings are helpful for the understanding of the physics and its applications of atmospheric pressure plasma jet in space physics, laser physics and other application areas.     

Volume added surface barrier discharge plasma excited by bipolar nanosecond pulse power in atmospheric air: optical emission spectra influenced by gap distance

In this paper, volume barrier discharge with different gap distances is added on the discharge border of high-voltage electrode of annular surface barrier discharge for generating volume added surface barrier discharge (V-SBD) excited by bipolar nanosecond high-voltage pulse power in atmospheric air. The excited V-SBDs consist of surface barrier discharge (d=0 mm) and volume added surface barrier discharges (d=2 mm and 3 mm). The optical emission spectra are recorded for calculating emission intensities of N₂ (C ³Ⅱ_u →B³Π_g ) and N₂⁺ (B ²Σ_u⁺ → X ²Σ_g⁺ ), and simulating rotational and vibrational temperatures. The influences of gap distance of V-SBD on emission intensity and plasma temperature are also investigated and analyzed. The results show that d=0 mm structure can excite the largest emission intensity of N ₂ (C ³ Π_u →B ³Π_g ), while the existence of volume barrier discharge can delay the occurrence of the peak value of the emission intensity ratio of N₂⁺ (B ²Σ_u⁺ → X ²Σ_g⁺ )/N ₂(C³Π_u →B³Π_g ) during the rising period of the applied voltage pulse and weaken it during the end period. The increasing factor of emission intensity is effected by the pulse repetition rate. The d=3 mm structure has the highest threshold voltage while it can maintain more emission intensity of N₂(C³ Π _u →B ³Π_g ) than that of d=2 mm structure. The structure of d=2 mm can maintain more increasing factor than that of the d=3 mm structure with varying pulse repetition rate. Besides, the rotational temperatures of three V-SBD structures are slightly affected when the gap distance and pulse repetition rate vary. The vibrational temperatures have decaying tendencies of all three structures with the increasing pulse repetition rate.