Optical Emission Spectroscopic Studies of ICP Ar Plasma

The ion line of 434.8 nm and atom line of 419.8 nm of Ar plasma produced by an inductively coupled plasma （ICP） were measured by optical emission spectroscopy and the influences from the working gas pressure, radio-frequency （RF） power and different positions in the discharge chamber on the line intensities were investigated in this study. It was found that the intensity of Ar atom line increased firstly and then saturated with the increase of the pressure. The line intensity of Ar^＋, on the other hand, reached a maximum value and then decreased along with the pressure. The intensity of the line in an RF discharge also demonstrated a jumping mode and a hysteresis phenomenon with the RF power. When the RF power increased to 400 W, the discharge jumped from the E-mode to the H-mode where the line intensity of Ar atom demonstrated a sudden increase, while the intensity of Ar^＋ ion only changed slightly. If the RF power decreased from a high value, e.g., 1000 W, the discharge would jump from the H-mode back to the E-mode at a power of 300 W. At this time the intensities of Ar and Ar^＋ lines would also decrease sharply. It was also noticed in this paper that the intensity of the ion line depended on the detective location in the chamber, namely at the bottom of the chamber the line was more intense than that in the middle of the chamber, but less intense than at the top, which is considered to be related to the capacitance coupling ability of the ICP plasma in different discharge areas.     

Luminous Activity Study of a Long Atmospheric Pressure DBD Afterglow

The experimental work reported here is devoted to the study of the luminous activity of a long dielectric barrier discharge （DBD） afterglow at atmospheric pressure. The discharge plasma is generated in a commercially available （AcXys Technologies） reactor, using a N2 flow of a few tens SL/min, whereas the luminous afterglow when channelled into a quartz tube extends at a distance of 50 cm, finishing in a luminous arrow at the tube＇s exit. The luminous activity of the afterglow is studied by means of photomultiplier scans and optical emission spectroscopy, revealing an interesting transient phase. An attempt is made to correlate this effect with the active species＇ creation and destruction mechanisms.     

Spectrum Blueshifting of Ultrashort UV Laser Pulse Induced by Ionization of Supersonic He and Ar Gas Jets

The predominant spectral blueshifting of a sub-picosecond UV laser pulse induced by ultrafast ionization of noble gases was investigated. Spectral measurements were made at various gas densities. Typical quasi-periodic structures in the blueshifted spectrum were obtained. The observations were in connection with the so-called self-phase modulation of laser pulses in the ultrafast ionization process which was simply simulated with an ADK （Ammosov-Delone-Krainov） ionization model. Some quantitative information can be deduced from the measurements and calculations.     

Study on the Property Evolution of Atmospheric Pressure Plasma Jets in Helium简

Nowadays atmospheric pressure plasma jets （APPJs） are being widely applied to many fields and have received growing interests from cold plasma community. A helium APPJ with co-axial double ring electrode configuration is driven by an AC high voltage power with an adjustable frequency of 1-60 kHz. Experiments are conducted for acquiring the electrical and optical properties of APPJ, including the discharge mode, current peak＇s phase and APPJ＇s length, etc. Moreover, the actions of Penning effect on APPJ are discussed by adding impurity nitrogen into highly pure helium. The results may contribute to further research and aPPlications of APPJs.     

The Optical Diagnosis of Underwater Positive Sparks and Corona Discharges

In this paper, two types of underwater discharges, spark discharge and corona discharge, are investigated by optical diagnosis using a high speed framing camera （HSFC） with the framing time within nanoseconds under the same experimental conditions. In order to capture the photographs of streamer propagation, the influence of the randomicity of the prebreakdown duration is taken into consideration. By increasing the conductivity of water, the randomicity reduces effectively. Experimental results show that, for a spark discharge, the process can be separated into three stages： the generation and propagation of a streamer, the generation and expansion of the discharge channel, and the development and annihilation of the plasma. The streamers do not directly move to the opposite electrode, but form a bush-like figure. With the increase of the number of branches, the velocity of streamer propagation slows down. The trajectory of the initial channel between electrodes is not straight. However, with the channel expanding, its shape transforms into a straight column. For a corona discharge, there are two stages： the generation and propagation of a streamer, and the stagnation and annihilation of the streamer. The initial streamer in a corona discharge is generated later than in a spark discharge. The forms of streamers for both kinds of discharge are similar; however, streamers generated by a corona discharge propagate with a slower velocity and the number of branches is less compared with a spark discharge. When the energy injection stops, the luminescence of plasma inside the discharge channel （spark discharge） or streamers （corona discharge） becomes weaker and weaker, and finally disappears.     

A N2 Plasma Light Source Generated in Hollow Cathode Discharge and Its Application in Lithographic Plate Making

Computer to conventional plate （CTCP） technology is getting more and more attention in printing industries. In this paper we report a nitrogen plasma light source generated in hollow cathode discharge （HCD）, Which is used for pre-sensitivity （PS） plate exposure. The N2 molecule emits abundant spectrum ranging from 350 nm to 460 nm. With the voltage of 580 V, current of 1.8 A and pressure of 70 Pa in the discharge an optical power density of 0.46 mW/cm2 is obtained. The optical power density could be further increased with optimizing the lens system. The phototonus efficiency of this source is discussed in detail based upon the chemical principle and the FTIR analysis on the coating material.     

Balmer Hα,Hβ and Hγ Spectral Lines Intensities in High-Power RF Hydrogen Plasmas

Hα（Balmer-alpha）, Hβ （Balmer-beta） and Hγ （Balmer-gamma） spectral line inten- sities in atomic hydrogen plasma are investigated by using a high-power RF source. The intensities of the Hα, Hβ and Hγ spectral lines are detected by increasing the input power （0-6 kW） of ICPs （inductively coupled plasmas）. With the increase of net input power, the intensity of Hα im- proves rapidly （0-2 kW）, and then reaches its dynamic equilibrium; the intensities of Hβ can be divided into three processes： obvious increase （0-2 kW）, rapid increase （2-4 kW）, almost constant （4-6 kW）; while the intensities of Hγ increase very slowly. The energy levels of the excited hydro- gen atoms and the splitting energy levels produced by an obvious Stark effect play an important role in the results.     

Characterization of Nitrogen Glow Discharge Plasma via Optical Emission Spectrum Simulation

Optical emission spectroscopy in nitrogen glow discharge plasma is simulated, and the collision excitations and characteristic emissions of the species （N2, N2^＋, N^＋, N） are investigated by a Monte Carlo model for nitrogen molecular gas discharge. The excitation rates of the main excited states are calculated and the corresponding relation and relative magnitude between the distribution of excitation rate of a certain excited state and the distributions of the emission rates of various lines originating from this excited level are also explored. The simulated results are compared with the experimental measurements in two typical discharge conditions. The luminescence mechanism of the line N2^＋： 391.4 nm is explained based on the microscopic plasma processes. The cathode glow in N2 discharge is found to be mainly caused by N^＋ impact excitation and the intensity of cathode glow decreases with the voltage. The corresponding relation between the emission rate or intensity of the 391.4 nm line and the production rate and the density of N2^＋ is also examined.     

Glow Discharge Plasma Nitriding of AISI 304 Stainless Steel

Glow discharge plasma nitriding of AISI 304 austenitic stainless steel has been carried out for different processing time under optimum discharge conditions established by spectroscopic analysis. The treated samples were analysed by X-ray diffraction （XRD） to explore the changes induced in the crystallographic structure. The XRD pattern confirmed the formation of an expanded austenite phase （TN） owing to incorporation of nitrogen as an interstitial solid solution in the iron lattice. A Vickers microhardness tester was used to evaluate the surface hardness as a function of indentation depth （μm）. The results showed clear evidence of surface changes with substantial increase in surface hardness.     

Intermediate Gas Phase of CHa/[Si（CH3）2O]5 Plasma and Its Effect on Structure of SiCOH Film

This paper investigated the radical behaviour of the plasma of a mixture of methane （CH4） and decamethylcyclopentasiloxane （DMCPS） by optical emission spectroscopy. The plasma was generated by electron cyclotron resonance （ECR） discharge and was used for depositing porous SiCOH low dielectric-constant film. In the ECR discharge plasma, CH, H, H2, C2, Si, O and SiO radicals were obtained. The CH, H and C2 radicals were from the dissociation of CH4, while the SiO. Si and O radicals from the dissociation of the Si-O chain. CHx radicals absorbed in the film were thermally unstable and could be removed by annealing. The dissociation of the Si-O chain led to an increase in a ratio of the Si-Ocage to Si-Onetwork. The removed of CHx radicals and the increased Si-Ocage to Si-Onetwork ratio were beneficial for reducing the film density and dielectric constant.     

Atmospheric Pressure Plasma Jet in Organic Solution: Spectra,Degradation Effects of Solution Flow Rate and Initial pH Value

The organic compounds of p-nitrophenol （PNP） solution was treated by the active species generated in a stirred reactor by an atmospheric pressure plasma jet （APPJ）. The emission intensities of hydroxyl （OH）, oxygen （O）, nitric oxide （NO）, hydrogen （H） and molecular （N2） were measured by optical emission spectroscopy （OES）. The relations between the flow rates of the PNP solution and degradation, the degradation effects and initial pH value of the solution were also investigated. Experimental results show that there exist intense emissions of O （777.1 nm）, N（337.1 nm）, OH （306-310 nm） and NO band （200-290 nm） in the region of plasma. Given the treatment time and gas flow rate, the degradation increased as a function of discharge energy and solution flow rate, respectively. The solution flow rate for the most efficient degradation ranged from 1.414 m/s to 1.702 m/s, and contributed very little when it exceeded 2.199 m/s. This indicates the existence of diffusion-controlled reactions at a low solution flow rate and activation- controlled reactions at a high solution flow rate. Moreover, increasing or decreasing the initial pH value of neutral PNP solution （pH=5.95） could improve the degradation efficiency. Treated by APPJ, the PNP solutions with different initial pH values of 5.95, 7.47 and 2.78 turned more acidic in the end, while the neutral solution had the lowest degradation efficiency. This work clearly demonstrates the close coupling of active species, photolysis of ultraviolet, the organic solution flow rate and the initial pH value, and thus is helpful in the study of the mechanism and application of plasma in wastewater treatment.     

Preparation of Copper Nanoparticles Using Dielectric Barrier Discharge at Atmospheric Pressure and its Mechanism简

Dielectric barrier discharge （DBD） cold plasma at atmospheric pressure was used for preparation of copper nanoparticles by reduction of copper oxide （CuO）. Power X-ray diffraction （XRD） was used to characterize the structure of the copper oxide samples treated by DBD plasma. Influences of H2 content and the treating time on the reduction of copper oxide by DBD plasma were investigated. The results show that the reduction ratio of copper oxide was increased initially and then decreased with increasing H2 content, and the highest reduction ratio was achieved at 20% H2 content. Moreover, the copper oxide samples were gradually reduced by DBD plasma into copper nanoparticles with the increase in treating time. However, the average reduction rate was decreased as a result of the diffusion of the active hydrogen species. Optical emission spectra （OES） were observed during the reduction of the copper oxide samples by DBD plasma, and the reduction mechanism was explored accordingly. Instead of high-energy electrons, atomic hydrogen （H） radicals, and the heating effect, excited-state hydrogen molecules are suspected to be one kind of important reducing agents. Atmospheric-pressure DBD cold plasma is proved to be an efficient method for preparing copper nanoparticles.     

Development of a 4 MV Laser-Triggered Multi-Stage Switch

A 22-stage 4 MV laser-triggered multistage multi-channel switch （LTS） was designed according to the hypothesis that the well-proportioned electrical field distribution is helpful in reducing the jitter of delay. Field distribution in the switch section is regulated by a metal field regulation ring and several gradient rings. In order to reduce the jitter further, a SFB/N2 mixture is chosen as the switching medium. The generalized standard deviation of the self-breakdown voltage and the deviation of the average value from the prediction is less than 4.4% and 13% respectively. Linearity of the self-breakdown voltage is better than 0.95. Triggered by a laser pulse of 35 mJ/3 ns, the delay is about 26 ns at a working voltage of 85±3% USB （Self-breakdown Voltage）. Maximum deviation of delay is less than =t=2.5 ns. Jitter is less than 1.5 ns. The delay and jitter decrease with the increase in the working ratio （the ratio of working voltage to USB）, pressure or voltage.     

Physics Analysis and Optimization Studies for a Fusion Neutron Source Based on a Gas Dynamic Trap

To further investigate the fusion neutron source based on a gas dynamic trap （GDT）, characteristics of the GDT were analyzed and physics analyses were made for a fusion neutron source based on the GDT concept. The prior design of a GDT-based fusion neutron source was optimized based on a refreshed understanding of GDT operation. A two-step progressive development route of a GDT-based fusion neutron source was suggested. Potential applications of GDT are discussed. Preliminary analyses show that a fusion neutron source based on the GDT concept is suitable for plasma-material interaction research, fusion material and subcomponent testing, and capable of driving a proof-of-principle fusion fission hybrid experimental facility.     

Study of Plume Characteristics of a Stationary Plasma Thruster

Electron density and temperature of the plume are measured by a double Langmuir probe in an experimental chamber. A numerical model based on both particle-in-cell scheme and direct simulation Monte Carlo hybrid method is developed to simulate the flow field of plume. The equation for plasma potential is solved by alternative direction implicit technique. The simulation is verified by comparing the computational results with the measured data. The study indicates that the electron temperature of flow field is about 2 eV and the electron density is about 2.5 ×10^16 - 5×10^15 m^-3 at the central line with a distance of 0.3 - 1.0 m downstream of the thruster exit. The model can well predict the flow field parameters of the steady plume. The efforts of this paper are referable for further investigation.     

Plasma Discharge Process in a Pulsed Diaphragm Discharge System

As one of the most important steps in wastewater treatment, limited study on plasma discharge process is a key challenge in the development of plasma applications. In this study, we focus on the plasma discharge process of a pulsed diaphragm discharge system. According to the analysis, the pulsed diaphragm discharge proceeds in seven stages： （1） Joule heating and heat exchange stage; （2） nucleated site formation; （3） plasma generation （initiation of the breakdown stage）; （4） avalanche growth and plasma expansion; （5） plasma contraction; （6） termination of the plasma discharge; and （7） heat exchange stage. From this analysis, a critical voltage criterion for breakdown is obtained. We anticipate this finding will provide guidance for a better application of plasma discharges, especially diaphragm plasma discharges.     

Study on a cold-cathode H- PIG-type ion source

A cold-cathode Penning Ion Gauge(PIG) type ion source as the internal ion source of an 11 MeV cyclotron is designed and tested at Institute of Fluid Physics.The design considerations and some testings are presented.Experimental results of Balmer-line-Emission show that the discharge characteristic,which is mainly determined by gas-flow rate,is not very sensitive to arc current and magnetic field in the operation ranges of the cyclotron.The arc power decreases and ascends while the gas-flow rate goes up from 0.5 SCCM to 20 SCCM.By improving the sealing design and reducing the machine tolerance of the source,the minimum power consumption reduces from 9 SCCM to 4 SCCM,thus having better energy efficiency and benefiting for the pumping system.Preliminary DC extractions show that H–microampere current ranges from several tens to hundreds under different operation conditions.Some problems during the experiments and future plan are discussed in the end.     

Analysis of a Partial Male-Sterile Mutant of Arabidopsis thaliana Isolated from a Low-Energy Argon Ion Beam Mutagenized Pool

A screen for Arabidopsis fertility mutants, mutagenized by low-energy argon ion beam, yielded two partial male-sterile mutants tc243-1 and tc243-2 which have similar phenotypes. tc243-2 was investigated in detail. The segregation ratio of the mutant phenotypes in the M2 pools suggested that mutation behaved as single Mendelian recessive mutations, tc243 showed a series of mutant phenotypes, among which partial male-sterile was its striking mutant characteristic. Phenotype analysis indicates that there are four factors leading to male sterility, a. Floral organs normally develop inside the closed bud, but the anther filaments do not elongate sufficiently to position the locules above the stigma at anthesis, b. The anther locules do not dehisce at the time of flower opening （although limited dehiscence occurs later）, c. Pollens of mutant plants develop into several types of pollens at the trinucleated stage. as determined by staining with DAPI （4＇,6-diamidino-2-phenylindole）. which shows a variable size. shape and number of nucleus. d. The viability of pollens is lower than that of the wild type on the germination test in vivo and vitro.     

Development of a 140 GHz Steerable Launcher for the HL-2A ECRH System

A new electron cyclotron resonance launcher system has been designed and installed on heating and current drive （ECRH/ECCD） the HL-2A tokamak to inject four beams and enable continuous millimeter-wave beam scanning independently in the toroidal and poloidal direc- tions for ECRH/ECCD experiments. The launcher is connected to four mm-wave lines capable of transmitting high power up to 3 MW with two 1 MW/140 GHz/3 s and two 0.5 MW/68 GHz/1 s beams. Based on ray tracing simulation using the TORAY-GA code, tile scanning range of wave beams is -15~~15~ in the toroidal direction and 0~~10~ in the poloidal one for 140 GHz beams, which could cover half of the cross section of plasmas and can satisfy the requirements of advanced physical experiments. The beam radii in the plasma is 17.1 mm and 20 mm for the two 140 GHz beams and 29.5 nnn for the two 68 GHz beams, respectively, allowing a very high localization of the absorbed power. The performance of the steering system was proven to be reliable and the linearity is perfect between the displacement of drive shaft and rotate angle of mirror. Addition- ally the injection performance of the wave beams was optinfized by simultaneously setting the injection angle and the polarization to realize desirable pure O- or X-mode injection.     

Oxygen-Free Conversion of Methane to Ethylene in a Plasma-Followed-by-Catalyst （PFC） Reactor

Oxygen-free conversion of methane to ethylene was investigated in a two-stage plasma-followed-by-catalyst （PFC） reactor. In the absence of catalyst, pulsed spark discharges and pulsed corona discharges were compared for methane conversion. The results showed that methane was mainly converted to acetylene, but pulsed spark discharges exhibited distinct advantages over the pulsed corona discharges in methane conversion. Thereby, pulsed spark discharges were employed and followed by Ag-Pd/SiO2 catalyst for achieving ethylene as a target product in the PFC reactor. Using the PFC reactor, a steady single-pass ethylene yield of 57% was obtained at a rate of methane conversion of 74%.