Experiments and Studies of Edge Plasma Radial Transport and Confinement Property on the HL-1M Tokamak

This paper describes a Mach/Langmuir probe array with five pins and six pins, which can measure not only parallel flows and the flow perpendicular to the magnetic field but also the radial and the poloidal electric field E. arid E as well. Experimental measurements of the edge fluctuations, velocities of the toroidal, the poloidal flow and electric field have been carried out on both of SOL and the boundary region of HL-1M for Ohmic, biased H-mode, Lower Hybrid Current Drive (LHCD), Supersonic Molecular Beam Injection (MBI), Multi-shot Pellet Injection (MPI), Neutral Beam Injection (NBI), Ion Cyclotron Resonance Heating (ICRH) and Electric Cyclotron Resonance Heating (ECRH) discharges. The results show that the suppressions of the fluctuations are related to poloidal rotations produced by different discharge modes in the improved particle confinement property, simultaneously the change of the radial and poloidal electric field is generated and becomes more negative at the Tokamak plasma edge, and the sheared poloidal flow is related to the reduction in fluctuation level, and the poloidal velocity is mainly dominated by the E × B drift.

Analysis of the Plasma Properties Affected by Magnetic Confinement with Special Emphasis on Helicon Discharges

A one-dimensional radial non-uniform fluid model is employed to study plasma behaviors with special emphasis laid on helicon discharges. The plasma density ne, electron temperature Te, electron azimuthal and radial drift velocities are investigated in terms of the plasma radius rp, magnetic field intensity B0 and gas pressure p0, by assuming radial ambipolar diffusion and negligible ion cyclotron movement. The results show that the magnetic confinement plays an important role in the discharge equilibrium, especially at low pressure, which significantly reduces Te compared with the case of a negligible magnetic field effect, and higher B0 leads to a greater average plasma density. Te shows little variations in the plasma density range of 1011 cm-3- 1013 cm-3 for p0 〈 3.0 mTorr. Comparison of the simulation results with experiments suggests that the model can make reasonable predictions of Te in low pressure helicon discharges.

Effect of Internal Antenna Coil Power on the Plasma Parameters in13.56 MHz/60 MHz Dual-Frequency Sputtering

The plasma property of a hybrid ICP/sputtering discharge driven by 13.56 MHz/60 MHz power sources was investigated by Langmuir probe measurement. For the pure sputtering discharge, the low electron density and ion flux, the rise of floating potential and plasma potential with increasing power, as well as the bi-Maxwellian distribution of electron en- ergy distributions （EEDFs） were obtained. The assistance of ICP discharge led to the effective increases of electron density and ion flux, the suppression of rise of floating potential and plasma potential, as well as the change of EEDFs from bi-Maxwellian distribution into Maxwellian dis- tribution. The increase of electron density and ion flux, and the EEDFs evolution were related to the effective electron heating by the induced electric field.

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Graphene-reinforced 7055 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering（SPS）. The structure and mechanical properties of the composites were investigated. Testing results show that the hardness, compressive strength, and yield strength of the composites are improved with the addition of 1wt% graphene. A clean, strong interface is formed between the metal matrix and graphene via metallurgical bonding on atomic scale. Harmful aluminum carbide（Al_4C_3） is not formed during SPS processing. Further addition of graphene（above 1wt%） results in the deterioration in mechanical properties of the composites. The agglomeration of graphene plates is exacerbated with increasing graphene content, which is the main reason for this deterioration.

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,CⅠ,CⅡ,CⅢ,CⅣ,ClⅠ,ClⅡparticles,and a small amount of CH,C_(3),C_(2),H_(2) neutral molecular groups in the plasma.The electron temperature of the discharge channel of the thruster was within 0.6–4.9 e V,and the electron density was within(1.1–3.0)×10^(18)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,LAPPT 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.

Microstructure and Mechanical Performance of Cu-SnO_2-rGO based Composites Prepared by Plasma Activated Sintering

A novel chemical technique combined with unique plasma activated sintering（PAS） was utilized to prepare consolidated copper matrix composites（CMCs） by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide（r GO）, SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2＋. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.

Microstructure and Properties of Plasma Spraying Boron Carbide Coating

Microstructure of plasma spray boron carbide coating was studied by SEM and TEM. Its physical, mechanical and electrical properties were measured. The results showed that high microhardness, modulus and low porosity of B4C coating were manufactured by plasma spray. It was lamellar packing and dense. The B4C coating examined here contained two principal structures and two impurity phase besides major phase. The relatively small value of Young's modulus, comparing with that of the bulk materials, is explained by porosity . The Fe impurity phase could account for the relatively high electrical conductivity of boron carbide coating by comparing with the general boron carbide materials.

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 10000 K and 1017 cm-3,respectively.These had maximum values of 13750 K and 2.3?×?1017 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 105 Pa and exhibited a maximum value of 2.69?×?105 Pa.

Effects of O_2 Plasma Treatment on the Chemical and Electric Properties of Low-k SiOF Films

With the progress of ULSI technology, materials with low dielectric constant are required to replace SiO2 film as the interlayer to scale down the interconnection delay. Fluorinated Si oxide thin films (SiOF) are a promising material for the low dielectric constant and the process compatibility in existing technology. However, SiOF films are liable to absorb moisture when exposed to air. By treating the SiOF films with O-2 plasma, it was found that the moisture resistibility of SiOF films was remarkably improved. The mechanism of the improvement in stability of dielectric constant was investigated. The results show that: 1) F atoms dissociated from the films and the bond angle of Si-O-Si decreased. 2) The plasma treatment enhanced the strength of Si-F bonds by removing unstable =SiF2 structures in the films. Resistibility of SiOF films in moisture was improved.

A STUDY ON THE STRUCTURE AND PROPERTIES OF POLYBUTYLALDEHYDE FORMED IN LOW TEMPERATURE PLASMA

The polybutylaldehyde obtained by plasma polymerization was investigated by means of IR, X-ray diffraction, GC-MS, elementary analysis, TEM, electron diffraction and contact angle measurements etc. The results showed that the polymer formed in plasma is amorphous crosslinked polymer, and its backbone is made of carbon atoms. The surface energy of the polymer film is independent of the polymerization conditions. No addition reaction has taken place in the carbonyl group of butylaldehyde in the plasma condition. The result of the wettability measurements showed that the polymer film is generally hydrophobic and the surface energy of the film is about 41 dyn/cm, in which the dispersion force contribution is the majority. The electron diffraction proved that some crystal substance, even the single crystals were present in the polymer. X-ray diffraction also proved the presence of crystal and showed about 15% crystaUinity fraction.

Underwater pulsed spark discharge influenced by the relative position between the top of a pin electrode and an insulating tube

Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges.The position relationship between the needle tip and insulation layer significantly affects the discharge patterns.We carried out experiments on underwater pulsed discharge with the needle tip protruding from,recessing into,and flushing with the insulating tube.The results are as follows.First,underwater pulsed discharge has a strong randomness under the experimental conditions.Different discharge patterns appeared under the same experimental environment.Second,recession into the insulator surface led to a higher probability of occurrence but a lower strength of spark discharge than protrusion.Third,between the needle tip protruding from and recessing into the insulation material,the average speed of propagation of underwater pulsed spark discharge decreased by an order of magnitude.The study shows that the optimum length of needle tip protruding from the insulation layer is 1 mm to obtain a strong underwater pulsed spark discharge.

Simulation of plasma properties in magnetron sputtering for two kinds of cathode targets

Introduction During magnetron sputtering process,the common structure of cathode target is planar target and cylindrical rotating target.In this study,cylindrical rotating target is used and two kinds of cathode targets were investigated by COMSOL Multiphysics software(The official network of COMSOL Multiphysics software.https://uk.comsol.com/).We will elucidate the difference between the two types of cathode target and determine the type of cathode target used in the final experiment.The system configuration We explore the plasma distribution in the radio frequency cavity,so the simulation process was divided into two steps:building RF cavity model and setting up plasma discharge parameters.The main part of the model included the radio frequency cavity substrate(divided into two tube parts and middle ellipsoid part),the cathode and the magnet.And the plasma discharge parameters are as follows:Ar gas was used with 1.5 Pa;magnetic field strength of iron core was set to 1000 Gs;the applied voltage of cathode was set to-160 V;and anode was set to 0 V.Conclusion For the long cathode target and the short cathode target,the main difference is the electric field distribution.Because the electric field lines are denser for the long cathode target,the electric field intensity is stronger,and then the initial energy obtained by electrons is higher.During the plasma discharge process,because of the high electron energy,the plasma density produced is more than the simulation of the short cathode target.And under the same simulation time,the residual energy of electrons is more for the long cathode target,which is the reason for the higher electron temperature.From the previous experimental experience,we know that the film quality formed by higher electron energy is better.The simulation in this work shows that the electron energy corresponding to the long cathode target is higher than that of the short cathode target,so we choose the long cathode target as the experimental target in the subsequent coating experiments.

Parametrization of Mean Radiative Properties of Optically Thin Steady-State Plasmas and Applications

Plasma radiative properties play a pivotal role both in nuclear fusion and astrophysics.They are essential to analyze and explain experiments or observations and also in radiative-hydrodynamics simulations.Their computation requires the generation of large atomic databases and the calculation,by solving a set of rate equations,of a huge number of atomic level populations in wide ranges of plasma conditions.These facts make that,for example,radiative-hydrodynamics in-line simulations be almost infeasible.This has lead to develop analytical expressions based on the parametrization of radiative properties.However,most of them are accurate only for coronal or local thermodynamic equilibrium.In this work we present a code for the parametrization of plasma radiative properties of mono-component plasmas,in terms of plasma density and temperature,such as radiative power loss,the Planck and Rosseland mean opacities and the average ionization,which is valid for steady-state optically thin plasmas in wide ranges of plasma densities and temperatures.Furthermore,we also present some applications of this parametrization such as the analysis of the optical depth and radiative character of plasmas,the use to perform diagnostics of the electron temperature,the determination of mean radiative properties for multicomponent plasmas and the analysis of radiative cooling instabilities in some kind of experiments on high-energy density laboratory astrophysics.Finally,to ease the use of the code for the parametrization,this one has been integrated in a user interface and brief comments about it are presented.

Effect of Spark Plasma Sintering Temperature on Electrochemical Properties of La_(0. 82)Mg_(0. 18)Ni_(3. 50)Co_(0. 15) Alloy

Electrochemical properties of La_（0. 82）Mg_（0. 18）Ni_（3. 50）Co_（0. 15） alloys synthesized by spark plasma sintering（ SPS） were investigated based on the electrochemical measurements,physical parameters and microstructure observation. The sintering behavior of La_（0. 82）Mg_（0. 18）Ni_（3. 50）Co_（0. 15） alloys at the temperatures of 900,950 and 1 000 ℃ is characterized by four stages,i. e.,initial slight shrinkage,expansion,abrupt shrinkage and slight expansion. The maximum shrinkage displacement increases with increasing sintering temperature. All of the alloys consist of（ La,Mg）_2（ Ni,Co）_7 phase; additionally,temperatures of 900 and 950 ℃ are beneficial to the formation of（ La,Mg）（ Ni,Co）_3 phase,whereas the LaNi_5 phase is easy to form in the alloy synthesized by SPS at 1 000 ℃. The electrochemical measurements indicate an evident change of the electrochemical performance of the alloys associated with increasing the sintering temperature. The discharge capacity of the alloys first increases and then decreases as sintering temperature rises,whereas their cycle stability clearly grows all the time.Furthermore,the charging-discharging potential difference and discharging efficiency both demonstrate that the electrochemical properties of the alloy electrodes first augment and then decline with increasing sintering temperature.

Self-Lubricating PEO Coating on an Al Alloy Produced by Vacuum Impregnation Post-treatment

The objective of this research was to develop a novel self-lubricating coating on an AA6061 aluminum alloy.Three coatings were prepared by the plasma electrolytic oxidation（PEO） process using 50-, 500-, and 1000-Hz pulsed direct current, respectively. The as-deposited coatings were then post-treated using two different methods, viz., ultrasonic vibration-aided vacuum oil impregnation（UVOI） and oil impregnation under ambient pressure（OIAP）. After posttreatment, an oil-containing, self-lubricating top layer was formed on the coatings. The effects of the coatings＇ surface morphologies and structures on their oil-holding capabilities were discussed. The results revealed that coatings prepared with higher frequency had a greater oil-holding capacity using OIAP post-treatment, while those prepared with lower frequency had a greater oil-containing capability using UVOI post-treatment. These phenomena are related to the morphologies of the coatings produced with various current modes. The tribological properties of the coatings before and after post-treatments were investigated by pin-on-disc sliding wear tests. Due to the formation of a lubricant-containing top layer, the post-treatment coatings had a lower friction coefficient and improved wear resistance compared with the asdeposited coatings. In addition, the coatings after UVOI treatment had better wear performance than those post-treated using the OIAP process. Among all coatings, the coating produced with a 50-Hz pulsed current followed by UVOI posttreatment achieved the lowest friction coefficient（0.03） and best wear resistance when sliding against a Si3N4 ceramic counterface. This study indicates that a novel self-lubricating coating can be prepared by a PEO process combined with vacuum oil impregnation post-treatment.

Analysis of microscopic properties of radiative shock experiments performed at the Orion laser facility

In this work we have conducted a study on the radiative and spectroscopic properties of the radiative precursor and the post-shock region from experiments with radiative shocks in xenon performed at the Orion laser facility. The study is based on post-processing of radiation-hydrodynamics simulations of the experiment. In particular, we have analyzed the thermodynamic regime of the plasma, the charge state distributions, the monochromatic opacities and emissivities, and the specific intensities for plasma conditions of both regions. The study of the intensities is a useful tool to estimate ranges of electron temperatures present in the xenon plasma in these experiments and the analysis performed of the microscopic properties commented above helps to better understand the intensity spectra. Finally, a theoretical analysis of the possibility of the onset of isobaric thermal instabilities in the post-shock has been made, concluding that the instabilities obtained in the radiative-hydrodynamic simulations could be thermal ones due to strong radiative cooling.

Preparation and properties of W–Cu–Zn alloy with low W–W contiguity

The W–Cu–Zn alloy with a-brass matrix and low W–W contiguity was prepared by method of electroless copper plating combined with spark plasma sintering（SPS） method.The effects of process and parameters on the microstructure and mechanical properties of the alloy were investigated.The W–Cu–Zn alloy with a relative density of 96 % and a W–W contiguity of about 10 % was prepared by original fine tungsten particles combined with wet mixing method and SPS solid-state sintering method at 800℃ for 10 min.The microstructure analysis shows that Cu–Zn matrix consists of nano-sized a-brass grains,and the main composition is Cu3Zn electride.The nano-sized Cu was coated on the surface of tungsten particles by electroless copper plating method,and the fairly low consolidation temperature and short solid-state sintering time result in the nano-sized matrix phase.The dynamic compressive strength of the W–Cu–Zn alloy achieves to1000 MPa,but the alloy shows poor ductility due to the formation of the hard and brittle Cu3Zn electrides.The fine-grain strengthening and the solution strengthening of the Cu–Zn matrix phase are responsible for the high Vickers microhardness of about 300 MPa for W–Cu–Zn alloy.