Numerical Analysis on Neutron Shielding Structure of ITER Vacuum Vessel

The neutron shielding component of ITER （International Thermonuclear Experimental Reactor） vacuum vessel is a kind of structure resembling a wall in appearance. A FE （finite element） model is set up by using ANSYS code in terms of its structural features. Static analysis, thermal expansion analysis and dynamic analysis are performed. The static results show that the stress and displacement distribution are allowable, but the high stress appears in the junction between the upper and lower parts. The modal analysis indicates that the biggest deformation exists in the port area. Through modal superposition, the single-point response has been found with the lower rank frequency of the acceleration seismic response spectrum. But the deformation and the stress values are within the permissible limit. The analysis results would benefit the work in the next step and provide some reference for the implementation of the engineering plan in the future.     

Thermal Performance Study of VPS-W Coatings on CuCrZr Under High Heat Flux

Three tungsten coatings with a thickness of 250 μm, 600μm and 220 μm, respectively, were deposited on a CuCrZr substrate by the vacuum plasma spraying technology. In order to study the thermal performance of the coatings, heat load limit, thermal fatigue lifetime and thermal response tests were performed by means of the electron beam irradiation with a heat flux from 0 MW/m^2 to 10 MW/m^2. Experimental results indicated that tungsten coatings on CuCrZr with a titanium or tungsten/copper interlayer could expel heat flux timely and had good thermal fatigue properties, titanium was a promising compliant layer which provided a reliable way to join tungsten onto the CuCrZr heat sink, even suffering from a heat flux of 10 MW/m^2 or withstanding 54 cycles of fatigue tests under 5 MW/m^2. However, the better quality of tungsten coating itself was necessary because its surface temperature was higher than that of the sample with a tungsten/copper interlayer.     

Numerical Investigation of Flow Fields in Inductively Coupled Plasma Wind Tunnels

Numerical simulations of 10 kW and 110 kW inductively coupled plasma （ICP） wind tunnels were carried out to study physical properties of the flow inside the ICP torch and vacuum chamber with air as tile working gas. Two-dimensional compressible axisymmetric Navier- Stokes （N-S） equations that took into account 11 species and 49 chemical reactions of air, were solved. A heat source model was used to describe the heating phenomenon instead of solving the electromagnetic equations. In the vacuum chamber, a four-temperature model was coupled with N-S equations. Numerical results for tile 10 kW ICP wind tunnel are presented and discussed in detail as a representative case. It was found that the plasma flow in the vacuum chamber tended to be in local thermoehemical equilibrium. To study the influence of operation conditions on the flow field, simulations were carried out for different chamber pressures and/or input powers. The computational results for the above two ICP wind tunnels were compared with corresponding experimental data. The computational and experimental results agree well, therefore the flow fields of ICP wind tunnels can be clearly understood.     

Arc Behaviours in Vacuum Interrupters with Axial Magnetic Field Electrodes

To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.     

Effects of Finite Aspect Ratio and Noncircular Plasma Flux Surface on Electron Temperature Gradient Driven Modesd

A gyrokinetic model with integral eigenmode equations is developed based on the local equilibrium of shaped tokamak plasmas. Effects of main geometric parameters （finite aspect ratio, elongation, triangularity, and Shafranov shift gradient） on the electrostatic electron temper- ature gradient （ETG） driven modes are investigated numerically. It is found that the finite aspect ratio has a general stabilizing effect, while the elongation can be either stabilizing or destabilizing, depending on the poloidal wavelength of the mode and other parameters. It is shown that a low aspect ratio enhances the stabilizing effect of elongation, and weakens its destabilizing effect as well.     

Polymer Surface Treatment by Atmospheric Pressure Low Temperature Surface Discharge Plasma： Its Characteristics and Comparison with Low Pressure Oxygen Plasma Treatment

The polymer treatment with a low-temperature plasma jet generated on the atmospheric pressure surface discharge （SD） plasma is performed. The change of the surface property over time, in comparison with low pressure oxygen （O2） plasma treatment, is examined. As one compares the treatment by atmospheric pressure plasma to that by the low pressure O2 plasma of PS （polystyrene） the treatment effects were almost in complete agreement. However, when the atmospheric pressure plasma was used for PP（polypropylene）, it produced remarkable hydrophilic effects.     

Study of Metal and Ceramic Thermionic Vacuum arc Discharges

The thermionic vacuum arc （TVA） is a new type of plasma source, which generates a pure metal and ceramic vapour plasma containing ions with a directed energy. TVA discharges can be ignited in high vacuum conditions between a heated cathode （electron gun） and an anode （tungsten crucible） containing the material. The accelerated electron beam, incident on the anode, heats the crucible, together with its contents, to a high temperature. After establishing a steadystate density of the evaporating anode material atoms, and when the voltage applied is high enough, a bright discharge is ignited between the electrodes. We generated silver and Al2O3 TVA discharges in order to compare the metal and ceramic TVA discharges. The electrical and optical characteristics of silver and Al2O3 TVA discharges were analysed. The TVA is also a new technique for the deposition of thin films. The film condenses on the sample from the plasma state of the vapour phase of the anode material, generated by a TVA. We deposited silver and Al2O3 thin films onto an aluminium substrate layer-by-layer using their TVA discharges, and produced micro and/or nano-layer Ag-Al2O3 composite samples. The composite samples using scanning electron microscopy was also analysed.     

Electromagnetic Calculation and Plasma Leakage Rate Analysis of the Magnetically Confined Plasma Rocket

An electromagnetic calculation and the parameters of the magnet system of the magnetically confined plasma rocket were established. By using ANSYS code, it was found that the leakage rate depends on the current intensity of the magnet and the change of the magnet position.     

Mixed Wastes Vitrification by Transferred Plasma

Thermal plasma technology provides a stable and long term treatment of mixed wastes through vitrification processes. In this work, a transferred plasma system was realized to vitrify mixed wastes, taking advantage of its high power density, enthalpy and chemical reactivity as well as its rapid quenching and high operation temperatures.
To characterize the plasma discharge, a temperature diagnostic is realized by means of optical emission spectroscopy （OES）. To typify the morphological structure of the wastes samples~ scan- ning electron microscopy （SEM）, and X-ray diffraction （XRD） techniques were applied before and after the plasma treatment.     

Inter-Calibration Between Plasma Instruments Onboard DEMETER

The in-situ measurements of the ionospheric plasma that we use come from two instruments of the scientific payload of the satellite DEMETER; the plasma analyser IAP （Instrument d＇analyse du plasma） and the Langmuir probe ISL （Instrument Sonde de Langmuir）. DEMETER is a micro-satellite realized by the CNES（Centre National d＇Etudes Spatiales, France） with a principal objective to seek a possible influence of the seismic activity on the electromagnetic waves in the ionosphere and on the ionospheric plasma. The satellite was placed on June 29, 2004, in a circular and quasi helio-synchronous orbit at -710 km altitude. The experiments function primarily at mid-latitudes （from ＋60° to -60°）. The IAP data were analysed to deduce the ion population （densities of the dominant ions, i.e. generally O^＋, H^＋ and He^＋） therefore the total ion density. The use of data IAP thus requires some precaution to make sure that the electric equilibrium conditions of the satellite, such as the satellite potential （Фsat）, are obtained during the treatment of routine, does not induce an error of measurement. When this potential is negative, the minority light ions H^＋ and He^＋ can be measured in a reliable way when their proportion is above 3% to 5% of that of O^＋. The critical limitation is： under certain conditions, the satellite potential becomes positive and reach a value about -0.5 V so that it becomes impossible to measure H^＋ ions. This is likely to involve a significant error on the composition and the density of the plasma. Therefore we carried out a calibration to estimate the missing density. The ISL experiment （Langmuir probe） provided the collected current/polarized tension characteristics of a cylindrical probe from which both electron density Ne and temperature Te were obtained. In some situations it is necessary to examine the accuracy of the electron density using another technique, for instance the high frequency （HF） spectrogram, provided by ICE （instrument champ     

Kinematics Simulation and Structure Optimization of Tilting and Lifting Mechanism of ITER Tractor

The ITER （international thermonuclear experimental reactor） tractor is an in-cask remote handling equipment, its tilting and lifting mechanism is important for the tractor operated with forty-five-ton plug in front of the ports of Hot Cell and VV （vacuum vessel） successfully. In order to better analyse the movement of this mechanism and decide the key design parameters accurately, a mathematical model of 7-1ink complicated plane mechanism was built up, and the calculation of design and kinematics simulation were implemented. The established mathematical model was proved to be valid by comparing the calculated result with that of kinematics simulation. Finally, the structure analysis and the optimization of its key part, tilting and lifting frame, were performed to guarantee the frame＇s strength in bearing the heavy load of plug.     

The Effect of Hydrostatic Pressure and Seismic Load on ITER Lower Cryopump Ports

The lower cryopump ports in International Thermonuclear Experimental Reactor （ITER） as a part of the vacuum vessel play many important roles. As the boundary of vacuum it must be ensured against structural damage. In this study a finite element model of the lower cryopump ports was developed by ANSYS code with a purpose to evaluate the stress and displacement level on it. Two kinds of loads were taken into account. One was the hydrostatic pressure including the normal operation pressure and test pressure. The other was the seismic load. The analysis results show that the peak stress does not exceed the allowable stress for either the hydrostatic pressure or the seismic load according to the ITER structural design criterion, which indicates that the structure has a good safety margin.     

Plasma-Etching Enhanced Mechanical Polishing for CVD Diamond Films

Chemically vapor deposited diamond films were etched at different parameters using oxygen plasma produced by a DC （direct current） glow discharge and then polished by a modified mechanical polishing device. Scanning electron microscope, atomic force microscope and Raman spectrometer were used to evaluate the surface states of diamond films before and after polishing. It was found that a moderate plasma etching would produce a lot of etch pits and amorphous carbon on the top surface of diamond film. As a result, the quality and the efficiency of mechanical polishing have been enhanced remarkably.     

Inactivation of Escherichia Coli Using Remote Low Temperature Glow Discharge Plasma

Low-temperature plasma is distinguished as a developing approach for sterilization which can deal with and overcome those problems such as thermal sensitivity and destruction by heat, formation of toxic by-products, higher costs and inefficiency in performances, caused by conventional methods. In this study, an experimental investigation was undertaken to characterize the effects of the operational parameters, such as treating time, discharge power and gas flow rate, of remote glow discharge air plasma. The results show that the inactivation of Escherichia coli can reach above 99.99% in less than 60 seconds and the optimal operational conditions for treating time, discharge power and gas flow rate were： 40 s, 80 W and 60 cm^3/min, respectively. The contribution of UV radiation during plasma germ deactivation is very limited.     

Simulation of Needle-Type Corona Electrodes by the Finite Element Method

This paper describes a software tool, called LEVSOFT, suitable for the electric field simulations of corona electrodes by the Finite Element Method （FEM）. Special attention was paid to the user friendly construction of geometries with corners and sharp points, and to the fast generation of highly refined triangular meshes and field maps. The execution of selfadaptive meshes was also implemented. These customized features make the code attractive for the simulation of needle-type corona electrodes. Some case examples involving needle type electrodes are presented.     

Numerical Simulation Approaches to Evaluating the Electromagnetic Loads on the EAST Vacuum Vessel

Numerical simulation approaches are developed to compute the electromagnetic forces on the EAST vacuum vessel during major disruptions and vertical displacement events, with the halo current also considered. The finite element model built with ANSYS includes the vacuum vessel, the plasma facing components and their support structure, and the toroidal and poloidal field coils. The numerical methods are explained to convince of its validity. The eddy current induced by the magnetic flux variation and the conducting current caused by the halo current are also presented for discussion. The electromagnetic forces resulting from the numerical simulation are proven to be useful for structure design optimization. Similar methods can be applied in the upgrades of the EAST device.     

Preliminary Design and Analysis of ITER In-Wall Shielding

ITER in-wall shielding （IIS） is situated between the doubled shells of the ITER Vacuum Vessel （IVV）. Its main functions are applied in shielding neutron, gamma-ray and toroidal field ripple reduction. The structure of IIS has been modelled according to the IVV design criteria which has been updated by the ITER team （IT）. Static analysis and thermal expansion analysis were performed for the structure. Thermal-hydraulic analysis verified the heat removal capability and resulting temperature, pressure, and velocity changes in the coolant flow. Consequently, our design work is possibly suitable as a reference for IT＇s updated or final design in its next step.     

Uniformity of Plasma Density and Film Thickness of Coatings Deposited Inside a Cylindrical Tribe by Radio Frequency Sputtering

Plasma surface modification of the inner wall of a slender tube is quite difficult to achieve using conventional means. In the work described here, an inner coaxial radio frequency （RF） copper electrode is utilized to produce the plasma and also acts as the sputtered target to deposit copper films in a tube. The influence of RF power, gas pressure, and bias voltage on the distribution of plasma density and the uniformity of film thickness is investigated. The experimental results show that the plasma density is higher at the two ends and lower in the middle of the tube. A higher RF power and pressure as well as larger tube bias lead to a higher plasma density. Changes in the discharge parameter only affect the plasma density uniformity slightly. The variation in the film thickness is consistent with that of the plasma density along the tube axis for different RF power and pressure. Although the plasma density increases with higher tube biases, there is an optimal bias to obtain the highest deposition rate. It can be attributed to the reduction in self-sputtering of the copper electrode and re-sputtering effects of the deposited film at higher tube biases.     

Comparison of Sterilizing Effect of Nonequilibrium Atmospheric-Pressure He/O2 and Ar/O2 Plasma Jets

The sterilizing effect of the non-equilibrium atmospheric pressure plasma jet by applying it to the Bacillus subtilis spores is invesigated. A stable glow discharge in argon or helium gas fed with active gas （oxygen）, was generated in the coaxial cylindrical reactor powered by the radio-frequency power supply at atmospheric pressure. The experimental results indicated that the efficiency of killing spores by making use of an Ar/O2 plasma jet was much better than with a He/O2 plasma jet. The decimal reduction value of Ar/O2 and He/O2 plasma jets under the same experimental conditions was 4.5 seconds and 125 seconds, respectively. It was found that there exists an optimum oxygen concentration for a certain input power, at which the sterilization efficiency reaches a maximum value. It is believed that the oxygen radicals are generated most efficiently under this optimum condition.     

Application of CCD Cameras to Investigations of Mixing on Boundaries of a Thermal Plasma Jet

Mixing of a thermal plasma jet with the surrounding atmosphere was studied using two CCD cameras （PCO SensiCam） situated detecting simultaneously the radiation of argon and nitrogen. The evaluation of image differences between two records showed that the location of regions on plasma jet boundaries characterised by stronger nitrogen radiation changes with the plasma flow rate. Close-to-laminar flow results in a small mixing rate and consequently low nitrogen optical emission on plasma jet boundaries. The increase of the flow rate leads to the formation of a relatively thick and stable layer on the boundaries characterised by strong nitrogen radiation. Further enhancement of the flow rate results in the formation of unstable regions of excited nitrogen molecules moving along the jet.