Strange Quasi-Repeller in a Kicked Rotor

A new kind of crisis was observed in a system where a transition from conservative to quasi-dissipative can be observed. The crisis signifies a sudden and intrinsic change of a stochastic web, which is formed by the end-results of the images of the discontinuous borderlines of the system function. In the crisis, a strange quasi-repeller can be defined. When changing the controlling parameter, the variation of the fractile dimension of the quasi-repeller obeys a logarithmic rule.     

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.     

Numerical Analysis of the Arc Plasma in a Simplified Low-voltage Circuit Breaker Chamber with Ferromagnetic Materials

This paper is devoted to the simulation of the arc plasma in a simplified low-voltage circuit breaker chamber. Based on a group of coupled governing equations, a three-dimensional （3-D） arc plasma model is built and solved by a modified commercial code. Firstly, this paper presents a solution of the stationary state of the arc plasma and discusses the distribution of some parameters throughout the chamber. Secondly, with the ferromagnetic materials included, the balance of the stationary state is broken and a transient course is calculated. In light of the simulation results, the temperature distribution sequence, the arc motion and the plasma jet are then described and analyzed in detail.     

Flow Control over a Conical Forebody by Duty-Cycle Actuations

Duty-cycle modulation alternately blowing from two opposite-facing plasma actuators on the leeward surface near the apex of a cone with a 10 semi-apex angle is adopted to control mean lateral force and moment, and the flow control mechanisms are presented. Pressure distributions over the forebody of the cone are measured by steady pressure tappings. The experiments are performed in a 3.0×1.6 m open-circuit wind tunnel at a wind speed of 20 m/s, a 45 angle of attack and a Reynolds number of 2×10 5 , based on the diameter of the base of the cone. Almost linearly proportional control of the lateral forces and moments over a slender conical forebody at a high angle of attack has been demonstrated by employing a pair of single dielectric barrier discharge plasma actuators near the apex of the cone, combined with a duty-cycle technique. The pressure distribution measurements indicate that the bi-stable vortex pattern appears to be shifted in the opposite direction when the port or starboard actuator is activated, while the other is kept off during the test. It is shown that the reduced pulse-repetition frequency based on the local diameter at the plasma actuator equal to one yields the highest effectiveness among the cases considered.     

Toward the Design of Multi Asymmetric Surface Dielectric Barrier Discharge (ASDBD) Actuators

This paper investigates the electrical and mechanical behaviors of a single-ASDBD actuator and a two-ASDBD one supplied in sinusoidal mode(1-10 kHz).The main objective of our research is to determine the optimum frequency values for the function of these actuators with a given power supply.For this purpose,we determine the electrical power density input to the actuators versus frequency through two methods:i) a semi-theoretical method,based on an impedance calculation,and ii) an experimental method,based on direct electrical measurements.These methods show that the addition of a second ASDBD changes the resonance frequency value of the actuator by moving it towards low frequencies.After characterizing the aerodynamic mobile layer structure induced by the single-ASDBD actuator,we analyze experimentally the mechanical response of a two-ASDBD actuator as a function of the inter-ASDBD distance.The experiments demonstrate that the induced electric wind velocity and the electro-mechanical yield of a twoASDBD actuator reach a maximum value for an optimum inter-ASDBD distance,which is a useful value for the design of highly efficient multi-ASDBD actuators.     

Design of the Control System of Toroidal Field （TF） Power Supply for J-TEXT Tokamak

J-TEXT, formerly TEXT-U at the University of Texas at Austin in USA, is a medium-sized tokamak at the Huazhong University of Science and Technology. The toroidal field （TF） power supply of this tokamak should provide a current of 160 kA and a flat duration of 500 ms for the toroidal field coils to generate a maximum toroidal field of 3 T at the geometric center of the vaccum vessel. This paper presents a design of a new control system which takes the real-time feedback control option for the TF power supply operation. The system was tested successfully during the commissioning. In the first experimental campaign of J-TEXT, the system effectively controlled the power supply to provide a fiat current up to 92.5 kA and therein the TF produced reached 1.74 T, which enabled the machine to generate the first plasma successfully.     

Spectrum Diagnosis for Fuchsia Plume of Hall Effect Thruster with Xenon as Propellant

The colour of the Hall effect thruster＇s plume is often light-green, and sometimes a fuchsia plume appears during experiments. Based on a spectrum and colour analysis, and a comparison with normal plumes, a conclusion is made that the density of the Xe ions and the temperature of electrons are low when the plume appears fuchsia. In this condition, most of the components of the plume are Xe atoms, and the ionization rate of the propellant is low.     

Damping Solitary Wave in a Three-Dimensional Rectangular Geometry Plasma

The solitary waves of a viscous plasma confined in a cuboid under the three types of boundary condition are theoretically investigated in the present paper.By introducing a threedimensional rectangular geometry and employing the reductive perturbation theory,a quasi-Kd V equation is derived in the viscous plasma and a damping solitary wave is obtained.It is found that the damping rate increases as the viscosity coefficient increases,or increases as the length and width of the rectangle decrease,for all kinds of boundary condition.Nevertheless,the magnitude of the damping rate is dominated by the types of boundary condition.We thus observe the existence of a damping solitary wave from the fact that its amplitude disappears rapidly for a → 0and b → 0,or ν→ +∞.     

Finding an optimization of the plate element of Egyptian research reactor using genetic algorithm

The second Egyptian research reactor ET-RR-2 went critical on the 27th of November 1997. The National Center of Nuclear Safety and Radiation Control （NCNSRC） has the responsibility of the evaluation and assessment of the safety of this reactor. The purpose of this paper is to present an approach to optimization of the fuel element plate. For an efficient search through the solution space we use a multi objective genetic algorithm which allows us to identify a set of Pareto optimal solutions providing the decision maker with the complete spectrum of optimal solutions with respect to the various targets. The aim of this paper is to propose a new approach for optimizing the fuel element plate in the reactor. The fuel element plate is designed with a view to improve reliability and lifetime and it is one of the most important elements during the shut down. In this present paper, we present a conceptual design approach for fuel element plate, in conjunction with a genetic algorithm to obtain a fuel plate that maximizes a fitness value to optimize the safety design of the fuel plate.     

Decoloration of Azo Dye Sunset Yellow by a Coaxial Insulated-Rod-to-Cylinder Underwater Streamer Discharge System

A coaxial insulated-rod-to-cylinder underwater streamer discharge system capable of injecting plasma into a large volume of water was developed and employed to decolorize azo dye sunset yellow. The rod type anode was covered by an insulator tube with a wall thickness of 0.4 mm. A series of slits with a width of 20 μm to 80 μm and a length of about 4 mm were cut onto the wall of the insulator tube. Depending on the solution conductivity, a cylindrical discharge region with a length of 60 mm and a wall thickness of 5 mm to 11 mm forms in the reactor. The influence of the solution conductivity, pH and pulse frequency on the decoloration of sunset yellow was investigated. The results show that the solution conductivity has little effect, while the solution pH and the pulse frequency have significant influence on the decoloration rate of sunset yellow. The decoloration rate of sunset yellow is increased with the increase in pulse frequency. A lower pH in solution promotes the decoloration of sunset yellow while a higher pH inhibits it.     

Estimation of the Lyman-α signal of the EFILE diagnostic under static or radiofrequency electric field in vacuum

The electric field induced Lyman-α emission diagnostic aims to provide a non intrusive and precise measurement of the electric field in plasma, using a beam of hydrogen atoms prepared in the metastable 2 s state. The metastable particles are obtained by means of a proton beam extracted from a hydrogen plasma source, and neutralised by interaction with vaporised caesium.When a 2 s atom enters a region where an electric field is present, it undergoes a transition to the2 p state(Stark mixing). It then quickly decays to the ground level, emitting Lyman-α radiation,which is collected by a photomultiplier. The 2 s→2 p transition rate is proportional to the square of the magnitude of the electric field, and depends on the field oscillation frequency(with peaks around 1 GHz). By measuring the intensity of the Lyman-α radiation emitted by the beam it is possible to determine the magnitude of the field in a defined region. In this work, an analysis of the behaviour of the diagnostic under static or radiofrequency electric field is presented. Electric field simulations obtained with a finite element solver of Maxwell equations, combined with theoretical calculations of the Stark mixing transition rate, are used to develop a model for the interpretation of photomultiplier data. This method shows good agreement with experimental results for the static field case, and allows to measure the field magnitude for the oscillating case.     

Calculation of the Critical Speed and Stability Analysis of Cryogenic Turboexpanders with Different Structures

A modularized code based on the Finite Element QZ (FEQZ) method is developed,for a better estimate of the critical speed and a more convenient method of rotor-dynamic stability analysis for a gas bearing high speed turboexpander rotor system with actual structure and appli-cation of a cryogenic turboexpander.This code is then validated by the experimental data of a gas bearing turboexpander,with a rotor diameter of 25 mm and a rated speed of 106,400 rpm.With this code,four rotors with different structures,available to the turboexpander,are parametrically analyzed by the available speed range,vibration modes and logarithmic attenuation rate.The results suggest that the rotor with a structure of two thrust collars on the system exhibits a better performance in the designed conditions.     

Effect of High-Frequency Electric Field on Propagation of Electrostatic Wave in a Non-Uniform Relativistic Plasma Waveguide

The effect of a high frequency （HF） electric field on the propagation of electrostatic wave in a 2D non-uniform relativistic plasma waveguide is investigated. A variable separation method is applied to the two-fluid plasma model. An analytical study of the reflection of electrostatic wave propagation along a magnetized non-uniform relativistic plasma slab subjected to an intense HF electric field is presented and compared with the case of a non relativistic plasma. It is found that, when the frequency of the incident wave is close to the relativistic electron plasma frequency, the plasma is less reflective due to the presence of both an HF field and the effect of relativistic electrons. On the other hand, for a low-frequency incident wave the reflection coefficient is directly proportional to the amplitude of the HF field. Also, it is shown that the relativistic electron plasma leads to a decrease in the value of reflection coefficient in comparison with the case of the non relativistic plasma.     

Second Discharge Characteristics of Aluminum Wire Electrical Explosion Under Various Argon Pressures

Electrical wire explosion is a promising method for the preparation of metal nanopowder, but the properties of metal nanopowder are affected by the second discharge process of electrical wire explosion. The second discharge characteristics of aluminum wire electrical ex- plosion under variant argon pressures were studied in a RLC discharge circuit. The results show that the curve of the second discharge voltages versus the pressure presents a U-shape. To clarify the roles of aluminum vapor and argon in the process of the second discharge, a spectrograph and a high speed framing camera were used to study the radiation spectrum and spatial distribution of the electrical explosion plasma. It is observed that argon participates in the second discharge process under low pressure. A discharge channel develops along the surface of the aluminum vapor. Under higher pressure, a second discharge takes place in the aluminum vapor and the discharge channel is inside the aluminum vapor.     

Experimental Investigation on Aerodynamic Control of a Wing with Distributed Plasma Actuators

Experimental investigation of active flow control on the aerodynamic performance of a flying wing is conducted.Subsonic wind tunnel tests are performed using a model of a 35°swept flying wing with an nanosecond dielectric barrier discharge(NS-DBD) plasma actuator,which is installed symmetrically on the wing leading edge.The lift and drag coefficient,lift-todrag ratio and pitching moment coefficient are tested by a six-component force balance for a range of angles of attack.The results indicate that a 44.5%increase in the lift coefficient,a 34.2%decrease in the drag coefficient and a 22.4%increase in the maximum lift-to-drag ratio can be achieved as compared with the baseline case.The effects of several actuation parameters are also investigated,and the results show that control efficiency demonstrates a strong dependence on actuation location and frequency.Furthermore,we highlight the use of distributed plasma actuators at the leading edge to enhance the aerodynamic performance,giving insight into the different mechanism of separation control and vortex control,which shows tremendous potential in practical flow control for a broad range of angles of attack.     

Structural Analysis and Calculation for the Radiation Baffle of Cryopumps

To decrease the radiation heat load of the cryopanel is considered to be necessary for the design of cryopumps. In general, a radiation baffle is mounted between the cryopanel and the heat source. The radiation baffle absorbs the majority of the radiated heat load. However, the motion of molecules to be pumped is baffled and the pumping speed is lowered at the same time. Therefore the selection of a good radiation baffle is a very important issue for the economical operation of the cryopump. By calculating and comprehensively analyzing the thermal transmission coefficients and the molecular transmission coefficients of baffles of different structures, a type of Chevron baffle is found to be more satisfactory. This paper focuses on the application of the Monte Carlo Method involved in the process of analysis and calculation.     

Optical measurements and analytical modeling of magnetic field generated in a dieletric target

Polarization rotation of a probe pulse by the target is observed with the Faraday rotation method in the interaction of an intense laser pulse with a solid target.The rotation of the polarization plane of the probe pulse may result from a combined action of fused silica and diffused electrons.After the irradiation of the main pulse,the rotation angle changed significantly and lasted ～2 ps.These phenomena may imply a persistent magnetic field inside the target.An analytical model is developed to explain the experimental observation.The model indicates that a strong toroidal magnetic field is induced by an energetic electron beam.Meanwhile,an ionization channel is observed in the shadowgraph and extends at the speed of light after the irradiation of the main beam.The formation of this ionization channel is complex,and a simple explanation is given.     

Spatial Characteristics of Thomson Scattering in a Linearly Polarized Laser Field

The spatial characteristics of Thomson scattering in a linearly polarized laser field are investigated. The results show that the electron＇s motion and spatial distributions of Thomson scattering depend sensitively on the phase η0 at which the electron is injected to the laser field. When η0 equals to 0 or π, the electron motion is a zigzag motion and the spatial distributions of the emission show fourfold or twofold symmetry. In other cases of phases, there is a steady drift motion of electron in the transverse direction, which results in the absence of the zigzag motion and a breakdown of the symmetry of the spatial distributions as well.     

Removal of NO and SO2 in Corona Discharge Plasma Reactor with Water Film

In this paper, a novel type of a corona discharge plasma reactor was designed, which consists of needle-plate-combined electrodes, in which a series of needle electrodes are placed in a glass container filled with flue gas, and a plate electrode is immersed in the water. Based on this model, the removal of NO and SO2 was tested experimentally. In addition, the effect of streamer polarity on the reduction of SO2 and NO was investigated in detail. The experimental results show that the corona wind formed between the high-voltage needle electrode and the water by corona discharge enhances the cleaning efficiency of the flue gas because of the presence of water, and the cleaning efficiency will increase with the increase of applied dc voltage within a definite range. The removal efficiency of SO2 up to 98%, and about 85% of NO~ removal under suitable conditions is obtained in our experiments.     

Transition from Spark Discharge to Constricted Glow Discharge in Atmospheric Air by Capacitor Coupled Discharge

The transition from a spark discharge to a constricted glow discharge in atmospheric air was studied with a capacitor coupled pin-to-water plasma reactor. The reason of the transition is considered to be of various factors, namely the change of the air gap due to the polarization of water molecules by the electric field, the feedback effect of the capacitors, and the ion trapping mechanism. The effects of the frequency of the power supply, inter-electrode gap, and coupled capacitance on the discharge transition were also investigated.