The current pulses characteristics of the negative corona discharge in SF_(6)/CF_(4)mixtures

This paper presents the results of numerical investigation of the current pulses characteristics in SF_(6)/CF_(4)mixtures for the negative point-plane corona discharge.The pressure and the temperature of gas mixtures are 0.4 MPa and 300 K,respectively.The CF_(4)content varies from20%to 80%.The 2D axisymmetric geometry with point-plane electrodes is investigated,and the three drift-diffusion equations are solved to predict the characteristics of the negative corona discharge.In addition,Poisson’s equation is coupled with the above three continuity equations to calculate the electric field.In order to calculate the electron impact coefficients,including the Townsend ionization and attachment coefficients,as well as the mobilities and diffusion coefficients for electrons,the two-term Boltzmann equation is solved.The characteristics of three ionic species at five stages of the first current pulse in 60%SF_(6)-40%CF_(4)and20%SF_(6)-80%CF_(4)mixtures are selected to discuss the development mechanism of current pulses.Moreover,the reduced electric field strengths at the corresponding time instants are presented to help understand the discharge process.The current waveform and the total number of three species are compared in all the cases to analyze the effects of the CF_(4)content on the discharge.The reduced electric field strength is also helpful in understanding the effects of CF_(4)content.When the CF_(4)content increases to 80%,the discharge is more intensive and the pulse frequency also increases.

The characteristics of negative corona discharge and radio interference at different altitudes based on coaxial wire-cylinder gap

The corona discharge from transmission lines in high-altitude areas is more severe than at lower altitudes. The radio interference caused thereby is a key factor to be considered when designing transmission lines. To study the influence of altitude on negative corona characteristics, an experimental platform comprising a movable small corona cage was established: experiments were conducted at four altitudes in the range of 1120-4320 m, and data on the corona current pulse and radio interference level of 0.8-mm diameter fine copper wire under different negative voltages were collected. The experimental results show that the average amplitude, repetition frequency and average current of the corona current pulse increase with increasing altitude. The dispersion of pulse amplitude increases with increase in altitude, while the randomness of the pulse interval decreases continuously. Taking the average current as an intermediate variable,the relationship between radio interference level and altitude is obtained. The result of this research has some significance for understanding the corona discharge characteristics of ultra-highvoltage lines.

Characteristic studies on positive and negative streamers of double-sided pulsed surface dielectric barrier discharge

The mechanisms of streamer generation and propagation in double-sided pulsed surface dielectric barrier discharge(SDBD)on both sides have been analyzed and investigated by experiment and numerical simulation.The fully exposed asymmetric SDBD has two discharge processes located on the high voltage electrode(HVE)side and the ground electrode(GE)side.Discharge images of the HVE side and GE side are taken by a digital camera under continuous pulse and ICCD(Intensified Charge Coupled Device)is utilized to diagnose the generation and propagation of streamers in single pulse discharge.In order to understand the physical mechanisms of streamer evolution more deeply,we establish a 2D simulation model and analyze it from the aspects of electron density,ion density,reduced electric field and electron impact ionization source term.The results show that the primary and secondary discharges on the HVE side and the GE side of the double-sided SDBD are composed of positive streamer and negative streamer,respectively.On the HVE side,the accumulation of positive charges on the dielectric surface causes the direction of the electric field to reverse,which is the principal factor for the polarity reversal of the streamer.On the GE side,both the negative charges accumulated on the dielectric surface and the falling voltage are the key factors for the streamer polarity switch.

Spectroscopic diagnosis of plasma in atmospheric pressure negative pulsed gas-liquid discharge with nozzle-cylinder electrode

The plasma characteristics of a gas-liquid phase discharge reactor were investigated by optical and electrical methods.The nozzle-cylinder electrode in the discharge reactor was supplied witha negative nanosecond pulsed generator.The optical emission spectrum diagnosis revealed that OH（A2∑＋ → X2Π,306–309 nm）,N32（CΠ→B3Πg,337 nm）,O（3p5p→3s-5s-0,777.2 nm）and O（3p3p→3s3s0,844.6 nm）were produced in the discharge plasma channels.The electron temperature（Te）was calculated from the emission relative intensity ratio between the atomic O 777.2 nm and 844.6 nm,and it increased with the applied voltage and the pulsed frequency and fell within the range of 0.5–0.8 e V.The gas temperature（Tg）that was measured by Lifbase was in a range from 400 K to 600 K.

First results of negative ion extraction with Cs for CRAFT prototype negative beam source

In order to understand the physics and pre-study the engineering issues for radio frequency(RF)negative beam source,a prototype source with a single driver and three-electrode accelerator was developed.Recently,the beam source was tested on the RF source test facility with RF plasma generation,negative ion production and extraction.A magnetic filter system and a Cs injection system were employed to enhance the negative ion production.As a result,a long pulse of 105 s negative ion beam with current density of 153 A m-2 was repeatedly extracted successfully.The source pressure is 0.6 Pa and the ratio of co-extracted electron and negative ion current is around0.3.The details of design and experimental results of beam source were shown in this letter.

Introduction to investigations of the negative corona and EHD flow in gaseous two-phase fluids

Research interests have recently been directed towards electrical discharges in multi-phase environments.Natural electrical discharges,such as lightning and coronas,occur in the Earth＇s atmosphere,which is actually a mixture of gaseous phase（air） and suspended solid and liquid particulate matters（PMs）.An example of an anthropogenic gaseous multi-phase environment is the flow of flue gas through electrostatic precipitators（ESPs）,which are generally regarded as a mixture of a post-combustion gas with solid PM and microdroplets suspended in it.Electrical discharges in multi-phase environments,the knowledge of which is scarce,are becoming an attractive research subject,offering a wide variety of possible discharges and multi-phase environments to be studied.This paper is an introduction to electrical discharges in multi-phase environments.It is focused on DC negative coronas and accompanying electrohydrodynamic（EHD） flows in a gaseous two-phase fluid formed by air（a gaseous phase） and solid PM（a solid phase）,run under laboratory conditions.The introduction is based on a review of the relevant literature.Two cases will be considered：the first case is of a gaseous two-phase fluid,initially motionless in a closed chamber before being subjected to a negative corona（with the needle-toplate electrode arrangement）,which afterwards induces an EHD flow in the chamber,and the second,of a gaseous two-phase fluid flowing transversely with respect to the needle-to-plate electrode axis along a chamber with a corona discharge running between the electrodes.This review-based introductory paper should be of interest to theoretical researchers and modellers in the field of negative corona discharges in single-or two-phase fluids,and for engineers who work on designing EHD devices（such as ESPs,EHD pumps,and smoke detectors）.

Evolution of ionization waves in a multi-pulsed plasma jet:the role of memory charges

In this paper,we discuss the properties of ionization waves(IWs)in a multi-pulsed plasma jet while using the two-dimensional computational approach.The IWs are generated by application of three short negative pulses with a repetition frequency 12.5 MHz.The simulations are performed continuously during a single run while accounting for charges accumulated inside(surface charges)and outside(space charges)the tube.The plasma forming gas mixture(He/O2=99.8%/0.2%)is injected through the discharge tube into the surrounding humid air.We show that an IW can emerge from the tube exit at a pulse rising edge(as a negative IW)and at a falling edge of the same pulse(as a positive IW).It is demonstrated that remnants of the negative and positive charges play an essential role in the discharge evolution.The first pulse travels the shortest distance as it propagates through the initially non-ionized environment.The IWs developing during the second pulse essentially enlarge the plasma plume length.At the same time,the IWs generated by the third pulse eventually decay due to the remnants of charges accumulated during the previous pulses.Accumulated memory charges can lead to the IW extinction.

Study on the discharge mechanism and EM radiation characteristics of Trichel pulse discharge in air

The Trichel pulse stage is an unstable stage of negative corona discharge that can also involve electromagnetic(EM)radiation signals.In this paper,the discharge mechanism and radiation characteristics of the Trichel pulse are studied in the needle-plate electrode configuration.The Trichel pulse currenl and its EM radiation signals are measured at different applied voltages.The results show that Trichel pulse discharge changes from the nindom pulse stage to the continuous pulse stage as the applied voltage increases.During these different stages,the normalized shape of the Trichel pulses remains unchanged,while the frequency of the EM radiation generated by the discharge remains unchanged.The discharge mechanism and EM radiation characteristics of the Trichel pulse are theoretically analyzed in the different stages.Both the positive ion sheath and the negative ion cloud play key roles in the formation of the Trichel pulse.The EM radiati on signal is generated by the rapidly changing Trichel pulse current,and the Trichel pulse current waveform determines the characteristics of the EM radiation signal.

China's First New Type Commercial Pulse Reactor——Xi'an Pulse Reactor

A new type of commercial reactor is first built up in China.This paper briefly describesits performances,working foundamentals and various possible uses.The reactor uses urani-um-zirconium hydride as fuel element and has a large prompt negative temperature coefficientof reactivity,featuring inherent safety and a fairly high pulsed-power capacity.

Review on ionization and quenching mechanisms of Trichel pulse

Trichel pulse is a kind of pulsed mode in negative DC corona discharge,which has attracted significant attention because of its considerable applications in industry.Over eighty years,plenty of effort including simulations and experiments has been spent to reveal the ionization and quenching mechanisms of Trichel pulse.By revisiting and summarizing the basic characteristics and well-accepted ionization and quenching mechanisms,this review provides a basic understanding and the current status of Trichel pulse.

THEORY AND EXPERIMENT ON THE VISCOUS HEATING OF FLUID DAMPER UNDER SHOCK ENVIRONMENT

A specially designed fluid damper used as negative shock pulse generator in the shock resistance test system to dissipate the shock input energy in transient time duration is presented. The theoretical modeling based on the three-dimensional equation of heat transfer through a fluid element is created to predict the viscous heating in the fluid damper under shock conditions. A comprehensive experimental program that investigates the problem of viscous heating in the fluid damper under different shock conditions is conducted on the shock test machine to validate the analytical expression. Temperature histories for the fluid within the damper at two locations, the annular-oriflce and the-end-of stroke of the damper, are recorded. The experimental results show that the theoretical model can offer a very dependable prediction for the temperature histories in the damper for increasing input velocity. The theoretical model and experimental data both clearly indicate that the viscous heating in the damper is directly related to the maximum shock velocity input and the pressure between the two sides of the piston head.

Investigation and active suppression of self-heating induced degradation in amorphous InGaZnO thin film transistors

Self-heating effect in amorphous InGaZnO thin-film transistors remains a critical issue that degrades device performance and stability, hindering their wider applications. In this work, pulsed current–voltage analysis has been applied to explore the physics origin of self-heating induced degradation, where Joule heat is shortly accumulated by drain current and dissipated in repeated time cycles as a function of gate bias. Enhanced positive threshold voltage shift is observed at reduced heat dissipation time, higher drain current, and increased gate width. A physical picture of Joule heating assisted charge trapping process has been proposed and then verified with pulsed negative gate bias stressing scheme, which could evidently counteract the self-heating effect through the electric-field assisted detrapping process. As a result, this pulsed gate bias scheme with negative quiescent voltage could be used as a possible way to actively suppress self-heating related device degradation.

NUMERICAL MODELING OF MULTI-CYLINDER ELECTRO-HYDRAULIC SYSTEM AND CONTROLLER DESIGN FOR SHOCK TEST MACHINE

A high fidelity dynamic model of a high-energy hydraulically-actuated shock test machine for heavy weight devices is presented to satisfy the newly-built shock resistance standard and simulate the actual underwater explosion environments in laboratory as well as increase the testing capability of shock test machine. In order to produce the required negative shock pulse in the given time duration, four hydraulic actuators are utilized. The model is then used to formulate an advanced feedforward controller for the system to produce the required negative waveform and to address the motion synchronization of the four cylinders. The model provides a safe and easily controllable way to perform a ＂virtual testing＂ before starting potentially destructive tests on specimen and to predict performance of the system. Simulation results have demonstrated the effectiveness of the controller.

A Control System Design to Establish Dose-Response Relationships in Wound Healing Therapy

Advanced biophysical wound healing therapies can apply mechanical, electrical, or light energy to re-stimulate healing processes in chronic wounds. Despite the growing evidence of the clinical efficacy of these therapies, the optimal treatment stimulation parameters remain unknown and there are no standard treatment protocols. We introduce a closed-loop control design as an experimental system to study the dose-response of wound healing therapy treatment within a prescribed multidimensional and multimodal stimulation parameter space. Systems engineering approaches are applied to the control problem for estimation of a transfer function and model equations derived for use in optimal model-based control. The experimental control system design consisted of simultaneous application of biophysical energies inputted into a wound system. A study design set up including the use of negative pressure wound therapy, electrical stimulation therapy, and photobiomodulation device systems was described. Treatment stimulation parameters were selected from experimental ranges used in the scientific literature. Classical control methods and model-based control were suggested for model selection and evaluation and design of the overall control system. An experimental design for multimodal biophysical wound healing therapy control system is introduced to establish the dose-response interactions for development of therapeutic applications and device design.