Stress wave analysis of high-voltage pulse discharge rock fragmentation based on plasma channel impedance model

High-voltage pulse discharge(HVPD)rock fragmentation controls a plasma channel forming inside the rock by adjusting the electrical parameters,electrode type,etc.In this work,an HVPD rock fragmentation test platform was built and the test waveforms were measured.Considering the effects of temperature,channel expansion and electromagnetic radiation,the impedance model of the plasma channel in the rock was established.The parameters and initial values of the model were determined by an iterative computational process.The model calculation results can reasonably characterize the development of the plasma channel in the rock and estimate the shock wave characteristics.Based on the plasma channel impedance model,the temporal and spatial distribution characteristics of the radial stress and tangential stress in the rock were calculated,and the rock fragmentation effect of the HVPD was analyzed.

The influence of pore characteristics on rock fragmentation mechanism by high-voltage electric pulse

High-voltage electric pulse(HVEP)is an innovative low-energy and high-efficiency technique.However,the underlying physics of the electrical breakdown within the rock,and the coupling mechanism between the various physical fields involved in HVEP still need to be further understood.In this study,we establish a 2D numerical model of multi-physical field coupling of the electrical breakdown of porous rock with randomly distributed pores to investigate the effect of pore characteristics(porosity,pore media composition)on the partial electrical breakdown of rock(i.e.the generation of a plasma channel inside the rock).Our findings indicate that the generation of a plasma channel is directionally selective and extends in the direction of a weak electrical breakdown intensity.As the porosity of the rock increases,so does the intensity of the electric field in the‘electrical damage’region—the greater the porosity,the greater the effectiveness of rock-breaking.As the fraction of pore fluid(S_(water)/S_(air))gradually declines,the generation time of the plasma channel decreases,and the efficacy of rock-breaking by HVEP increases.In addition,in this study,we conducted an indoor experiment utilizing an electric pulse drill to break down the rock in order to recreate the growth mode of the plasma channel in the rock.Moreover,the experimental results are consistent with the simulation results.In addition,the development of this type of partial electrical breakdown is confirmed to be related to electrode polarity and pore characteristics via the experiment of the symmetrical needle-needle electrode arrangement,which further demonstrates the mechanism of partial electrical breakdown.This research is significant for comprehending the process of electric impulse rock-breaking and gives theoretical guidance and technological support for advancing electric impulse drilling technology.

Removal of phenol by activated alumina bed in pulsed high-voltage electric field

A new process for removing the pollutants in aqueous solution-activated alumina bed in pulsed high-voltage electric field was investigated for the removal of phenol under different conditions. The experimental results indicated the increase in removal rate with increasing applied voltage, increasing pH value of the solution, aeration, and adding Fe^2＋. The removal rate of phenol could reach 72.1% when air aeration flow rate was 1200 ml/min, and 88.2% when 0.05 mmol/L Fe^2＋ was added into the solution under the conditions of applied voltage 25 kV, initial phenol concentration of 5 mg/L, and initial pH value 5.5. The addition of sodium carbonate reduced the phenol removal rate. In the pulsed high-voltage electric field, local discharge occurred at the surface of activated alumina, which promoted phenol degradation in the thin water film. At the same time, the space-time distribution of gas-liquid phases was more uniform and the contact areas of the activated species generated from the discharge and the pollutant molecules were much wider due to the effect of the activated alumina bed. The synthetical effects of the pulsed high-voltage electric field and the activated alumina particles accelerated phenol degradation.

Removal of Volatile Organic Compounds (VOCs) Mixture by Multi-Pin-Mesh Corona Discharge Combined with Pulsed High-Voltage

Removal of single component and binary mixtures of benzene and m-xylene using a multi-pin-mesh reactor was studied to find the decomposition characteristics, carbon balance and CO2 selectivity. The decomposition rate of benzene in mixture was approximately 16% lower than that of single component benzene. However, the decomposition rate of m-xylene in mixture was slightly higher than that of single component m-xylene. Carbon balance of the mixture decomposition process achieved a lower level than that of single component benzene/m-xylene. Increase in the specific input energy was helpful to improve CO2 selectivity in the single component decomposition process, while the specific input energy had a negligible effect on CO2 selectivity in the mixture decomposition process. By changing the oxygen content in background gas, we found that different types of radicals showed different reaction activities toward benzene and m-xylene. Benzene was more likely to react with nitrogen-containing radicals, while m-xylene was more likely to react with oxygen-containing radicals.

Effects of High-voltage Pulse Electric Field Treatment on the Structure Stability of Konjac Glucomannan

Structures of KGM treated in two high-voltage pulse electric fields were characterized by infrared spectroscopy,Raman spectroscopy,X-ray diffraction and so on.The results showed that intermolecular hydrogen bonding interactions of KGM were reduced after being treated with high-voltage pulse electric field,but there was no significant effect on its fiber chain form and thermal characteristics.Results of the study can provide a useful reference for further study on the structure and property of KGM,and especially can provide theoretical basis for the effect of physical field on the foodstuff deep processing related to KGM.

A novel variable polarity welding power based on high-frequency pulse modulation

A new type of variable polarity welding power modulated with high-frequency pulse current is developed. Series of high-frequency pulse current is superimposed on direct-current-electrode-negative （DCEN）, which can improve the crystallization process in the weld bead as a result of the electromagnetic force generated by pulse current. Digital signal processor （DSP） is used to realize the closed-loop control of the first inverter, variable polarity output of the second inverter and high-frequency pulse current superposition.

Strengthening leaching effect of Carlin-type gold via high-voltage pulsed discharge pretreatment

A high-voltage pulsed discharge(HVPD)pretreatment was used to strengthen the leaching effect of Carlin-type gold ore containing arsenic.Optimal results of the pretreatment experiments were obtained at the following operating conditions:a spherical gap spacing of 20 mm,pulse number of 100,and voltage of 30 kV.The leaching rate of gold was increased by 15.65%via the HVPD pretreatment.The mass fraction of–0.5+0.35 mm and–0.35+0.1 mm was increased by 10.97%and 6.83%compared to the untreated samples,respectively,and the Au grade of–0.1 mm was increased by 22.84%.However,the superiority of the HVPD pretreatment would be weakened by prolonged grinding time.Scanning electron microscopy results indicated that the pretreated products presented as a melting state and then condensation,accompanying by some pore formation.More micro-cracks were generated at the interface of the ore and the original crack were expended via pulsed discharge pretreatment,with the contact area between the leaching reagent and ore increased,the leaching reaction rate enhanced and the leaching effect strengthened.

Design and Simulation for the Pulse High-Voltage DC Power Supply (HVPS) of 1.2 MW/2.45 GHz HT-7U Lower Hybrid Current Drive System

The superconducting tokamak HT-7U [1] has been designed by the Institute of Plasma Physics since 1998 and will be set up before 2003. The 1.2 MW /2.45 GHz HT-7U LHCD (Lower hybrid current drive) system which being the most efficient non-induction device can heat the plasma and drive the plasma current has been efficiently in operation 'owl and a particular design of the 2.8 MW/-35 kV high-voltage DC power supply has been already completed and will apply to the klystron of LHCD on HT-7 and the future HT-7U, and the project of the power supply has been examined and approved professionally by an authorized group of high-level specialist in the institute of Plasma Physics. The detailed design of the power supply and the simulation results are referred in the paper.

Photographic Study on Spark Discharge Generated by a Nanosecond High-Voltage Pulse over a Water Surface

Spark discharge generated by a nanosecond positive high-voltage pulse over a water surface at atmospheric pressure in air was studied using a high speed camera system. Faint streamers form near the pin electrode and propagate towards the water surface. The time for the streamer propagating across the air gap was estimated to be about 50 ns to 60 ns with a propagation velocity of ～1.3 × 10^5 m/s. It was found that the water conductivity and the gap distance have no significant effect on the propagation velocity of the streamer. After the streamers touch the water surface a brilliant spark channel forms across the air gap. The maximum diameter at the middle of the spark channel is about 1 mm, and approximately contracts with a radical velocity of about 2.0× 10^3 m/s. No significant dependence of the maximum diameter and decay velocity of the spark channel on the water conductivity and the gap distance were recognized in the present work. The maximum conduction current for a gap distance of 5 mm is significantly larger than that for a gap distance of 10 mm at the same water conductivity, and shows an increasing tendency with increasing water conductivity for a fixed gap distance. Based on the maximum conduction current, the effect of water conductivity and gap distance on the electron density of the spark discharge plasma at the peak current was investigated. Within the range studied, the electron density in the spark channel is about 10^15 cm^-3 and increases with water conductivity at a fixed gap distance.

Influence of high frequency pulse on electrode wear in micro-EDM

An electromagnetic coupling mathematical model is established by finite element method and is verified by the contrastive experiments of copper matrix Ni-TiN cylindrical coating electrode,copper electrode and Cu50 W electrode.The wear mechanism of Ni-TiN/Cu composite electrode in the case of high-frequency pulse current is studied,and the influence of the fluctuation frequency of discharge current on electrode wear in micro-EDM is found out.Compared with the electrode made from homogeneous material,the high frequency electromagnetic properties of Ni-TiN composite layer can be used effectively to inhibit the effect of high frequency pulse on the electrode and improve the distribution trend of current density.

Inactivation of Bacteria in Oil Field Injected Water by a Pulsed Plasma Discharge Process

Pulsed plasma discharge was employed to inactivate bacteria in the injection water for an oil field. The effects of water conductivity and initial concentration of bacteria on elimination efficiency were investigated in the batch and continuous flow modes. It was demonstrated that Fe2＋ contained in injection water could enhance the elimination efficiency greatly. The addition of reducing agent glutathione （GSH） indicated that active radicals generated by pulsed plasma discharges played an important role in the inactivation of bacteria. Moreover, it was found that the microbial inactivation process for both batch and continuous flow mode well fitted the model based on the Weibull＇s survival function.

Simulation method of near-fault pulse-type ground motion

The two characteristics of near-fault ground motions, i.e., the forward directivity effect and permanent displacement effect, result in long period and large velocity pulse in the velocity time history and large step pulse in the displacement time history. Considering the two effects, a simple expression of continuous function for equivalent velocity pulse time history is presented in this paper. The equivalent pulse model, in which the pulse period, peak velocity and pulse shape are described by five parameters, is highly advantageous to fit and simulate the pulse-type velocity time history. The equivalent pulse model comprises only one low-frequency component while the high-frequency component of a pulse-type earthquake record cannot be considered. Based on 28 records of 11 earthquakes, the pulse frequency of pulse-type records is generally less than 1 Hz. Therefore the low-frequency component and high-frequency component are simulated respectively and combined them together to generate a pulse-type ground motion.

Effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge in atmospheric airflow

In this paper,an asymmetric electrode geometry(the misalignment between the ends of highvoltage and grounded electrodes)is proposed in order to investigate the effects of the transverse electric field on nanosecond pulsed dielectric barrier discharge(DBD).The results show that diffuse discharge manifests in the misaligned region and the micro-discharge channel in the aligned region moves directionally.Moreover,the diffuse discharge area increases with the decrease of the discharge gap and pulse repetition frequency,which is consistent with the variation of the moving velocity of the micro-discharge channel.When airflow is introduced into the discharge gap in the same direction as the transverse electric field,the dense filamentary discharge region at the airflow inlet of asymmetric electrode geometry is larger than that of symmetric electrode geometry.However,when the direction of the airflow is opposite to that of the transverse electric field,the dense filamentary discharge region of asymmetric electrode geometry is reduced.The above phenomena are mainly attributed to the redistribution of the space charges induced by the transverse electric field.

Numerical simulation of super-short pulsed discharge in helium with particle-in-cell Monte Carlo collisions technique

This paper reports that a simulation of glow discharge in pure helium gas at the pressure of 1.333×10^3 Pa under a high-voltage nanosecond pulse is performed by using a one-dimensional particle-in-cell Monte Carlo collisions （PIC-MCC） model. Numerical modelling results show that the cathode sheath is much thicker than that of anode during the pulse discharge, and that there exists the phenomenon of field reversal at relative high pressures near the end of the pulse, which results from the cumulative positive charges due to their finite mobility during the cathode sheath expansion. Moreover, electron energy distribution function （EEDF） and ion energy distribution function （IEDF） have been also observed. In the early stage of the pulse, a large amount of electrons can be accelerated above the ionization threshold energy. However, in the second half of the pulse, as the field in bulk plasma decreases and thereafter the reverse field forms due to the excessive charges in cathode sheath, although the plasma density grows, the high energy part of EEDF decreases. It concludes that the large volume non-equilibrium plasmas can be obtained with high-voltage nanosecond pulse discharges.

Oxidation of S(Ⅳ)in Seawater by Pulsed High Voltage Discharge Plasma with TiO_2/Ti Electrode as Catalyst~

Oxidation of S（IV） to S（VI） in the effluent of a flue gas desulfurization（FGD） sys- tem is very critical for industrial applications of seawater FGD. This paper reports a pulsed corona discharge oxidation process combined with a TiO2 photocatalyst to convert S（IV） to S（VI） in artificial seawater. Experimental results show that the oxidation of S（IV） in artificial seawater is enhanced in the pulsed discharge plasma process through the application of TiO2 coating electrodes. The oxidation rate of S（IV） using Ti metal as a ground electrode is about 2.0x10-4 mol. L 1. min-1, the oxidation rate using TiO2/Ti electrode prepared by annealing at 500 ~C in air is 4.5x 10-4 tool. L-a ~ min-1, an increase with a factor 2.25. The annealing temper- ature for preparing TiO2/Ti electrode has a strong effect on the oxidation of S（IV） in artificial seawater. The results of in-situ emission spectroscopic analysis show that chemically active species （i.e. hydroxyl radicals and oxygen radicals） are produced in the pulsed discharge plasma process. Compared with the traditional air oxidation process and the sole plasma-induced oxidation process, the combined application of TiO2 photocatalysts and a pulsed high-voltage electrical discharge process is useful in enhancing the energy and conversion efficiency of S（IV） for the seawater FGD system.

High-frequency Resonance Analysis and Impedance Reshaping Control of MMC-HVDC System Based on Frequency Coupling Impedance Model

In recent years, high-frequency resonance (HFR) events occurred in several modular multilevel converter based high-voltage direct current (MMC-HVDC) projects. The time delay of an MMC-HVDC system is the critical factor that induces HFR. The frequency coupling affects the impedance characteristics of an MMC and further deteriorates system stability. Therefore, in this paper, a multi-input multi-output admittance model of an MMC-HVDC system is developed to analyze its frequency characteristics. The effects of current loop, power loop, phase-locked loop, and operating point on the MMC frequency coupling degree are analyzed in detail. Meanwhile, to further suppress HFR in the MMC-HVDC system, an enhanced impedance reshaping control strategy based on the equivalent single-input single-output impedance model is proposed. Finally, the accuracy of the enhanced impedance model and the effectiveness of the impedance reshaping control are verified by electromagnetic transient simulations in PSCAD.

Thermal Performance of a 4 K High-Frequency Pulse Tube Cryocooler with Different Working Fluids

The high-frequency pulse tube cryocooler(HPTC)represents a promising miniature cryocooling technology due to its compact structure and the absence of low-temperature moving components.However,limited to the non-ideal gas effect of4He,the HPTC is hard to obtain high cooling performance in the liquid helium temperature range.3He as the working fluid can effectively improve the cooling performance of the HPTC,but the high cost hinders its wide application.In consideration of both cooling performance and cost-effectiveness,this paper explores the feasibility of utilizing^(3)He-^(4)He mixtures as the working fluid for HPTCs.Firstly,the experimental results of a developed HPTC based4He are reported.With a total power consumption of 575 W,the lowest temperature of 3.26 K was observed.And the measured cooling power at 4.2 K was 20.8 mW.Then the theoretical utmost efficiency of the cryocooler was calculated in terms of the thermophysical properties of the working fluids,using ^(3)He-^(4)He mixtures with different compositions as the working fluids.The whole machine modeling of the HPTC was further carried out,and the influence of the working fluids with different components on the structural parameters such as double-inlet and inertance tube,and operating parameters such as pressure and frequency were analyzed.The calculated results show that the cooling power is expected to be increased to36 mW and 53 mW if the equimolar ^(3)He-^(4)He mixture and pure ^(3)He are used,respectively.

Single-frequency Er:YAG ceramic pulsed laser with frequency stability close to 100 kHz

A single-frequency 1645 nm pulsed laser with frequency stability close to 100 kHz was demonstrated. The laser oscillator is injection-seeded by a single-frequency narrow linewidth Er∶Y_(3)Al_(5)O_(12)(Er:YAG) nonplanar ring oscillator and frequency stabilized by the modified Pound–Drever–Hall method. The pulse repetition rate can be set from 100 to 500 Hz with the frequency stability from 82.72 kHz to 134.44 kHz and pulse energy from 9.84 mJ to 19.55 mJ. To our knowledge, this is the best frequency stability of a single-frequency pulsed laser with injection-seeding.

Fusion power supply advances by the J-TEXT engineering team

To meet the stringent requirements of the fusion power supply for large-scale fusion devices,the J-TEXT engineering team has carried out key technology research and applications in several important directions of fusion power supply.This article presents the advances made by the J-TEXT engineering team in recent years in the following areas:(1) a high-voltage power supply for an auxiliary heating system;(2) a breakdown protection device for an auxiliary heating power supply;(3) magnetic field compatibility;(4) a high-voltage pulsed power supply for a fieldreversed configuration;(5) a large physics experimental facility control system.The research backgrounds,technical progress,test results,applications,summaries and prospects are described in detail in each part.These innovative research results and valuable engineering experience can promote the progress of fusion power supply technology,and also lay a foundation for the development of power supplies with higher parameters in the future.