DC active power filter based on model predictive control for DC bus overvoltage suppression of accelerator grid power supply

The China Fusion Engineering Test Reactor plans to build a 200 k V/25 A acceleration grid power supply(AGPS)for the negative-ion-based neutral beam injector prototype system.The AGPS uses a rectifier-inverter-isolated step-up structure.There is a DC bus between the rectifier and the inverter.In order to limit DC bus voltage ripple and transient fluctuations,a large number of capacitors are used,which degrades the reliability of the power supply and occupies a large amount of space.This work finds that due to the difference in the turn-off time of the rectifier and the inverter,the capacitance mainly depends on the rectifier current when the inverter is turned off.On this basis,an active power filter(APF)scheme is proposed to absorb the current.To enhance the dynamic response ability of the APF,model predictive control is adopted.In this paper,the circuit structure of the APF is introduced,the prediction model is deduced,the corresponding control strategy and signal detection method are proposed,and the simulation and experimental results show that APF can track the transient current of the DC bus and reduce the voltage fluctuation significantly.

Simulation of a helicon plasma source in a magnetoplasma rocket engine

The helicon plasma source,which generates high thrust and high impulse,is of vital importance for magnetoplasma rocket engines.In this work,a multi-component,two-dimensional,axisymmetric fluid model coupled with an electromagnetic field was developed to model the helicon discharge.The simulation results demonstrate that:(i)the discharge mode changes twice—each conversion is accompanied by a plasma density jump and an electron temperature peak in the discharge;(ii)when the input current increases,the plasma density increases,and ionization occurs faster;(iii)the background magnetic field clearly enhances the discharge;(iv)the plasma density may be smaller if the discharge has not entered the wave mode.

Effect of shock wave formation on propellant ignition in capillary discharge

In order to study the effect of shock wave formation on propellant ignition in capillary discharge,the shock wave formation process was analyzed using experimental and theoretical methods;the plasma jet temperature was measured,and closed bomb and 30 mm gun experiments were carried out.The results show that the first shock wave has a smaller value and larger range of influence,while the second shock wave has a larger value and smaller range of influence.A plasma jet can generate a shock wave at the nozzle according to the calculated plasma pressure and velocity,which is well confirmed by experiments and calculations.The plasma jet temperature is high during the formation of a shock wave and then decreases sharply.Plasma ignition can increase the burning rate of a propellant by about 30%by increasing the burning surface area of the propellant.Compared to conventional ignition,the average maximum chamber pressure and average muzzle velocity of plasma ignition are increased by 9.1 MPa and29.3 m·s^(-1)(~3%),respectively,in a 30 mm gun.Plasma ignition has strong ignition ability and short ignition delay time due to the generation of a shock wave.By increasing the burning rate of the propellant,the muzzle velocity can be greatly improved when the maximum chamber pressure increases a little.The characteristics of the shock wave can be applied in the application of the capillary discharge plasma.For example,it can be applied in fusion,launching and combustion.

Recent results of fusion triple product on EAST tokamak

High fusion triple product has been obtained in the advanced scenarios with high normalized beta(βN)on the Experimental Advanced Superconducting Tokamak(EAST).A record value of ni0Ti0τE1.0×1019m^(-3)ke V s for EAST deuterium plasma has been achieved,which is due to the formation of strong and broad internal transport barriers(ITBs)in ne,Teand Tiprofiles.Analysis shows that the strong ITB formation could be attributed to the reduction of transport from ITG modes.Based on the analysis,the physical mechanisms and methods to furtherimprove the plasma performance are discussed.

The far-field plasma characteristics of LHT40 low-power Hall thruster for commercial aerospace applications

To achieve a better insight into the far-field plasma spatial distribution and evolution characteristics of the 300 W class low-power Hall thruster(LHT)for commercial aerospace applications,a dedicated and integrated plasma diagnostic system composed of seventeen Faraday cups(FC)and two triple Langmuir probes(TLP)is established to investigate the timeaveraged in situ spatial distribution characteristics of far-field ions and electrons.The ion current density(ICD),plasma potential,plasma density,and electron temperature at 1000 mm downstream of 300 W class LHT for commercial aerospace applications in the azimuthal angle range of-90°to 90°were investigated under the conditions of different anode mass flow rates and discharge voltages.The results demonstrated that ICD,beam divergence angle,and mass utilization efficiency increased with increasing anode mass rate.The double-wings phenomenon was observed in the spatial distribution of ICD at large angles from the thruster axis,which is attributed to charge exchange collisions at increasing vacuum backpressure.The plasma electron temperature,electron density,and plasma potential parameters derived from the TLP decreased rapidly in the angle range from 0°to 30°and did not exhibit significant variations above 30°,which was also in good agreement with the results of the measured divergence angle of the FC.The discrepancy of average ion speed was calculated.The maximum error is better than 31.5%which checks the consistency between the TLP’s results and that of FC to some extent.

Magnetic field induction and magnetic force distribution profiles in plasma focus discharge device

We report a simple-to-perform technique to investigate the distribution of the azimuthal magnetic field induction,Bθ,and the induced magnetic force acting on the plasma current sheath(PCS)in a plasma focus(PF)discharge.This in situ measurement technique can undoubtedly be beneficial when other fast-imaging techniques are not available.techniques are not available.Experimental work was conducted in the low-energy Mather-type EAEA-PF1 device operated in argon.The axial distribution(Bθ)z along the coaxial electrodes system was measured with a four magnetic-probe set technique at different radial distances(r=2.625×10^(−2) to 4.125×10^(−2) m)within the annular space between the coaxial electrodes during the 1st and 2nd half cycles of the discharge current waveform,where inner electrode of coaxial electrode system has a+ve polarity and−ve polarity,respectively.Axial,radial and total magnetic force distribution profiles were estimated from Bθdata.Investigation of PCS shape in terms of its inclination(curvature)angle,θ,along the axial rundown phase and the correlation between the magnetic forces per unit volume acting on the PCS,the inclination angleθof the PCS,and the formation of a powerful PF action during the 1st and 2nd half cycles is carried out.Dependence of inclination angle,θ,on total magnetic force per unit volume acting on PCS axial motion was studied,separately,during the 1st and 2nd half cycles.

Three-dimensional non-equilibrium modeling of a DC multi-cathode arc plasma torch

In this paper,a three-dimensional non-equilibrium steady arc model is used to investigate the temperature,velocity and electromagnetic field in multi-cathode arc torch,and the formation mechanism of a large-area,uniform and diffused arc plasma is analyzed.The numerical simulation results show that a large volume plasma region can be formed in the central region of the generator during discharge.During this process,the maximum electron temperature appears near the cathode and in the central convergence region,while the maximum heavy particle temperature only appears in the central convergence region.This phenomenon is consistent with the experimental arc images.Near the cathode tip,the arc column is in a contraction state.In the area slightly away from the cathode,the six arc columns begin to join together.In the plasma generator,there is a large-scale current distribution in all directions of X,Y and Z,forming a stable arc plasma with a wide range of diffusion.The calculated electron temperature distribution is in good agreement with the measured electron temperature.The results suggest that the largearea diffused arc plasma in the multi-cathode arc torch is the combined effect of current distribution,convection heat transfer and heat conduction.

Evaluation of influence of cold atmospheric pressure argon plasma operating parameters on degradation of aqueous solution of Reactive Blue 198(RB-198)

The intention of this work is to remove Reactive Blue 198(RB-198)dye components from simulated water solution using cold atmospheric pressure argon plasma jet.Aqueous solutions of RB-198 dye were treated as a function of various operating parameters such as applied potential,reaction time and distance between the plasma jet and surface of the liquid.The efficiency of the degradation of RB-198 molecules was explored by means of UV-Vis spectroscopy.The reactive species involved during the treatment process were examined by optical emission spectra(OES).The present hydroxyl radicals(OH·radical)and hydrogen peroxide(H2O2)in the plasma-treated aqueous dye solutions were investigated using various spectroscopic techniques.The other parameters such as total organic carbon(TOC),conductivity and p H were also reviewed.The toxicity of plasma-treated RB-198 solution was finally studied by diffusion bacterial analysis and by tracking seed germination processes.The results show that a higher degradation percentage of99.27%was acquired for the RB-198 treated at higher reaction time and applied potential,and shorter distance between the plasma jet and water surface.This may be due to the formation of various reactive oxygen(OH·radical,atomic oxygen(O)and H2O2)and nitrogen species(nitric oxide(NO)radicals and N2 second positive system(N2 SPS))during the processes as confirmed by OES analysis and other spectroscopy analysis.TOC(17.7%-81.8%)and pH(7.5-3.4)values of the plasma-treated RB-198 decreased significantly with respect to various operation parameters,which indicates the decomposition of RB-198 molecules in the aqueous solution.Moreover,the conductivity of plasma-treated RB-198 aqueous solutions was found to have increased linearly during the plasma treatment due to the formation of various ionic species in aqueous solution.The toxicity analysis clearly exhibits the non-toxic behavior of plasma-treated RB-198 aqueous solution towards the bacterial growth and germination of seeds.

Vickers hardness change of the Chinese low-activation ferritic/martensitic steel CLF-1 irradiated with high-energy heavy ions

In the present work,the irradiation hardening behavior of a Chinese low-activation ferritic/martensitic steel CLF-1,a candidate for fusion reactor blankets,is studied.Specimens were irradiated with high-energy14N and56Fe ions at the terminal of a cyclotron to three successively increasing damage levels of 0.05,0.1 and 0.2 displacements per atom(dpa)at about-50°C.The energy of the incident ions was dispersed to 11 successively decreasing grades using an energy degrader,thereby generating an atomic displacement damage plateau in the specimens from the surface to a depth of 25μm,which is sufficiently broad for the Vickers hardness test.Eight different loads(i.e.98 mN,196 m N,490 m N,980 m N,1.96 N,4.9 N,9.8 N and 19.6 N)were applied to the specimens to obtain the depth profiles of the Vickers hardness by using a microhardness tester.Hardening was observable at the lowest damage level,and increased with increasing irradiation dose.A power-law correlation of the Vickers hardness with the damage level(HV0=1.49+0.76 dpa0.31)is proposed.Testing with a nano-indentation technique was also performed,and a linear relationship between the Vickers micro-hardness and the nanohardness(HV0=0.83 H0)was observed.A comparison with other RAFM steels(CLAM,JLF-1,F82 H,EUROFER97 etc.)under neutron or charged particle irradiation conditions shows that most of the RAFM steels exhibit similar power-law exponents in the dose dependence of irradiation hardening.The difference in the irradiation hardening may be attributed to differences in microstructure prior to irradiation.

Accuracy improvement of quantitative analysis of calorific value of coal by combining support vector machine and partial least square methods in laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy(LIBS) is a potential technology for online coal property analysis,but successful quantitative measurement of calorific value using LIBS suffers from relatively low accuracy caused by the matrix effect.To solve this problem,the support vector machine(SVM) and the partial least square(PLS) were combined to increase the measurement accuracy of calorific value in this study.The combination model utilized SVM to classify coal samples into two groups according to their volatile matter contents to reduce the matrix effect,and then applied PLS to establish calibration models for each sample group respectively.The proposed model was applied to the measurement of calorific values of 53 coal samples,showing that the proposed model could greatly increase accuracy of the measurement of calorific values.Compared with the traditional PLS method,the coefficient of determination(R2) was improved from 0.93 to 0.97,the root-mean-square error of prediction was reduced from 1.68 MJ kg-1 to1.08 MJ kg-1,and the average relative error was decreased from 6.7% to 3.93%,showing an overall improvement.

Dynamic dielectric recovery performance of serial vacuum and SF6 gaps in HVDC interruption and its regulation method

Vacuum gaps have rapid dynamic dielectric recovery speed while SF6 gaps have high insulation strength. The series-connected vacuum and SF6 gaps are used as the main switch(MS), which combines their advantages. The work aims to verify the feasibility of serial vacuum and SF6 gaps in mechanical HVDC interruption. The test circuit of the dynamic dielectric recovery performance(DDRP) is set up. The DDRP is tested under free recovery condition by the high voltage pulse source. The DDRP of the vacuum circuit breaker(VCB) and SF6 gas circuit breaker(GCB) in DC interruption with active current injection is analyzed and compared. The test results indicate that the dielectric recovery duration of the VCB is below 30 μs while that of the GCB is above 100 μs. In order to achieve the cooperation between the VCB and GCB, a novel hybrid HVDC circuit breaker(CB) based on series-connected vacuum and SF6 gaps is proposed. The ‘voltage-zero’ duration is created by introducing the follow current loop and there more recovery time for the dielectric recovery of the MS. The voltage distribution is controlled by the voltage dividing method so that the VCB undertakes the initial transient recovery voltage(TRV) and the later TRV is took by the GCB. The theoretical synergy characteristic of the novel HVDC CB is obtained. The paper supplies a new method to improve the custom mechanical HVDC CB, which is useful to achieve the HVDC CB with less serial breaks.

Recent ICRF coupling experiments on EAST

Recent ion cyclotron resonance frequency（ICRF） coupling experiments for optimizing ICRF heating in high power discharge were performed on EAST. The coupling experiments were focus on antenna phasing and gas puffing, which were performed separately on two ports of the ion cyclotron resonance heating（ICRH） system of EAST. The antenna phasing was performed on the I-port antenna, which consists of four toroidally spaced radiating straps operating in multiple phasing cases; the coupling performance was better under low wave number ∣k;∣（ranging from 4.5 to 6.5）. By fuelling the plasma from gas injectors, placed as uniformly spaced array from top to bottom at each side limiter of the B-port antenna, which works in dipole phasing, the coupling resistance of the B-port antenna increased obviously.Furthermore, the coupling resistance of the I-port antenna was insensitive to a smaller rate of gas puffing but when the gas injection rate was more than a certain value(>1021 s;), a sharp increase in the coupling resistance of the I-port antenna occurred, which was mainly caused by the toroidal asymmetric boundary density arising from gas puffing. A more specific analysis is given in the paper.

Effect of distances between lens and sample surface on laser-induced breakdown spectroscopy with spatial confinement

Spatial confinement can significantly enhance the spectral intensity of laser-induced plasma in air. It is attributed to the compression of plasma plume by the reflected shockwave. In addition,optical emission spectroscopy of laser-induced plasma can also be affected by the distance between lens and sample surface. In order to obtain the optimized spectral intensity, the distance must be considered. In this work, spatially confined laser-induced silicon plasma by using a Nd：YAG nanosecond laser at different distances between lens and sample surface was investigated.The laser energies were 12 mJ, 16 mJ, 20 mJ, and 24 mJ. All experiments were carried out in an atmospheric environment. The results indicated that the intensity of Si（I） 390.55 nm line firstly rose and then dropped with the increase of lens-to-sample distance. Moreover, the spectral peak intensity with spatial confinement was higher than that without spatial confinement. The enhancement ratio was approximately 2 when laser energy was 24 mJ.

Influence of dielectric barrier discharge treatment on mechanical and dyeing properties of wool

Physical and chemical properties of wool surface significantly affect the absorbency,rate of dye bath exhaustion and fixation of the industrial dyes.Hence,surface modification is a necessary operation prior to coloration process in wool wet processing industries.Plasma treatment is an effective alternative for physiochemical modification of wool surface.However,optimum processing parameters to get the expected modification are still under investigation,hence this technology is still under development in the wool wet processing industries.Therefore,in this paper,treatment parameters with the help of simple dielectric barrier discharge plasma reactor and air as a plasma gas,which could be a promising combination for treatment of wool substrate at industrial scale were schematically studied,and their influence on the water absorbency,mechanical,and dyeing properties of twill woven wool fabric samples are reported.It is expected that the results will assist to the wool coloration industries to improve the dyeing processes.

Accurate quantitative CF-LIBS analysis of both major and minor elements in alloys via iterative correction of plasma temperature and spectral intensity

The chemical composition of alloys directly determines their mechanical behaviors and application fields. Accurate and rapid analysis of both major and minor elements in alloys plays a key role in metallurgy quality control and material classification processes. A quantitative calibration-free laser-induced breakdown spectroscopy（CF-LIBS） analysis method, which carries out combined correction of plasma temperature and spectral intensity by using a secondorder iterative algorithm and two boundary standard samples, is proposed to realize accurate composition measurements. Experimental results show that, compared to conventional CF-LIBS analysis, the relative errors for major elements Cu and Zn and minor element Pb in the copperlead alloys has been reduced from 12%, 26% and 32% to 1.8%, 2.7% and 13.4%, respectively.The measurement accuracy for all elements has been improved substantially.

Thermal analysis on the EAST tungsten plasma facing components with shaping structure counteracting the misalignment issues

Tungsten monoblock type tiles with ITER dimensions along with supporting cassette components were installed at EAST＇s upper diverter during 2014 and EAST＇s lower diverter will also be upgraded in the future. These cassette structures pose critical issues on the high cumulative incident heat flux due to the leading edges and misalignments （0 ～ 1.5 mm）, which may result in the destruction or even melting of the tungsten tile. The present work summarizes the thermal analysis using ANSYS multiphysics software 15.0 performed on the actively cooled W tiles to evaluate the shaping effect on surface temperature. In the current heat flux conditions （Q11 ～ 100 MW m-2）, the adopted chamfer shaping （1 ×1 mm） can only reduce the maximum temperature by about 14%, but it also has a melting risk at the maximum misalignment of 1.5 mm. The candidate shaping solutions elliptical （round） edge, dome and fish-scale are analyzed for comparison and are identified not as good as the dual chamfer structure. A relatively good dual chamfer （2 ×13 mm） shaping forming a symmetrical sloping roof structure can effectively counteract the 1.5 mm misalignment, reducing the maximum temperature by up to 50%. However, in the future heat flux conditions （Q11 ～287 MW m-2）, it may only endure about 0.5 mm misalignment. Moreover, no proper shaping solution has been found that can avoid melting at the maximum misalignment of 1.5 mm. Thus, the engineering misalignment has to be limited to an acceptable level.

Numerical simulation of inducing characteristics of high energy electron beam plasma for aerodynamics applications

potential flow control method for large scale flow.In this paper,a computational fluid dynamics model coupled with a multi-fluid plasma model is established to investigate the aerodynamic characteristics induced by electron beam plasma.The results demonstrate that the electron beam strongly influences the flow properties,not only in the boundary layers,but also in the main flow.A weak shockwave is induced at the electron beam injection position and develops to the other side of the wind tunnel behind the beam.It brings additional energy into air,and the inducing characteristics are closely related to the beam power and increase nonlinearly with it.The injection angles also influence the flow properties to some extent.Based on this research,we demonstrate that the high energy electron beam air plasma has three attractive advantages in aerodynamic applications,i.e.the high energy density,wide action range and excellent action effect.Due to the rapid development of near space hypersonic vehicles and atmospheric fighters,by optimizing the parameters,the electron beam can be used as an alternative means in aerodynamic steering in these applications.

Geodesic acoustic mode in a reduced two-fluid model

A reduced two-fluid model is constructed to investigate the geodesic acoustic mode（GAM）. The ion dynamics is sufficiently considered by including an anisotropic pressure tensor and inhibited heat flux vector, whose evolutions are determined by equations derived from the 16-momentum model. Electrons are supposed to obey the Boltzmann distribution responding to the electrostatic oscillation with near ion acoustic velocity. In the large safety factor limit, the GAM frequency is identical with the kinetic one to the order of 1 q2 when zeroing the anisotropy. For general anisotropy, the reduced two-fluid model generates the frequency agreeing well with the kinetic result with arbitrary electron temperature. The present simplified fluid model will be of great use and interest for young researchers and students devoted to plasma physics.

Delicate scale multipeak and flat-top structures of solitary waves in multicomponent plasmas

Numerically the delicate scale multipeak structures of the electrostatic solitary waves are found for the three-component（electron-positron-ion,i.e.,EPI） plasmas.The complicated homoclinic phase portraits for this two-degree-of-freedom system are presented,which indicate that the system exhibits more abundant nonlinear phenomena.This finding is very useful to unveil the coherent dynamical behavior in laser-plasma interaction.It has an implication of electron acceleration by a laser with soliton wave mechanism.

The Effect of Ion Motion on Laser-Driven Plasma Wake in Capillary

The effect of ion motion in capillary-guided laser-driven plasma wake is investigated through rebuilding a two-dimensional analytical model.It is shown that laser pulse with the same power can excite more intense wakefield in the capillary of a smaller radius.When laser intensity exceeds a critical value,the effect of ion motion reducing the wakefield rises,which becomes significant with a decrease of capillary radius.This phenomenon can be attributed to plasma ions in smaller capillary obtaining more energy from the plasma wake.The dependence of the difference value between maximal scalar potential of wake for two cases of ion rest and ion motion on the radius of the capillary is discussed.