Preparation and particle size characterization of Cu nanoparticles prepared by anodic arc plasma

Copper nanoparticles were successfully prepared in large scale by means of anodic arc discharging plasma method in inert atmosphere. The particle size, specific surface area, crystal structure, and morphology of the samples were characterized by X-ray diffraction （XRD）, BET equation, transmission electron microscopy （TEM）, and the corresponding selected area electron diffraction （SAED）. The experimental results indicate that the crystal structure of the samples is fcc structure the same as that of the bulk materials. The specific surface area is 11 m^2/g, the particle size distribution is 30 to 90 nm, and the average particle size is about 67 nm obtained from TEM and confirmed from XRD and BET results. The nanoparticles with uniform size, high purity, narrow size distribution and spherical shape can be prepared by this convenient and effective method.

Study of electron-extraction characteristics of an inductively coupled radio-frequency plasma neutralizer

Inductively coupled radio-frequency（RF） plasma neutralizer（RPN） is an insert-free device that can be employed as an electron source in electric propulsion applications.Electron-extraction characteristics of the RPN are related to the bulk plasma parameters and the device＇s geometry.Therefore,the effects of different electron-extraction apertures and operational parameters upon the electron-extraction characteristics are investigated according to the global nonambipolar flow and sheath model.Moreover,these models can also be used to explain why the electron-extraction characteristics of the RPN strongly depend upon the formation of the anode spot.During the experimental study,two types of anode spots are observed.Each of them has unique characteristics of electron extraction.Moreover,the hysteresis of an anode spot is observed by changing the xenon volume-flow rates or the bias voltages.In addition,the rapid ignited method,gas-utilization factor,electron-extraction cost and other factors that need to be considered in the design of the RPN are also discussed.

PARTICLE SIZE AND MICROSTRUCTURE OF Ni NANOPOWDERS PREPARED BY ANODIC ARC PLASMA

Pure Ni nanopowders were successfully prepared by the method of anodic arc disch arged plasma with homemade experimental apparatus. The particle size, mircostruc ture and morphology of the particles by this process were characterized via X-ra y powder diffraction (XRD), transmission electron microscopy (TEM) and the corre sponding selected area electron diffraction (SAED); The specific surface area an d pore parameters were investigated by multi-point full analysis of nitrogen ads orption-desorption isotherms at 77K by Brunauer- Emmett-Teller (BET) surface are a analyzer; The chemical composition were determined by X-ray energy dispersive spectrometry (XEDS) equipped in SEM and element analyze instrument. The experime nt results indicate that the samples by this method with high purity,the crystal structure of the particles is as same as the bulk material, is fcc structure, w ith average particle sizes about 47nm, ranging from 20 to 70nm, and distributed uniformly in spherical chain shapes, the specific surface areavis 14.23m2/g, po re volume of pore is 0.09cm3/g and average pore diameter is 23nm.

Volt-ampere characteristics of a nitrogen DC plasma arc with anode melting

The characteristics of a nitrogen arc using a graphite cathode and a melting anode in a pilot-scale plasma furnace are investigated. The voltage is examined as a function of current and apparent plasma length. The voltage increases non-linearly with the increase of apparent plasma length, with the current fixed. The experimental data so obtained are compared with the predictions of the Bowman model for the electric arc, and with numerical simulations as well. The level of agreement between the experimental data at the melting anode and the numerical predictions confirms the suitability of the proposed the Bowman model. These characteristics are relevant to the engineering design and evaluation of a DC plasma furnace and reactor for the treatment of hazardous fly ash waste.

Effects of anode material on the evolution of anode plasma and characteristics of intense electron beam diode

In this paper,three kinds of materials including graphite,titanium(Ti)and molybdenum(Mo)are used as anodes to figure out the influence factors of anode material on the characteristics of the intense electron beam diode.The results show that the characteristics of diode are mainly determined by the cathode plasma motion under a 15 mm diode gap,in which the typical electron beam parameters are 280 kV,3.5 kA.When the diode gap is reduced to 5 mm,the voltage of the electron beam reduces to about 200 kV,and its current increases to more than 8.2 kA.It is calculated that the surface temperatures of Ti and Mo anodes are higher than their melting points.The diode plasma luminescence images show that Ti and Mo anodes produce plasmas soon after the bombardment of electron beams.Ti and Mo lines are respectively found in the plasma composition of Ti and Mo anode diodes.Surface melting traces are also observed on Ti and Mo anodes by comparing the micromorphologies before and after bombardment of the electron beam.These results suggest that the time of anode plasma generation is closely related to the anode material.Compared with graphite,metal Ti and Mo anodes are more likely to produce large amounts of plasma due to their more significant temperature rise effect.According to the moment that anode plasma begins to generate,the average expansion velocities of cathode and anode plasma are estimated by fitting the improved space-charge limited flow model.This reveals that generation and motion of the anode plasma significantly affect the characteristics of intense electron beam diode.

Influence of Cathode Plasma on Breakdown Formation in Plasma-Anode Explosive-Emission Source

Breakdown formation in an explosive-emission electron source is related to the interelectrode gap filling with plasma propagating from the cathode and formed at the anode and in the interelectrode gap under the electron beam action. Plasma anode is used to increase the beam current density. Preliminary interelectrode gap filling with plasma in the explosive-emission source decreases the influence of uncontrolled plasma arrival from the anode on the diode processes, promotes current density increase and duration of generated electron beams. The paper considers the influence of the cathode geometry on the breakdown formation in the plasma-anode explosive-emission electron source. The data on obtaining of microsecond electron beams with current density of 30 A/cm^2 and 1.5-2 kA/cm^2 are presented.

Anode Plasma Influence on Breakdown Formation in Explosive-Emission Electron Sources

Breakdown formation in the explosive-emission sources is related to the interelectrode gap filling with the cathode and anode plasma generated at the anode and in the gap under the beam influence. Under conditions of saturation of the cathode plasma emissive ability as well as when the measures on the emission boundary stabilization are taken, the anode plasma has the deciding part in the formation of the electron source breakdown. The paper presents the results of the anode plasma investigations obtained to solve the problem of the electron beam length increase in the explosive-emission sources. The data concerning the gas release from the anode, the mechanism of the anode plasma formation and the anode plasma influence on the parameters of the generated electron beam are presented as well.

Simulational Investigation of a High-Efficiency X-Band Magnetically Insulated Line Oscillator

Abstract The magnetically insulated line oscillator （MILO） is a gigawatt-class, coaxial crossed-field microwave tube, which is at present a major hotspot in the field of high-power mi- crowaves （HPM） research. In order to improve the power conversion efficiency and eliminate or at least minimize anode plasma formation in the load region and radio frequency （RF） breakdown in the slow wave structure （SWS） section, an X-band MILO is presented and inyestigated nu- merically with KARAT code. The design idea is briefly presented and the simulation results are given and discussed. In the simulation, HPM is generated with peak power of 3.4 GW, maximum electric field of about 1 MV/cm, and peak power conversion efficiency of 14.0%, when the voltage is 559.1 kV and the current is 43.2 kA. The microwave frequency is pure and falls in the X-band of 9.0 GHz. The theoretical investigation and the simulation results are given to prove that the anode plasma formation and the RF breakdown can be effectively avoided or at least minimized, respectively.