Cathode erosion site distributions in an applied-field magnetoplasmadynamic thruster

Erosion can influence cathode life,and is thus considered to be one of the main factors limiting the application of applied-field magnetoplasmadynamic thrusters.In this paper,erosion sites on graphite cathodes are studied so as to identify the influence of applied magnetic field and the ratio of propellant mass flow rate supplied from cathode and anode.The experiment results show that the application of applied magnetic field can significantly reduce the erosion rate of the cathode compared to that without magnetic field.The erosion sites on the cathode vary with the relative position of the convergent-divergent magnetic field,and are mainly distributed in the divergent part of the field.The erosion sites on the cathodes are found to be related to the propellant supply.The decreasing anode mass flow rate enlarges the range of erosion.These results are much helpful for the analysis of cathode erosion site location since they provide evidences of erosion mechanisms and point out the directions for further research.

Electron population properties with different energies in a helicon plasma source

The characteristics of electrons play a dominant role in determining the ionization and acceleration processes of plasmas.Compared with electrostatic diagnostics,the optical method is independent of the radio frequency(RF)noise,magnetic field,and electric field.In this paper,an optical emission spectroscope was used to determine the plasma emission spectra,electron excitation energy population distributions(EEEPDs),growth rates of low-energy and highenergy electrons,and their intensity jumps with input powers.The 56 emission lines with the highest signal-to-noise ratio and their corresponding electron excitation energy were used for the translation of the spectrum into EEEPD.One discrete EEEPD has two clear different regions,namely the low-energy electron excitation region(neutral lines with threshold energy of13–15 eV)and the high-energy electron excitation region(ionic lines with threshold energy?19 e V).The EEEPD variations with different diameters of discharge tubes(20 mm,40 mm,and 60 mm)and different input RF powers(200–1800 W)were investigated.By normalized intensity comparison of the ionic and neutral lines,the growth rate of the ionic population was higher than the neutral one,especially when the tube diameter was less than 40 mm and the input power was higher than 1000 W.Moreover,we found that the intensities of low-energy electrons and high-energy electrons jump at different input powers from inductively coupled(H)mode to helicon(W)mode;therefore,the determination of W mode needs to be carefully considered.

Special issue on selected papers from CEPC 2020

The development of electric propulsion has taken decades and in fact, began flight testing as early as the 1960s. However, it was initially slow to develop as an alternative to chemical propulsion systems due to the lack of available on-board electrical power for space vehicles. Since the turn of this century, the booming satellite market, and in particular for small satellites, has driven the demand for propulsion systems with high specific impulse, precisely adjustable thrust, long lifetime, and adaptable for different kinds of small vehicles.

Polyacrylic acid sodium salt film entrapped Ag-nanocubes as molecule traps for SERS detection

提高表面的拉曼光谱学(重量的单位) 是为踪迹化学药品的一种快分析技术；然而，吸附 analytes 要求活跃重量的单位底层，因此为底层与需要的亲密关系限制目标种类到那些。这里我们现在的联网的 polyacrylic 酸钠盐(PAAS ) 电影骗诱 Ag-nanocubes (作为 Ag-nanocubes@PAAS 表示了) 作为为有或没有高亲密关系的 analytes 的有效重量的单位底层。一次 analyte 水的答案在干燥 Ag-nanocubes@PAAS 底层上被扔，嗜酒的 PAAS 变得肿强迫 Ag-nanocubes 松开，当时在在 Ag-nanocubes 之中的空隙弥漫的 analytes。当弄干时， PAAS 缩小并且拉 Ag-nanocubes 回到他们的以前的聚集的状态，当 PAAS 网络为重量的单位察觉在在 Ag-nanocubes 之间的小差距耽搁 analytes 时。没有强壮的亲密关系，策略为 Ag 为不仅 singleanalytes 而且 multi-analytes 被证明有效，在环境在能吸附、非能吸附的污染物质的基于重量的单位的同时的 multi-analyte 察觉显示出它的潜力。

Hexagonally arranged arrays of urchin-like Ag hemispheres decorated with Ag nanoparticles for surface-enhanced Raman scattering substrates

The surface topography of noble metal particles is a significant factor in tailoring surface-enhanced Raman scattering （SERS） properties. Here, we present a simple fabrication route to hexagonally arranged arrays of surface-roughened urchin- like Ag hemispheres （Ag-HSs） decorated with Ag nanoparticles （Ag-NPs） for highly active and reproducible SERS substrates. The urchin-like Ag-HS arrays are achieved by sputtering Ag onto the top surface of a highly ordered porous anodic aluminum oxide （AAO） template to form ordered arrays of smooth Ag-HSs and then by electrodepositing Ag-NPs onto the surface of each Ag-HS. Owing to the ordered arrangement of the Ag-HSs and the improved surface roughness, the urchin-like hierarchical Ag-HS arrays can provide sufficient and uniform ＂hot spots＂ for reproducible and highly active SERS effects. Using the urchin-like Ag-HS arrays as SERS substrates, 10-7 M dibutyl phthalate （a member of plasticizers family） and 1.5 × 10-5 M PCB-77 （one congener of polychlorinated biphenyl, a notorious class of pollutants） are identified, showing promising potential for these substrates in the rapid recognition of organic pollutants.

ZnO-nanotaper array sacrificial templated synthesis of noble-metal building-block assembled nanotube arrays as 3D SERS-substrates

这份报纸描述一个 ZnO-nanotaper 数组为有试管墙的 nanotubes 的数组的制造的合成途径由 Ag-nanoplates， Au-nanorods， Pt-nanothorns 或 Pd-nanopyramids 的大楼块装配了的牺牲的 templated，因此拥有高密度的 3D 在有 nano 尖端，角落或边的附近的积木的 sub-10-nm 差距的热点。另外，这些层次 nanostructure 数组与富有的表面化学拥有高表面区域，对捕获 analyte 有益。Ag-nanoplateassembled nanotube 数组能被用作散布的敏感提高表面的拉曼(重量的单位) 有好信号一致性和重制度的底层。用如此的 Ag ，层次 nanostructure 作为重量的单位底层穿，不是仅仅有 10 <啜class=“ a-plus-plus ”> 14 M 玫瑰精 6G 识别，而且 10 <啜class=“ a-plus-plus ”> 7 M polychlorinated 联本基(印刷电路板，坚持的器官的污染物质的一个臭名昭著的班)被认出，并且甚至印刷电路板的二同种的物能在混合物被识别，在环境器官的污染物质的基于重量的单位的快速的察觉显示出材料的潜在的应用。

Selective laser melting of dense and crack-free AlCoCrFeNi_(2.1) eutectic high entropy alloy: Synergizing strength and ductility

Additively manufactured high-entropy alloys generally suffer from low strength and/or poor ductility.In this work,by leveraging the good castability of eutectic high entropy alloys and high cooling rate of selective laser melting(SLM),we report a nearly fully dense and crack-free as-SLM AlCoCrFeNi_(2.1) eutectic high entropy alloy with an exceptional strength-ductility synergy,showing an ultrahigh yield strength of 982.1±35.2 MPa and an ultimate tensile strength of 1322.8±54.9 MPa together with an elongation to fracture of 12.3±0.5%.Such strength-ductility enhancement is owing to the heterogeneous eutectic microstructure consisting of the columnar,equiaxed,and“L-shape”cells with much refined sizes down to nanoscales.The morphology of cells in the transition zone is related to the misorientation between the growth direction of adjacent layers.This heterogeneous eutectic microstructure is the result of the graingrowth behavior dominated by the mechanisms of the epitaxial growth and growth of heterogeneous nuclei in SLM.Our current results provide a new methodology for the future design of ultrahigh-strength and ductile SLM-fabricated metallic materials including HEAs,and other printable alloys for various structural applications.

Origin of strong and narrow localized surface plasmon resonance of copper nanocubes

Inexpe nsive copper nano particles are generally thought to possess weak and broad localized surface plasm on resonance(LSPR).The,present experimental and theoretical studies show that tailoring the Cu nanoparticle to a cubic shape results in a single intense,narrow,and asymmetric LSPR line shape,which is even superior to round-shaped gold nanoparticles.In this study,the dielectric function of copper is decomposed into an interband transition component and a free-electron component.This allows interband transition-induced plasmon damping to be visualized both spectrally and by surface polarization charges.The results reveal that the LSPR of Cu nanocubes originates from the comer mode as it is spectrally separated from the interb and transitions.In additi on,the interband tran sitions lead to severe damping of the local electromagnetic field but the cubic corner LSPR mode survives.Cu nanocubes display an extinction coefficient comparable to the dipole mode of a gold nanosphere with the same volume and show a larger local electromagnetic field enhancement These results will guider-development of in expensive plasmonic copper-based nano materials.

Coupling plasma plume of a low-power magnetically shielded Hall thruster with a hollow cathode

The coupling region of a Hall thruster with a hollow cathode is the region between the cathode and the thruster plume.The characteristics of plasma in that region are complicated and strongly associated with the thruster working conditions and the cathode position.In this paper,a laboratory 100 W class magnetically shielded Hall thruster was coupled with a hollow cathode.Optical imaging and electrostatic probe were employed to monitor and scan the plasma plume.Plume characteristics in the coupling region in non-self-sustained mode and self-sustained mode were compared.Evolution of the coupling plume with the cathode position was studied.Experiments show that,when turning the thruster into self-sustained mode or moving the cathode further away axially,the discharge current can be reduced by 6.4–10.6%restraining the electron current and improving ionization.In particular,when the cathode is moved further,the electron conduction near the channel walls is suppressed.The electron current is reduced by 27.4%and the ion beam current is increased by 7%.Overall,this work shows that the working mode of the thruster and the position of the cathode greatly affect the coupling plasma plume.Both play an important role in improving the utilizations of propellant and current.

The azimuthal currents in the ion-driven magnetic nozzle

Ion-driven magnetic nozzles(Ti>Te)are designed as intrinsic parts of cutting-edge propulsive technologies such as variable specific impulse magnetoplasma rockets(VASIMRs)and applied-field magnetoplasmadynamic thrusters.Employing a two-dimensional axisymmetric particle-in-cell(PIC)code,in the ion-driven magnetic nozzle,the compositions and distributions of azimuthal currents in different axial regions are investigated under various inlet ion temperatures Ti0 and found to differ dramatically from that in the electron-driven magnetic nozzles.Previously reported to be all paramagnetic and vanishing under a high magnetic field,the azimuthal currents resulting from the E 3 B drift are shown to turn diamagnetic and sustain a considerable magnitude when Ti0 is considered.The previously reported profile of diamagnetic drift current is altered by the introduction of inlet ion temperature,and the paramagnetic part is significantly suppressed.Moreover,a wide range of paramagnetic currents appear downstream due to the inward detachment of ions,which can also be reduced by increasing inlet ion temperature.Albeit considered in this paper,the azimuthal currents resulting from grad-B and curvature drift are still negligible in all cases of interest.The magnitude of diamagnetic azimuthal currents increases with amplifying Ti0,indicating a clear physical image of energy transformation from ion thermal energy to the directed kinetic energy through electromagnetic processes in the magnetic nozzle.Additionally,the magnetic inductive strength also has noticeable impacts on the azimuthal currents,the current magnitude tends to decrease as the magnetic field increases,and over-increment of it may result in larger divergence angles and lower nozzle efficiency.