Investigation of the diocotron instability of an infinitely wide sheet electron beam by using the macroscopic cold-fluid model theory

This paper investigates the diocotron instability of an infinitely wide relativistic sheet electron beam in conducting wMls propagating through a uniform magnetic field by using the macroscopic cold-fluid model theory. Assuming low- frequency perturbations with long axial wavelengths, the eigenvalue equation and the dispersion relation are acquired for a sheet electron beam with sharp boundary profile and uniform density. The results presented in this paper has developed the use of the macroscopic cold-fluid model theory by extending the parameter of the electron cyclotron frequency ωc to a wider usage range, which is restricted to be much larger than the plasma frequency ωp in the previous research work. Theoretical analyses and numerical calculations indicate that the transport of the sheet electron beam will be completely stabilized by augmenting the normalized beam thickness to a conductor gap larger than a threshold λb, which is greatly dependent on the parameter ωc/ωp. The larger ωc/ωp is, the smaller λb will be needed. Moreover, the system parameters, including the wave number kx of the perturbations and the relativistic mass factor γb, will also influence the growth rate of diocotron instability obviously.

Investigation of intense sheet electron beam transport using the macroscopic cold-fluid model and the single-particle orbit theory

The focusing and the stable transport of an intense elliptic sheet electron beam in a uniform magnetic field are investigated thoroughly by using the macroscopic cold-fluid model and the single-particle orbit theory.The results indicate that the envelopes and the tilted angles of the sheet electron beam obtained by the two theories are consistent.The single-particle orbit theory is more accurate due to its treatment of the space-charge fields in a rectangular drift tube.The macroscopic cold-fluid model describes the collective transport process in order to provide detailed information about the beam dynamics,such as beam shape,density,and velocity profile.The tilt of the elliptic sheet beam in a uniform magnetic field is carefully studied and demonstrated.The results presented in this paper provide two complete theories for systemically discussing the transport of the sheet beam and are useful for understanding and guiding the practical engineering design of electron optics systems in high power vacuum electronic devices.

Research on microstructure and property of electron beam welding joints of titanium alloy sheets

This paper reports research into the microstructures and properties of electron beam welding （EBW） joints of a Ti alloy sheet. To control the TC4 sheet joint formation during electron beam welding is not an easy task. However, the electron beam current has a significant influence on joint formation and a good appearance of a T-joint can be obtained by increasing the heat input and using the electron beam scan method. It was found that all acicular martensite in the fusion zone （FZ） consisted primarily of α＇ phase titanium, with some β phase present. Grain coarsening occurred in the heat-affected zone （HAZ） due to transformation of the β phase. Butt joints possessed high strength, hardness of the fusion zone, and the heataffected zone of these joints performed better than that of the parent metal. The highest shear strength of T-joint was 615 MPa and the fracture mechanism was a gliding fracture.

Electronic Excitation Temperature in DC Positive Streamer Discharge

The electronic excitation temperature in a direct current positive streamer discharge based on ultra-thin sheet electrodes was measured by optical emission spectrometry in order to deposit materials for potential future applications. It was remarkable that the electronic excitation temperature （Text） did not vary monotonically with the discharge current, but demonstrated a peak at a certain position. In a mixture of oxygen and argon （80% oxygen）, the maximum Texc reached about 6300 K at an average current of 600 pA. Both the positive ions accumulation in the discharge region and the increase of the local temperature around the streamer channel caused by Joule heating are considered to be the main reasons for the variations of Texc.

Splitting Process of Na-Birnessite Nanosheet via Transmission Electron Microscopy

The intermediate phase of hydrothermal synthesis of the Na0.44MnO2(NMO)nanowires is systematically investigated by means of transmission electron microscopy(TEM).The coexistence of Na-birnessite and NMO is commonly observed in the nanosheets.The NMO nanobelts in general have the width of~15 nm embedded in the(001)oriented Na-birnessite nanosheet.It is also found that the nanosheets of this intermediate phase often split along the NMO and Na-birnessite interface.Our structural study also shows that the NMO nanobelts prefer to grow along the[001]direction and gives rise to the[001]elongated NMO nanowires.Based on our TEM observations,the visible lattice mismatch and the resultant strain at the NMO/Na-birnessite interface play a critical role for formation of notable splitting structures in this kind of nanomaterial.The mechanism for the formation of the[001]NMO nanobelt is briefly discussed.

Dual-Mode Terahertz Extended Interaction Oscillator Driven by a Pseudospark-Sourced Sheet Electron Beam

A terahertz dual-mode extended interaction oscillator (EIO) driven by a pseudospark-sourced sheet electron beam (SEB) was presented.The major advantages of the newly developed circuit include 1) high-density SEB interacting with the TM_(11) and TM_(31) modes,respectively,and 2) high output power of over 1 kW at the subterahertz frequency range.Two different types of 2π modes and their output characteristics were studied,and the circuit was optimized to ensure efficient outputs of two standing-wave modes.The three-dimensional (3D) particle-in-cell (PIC) simulation predicts the maximum output power of 1.3 kW with the 3-dB bandwidth of ~0.5 GHz at 303 GHz when operating at the TM_(11)mode,and 3.18 kW with the 3-dB bandwidth of ~0.85 GHz at 364 GHz when operating at the TM_(31)mode.

Observations of kinetic Alfvén waves and associated electron acceleration in the plasma sheet boundary layer

Kinetic Alfvén waves(KAWs),with a strong parallel disturbed electric field,play an important role in energy transport and particle acceleration in the magnetotail.On the basis of high-resolution observations of the Magnetospheric Multiscale(MMS)Mission,we present a detailed description of the acceleration process of electrons by KAWs in the plasma sheet boundary layer(PSBL).The MMS observed strong electromagnetic disturbances carrying a parallel disturbed electric field with an amplitude of up to 8 mV/m.The measured ratio of the electric to magnetic field perturbations was larger than the local Alfvén speed and was enhanced as the frequency increased,consistent with the theoretical predictions for KAWs.This evidence indicates that the electromagnetic disturbances should be identified as KAWs.During the KAWs,the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel directions are significantly enhanced,implying occurrences of electron beams at higher energies.Additionally,the KAWs became more electrostaticlike and filled with high-frequency ion acoustic waves.The energy enhancement of electron beams is in accordance with the derived work done with the observed parallel disturbed electric field of KAWs,indicating electron acceleration caused by KAWs.Therefore,these results provide direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.

Electron transfer from sulfate-reducing bacteria biofilm promoted by reduced graphene sheets

Reduced graphene sheets (RGSs) mediate electron transfer between sulfate-reducing bacteria (SRB) and solid electrodes, and promote the development of microbial fuel cells (MFC). We have investigated RSG-promoted electron transfer between SRB and a glassy carbon (GC) electrode. The RGSs were produced at high yield by a chemical sequence involving graphite oxidation, ultrasonic exfoliation of nanosheets, and N2H4 reduction. Cyclic voltammetric testing showed that the characteristic anodic peaks (around 0.3 V) might arise from the combination of bacterial membrane surface cytochrome c3 and the metabolic products of SRB. After 6 d, another anodic wave gradually increased to a maximum current peak and a third anodic signal became visible at around 0 V. The enhancements of two characteristic anodic peaks suggest that RSGs mediate electron-transfer kinetics between bacteria and the solid electrode. Manipulation of these recently-discovered electron-transport mechanisms will lead to significant advances in MFC engineering.

Fabrication, microstructure and properties of electron beam-physical vapor deposited TiAl sheet and TiAl/Nb laminated composites

The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.

Preparation of Ti-Al alloy sheet by electron beam physical vapor deposition

Ti-Al thin sheet with dimension of 450 mm×450 mm×0.2 mm was prepared by electron beam physical vapor deposition(EB-PVD) technology. The surface and cross-section pattern of as-deposited sample were studied by SEM and AFM,and then the composition and phase were analysed by XRD and EPMA. Finally,the effect on deposit by re-evaporation of Al was explored by calculating the ratio of re-evaporating capacity with depositing capacity of Al on the substrate. The results indicate that the evaporation process with Nb addition into the molten pool makes it earlier to reach the steady-state. The existing equiaxed crystal and columnar crystal along the cross-sectional may be caused by the transformation latent heat released during the transition course of atoms from gaseous state to solid state. The effect on deposit by re-evaporation of Al can be neglected because the re-evaporating capacity of Al is far below that of the depositing capacity.

适用于共晶焊的肖特基二极管背面金属化工艺优化

[目的]为了降低成本,减少污染,提高工艺效率,对肖特基二极管背面金属化工艺进行研究,探索锡锑合金替代金系合金的最佳不持温镀膜金属化工艺.[方法]通过持温镀膜与不持温镀膜对比实验,分析电子束蒸发镀膜基片温度对阴极金属层间黏附性和导电性,以及薄膜厚度对空洞率的影响,得到适用于批量共晶焊的肖特基二极管背面金属化最优工艺参数.[结果]当基片温度为180℃时,不持温镀膜的剪切力为64.53 N,高于持温镀膜的剪切力;当金属化锡锑合金膜厚为3μm时,共晶焊的空洞率低于5%,符合共晶焊要求;电子束蒸发镀膜背面金属层方块电阻随基片温度升高先减小后增大,温度在180~240℃之间,方块电阻随基片温度的变化不大.[结论]用于共晶焊的肖特基二极管背面金属化的最优工艺为基底温度升到180℃后在自然降温的同时进行多层金属镀膜,锡锑合金镀膜厚度为3μm.

Dependence of Performance of Organic Light-emitting Devices on Sheet Resistance of Indium-tin-oxide Anodes

The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

The 600 keV electron injections in the Earth's outer radiation belt:A statistical study

Relativistic electron injections are one of the mechanisms of relativistic(≥0.5 MeV) electron enhancements in the Earth’s outer radiation belt. In this study, we present a statistical observation of 600 keV electron injections in the outer radiation belt by using data from the Van Allen Probes. On the basis of the characteristics of different injections, 600 keV electron injections in the outer radiation belt were divided into pulsed electron injections and nonpulsed electron injections. The 600 keV electron injections were observed at 4.5 < L <6.4 under the geomagnetic conditions of 450 nT < AE < 1,450 nT. An L of ~4.5 is an inward limit for 600 keV electron injections. Before the electron injections, a flux negative L shell gradient for ≤0.6 MeV electrons or low electron fluxes in the injected region were observed. For600 keV electron injections at different L shells, the source populations from the Earth’s plasma sheet were different. For 600 keV electron injections at higher L shells, the source populations were higher energy electrons(~200 keV at X ~–9 R_(E)), whereas the source populations for 600 keV electron injections at lower L shells were lower energy electrons(~80 keV at X ~–9 R_(E)). These results are important to further our understanding of electron injections and rapid enhancements of 600 keV electrons in the Earth’s outer radiation belt.

Macro-microscopic morphology and phase analysis of TiAl-based alloys sheet fabricated by EB-PVD method

TiAl-based alloys sheet with thickness of 0.3-0.4 mm as well as dimension of 150 mm×100 mm was fabricated successfully by using electron beam-physical vapor deposition(EB-PVD) method. The microscopic morphology and phase composition of specimens in various states were analyzed by atomic force microscope(AFM), scanning electron microscope(SEM) and X-ray diffractometer(XRD), respectively. The results indicate that the as-deposited TiAl-based alloys sheet has good surface quality and is composed of γ, α2 and τ phase. There is natural delamination inside the sheet, of which the microstructure is columnar crystal, and the component shows a gradient change along the normal direction of substrate. After the vacuum hot pressing treatment and subsequent homogenization treatment, the columnar crystal transforms into the coarse fully lamellar microstructure, the delamination phenomenon and τ phase disappear, α2 phase decreases obviously, and the composition tends to uniformization.

Contribution of patchy reconnection to the ion-to-electron temperature ratio in the Earth’s magnetotail

The ion-to-electron temperature ratio is a good indicator of the processes involved in the plasma sheet.Observations have suggested that patchy reconnection and the resulting earthward bursty bulk flows(BBFs)transport may be involved in causing the lower temperature ratios at smaller radial distances during southward IMF periods.In this paper,we estimate theoretically how a patchy magnetic reconnection electric field can accelerate ions and electrons differently.If both ions and electrons are non-adiabatically accelerated only once within each reconnection,the temperature ratio would be preserved.However,when reconnection occurs closer to the Earth where magnetic field lines are shorter,particles mirrored back from the ionosphere can cross the reconnection region more than once within one reconnection;and electrons,moving faster than ions,can have more crossings than do ions,leading to electrons being accelerated more than ions.Thus as particles are transported from tail to the near-Earth by BBFs through multiple reconnection,electrons should be accelerated by the reconnection electric field more times than are ions,which can explain the lower temperature ratios observed closer to the Earth.

Microstructure and properties of Ni-based superalloy sheet prepared by EB-PVD

Large-scale Ni-based superalloy sheet was prepared by electron beam physical vapour deposition. Microstructures and micropores of as-deposited and heat treated superalloy sheets were studied by scanning electron microscope, atomic force microscope, and optical microscope. The results show that the as-deposited superalloy sheet is mainly composed of columnar grain, whose major axes are parallel to the normal line of the sheet. The average diameter of crystalline grains in minor axis direction is about 300nm. After heat treatment, the superalloy sheet consists of equiaxed grains, the nanopores with high interfacial energy gather and form fewer pores with larger size, and there is notable increase in toughness.

Use of a Mid-Infrared Free-Electron Laser (MIR-FEL) for Dissociation of the Amyloid Fibril Aggregates of a Peptide

Amyloid fibrils are deposited in various tissues in the body, and are linked to the putative causes of serious diseases such as amyloidosis. Although the conditions of the disease would be expected to improve if the fibril structure could be destroyed, the aggregated structure is stable under physiological conditions. Recently, we found that the amyloid fibrils of lysozyme could be refolded into their active form by using a mid-infrared free-electron laser (MIR-FEL) tuned to the amide I band (corresponding to the C=O stretch vibration), with the MIR-FEL having specific oscillation characteristics of a picosecond pulse structure, a tunable wavelength within mid-infrared frequencies, and high photon density. In the study, we tested the usability of the FEL for dissociation of aggregates of pathological amyloid fibrils by using a short peptide of human thyroid hormone. The fibrils (after being placed on a glass slide) were irradiated using the FEL tuned to the amide I band (1644 cm?1), and those in situ were analyzed by Congo-Red assay, scanning-electron microscopy, and transmission-electron microscopy. All of the results obtained using these microscopic analyses indicated that the amyloid fibril formation was considerably decreased by FEL irradiation. Moreover, upon irradiation, a strong fibril peak at the amide I band in the infrared spectrum was transformed into a broad peak. These results imply that the β-sheet-rich structure of the amyloid fibrils changed into non-ordered or unspecified structures after the FEL irradiation. This FEL irradiation system, combined with various analytical methods, shows promise for the dissociation of amyloid aggregates.

太赫兹带状注器件

带状注是指束流截面近似为矩形或椭圆形的电子注,且具有大的宽高比。相对于传统的圆形注,带状注具有很多优点,例如大电流和大互作用面积等。由于太赫兹波具有高频率、宽频带、高传输速率等优点,因此太赫兹科学与技术近年来发展迅速。作为一种新型的真空电子器件,太赫兹带状注器件在高功率、高增益、高效率及小型化方面具有良好的技术优势。但是,带状注在传输过程中易出现Diocotron不稳定性,难以保持长距离稳定的聚焦传输,从而导致带状注的技术优势难以发挥。本文综述了带状注的产生成形方式和聚焦传输方法,以及太赫兹带状注器件的研究进展,同时讨论了它所面临的挑战和未来的发展方向。

热电制冷片热端换热性能仿真分析

提出热电制冷片热端换热性能仿真分析,为其实际应用提供换热性能基础数据。上述方法以某品牌热电制冷散热器为研究对象,使用Icepak电子热分析仿真软件构建该散热器的热电制冷片换热仿真模型,并对该模型实施网格划分后生成热电制冷片换热计算点。通过设置热电制冷片热端换热性能仿真假设、边界条件和热电制冷片热端散热方式,使用网格划分后的热电制冷片换热仿真模型模拟不同散热方式、不同热电制冷片高度情况时热电制冷片热端换热性能。仿真结果表明,热电制冷片热端换热性能受其热电制冷片高度和散热方式影响较大,与散热器温度无关,当热电制冷片高度为2.0mm,散热方式为强制风冷散热时,热电制冷片的热端换热性能较好。