Terahertz coherent transition radiation based on an ultrashort electron bunching beam

The experimental result of terahertz （THz） coherent transition radiation generated from an ultrashort electron bunching beam is reported. During this experiment, the window for THz transmission from ultrahigh vacuum to free air is tested. The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed. With the help of improved Martin-Puplett interferometer and Kramers-Krong transform, the longitudinal bunch length is measured. The results show that the peak power of THz radiation wave is more than 80 kW, and its radiation frequency is from 0.1 THz to 1.5 THz.

Tunable terahertz radiation from arbitrary profile dielectric grating coated with graphene excited by an electron beam

In this paper, the enhanced terahertz radiation transformed from surface plasmon polaritons, excited by a uniformly moving electron bunch, in a structure consisting of a monolayer graphene supported on a dielectric grating with arbitrary profile is investigated. The results show that the grating profile has significant influence on the dispersion curves and radiation characteristics including radiation frequency and intensity. The dependence of dispersion and radiation characteristics on the grating shape for both the symmetric and asymmetric gratings is studied in detail. Moreover, we find that, for an asymmetric grating with certain profile, there exist two different diffraction types, and one of the two types can provide higher radiation intensity comparing to the other one. These results will definitely facilitate the practical application in developing a room-temperature, tunable, coherent and miniature terahertz radiation source.

Electron-beam radiation effects on the structure and properties of polypropylene at low dose rates

While the high-energy radiation effects on polypropylene, which are crucial for the cable industry for nuclear power plants, have been thoroughly studied, the property changes of PP at low-dose-rate electron-beam irradiation are far from elucidated. Herein, the influence of electron-beam irradiation on the structure and properties of PP was examined. The static EB irradiation conditions were 1.2 MeV at a low dose rate of 20 kGy/h to achieve absorbed doses ranging from 45, to 60, 100, and 200 kGy.The molecular structure was first evaluated by measuring the carboxyl index and the relative radical concentrations via Fourier transform infrared spectroscopy and electron spin resonance, respectively. Mechanical, differential scanning colorimetric, and rheological tests were carried out to further investigate the changes in the properties(tensile, crystalizing, and viscoelastic properties) of irradiated PP, which showed good agreement with the structural analysis results. We found that radio-oxidative degradation(chain scission) was predominant, which can be due to the low dose rate facilitating oxygen diffusion into the PP matrix during electron-beam irradiation.

Degradation characteristic of 4-bromdiphenyl ether in mixed solutions by electron beam irradiation

The degradation characteristic of 4-bromdiphenyl ether （BDE-4） was investigated in different solutions.The study indicates that the process of direct degradation of this compound is dependent upon the bromine and the ether bond connected to diphenyl by electron beam.laser flash photolysis was employed to determine the degradation of each species （cationic,neutral,and anionic）.From these data,intermediate products of BDE-4 degradation were shown for direct irradiationdegradation.The neutral radical was formed during the photolysis of these compounds.For all the compounds,diphenyl ether and hydroxybiphenyl were observed as common products.Reaction of the BDE-4 under electron beam was debromide.The debromide rate of BDE-4 at pH=5.5 is somewhat lower than that of BDE-4 at pH=10.0.The decomposition rate for BDE-4 is 99.8% at pH=10.0 on the dose of 14 kGy.BDE-4 from its radical could provide bromine ion into water and the cation radical of BDE-4 formed quickly recombine with hydrogen radical and formed phenyl ether.

Analysis of the Power System from an Electron Beam Accelerator and the Correlation with the Theoretical Dosimetry for Radiation Processing

Dynamitron DC1500/25/04 type EBA （Electron beam accelerator）, model JOB 188, was manufactured by IBA Industrial （Radiation Dynamics, Inc.） and installed at IPEN-CNEN/SP, in 1978. The technical specifications of the EBA are： energy 0.5 to 1.5 MeV; beam current： 0.3 to 25.0 mA; beam scanning： 60 to 120 cm; beam width： 25.4 mm and frequency： 100 Hz. Nowadays, this accelerator has been used for innumerable applications, such as： For sterilization of medical, pharmaceutical and biological products, treatment of industrial and domestic effluents and sludge, preservation and disinfestations of foods and agricultural products. Other important application are lignocellulosic material irradiation as a pre-treatment to produce ethanol bio-fuel, decontamination of pesticide packing, solid residues remediation, organic compounds removal from wastewater, treatment of effluent from petroleum production units, crosslinking of foams, wires and electric cables. Electron accelerator JOB 188 is, also, very important composite and nanocomposite materials and carbon fibers irradiation, irradiated grafting ion-exchange membranes for fuel cells application, natural polymers and multilayer packages irradiation and biodegradable blends production. The energy of the electron beam is calculated as a function of the current in the accelerator high-voltage divisor, taking into account the thickness and density of the material to be irradiated. This energy is calculated considering the electron through the entire material and the distance from the titanium foil window, so that the absorbed doses at the points of entrance and exit are equivalent on the material. The dose is directly proportional to the beam current and the exposure time of the material under the electron beam and inversely proportional to the scan width. The aim of this paper is to analyze the power system parameters of the EBA Dynamitron DC 1500/25/04, such as, voltage and RMS （Root-mean-square） current in the oscillator system, high voltage generator and waveform. For this purpose software developed in the Radiation Technology Center at IPEN/CNEN-SP to simulate the energy efficiency of this industrial accelerator. Finally, it is also targeted to compare theoretical dosimetry using parameters of energy and beam current with data from the accelerator power system. This knowledge and technology will be very useful and essential for the control system upgrade of EBA, mainly Dynamitron DC 1500/25/04 taking into consideration that radiation processing technology for industrial and environmental applications has been developed and used worldwide.

Sub-picosecond electron bunch length measurement using coherent transition radiation at SXFEL

Longitudinal electron bunch length plays a significant role in single-pass free-electron lasers(FEL), as the high-gain FEL process depends strongly on the high peak current of electron bunches. Longitudinal electron bunch length was measured by detecting the interferogram of coherent transition radiation generated by electron bunches using a THz interferometer and a Golay cell(spectral range0.02-20 THz) at Shanghai X-ray free-electron laser. The detailed process of measurement and data analysis are discussed herein. Furthermore, the electron bunch length was estimated based on the dispersive strength R_(56) of the bunch compressor and the energy spread δ of electron bunches, which were obtained via experiments. The comparison showed that the measured bunch length was consistent with the estimated bunch length.

Selective linear etching of monolayer black phosphorus using electron beams

Point and line defects are of vital importance to the physical and chemical properties of certain two-dimensional(2D)materials.Although electron beams have been demonstrated to be capable of creating single-and multi-atom defects in 2D materials,the products are often random and difficult to predict without theoretical inputs.In this study,the thermal motion of atoms and electron incident angle were additionally considered to study the vacancy evolution in a black phosphorus(BP)monolayer by using an improved first-principles molecular dynamics method.The P atoms in monolayer BP tend to be struck away one by one under an electron beam within the displacement threshold energy range of 8.55-8.79 eV,which ultimately induces the formation of a zigzag-like chain vacancy.The chain vacancy is a thermodynamically metastable state and is difficult to obtain by conventional synthesis methods because the vacancy formation energy of 0.79 eV/edge atom is higher than the typical energy in monolayer BP.Covalent-like quasi-bonds and a charge density wave are formed along the chain vacancy,exhibiting rich electronic properties.This work proposes a theoretical protocol for simulating a complete elastic collision process of electron beams with 2D layers and will facilitate the establishment of detailed theoretical guidelines for experiments on 2D material etching using focused high-energy electron beams.

Finite element analysis on electron beam brazing temperature and stresses of stainless steel radiator

Based on thermal-elasto-plastic finite element theory, a two-dimensional finite element model for calculating electron beam brazing temperature and residual stress fields of stainless steel radiator are presented. The distributions of temperature and residual stress are studied. The resuhs showed that temperature distribution on brazing surface is rather uniform, ranging from 1 026 ℃ to 1 090 ℃. The residual stresses are varied from initial compressive to tensile , and the variation of residual stress is very little in total zone of brazing surface.

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.

Radiolytic degradation and mechanism study of electron beam-irradiated solutions of 4-tert-octylphenol

In this study, we have investigated the degradation and primary radiolytic degradation mechanism of 4-tert-octylphenol (4-t-OP) by using of electron beam (EB) -irradiation. The results show that at an absorbed dose of 10 kGy and an initial concentration of 25 mg·L -1 , the degradation of 4-t-OP in a methanol/water reduction system is higher than in a acetonitrile/water oxidation system by 19.4% and higher than in an acetone/water system by 26.8%, which is due to both of ·OH and e aq - playing an important role in the decomposition of 4-t-OP, although the latter is more effective. The degradation rate of 4-t-OP will decrease with increment of absorbed dose in a methanol/water solution, and increase with decrement of initial concentration at a constant absorbed dose. The degradation efficiency will also decrease with the addition of anions and H 2 O 2 into the solution. A system saturated with N 2 will make an increment in the degradation of 4-t-OP. The pH value of solution has been also found to affect the degradation efficiency, while the degradation is more efficient in alkaline conditions. Finally, the initial products involved in degradation reaction have been determined to be ethylbenzene, styrene, bicyclo[4.2.0]octa-1,3,5-triene, 2,2,4-trimethylpentane and p-tert-butyl-phenol, which may arise from e aq - attack at the position of the alkyl side chain of 4-t-OP molecule. The results have been revealed that EB irradiation is a promising method for degradation of 4-t-OP, and e aq - may be main reactive species to attack at the position of the alkyl side chain of 4-t-OP.

Preparation and mechanical properties of NiCoCrAlY/NiCr laminates by electron beam physical vapor deposition

Laminates with alternating layers of NiCoCrAlY and NiCr were fabricated by using electron beam physical vapor deposition (EB-PVD) method. The influence of the substrate temperature on morphology of the laminates was investigated. The results show that in order to produce NiCoCrAlY/NiCr laminates with lower porosity, higher substrate temperature is required. The mechanical properties of the as-deposited samples and heat-treated samples were examined using tensile tests. The stress-strain curve of the as-deposited laminate shows a typical characteristic of multilayered materials and the fracture behavior is improved by annealing the samples at high temperatures. The tensile strength of the samples annealed at 760℃ is 658.4MPa, and the elongation reaches 6.2%.

EB-PVD热障涂层对高温合金基体断裂特征影响的研究

采用EB -PVD方法在K3合金上 (包括铸态和经标准热处理两种状态 )沉积了由NiCoCrAlY金属粘结层和YSZ涂层顶层组成的双层结构的热障涂层 .对未涂层和涂层试样的拉伸性能进行了评估 ,并分析了涂层的制备和中间处理过程中基体的微观结构的变化 .结果表明 ,在热障涂层的沉积以及中间处理过程中 (真空前处理及后处理 ) ,基体的铸态组织得到改善 ,产生了析出强化 ,使得在铸态K3合金基体上沉积热障涂层后基体的拉伸强度由 80 0MPa提高到 10 5 0MPa 。

电子束物理气相沉积(EB-PVD)技术研究及应用进展

概述了近几年来快速发展的新兴材料加工工艺技术——电子束物理气相沉积(EB-PVD)技术的研究及应用现状,着重阐述了电子束物理气相沉积(EB-PVD)过程的主要工艺参数和制备高温合金板材显微组织的形成机理。

EB-PVD梯度热障涂层的热循环失效机制

研究了一种新型梯度结构的ＥＢ－ＰＶＤ（电子束物理气相沉积）热障涂层的热循环性能，并分析了涂层的失效机制结果表明，由于ＮＩＣｏＣｒＡｌＹ粘结层以及在粘结层上形成的 ＮｉｓＡｌ薄层发生了选择性氧化，从而在粘结层和梯度过渡层之间形成了一层Ａｌ２Ｏ３层、随着热循环时间增长， Ａｌ２Ｏ３层不断增厚，而且在热循环应力作用下，涂层最终沿Ａｌ２Ｏ３层内部断裂失效．

微叠层结构EB-PVD热障涂层

采用EB-PVD非连续沉积工艺制备了微叠层结构热障涂层,对涂层结构和晶体形貌进行了SEM观察和分析,采用激光脉冲法测定了涂层的热扩散系数,并采用增重法研究了涂层的氧化动力学特征,分析了氧化后的元素扩散情况。结果表明,非连续EB-PVD沉积工艺制备的涂层具有明显的层状特征,常规EB-PVD热障涂层的柱状晶结构被周期性地打破;但在每一层中,柱状晶结构得以保留,且晶粒更加细化。微叠层热障涂层的热扩散系数比常规热障涂层降低20%-30%,涂层热扩散系数的降低主要与层间界面和晶粒的细化减小了声子的平均自由程有关。微叠层结构热障涂层的氧化增重速率明显低于常规试样,遵循典型的抛物线规律,垂直于元素扩散方向的层间界面和细晶更有效地降低或阻止了O、Al、Ni、Cr等元素的扩散,可能是氧化增重速率较低的主要原因。

垂直裂纹对EB-PVD热障涂层热循环失效模式的影响

对电子束物理气相沉积(EB-PVD)双层结构热障涂层在热循环过程中形成的陶瓷层垂直裂纹对涂层失效模式的影响进行了研究.结果表明,陶瓷层表面垂直裂纹出现在热循环初期,但并未造成涂层的早期剥落;随着热循环次数增加,垂直裂纹网格变密.有限元计算表明,垂直裂纹的形成在试样中部产生了类似于试样边缘的剪应力集中效应.经过长时间热循环后,当陶瓷层等轴晶区的强度或者热氧化生长层(TGO)的强度小于边缘效应产生的剪应力对,涂层在试样的中部以垂直裂纹网格形状发生剥落失效.

EB—PVD梯度热障涂层的制备及其热疲劳性能

采用 ＥＢ—ＰＶＤ的方法，连续蒸发按一定组分比混合的 Ａ１＋Ａｌ２Ｏ３＋ＺｒＯ２混合源，在 Ｎｉ基高温合金基体上制备了一种新型结构的热障涂层，ＳＥＭ和ＥＤＳ的观察、分析表明，这种涂层实现了由金属粘结层向陶瓷顶层的微观结构的梯度过渡和化学成分的连续变化．涂层的基本结构为 ＮｉＣｏＣｒＡｌＹ／ Ｎｉ３Ａｌ／ Ｎｉ３Ａｌ＋Ａｌ２Ｏ３／ Ａｌ２Ｏ３／ Ａｌ２Ｏ３＋ ＺｒＯ２／ ＺｒＯ２这种梯度热障涂层在１０５０℃的抗高温氧化性能优于传统的二层结构的热障涂层经１０５０℃保温３０ ｍｉｎ，迅速冷却至室温的热循环测试３００次后，涂层没有发生剥落。

基体温度对TC11钛合金EB-PVD修复层组织及振动疲劳寿命的影响

为了研究温度对修复层性能的影响,采用电子束物理气相沉积（EB-PVD）技术在TC11平板试样上制备了修复层,利用X射线衍射仪（XRD）、扫描电子显微镜（SEM）和能谱仪（EDS）研究了不同温度下修复层的成分及组织形貌变化,并通过振动疲劳试验等方法研究了温度对修复层振动疲劳寿命的影响。结果表明：在600~800℃进行修复时,修复层为柱状晶组织。修复层的致密性随温度升高而变大,这种变化也会影响修复后试片的振动疲劳性能,修复层柱状晶结构间隙处形成的裂纹源会造成试片疲劳性能的下降。