Development of femtosecond photocathode RF gun

Femtosecond electron bunches are essential for the observation of ultrafast reactions and phenomena in materials. To improve the time resolution of pulse radiolysis and ultrafast electron diffraction (UED), which involve the use of ultrashort electron bunches and ultrashort light, a femtosecond photocathode RF gun driven by a femtosecond laser was investigated experimentally. Bunch charge generated in the RF gun was studied based on the Schottky effect. Thermal emittance was estimated as 0.26 mm mrad at an rms laser spot size of 0.21 mm. Bunch length and longitudinal emittance were obtained as 180 fs and 0.87 deg keV, respectively, at a bunch charge of 3.5 pC and rms laser spot size of 0.38 mm.     

Effect of filament heating current on electron beam of directly heated strip-type electron gun

The method of Electron Beam-Physical Vapour Deposition (EB-PVD) for handling large substrates is well established in the metallurgical industry, where sweeping axisymmetric electron guns or multiple pencil guns are routinely used to cover a large target area. The non-uniformity in current density in those methods can be overcome, to a large extent, by using the strip-type electron gun. In this paper, we propose to use an AC-heated strip-type electron gun to cover large target areas. The magnetic field generated by the alternating filament current oscillates the beam in a direction parallel to the filament length, thereby eliminating the need for applying an external electric or magnetic field for sweeping the beam. The non-uniformity in the current density within the strip electron beam, arising due to finite length of the filament, is reduced by the use of dummy filaments on both ends of the active filament. These results are supported by electron trajectory simulations.     

Attenuation of electron gun generated surges in an electron beam evaporation system using ferrite beads

Vacuum breakdown is a very common problem during the operation of any electron gun, more so for e-guns used for vacuum evaporation. This not only spoils the coating or welding job but also causes damage to the electronics of the power system. This paper discusses an approach to attenuate the breakdown current near the gun itself, so that the surge does not propagate to cause any detrimental effect on the power source and thereby on the job. In this paper, ferrite beads on both the feed lines have been used to suppress the high frequency content and reduce the amplitude of the breakdown signal. An induction coil sensor has been designed to monitor the breakdown signal. The high frequency surge in the MHz range could be attenuated to a lower range of KHz by use of ferrite bead. A detailed quantitative analysis of the breakdown signal has been presented in this paper.     

RF properties of a X-band hybrid photoinjector

An INFN-LNF/UCLA/SAPIENZA collaboration is developing a hybrid photoinjector in X-band. A hybrid photoinjector is a novel high brightness electron source that couples a standing wave cell cavity (acting as an RF gun) directly to a multi-cell travelling-wave structure. This configuration offers a number of advantages over the split standing wave/travelling-wave system. Most notably the reflected RF transient is almost completely suppressed, thus eliminating the need for a circulator and the bunch lengthening effect that occurs in the drift section of the split system. These properties allow scaling of the device to higher field and frequencies, which should dramatically improve beam brightness. The RF coupling between the standing and the traveling wave sections is accomplished in the fourth cell encountered by the beam, with the SW section electrically coupled to it on-axis. This mode of coupling is particularly advantageous, as it is accompanied by a 90° phase shift in the accelerating field, resulting in strong velocity bunching effects on the beam that reverse the usual bunch lengthening induced after the gun exit in standard 1.6 cell photoinjectors. In this scenario, from the beam dynamics point of view, it is seen that device may produce ten's of femtosecond beams at ∼3.5 MeV and the emittance compensation dynamics remains manageable even in the presence of strong compression. We present here a survey of the device characteristics. In particular we show the results of the electromagnetic simulations, a beam dynamics analysis related to the temperature tuning of the SW and TW section, and a RF characterization using bead pull and scattering coefficient measurements of a device prototype.     

Development of a three-stage, light-gas gun at the University of Dayton Research Institute

An elusive goal of the hypervelocity impact community has been the evaluation of the ballistic response of space hardware to impact velocities ranging from 8 to 11 km/s using projectiles with known properties. The design, development, and use, during the 1960s, of a three-stage, light-gas gun at McGill University is reviewed. The developers of this gun claim that they were able to launch cylindrical, 12.7-mm-diameter Lexan disks with masses of 1.5 and 1.1 g to velocities of 9.6 and 10.5 km/s, respectively. This paper presents the results of an internally funded program at the University of Dayton Research Institute (UDRI) to duplicate the published performance of the McGill University launcher. A support structure and various components of a third stage which used an 8.1-mm-diameter launch tube were added to the UDRI 75/30-mm, two-stage, light-gas gun, making the arrangement of the components similar to the one used by McGill University. Work on the development of the UDRI three-stage, light-gas gun is a continuing effort, with the goal of successfully launching small diameter (3 mm or less) aluminum spheres to velocities in excess of 9 km/s. To date, the highest projectile velocity achieved with the UDRI three-stage, light-gas gun has been 8.65 km/s.     

新型机枪枪架及其动态特性分析

以某型重机枪为研究对象,在不改动枪身的前提下设计了一种新型弹性三角枪架。通过建立机枪有限元模型,分析计算了其固有特性;建立基于刚柔耦合多体系统动力学的机枪虚拟样机模型,求解出其在连发状态下的动力响应。所得结果与原有三脚架进行了分析比较,证明了新型三脚架的优越性。     

Experimental development and deposition of nanocomposite films by a hybrid dc magnetron sputtering and cluster gun technique

A novel hybrid experimental prototype involving dc magnetron sputtering combined with an ingenious nanocluster source has been developed to deposit nanocomposite coatings by incorporating pre-formed clusters into a sputtered coating under high vacuum conditions. An electromagnetic fuel injector was connected with the nanocluster chamber and then optimised along with the sputtering chamber in order to incorporate the clusters in the coating matrix. The injection flux was primarily controlled by: the argon pressure and the amount of nanoclusters, the duration and repetition time of the injection and distance between the nozzle of the injector and the substrates. Several experiments were carried out on various substrates such as carbon tape, Al, Si and M2 steel with different nanoparticles of WO₃, SiC and WS₂. The preliminary characterization, consisting in the phase analysis, SEM micrographs and elemental composition, allowed confirming the presence of the clusters attached to the carbon tape when a free plasma injection was performed. Furthermore, the co-existence of Ti and TiN matrixes containing the SiC, WO₃ and WS₂ nanoparticles was confirmed.     

火炮磁流变后坐阻尼器的设计与可控性分析

以高冲击、高速环境下的某口径火炮反后坐装置为研究对象,讨论了后坐阻力对火炮静止性和射击稳定性的影响,研究了磁流变阻尼器对火炮后坐运动的控制作用。设计了火炮磁流变后坐阻尼器及冲击试验平台;考虑冲击载荷激励下惯性力的影响,建立了火炮反后坐装置动力学模型并进行了计算仿真,对所设计长行程磁流变阻尼器进行了冲击试验,测试其在冲击载荷下的动态特性,并进行了后坐过程半实物仿真控制。试验结果表明设计的长行程火炮用磁流变阻尼器可有效抑制冲击载荷激励作用,为进一步实现火炮后坐力与行程控制的一体化设计和工程应用奠定了基础。     

Formation of graphite re-deposition layer by hydrogen RF plasma

It has been revealed that a graphite re-deposition layer is formed in a fusion plasma device and can trap fuel atoms when a carbon-based material is applied as a plasma facing component. However, there are not sufficient data for quantitative prediction of hydrogen and carbon behavior with the formation of the re-deposition layer under several plasma conditions. We produced a graphite re-deposition layer on quartz substrates by a sputtering method using hydrogen RF plasma. The re-deposition layer was approximately uniformly formed on the substrate located on the ground electrode, but in some experimental conditions no deposition was observed there. This is due to the effect of re-sputtering by the incident hydrogen ions. It was found that the layer formed on and around the ground electrode had a dense columnar structure and a packed fibrous structure, respectively. With varying RF power or hydrogen pressure, the H/C ratio changed between approximately 0.1 and 0.45, and is considerably larger than that for absorption into graphite bulk. This indicates that the formation of graphite re-deposition layer makes tritium inventory in a D-T fusion reactor to dramatically grow. The plasma parameters in each experimental condition were investigated by the Langmuir probe method.     

火炮磁流变阻尼器试验分析与动态模型

火炮磁流变阻尼器工作在高速高冲击条件下,其动力特性及其力学模型与常用的磁流变阻尼器存在较大不同。针对某型号火炮设计了反后坐用磁流变阻尼器,并进行了5种不同电流下的动态测试,验证了该阻尼器对反后坐控制的可行性。由试验分析得,火炮磁流变阻尼器的输出力不仅与控制电流和后坐速度有关,还与高冲击条件下的磁流变效应的复杂性、惯性力、腔体内气体压力等因素有关。提出了用改进的多项式模型描述火炮磁流变阻尼器,该模型具有形式简洁,易于求解逆模型,便于实时控制等优点。通过参数辨识后的模型能较好的描述火炮反后坐过程中阻尼器的输出力。     

Inductively coupled RF oxygen plasma characterization by optical emission spectroscopy

Optical emission spectroscopy was applied for the characterization of inductively coupled RF oxygen plasma at pressures between 10 and 300 Pa. The plasma was generated with an RF generator at a frequency of 27.12 MHz and output power of 300 W. Spectra were measured in the range 200-1100 nm by an optical spectrometer. At high pressure, the main spectral features observed were the wavelengths of the atomic oxygen transitions at 777.2 and 844.6 nm. Molecular oxygen band at 762 nm was observed as well. The atomic emission intensity showed a maximum when the pressure was about 75 Pa, while molecular band intensity increased monotonically as the total pressure increased. On decreasing the oxygen pressure, other atomic and molecular features appeared in spectra, such as H atomic lines, molecular OH band, and O₂⁺ band. The behavior of spectral features was explained by collision phenomena in the ionized gas.     

SnS thin-films by RF sputtering at room temperature

Tin monosulfide (SnS) is of interest as a potential solar cell absorber material. We present a preliminary investigation of the effects of sputtering conditions on SnS thin-film structural, optical, and electronic properties. Films were RF sputtered from an SnS target using an argon plasma. Resistivity, stoichiometry, phase, grain size and shape, bandgap, and optical absorption coefficient can be varied by modifying argon pressure for a fixed deposition time. Most films have an indirect bandgap in the range of 1.08-1.18 eV. XRD patterns confirmed the films as mostly crystalline, and grain morphology was examined using profile and surface SEM images.     

YO!—a time-of-arrival receiver for removal of helicity-correlated beam effects

A parity violation experiment, G⁰, at Jefferson Lab is sensitive to arrival time differences, at the target, of electron beams in the two helicity states. Instead of the Jefferson Lab standard 499 MHz beam structure, G⁰ uses a 31.1875 MHz structure where only 1 out of 16 microbunches contains electrons. Photon counters triggered by time-of-arrival at the target mandate that timing must be independent of delays associated with different orbits taken by the electrons in two helicity states. Corrections to the parity violating asymmetries due to any arrival time differences require the generation of a clean 31.1875 MHz trigger signal and phase matching this signal to the beam's arrival at the target. The time of arrival receiver, named the YO! receiver, has 10 kHz output bandwidth which is sufficiently larger than the settling time (500 μs) of the ≈30 Hz helicity flip. This enables the correction of each helicity bin for any orbit-induced timing inequalities. The device combines conventional receiver and DSP techniques for maximum sensitivity, bandwidth and flexibility and eliminates the 2π/n phase shifts associated with frequency dividers by means of a sampling phase detection scheme. This paper describes the performance of this device during bench testing, commissioning and in data taking phase of the experiment.     

不同衬底上ZnO薄膜的射频磁控溅射制备及结构

利用射频磁控溅射镀膜的方法,在c面蓝宝石、石英玻璃和载破片衬底上成功制备了ZnO薄膜。用x射线衍射和扫描电子显微镜进行了结构分析并观察了样品的表面形貌。结果表明：制备的ZnO薄膜具有良好的C轴择优取向结晶度,并在石英玻璃和载玻片衬底上的ZnO薄膜表面发现了[101]取向的“米粒状”晶粒。     

Improvement of the beam lifetime by applying an rf electric kick field in the compact storage ring

The lifetime of the stored electron beam in the compact storage ring AURORA is governed by the Touchek effect. It has been shown that it is appreciably increased by applying a vertical rf kick field to the electron beam without giving harmful effect to the beam stability. Interferometric measurement of the radiation beam profile showed an increase in the beam size, indicating the reduction of the Touchek effect. Application of the field with increase in power has induced collective excitation of the betatron oscillation.     

Structural and optical properties of yttrium trioxide thin films prepared by RF magnetron sputtering

Yttrium trioxide (Y₂O₃) thin films have been deposited on silicon (111) at different RF powers and the sputtering pressures by RF magnetron sputtering. The influences of the RF power and the sputtering pressures on the structural and optical properties of Y₂O₃ thin films were investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscope (AFM) and spectroscopic ellipsometer (SE). The results show that chemical composition of as-deposited Y₂O₃ film is apparently close to the stoichiometric ratio and it is crystallized but crystallinity is poor. The monoclinic and cubic fluorite-like structure can coexist in as-deposited Y₂O₃ film. A four-layer-structured optical model consisting of silicon substrate, silicon dioxide (SiO₂) interlayer, Y₂O₃ layer and a surface roughness (SR) layer is built for interpreting preferably the results measured by spectroscopic ellipsometry. With the increase of RF power or decrease of sputtering pressure, the refractive index and optical bandgap of sputtered Y₂O₃ film is increased and the extinction coefficients is decreased.     

射频无电极放电氮气等离子体光源研究

本文报道了一种利用射频无电极放电激励的氮气等离子体新型光源，测出了辐射光谱、光功率、工作气压等光源相关参数，优化实验条件得出的电光转换效率达22．05％。最后运用此光源成功的对一种印刷预涂感光版（pre-sensitive plate，PS版）进行了曝光，通过曝光前后PS版感光层颜色的光密度变化评价了感光效果。     

射频反应磁控溅射制备低辐射薄膜

采用射频反应磁控溅射法制备了低辐射薄膜.对低辐射膜的薄膜结构的设计和测试结果表明：较合适的膜层结构是空气/二氧化钛/钛/银/二氧化钛/玻璃基片的多层结构.用扫描电镜分析了保护层钛层的作用,研究表明：银膜很容易氧化失效,失去反射红外紫外光作用,在表面镀覆钛保护层可以很好地保护银,避免银氧化,从而提高使用寿命.用分光光度计测试样品的透射率,当保护层钛层厚度为1 nm时,相应的膜系在可见光区（380 nm～780 nm）,最高透射率可达82.4%,平均透射率是75%;在近红外区（780 nm～2500 nm）的平均透射率为16.2%,可以满足建筑物幕墙玻璃等低辐射膜的要求.     

Low perveance confined-flow Pierce gun for a 0.14 THz broadband folded waveguide traveling wave tube

An approach for designing an electron gun for a high efficiency, high linearity 0.14 THz traveling wave tube (TWT), has been presented. A Pierce electron gun of beam perveance 0.0047 μP has been designed for a high gain, high linearity and high efficiency 0.14 THz TWT using CST STUDIO SUITE Charged Particle Simulation soft and electronic optical software TAU. The initial gun geometry, as obtained from the Vaughan iterative synthesis method, has been used as input for simulation of the electron gun. An M-type dispenser cathode of diameter 0.8 mm has been used for cathode loading of 2.75 A/cm². The magnetic focusing with integral-pole-piece barrel assembly and periodic-permanent magnets (PPM) have been designed using CST and TAU. The practical problem of linking requisite cathode flux to the cathode for confined flow of the electron beam with low convergence factor has been sorted out by gradually increasing the PPM magnetic field. The magnetic field has been increased in steps from the gun and over the first five magnets varying from Brillouin field (B_B) value to twice B_B for achieving the electron beam with scalloping less than 10%. Simulation results show that the design method is reasonable for obtaining a 0.14 THz TWT electron gun and periodic-permanent magnets (PPM).