Modernization of the injector for a multibeam proton accelerator

Within the program for the development of high-current charged-particle accelerators with a high acceleration rate, an injector for a 19-beam proton accelerator with a multibeam ion injection mode is described. The injector contains an ion gun with a duoplasmatron-type H₂ ion source and a multiaperture ion-optical system regulating the inclination of the ion-beam current tubes at the inputs of the corresponding channels of the accelerating structure. The cold-cathode ion source contains a system for transporting plasma from the cathode to its output aperture in magnetic fields of complex configurations, which allows stable pulsed generation of proton beams with a current amplitude of up to 3 A at an operating gas pressure in the discharge chamber of 0.2 Torr and a decrease in the flow of unionized gas emerging from the source to 2 cm³/h. It is shown that the developed ion source and the ion-optical system make it possible to increase the phase density of the beam current at the inputs of the accelerating-structure channels and to change the divergence angles.     

Voltage holding study of 1 MeV accelerator for ITER neutral beam injector

Voltage holding test on MeV accelerator indicated that sustainable voltage was a half of that of ideal quasi-Rogowski electrode. It was suggested that the emission of the clumps is enhanced by a local electric field concentration, which leads to discharge initiation at lower voltage. To reduce the electric field concentration in the MeV accelerator, gaps between the grid supports were expanded and curvature radii at the support corners were increased. After the modifications, the accelerator succeeded in sustaining -1 MV in vacuum without beam acceleration. However, the beam energy was still limited at a level of 900 keV with a beam current density of 150 A∕m(2) (346 mA) where the 3 × 5 apertures were used. Measurement of the beam profile revealed that deflection of the H(-) ions was large and a part of the H(-) ions was intercepted at the acceleration grid. This causes high heat load on the grids and the breakdowns during beam acceleration. To suppress the direct interception, new grid system was designed with proper aperture displacement based on a 3D beam trajectory analysis. As the result, the beam deflection was compensated and the voltage holding during the beam acceleration was improved. Beam parameter of the MeV accelerator was increased to 980 keV, 185 A∕m(2) (427 mA), which is close to the requirement of ITER accelerator (1 MeV, 200 A∕m(2)).     

医用直线加速器自动摆位系统设计

研发一套自动摆位系统以提高放射治疗摆位的精度和效率。该摆位和传送装置,可实现患者自动摆位,并在患者治疗结束后,通过传送装置将其送出机房,同时将下一个需要治疗的患者送入机房。提高了放射治疗的精确性和医用直线加速器的工作效率,同时减小了技术人员的劳动强度和接受的辐射剂量。试验表明,本系统能提高医用直线加速器摆位的效率和精度,具有较高的临床应用价值。     

Experimental study on dynamic characteristics of linear parametrically excited system

An electromagnetic device, acting like a spring with alternating stiffness, has been designed to parametrically excite the cantilever beam transversely in the laboratory. It showed good potential for the experimental investigation of linear parametric system. Therefore, experiments for the natural frequency, the response (both free and forced) spectra and frequency response characteristics of a cantilever beam under electromagnetic excitation, are, respectively, conducted to study the dynamic characteristics of linear parametrically excited system. The vibrational model of the cantilever beam system is established using the assumed mode method. Theoretical results, related to the natural frequency, response spectra and external resonant condition, are presented to verify the experimental results. It is shown that the dynamic characteristics of linear time-periodic system do have some typical features, which differ distinctly from that of the linear time-invariant system.     

Experimental study of ion beam optics in a two-stage accelerator

Hydrogen ion beam optics in a two-stage linear acceleration system is studied by examining the beam divergence as a function of the voltage and gap distribution, the beam perveance, the background gas pressure, the aspect ratio, and the total accelerating energy (60-110 keV). The system consists of four electrodes with single, cylindrical, straight-bore apertures acting as an extraction-accel-decel column. An optimum relation between the field ratio and the extraction perveance is obtained from measurements for the minimum beam divergence condition. The HWHM divergence angle is <0.3 degrees under optimum conditions. Qualitative agreement between the measurements and a previous theoretical study is noticed. A potential application of the results to high energy neutral beam injectors for fusion research is also discussed.     

A pulse power supply of the linear induction accelerator

A pulse power system of the induction electron accelerator intended for parameters of 2 MeV, 2 kA, and operating in the double-pulse mode is presented. The schematic diagram and main elements of the pulse system are described, and the main technical solutions intended to produce a set of pulses with 21-kV peak voltages, peak currents of up to 8 kA, and 200-ns durations across a resistive-inductive load are indicated. The experimental data, which were obtained when separate units and the whole power system operated on the rated duty, are given.     

船用增速器系统变形分析

根据多体动力学原理,建立了变形传递矩阵,实现了各零部件变形的累加.利用有限元软件ANSYS对船用增速器的各主要零部件进行了有限元分析,得到了各主要零部件在工作栽荷下的变形量.并通过累加最终得到了两啮合齿轮的中心距及轴线夹角的变化量,为结构优化和齿轮的几何啮合仿真提供初始数据.     

Experimental study on integration of laser-based additive/subtractive processes for meso/micro solid freeform fabrication

Solid freeform fabrication has attracted considerable attention lately because of its ability to build a 3D structure with a complex and arbitrary shape. This work presents initial studies to adapt this technology for the fabrication of meso-/micro-3D structures. A pulsed Nd:YAG laser was used for laser microdeposition (additive) and micromachining (subtractive) processes. An ultrasonic-based micropowder feeding system was developed to generate precise patterns of micropowders on a substrate without any pre-processing. Laser microdeposition of copper and stainless steel micropowders was accomplished. The characterization of micromachining was performed on stainless steel and copper plates with a laser beam of wavelengths of 355 nm and 266 nm. The integration of laser microdeposition and micromachining processes improved the resolution and edge quality of the meso-/micropatterns.     

Experimental study of the role of gas-liquid scheme injector as an acoustic resonator in a combustion chamber

In a liquid rocket engine, the role of gas-liquid scheme injector as an acoustic resonator or absorber is studied experimentally for combustion stability by adopting linear acoustic test. The acoustic-pressure signals or responses from the chamber are monitored by acoustic amplitude. Acoustic behavior in a rocket combustor with a single injector is investigated and the acoustic-damping effect of the injector is evaluated for cold condition by the quantitative parameter of damping factor as a function of injector length. From the experimental data, it is found that the injector can play a significant role in acoustic damping when it is tuned finely. The optimum tuning-length of the injector to maximize the damping capacity is near half of a full wavelength of the first longitudinal overtone mode traveling in the injector with the acoustic frequency intended for damping in the chamber. When the injector has large diameter, the phenomenon of the mode split is observed near the optimum injector length and thereby, the acoustic-damping effect of the tuned injectors can be degraded.     

一种新型线性电机及其在直线运动系统中的应用

针对传统直线运动系统在某些场合下存在体积大、安装调试难度高、系统动态性不好的问题,提出了用一种新型线性电机控制直线运动的方法。该电机的特点是电机轴中空,丝杠可以直接穿过电机轴,在该电机控制的直线运动系统中,丝杠一般不动,电机在丝杠上平动,从而使运动系统具有安装调试方便、体积小、动态响应特性好等特点。     

Testing the prototype detectors for the muon tracking system of the CBM experiment at the CERN PS accelerator

Performance of the gas-filled detector prototypes based on the GEM, TGEM, and Micromegas technologies was studied on the test beam of the CERN PS accelerator. Three-component mixtures based on Ar and He were used as the working gas. For all tested detector prototypes, the gas amplification factors were measured, and the detection efficiencies, cluster distributions, and the radii of the charge cloud collected on the readout electrode were estimated.     

An experimental study on the spray characteristics of a dual-orifice type swirl injector at low fuel temperatures

The objective of this study is to investigate the effects of fuel temperature on the spray characteristics of a dual-orifice type swirl injector used in a gas turbine. The major parameters affecting spray characteristics are fuel temperature and injection pressure entering into the injector. In this study, the spray characteristics of a dual-orifice type swirl injector are investigated by varying fuel temperature from — 30°C to 120°C and injection pressure from 0.29 to 0.69 MPa. Two kinds of fuel having different surface tension and viscosity are chosen as atomizing fluids. As a result, injection instability occurs in the low fuel temperature range due to icing phenomenon and fuel property change with a decrease of fuel temperature. As the injection pressure increases, the range of kinematic viscosity for stable atomization becomes wider. The properties controlling the SMD of spray is substantially different according to the fuel temperature range.     

Control system of a linear induction accelerator of an X-ray complex: Structure,hardware, and test performance

The structure, operation logic, and hardware tools of the control system of a linear induction accelerator for an X-ray complex are considered. The hardware developed in the CompactPCI standard for the control system is described. The possibility of embedding of smart microelectronic equipment into high-voltage elements of the facility is analyzed.     

17.1 nm波段光电成像系统分辨率的实验研究

设计了17.1 nm波段光电成像系统,用于对波长为17.1 nm的极紫外光进行成像。该成像系统分为三大部分:光源、单色仪和探测系统。一个调Q的Nd∶YAG激光器(Continuum 9000)用来产生激光等离子体,掠入射单色仪由2块球面聚焦镜和1块600 L/mm的球面掠入射光栅组成,经单色仪分光后得到波长为17.1 nm的单色光,探测器是微通道板(MCP)和荧光屏组件共同组成,Kodak400型胶卷被用于记录狭缝的像。结果获得了一宽度为3 mm的狭缝的像,实验测得130 μm的成像系统的空间分辨率,好于相同条件下文献[6]的结果。     

Startup of the Proton Radiographic Facility at the U-70 accelerator

The first results of Proton Radiographic Facility operation on the beam with energies of 50–70 GeV extracted from the U-70 synchrotron at the Institute for High Energy Physics are presented. This facility is capable of forming proton radiographic images of samples with an optical thickness as large as 450 g/cm² and a field of view of 220 mm or more.     

Experimental investigation on focusing characteristics of a He-Ne laser using circular Fresnel zone plate for high-precision alignment of linear accelerators

We experimentally investigate the focusing characteristics of a He-Ne laser at the focal region for the high-precision alignment of long-distance linear accelerators using a circular Fresnel zone plate. The laser wave passing through the Fresnel zone plate having a focal length of 66.7 m propagates for a 268-m-long distance at atmospheric pressure. A new laser-based alignment system using Fresnel zone plates as the alignment targets is discussed. The transverse displacement of the focused spot of the laser is measured as a function of the displacement of the target by a detector installed at the focal point. Systematic studies on the focusing characteristics and alignment precision have been successfully conducted in this experiment. The experimental results are in good agreement with theoretical calculations, and the alignment precision of the target is determined to be less than ±30 μm. In this study, we perform a detailed experimental investigation on the laser propagation and focusing characteristics using the circular Fresnel zone plate at the focal region along with theoretical calculations.     

Experimental spectral damage prediction of a linear elastic system using acceleration response

The fatigue-related behavior of a linear elastic system (LES) can be efficiently identified using acceleration response if the frequency response function between the acceleration input and the stress response (FRFas) can be predetermined. In this paper, the spectral damage of an LES is predicted using energy isoclines, whose function consists of both FRFas and the fatigue material properties of the LES. The accuracy of the proposed method was verified through a uniaxial vibration test using flexible specimens and a comparison of the acceleration-based and strain-based spectral damage at the location of interest.     

直线压缩机油泵系统仿真与实验研究

直线压缩机是一种新型的高效压缩机,传统的供油机构已经不再适用,为了开发新型供油系统,对一种利用压缩机机体振动来供油的油泵系统进行了仿真和实验研究.研究结果表明：这种油泵系统是行之有效的,其泵油量随机体振幅及振动频率的增大而增大;当机体振动一定时,泵油量随油泵固有频率的增大而减小,并未发生共振现象;系统阻尼与润滑油粘度有关,减小润滑油粘度可增加油泵系统的泵油量及效率;油泵的功耗影响着直线压缩机的效率,通过减小泵油高度、输油管道长度及壁面粗糙度,优化吸排油腔设计,以减小油泵功耗,从而提高直线压缩机效率.该油泵系统具有结构简单,体积小,效率高等特点,完全可以满足直线压缩机的需求.     

Generation, transport, and detection of linear accelerator based femtosecond-terahertz pulses

The generation and detection of intense terahertz (THz) radiation has drawn a great attention recently. The dramatically enhanced energy and peak electric field of the coherent THz radiation can be generated by coherent superposition of radiated fields emitted by ultrafast electron bunches. The femtosecond (fs)-THz beamline construction at the Pohang Accelerator Laboratory (PAL) was completed in the end of 2009. The fs-THz beamline at PAL can supply ultrafast and intense fs-THz radiation from a 75 MeV linear accelerator. The radiation is expected to have frequency up to 3 THz (～100 cm(-1)) and the pulse width of <200 fs with pulse energy up to 10 μJ. This intense THz source has great potential for applications in nonlinear optical phenomena and fields such as material science, biomedical science, chemistry, and physics, etc.     

Interactions at the head–tape interface of a linear tape system

In this study, tape cycling experiments were performed using two different experimental metal particle media in combination with a Travan™ linear tape system. The aim was to investigate the effect of head/tape contact on the tribological properties and signal performance of the system. A combination of cycling at extreme environmental conditions, use of experimental media, and cycling beyond the normal limit of operation ensured a worst-case scenario for the head–tape interactions. Auger electron spectroscopy (AES) and atomic force microscopy (AFM) were used to characterize the chemical and physical surface changes that occurred on and in the head surfaces. X-ray photoelectron spectroscopy (XPS) was used to identify the chemical changes that occurred at the media surface and these changes were correlated to variation in signal dropout rate. Measurements were made as functions of number of cycles.The cycling experiments for the two different tapes were performed at conditions of 32°C, 80% RH and 5°C, 10% RH and transfer of material from the media to the head was observed at each condition for both tape types. The degree of material transfer was influenced by the environmental operating conditions, but was governed by localized heating effects, such as those originating from active magnetoresistive (MR) elements and frictional interactions between the head and media. XPS analyses of the surface of the media revealed a reduction of nitrogen with increasing number of cycles indicating binder depletion. Significant differences in elemental concentrations were also detected between areas corresponding to regions directly under the cartridge belt compared to those off belt.