A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

基于磁质谱原理的新型同位素质量分离器的数值研究

基于磁质谱原理设计了新型同位素质量分离器。不同质量的离子在轴对称电场和磁场中聚焦于不同位置并进入各自收集器,从而实现质量分离。由哈密顿原理推导出离子在分离器中运动轨迹的解析方程,结合电子恒温磁流体力学方程构建等离子体束流轨迹的混合数学模型。基于该混合数学模型,应用matlab模拟等离子体束流的聚焦和质量分离。从仿真结果可以看出,当忽略鞘层屏蔽效应时,束流在电场力作用下绕着对称轴做螺旋运动;当考虑鞘层屏蔽效应时,电子在弱磁场中受束缚作用较小,在鞘层中迅速积累,外电场很大程度上被鞘层屏蔽,束流运动半径迅速增加,尚未聚焦就到达外电极。随着轴向磁场的增强,鞘层屏蔽效应减弱。通过选取适当的磁场强度,可使不同质量的离子按荷质比的顺序分离,聚焦点的距离取决于离子质量。本研究对等离子体束流电磁控制进行了探索,该结果可为高纯度物质质量分离器的研制奠定理论基础。     

A magnetic analyzer of a helical electron beam based on a controlled magnetic mirror

A magnetic analyzer of a helical subrelativistic electron beam formed by a three-electrode magnetron-injector gun in the field of a cryomagnet is described. Electrons are separated in transverse velocities by a magnetic field adiabatically increasing along the beam direction. The analyzer was used to measure the electron spread in velocities and the pitch factor of a microsecond helical electron beam with an electron energy of 300 keV and a current of 100 A.     

A very low energy compact electron beam ion trap for spectroscopic research in Shanghai

In this paper, a new compact low energy electron beam ion trap, SH-PermEBIT, is reported. This electron beam ion trap (EBIT) can operate in the electron energy range of 60-5000 eV, with a current density of up to 100 A/cm(2). The low energy limit of this machine sets the record among the reported works so far. The magnetic field in the central drift tube region of this EBIT is around 0.5 T, produced by permanent magnets and soft iron. The design of this EBIT allows adjustment of the electron gun's axial position in the fringe field of the central magnetic field. This turned out to be very important for optimizing the magnetic field in the region of the electron gun and particularly important for low electron beam energy operation, since the magnetic field strength is not tunable with permanent magnets. In this work, transmission of the electron beam as well as the upper limit of the electron beam width under several conditions are measured. Spectral results from test operation of this EBIT at the electron energies of 60, 315, 2800, and 4100 eV are also reported.     

A 2.45 GHz electron cyclotron resonance proton ion source and a dual-lens low energy beam transport

The structure and preliminary commissioning results of a new 2.45 GHz ECR proton ion source and a dual-lens low energy beam transport (LEBT) system are presented in this paper. The main magnetic field of the ion source is provided by a set of permanent magnets with two small electro-solenoid magnets at the injection and the extraction to fine tune the magnetic field for better microwave coupling. A 50 keV pulsed proton beam extracted by a three-electrode mechanism passes through the LEBT system of length of 1183 mm. This LEBT consists of a diagnosis chamber, two Glaser lenses, two steering magnets, and a final beam defining cone. A set of inner permanent magnetic rings is embedded in each of the two Glaser lenses to produce a flatter axial-field to reduce the lens aberrations.     

Concepts for the magnetic design of the MITICA neutral beam test facility ion accelerator

The megavolt ITER injector concept advancement neutral injector test facility will be constituted by a RF-driven negative ion source and by an electrostatic Accelerator, designed to produce a negative Ion with a specific energy up to 1 MeV. The beam is then neutralized in order to obtain a focused 17 MW neutral beam. The magnetic configuration inside the accelerator is of crucial importance for the achievement of a good beam efficiency, with the early deflection of the co-extracted and stripped electrons, and also of the required beam optic quality, with the correction of undesired ion beamlet deflections. Several alternative magnetic design concepts have been considered, comparing in detail the magnetic and beam optics simulation results, evidencing the advantages and drawbacks of each solution both from the physics and engineering point of view.     

活塞式磁性液体减振器的阻尼分析和实验研究

根据磁性液体的磁粘特性,当磁性液体周围施加垂直于其涡旋矢量方向的磁场时,磁性液体的粘度增加,利用磁性液体作为减振器的阻尼液,通过改变磁场可以调节振动系统的阻尼比,从而达到减振的目的。根据这一特性,提出一种活塞式磁性液体减振器。根据磁性液体的流动方程和连续性方程,建立了减振器中磁性液体的动力学模型,并得到减振器阻尼力与振动速度之间的表达式以及减振系统的阻尼比。设计实验,将磁性液体减振器安装在悬臂梁自由端,利用线圈对减振器施加均匀磁场,研究不同线圈电流时磁性液体减振器对梁振动阻尼比的影响。实验表明,在所假设的条件下,实验结果与理论结果的一致性较好。同时得出,在一定范围内,活塞式磁性液体减振器的阻尼效果随着线圈电流的增大而增大。     

Control of the Distribution of the Electron Beam Dose in Radiation Therapy

A method for an active control of the dose distribution produced by an electron beam in a substance is proposed. This method is based on the effect of a magnetic field on charged particles. The results of the calculations of the dose distribution for the irradiation of water as a tissue equivalent by a beam of electrons with energies of 20–30 MeV under the exposure of a magnetic field below 2.5 T are presented. Applying a field results in a dose distribution maximum at a depth of 3–6 cm. Varying the magnetic field configuration and electron energy can modify the dose distribution profile and the maximum position. This method is promising for the use in radiation therapy.     

Nanosecond response 'gasket-type' magnetic loop current monitor for relativistic electron beam current measurements

A fast response magnetic loop current monitor has been developed to measure relativistic electron beam return currents. The monitor has a rise time of about a nanosecond and a high degree of symmetry with moderate sensitivity, variable from about 1 to 10 V/kA. This simple monitor, with a thickness of 0.254 mm or less, is thin enough to be placed between segments of return current path in the diode or drift tube regions, is insensitive to flashover, beam and plasma bombardment, and radiation effects, and measures net current, thus offering some advantages over conventional magnetic probes, since the main components are outside of the vacuum region. Design criteria, an equivalent circuit analysis, and typical calibration waveforms are presented. Experimental current measurements for a pinched electron beam diode configuration using both conventional magnetic probes and 'gasket-type'current monitors with the FX-75 relativistic electron beam accelerator are presented.     

Increasing the Efficiency of Target Irradiation with Photon and Electron Beams in Radiation Therapy

An experimental method for actively controlling the dose distribution produced by electron beams in a substance is described. This method is based on the action of a magnetic field on charged particles (on secondary electrons for a photon beam). Investigations for electron beams with energies of 10 to 70 MeV in a magnetic field B = 1.16 T were performed using a race-track microtron at the Skobel'tsyn Institute of Nuclear Physics, Moscow State University (SINP MSU). It is shown that, in a homogeneous magnetic field, an additional maximum appears in the dose distribution for an electron beam, and a plateau appears in the dose distribution for a photon beam.     

Beam optics in a MeV-class multi-aperture multi-grid accelerator for the ITER neutral beam injector

In a multi-aperture multi-grid accelerator of the ITER neutral beam injector, the beamlets are deflected due to space charge repulsion between beamlets and beam groups, and also due to magnetic field. Moreover, the beamlet deflection is influenced by electric field distortion generated by grid support structure. Such complicated beamlet deflections and the compensations have been examined utilizing a three-dimensional beam analysis. The space charge repulsion and the influence by the grid support structure were studied in a 1∕4 model of the accelerator including 320 beamlets. Beamlet deflection due to the magnetic field was studied by a single beamlet model. As the results, compensation methods of the beamlet deflection were designed, so as to utilize a metal bar (so-called field shaping plate) of 1 mm thick beneath the electron suppression grid (ESG), and an aperture offset of 1 mm in the ESG.     

Electron-electron interactions in cathode objective lenses

The impact of electron-electron interactions on the electron-optical performance of imaging cathode objective lenses is evaluated. Three types of cathode objectives are considered: decelerating and accelerating electrostatic, and combined magnetic lenses. The beam blur is calculated for field sizes ranging from 50 microm x 50 microm to 500 microm x 500 microm and total beam currents ranging from 200 nA to 20 microA. The functional dependence of the beam blur upon electron beam current and current density is elucidated in detail.     

Investigation of the homogeneity of a high-power ion beam formed by a diode with a closed electron drift

The results of an investigation of the energy-density distribution over the cross section of a pulsed ion beam formed with a passive-anode diode in the mode of magnetic insulation and a closed electron drift in the anode–cathode gap are presented. Diodes of two types are studied: with external magnetic insulation (B_r diode) on the BIPPAB-450 accelerator (400 kV, 80 ns) and self-magnetic insulation of electrons (spiral diode) on the TEMP-4M accelerator (250 kV, 120 ns). In the investigated diodes, various processes are used to form anode plasma: a breakdown over the surface of a dielectric coating on the anode and ionization of the anode surface with accelerated electrons (B_r diode), as well as explosive emission of electrons (spiral diode). To analyze the ion-beam energy density, thermal-imaging diagnostics is used with a spatial resolution of 1–2 mm. The energy-density is calculated from the one-dimensional Child–Langmuir relationship. It is shown that a continuous plasma layer is efficiently formed on the working anode surface for all the investigated diodes. The anode-plasma concentration is rather high, and the beam-energy density is limited by the space charge of ions, but not by the plasma concentration. It is found that, when the magnetic field in the Br-diode anode–cathode gap decreases or the electron current in the spiral diode increases, the energy density of the high-power ion beam rises significantly, but the beam homogeneity decreases.     

Study of ion beam transport from the SECRAL electron cyclotron resonance ion source at the Institute of Modern Physics

Ion beam transport from the Superconducting Electron Cyclotron Resonance ion source with Advanced design in Lanzhou (SECRAL) electron cyclotron resonance ion source was studied at the Institute of Modern Physics during 2010. Particle-in-cell simulations and experimental results have shown that both space charge and magnetic aberrations lead to a larger beam envelope and emittance growth. In the existing SECRAL extraction beam line, it has been shown that raising the solenoid lens magnetic field reduces aberrations in the subsequent dipole and results in lower emittance. Detailed beam emittance measurements are presented in this paper.     

Vibration analysis of a ferromagnetic plate subjected to an inclined magnetic field

The magnetic traction on a deformable ferromagnetic material is deduced based on the classical magnetoelastic model. The vibration frequency of a ferromagnetic beam subjected to an inclined magnetic field is analyzed by employing formulations of the magnetic force. The result for the condition of longitudinal magnetic field is the same trend as that of the previous experiment carried out by Takagi et al. [Analysis and experiment of dynamic deflection of a thin plate with a coupling effect. IEEE Transactions on Magnetics 1992;28(2):1259–62]. Moreover, experimental tests have been carried out to study the free vibration of a magnetic plate subjected to an inclined magnetic field.     

Analysis of dynamic characteristics for vibration of flexural beam in ultrasonic transport system

An object transport system is an essential device in the factory automation system (FAS). Generally, an object transport system is driven by a conveyor belt system or a magnetic levitation system. However, contact force in the conventional transport system can damage precision optical components, while the magnetic field can destroy the inner structure of the semiconductor. The ultrasonic transport system transports objects on an elastic body using an ultrasonic wave. When an ultrasonic wave is applied to a flexural beam, the flexural beam vibrates to excite the air layer, which lifts up the object on the beam to transport. In this paper, the dynamic characteristics of the ultrasonic transport system are theoretically analyzed. Through normal mode expansion, the modeling equation for steady state response of ultrasonic vibration is expressed and the natural frequency of the flexural beam in each mode is also estimated by using the finite element method (FEM). This paper was recommended for publication in revised form by Associate Editor Eung-Soo Shin Sang-Hwa Jeong received his M.S. degree in Mechanical Engineering from KAIST, Korea, in 1985 and his Ph.D. degree from North Carolina State University, USA, in 1992. Dr. Jeong is currently a professor at the department of Mechanical Engineering of Chosun University in Gwangju, Korea. His research fields are microactuator design, ultrasonic transport system, and SMA actuator of robot finger.     

Novel methods for improvement of a Penning ion source for neutron generator applications

Penning ion source performance for neutron generator applications is characterized by the atomic ion fraction and beam current density, providing two paths by which source performance can be improved for increased neutron yields. We have fabricated a Penning ion source to investigate novel methods for improving source performance, including optimization of wall materials and electrode geometry, advanced magnetic confinement, and integration of field emitter arrays for electron injection. Effects of several electrode geometries on discharge characteristics and extracted ion current were studied. Additional magnetic confinement resulted in a factor of two increase in beam current density. First results indicate unchanged proton fraction and increased beam current density due to electron injection from carbon nanofiber arrays.     

Magnetic compound refractive lens for focusing and polarizing cold neutron beams

Biconcave cylindrical lenses are used to focus beams of x rays or neutrons using the refractive properties of matter. In the case of neutrons, the refractive properties of magnetic induction can similarly focus and simultaneously polarize the neutron beam without the concomitant attenuation of matter. This concept of a magnetic refractive lens was tested using a compound lens consisting of 99 pairs of cylindrical permanent magnets. The assembly successfully focused the intensity of a white beam of cold neutrons of one spin state at the detector, while defocusing the other. This experiment confirmed that a lens of this nature may boost the intensity locally by almost an order of magnitude and create a polarized beam. An estimate of the performance of a more practically dimensioned device suitable for incorporation in reflectometers and slit-geometry small angle scattering instruments is given.     

一种工作辊精细冷却喷嘴电磁阀的设计与仿真分析

分别建立了圆柱形螺线管电磁阀、矩形铁芯电磁阀的ANSYS模型并求解,得出了磁场强度大小分布情况,得到电磁力与铁芯结构变化的规律和电磁力与电流、线圈匝数的变化规律。在线圈匝数、电流相同的情况下,矩形铁芯电磁阀产生的电磁力可比圆柱铁芯大125%,在要求一定的电磁力的情况下,矩形铁芯阀体可小型化,为精细冷却喷射梁上的喷嘴紧凑设计提供了理论依据。     

Short note on parallel illumination in the TEM

Parallel illumination conditions are required for several experiments in the transmission electron microscope (TEM). The image rotation induced by the helical trajectory of electrons passing through the magnetic field of the TEM lenses inevitably induces an inclination of the beam relative to the optical axis in the object plane--even for an electron which travels parallel to the optical axis in the far field. This angle (shear angle) is vectorially added to the convergence angle; it depends both on the distance to the optical axis and the magnetic field. By using a beam tilt compensation method, the minimum shear angle is found to be of the order of 1 mrad for a field of view of 2 microm in a 200 kV TEM. In practice, "parallel illumination" can only be obtained for fields of view 1 microm.