HL-2M装置中性束注入加热系统研制进展

为开展磁约束堆芯燃烧等离子体物理实验,正在建造的HL-2M装置拟建造3条5 MW的中性束注入加热束线。简要概述了HL-2M装置NBI加热系统的总体规划,第1条5MW-NBI加热束线的设计,离子源调试实验,注入器核心部件的安装和测试结果。通过调试,目前单个离子源引出束流达到36 A,加速电压75 kV,离子束功率达到2.4 MW,脉冲宽度3 s。通过测试发现:注入器的4条离子束汇聚角误差小于±0.1°,残留离子偏转磁体的磁场测试值与模拟计算值偏差小于±5%,注入器静态真空值达到1.0×10-3 Pa。注入器采用大型非标低温泵,低温泵的抽速达到2.40×106 L/s。第1条5MW-NBI加热束线的试装和测试结果表明,该束线能够满足HL-2M装置NBI加热的技术要求。     

HL-2M装置5MW-NBI加热束线偏转磁体研制

根据HL-2M装置5MW-NBI加热束线总体设计参数、注入器的部件空间布局、几何汇聚特点等,建立了基于8饼线圈的注入器偏转磁体3D模型。利用电磁场模拟软件CST Studio详细模拟了注入器的偏转磁体产生的偏转磁场分布,不同成份离子束的偏转轨迹。在模拟分析结果的基础上优化了偏转磁体的物理结构,完成了磁体的工程设计、加工和测试。偏转磁体的磁场测试结果表明,测试值与CST计算值的偏差小于±5%,达到注入器偏转磁体设计要求。     

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According to the design parameters of 5MW-NBI beam line of HL-2M tokamak, spatial arrangement of components, geometrical focus characters and so on, 3D model of the deflecting magnet with 8 groups of wires is built up. With an electromagnetic field simulation software-CST Studio, the deflection magnetic field distribution and deflection trajectories of ion beams with different components are obtained. With the simulation results the physical structure of deflecting magnet is optimized, the engineering design of the magnet is completed and then the manufacture and test are finished. The testing result of the magnetic field distribution of the deflecting magnet shows: the error between measurement value and calculation result is less than ±5%, and the machined deflecting magnet can meet the design requirement.     

Primary result of ~(236)U measurement with accelerator mass spectrometry at CIAE

The rare isotope 236U has a half-life of 2.342(3)×107 years,and is produced principally by thermal neutron capture on 235U.The isotopic atom ratio of 236U/238U depends on the integral thermal neutron flux received by the material of interest.236U is potentially useful as a "fingerprint" for indicating the presence of neutron-irradiated uranium usually originating from nuclear activity.By extracting negative molecular ion UO- from the uranium oxide target,simulating the 236U16O- beam transport with 238U16O- and 208Pb12 6O- pilot molecular ion beam,transporting the 236U-containing ion beam with a high resolution injection magnet analyzer and electrostatic analyzer system,and finally identifying and detecting 236U with a time-of-flight detector(TOF),a method for AMS(Accelerator Mass Spectrometry) measurement of 236U was established on the HI-13 Accelerator AMS system at China Institute of Atomic Energy.     

The spectrometer for the GunLab experiment

The spectrometer for the GunLab experiment is described. This spectrometer incorporates a dipole magnet, a fluorescent screen, and a CCD camera and is designed to measure the momentum of electron beams in the range of 1–10 MeV/c with a resolution of 0.1%. If a transversely deflecting RF cavity is installed in front of the dipole magnet, one may investigate the longitudinal phase portrait of a beam. The spectrometer is distinctive in that a Hall sensor is placed in the magnetic field of the dipole magnet. This sensor allows one to accurately measure the magnetic field and, consequently, the momentum of an electron beam.     

A new method to generate relativistic comb bunches with tunable subpicosecond spacing

We propose and analyze a scheme to produce comb bunches, i.e. a bunch consisting of micro-bunch trains, with tunable subpicosecond spacing. In the scheme, the electron beam is first deflected by a deflecting cavity which introduces a longitudinal-dependent linear transverse kick to the particles. After passing through a drift space, the transverse beam size is linearly coupled to the longitudinal position of the particle inside the beam, and a mask is placed there to tailor the beam, then the mask distribution is imprinted on the beam's longitudinal distribution. A quadrupole magnet and another deflecting cavity are used in the beam line to compensate the transverse angle due to the first deflecting cavity. Analysis shows that the number, length, and spacing of the trains can be controlled through the parameters of the deflecting cavity and the mask. Such electron bunch trains can be applied to an infrared free electron laser, a plasma-wakefield accelerator and a supper-radiance THz source.     

Electromagnetic modeling of the CSNS Hion source extraction system

A Penning surface H^- ion source test stand has been developed for the China Spallation Neutron Source (CSNS) at the Institute of High Energy Physics (IHEP). H^- beams with a current up to 50 mA and a pulse length up to 520μs at a repetition rate of 25 Hz are obtained at present. In order to improve the extraction system based on both the results of the emittance measurements in experiment and the simulation results of the effect of the extraction system on the beam emittance, three dimensional electromagnetic finite element analysis and particle tracking are undertaken. First, the magnetic field of the deflecting magnet is studied in detail, and then the effect of the extraction geometry on the beam transport is also investigated.     

Modulation of A 10 keV ion beam

Density modulation of a 10 keV - 1 mA - He⁺-ion beam at frequencies up to MHz has been achieved by deflecting the beam ions across an aperture. The modulation mechanism depends mainly on the periodical disturbance of the beam space charge neutrality.     

Electromagnetic modeling of the CSNS H- ion source extraction system

A Penning surface H^- ion source test stand has been developed for the China Spallation Neutron Source (CSNS) at the Institute of High Energy Physics (IHEP). H^- beams with a current up to 50 mA and a pulse length up to 520μs at a repetition rate of 25 Hz are obtained at present. In order to improve the extraction system based on both the results of the emittance measurements in experiment and the simulation results of the effect of the extraction system on the beam emittance, three dimensional electromagnetic finite element analysis and particle tracking are undertaken. First, the magnetic field of the deflecting magnet is studied in detail, and then the effect of the extraction geometry on the beam transport is also investigated.     

在托卡马克装置杂散磁场下未中性化离子偏转轨道的计算与分析

本文给出了在托卡马克装置杂散磁场下中性束注入器内未中性化离子偏转轨道的计算结果,并分析了在装置的中性束注入器上实现的可能性。     

混合型波荡器的3维优化

 以波荡器辐射波和共振电子能及混合型波荡器的解析计算为基础，通过3维磁场的有限元计算，在欧洲光源横向优化基础上，给出了同步辐射和自由电子激光用混合型波荡器纵向优化参数，进而给出了用于DUV FEL混合型波荡器的设计计算参数。加侧位和顶部永磁块后，峰值磁场分别提高到0.722T和0.773T，辅助以1μm量级分辨率的磁间隙调节机械系统，磁场分辨率好于10^-4T量级。     

通过极化原子束的磁偏转实现激光同位素浓缩

本文描述一种通过极化原子束的磁偏转实现同位素和同质异能素浓缩的新方法。用具有不同频率和偏振的激光进行选择性光抽运,使束中两同位素的原子分别反向高度极化,然后使这些反向极化的原子在经过自旋选态磁铁后沿不同方向偏转,从而实现同位素浓缩。推算了此法的选择性和产量,与其他方法相比,讨论了其优缺点和可能的应用前景。提出了用锂或钾进行实验的方案。 关键词：     

EAST-NBI磁偏转系统束传输特性模拟研究

根据EAST-NBI偏转系统工作原理,分析了束流在偏转系统传输的基本过程和特点。利用直接蒙特卡罗方法,发展了中性束注入器束偏转区域束流传输模拟程序。结果显示:EAST-NBI磁偏转系统可很好地剥离束流中的剩余离子;束偏转区域束流再电离损失约为2.43%;束流180°偏转所带来线聚焦过程使偏转磁体磁极护板局部面临较高的热流密度。     

Study of the design of CSNS MEBT

The design of CSNS MEBT has two objectives: (1) to match the beam both in the transversal direction and the longitudinal direction from RFQ into DTL; (2) to further chop the beam into the required time structure asked by RCS. It is very difficult and critical to control well the emittance growth and in the meantime to match and chop the beam. Firstly, the optical design is done and optimized, and the multi-particle simulations show that the maximum emittance growth is successfully controlled within 14%. Secondly, based on the different beam envelopes obtained by TRACE-3D and PARMELA, the least deflecting angle of the chopper is determined by TRACE-3D. At last, the field of steering magnet is determined through simulations.     

400 Kev heavy ion implanter

An experimental 400 Kev heavy ion implanter has been constructed and put into operation in the Department of Physics, the Peking Normal University. The equipment works on a system of acceleration, analysis, scan, and acceleration (or deceleration). It is composed of the radiofrequency heavy ion source, the front accelerating system, the double focusing symmetrical magnet, the deflexion scanning system, the post-accelerating tube, and the target chamber. The deflecting angle of the magnet is 90°. At present, more than twenty different species of ion beam, such as B, P, As, Al, Mg, Zn, Hg, etc. have been extracted. The extracted ions are used in research work on semiconductors, metals, and superconductive materials. The beam current on the target ranges between 10 μA and 200 μA, and the doping uniformity is ±1.4%.     

Kicker magnet modulator in the 2-GeV Pohang light source

The 2.0-GeV Pohang light source (PLS) is a third-generation synchrotron light source that is the first such facility in Korea and the fifth in the world. The PLS mainly consisted of a full-energy injection linac and a storage ring. Four kicker magnets are installed in the storage ring tunnel to move the stored beam orbit in the storage ring closer to the injected beam from the beam transfer line. The injected beam then falls into the storage ring beam dynamic aperture. A kicker magnet modulator drives all four kicker magnets to maintain field balance and synchronized kick of the beam. Specification of the kicker magnet modulator is ~6.0-μs-full width, 200-ns flattop width with ±0.2% regulation, ~24-kA peak current, and 10-Hz repetition rate. Two thyratron switches (EEV CX-1536AX) are used in the system. As the inverse voltage is dangerous to thyratron operation, a new surge suppression circuit was developed. The kicker modulator has been operated very reliably since its installation in August 1995. In this article, design, simulation, and experimental results of the kicker magnet modulator are discussed. In addition, measurement result of spatial B-field distribution in the kicker magnet and maximum operating range of kicker magnet are discussed     

Research and development of an electron beam focusing system for a high-brightness X-ray generator

A new type of rotating anticathode X-ray generator, where an electron beam of up to 60 keV irradiates the inner surface of a U-shaped Cu anticathode, has achieved a beam brilliance of 130 kW mm(-2) (at 2.3 kW). A higher-flux electron beam is expected from simulation by optimizing the geometry of a combined-function-type magnet instead of the fringing field of the bending magnet. In order to minimize the size of the X-ray source the electron beam has been focused over a short distance by a new combined-function bending magnet, whose geometrical shape was determined by simulation using the Opera-3D, General Particle Tracer and CST-STUDIO codes. The result of the simulation clearly shows that the role of combined functions in both the bending and the steering magnets is important for focusing the beam to a small size. FWHM sizes of the beam are predicted by simulation to be 0.45 mm (horizontal) and 0.05 mm (vertical) for a 120 keV/75 mA beam, of which the effective brilliance is about 500 kW mm(-2) on the supposition of a two-dimensional Gaussian distribution. High-power tests have begun using a high-voltage 120 kV/75 mA power supply for the X-ray generator instead of 60 kV/100 mA. The beam focus size on the target will be verified in the experiments.     

10 MeV质子等时性回旋加速器的设计研究

给出10MeV质子等时性回旋加速器的等时性磁场设计,中心区的设计以及加速后最终的束流品质,该加速器可作为正电子断层扫描装置的配套设备,用于生产中短寿命放射性同位素等.它沿半径方向只用一套线圈励磁,等时性磁场的建立完全由磁极形状决定.中心区的设计满足了轨道中心化的要求,并给出较大的横向和纵向接受度,以获得足够的束流强度. 经过172圈加速后,最终的束流品质满足要求.     

Two-Dimensionally Deflecting Mirror Using Electromagnetic Actuation

This paper describes the structure and characteristics of a deflecting mirror using electromagnetic actuation. We used a moving magnet structure for mirror actuation and focused on designing a mirror structure with effective magnetic force (for low-power operation) and a simple fabrication process (to achieve low manufacturing cost). In this design, the magnetic forces of attraction and repulsion are simultaneously used for mirror deflection, allowing the mirror to be operated with low current. Moreover, the structures of the yoke core and magnet bar have been designed to further reduce the operating current. Such a mirror structure is simple and can be easily fabricated with a small number of components. This structure can be used not only for a one-dimensionally deflecting mirror but also for a two-dimensionally deflecting mirror by attaching a second yoke core.     

Evidence for microbunching "sidebands" in a saturated free-electron laser using coherent optical transition radiation

We report the first measurements of z-dependent coherent optical transition radiation (COTR) due to electron-beam microbunching at high gains ( >10(4)) including saturation of a self-amplified spontaneous emission free-electron laser (FEL). In these experiments the fundamental wavelength was near 530 nm, and the COTR spectra exhibit the transition from simple spectra to complex spectra ( 5% spectral width) after saturation. The COTR intensity growth and angular distribution data are reported as well as the evidence for transverse spectral dependencies and an "effective" core of the beam being involved in microbunching.