速度选择器参数设计及其中子光学特性

速度选择器是中子小角散射谱仪的关键部件之一,可获得有一定宽度的单色中子束,本文针对不同参数模型,用Vitess程序进行了计算和优化设计,根据客观需求,得到优化的速度选择器参数。并对速度选择器后中子光学特性进行分析,发现转子倾角和束流发散度对中子光学特性影响明显。     

机械速度选择器特征参数计算

介绍了中子小角散射谱仪中,中子单色化部件机械速度选择器参数。对速度选择器常数、透过率和波长分辨率作了分析计算,得到了这些参数是由其本身几何参数决定,与入射中子波长无关。阐述了使用山嵛酸银对速度选择器的选择波长标定和使用飞行时间谱仪对其选择波长和波长分辨率测量计算方法。并通过实际速度选择器的计算,得到了速度选择器的相关参数。     

中子单色器模拟分析研究

为研究单色器对中子能谱的选择规律,本文利用MCSTAS程序模拟分析了机械速度选择器与晶体单色器几个特征参数对中子能量选择影响。分析结果显示经机械速度选择器单色选择中子注量率要下降1~2个量级,而晶体单色器要下降2~3个量级。因此,对于单色化要求比较高选用晶体单色器,对于实验时间要求较高的选用机械速度选择器。     

2×6 MV串列加速器头部附近电场设计优化

为了给2×6 MV串列加速器提供高压电极与均压环尺寸，根据设计要求及已有参数，采用电磁场仿真软件计算了串列加速器的二维电场强度分布，针对高压电极结构、均压环截面形状及环间距等因素对串列加速器电场强度分布的影响提出了优化措施。仿真结果表明：直筒结构的高压电极与均压环接壤处电场强度分布不均匀，而圆弧过渡结构的高压电极具有屏蔽作用，比直筒时电场强度分布更均匀；优化均压环截面形状与减小环间距可降低环间电场畸变，但后者对减小均压环表面的电场贡献更大。最终优化后得到高压电极与均压环的尺寸可满足新研制的串列加速器要求。     

机械速度选择器标定技术及标定实验

机械速度选择器作为关键部件广泛应用于中子散射谱仪上,研发标定技术、研制标定设备及开展标定实验是机械速度选择器应用的前提。本文基于中国先进研究堆小角中子散射谱仪,设计了标定中子飞行时间设备的结构,确定了设备的参数。研究了漏计数对波长分辨率测量的影响,发现波长分辨率测量误差取决于死时间及高斯峰位计数率之积,若死时间不变,波长分辨率测量误差随高斯峰位计数率的增加而变大。开展了飞行时间法机械速度选择器标定实验,发现单色中子波长的理论计算结果与实验数据的高斯拟合结果非常接近;波长分辨率实验值随波长的增加而增加,与波长分辨率计算值有一定差距,这些变化和差距源自束流发散。使用漏计数对波长分辨率测量影响的规律分析了实验结果,计算出了样品位置中子通量密度上限;使用VITESS软件模拟得出了不同波长样品位置中子通量密度并验证了二维可调狭缝调节中子通量密度的效果。     

反应堆下腔室结构优化设计

对目前现有的反应堆下腔室结构的不足进行优化分析,针对性地提出解决措施。分析中重点从下腔室结构的稳定性、可靠性和流场的不均匀性入手,采用简化结构和计算流体力学(CFD)计算下腔室流场,使反应堆下腔室具有结构简单、稳定可靠、流场均匀等特点。     

机械速度选择器标定技术及标定实验

机械速度选择器作为关键部件广泛应用于中子散射谱仪上,研发标定技术、研制标定设备及开展标定实验是机械速度选择器应用的前提。本文基于中国先进研究堆小角中子散射谱仪,设计了标定中子飞行时间设备的结构,确定了设备的参数。研究了漏计数对波长分辨率测量的影响,发现波长分辨率测量误差取决于死时间及高斯峰位计数率之积,若死时间不变,波长分辨率测量误差随高斯峰位计数率的增加而变大。开展了飞行时间法机械速度选择器标定实验,发现单色中子波长的理论计算结果与实验数据的高斯拟合结果非常接近;波长分辨率实验值随波长的增加而增加,与波长分辨率计算值有一定差距,这些变化和差距源自束流发散。使用漏计数对波长分辨率测量影响的规律分析了实验结果,计算出了样品位置中子通量密度上限;使用VITESS软件模拟得出了不同波长样品位置中子通量密度并验证了二维可调狭缝调节中子通量密度的效果。     

钎焊板翅结构残余应力的分布与优化研究

利用有限元法对不同操作条件下的钎焊板翅结构残余应力进行分析。计算结果表明,成型后的板翅结构单元中存在较大的残余应力,最大残余应力出现在钎角附近。钎焊过程中的固化急速冷却速度对钎焊残余应力有显著影响。急速冷却速度越快,越有利于材料性能的提升,但是钎角附近的残余拉伸应力也越大。另外,采用加压组装工艺可在钎焊后的板翅结构中产生残余压应力,有效提高了钎焊板翅结构的服役安全和寿命。     

EAST-NBI抑制极电源IGBT串联技术的研究

中性束注入器(Neutral Beam Injector,NBI)是东方超环(Experimental Advanced Superconducting Tokamak,EAST)核聚变实验装置辅助加热的重要组成部分。目前NBI离子源引出系统采用四电极结构,即加速电极、梯度电极、抑制电极和地电极。抑制极电源是为其中的抑制电极提供负电位的高压直流电源。根据抑制极电源输出特性的要求,输出端采用串联绝缘栅双极型晶体管(Insulated Gate Bipolar Transistor,IGBT)作为调制开关。为研究IGBT串联技术对均压效果和抑制极电源输出特性的影响,采用PSpice软件对IGBT开关进行了建模,并进行了不同电路参数下的仿真。仿真表明:一定条件下,电阻电容二极管(Resistance Capacitance Diode,RCD)缓冲电路中电容参数对动态均压效果和电源关断特性具有决定性影响,缓冲电阻影响电容的放电时间及放电电流峰值。最后给出了相应的实验测试结果。该研究结果可以明确缓冲电路参数与均压效果以及抑制极电源开关特性之间的定量关系,为抑制极电源开关特性的进一步优化及其与加速极电源的特性匹配提供数据指导,对于NBI离子源的安全稳定运行具有重要意义。     

小角中子散射谱仪机械速度选择器标定系统修复及实验测量

正机械速度选择器标定为测量谱仪样品位置中子波长和波长分辨率随机械速度选择器转速及倾斜角的变化。机械速度选择器标定系统已完成研制和调试工作。标定实验条件为:CARR反应堆功率30 MW,冷源未启动,准直系统推入12m中子导管。在机械速度选择器6 016、5 015、4 525、3 823、3 001r·min~(-1)等5个不同转速下,分别使     

自由空气电离室电场分布的研究

自由空气电离室作为X射线空气比释动能的初级标准装置被国内外计量机构广泛使用。本文使用有限元分析法研究自由空气电离室内的电场分布。研究结果发现,通过添加保护电极与保护环保持内部电场均匀性的同时,铅屏蔽外壳的电势对自由空气电离室内部电场同样具有影响。模拟计算结果表明,对铅屏蔽外壳、保护电极与保护环施加适当的电压,同时优化自由空气电离室的设计结构,可优化自由空气电离室内部电场分布。     

Measurements of distribution of self-bias potential on an RF-plane electrode in plasma etching devices

The self-bias potential (V_dc) induced on an RF-powdered electrode (153 mm Ø) in a plasma is measured using electrical probes which are buried in, de-insulated from, and RF-connected to the electrode. The configuration of the probes allows to study the distribution of V_dc discretely on the electrode. The potential is homogeneous in the absence of external magnetic field. In the presence of a homogeneous magnetic field parallel to the electrode, it is reduced and a monotonous gradient takes place in its distribution due to the plasma shift induced by E × B drift. When the magnetic field is rotated along the axis of the RF-electrode at a frequency less than 50 Hz, the distribution, which is almost identical to the one in a static field, rotates with the magnetic field. On the coordinate system rotating with the magnetic field, the probes are regarded to be rotating. The potential distribution is obtained as a continuous function of the azimuthal angle. Thus the rotation of the field provides information for the experimental interpolation.     

基于轮转电极的多电极电容式棒位测量传感器静态特性研究

电容式棒位测量传感器是200 MW低温核供热堆控制棒水压驱动系统的关键测量部件,其精度和可靠性直接关系到反应堆的安全性。本文基于有限元方法建立了电容式棒位测量传感器的理论模型,对两电极电容式棒位测量传感器检测场的灵敏度分布特性进行了分析。结果表明,在检测场内存在一个特定区域,被测杆向该区域偏移时偏心误差较小。基于该特性提出了多电极电容式棒位测量传感器的设计方案和轮转电极的电容检测方法,针对该传感器,利用有限元模型进行了传感器结构优化和被测杆偏心误差分析,完成了传感器静态特性实验并验证了模型计算结果。分析结果表明,多电极电容式棒位测量传感器与轮转电极的电容检测方法能有效利用检测场的灵敏度分布特性,优化后传感器的偏心误差能达到棒位测量不失步的要求。研究成果为电容式棒位测量传感器的设计和优化提供了新的方向。     

The use of the Wien filter to eliminate object slit scattering in MeV ion nanobeam systems

One of the fundamental limitations in the performance of MeV ion microbeam focusing systems is the effect of ion scattering at the edges of the object aperture. As the aperture is reduced in the search for smaller spot sizes, the fraction of scattered to unscattered beam increases. The scattered beam contains lower energy particles which can be transmitted through the system to create a halo of over-focused particles surrounding the final image. Removal of this halo is critical to achieving small spot sizes, especially in single ion applications.In this paper, we discuss the use of a Wien filter (crossed magnetic and electrostatic fields) to deflect the reduced energy scattered particles and ensure that only ions with the correct energy are accepted into the lens. This paper reviews the beam optics of Wien filter systems and presents calculations of the parameters required to obtain useful energy dispersion.     

用于双离子束注入器的杂质消除系统

研制了一套用于双离子束注入器的杂质消除系统，该系统由两台速度选择器、1台单透镜和1台双孔选束光阑组成，可实现不同荷质比的两种离子束在同时传输过程中消除杂质离子。该技术已用于1台H⁺₂和He⁺两种离子束同时传输的50 keV双离子束注入器，实现了1台加速器同时产生、传输两种离子束，并同轴注入靶内，离子束纯度好于99.9%。     

西安脉冲堆超热中子束的理论设计

建立超热中子束孔道筛选的三维扩散型,并用蒙特卡罗程序MCNP／4B验证了热柱孔道是实现超热中子束的佳孔道,还建立了硼中子俘获治疗（BNCT）所需超热中子束的理论设计方法,对超热中子束过滤材料的特性进行了分析,提出了将西安脉冲堆热柱孔道改造成超热中子束孔道的3种材料组合方案。     

Numerical Study of Pulsed Dielectric Barrier Discharge at Atmospheric Pressure Under the Needle-Plate Electrode Configuration

In this paper,we study the characteristics of atmospheric-pressure pulsed dielectric barrier discharge (DBD) under the needle-plate electrode configuration using a one-dimensional self-consistent fluid model.The results show that,the DBDs driven by positive pulse,negative pulse and bipolar pulse possess different behaviors.Moreover,the two discharges appearing at the rising and the falling phases of per voltage pulse also have different discharge regimes.For the case of the positive pulse,the breakdown field is much lower than that of the negative pulse,and its propagation characteristic is different from the negative pulse DBD.When the DBD is driven by a bipolar pulse voltage,there exists the interaction between the positive and negative pulses,resulting in the decrease of the breakdown field of the negative pulse DBD and causing the change of the discharge behaviors.In addition,the effects of the discharge parameters on the behaviors of pulsed DBD in the needle-plate electrode configuration are also studied.     

Characteristics of a radio-frequency cold atmospheric plasma jet produced with a hybrid cross-linear-field electrode configuration

Cold atmospheric plasma (CAP) jet has wide applications in various fields including advanced materials synthesis and modifications, biomedicine, environmental protection and energy saving, etc. Appropriate control on the volume, temperature and chemically reactive species concentrations of the CAP jet is of great importance in actual applications. In this paper, an radio-frequency atmospheric-pressure glow discharge (RF-APGD) plasma generator with a hybrid cross-linear-field electrode configuration is proposed. The experimental results show that, with the aid of the copper mesh located at the downstream of the traditional co-axial-type plasma generator with a cross-field electrode configuration, a linear field between the inner powered electrode of the traditional plasma generator and the copper mesh can be established. This liner- field can, to some extent, enhance the discharges at the upstream of the copper mesh, resulting in small increments (all less than 12.5%) of the species emission intensities, electron excitation temperatures and gas temperatures by keeping other parameters being unchanged. And due to the intrinsic transparent and conducting features of the grounded copper mesh to the gas flowing, electric current and heat flux of the plasma plumes, a plasma region with higher concentrations of chemically reactive species and larger plasma plume diameters is obtained at the downstream of the grounded copper mesh on the same level of the gas temperature and electron excitation temperature compared to those of the plasma free jet. In addition, the charged particle number densities at the same downstream axial location of the grounded copper mesh decrease significantly compared to those of the plasma free jet. This means that the copper mesh is also, to some extent, helpful for separating the chemically reactive neutral species from the charged particles inside a plasma environment. The preceding results indicate that the cross-linear-field electrode configuration of the plasma generator is an effective approach for tuning the characteristics of the RF-APGD plasma jet in order to obtain an appropriate combination of the plasma jet properties with higher chemically reactive species concentrations, especially relative higher number densities of neutral species, larger plasma volumes and lower gas temperatures.     

Characteristics of Resistive Electrode in MHD Generator Duct and a Minimizing Technique for Internal Power Loss

Two-dimensional current distribution in two regions—resistive electrode and plasma—are studied to optimize the shape of the resistive electrode in the MHD generator. Numerical computations are made for an example of potassium-seeded argon in non-equilibrium. As a first step, the performance is analyzed on an electrode of rectangular shape, and calculations performed more quantitatively than in the previous work by Maxwell et al. reveal that better uniformity is obtained for the current distribution along the electrode surface by increasing the thickness and resistivity of the electrode. The uniformity is found to improve also when the load current is increased.

To diminish the power loss produced in the resistive layer, the electrode shape is optimized by eliminating from the rectangular resistive electrode the portion that produces the power loss. The electrode thus optimized in shape has an effective internal resistance that is independent of the value of the resistivity of the resistive layer. Consequently, in the optimized electrode, the power loss is independent of the uniformity of current distribution along the electrode surface, whereas it depends on the uniformity when a rectangular-shaped electrode is used.     

Study of ionic wind based on dielectric barrier discharge of carbon fiber spiral electrode

Based on the idea that a large number of charged particles can be generated by a high-frequency alternating current(AC)dielectric barrier discharge(DBD),and charged particles can be accelerated directionally by a direct current(DC)electric field,a new type of ionic wind formation method is proposed in this paper.To this end,a carbon fiber spiral electrode serves as the generation electrode and a metal rod electrode as the collection electrode,with AC and DC potentials applied respectively to the generation electrode and the collection electrode to form an AC-DC coupled electric field.Under the action of the coupled electric field,a dielectric barrier discharge is formed on the carbon fiber spiral electrode,and the electrons generated by the discharge move from the generation electrode to the collection electrode in the opposite direction of the electric field vectors.During the movement,energy is transferred to the gas molecules by their colliding with neutral gas molecules,thereby forming a directional gas stream movement,i.e.ionic wind.In the research process,it is verified through electric field simulation analysis and discharge experiment that this method can effectively increase the number of charged particles in the discharge process,and the velocity of the ionic wind is nearly doubled.On this basis,the addition of a third electrode forms a distinct discharge region and an electron acceleration region,which further increases its velocity.The experimental result shows that the ionic wind speed reaches up to 2.98 m s^?1.Thanks to the ability of the electrode structure to generate an atmospheric pressure DBD plasma and form an ionic wind,we can create a noise-free air purification device without resorting to a fan,with this device having good application prospects in the field of air purification.