静电单透镜在低能强流离子束输运中的应用

本文介绍北京大学重离子所RFQ组利用静电单透镜进行低能强流离子束束流输运的情况.在北京大学1 MeV ISR RFQ加速器的升级改造中,我们在低能输运段使用了2个静电单透镜进行调束,当引出电压为22kV时,在RPQ入口处得到了归一化均方根发射度为0.12 7× mm·mrad、峰值流强6 mA的脉冲氧离子束(相当于24mA质子束流).以及用静电单透镜聚焦强流氢离子束的初步实验实验.     

400 kV强流中子发生器的物理设计

对400 kV强流中子发生器进行了物理设计。采用Poisson/Superfish软件对中子发生器高压电极和加速管的电场分布进行了模拟,结果显示,各关键区域的空间电场最大值远低于击穿电场限值。以强流束旁轴包络方程为基本模型,发展了强流束传输系统束包络的计算机模拟程序IONB1.0,模拟了中子发生器传输系统中40 mA的D束流包络。结果显示,设计方案中所采取的两间隙高梯度加速结构有较强的聚焦性能,能有效抵消强流束空间电荷效应造成的束流发散,加速管出口处的束包络半径约3 cm,由加速管出口处的空间电荷透镜和三重四极磁透镜组成的传输系统能将束流聚焦在约140 cm处的靶上,且束斑直径小于2 cm。     

750KeV,50mAH—RFQ预注入器调整结果

文章介绍西德DESY研究所750keV负氢离子预注入器的调整结果。通过提高弧流,磁控管型H~-离子源可以引出18keV,60—80mA的H~-脉冲离子流。发现外部磁场可以在螺旋管内部感生一个方向大体相同的磁场。在低能输运段,离子束空间电荷中和所需的时间约100μs。在离子源引出束流约65mA时,经两对螺旋管聚焦和RFQ加速后可以获得能量为750±8.8keV,聚团半宽度约0.8ns,发射度约3mm·mrad,束流为52mA的脉冲H~-流;其中33mA以上的束流处于1mm·mrad以内。     

强流脉冲束在轴对称静电场中传输的自洽计算

为计算强流脉冲束在轴对称静电场六维相空间中的传输，设计了一个计算程序。此程序可以计算由漂浮空间、三圆单筒透镜、三膜片单透镜、双圆筒透镜、静电加速管组成的离子光学系统。为了得到强流束传输的自治解，程序采用了迭代过程。用此程序计算了300kV强流脉冲束加速器的光路，所得结果合理。     

强流RFQ注入系统研制

本文介绍研制的强流RFQ注入系统。系统包括强流离子源、聚焦透镜、束流切割器等,注入系统在RFQ入口处形成了束流能量75keV、流强42mA、α参数为1．79、β参数为0．0596mm／mrad、束流脉冲频率1-100Hz、束流占空比1％-100％、发射度小于95．2πc mm mrad的质子束,可满足强流RFQ对束流注入品质的要求。     

强流离子束的最佳聚焦

在同时考虑束流发射度和空间电荷效应情况下,推导出了轴对称强流离子束的最佳聚焦条件,并根据数值计算结果,绘制出了最佳聚焦条件下确定束腰半径、束腰位置和固定靶上最小束半径的通用关系曲线。     

强流ECR离子源研究进展

研制了一台用于强流质子加速器的强流ECR离子源,建立了无油、大抽速的离子源实验台架,解决了微波功率馈送、放电室结构、高压打火和微波窗板损坏等问题,特别是对影响离子源寿命的窗板问题,做了独创性的改进,有效地解决了窗板容易损坏的难题,获得了很好的结果。离子源的引出能量达到70 keV,最大引出束流100mA,质子比好于80％,归一化rms发射度小于0.2π mm·mrad,离子源通过了12 h连续运行的可靠性考验。另外,设计加工了用于低能束流传输段的螺旋管透镜,设计加工了束流脉冲化装置,下一步将开展低能离子束的传输特性及脉冲化研究。     

永磁强流ECR离子源

文章介绍一台2.45 GHz永磁强流ECR离子源,其直径为10 cm,长10 cm,重量不足5 kg,可工作在直流模式和脉冲模式.脉冲模式引出的氢离子束峰值流强大于100 mA,束流密度达到500 mA/cm2;直流模式引出束流达到60 mA,束流密度为300 mA/cm2.两种模式的质子比均达到80%.     

600 kV毫微秒脉冲中子发生器研制

研制了600kVns脉冲中子发生器(CPNG 6)。CPNG 6由高压电源(输出电压为600kV,电流为15mA,高压稳定度和纹波均≤0.1%)、2214mm×1604mm×1504mm不锈钢高压电极及安装在内的高频离子源、预加速间隙透镜、初聚焦系统、切割器、90°磁分析器等构成的头部设备,均匀场加速管,漂移管,偏转磁铁,0°直流束和45°脉冲束流管道,无油分子泵真空系统等组成。在脉冲束流管道上安装有强流毫微秒脉冲化聚束装置。阐述了该器的方案要点和各部件的主要技术性能及特点。     

CSNS直线加速器空间电荷效应的模拟研究

本文利用三维空间电荷效应程序IMPACT-Z对直线加速器中的空间电荷效应进行了模拟研究,从单粒子动力学和多粒子动力学角度分析了束流在不同峰值流强下的发射度变化。在15 mA流强下,比较了束流初始失配对束流发射度的影响,结果显示横向失配对发射度束流品质影响更大,实际调束过程中应保证束流失配因子不超过1.4。     

STUDY OF THE FOCUSED ION BEAM AND ITS APPLICATION TO METAL IMPLANTATION MODIFICATION

The properties and designment of the strong focusing lens system and the application to metal modification of gear cutting tools are described. The focused ion beam produced by a special three asymmetric voltage lens has the unique features of short midfocal length, strong focusing and omitted focusing electric power. These properties of strong focusing lens system are due to the application of the high energy ratio of 20 to 50 onto the lens.     

Design of a compact focusing lens system with short acceleration tube at 300 kV

A compact focusing lens system with high demagnification over 1500 was designed to form an ion nanobeam with 346 keV energy by adding a short distance acceleration tube for beam acceleration and focusing downstream of the existing double acceleration lens system. The demagnification, focusing points and aberrations of the acceleration tube were studied using beam trajectory calculation. The acceleration tube was designed to have a length of 140 mm and a demagnification of 2 at its acceleration tube voltage of 300 kV, which resulted in a new compact focusing lens system with a total length of about 640 mm. In addition, the maximum voltage and electric-field of the acceleration tube were confirmed experimentally on the built device to be 300 kV and 30 kV/cm, respectively. The final beam size formed by the system was estimated to be 130 nm in diameter using the design parameters. The result suggests that an ion nanobeam of 346 keV can be formed by an apparatus having the reasonable length of 2 m, which permits us to develop a system for 1 MV by elongating its tube length.     

CSRe分子离子研究装置低能传输线物理设计

本文完成了CSRe分子离子研究装置低能传输线的物理设计。采用Poisson/Superfish软件对150 kV倍压型高压加速器的电场分布进行了模拟,结果显示,加速器各区域空间电场强度均远低于击穿电场强度限值。利用Beampath程序对离子源引出的分子离子束在高压加速器中的传输进行了模拟,束流包络显示,加速区电场对分子离子束具有较强的聚焦作用,加速管出口束斑尺寸较小。采用Trace-3D程序设计了高分辨能力的磁分析系统和RFQ加速器的注入匹配段。通过Beampath程序的模拟,分析出了质量数为150的分子离子束,并由三单元四极透镜实现了分析束流与直线加速器RFQ的注入匹配。     

高流强RFQ质子加速器研制

在国家“973”计划洁净核能项目的支持下,中国科学院高能物理研究所与中国原子能科学研究院合作,建成了我国首台强流质子加速器。它是1台四翼型结构的射频四极（radio-frequencyqaudrupole,RFQ）加速器,这种先进加速结构可为来自离子源的低能强流束提供周期性强聚焦,并同时在纵向对束流进行聚束和加速。我国建成的这台RFQ加速器束流能量为3.5MeV,脉冲流强达46mA,束流工作比大于7%。本文将介绍这台RFQ加速器的物理设计、研制、调试和出束实验的结果。     

Control of Beam Energy and Flux Ratio in an Ion-Beam-Background Plasma System Produced in a Double Plasma Device

Plasmas containing ion beams have various applications both in plasma technology and in fundamental research. The ion beam energy and flux are the two factors characterizing the beam properties. Previous studies have not achieved the independent adjustment of these two parameters. In this paper, an ion-beam-background-plasma system was produced with hotcathode discharge in a double plasma device separated by two adjacent grids, with which the beam energy and flux ratio(the ratio between the beam flux and total ion flux) can be controlled independently. It is shown that the discharge voltage(i.e., voltage across the hot-cathode and anode) and the voltage drop between the two separation grids can be used to effectively control the beam energy while the flux ratio is not affected by these voltages. The flux ratio depends sensitively on hot-filaments heating current whose influence on the beam energy is relatively weak,and thus enabling approximate control of the flux ratio     

Focusing characteristics of the relativistic electron beam transmitting in ion channel

Based on the beam–plasma system model established in this paper, the trajectory of the electron beam in the ion channel is studied quantitatively through the envelope equation. Under different initial system parameters, the focusing transmission conditions of the beam in the ion channel are discussed. Then, a series of particle-in-cell simulations are performed, which generally versifies the theoretical results and shows some further details of the focusing behavior of the beam. It is found that the deceleration of some electrons around the focusing point or the beam–plasma interaction at the ion channel boundary will result in the generation of the residual electrons,which forms the electron return current that leads to the new instabilities influencing the focusing characteristics of the beam.     

Mapping ion beam induced current changes in a commercial MOSFET

We demonstrate a novel nuclear microprobe imaging and analysis modality for micrometre-scale field effect transistor devices probed with focused beams of MeV ions. By recording the drain current as a function of time during ion irradiation it is possible to identify current transients induced by the passage of single ions through the sensitive structures of the device. This modality takes advantage of the fact that the ionization produced by the passage of a single ion acts in an equivalent way to a transient change in the gate bias which therefore modulates the drain current as a function of time. This differs from the traditional ion beam induced charge technique where the ionization drifts in an internal electric field and induces a single charge pulse in an electrode applied to the device. Instead a richer variety of phenomena are observed, with different time constants which depend on the proximity of the ion strike to the channel of the device. The signals may be used to examine device function, radiation sensitivity or to count ion impacts within the channel.     

脉冲离子束作用下金属氚化物氦释放测量技术研究

为认识脉冲离子束作用下金属氚化物的氦释放行为,建立了脉冲离子束作用下金属氚化物氦释放测量系统。利用标准体积气体取样装置,采用气体反扩散法,对系统的容积比、灵敏度进行了实验标定。在此基础上,发展了脉冲离子束作用下金属氚化物氦释放的测量技术,开展了脉冲离子束作用下金属氚化物氦释放实验研究。结果显示,单次脉冲离子束作用下金属氚化物的氦释放呈脉冲式,释放量最大可达10~(13)个原子以上。     

高功率紫外超短激光脉冲光束质量研究

通过搭建传输和聚焦光学系统,采用CCD相机测量了高功率紫外超短脉冲激光系统的光束质量参数,如紫外种子光及其经过KrF准分子激光器放大后的焦斑光强空间分布、焦斑尺寸及极限衍射倍数β。结果表明,紫外种子光光束质量良好,β接近于1。经放大后,光束质量劣化,β达到6左右。经分析,光学元件的表面缺陷可能是导致光束质量下降的主要因素。