SESRI 300 MeV同步加速器注入线的传输效率与接受效率

为了完成SESRI300MeV同步加速器的束流调试,使用Tracewin软件和加速腔电磁场分布文件建立了该加速器注入线从离子源出口到注入点的全尺寸模型,在多粒子模式下计算了两种典型粒子束(质子、²⁰⁹Bi³²⁺)在不同状态下的加速传输,得到了注入线上束流相空间的变化过程和注入线的传输效率与接受效率.研究结果表明,300 MeV同步加速器注入线在加速不同荷质比的离子束流时,电磁场参数设置基本与荷质比成反比.束流的接受效率主要由射频四极加速腔出口发射度决定,质子束和重离子束的接受效率差别较大.在射频四极加速腔出口发射度为0.1πmm·mrad时,²⁰⁹Bi³²⁺束接收效率达到92.13%,质子束的接收效率为68.18%.分析束流传输过程表明,当横向发射度过大时,束流会因为纵向能散展宽和相位展宽而无法被最终接受.在现有配置下,质子束存在横向聚焦力不够、接受效率较低的问题.通过额外增加2个四极铁能够将质子束的接受效率由68.18%提升至83.61%.     

EicC束流冷却方案设计与模拟

对核子内部结构的研究是当前理论和实验研究的重要前沿,高能散射实验是探索核子结构的理想工具。中国科学院近代物理研究所计划在已开建的强流重离子加速器项目(HIAF)的基础上,升级建造中国极化电子离子对撞机(EicC)。EicC将提供质心系能量为15～20 GeV的电子和质子双极化束流,对撞亮度设计指标为2×10³³ cm^-2s^-1,离子束的有效冷却是EicC实现亮度目标的关键。针对离子束流初始发射度大、能量高、流强强的特点,EicC采用两级束流冷却方案,首先在增强器(BRing)中利用常规直流电子冷却器降低离子束流发射度,其次在对撞环(pRing)中采用基于能量回收型直线加速器(ERL)的高能束团冷却系统,抑制对撞过程中的离子束发射度增长。以质子束为例,模拟研究了EicC束流冷却装置中电子束的尺寸、温度、冷却段的磁场和束流光学参数对冷却速率和冷却过程的影响,最终得到了满足亮度要求的束流冷却参数。     

低能强流混合离子束空间电荷补偿度研究

空间电荷效应是影响束流传输和束流品质的一个重要因素，特别是对于低能量强流离子束来说。离子束与束流传输线中的剩余气体分子通过电离反应等产生大量二次电子，受离子束的空间电势约束，可以部分补偿空间电荷效应。为了深入研究强流束在低能段的传输，需要准确测量束流的空间电荷补偿度(SCCD)，尤其是混合束流的SCCD。利用一台三栅网式能量分析仪和一台基于128通道皮安表系统构成的束流剖面探测器，分别测量了不同流强和束流分布下的混合O离子束的二次离子能量分布和束流流强分布，从而计算得出SCCD。实验结果表明，在1.0×10^-5 Pa的真空度下，不同流强的混合O离子束的SCCD基本在70%左右；不同束流分布对空间电势分布影响较大，对离子束的SCCD也会有一定程度的影响。     

低能离子束诱导Ag表面纳米金字塔微结构

利用离子束溅射诱导实验方法,在单晶Si(100)基底上辅助沉积银膜,研究了低能Ar+离子束30°入射时,不同离子束能量和束流密度以及基底温度对Ag纳米结构的影响.结果表明:在较低基底温度下(32~100℃)辅助沉积银膜,膜层表面会呈现排列紧密、晶粒尺寸一致的金字塔状纳米结构.当温度升高时(32~200℃),纳米微结构横向尺寸λc迅速增加,而粗糙度先减小(32~100℃)后迅速增大(100~200℃);当离子束能量1 400eV、束流密度15~45μA/cm2时,在相同温度下,随着离子束束流密度的增大,纳米晶粒横向尺寸基本不变,粗糙度略有增加;当离子束流密度为15μA/cm2、能量1 000~1 800eV时,在相同温度下,随着离子束能量的增加,银纳米结构尺寸增加,而表面粗糙度先增加,然后缓慢减小.自组织纳米结构的转变是溅射粗糙化和表面驰豫机制相互作用的结果.     

空间电荷效应对热场致发射中诺廷汉效应的影响

热场致发射阴极所产生的强流电子束具有很强的空间电荷效应,为研究该效应对热场致发射过程中诺廷汉（Nottingham）效应的影响机理,在理论分析的基础上,用数值方法研究了不同逸出功和多个外加电场条件下考虑空间电荷效应对诺廷汉效应结果的影响,并与不考虑空间电荷效应时的情形进行了对比. 结果表明：空间电荷效应的强弱会显著影响到阴极表面的稳态电场,进而对诺廷汉效应产生不可忽略的影响;当逸出功在3.0–4.52 eV、外加电场在3×10⁹–9×10⁹ V/m范围内时,考虑空间电荷效应的影响后,热场致发射电子所带走的平均能量较不考虑空间电荷效应时增加0–2.5 eV,且温度越高或外加电场越大时,该增加值越大;考虑空间电荷效应对诺廷汉效应的影响后,热场致发射电子从阴极带走的平均能量随外加电场的增加呈非线性下降规律;当阴极表面温度较高时,诺廷汉效应中的冷却效应随二极管间隙距离的变大而增强. 关键词： 热场致发射 诺廷汉效应 空间电荷效应 阴极表面电场     

激光加速质子束空间电荷力研究（英文）

激光加速器可以输出具有独特品质的质子束,例如μm尺寸、ps脉冲长度和高峰值电流。强流粒子束的空间电荷力效应较强,对面向应用的束流传输提出了挑战。通过二维PIC模拟研究了激光加速后与质子速度接近的电子的影响。采用椭球模型估算空间电荷力的影响,比较不同电荷分布的差异。结果表明每束团质子数超过10¹⁰后空间电荷力显著影响质子束传输,甚至严重破坏束流品质。空间电荷力的影响在20 ps后显著减弱,离开靶约1.2 mm。     

强流离子束流聚焦状态的数值模拟

结合空间电荷透镜的原理图以及离子束流的磁流体运动方程对离子束流聚焦状态进行了理论研究。采用层流非碰撞模型数值计算了离子束流不同初始半径以及不同入射角的束流出射角、焦距以及最小焦斑半径。理论分析了能散度、色散像差等因素对束流最小焦斑半径的影响。在离子束流遵循能量和角动量守恒的原则下,对不同入射角度的离子束流的束流最大半径进行了模拟计算。研究表明,束流入射角度增大,会聚角和最小焦斑半径减小,焦距增大。束流半径增大,会聚角、焦距和最小焦斑半径都增大。最佳会聚角所在的平滑区域内束流的发散度以及能散度对最小焦斑半径的影响较大。束流发散度或者能散度的增加,都能导致最小焦斑半径的增大。入射角度绝对值相同的束流,束流最大半径相同。     

高能强流负离子束系统束光学特性的数值模拟

基于负离于-中性束注入器中强流负离子束引出与加速系统的特点所建立的数值模拟模型和计算程序,通过数值模拟研究了强流负离子束系统电磁场位形、几何参数、等离子体参数、束流密度和负离子剥离损失对负离子束光学特性的影响。对8电极800keV强流负离子束系统的初步优化结果表明对引出流密度为2lmA·cm-2的H-离子束,当负离子初始温度为0.2eV时,由系统出射的85％束散角可达到0.23°。     

BRISOL铝同位素放射性核束的产生

北京放射性核束装置在线同位素分离器(BRISOL)采用100 MeV回旋加速器提供的最大200μA的质子束打靶在线产生放射性核束。在BRISOL上已经使用氧化钙靶、氧化镁靶产生了Na⁺、K⁺等放射性核束。为了产生铝同位素放射性核束,研发了碳化硅靶材,开展了碳化硅靶产生铝放射性核束的实验研究。在BRISOL装置上首次产生了铝同位素放射性核束,其中^26gAl⁺的束流强度为8.7×10⁷ pps,²³Al⁺的束流强度为2.2×10² pps,同时将BRISOL靶能承受的质子束流强提升至15。     

射频离子源离子束成分光谱测量

为HL-2A 装置中性束注入器研制了引出束功率为1MW 的射频离子源。在测试平台上,实验离子源已经成功引出了束能量和束电流分别为35keV 和12.4A、束质子比为79%、脉宽为100ms 的氢离子束,达到了设计束功率要求的44%。在射频离子源实验平台上,利用多普勒频移光谱方法测量了离子源引出束流成分比例,对比了束流成分和射频离子源引出束流之间的关系。实验数据分析表明,在10A 引出束流的情况下,离子流成分 H⁺ ₁、H⁺ ₂ 和H⁺ ₃ 分别为75%、18%和7%。并且当引出束流从3.3A 升至10.4A 时,H⁺ ₁ 从37%升至78%,而H⁺ ₃ 则从19%降至9%。     

低能强流质子束空间电荷补偿度研究(英文)

对于低能强流离子束来说,空间电荷效应的存在将导致束流发散、发射度增加等一系列问题,从而降低束流品质。幸运的是,当束流由离子源引出通过低能传输线时会与其中的剩余气体发生电离反应,产生二次电子与二次离子;二次电子在束流自身产生的电场作用下,在束流中积累并中和部分空间电荷,达到抑制空间电荷效应的效果。为了测量空间电荷中和程度,中国科学院近代物理研究所研制了一台三栅网式能量分析仪用以测量电离过程中产生的二次离子能量来间接计算空间电荷中和度。实验结果表明,对于40 keV, 18.5 mA的质子束,真空度为1.510*3 Pa 时得到最佳补偿度;真空度一定的情况下,空间电荷补偿度随束流流强增加而变大。For high-intensity low-energy ion beams, space charge effect is a main cause of beam divergence  and emittance growth. Fortunately, residual gas molecules in the drift space tend to be ionized and neutralize the beam space charge spontaneously. The level of Space Charge Neutralization (SCN)is measured through the detection of created secondary ion energy distribution in the beam region. A so-called non-interceptive Three-grid Energy Analyzer (TEA) has been designed and manufactured at Institute of Modern Physics, Chinese Academy of Sciences (IMP). This paper will present the detailsof the TEA detector and the application to diagnose proton beam SCN level in the Low Energy Beam Transport (LEBT) line. As a preliminary result, for an 18.5 mA proton beam a best compensating point appears at the vacuum pressure of 1.510*3 Pa. And the neutralization level is advanced with thegrowth of beam current in a constant vacuum pressure.     

Experimental and computational study of the passage of an electron beam through the curvilinear element of the Drakon stellarator system in a tenuous plasma

Results are presented from the first stage of studies on the passage of an electron beam with energy 100–500 eV in a magnetic field of 300–700 Oe through the curvilinear solenoid of the KRéL unit, the latter being a prototype of the closing segment of the Drakon stellarator system, in the plasma-beam discharge regime. The ion density at the end of the curvilinear part of the chamber, n _i ≈8×10⁸–10¹⁰ cm⁻³, the electron temperature T _e ≈4–15 eV, and the positions at which the beam hits the target for different distances from it to the electron source are determined experimentally. The motion of the electron beam is computationally modeled with allowance for the space charge created by the beam and the secondary plasma. From a comparison of the experimentally measured trajectories and trajectories calculated for different values of the space charge, we have obtained an estimate for the unneutralized ion density of the order of 5×10⁷ cm⁻³. Zh. Tekh. Fiz. 69, 22–26 (February 1999)     

HL—1M中性束注入系统研制及中性束加热初步实验

ＨＬ－１Ｍ 中性束注入系统是在国家“八六三计划”的支持下,由中俄合作研制的。介绍了中性束注入系统及其各个子系统的性能参数及调试结果,给出了中性束加热的初步实验结果     

Mechanisms of ion-beam-enhanced diffusion in amorphous silicon

We have investigated ion-beam-enhanced diffusion of Au in undoped and B doped amorphous Si. The diffusion coefficients depend linearly on ion flux and exibit an Arrhenius-like temperature dependence with an activation energy of 0.37 eV in the temperature range 200–350° C. Moreover the diffusivity is enhanced by a factor of 5 by B-doping at a concentration of 1×10²⁰ atoms/cm³. A similar enhancement is observed in thermal diffusion of Au which has an activation energy of 1.5 eV. On the basis of these results a model for the ion-beam-enhanced diffusion of Au is proposed where the high density of defects present in amorphous Si act as traps for the fast moving interstitial Au atoms. The effectiveness of this trapping process can be changed by the high concentration of mobile defects generated by the beam and also by a change in the charge state of the traps induced by the presence of B.     

Eine Atomstrahlquelle für überthermische Energien

A Penning ion source has been used to produce a potassium atomic beam of hyperthermal energies. The energy distribution spreads from below 0.3 eV to about 20 eV. At 1 m distance from the source the current density within a 25% energy window at 1 eV is 2 · 10⁶ atoms · sec^?1· mm^?2.     

Formation of ac Discharges Between Glass Insulated Electrodes in Ne+1% N2 Mixtures. III. Discharge Development and Space Charge

The investigation of the optical space-time-structure of the discharge development was made for various values of p^D (1,3 kPacm, 33,4 kPacm) by means of the variation of the electrode distance for two gas pressures. The broadening of the bistable region with growing electrode distance can be explained by the effect of the positive space charge as a virtual anode. Thus the space charge memory is dependent on the value of p^D. If the space charge breakdown takes place, a light front moves from the anode to the cathode, its velocity, varying from 3 · 10⁴ cm/s to 8 · 10⁵ cm/s. In the volume an optical structure develops which is analogous to that of a medium pressure glow discharge. If the time between successive discharge pulses is too short, then the decay of the positive space charge is incomplete and there is no Townsend phase. The process depends, via the ion drift velocity, on the electrode distance.     

电子束发射度变化的解析估计

本文使用一般包络方程理论推导出轴对称电子束在傍轴近似下的稳态传输过程中的发射度变化公式。结果表明电子束发射度变化与引导磁场及离子通道电场无直接关系,而仅仅与电子束分布的变化有关;发射度变化的本质是电子束的静电势能和横向运动的动能之间的转换。本文的解析结果与数值模拟结果符合得相当好。本文还定性讨论了电子束平均正则角动量对发射度变化的影响。     

Laser ion beam formation for nanotechnologies

It is suggested to generate cold ion beams by laser collimation and subsequent laser ionization of a primary atomic beam. The primary beam, formed by a standard method, is collimated through transverse cooling by resonance laser radiation. Laser radiation is also used for the multistep ionization of atoms in the collimated beam. Advantages of the proposed method are a low scatter of the initial ion energy (below 10^?1 eV) and a high emittance in the region of the virtual source (～10^?6 cm rad at a beam current on the level of microamperes). The high monochromaticity of the obtained ion beam allows the chromatic aberration effect to be significantly suppressed, which implies good prospects for using such sources in ion beam lithography. The proposed method also allows the spectrum of elements used in ion beam sources to be expanded, which is an independent technological advantage.     

Performance evaluation of self-breakdown-based single-gap plasma cathode electron gun

This paper presents the experimental studies on self-breakdown-based single-gap plasma cathode electron (PCE) gun (5–20 kV/50–160 A) in argon, gas atmosphere and its performance evaluation based on particle-in-cell (PIC) simulation code ‘OOPIC-Pro’. The PCE-Gun works in conducting phase (low energy, high current) of pseudospark discharge. It produces intense electron beam, which can propagate more than 200 mm in the drift space region without external magnetic field. The profile of this beam in the drift space region at different breakdown conditions (i.e., gas pressures and applied voltages) has been studied and the experimental results are compared with simulated values. It is demonstrated that ～30% beam current is lost during the propagation possibly due to space charge neutralization and collisions with neutral particles and walls.     

用负温度高能离子束的相对论多普勒效应实现从红外到X射线连续调谐激光器

利用负温度高能离子束的相对论多普勒效应,可能实现从红外到X射线连续调谐激光器。调谐范围△ν_T=2ν₀βγ。离子束从零到c调速时,激光频率为0—∞。本文给出了激光参数的相对论变换式,计算了负温度相对论离子束激光器的增益、阈值和输出特性,提出了用激光束对相对论离子束进行共振激发的方法,并讨论了He⁺离子束及Ar⁺离子束激光器的设计参数。 关键词：