正对撞束束补偿的理论和模拟研究

束束效应是限制对撞机性能提高的重要因素,其限制作用可以通过补偿机制来改善。针对正对撞束束效应,提出两种实现束束补偿的对撞机结构,并对实现束束补偿的原理和需要满足的条件进行分析。提出利用能量回收型直线加速器产生的电子束流进行正对撞束束补偿的方案,并且基于超级质子质子对撞机进行模拟研究,研究了补偿前后束流粒子分布、频移和粒子损失等变化情况。束束补偿可以减小束团内部粒子的频散,减小束流损失,提高束流寿命,可以大幅提高单束团流强,从而提高对撞机亮度。     

北京正负电子对撞机中的束束作用偏转效应

 利用静电分离器对正负电子束团在垂直方向上的相对轨道偏差进行了扫描,并用数字示波器对束流轨道的变化进行监视,在北京正负电子对撞机(BEPC)上完成了垂直方向上的束束作用偏转效应的观察与测量。实验过程和实验结果可为北京正负电子对撞机改进工程(BEPCⅡ)的对撞调节提供参考依据。把束团之间相对位置偏差的测量转换为对束流偏转角度的测量是可行的,也是有效克服束流位置探测器分辨率不足的一种方法。     

BEPCⅡ束流相关本底的蒙特卡罗模拟研究(Ⅲ)——Touschek效应

介绍了Touschek效应本底研究的意义、Touschek效应的作用原理和建模方法. 使用自主开发及通用的模拟工具, 系统研究了BEPCⅡ工作条件下BESⅢ主要探测器的Touschek本底. 模拟和计算束流寿命的比较表明当前的模拟结果是有参考价值的, 建模方法是可行的. 探测器的模拟结果表明Touschek本底不会影响将来BESⅢ的正常稳定运行, 不会造成探测器的辐照损伤.     

水平交叉对撞时束束作用导致的水平synchro-betatron共振

在交叉对撞时, 束束作用可能会激发synchro-betatron共振. 通过数值模 拟对此进行了研究. 结果表明, 当ν_x,π\gtrsim (p+rν_s)/q时,可能会出现水平方向的synchro-betatron共振.     

BEPCⅡ直线加速器的误差和抖动效应

为达到BEPCⅡ 直线加速器的设计指标,系统地研究了误差和抖动(Jitter)效应对束流性能的影响。误差效应包括束流的初始偏轴和聚焦透镜偏轴导致的色差效应;束流的初始偏轴和加速结构偏轴导致的尾场效应等。主要的抖动效应包括相位漂移抖动和高频功率源中调制器电压的抖动影响等。确定了在BEPCⅡ直线加速器上对误差和抖动的限制,如来自电子枪的束流的初始偏轴应小于等于0.3 mm,加速结构和聚焦磁铁的安装误差应小于等于0.2 mm,相位漂移抖动误差应小于等于2°,调制器的电压抖动误差应小于等于0.1%。并进一步确认了必须采用相位控制系统和束流轨道校正系统,以抑制这些误差效应的影响,达到正、负电子束流能散度小于等于0.5% 和电子束束流发射度小于等于0.25 mm·mrad,正电子束束流发射度小于等于1.60 mm·mrad 的设计目标。     

BEPCⅡ超导腔高次模阻抗抑制优化研究

BEPCⅡ500MHz超导腔是BEPCⅡ储存环的关键设备,腔中高次模的分布和阻抗将很大程度上直接影响束流的稳定.因此,研究BEPCⅡ超导腔的高次模分布和高次模吸收器的吸收效果对实现BEPCⅡ指标至关重要.为此,通过改变高次模吸收器的位置、铁氧体吸收材料的长度、厚度以及腔的渐变过渡波导的角度等对BEPCⅡ超导腔高次模阻抗抑制进行了模拟优化研究,从而找到并确定了吸收器对高次模阻抗抑制的最优值.同时,为证实模拟计算结果的正确性,对BEPCⅡ超导模型腔进行了高次模分布和吸收测量,得到了与计算一致的结果.结果表明,经过细致优化腔的高次模吸收器,腔中大部分高次模被深度吸收了,那些具有潜在危险的高次模阻抗值降到了阈值以下,满足BEPCⅡ束流阻抗要求     

北京正负电子对撞机mini-β方案中束-束相互作用的研究

为实施mini-β方案,北京正负电子对撞机(BEPC)采用高频腔压缩束长,对撞亮度随着高频腔压的升高而下降是BEPC所遇到的特殊的束-束相互作用问题,此工作就是要搞清楚其物理机制并找到解决办法.研究结论指出对于BEPC,束长σs对束-束相互作用的影响主要表现在“沙漏”效应和束长对横向自由振荡的相位平均效应.这两个相互制约的因素使得BEPC的亮度对于束长和对撞点垂直β函数的比值有一个最佳范围,并由模拟结果给出了初步的范围.     

BEPC静电分离器分路阻抗和功率损耗研究

通过测量BEPC静电分离器各主要模式的分路阻抗,分析了BEPC运行过程中静电分离器的高压电缆隔离层不时烧化的原因,同时对BEPC流强进一步提高时静电分离器中的功耗进行了计算.     

多粒子模拟方法分析北京正负电子对撞机储存环束团长度拉伸效应

采用多粒子模拟方法,分析了北京正负电子对撞机(BEPC)储存环纵向不稳定性,给出了BEPC储存环束团长度与单束流强的关系,得出了阈值流强.模拟结果与BEPC95年4月实测结果符合较好.     

北京正负电子对撞机mini—β方案中束一束相互作用的研究

为实施mini-β方案,北京正负电子对撞机（BEPC)采用高频腔压缩束长,对撞亮度随着高频腔压的升高而下降是BEPC所遇到的特殊的束－束相互作用问题,此工作就是要搞清楚其物理机制并找到解决办法。研究结论指出：对于BEPC,束长σs对束－束相互作用的影响主要表现在“沙漏”效应和束长对横向自由振荡的相位平均效应。这两个相互制约的因素使得BEPC的亮度对于束长和对撞点垂直β函数的比值有一个最佳范围,并由模拟结果给出了初步的范围。     

Analytical treatment of the nonlinear electron cloud effect and the combined effects with beam-beam and space charge nonlinear forces in storage rings

In this paper we treat first some nonlinear beam dynamics problems in storage rings, such as beam dynamic apertures due to magnetic multipoles, wiggles, beam-beam effects, nonlinear space charge effect, and then nonlinear electron cloud effect combined with beam-beam and space charge effects, analytically. This analytical treatment is applied to BEPC Ⅱ. The corresponding analytical expressions developed in this paper are useful both in understanding the physics behind these problems and also in making practical quick hand estimations.     

Analytical treatment of the nonlinear electron cloud effect and the combined effects with beam-beam and space charge nonlinear forces in storage rings

In this paper we treat first some nonlinear beam dynamics problems in storage rings, such as beam dynamic apertures due to magnetic multipoles, wiggles, beam-beam effects, nonlinear space charge effect, and then nonlinear electron cloud effect combined with beam-beam and space charge effects, analytically. This analytical treatment is applied to BEPC II. The corresponding analytical expressions developed in this paper are useful both in understanding the physics behind these problems and also in making practical quick hand estimations.     

On stochastic complex beam-beam interaction models with Gaussian colored noise

This paper is to continue our study on complex beam-beam interaction models in particle accelerators with random excitations Y. Xu, W. Xu, G.M. Mahmoud, On a complex beam-beam interaction model with random forcing [Physica A 336 (2004) 347-360]. The random noise is taken as the form of exponentially correlated Gaussian colored noise, and the transition probability density function is obtained in terms of a perturbation expansion of the parameter. Then the method of stochastic averaging based on perturbation technique is used to derive a Fokker-Planck equation for the transition probability density function. The solvability condition and the general transforms using the method of characteristics are proposed to obtain the approximate expressions of probability density function to order ε.Also the exact stationary probability density and the first and second moments of the amplitude are obtained, and one can find when the correlation time equals to zero, the result is identical to that derived from the Stratonovich-Khasminskii theorem for the same model under a broad-band excitation in our previous work.     

高强度三倍频近场测量实验与模拟计算的误差分析

 测量了高强度三倍频实验的1ω 光和3ω 光的近场光束质量，将测量和模拟计算所得到3ω 光近场光束质量作了对比，重点对模拟计算得到的3ω 光近场光束质量所存在的误差进行了探讨，分析了现有的模拟计算程序中还未考虑到的影响3ω 光光束质量的主要因素，建议在以后的模拟计算程序中再进行优化设计，并讨论了改善3ω 光光束质量应采取的必要措施。     

电子束收集极对大间隙速调管输出腔效率的影响

 利用高频电磁软件对带电子束收集极的S波段大间隙输出腔进行了高频特性分析,采用3维PIC程序模拟了电子束收集极对大间隙速调管输出效率的影响。研究结果表明：收集极的存在会改变输出腔的本征谐振频率和电子束路径上的特性阻抗等高频特性,但收集极可以短路间隙附近的径向电场,减小电子束的空间电荷压力,同时对群聚电子进行再加速,从而提高大间隙速调管的输出效率;在束电压700 kV,直流电流6 kA时,优化后的带收集极的大间隙输出腔可稳定提取大于1.68 GW的微波功率,提取效率约40.1%,比无收集极时提高约5%。     

Method study of parameter choice for a circular proton–proton collider

In this paper we show a systematic method of appropriate parameter choice for a circular proton–proton collider by using an analytical expression for the beam–beam tune shift limit, starting from a given design goal and technical limitations. A suitable parameter space has been explored. Based on the parameter scan, sets of appropriate parameters designed for a 50 km and 100 km circular proton–proton collider are proposed.     

RIBLL传输效率研究

利用实验测量和Monte Carlo模拟的方法,研究了RIBLL的传输效率。分析了影响传输效率的主要因素, 发现碎片的动量分布形式对传输效率的模拟结果有重要的影响。 另外通过比较, 发现大部分碎片传输效率的模拟结果稍大于实验测量结果, 两者最大相差约几十倍, 这可以帮助估算次级束流强度, 指导实验设计。 he transmission of RIBLL has been studied by experimental measurement and Monte Carlo simulation methods. The analysis of influence factors of the simulated transmission has been accomplished, and it was found that the momentum distribution of fragments is one of the most important factors influencing the simulation results. Furthermore, through comparing the measured and simulated results, it is found that the simulated result is larger than the measured transmission for most fragments and the maximal difference between them is about several tens of times. This simulation is a good theory tools for estimating the intensity of the secondary beam and designing the experiment in the future.     

Varian 2300C 直线加速器6 MV X线的蒙特卡罗模拟

摘要: 利用先进的蒙特卡罗治疗头模拟程序BEAMnrc, 依据商家提供的详细设计资料, 集成多项优化模拟参数, 对医用直线加速器射线束传输部分进行了模拟, 获得与测量数据一致的模拟结果。 对复杂多叶光栏模型进行了建模, 模拟了非规则野的剂量分布, 以用于后续研究工作。 Based on the detail head structure designing provided by the manufacture, the ray transmission of VARIAN Clinic 2300C 6 MV X beam was simulated by Monte Carlo code, BEAMnrc. To accelerate the simulation efficiency, multiple optimized parameters were optimized. The simulated and the measured data were well coincident. The dose distribution of a complicated irregular field formed by MLC (Multi Leaf Collimators) was simulated, which are the base for further research work.     

3cm相对论返波荡器的粒子模拟研究

 运用全电磁的相对论的25维粒子模拟程序MAGIC模拟分析了3cm相对论返波管中注波互作用的非线性过程，得到了器件微波输出功率，效率，工作频率等参量，模拟结果与实验数据较好地一致。对电子注特性参数，慢波结构尺寸，引导磁场进行了优化，获得了器件最佳化运行的工作参数。