571.2MHz次谐波聚束腔的高频电磁场效应

高频谐振腔中的电磁场通常以两种方式影响谐振腔的特性. 一种方式是通过作用在谐振腔内壁上的高频热, 这主要 由高频功率的欧姆损耗导致; 另一种方式是通过作用在谐振腔内壁上的洛仑兹力, 这主要由谐振腔内壁上的面电流 和面电荷导致. 联合使用有限差分软件Superfish和有限元软件ANSYS，本文对571.2MHz次谐波聚束腔中的高频电磁场 效应进行了研究. 此外, 本文还对BEPCⅡ未来预注入器第1个次谐波聚束腔中的高频热效应进行了讨论.     

双束流负载效应

分析研究了双束流储存环上的束流负载效应.束团纵向尾场的作用分别为:能量损失、同步频移和耦合束不稳定性,这里只研究前两个方面.以来团连续分布的束团串情形和均匀分布情形为例,给出了同步相移、频移与高次模参数及高频腔分布的关系.研究结果有助于优化高频腔的工作模式(通过调节调谐杆的位置来改变高次模的频率)和环上束团的分布,以减小束流负载效应.当高频腔关于对撞点对称分布时,正负电子的束流负载效应相同,可以用补偿单束流负载效应的方法来补偿正负电子束团的相位.     

医用回旋加速器回旋频率与磁场的调谐

高频谐振腔在回旋加速器实际运行过程中受束流负载、重力和热损耗引起的腔体变形等因素的影响,其谐振频率会发生一定的偏移,导致高频工作频率会随着谐振腔的谐振频率而变化.为满足等时性加速的要求,当高频工作频率发生改变时磁场强度也应进行相应的变化,即励磁电流的大小需要相应改变,使得粒子回旋频率与高频谐振频率相匹配以克服滑相.首先通过有限元仿真软件建立静磁场模型模拟不同励磁电流下回旋加速器的平均磁场,然后理论分析磁场与谐振频率的关系,最后得到励磁电流在小区间变化时与谐振频率的关系;根据计算的不同谐振频率对应的最佳励磁电流,完成励磁电流的自动跟频.在保证最大碳膜束流的情况下,实验得到不同谐振频率对应的最佳励磁电流,使理论得以验证.根据其关系实现了励磁电流自动调节,克服了滑相,保证了法拉第束流的稳定输出.该方法使得励磁电流能够快速、准确地寻找并跟踪谐振腔频率,克服了频率偏移导致的滑相,完成束流的稳定输出.     

粒子束团状态对测量束流发射度及能量的影响

为了验证国产质子注入器的参数是否满足需求,注入器团队设计了束流测量系统用于测量国产质子直线注入器束流的流强、发射度、能量以及能散等关键指标。此测量系统包含了采用变聚焦法测量发散度、采用分析磁铁测量束流能量和能散的主要功能。利用束流输运线设计软件Tracewin(版本2.11.4.1)进行了系统束线的物理设计,对束测系统测量质子束流的发散度和能量的精度进行了模拟计算。由于经过RFQ-(APF)DTL加速后的粒子束团为“拖尾”的非理想粒子束团,需要针对非理想束团对束测系统测量发射度和能量产生的影响进行分析。通过对模拟计算结果的分析,发现相对于测量理想粒子束团的结果非理想粒子束团对束测系统测量发射度精度影响较大;非理想粒子束团对束测系统测量能量精度影响较小。     

L波段强流单束团注入器的束流动力学计算

自由电子激光器要求高亮度、低能散度的电子束注入波荡器(Undulator)。本文叙述提供高亮度电子束的高频电子直线加速器中的注入器部分的设计计算。注入器由L波段(1300MHz)的十二分频和三分频两个谐振腔预聚束器和一个基波频率的变相速聚束器组成。粒子运动方程中考虑了空间电荷效应和束流负载效应。电子枪的注入参数:脉冲宽度T=4ns;电流I=5A;电子的初始动能E_0=100keV;电子束分布为高斯型。参数优化设计结果:单束团宽度小于25ps,峰值电流达400A以上,电子的平均归一化能量>4,束团内的能量差小于200keV。     

作为BEPCII预注入器的光阴极注入器

 为了提高并且采用双束加速技术以进一步提高BEPCII正电子从直线加速器注入到储存环的速率,BEPCII(Beijing Electron Positron Collider Upgrade Project) 正在建造带有两个次谐波聚束腔的新预注入器。提出了使用光阴极注入器作为BEPCII预注入器的新方案,其性能优于次谐波聚束系统：发射度和能散至多为次谐波聚束系统的1/4,100%的传输效率,没有卫星束团的干扰,等。此外,还分别对光阴极注入器在高电荷量和低电荷量两种情况下的束流动力学进行了模拟计算和优化研究,并将其性能与正在建造的次谐波聚束系统和旧聚束系统的性能进行了比较和讨论。由此光阴极注入器产生的电子束还可以在将来用作激光-等离子体或激光-非传导性加速结构的尾场加速研究。     

超导加速器CW模式的高阶模初步分析

 超导加速器由于具有极高的Q值，因此表现出较强的腔束相互作用，尤其是在以CW模式运行下，严重时会产生束流崩溃(BBU)效应。德国TESLA式的9-cell超导串腔在束流负载为1 mA，束团重复频率为81.25 MHz情况下，对其高阶模的产生及相应的功率水平进行了分析。结果表明：对于该腔的主要高阶模，谐振偏差值在π/4以上，束流没有发生谐振，高阶模功率在mW量级。     

HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并，为研究BRing中的束流负载效应对束团合并的影响，对238U35+束流进行了粒子跟踪模拟。模拟结果显示，在束团合并过程中，束流负载效应引起束团长度和束团中心位置的振荡，导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变，是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响，采用多谐波前馈系统进行补偿，达到了补偿束团合并过程中的束流负载效应的目的，从而确保了BRing中引出束流的品质，同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。     

光阴极RF腔注入器束流发射度研究

 分析了光阴极RF腔注入器中的RF场效应和空间电荷效应，给出了电子在加速腔中束流发射度的解析表达式，它说明在加速过程中束流发射度是振荡变化的。利用SUPERFISH和GPT程序模拟计算了光阴极1+1/2腔注入器输出束流发射度与加速场强、注入相位、束团大小和形状、束团电荷的关系。适当选择这些条件，可以获得横向发射度小于2πmm·mrad 的输出束流。     

BEPCⅡ未来预注入器的优化研究

BEPCⅡ未来的预注入器由热阴极电子枪、两个次谐波聚束器(SHB)、行波预聚束器以及行波聚束器组成.除电子枪以外,各个部分都位于螺线管磁场中.使用PARMELA和EGUN程序模拟和优化了预注入器的束流动力学.对SHB的聚束电压和漂移距离、预聚束器与聚束器的相位和加速梯度、螺线管磁场的形状等都进行了细致的研究和优化,并讨论了聚束器出口10ps束长内电荷量的极限值.     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.