Analysis of the impacts of mechanical errors on the RF performance of a single spoke cavity

Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.     

Study on the HOMs coupler design of spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of high power proton linac for an Accelerator Driven Sub-critical System (ADS).Considering that the High Order Modes (HOMs)in the superconducting cavity have far reaching influence on power dissipation and beam stability,the analysis of HOMs of the spoke cavity is needed.In this paper,we put emphasis on the analysis of HOMs of the spoke cavity and the HOMs coupler design.     

Study on the HOMs coupler design of spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of high power proton linac for an Accelerator Driven Sub-critical System (ADS). Considering that the High Order Modes (HOMs) in the superconducting cavity have far reaching influence on power dissipation and beam stability, the analysis of HOMs of the spoke cavity is needed. In this paper, we put emphasis on the analysis of HOMs of the spoke cavity and the HOMs coupler design.     

Design study on very low Beta spoke cavity for China-ADS

Very low Beta superconducting spoke cavity is one of the key challenges for the China-ADS project. In this paper, a new structure of 3βλ/2 spoke cavity is first studied in detail. Its RF and mechanical properties are simulated using CST-MWS and ANSYS, and compared with the traditional βλ/2 spoke structure.     

Design of a 325 MHz SC Spoke040 cavity at IHEP

A spoke cavity is a TEM-class superconducting resonator with particular advantages: compact structure and high shunt impedance. The 325 MHz β =0.40(β =v/c, v is the velocity of particle and c is the velocity of light)single spoke cavity(Spoke 040) is adopted for the Chinese ADS(Accelerator Driven Sub-critical System) project. The physics and mechanical design has been accomplished, and the fabrication of a prototype is currently in progress. In this paper, the optimization processes for the main radio frequency(RF) and mechanical parameters are analyzed in detail. Two kinds of cavity end-walls(flat and convex) are compared. The convex end-wall is preferred in order to improve mechanical performance of the cavity. Two prototypes of the Spoke 040 cavity are in the machining stage,and should be finished in early 2014.Vertical testing is also under preparation.     

325 MHz spoke腔的二次电子倍增效应

采用CST软件的粒子工作室模块, 对spoke超导腔中可能发生的二次电子倍增效应进行了分析研究,并采用二次电子倍增效应发生后形成稳定状态时的粒子数增长率来表征其强度。模拟计算表明：该腔存在两处二次电子倍增效应,spoke柱两端的两点一阶倍增; spoke腔两端侧壁与中心圆筒交界处的单点一阶倍增;二次电子倍增在加速腔压为0.65 MV时的增长率最高,而腔压大于1 MV时,增长率均为负,即无倍增发生。     

Cold RF test and associated mechanical features correlation of a TESLA-style 9-cell superconducting niobium cavity built in China

The RF performance of a 1.3 GHz 9-cell superconducting niobium cavity was evaluated at cryogenic temperatures following surface processing by using the standard ILC-style recipe. The cavity is a TESLA-style 9-cell superconducting niobium cavity, with complete end group components including a higher order mode coupler, built in China for practical applications. An accelerating gradient of 28.6 MV/m was achieved at an unloaded quality factor of 4×10⁹. The morphological property of mechanical features on the RF surface of this cavity was characterized through optical inspection. Correlation between the observed mechanical features and the RF performance of the cavity is attempted.     

Study on the RF performance of 2-cell superconducting cavity

The physical design of the 2-cell superconducting cavity is presented. The RF parameters of the cavity and HOMs （high order modes） are reported. In this paper, we put the emphasis on the analysis of the HOMs and interaction between beam and cavity.     

Tuning for the first 9-cell TESLA cavity of PKU

A method based on circuit model is used to tune the first home-made 9-cell TESLA type superconducting niobium cavity at Peking University.After tuning,a flat field profile with a final π-mode frequency within 3 kHz of target frequency is achieved.The field flatness is measured by a bead-pull method,and the relative electric field is calculated from the frequency shift perturbed by the bead stepping along the axis of the cavity.     

Study on the RF performance of 2-cell superconducting cavity

The physical design of the 2-cell superconducting cavity is presented.The RF parameters of the cavity and HOMs (high order modes) are reported.In this paper,we put the emphasis on the analysis of the HOMs and interaction between beam and cavity.     

Tuning for the first 9-cell TESLA cavity of PKU

A method based on circuit model is used to tune the first home-made 9-cell TESLA type superconducting niobium cavity at Peking University. After tuning, a flat field profile with a final π-mode frequency within 3 kHz of target frequency is achieved. The field flatness is measured by a bead-pull method, and the relative electric field is calculated from the frequency shift perturbed by the bead stepping along the axis of the cavity.     

1.3 GHz 9单元Ichiro型模型铜腔的预调谐

以常用的多单元超导腔预调谐方法为基础,搭建了一套完整的预调谐系统,并实现了超导腔预调谐测量的自动化。实验首先通过网络分析仪对超导腔进行测量,利用Labview进行数据采集,并协同控制步进电机。通过“拉小珠”的微扰法,测量沿小珠运动路径的场分布。编写了一套Java程序,通过矩阵运算,计算出9单元腔各个腔单元频率的校正量。根据计算结果对9单元腔的某个单元进行挤压或拉抻,经多次上述操作后,在较高精度范围内,可将9单元铜腔的每个腔单元调谐至预期的目标频率。     

Experimental progress in optical manipulation of single atoms for cavity QED

Cavity QED, as a fundamental system and research field, not only illuminates the primary aspects of decoherence and coherence in quantum dynamics, but also advances quantum information science. Manipulation of single atoms, in the context of cavity QED, is the essential element and has been becoming a hot issue for the past two decades. In this review paper, we will concentrate on the experimental aspects for manipulating the neutral atoms strongly coupled to a high-finesse cavity in the optical regime, including atomic cooling and trapping, different configurations of atom transportation and the wide variety of quantum outgrowths based on cavity QED, such as one atom laser, single photon source, etc. The cavity QED system at Shanxi University is briefly introduced.      

1.3 GHz 9单元Ichiro型模型铜腔的预调谐

 以常用的多单元超导腔预调谐方法为基础,搭建了一套完整的预调谐系统,并实现了超导腔预调谐测量的自动化。实验首先通过网络分析仪对超导腔进行测量,利用Labview进行数据采集,并协同控制步进电机。通过“拉小珠”的微扰法,测量沿小珠运动路径的场分布。编写了一套Java程序,通过矩阵运算,计算出9单元腔各个腔单元频率的校正量。根据计算结果对9单元腔的某个单元进行挤压或拉抻,经多次上述操作后,在较高精度范围内,可将9单元铜腔的每个腔单元调谐至预期的目标频率。     

Faithfully probabilistic teleportation of an unknown atomic state and cavity field state with a single measurement

This paper shows that, based on the single-photon JC model depicting the resonant interaction of a two-level atom with a single cavity mode, an unknown atomic state and cavity photon superposition state can be faithfully telcported with only a single measurement. The scheme is probabilistie, its success lies on the event that the sender atom （or the medi-atom, for teleportation of cavity field state） is detected in the higher state. The scheme is in contrast to the previous ones of using a maximally two-particle entangled state as quantum channel.[第一段]     

Effect of cavity geometry on the performance of a gyrotron

The effect of interaction cavity geometry on the gyrotron performance in terms of cold cavity parameters (Q value and axial electric field profile), Ohmic wall loss, start oscillation current and interaction efficiency are analyzed in detail in this article. The measurement of Q value and axial electric field profile is also performed for the cavities with different geometries by using non-destructive and perturbation techniques, respectively. Scattering matrix code is used for the computation of Q value and axial electric field profile and results are compared with the experimental data. A Particle-in-Cell code and a specific beam–wave interaction computation code based on generalized non-linear theory are used in the efficiency calculations. For all numerical and experimental analyses, the case of 42 GHz, 200 kW gyrotron is considered here.     

CSNS-II超导椭球腔形变电场平坦度仿真分析

超导椭球腔是一种通过冲压零件和电子束焊接而成型的薄壁结构,在加工过程中存在不可避免的形变,如单元倾斜、偏轴,单元长度偏差,从而影响椭球腔的轴向电场平坦度,进而降低椭球腔的运行电场梯度。因此,在椭球腔加工成型后要进行预调谐处理。椭球腔预调谐是通过对椭球腔整形,包括倾斜和偏轴矫正,单元长度矫正,以达到提高轴向电场平坦度的目的。采用COMSOL多物理场耦合软件对CSNS-II（China Spallation Neutron Source Phase II）超导椭球腔可能存在的形变进行了仿真计算,研究了各单元形变量对电场平坦度的影响,分析了腔体调谐位移量对电场平坦度的影响,为椭球腔预调谐提供数据参考,也为预调谐机的设计研制提供指导。另外,确定了椭球腔机械形变的要求,确保椭球腔机械加工质量满足CSNS-II升级的实际工程需求。     

RF measurements of a C-band cavity beam position monitor

RF cold test of a novel C-band cavity beam position monitor (PBM) to be used in the SDUV-FEL Test Facility is described. The test results are presented and some characteristics discussed. The main parameters obtained are in reasonable agreement with the analytical estimations. Effective suppression of the common mode has been demonstrated. The position sensitivity over the test region of ±0.5 mm is about －21.58 dB/10 μm for the TM₁₁₀ mode and is linear in the central region of the BPM cavity.     

基于非准直外腔的单频激光高阶回馈效应研究

对基于非准直外腔的单频激光高阶回馈现象及产生机理进行了研究,获得了调制幅度不均匀的高分辨率多重高阶回馈条纹,分析了多重高阶回馈条纹的特点及产生机制。提出采用基于光路阻挡的实验方法,在回馈镜反射率大于90%的强回馈中,发现了单重高阶回馈效应,获得了调制幅度均匀、无大包络的高分辨率单重高阶回馈条纹,其分辨率达到/10,而且还有进一步提高的潜力。单重高阶回馈条纹不但具有多重高阶回馈时高分辨率的优点,还具有传统弱回馈时调制幅度均匀、类正弦等特性,对进一步研制高精度回馈测量系统具有重要意义。     

输入腔高频场的矩阵分析

应用模匹配理论推导和建立了单级突变的矩阵方程,并分析给出了具有多级突变和渐变结构级联情况下波导腔体的处理方法。在理论推导的基础上,通过编制程序计算出多级突变结构波导腔体模匹配系数级联矩阵,并由矩阵参数得到所需的腔体谐振频率和Q值等物理特性参量。实际计算结果表明,由程序模拟输入腔计算得到的数据结果与腔体的冷测实验结果基本一致,为进一步的注波互作用研究和回旋速调管的设计工作提供了参考依据。