DC-SC光阴极注入器的束载实验的调试进展

 北京大学射频超导实验室设计了新型超导光电子枪——DC-SC光阴极注入器，目标是为自由电子激光平台提供能量在2~3MeV，脉宽小于10ps，脉冲重复频率为81.25MHz，平均流强约为1mA的低发射度电子束。现在已经建成了DC-SC光阴极注入器实验平台，包括激光驱动光阴极系统，Pierce直流高压加速结构，1.3GHz 1＋1/2纯铌超导腔，恒温器低温系统，4.5kW连续波微波系统，1/16分频与同步控制系统，束流诊断系统和能量分析系统等。并且完成了超导腔的静态实验，直流加速结构也经过了100μA低电流测试。实验结果符合设计要求，整体调试后即可以进行束载实验。     

Geometry dependent multipacting of a superconducting quarter-wave resonator at PKU

A superconducting quarter-wave resonator (QWR) of frequency=162.5 MHz and β=0.085 (β =v/c) has been designed at Peking University. The multipacting (MP) simulation and analysis for the QWR with CST Particle Studio has been performed. The simulation results reveal that there is no sign of MP with its normal operating accelerating gradients in the range of 6-8 MV/m. The accelerating gradient range that may incur MP is from about 1.4 to 3.2 MV/m, and the places where MP may be encountered are mainly located at the top part of the QWR. So the effect of different top geometries on MP has also been studied in depth. Our results show that an inward convex round roof is better than other round roofs, and plane roofs have an advantage over round roofs on the suppression of MP in general. While considering the optimization of its electromagnetic (EM) design, our initial designed model is also acceptable.     

基于波形构型分析的脉冲电路设计方法研究

在脉冲电路设计中,需要根据实际应用的波形要求和负载特性选择、设计其电路构型。工程设计中常用的时域波形叠加和参数扫描等波形构型设计方法存在较大局限性,难以形成对脉冲波形构型的物理本质、脉冲电路结构对负载的适应性等方面的系统认识。从分析影响脉冲波形构型的基本要素入手,从时域和频域角度对脉冲波形构型及其电路实现方法进行系统的分析和归纳,给出时域和频域的电路构型设计方法及相应的电路参数解算方法,使设计人员可采用解析分析方法判断电路中元器件参数的调整方向,同时推动电路设计创新。     

北京大学高功率相干Terahertz光源设计

给出北京大学射频超导组拟建的准单色、高平均功率、波长可调的相干THz光源的系统设计. 该装置是根据相干扭摆器自发辐射原理, 采用自主原创的DC-SC超导光阴极注入器提供的高品质电子束经过磁压缩单次通过扭摆器产生0.25—0.5THz之间的光. 该装置提供的THz光具有波长连续可调、功率高、相干性好、单色性好、线偏振等特点, 为生物、医学、材料科学、通信等领域提供强有力的研究工具.     

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.     

A preliminary study of the feasibility of using superconducting quarter-wave resonators foraccelerating high intensity proton beams

The superconducting (SC) cavities currently used for the acceleration of protons at a low velocity range are based on half-wave resonators. Due to the rising demand on high current, the issue of beam loading and space-charge problems has arisen. Qualities of low cost and high accelerating efficiency are required for SC cavities, which are properly fitted by using SC quarter-wave resonators (QWR). We propose a concept of using QWRs with frequency 162.5 MHz to accelerate high current proton beams. The main factor limiting SC QWRs being applied to high current proton beams is vertical beam steering, which is dominantly caused by the magnetic field on axis. In this paper, we intend to analyze steering and eliminate it to verify the qualification of using QWRs to accelerate high intensity proton beams.     

RF characters study of a pick-up parallel-setting HOM coupler

A pick-up parallel-setting high order mode coupler （pps-HOM coupler） has been fabricated at Peking University. It has been tested on a coaxial transmission line and a 2-cell TESLA-shape copper cavity. The test result of the 2-cell TESLA cavity shows that the coupler can cut off the fundamental mode TM010 and absorb HOMs electively. As its RF properties are insensitive to the probe dip length, there is no need to adjust the probe repeatedly during practical operation.     

北京大学加速器质谱计

北京大学重离子物理研究所和技术物理系研制的加速器质谱计于１９９２年圆满建成并投入使用，在两年多的运行中，性能不断得到改进，并取得了大量的应用成果，简要介绍其性能特点，运行情况和应用概况。     

A preliminary quadrupole asymmetry study of a β=0.12 superconducting single spoke cavity

An Accelerator Driven System(ADS) has been launched in China for nuclear waste transmutation. For the application of high intensity proton beam acceleration, the quadrupole asymmetry effect needs to be carefully evaluated for cavities. Single spoke cavities are the main accelerating structures in the low energy front-end. The single spoke cavity has small transverse electromagnetic field asymmetry, which may lead to transverse RF defocusing asymmetry and beam envelope asymmetry. A superconducting single spoke resonator(PKU-2 Spoke) of β=0.12 and f =325 MHz with a racetrack-shaped inner conductor has been designed at Peking university. The study of its RF field quadrupole asymmetry and its effect on transverse momentum change has been performed. The quadrupole asymmetry study has also been performed on a β=0.12 and f =325 MHz ring-shaped single spoke cavity. Our results show that the quadrupole asymmetry is very small for both the racetrack-shaped and the ring-shaped single spoke cavity.     

Magnetic property improvement of niobium doped with rare earth elements

A new idea is proposed by the PKU group to improve the magnetic properties of the Type-II superconductor niobium.Rare earth elements like scandium and yttrium are doped into ingot niobium during the smelting processes. A series of experiments have been done since 2010. The preliminary testing results show that the magnetic properties of niobium materials have changed with different doping elements and proportions while the superconductive transition temperature does not change very much. This method may increase the superheating magnetic field of niobium so as to improve the performance of the niobium cavity, which is a key component of SRF accelerators. A Tesla-type single-cell cavity made of scandium-doped niobium is being fabricated.