RF deflecting cavity design for bunch length measurement of photoinjector at Tsinghua University

RF deflecting cavity can be used for bunch length measurement and is designed to diagnose the beam produced by the photocathode electron gun which was built at Tsinghua University for the Thomson scattering experiment. Detailed discussion and calculation for measuring the 3.5 MeV bunch and another with further acceleration to 50 MeV, which is under development, are presented. A standing-wave deflecting cavity working at 2856 MHz is designed and the power feeding system has been planned.     

First experimental research of the bunch compressor at CAEP

Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics （CAEP）. The length of the bunch after compressor is found to be about 0.7 ps （rms） and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed.     

Study on CYCIAE-100 radiation field and residual radioactivity

The accelerators should be properly designed to make the radiation field produced by beam loss satisfy the dose limits. The radiation field for high intensity H^－ cyclotron includes prompt radiation and residual radiation field. The induced radioactivity in accelerator components is the dominant source of occupational radiation exposure if the accelerator is well shielded. The source of radiation is the beam loss when cyclotron is operating. In this paper, the radiation field for CYCIAE-100 is calculated using Monte Carlo method and the radioactive contamination near stripping foil is studied. A method to reduce the dose equivalent rate of maintenance staff is also given.     

Ultra-low emittance X-band photocathode RF gun

In this paper, we present the simulation results of a 1.6 cell X-band photocathode RF gun for ultra-low emittance electron beams. It will work at 9.3 GHz. The emittance, bunch length, electron energy and energy spread at the gun exit are optimized at bunch charge of 1pC using PARMELA. Electron bunches with emittance about 0.1 mm·mrad and bunch length less than 100 fs can be obtained from this gun. A PITZ type coupler is adopted in this gun and an initial simulation by MAFIA is also given in this paper.     

Study on CYCIAE-100 radiation field and residual radioactivity

The accelerators should be properly designed to make the radiation field produced by beam loss satisfy the dose limits. The radiation field for high intensity H- cyclotron includes prompt radiation and residual radiation field. The induced radioactivity in accelerator components is the dominant source of occupational radiation exposure if the accelerator is well shielded. The source of radiation is the beam loss when cyclotron is operating. In this paper, the radiation field for CYCIAE-100 is calculated using Monte Carlo method and the radioactive contamination near stripping foil is studied. A method to reduce the dose equivalent rate of maintenance staff is also given.     

Terahertz coherent transition radiation based on an ultrashort electron bunching beam

The experimental result of terahertz (THz) coherent transition radiation generated from an ultrashort electron bunching beam is reported.During this experiment,the window for THz transmission from ultrahigh vacuum to free air is tested.The compact measurement system which can simultaneously test the THz wave power and frequency is built and proofed.With the help of improved Martin-Puplett interferometer and Kramers-Krong transform,the longitudinal bunch length is measured.The results show that the peak power of THz radiation wave is more than 80 kW,and its radiation frequency is from 0.1 THz to 1.5 THz.     

Characteristics of terahertz coherent transition radiation generated from picosecond ultrashort electron bunches

This paper presents a method of generating terahertz (THz) coherent transition radiation (CTR) from picosecond ultrashort electron bunches including single and train bunches, which are produced by a photocathode radio frequency gun. The radiation characteristics of THz CTR including formation factor and energy spectrum are analysed in detail. With the help of a 2-dimensional particle-in-cell simulation, the radiation characteristics including power, energy and magnetic field are analysed. The results show that the radiation frequency can be adjusted by tuning the repetition frequency of the train bunch and the energy can be enhanced with the train bunches.     

Design and cold test of a rectangular cavity beam position monitor

The CBPM is a kind of monitor which is used for the measurement of beam transverse position. It is becoming increasingly popular due to its high potential in resolution performance. In theory, the resolution can reach about 1 nanometer. In this paper, a rectangular CBPM is designed for it has better X-Y isolation than a cylindrical one. It has been simulated and measured, and the results agree with each other very well. The procedures and results for the simulation and the cold test will be shown later and it will be proved that this is a reliable method for the CBPM design.     

磁控管的电荷分布

回顾了几种磁控管理论模型,对这些理论模型中得到的电荷分布进行了分析。利用计算机对X波段磁控管进行PIC模拟,监视粒子相空间分布,并与理论结果进行对比,证明布里渊理论能部分解释轮轭层的高度及其内部的电荷密度分布,但模拟结果中电子在相空间存在一定的分布,而布里渊理论采用的是单粒子运动理论,因此无法解释模拟结果中轮轭边界下降沿特性。模拟得到的轮辐内电荷分布与各种理论均有较大差异,分析发现,不同的轮轭边界下降沿特性是造成差异的主要原因。讨论了利用导向中心流体理论得到更准确的轮辐内电荷分布的可能方法。     

1 MV紧凑型重频Marx发生器绝缘设计和数值分析

 通过分析六氟化硫气体在静态高电压和脉冲高电压作用下的绝缘特性对Marx模块式开关结构和外筒尺寸进行了优化设计,着重优化设计了Marx发生器中的两个关键绝缘部位——开关腔体结构和外金属筒与顶部电容绝缘距离,并通过数值模拟计算,分析了该区域的局部3维电场强度分布。结果表明:最大场强均小于六氟化硫的沿面闪络和电击穿场强阈值。对模块式开关腔和外筒尺寸进行优化得到的绝缘结构满足0.3 MPa下六氟化硫的绝缘要求。