LLRF超导腔体控制系统的测试

中国科学院近代物理研究所自主研发的ADS注入器Ⅱ第一代高频低电平(LLRF)控制系统,工作频率为162.5 MHz;LLRF系统是由基于I/Q采样的正交解调技术构成的全数字闭环反馈控制系统,其主要功能是实现超导腔腔体电压幅值稳定控制、相位稳定控制与腔体谐振频率控制;LLRF控制系统在液氦温区超导腔上进行了系统稳定度和性能的在线测试,根据实验数据计算得超导腔体电压幅度稳定度为±3.4‰,相位稳定度为±0.3°,腔体表面峰值电场(Epk)能长时间稳定在25.1 MV/m。通过实验测试,检验了LLRF控制系统的性能,并对测试过程中出现的问题进行了分析,为将来超导腔LLRF控制系统运行积累了经验。     

A vertical test system for China-ADS project injector II superconducting cavities

To test superconducting cavities, a vertical test system has been designed and set up at the Institute of Modern Physics （IMP）. The system design is based on VCO-PLL hardware and the NI Labview software. The test of the HWR010#2 superconducting cavity shows that the function of this test system is satisfactory for testing the low frequency cavity.     

Full period superconducting section physics design for injector Ⅱ of China-ADS

The China Accelerator Driven Subcritical System (China-ADS) project, which is a strategic plan and aims to design and build an ADS demonstration facility, has been proposed and launched actively in China. Injector Ⅱ as one of the parallel injectors of China-ADS, and is prompted by the Institute of Modern Physics (IMP). In this paper, a new scheme with full period lattice structure for the SC section is proposed. In the new scheme, there are sixteen periods, with one superconducting solenoid and one superconducting cavity included in each period. All of the elements are contained in four cryomodules. The dreadful influence of the mismatch caused by period structural change can be avoided, and the beam quality is favorable. In addition, this new scheme has certain advantages in reducing the project's difficulty and construction risk. The details of the design and beam dynamic simulation for the full period lattice structure are given in this paper.     

A vertical test system for China-ADS project injector Ⅱ superconducting cavities

To test superconducting cavities, a vertical test system has been designed and set up at the Institute of Modern Physics (IMP). The system design is based on VCO-PLL hardware and the NI Labview software. The test of the HWR010#2 superconducting cavity shows that the function of this test system is satisfactory for testing the low frequency cavity.     

Full period superconducting section physics design for injector Ⅱ of China-ADS

The China Accelerator Driven Subcritical System （China-ADS） project, which is a strategic plan and aims to design and build an ADS demonstration facility, has been proposed and launched actively in China. Injector Ⅱ as one of the parallel injectors of China-ADS, and is prompted by the Institute of Modern Physics （IMP）. In this paper, a new scheme with full period lattice structure for the SC section is proposed. In the new scheme, there are sixteen periods, with one superconducting solenoid and one superconducting cavity included in each period. All of the elements are contained in four eryomodules. The dreadful influence of the mismatch caused by period structural change can be avoided, and the beam quality is favorable. In addition, this new scheme has certain advantages in reducing the project＇s difficulty and construction risk. The details of the design and beam dynamic simulation for the full period lattice structure are given in this paper.     

C-ADS超导轮辐腔Spoke021的电磁设计与优化

为满足C-ADS项目建设对超导轮辐腔Spoke021的需求,对Spoke021进行了详细的电磁参数优化。对Spoke021的参数化模型进行参数扫描,针对腔体的关键电磁特征量寻找可能存在的极值,详细分析、解释了优化过程中各个参数发生变化的物理意义。在Spoke021各参数达到最终优化值时,表征腔体性能的两个关键比值分别为:E_p/E_(acc)=3.14,Bp/E_(aCC)=4.77 mT/(MV/m)。考虑到次级电子倍增(Multipacting,MP)对Spoke021运行中所能达到的性能指标有很重要影响,对腔体的MP进行了建模分析。结果表明,当Spoke021工作在E_(acc)=10 MV/m情况下,没有发生MP,优化得到的参数可以满足Spoke021工程设计的需要;最后计算了腔体的TTF曲线,表明该腔体具有较宽的速度接受度。     

Mechanical design and analysis of a low beta squeezed half-wave resonator

A superconducting squeezed type half-wave resonator(HWR)ofβ=0.09 has been developed at the Institute of Modern Physics,Lanzhou.In this paper,a basic design is presented for the stiffening structure for the detuning effect caused by helium pressure and Lorentz force.The mechanical modal analysis has been investigated the with finite element method(FEM).Based on these considerations,a new stiffening structure is proposed for the HWR cavity.The computation results concerning the frequency shift show that the low beta HWR cavity with new stiffening structure has low frequency sensitivity coefficient df/dp and Lorentz force detuning coefficient KL,and stable mechanical properties.     

An untuned MA-loaded cavity for HIRFL-CSR

In order to realize high energy density physics and plasma physics research at HIRFL-CSR, a magnetic alloy （MA）-loaded cavity has been studied. According to the theoretical calculation and simulation for the MA-loaded cavity, we achieved a better result. The MA-loaded cavity had a higher μQf value, with a higher shunt impedance and a higher accelerating gradient. The accelerating gradient was about 95 kV/m at 1.8003 MHz, 130 kV/m at 0.9000 MHz. Compared with the ferrite-loaded cavities that are used at HIRFL-CSR, with about 10 kV/m accelerating gradient, the MA-loaded cavity obviously has an advantage. The results of the theoretical calculation and the simulation, which meet the design requirements are in good agreement.     

Numerical optimization and multi-particle dynamics simulation of the radial matching section of the RFQ

The ABC code is an optimization program for the development of matching channels and dynamical matchers in radio frequency quadrupole (RFQ) structures, and a new approach to this code to define the geometry of the radial matching section of the RFQ has been developed. This approach is based on the application of the numerical optimization step by step. This optimization is intended to search for the initial matching condition of a beam, the optimization of parameters of a cell of the channel on given characteristic parameters and traces of a beam in linear channels in both forward and backward directions. To further verify the results of the optimization, multi-particle beam dynamics simulations have been carried out using the BEAMPATH and TRACK codes. The result of the beam dynamics simulation shows that the optimization result of the ABC code is reasonable and this approach provides an opportunity to redesign the structure of the radial matching section of the RFQ.     

Study on the frequency tuning of the half-wave resonator at IMP

The RF and mechanical coupled analyses are essential in superconducting cavity design in order to predict the deformation of the cavity walls and the frequency shift caused by the deformation. In this paper, the detuning caused by both bath helium pressure and Lorentz force is analysed and a tuning system has been investigated and designed to compensate the detuning by deforming the half-wave resonator along the beam axis. The simulations performed with ANSYS code show that the tuning system can adjust and compensate the frequency drift due to external vibrations and helium pressure fluctuation during operation.