Development of a 325 MHz β =0.12 superconducting single spoke cavity for China-ADS

Twelve very low Beta superconducting single spoke cavities, whose Beta is only 0.12 (Spoke012) when operating at 325 MHz, are adopted in Injector I for China-ADS linac. This type of spoke cavity is believed to be one of the key challenges for its very low geometric Beta. So far, in collaboration with Peking University and Harbin Institute of Technology, IHEP has successfully designed, fabricated, and tested the Spoke012 prototype cavity. This paper presents the details of the design, fabrication and test results for Spoke012 prototype cavity.     

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.     

BEPCⅡ零模束流反馈系统研制

 为了抑制BEPCⅡ多束团(93团)、大流强（910 mA）时的纵向振荡（零模）,引入了BEPCⅡ零模束流反馈系统。该系统首次应用于BEPCⅡ储存环上,它包括了束流信号采集、滤波、下变频、鉴相、移相等几个部分。使用该系统后,束流的纵向边带被抑制度大于10 dB,这表明,系统能够抑制束流的纵向振荡。     

BEPCⅡ高频系统的建造

北京正负电子对撞机二期(BEPCⅡ)的高频系统已于2006年11月投入运行, 它包括了3个子系统:     

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。     

Low beta spoke cavity multipacting analysis

The simulation and analysis for electron multipacting phenomenon in a low β spoke superconducting cavity in ADS proton accelerator are proposed. Using both CST and Track3P codes, the electron multipacting calculation for β=0.12 spoke superconducting cavity is implemented. The methods of multipacting calculation on both codes are studied and described. With the comparison between the calculation results and the cavity vertical test result, the accuracy and reliability of different codes on calculating multipacting are analyzed. Multipacting calculation can help to understand the results of vertical test and also can help to do the optimization in cavity design.     

A tuning system for BEPCⅡ

The tuning system plays a very important role when a superconducting cavity is in operation. It cooperates with other control loops to adjust the cavity frequency with high precision, reduce the reflection power, guarantee the stability of beam, and ensure the safety of the superconducting cavity. This paper focuses mainly on the tuning system working principle, the working state and problems that Beijing Electron Positron Collider (BEPC ) has encountered during operation.     

Horizontal test for BEPC 500 MHz spare cavity

The horizontal test for the BEPC 500 MHz spare cavity has been completed at IHEP. The maximum voltage of the cavity reached 2.17 MV, while Q 0 was 5.78 × 108 . The process and results of the high power horizontal test are presented and discussed in this paper.     

A digital low-level radio-frequency system R&D for a 1.3 GHz nine-cell cavity

To test and verify the performance of the digital low-level radio-frequency (LLRF) and tuner system designed by the IHEP RF group, an experimental platform with a retired KEK 1.3 GHz nine-cell cavity is set up. A radio-frequency (RF) field is established successfully in the cavity and the frequency of the cavity is locked by the tuner in ±0.5° (about ±1.2 kHz) at room temperature. The digital LLRF system performs well in a five-hour experiment, and the results show that the system achieves field stability at amplitude <0.1% (peak to peak) and phase <0.1° (peak to peak). This index satisfies the requirements of the International Linear Collider (ILC), and this paper describes this closed-loop experiment of the LLRF system.     

BEPCⅡ国产500 MHz超导腔运行综述

北京正负电子对撞机二期(BEPCⅡ),国产500 MHz超导腔经过紧张的安装调试于2017年10月正式投入带束流运行。首先对此国产超导腔两次降温调试的相关参数进行了监测和对比分析;其次研究了通过高功率老练的方法改善超导腔的品质因数,并实时监测超导腔老练过程中的辐射剂量;最后对超导腔的带束流运行情况进行了介绍分析。结果表明:BEPCⅡ国产500 MHz超导腔虽然放置了6年,但是状态良好,通过高功率老练能够降低超导腔的辐射剂量,改善其性能,完全满足束流运行要求。