机械工程学报

ZHENG Lifang
School of Mechanical Engineering,
University of Science and Technology Beijing,
Beijing 100083, China

Institute of High Energy Physics,
Chinese Academy of Sciences,
Beijing 100049, China

JI Quan
Institute of High Energy Physics,
Chinese Academy of Sciences,
Beijing 100049, China

WANG Li
School of Mechanical Engineering,
University of Science and Technology Beijing,
Beijing 100083, China

LI Xunfeng
School of Mechanical Engineering,
University of Science and Technology Beijing,
Beijing 100083, China

Institute of High Energy Physics,
Chinese Academy of Sciences,
Beijing 100049, China

XU Shaowang
Institute of High Energy Physics,
Chinese Academy of Sciences,
Beijing 100049, China

DONG Sujun

ZHAO Libin
Department of Flight Vehicle Design
and Applied Mechanics,
Beihang University,
Beijing 100083, China

LIU Jianping
School of Mechanical Engineering,
Tianjin University,
Tianjin 300072, China

STRUCTURE DESIGN OF THE BEIJING SPECTROMETER Ⅲ BEAM PIPE*

Abstract: The Beijing spectrometer Ⅲ (BESⅢ) beam pipe is in the center of the BESⅢ, which is the detector of the upgrade project of Beijing electron and positron collider (BEPCⅡ). Electrons and positrons collide in the BESⅢ beam pipe. According to the demands of the BEPCⅡ, a key program of Chinese Academy of Sciences, the BESⅢ beam pipe is designed based on the finite elements analysis. The BESⅢ beam pipe is installed in the inner cylinder of the BESⅢ drift chamber. As a vacuum tube, the BESⅢ beam pipe is designed as 1 000 mm in length, 63 mm in inner diameter and 114 mm in outer diameter, respectively. The BESⅢ beam pipe consists of a central beryllium pipe cooled by EDM-1, the oil No.1 for electric discharge machining, and two extended copper pipes cooled by deionized water (DW). The three parts are jointed by vacuum welding. Factors taken into account in the design are as follows. ① The wall thickness of the central beryllium pipe should be designed as small as possible to reduce the multi-scattering and improve the particle momentum resolution. And the wall thickness of the extended copper pipe should be designed as large as possible to protect the detectors from the backgrounds. ② The BESⅢ beam pipe must be sufficiently cooled to avoid the damage and prevents its influence to the BESⅢ drift chamber (DC) operation. The inner surface temperature of the DC inner cylinder must be maintained at 293±2 K. ③ The magnetic permeability of the materials used in the BESⅢ beam pipe must be less than 1.05 H/m to avoid large magnetic field distortions. ④ The static pressure of the vacuum chamber of the BESⅢ beam pipe must be less than 800 mPa. The simulating results show that the designed structure of the BESⅢ beam pipe satisfies the requirements mentioned above. The structure design scheme is evaluated and adopted by the headquarters of BEPCⅡ.

Key words: Beam pipe Beijing spectrometer Ⅲ Structure design Beijing electron and positron colliderⅡ

* This project is supported by Key Programs of Chinese Academy of Sciences (No. KJ95T-03). Received May 29, 2007; received in revised form Novem- ber 9, 2007; accepted November 15, 2007

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Biographical notes

ZHENG Lifang is currently a PhD candidate in School of Mechanical Engineering, University of Science and Technology Beijing, China. Her research interests include mechanical design and manufacturing, etc.
Tel: +86-10-62334994; E-mail: zhenglifang1213@163.com

JI Quan is currently an engineer in Institute of High Energy Physics, Chinese Academy of Sciences, China. His research interests include mechanical design and manufacturing, etc.
Tel: +86-10-88236070; E-mail: jiq@ihep.ac.cn

WANG Li is currently a professor in School of Mechanical Engineering, University of Science and Technology Beijing, China. His research interests include refrigeration, cryogenics, mechanical design and manufacturing, etc.
Tel: +86-10-62334425; E-mail: liwang@me.ustb.edu.cn

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