4.1 Beam pipe
4.1.1 Introduction
The detector beam pipe, which extends longitudinally over –0.6m<z<0.6m, will be
designed to satisfy the detector requirements. The wall of the pipe should be as thin as
possible in the central region to minimize the multiple scattering of particles traversing it. Its
radius was chosen to be as small as possible to ease installation through the inner diameter of
the vertex detector, but large enough to ensure good pumping conductance, vacuum stability
and mechanical rigidity. To allow installation and general access to the sub-detectors, the
beam pipe will be assembled together with the vertex detector.
4.1.2 Beam pipe design
The beam pipe of BES I is an aluminum cylinder, 0.3mm thick, wrapped by a 2mm thick
carbon fiber，which has 1.04*10-2 r.l。
The ideal material for the beam pipe is beryllium. The beam pipe of BES II, together with
the vertex chamber, is designed and constructed by Colorado State University, which is a
1.27mm thick beryllium cylinder, wrapped by a 0.75mm carbon fiber, has a total 4*10-3 r.l。
The BESIII beam pipe will refer to BESII, the central section of the beam pipe is a
beryllium cylinder, 35mm in radius and 1.25 mm thick, extending up to the length of about
0.3m. The length of the beryllium section will be limited in order to minimize handling
problems and cost. The radius of the beam pipe is constrained by the inner radius of the vertex
detector. A cylindrical aluminum alloy part extends up to the flanges. Both flanges at the end
of the pipe will connect to the machine beam pipe.
The beam pipe is attached to the vertex detector support structure and is accessible from the
inner cylinder of the drift chamber, allowing positioning of the beam pipe during access.
The detail design will be cooperated with the interaction region design, it is closely related
to the beam line magnets near the interaction point and the luminosity detector. The mask will
be taken into account to reduce the synchrotron radiation if necessary.
4.1.3 R&D programs
The design of the beam pipe is mainly constrained by the need to be able to operate in the
radiation environment reached at the highest luminosity. Detailed simulations of the radiation
backgrounds should be performed to understand the beam pipe geometry, materials and mask.
We will know how to attach the beam pipe on the vertex detector support structure and
how to joint the beam pipe of the experiment from the machine beam pipe.
The radio-frequency (RF) properties of the beam pipe should also be studied to understand
its influence on the machine stability and beam coast lifetime. Calculations to determine the
stability of the pipe should also be done when diameter and wall thickness are given.
More R&D is needed to fully understand the exact requirements of the production
technique if we decide to construct it in China.
4.1.4 Timescale
1/2
R&D
1y
Machining
0.5y
Test and Assembly
0.5y
Total
2y
4.1.5 Cost Estimate
1)R&D:
100k
2)Testing
100k
3)Machining
400k
4)Assembly
100k
5)Contingency
100k
Total
800k
2/2