Abstract
The beam energy measurement system is significant and profit for both BES-III detector and BEPC-II accelerator. The detection of the high energy scattering photons is realized by virtue of the Compton backscattering principle. Many advanced techniques and precise instruments are employed to acquire the highly accurate measurement of positron/electron beam energy. During five years’ running period, in order to satisfy the requirement of data taking and enhance the capacity of measurement itself, the upgradation of system is continued, which involves the components reformation of laser and optics subsystem, replacement of view-port of the laser to vacuum insertion subsystem, the usage of electric cooling system for high purity germanium detector, and the refinement of data acquisition and processing subsystem. The upgrading of system guarantees the smooth and effective measuring of beam energy at BEPC-II and accommodates the accurate offline energy values for further physics analysis at BES-III.
Highlights
The upgraded Beijing electron-positron collider (BEPC-II) is a τ-charm factory with a beam energy ranging from 1.0 to 2.3 GeV and the design peak luminosity of 1033 cm−2∙s−1 [1] [2] at 1.89 GeV, which was achieved at the evening of April 5, 2016
As aforementioned in the working scheme, the backscattering high energy photons will be detected by a HPGe detector, which is a key instrument of beam energy measurement system (BEMS)
It will be dangerous to the BEMS staff who enter the corridor, the door of corridor is interlocked with the laser
Summary
The upgraded Beijing electron-positron collider (BEPC-II) is a τ-charm factory with a beam energy ranging from 1.0 to 2.3 GeV and the design peak luminosity of 1033 cm−2∙s−1 [1] [2] at 1.89 GeV, which was achieved at the evening of April 5, 2016. A large amount of data are obtained and analyzed, the statistical uncertainties in physics analysis become smaller and smaller, at the same time the systematic uncertainties play more and more prominent roles [5]-[7], one of which is the uncertainty due to the measurement of beam energy To decrease such an uncertainty, starting from year 2007, a high accuracy beam energy measurement system (BEMS) located at the north crossing point (NCP) of BEPC-II was designed, constructed, and put into the commissioning at the end of 2010 [8]-[11]. The whole system can be sub-divided into four parts according to their technique and engineering characters: 1) laser source and optics system, which supplies low energy laser and focused photons; 2) laser to vacuum insertion system, where a laser beam collides with electron or positron beam; 3) HPGe detector to measure backscattering high energy photons; 4) data acquisition and running control system for information processing and analyzing.
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