B. G. Sun

New methods of measuring emittance using beam position monitors

Stripline position monitors can be used as a nonintercepting emittance monitor and it is independent of the beam distribution. Usually, difference/sum ratio method is used to pick up the second moment. Two new methods are put forward, which are a log-ratio method and a combined method. The analysis and comparing of these methods are introduced. Change the current of quadrupole magnets m times (mges6) upstream from BPM to change the Transfer matrix, and then the emittance can be calculated.

Carbonization process and SiC formation at C60/Si(111) interface studied by SRPES

Carbonization process and SiC formation upon annealing the Si(111) surface covered by C60 molecules with the thickness of 1.3 nm have been investigated by using synchrotron radiation photoelectron spectroscopy (SRPES), X-ray photoemission (XPS) and reflection high energy electron diffraction (RHEED) in NSRL. C60 molecules are chemisorbed on the Si(111) surface at room temperature, via Si-C60 hybridization to form covalent bonds, which can be explained by adsorption model including two adsorption configurations S3 and L With annealing the sample, the Si-C60 hybridization weakened C-C bonds internally in C60 molecules and enhanced the formation of SixC60, an intermediate species. Further annealing the sample to 650°C will lead to the decomposition of C60 molecules, the released carbon fragment will bond with external silicon atoms to form SiC. While annealing the sample to 850°C, decomposition of all C60 molecules was accomplished, and only a SiC film was left on the surface.

Bunch-by-bunch measurement and feedback system of HLS

In this paper, HLS (Hefei light Source) bunch-by-bunch measurement and feedback system will be introduced. This system is integrated with longitudinal oscillation measurement system, fast vector control, fiber notch filter and bunch current detection system. The detail of the two fronts will be shown. Some experimental results by this system are also present in this paper, as phase-space tracing, mode dumping rate, and feedback experiments.

Development of Measurement and Transverse Feedback System at HLS

In order to cure and damp coupled bunch (CB) instabilities caused by the high order modes (HOMs) of the RF cavity and the resistive wall impedance of the Ring vacuum chamber. HOMs are ineluctable during the operation of the accelerator. An observer system characterized by bunch by bunch measurement of transverse β oscillation and longitudinal synchrotron phase oscillation has been constructed and commissioned at Hefei Light Source (HLS) [1, 2]. A transverse bunch-by-bunch feedback system is under construction. The design and development of the observe systems, as well as diagnostics results of machine instabilities are presented in this paper.

The Study of New Signal Processing Technique in Photon Beam Position Monitors

A log-ratio signal processing technique in photon beam position monitors (PBPMs) was presented in this paper. The main performances (e.g. sensitivity, position offset and linearity range) of split PBPM and two-wire PBPM were analyzed. An inexpensive logarithmic and log-ratio amplifier chip (LOG112) that can measure currents from 0.1nA to 3.5mA was used in circuits.

Several new beam measurement systems for HLS

This paper describes several new beam instruments for Hefei light source (HLS). These new beam instruments include a tuning measurement system to measure the beam tune and chromaticity, a DCCT measurement system to measure the beam DC current and beam life, and a closed orbit measuring system to measure the beam position. Some applications of these measurement systems and their measurement results are presented.

Measurement and Research of Beam-Based Alignment With AC k-Modulation at HLS

A new beam-based alignment (BBA) measurement system with AC k-modulation module was developed recently at Hefei Light Source (HLS), which equipped the quadrupole magnets on the storage ring with a current shunt system which was able to vary the magnet current of a given quadrupole at a given frequency. The corresponding closed orbit oscillation amplitude measured for different beam positions in the quadrupole reached a minimum when the beam was centered in the quadrupole. Amplitude estimation algorithms of software lock-in amplifier and interpolated FFT were discussed. A V-shaped curve was used to determine the offset; a method using a parabola fit to determine the offset was also discussed. This BPM-to-quadrupole offset was determined at HLS with an accuracy of ~50 mum. The reproducibility of the beam based alignment using this technique is about 20 mum (RMS)

Transverse beam size measurement system using visible synchrotron radiation at HLS II

An interferometer system and an imaging system using visible synchrotron radiation (SR) have been installed in HLS II storage ring. Simulations of these two systems are given using Synchrotron Radiation Workshop(SRW) code. With these two systems, the beam energy spread and the beam emittance can be measured. A detailed description of these two systems and the measurement method is given in this paper. The measurement results of beam size, emittance and energy spread are given at the end.

Development of transverse feedback system and instabilities suppress at HLS

In order to cure and damp coupled bunch instabilities (CBI), a bunch-by-bunch (BxB) measurement and transverse feedback system is under commission at Hefei light source (HLS). In this paper we introduce the overview of the measurement and analogy transverse BxB feedback system in emphases. The measurement system is dedicated to observe the beam instability and works as a part of the analogy and digital transverse BxB feedback system. The development of several characterized components and stripline feedback kicker as well as the experiment result of the feedback system in HLS ring is also presented in this paper.

Development of digital transverse bunch-by-bunch feedback system of HLS

Hefei light source (HLS) operates at high beam current with many bunches. Multi-bunch instabilities degrade beam quality. An FPGA based digital transverse bunch-by-bunch feedback system was under development in HLS to suppress beam instabilities. The design of the digital feedback system and primary experiment results are presented in this paper. Further improving of the feedback system and investigating of the characteristics of the feedback loop are the future work.