Sun Baogen

A study of pickup and signal processing for HLS- II bunch current measurement system

For the HLS-II bunch current measurement system, in order to obtain the absolute value of bunch current, the calibration factor should be determined by using DCCT. At the HLS storage ring, the stretch effect of bunch length is observed and the change rate is about 19% when the bunch current decays over time and this will affect the performance of bunch current detection. To overcome the bunch stretch influence in the HLS-II bunch current measurement, an evaluation about pickup type and signal processing is carried out. Strip-line pickup and button pickup are selectable, and the theoretical analysis and demonstration experiment are performed to find out an acceptable solution for the bunch current measurement system at HLS-II. The experimental data analysis shows that the normalized calibration factor will change by about 27% when the bunch length change by about 19% if using the button pickup and processing by peak value of bunch signal, the influence will be reduced to less 2% if adopting the strip-line pickup and integral.

Beam emittance investigation in high brightness injector using different driver laser profiles

Beam emittance plays an important role in any accelerator, and it is a main parameter to judge the performance of an accelerator. Emittance optimization is an indispensable part in conditioning and operation of the facility. For a laser-driven high brightness injector, different time structure of the laser pulse has different effects on transverse emittance. In order to compare Gaussian and flat-top laser pulse, systematic simulations of 500 pC have been done. From the simulation results, one can see that flat-top pulse laser will yield smaller minimal transverse beam size and transverse beam emittance than Gaussian pulse laser.

A new measurement method for electrode gain in an orthogonally symmetric beam position monitor

The new beam position monitor (BPM) system of the injector at the upgrade project of the Hefei Light Source (HLS II) has 19 stripline beam position monitors. Most consist of four orthogonally symmetric stripline electrodes. Differences in electronic gain and mismachining tolerance can cause changes in the beam response of the BPM electrodes. This variation will couple the two measured horizontal positions, resulting in measuring error. To alleviate this effect, a new technique to measure the relative response of the four electrodes has been developed. It is independent of the beam charge, and the related coefficient can be calculated theoretically. The effect of electrode coupling on this technique is analyzed. The calibration data is used to fit the gain for all 19 injector beam position monitors. The results show the standard deviation of the distribution of measured gains is about 5%.

A waveguide overloaded cavity kicker for the HLS II longitudinal feedback system

In the upgrade project of Hefei Light Source (HLS II), a new digital longitudinal bunch-by-bunch feedback system will be developed to suppress the coupled bunch instabilities in the storage ring effectively. We design a new waveguide overloaded cavity longitudinal feedback kicker as the feedback actuator. The beam pipe of the kicker is a racetrack shape so as to avoid a transition part to the octagonal vacuum chamber. The central frequency and the bandwidth of the kicker have been simulated and optimized to achieve design goals by the HFSS code. A higher shunt impedance can be obtained by using a nose cone to reduce the feedback power requirement. Before the kicker cavity was installed in the storage ring, a variety of measurements were carried out to check its performance. All these results of simulation and measurement are presented.

The Commission of HEFEI Light Source After Reconstruction

Hefei light source was updated. Both the kicker system and RF system were reconstructed completely, and commissioned well. Two methods were used to suppresse transverse coupling instability. After the effect of SCW is compensated, beam life was increased. The global closed orbit is realized firstly in Hefei electron storage ring.

Application of frequency domain technique in HLS

The paper introduce the measurement of some beam parameters for Hefei Light Source (HLS) by frequency domain technique, which include the betatron tune, average beta function, natural chromaticity, corrected chromaticity, and center frequency. Additionally, the measurement of the influence of DC clearing electrodes on the betatron tune shift is also described. Some measurement results are given. The measurement results are compared with the theoretical values and shown to be in good agreement.

Measurement of length with high accuracy and large range

Abstract This paper introduces an intelligent system of length measurement, which consists of a linear CCD, a grating, and a microcomputer. Because the system uses a new fine-divisions method of moire fringes, the resolution is greatly increased. The theoretical analysis and the experimental results are given in this paper.