• S.C. Zhang, D.H. He, Q.K. Jia, Z. Jin, W. Li, S. Lu, L. Shang, B. Sun, Y. Wang, C. Yao, R. Zhuo
  USTC/NSRL, Hefei, Anhui

A photocathode injector system is developing at NSRL. A BNL type S-band photocathode RF gun has been built. The emittance will be compensated by a Solenoid. The driving laser is a high-Q product. It will be reformed into uniform distribution in the transverse distribution, but will not in the longitudinal direction. The whole system will be tested soon.

• A. Bocci, A. Drago, A. Marcelli
  INFN/LNF, Frascati (Roma)
• C. Li, Z. Qi, B. Sun, B.Y. Wang, J.G. Wang, Z.Y. Wu
  USTC/NSRL, Hefei, Anhui
• J.P. Piotrowski
  VIGO System S.A., Ozarow Maz.

Real time diagnostics is a fundamental tool for accelerator physics, particularly important to improve performances of existing synchrotron radiation sources, colliders and a key issue for 4th generation sources and FELs. We report the first measurements in the time and frequency domain performed at Hefei Light Source (HLS), the SR facility of the National Synchrotron Radiation Laboratory (NSRL), of the longitudinal bunch lengths. A fast uncooled HgCdTe photodiode optimized in the mid-IR range has been used to record at the IR port the length of the e^- bunches. IR devices are compact and low cost detectors suitable for a bunch-by-bunch longitudinal diagnostics. The data are useful to investigate longitudinal oscillations and characterize the bunch length. The IR signal has been used to measure the synchrotron oscillation frequency, its harmonics in the multi-bunch mode and the bunch lengths in multi-bunch mode at different beam currents. For the first time, simultaneously, data have been collected at visible wavelengths using a fast photodiode at the diagnostics beamline of HLS. A comparison between IR data and diagnostics realized in the visible will be presented and discussed.

• J. Fang, P. Li, P. Lu, Q. Luo, B. Sun, X.H. Wang
  USTC/NSRL, Hefei, Anhui

The strip-line beam position monitor can be used as a non-intercepting emittance measurement monitor. The most important part of emittance measurement is to pick up the quadrupole component. To improve the accuracy of measurement, the response of the strip-line BPM pickups will be mapped before it’s installed in the HLS LINAC. This paper introduce the calibration system of the BPM, which consists of a movable antenna and a RF signal source, simulating the beam , a BPM moving bench with its control system, and an electronics system. When the position calibration is done first, the offset between electronic center and mechanical one of the BPM and the position sensitivity are gotten. There are two methods for quadrupole component calibration: one is indirect evaluation method that estimates the sensitivity of quadrupole component by the factor of position second moment; the other is direct method by simulation of a Gaussian beam through together many Gaussian weighted grid points. The results of two methods are given and compared. The effect of antenna’s diameter upon the fitting size of simulate beam has also been analyzed.

• L.M. Gu, S.F. Lin, P. Lu, C.B. Shen, B. Sun
  USTC/NSRL, Hefei, Anhui

The stability of synchrotron radiation source is of great significance for users, and an accurate and reliable photon beam position monitor (PBPM) is essential for success of synchrotron radiation experiments. Recently, we development a new PBPM called staggered pair photon beam position monitor for photon beam position measurement in Hefei Light Source (HLS). Its main advantage is to reduce the influence of bunch size. Usually, difference over sum (Δ/Σ) method is used to process the photon beam signal. Two new methods are put forward, which are a ratio method and a log-ratio method. For photon beam with Gaussian distribution, differences among methods of Δ/Σ, ratio and log-ratio are introduced. Some calculating results are given for three signal processing methods. Comparing those three methods of position signal processing, log-ratio method is found to have the widest range of linearity, and can obtain identical beam position with different bunch size. Based on that, we also compare staggered pair monitor with double-blade monitor. The staggered pair monitor is found to have higher sensitivity, as well it can ignore the influence of bunch size.

• J.Q. Lan, B. Sun, H. Xu, J. Zhang
  USTC/NSRL, Hefei, Anhui

Radial alternating magnetic field is generated to act on polarized beam to give rise to resonant depolarization and calibrate the energy of electron by feeding power to a pair of vertical installed striplines in HLS. In the paper, the relationship between depolarization time and power fed into the striplines is investigated, and spin frequency spread is considered too. As a result, a depolarization time of 60s is acquired with an amplifier power of 15W fed into the striplines.

• Q. Luo, D.H. He, B. Sun
  USTC/NSRL, Hefei, Anhui

Funding: National “985 Project” （173123200402002); National Natural Science Foundation(10875117)

A new high brightness injector is planned to be installed at HLS, NSRL. It is based on a new photocathode RF electron gun. To steer the beam along the optimal trajectory, higher precision controlling of beam position is required. The positional resolution of the BPM system designed for the new RF gun should be higher than 10 μm. A new cavity BPM design is then given instead of old stripline one because of its higher positional resolution. In a normal symmetrical pill-box BPM design, machining tolerance will result in x-y coupling, which will cause cross-talk problem. A novel design is then presented here. To solve the problem before, a position cavity which has a racetrack cross section is used instead of a pill-box one. The ideal resolution of this design could be less than 3 nm.

• J.G. Wang, B. Sun, B.Y. Wang, H. Xu
  USTC/NSRL, Hefei, Anhui

In HLS streak camera system has been built. The system is used to measure some parameters of bunch like bunch length, longitudinal bunch profile and synchrotron frequency and so on, as it may report a direct derivation of fundamental machine characteristics. The system mainly consists of the synchrotron light extracting optics setup, the OPTOSCOPE streak camera and PC with a frame grabber interface card. The light extracting optics setup is used to extract synchrotron light at the bending magnet and the setup consists of the light extracting path and the optics imaging system. The streak camera realizes the functions of acquiring light and imaging. PC with a frame grabber interface card and ARP-Optoscope software package is used to monitor the light in real-time, acquire the image of light and analyze the data. The streak camera system operates with either synchroscan sweep mode or dual time base sweep mode. At present, some results are given, which include the bunch lengthening, the longitudinal bunch profile and the synchrotron frequency. These results are compared with the results acquired by using oscilloscope.

• X.H. Wang, J. Fang, P. Lu, Q. Luo, B. Sun, J.G. Wang
  USTC/NSRL, Hefei, Anhui

A high brightness injector has been developing in HLS (Hefei Light Source), and the design of beam parameter measurement system is presented in this paper. The whole system will measure beam position, beam current, emittance of beam, bunch length, beam energy and energy spread. For the beam position, we have designed three types of BPMs: stripline BPM, with the resolution of 20 μm; cavity BPM, with the resolution of 10 μm, and resonant stripline BPM*. The beam position processor Libera will be used. The beam current will measured using the ICT and FCT. When going out of the gun, the energy of the beam is about 4MeV – 5MeV, and the emittance of the beam is charge-dominated, so we use a set of slits with the width of 90 μm to split the beam to beamlets. The bunch length is measured using OTR and streak camera. Before entering the bending magnet, the beam will go pass a very narrow slit, with the width of 90 μm, and the resolution of energy spread will be improved.

*M.Dehler, “Resonant Strip line BPM for Ultra Low Current Measurements”, Proceedings of DIPAC 2005, Lyon, France, p.286-288

• Y.B. Chen, L. Liu, M. Meng, B. Sun, J.H. Wang, L. Wang, Y.L. Yang, Z.R. Zhou
  USTC/NSRL, Hefei, Anhui

A bunch-by-bunch analogue transverse feedback system at the Hefei Light Source (HLS) is to cure the resistive wall instability and the transverse coupled bunch instabilities. The kicker of the feedback system has four 21-cm-long electrodes of stripline type mounted in a skew 45°. Calculation and Simulation of the transverse kicker are shown.

• J.H. Wang, Y.B. Chen, W. Li, L. Liu, M. Meng, B. Sun, L. Wang, Y.L. Yang, Z.R. Zhou
  USTC/NSRL, Hefei, Anhui
• J. Cao, J. Yue
  IHEP Beiing, Beijing
• D.K. Liu
  SINAP, Shanghai
• L. Ma
  IHEP Beijing, Beijing
• K.R. Ye
  SSRF, Shanghai

In this paper, we introduce the BxB transverse feedback systems at Hefei Light Source (HLS), which employ an analog system and a digital system. The construction and commissioning for two feedback systems, as well as the instability analysis of beam and the experiment result of the feedback system in HLS are also presented in this paper.

• Y.L. Yang, Y.B. Chen, W. Li, L. Liu, M. Meng, B. Sun, J.H. Wang, L. Wang, Z.R. Zhou
  USTC/NSRL, Hefei, Anhui

As low injection energy and multi-turn injection at HLS, the task of diagnosing and curing coupled-bunch instabilities becomes ever harder. The transverse analog feedback system has been redeveloped to improve effect, recently. In this paper, the new improved designs are described and new system's commissioning results are discussed. The transverse coupled bunch instability at 200MeV injection status is also experimentally studied.

• Z.R. Zhou, Y.B. Chen, M. Meng, B. Sun, J.H. Wang, L. Wang, Y.L. Yang
  USTC/NSRL, Hefei, Anhui
• K. Kobayashi, T. Nakamura
  JASRI/SPring-8, Hyogo-ken

Hefei Light Source (HLS) is an 800MeV storage ring with bunch rate of 204 MHz, the harmonics of 45, and circumference of 66 meters. HLS injection works at 200MeV, where the multi-bunch instabilities limit the maximum stored current. A digital transverse bunch-by-bunch feedback system has recently been commissioned at HLS to suppress the multi-bunch instabilities during injection. We employ the SPring-8 FPGA based feedback processor and modified it at NSRL to process horizontal and vertical oscillation signals, independently and simultaneously by one single processor. The design of the digital transverse feedback system and the experiment results are presented in this paper.