Junhua Wang

Design and test results of kicker units for the positron accumulator ring at the APS

Three fast kicker units have been designed, tested, and installed in the positron accumulator ring (PAR) at the Advanced Photon Source (APS) for beam injection and extraction. The performance of these kicker units has been satisfactory. This paper presents the design and test results.

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.

A linear MOSFET regulation system to improve the performance of the booster-ramping power supplies at the APS

The APS booster ring uses ramping power supplies to power the sextupole, quadrupole, and dipole magnets as the beam energy ramps up linearly to 7 GeV. Due to the circuit topology used, those supplies are unable to follow the linear ramp to the desired accuracy. The best regulation achieved is 0.5% while 0.1 % is desired. In addition to the unsatisfying regulation, those supplies are sensitive to AC line perturbations and are not able to reject AC line noises higher than a few tens of Hertz. To improve the performance, a linear MOSFET regulation system using paralleled MOSFET devices in series with the power supply is proposed. The system uses a real-time current feedback loop to force the MOSFETs to work in the linear operation mode. By using this linear MOSFET regulator, the voltage drop on MOSFETs, and hence the voltage imposed on magnets, can be regulated very quickly. As a result, the regulation of the magnet current can be improved significantly. Experiments and simulation have been performed to verify the proposed method. Results show that, with the linear regulator, the current regulation can be improved to better than 0.1%. Because of the high bandwidth of the linear regulator, it can reduce the harmonic content in the output current as well as reject the AC line disturbance.

A linear mosfet regulator for improving performance of the booster ramping power supplies at the APS

The APS booster ring uses ramping power supplies to power the sextupole, quadrupole, and dipole magnets as the beam energy ramps up linearly to 7 GeV. Due to the circuit topology used, those supplies are unable to follow the linear ramp to the desired accuracy. The best regulation achieved is 0.25% while 0.1% is desired. In addition to the unsatisfying regulation, those supplies are sensitive to AC line perturbation and are not able to reject AC line noises of more than a few tens of hertz. To improve the performance, a linear MOSFET regulation system using paralleled MOSFET devices in series with the power supply is proposed. The system uses a realtime current feedback loop to force the MOSFETs to work in the linear operation mode. By using this linear MOSFET regulator, the voltage drop on MOSFETs, and hence the voltage imposed on magnets, can be regulated very quickly. As a result, the regulation of the magnet current can be improved significantly. So far the simulation results show that with the linear regulator, the current regulation can be improved to better than 0.1%. Because of the high bandwidth of the linear regulator, it can reduce the harmonic content in the output current as well as reject the AC line disturbance. This paper discusses the circuit topology, the regulation method, and the simulation results.

Optical-fiber notch filter for storage ring transverse feedback system

An optical-fiber two-tap FIR (Notch) filter has been developed for storage ring transverse feedback system of Hefei light source. The optical notch filter has advantages of low loss, which is not related to the size of the storage ring, high-frequency response, and compact in size. Measurements have been done with storage ring beam signals. The paper presents the principle and the experimental results.

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.

Bunch length measurement in time domain for HLS

A simple measurement method of beam bunch length in time domain for HLS (Hefei Light Source) has been proposed. The bunch length measurement system is composed of an optical system, a high speed photo- receiver and a wide bandwidth oscilloscope. The photo- receiver which is made by FEMTO has high sensitivity and high bandwidth, which converts the synchrotron radiation light into electronic signal. The oscilloscope which is made by Tektronix is TDS7704B, which has a high bandwidth up to 7GHz and show the bunch length in time domain. The measurement results of the bunch length and its analysis are given. We compare the results with that measured by the conventional method using a streak camera.

Methods of measurement for the beam-based alignment system in HLS

The beam-based alignment system is given in HLS (Hefei light source), in which a switchable shunt resistor was installed on quadrupole to bypass a small percentage of the magnet current. The system can be used to position the beam in the magnetic center of quadrupoles. In measurement, some methods (linear fitting with single corrector, parabola fitting with single corrector, linear fitting with local bump, and parabola fitting with local bump) are used. These measurement results are given, and compared among above methods.

Design and simulation of fast pulsed kicker/bumper units for the positron accumulator ring at APS

In the design of fast pulsed kicker/bumper units for a positron accumulator ring at APS, different pulse forming networks were considered and different structures for the magnet were studied and simulated. Some design considerations and computer simulation results of different designs are described.<<ETX>>