BPM System Development and Applications in Commission of SXFEL-UF
B. Gao
SARI-CAS, Pudong, Shanghai, People’s Republic of China
J. Chen, Y.B. Leng
SSRF, Shanghai, People’s Republic of China
SXFEL is a soft X-ray free electron laser user facility that is current being commissioned in Shanghai. It is based on a 1.5 GeV normal conducting high gradient C-band (linear accelerator) LINAC and contains two FEL beamline, a seeded FEL beamline and a SASE beamline, and five experimental stations. The performance of X-ray FEL depends strongly on the quality of the electron beam and single shot stability. We have developed a BPM system including SBPM and CBPM. The resolution of SBPM is better than 4μmeters, and the resolution of CBPM is better than 176 nm. Because of its excellent position resolution, it plays an important role in the SASE beamline commissioning. The beam adjusters rely on this system to find and maintain an ideal track, and complete the debugging of the SBP beamline within 21 days. This paper presents the system design, methods used to determine the resolution, the performance, and the applications of those BPMs.
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Research on the Optimal Amplitude Extraction Algorithm for Cavity BPM
48
J. Chen, Y.B. Leng, T. Wu, Y.M. Zhou
SSRF, Shanghai, People’s Republic of China
S.S. Cao, B. Gao
SARI-CAS, Pudong, Shanghai, People’s Republic of China
The wake field of different modes of cavity BPM carries different bunch information, the amplitude and phase of the signals of different modes can be extracted through the signal processing method to obtain the characteristic parameters of the source bunch. In the application of bunch charge and position measurement, the accurate amplitude extraction method for cavity BPM signal is the primary issue to be considered when designing the data acquisition and processing system. In this paper, through theoretical analysis and numerical simulation, it is proved that the optimal algorithm of amplitude extraction for CBPM exists, and the dependence between the data processing window size and the decay time of the cavity BPM under the optimal design is given. In addition, the relationship between the optimized amplitude extraction uncertainty and the noise-to-signal ratio, sampling rate of data acquisition and processing system, and the decay time of the cavity BPM is also proposed, which can also provide clear guidance for the design and optimization of the CBPM system.
S.S. Cao
SARI-CAS, Pudong, Shanghai, People’s Republic of China
R. Jiang, Y.B. Leng, R.X. Yuan
SSRF, Shanghai, People’s Republic of China
SHINE is a newly proposed high-repetition-rate X-ray FEL facility and will be used to generate brilliant X-rays between 0.4 and 0.25 keV. To guarantee the high performance of FEL light pulses, it put a strict requirement on the monitoring of electron bunch trajectory. The position resolution of each bunch at the undulator section is required to be better than 200 nm at a bunch charge of 100 pC. The cavity beam position monitor (CBPM) is widely used in FEL facilities for its unique high resolution and high sensitivity. The output signals of an ideal pillbox cavity are proportional to the resonant frequency. Compared with the C-band cavity, the X-band cavity is expected to have a higher signal-to-noise ratio which is especially helpful at low bunch charge. Therefore, an X-band CBPM prototype is developed for SHINE. This paper will focus on the difficulties encountered during the design and production process and the solutions.
Research on Resolution of Orbit Based on Clustering Analysis and BP Neural Network in SSRF
88
R. Jiang, Y.B. Leng, N. Zhang
SSRF, Shanghai, People’s Republic of China
Y.M. Deng
SINAP, Shanghai, People’s Republic of China
Keeping the beam current’s normal motion is an important mission for Shanghai Synchrotron Radiation Facility (SSRF). So the Orbit (rms)x/y is an main parameter for SSRF’s running. However, the orbital resolution has been constrained by the accuracy of acquired data. To eliminate BPM’s failure causing the inaccurate orbital resolution, the work based on clustering analysis and BP neural network to removed the abnormal BPM and recalculate the resolution of orbit. Data came from the machine research. The analysis results showed that the rms value of orbit is 100.75±6.87 um (x direction) and 14.9±0.6 um (y direction) using all BPM’s data but the recalculate value is 98.03±6 um (x direction) and 2.6±0.4 um (y direction) when eliminate the data of faulty BPM. The analysis result indicated that the method can optimize the resolution of orbit and next work is further to evaluate the orbital resolution with more operation data.
The First Beam Experiment Result of the Protype of Wire Scanner for SHINE
232
F.Z. Chen, J. Chen, B. Gao, Y.B. Leng
SSRF, Shanghai, People’s Republic of China
J. Wan
SINAP, Shanghai, People’s Republic of China
As a kind of quasi-non-destructive beam size monitoring, SHINE will employ dozens of wire scanners. The preliminary study is confronted with motion control difficulty. To reduce the ultrahigh coordinate about wire movement with beam loss data acquisition, a new method has been proposed in the SXFEL test platform. The strategy is utilizing the beam jitter, which is of the same magnitude with the beam size. Combine with the jitter of the beam position, we move tungsten wires in a few of different position to realize the measurement. This paper will present our experiment design as well as a furthermore plans about the prototyping design.
Bunch Arrival Time Measurement System Test for SHINE
396
Y.M. Zhou, J. Chen, Y.B. Leng
SSRF, Shanghai, People’s Republic of China
S.S. Cao
SARI-CAS, Pudong, Shanghai, People’s Republic of China
To achieve high-precision synchronization between electron bunches and seeded lasers, a femto-second resolution bunch arrival time measurement system (BAM) is required at SHINE (Shanghai High repetition rate XFEL aNd Extreme light facility). The bunch signal from a GHz-bandwidth cavity monitor is mixed with a reference signal from the device synchronization clock in the RF front-end. Then, the generated IF signal is collected by the digital acquisition system. In the pre-research stage, four sets of cavity monitors with different frequencies and load quality factors and three sets of analog front-ends with different schemes were performed, but now only one monitor with the attenuation time constant of 200 ns was installed for beam experiment testing. The system can measure the bunch charge, bunch arrival time, and bunch flight time. The first results will be presented in this paper.
X. Yang, J. Wan
SINAP, Shanghai, People’s Republic of China
L.W. Lai, Y.M. Zhou
SARI-CAS, Pudong, Shanghai, People’s Republic of China
Y.B. Leng, W.M. Zhou, Y.M. Zhou
SSRF, Shanghai, People’s Republic of China
Digital signal processors that can handle 1 MHz bunch rate BPM signal processing is under development for SHINE. At the same time, two general purpose processor prototypes for all BPM signal sampling and processing have been developed. One uses 14bits ADC, the other uses 16bits ADC. Both processors have been completed. This paper will introduce the tests of the processors and the related performance evaluations.
Non-Invasive Machine Parameters Measurement in a Storage Ring Based on Bunch-by-Bunch 3d Position Data Correlation Analysis
X.Y. Xu, Y.B. Leng
SSRF, Shanghai, People’s Republic of China
X.Y. Xu
University of Chinese Academy of Sciences, Beijing, People’s Republic of China
X.Y. Xu
SINAP, Shanghai, People’s Republic of China
In order to improve machine performance, the machine parameters of the storage ring (including optics parameters and insert devices parameters, etc.) need to be accurately measured. It is difficult to measure them with traditional methods during the user operation run. The behaviour of each bunch in the ring will not be exactly the same, but has its own personality (different transverse positions, longitudinal phases and different bunch charges). If the bunch-by-bunch 3D position can be accurately measured, every individual bunch can be used as probes to extract the dynamics parameters of the storage ring. Based on a broadband oscilloscope with a high sampling rate, a bunch-by-bunch three-dimensional parameter measurement system was built at the Shanghai synchrotron radiation facility(SSRF). The measurement uncertainty of longitudinal phase is less than 0.2 ps, the uncertainty of transverse position is less than 10 um and the charge uncertainty is 0.3% under the condition that the bunch charge is 600 pC. A general software package was developed to process the bunch signals and extract bunch parameters. The functions of this software package mainly include three-dimensional position, charge extraction, refilled charge signal stripping, and cable reflection signal stripping. Using this software package, the injection transient process was studied and the momentum contraction factor, dispersion function, and longitudinal damping oscillation parameters measurement were realized during the normal operation at SSRF. Because the software package does not require special acquisition equipment and does not have strict requirements on the state of the accelerator, the software package can be widely used in the bunch-by-bunch measurement of all ring accelerators.
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