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Fault detection continues to be a relevant and ongoing topic in multiterminal High Voltage Direct Current (MT-HVDC) grid protection. In MT-HVDC grids, however, high DC-fault currents result from a failure of a complex protective threshold in traditional protection schemes, making Voltage Source Converter (VSC) vulnerable to such potent transient currents. In this innovative single-ended DC protection scheme, multiple time window segments are used to consider the effects of the transient period across limiting inductors at each end of the link. Multiple segments of 0–0.8, 0.8–1.5, and 1.5–3.0 ms reduce relay failure and improve the sensitivity to high fault impedance while requiring minimal computational effort. It employs feature extraction tools such as Stationary Wavelet Transform and Random Search (RS)-based Artificial Neural Networks (ANNs) for detecting transmission line faults within DC networks. Its goal is to improve the accuracy and reliability of protective relays as a result of various fault events. Simulations showed that the proposed algorithms could effectively identify any input data segment and detect DC transmission faults up to 500 ohms. Accuracy for the first segment is 100% for fault impedance up to 200 ohms, whereas the second and third segments show 100% accuracy for high impedance faults up to 400 ohms. In addition, they maintain 100% stability even under external disturbances.

The accuracy and stability of beam position moni-tors(BPMs) are important for all kinds of measurement systems and feedback systems in particle accelerator field. A proper method detecting faulty beam position monitor or monitoring their stability could optimize accel-erator operating conditions. With development in ma-chine learning methods, a series of powerful analysis approaches make it possible for detecting beam position monitor’s stability. Here, this paper proposed a clustering analysis approach to detect the defective BPMs. The method is based on the idea that cluster centres are char-acterized by a higher density than their neighbours and by a relatively large distance from points with higher densi-ties. The results showed that clustering by fast search and find of density peaks could classify beam data into dif-ferent clusters on the basis of their similarity. And that, aberrant data points could be detected by decision graph. So the algorithm is appropriate for BPM detecting and it could be a significant supplement for data analysis in accelerator physics., Proceedings of the 7\textsuperscript{th} Int. Beam Instrumentation Conf., IBIC2018, Shanghai, China

High degree of transverse field coherence is one of the unique properties of an FEL compared with a 3rd gen-eration storage ring light source. As a result, the FEL advances the development of innovative research and technology that was not previously feasible. A truly coherent source should be coherent in all orders de-scribed from the intensity correlation functions. In this paper, second order intensity correlation of FEL radia-tion is investigated based on the Hanbury Brown-Twiss intensity correlation method. The statistical properties of radiation produced from SASE was also investigated and compared with the statistical proper-ties of a phase-locked laser. The results show that the statistical properties of a SASE mode behave as a cha-otic source, which is significantly different from the properties of a phase-locked laser beam., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

During the past several years a digital BPM (DBPM) processor has been developed at the SINAP. After continuous development and optimization, the processor has been finalized and has come to batch application on the signal processing of cavity BPMs and stripline BPMs at the Dalian Coherent Light Source (DCLS) and the Shanghai Soft X-ray FEL (SXFEL). Tests have been done to evaluate the performances, such as the noise level, the SNR and the cross talk. The system resolution of the cavity and stripline BPMs can achieve 1um and 10um respectively. The test results on the Shanghai Deep-Ultra-Violet (SDUV) and the DCLS will be introduced., Proceedings of the 5th Int. Beam Instrumentation Conf., IBIC2016, Barcelona, Spain

A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility (SSRF) storage ring. The electron beam size is derived by unfolding the radiation image and the point spread function (PSF) with deconvolution techniques. The performance of the pinhole is determined by the accuracy of the PSF measurement. This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes. Applying this method at SSRF, the PSF value of the pinhole is revised from 37 to 44 μm. The deviation in beam size between the theoretical value and the measured value is minimized to 4% after calibration. This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5 μm.

This article proposes a new test method to evaluate the performance of cavity beam position monitors using the actual beam as the exciting signal. The new method sepa-rates the signals of different modes and improves the measurement accuracy by eliminating unwanted cou-plings from other sources., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

High current and stable beams are preferred to a light source, so the suppression of the oscillations due to the frequent injections during top-off operations get the attention at the Shanghai Synchrotron Radiation Facility (SSRF). To evaluate the possibility of further optimizations, a bunch-by-bunch position monitor is used to study the behavior of the injected bunch. The injected part is isolated from the stored one by decomposing the position matrix of all the bunches in the storage ring. Frequency feature, motion lifetime and other characteristic parameters of the injection mode have been compared with those of the stored mode., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

An SR interferometer, which was used to monitor the transverse beam size in the SSRF ring, had been implemented and put into operation since 2009. The direct projection and curve fitting was adopted for raw image data processing. Any CCD alignment error could introduce some beam size measurement error in this case. Using primary component analyzing (PCA) method to process raw image data, the horizontal and vertical distribution information can be decoupled and the misalignment information of CCD can be derived. Beam experiment results will be discussed in this paper., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

Shanghai Soft X-ray FEL Test Facility (SXFEL) has started the infrastructure construction in 2015. All beam diagnostic systems are under processing and measurement, including C-band Low-Q cavity BPMs. This paper presents the progress of the cavity BPM system, including design and the measurements on a lab platform. Measurements shown that the cavity BPM frequency is 4.7GHz±8MHz, and the complete test platform verify that the cavity BPM system, which including signal processing electronics can work as expected., Proceedings of the 4th International Beam Instrumentation Conference, IBIC2015, Melbourne, Australia

As a user facility, the reliability and stability are very important. Besides using high-reliability hardware, the rapid fault diagnosis, data mining and predictive analytic s are also effective ways to improve the efficiency of the accelerator. A beam data logging system was built at SSRF, which was based on NoSQL database. The logging system stores beam parameters under some predefined conditions. The details of the system will be reported in this paper., Proceedings of the 15th Int. Conf. on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2015, Melbourne, Australia

An intelligent trigger abnormal beam operation monitoring processor has been designed at the SSRF. By applying digital signal processing algorithms in FPGA, the processor keeps monitoring the beam operation status. It will output a trigger signal and store the turn-by-turn beam position data when abnormal events detected. The abnormal events include injection, beam loss, and abnormal disturbance. This ability makes the processor a powerful tool for abnormal operation causes analysing and machine study., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Digital BPM processor with turn-by-turn capability has been widely used in synchrotron radiation facilities over the world, which is proved to be very useful and powerful for daily operation and linear optics study but not good enough in the case of individual bunch information required. In order to sufficient individual bunch diagnostics requirements a development plan of the next generation DBPM processor with bunch-by-bunch capability has been initiated in SINAP since 2012. The whole development was divided into three steps: a concept processor based on digital oscilloscope IOC, an algorithm prototype processor based on commercial high speed ADC board, and a custom designed dedicated processor. The progress of this work and several preliminary beam experiments will be discussed in this paper., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA

Beam position is one of the most important parameters in a particle accelerator. The more accurate and precise the measurement system is, the more features of the beam dynamics could be revealed. A method called model-independent analysis (MIA) takes advantage of multiple beam position monitors (BPM) on the storage ring to obtain the actual beam positions by removing the random noise of each BPM. Inspired by MIA, the original voltage waveforms obtained from the electrodes of a single BPM can also be decomposed to get the beam position information. This article discusses the results of the experiments and the evaluation of the performance of the BPM at the Shanghai Institute of Applied Physics., Proceedings of the 6th Int. Particle Accelerator Conf., IPAC2015, Richmond, VA, USA