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Cheng, Weixing

Publications and source records attributed to Cheng, Weixing.

13 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Dedicated beam position monitor pair for model-independent lattice characterization at NSLS-II

This paper reports recent lattice characterization results obtained at the National Synchrotron Light Source II (NSLS-II) storage ring, conducted without reliance on a lattice model. A pair of beam position monitors (BPMs) with bunch-by-bunch (B$\times$B) resolution, were recently installed in a section of the storage ring free of magnetic fields. The new BPM pair measured the beam, or bunch’s transverse Poincaré map precisely after the beam was excited. Linear one-turn-matrices (OTM) were then derived, and from these, the 4-dimensional coupled Twiss parameters were extracted at the locations of the BPM pair. By normalizing beam oscillation amplitudes with the Twiss parameters, the global action-variables were obtained. Additionally, these action-variables facilitated the measurement of the local Twiss parameters observed by other BPMs independent on lattice model. This method is general, and particularly useful in certain scenarios such as a round beam mode in a diffraction-limited light source ring. We applied it to assess both weakly and strongly coupled lattices at the NSLS-II ring. Through analysis of the strongly coupled lattice, the quadrupole tilt errors were estimated to be less than 400 μrad. Utilizing the BPMs’ B$\times$B resolution, for the first time we observed the variations of the linear lattice along a long bunch-train.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Measurement and analysis of fast transient instabilities

In this study, a novel beam diagnostics technique to detect fast beam transient instabilities and glitches has been developed at National Synchrotron Light Source II (NSLS-II). Vertical spikes of beam size and centroid have been observed occasionally and randomly during high current operations. These spikes are believed to be caused by ion instabilities associated with vacuum activity localized in the ring. With the functionality of gated beam position monitor (BPM), the newly developed technique utilizes turn-by-turn (TBT) data to detect beam centroid glitches. Whenever one turn trajectory deviates from a predefined window, a global control event is generated to trigger an online TBT data acquisition. The data acquisition is synchronized for all BPMs around the ring. In the meantime, the bunch-by-bunch (BxB) data, which is acquired from a single dedicated feedback BPM, has also been collected for analyzing possible coupled bunch instabilities (CBI). In addition to CBI caused mainly by ion bursts, other types of fast transient motions, such as, the top-off residual disturbance and fast orbit disturbance, have been captured with the new tool. Lastly, the sources of the glitches can be approximately localized with the synchronized TBT data from multiple BPMs around the ring.

43 PARTICLE ACCELERATORS↗
DOE OSTI2018

Beam position monitor gate functionality implementation and applications

We introduce a novel technique to implement gate functionality for the beam position monitors (BPM) at the National Synchrotron Light Source II (NSLS-II). The functionality, now implemented in FPGA, allows us to acquire two separated bunch-trains’ synchronized turn-by-turn (TBT) data simultaneously with the NSLS-II in-house developed BPM system. The gated position resolution is improved about 3 times by narrowing the sampling width. Experimentally we demonstrated that the machine lattice could be transparently characterized with the gated TBT data of a short diagnostic bunch-train Cheng et al., 2017; Li et al., 2017. Other applications, for example, precisely characterizing storage ring impedance/wake-field through recording the beam positions of two separated bunch trains has been experimentally demonstrated.

43 PARTICLE ACCELERATORS↗
DOE OSTI2017

Experimental evidence of ion-induced instabilities in the NSLS-II storage ring

Fast ion instability has been identified as one of the most prominent instabilities in the recently constructed NSLS-II storage ring at Brookhaven National Laboratory. At a relatively low beam current (~ 25 mA) multi-bunch fills, ion-induced instabilities have already been observed during the early stages of machine commissioning. At present user operation with 250 mA in ~1000 bunches, the fast ion still remains the dominant instability, even after months of vacuum conditioning at high current. Ion-induced dipole motions of the electron beam have been suppressed using the transverse bunch-by-bunch (BxB) feedback system. However other adverse effects of this instability, such as the vertical beam size increase along the bunch train cannot be cured by the feedback system. Therefore, to achieve the NSLS-II design current of 500 mA while maintaining a small vertical beam emittance, it is important to further understand the fast ion instability and develop mitigation techniques. This paper reports on a series of ion-instability observations at various fill patterns and beam currents using start-of-art NSLS-II diagnostic tools.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

Beam measurements using visible synchrotron light at NSLS2 storage ring

Visible Synchrotron Light Monitor (SLM) diagnostic beamline has been designed and constructed at NSLS2 storage ring, to characterize the electron beam profile at various machine conditions. Due to the excellent alignment, SLM beamline was able to see the first visible light when beam was circulating the ring for the first turn. The beamline has been commissioned for the past year. Besides a normal CCD camera to monitor the beam profile, streak camera and gated camera are used to measure the longitudinal and transverse profile to understand the beam dynamics. Measurement results from these cameras will be presented in this paper. A time correlated single photon counting system (TCSPC) has also been setup to measure the single bunch purity.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

Beam Meassurements Using Visible Synchrotron Light at NSLSII Storage Ring

Visible Synchrotron Light Monitor (SLM) diagnostic beamline has been designed and constructed at NSLS2 storage ring, to characterize the electron beam profile at various machine conditions. Thanks for the excellent alignment, SLM beamline was able to see the first visible light when beam was circulating the ring for the first turn. The beamline has been commissioned for the past year. Besides a normal CCD camera to monitor the beam profile, streak camera and gated camera are used to measure the longitudinal and transverse profile to understand the beam dynamics. Measurement results from these cameras will be present in this paper. A time correlated single photon counting system (TCSPC) has been setup and measures the single bunch purity using visible light, preliminary TCSPC measurement result will be presented as well.

36 MATERIALS SCIENCE↗
DOE OSTI2015

NSLS-II SR Commissioning Report

The NSLS-II storage ring (SR) phase I commissioning has been successfully completed in May 12, 2014. In accordance to the project milestone, 25 mA average current was achieved in the storage ring with PETRA III 500 MHz 7-cell PETRA-III RF cavity but w/o ID’s and Landau cavities. In about 5 weeks we delivered a 3 GeV beam to the ring injection straight section, made the 1st turn around the ring, achieved hundreds of turns optimizing injection, stored beam having sextupoles and RF turned ON. Injection efficiency was achieved 95%, close orbit rms value is ~100 um, tune and chromaticity were measured and adjusted as desired, and beam lifetime was a few hours depending on the stored beam current. This report consists of a summary, a chronological part, the injector system performance in Ch3, SR commissioning experience in Ch4 and the outlook of remaining work in Ch5. The SR commissioning experience includes the software experience, hardware (timing, diagnostics, RF, vacuum, PS) operation experience, the strategy for initial injection beam to the stored beam, measurement of the linear optics and control to the desired value, nonlinear beam dynamics study, beam instability study, the subsystem reliability and fault study at different scenarios.

36 MATERIALS SCIENCE↗