arXiv subjects

Wei-Min Li

Publications and source records attributed to Wei-Min Li.

5 recordsLinked to original sources

arXiv2016

Compensation for Booster Leakage Field in the Duke Storage Ring

The High Intensity Gamma-ray Source (HIGS) at Duke University is an accelerator-driven Compton gamma-ray source, providing high flux gamma-ray beam from 1 MeV to 100 MeV for photo-nuclear physics research. The HIGS facility operates three accelerators, a linac pre-injector (0.16 GeV), a booster injector (0.16-1.2 GeV), and an electron storage ring (0.24-1.2 GeV). Because of proximity of the booster injector to the storage ring, the magnetic field of the booster dipoles close to the ring can significantly alter the closed orbit in the storage ring being operated in the low energy region. This type of orbit distortion can be a problem for certain precision experiments which demand a high degree of the energy consistency of the gamma-ray beam. This energy consistency can be achieved by maintaining consistent aiming of the gamma-ray beam, therefore, a steady electron beam orbit and angle at the Compton collision point. To overcome the booster leakage field problem, we have developed an orbit compensation scheme. This scheme is developed using two fast orbit correctors and implemented as a feedforward which is operated transparently together with the slow orbit feedback system. In this paper, we will describe the development of this leakage field compensation scheme, and report the measurement results which have demonstrated the effectiveness of the scheme.

physics.acc-ph↗

arXiv2016

Study of Magnetic Hysteresis Effects in a Storage Ring Using Precision Tune Measurement

With advances in accelerator science and technology in the recent decades, the accelerator community has focused on the development of next-generation light sources, for example the diffraction-limited storage rings (DLSRs), which requires precision control of the electron beam energy and betatron tunes. This work is aimed at understanding magnet hysteresis effects on the electron beam energy and lattice focusing in the circular accelerators, and developing new methods to gain better control of these effects. In this paper, we will report our recent experimental study of the magnetic hysteresis effects and their impacts on the Duke storage ring lattice using the transverse feedback based precision tune measurement system. The major magnet hysteresis effects associated with magnet normalization and lattice ramping are carefully studied to determine an effective procedure for lattice preparation while maintaining a high degree of reproducibility of lattice focusing. The local hysteresis effects are also studied by measuring the betatron tune shifts resulted from adjusting the setting of a quadrupole. A new technique has been developed to precisely recover the focusing strength of the quadrupole by returning it to a proper setting to overcome the local hysteresis effect.

physics.acc-ph↗

arXiv2015

First commissioning of the HLS-II storage ring

To meet the increasing requirements of synchrotron radiation users, the upgrade project to enhance the performance of Hefei Light Source (HLS), named HLS-II, was launched in 2010, and in 2014 the first commissioning of HLS-II was successfully completed. After the commissioning, the main design goals for the HLS-II storage ring have been achieved, with natural emittance of electron beam lower than 40 nm-rad at 800 MeV, five insertion devices installed in straight sections and root mean square (rms) jitter of closed orbit smaller than 4 μm, making HLS-II at a higher level among the same class of machines in the world. This paper reports on the results of the commissioning of the HLS-II storage ring, which includes linear optics correction, compensation of insertion devices effect and closed orbit feedback.

physics.acc-ph↗

arXiv2015

Improved step-by-step chromaticity compensation method for chromatic sextupole optimization

The step-by-step chromaticity compensation method for chromatic sextupole optimization and dynamic aperture increase was proposed by E. Levichev and P. Piminov (E. Levichev and P. Piminov, 2006 [1]). Although this method can be used to enlarge the dynamic aperture of storage ring, it has some drawbacks. In this paper, we combined this method with evolutionary computation algorithms, and proposed an improved version of this method. In the improved method, the drawbacks are avoided, and thus better optimization results can be obtained.

physics.acc-ph↗

arXiv2013

Strong ties promote the epidemic prevalence in susceptible-infected-susceptible spreading dynamics

Understanding spreading dynamics will benefit society as a whole in better preventing and controlling diseases, as well as facilitating the socially responsible information while depressing destructive rumors. In network-based spreading dynamics, edges with different weights may play far different roles: a friend from afar usually brings novel stories, and an intimate relationship is highly risky for a flu epidemic. In this article, we propose a weighted susceptible-infected-susceptible model on complex networks, where the weight of an edge is defined by the topological proximity of the two associated nodes. Each infected individual is allowed to select limited number of neighbors to contact, and a tunable parameter is introduced to control the preference to contact through high-weight or low-weight edges. Experimental results on six real networks show that the epidemic prevalence can be largely promoted when strong ties are favored in the spreading process. By comparing with two statistical null models respectively with randomized topology and randomly redistributed weights, we show that the distribution pattern of weights, rather than the topology, mainly contributes to the experimental observations. Further analysis suggests that the weight-weight correlation strongly affects the results: high-weight edges are more significant in keeping high epidemic prevalence when the weight-weight correlation is present.

physics.soc-ph↗