Li Wei-Min

The beam loss monitoring system for HLS storage ring

Abstract A beam loss monitoring system has been established at HLS. This paper gives its principle and scientific grounds. Study on the rings TBA structure and utilization of Monte-Carlo calculation to the shower electrons is important in its design. The system composition and performance are also introduced. The detector BLMs, data acquisition devices and host PC are linked via CAN bus. This system is helpful to analyze beam loss distribution and regulate the machine operation parameters.

Lattice study for the HLS-II storage ring *

The Hefei Light Source (HLS) is undergoing a major upgrade project, named HLS-II, to obtain lower emittance and more insertion device straight sections. Undulators are the main insertion devices in the HLS-II storage ring. In this paper, based on the built database of lattice parameters for the HLS-II storage ring obtained by the global scan method, we use the quantity related to the brightness of undulator radiation to more directly search for high brightness lattices. Lattice solutions for achromatic and non-achromatic modes have been easily found with lower emittance, smaller beta functions at the center of insertion device straight sections and lower dispersion in non-zero dispersion straight sections compared with the previous lattice solutions. In this paper, the superperiod lattice with alternating high and low horizontal beta functions in long straight sections for the achromatic mode is studied using the multiobjective particle swarm optimization algorithm.

Lattice optimization for the HLS-II storage ring

The upgrade project of the Hefei Light Source (HLS), named HLS-II, is under way, which includes the reconstruction of its storage ring. The HLS-II storage ring has lower emittance and more straight sections available for insertion devices as compared with the present HLS storage ring. The scan method is applied to the linear lattice optimization for the HLS-II storage ring to get thorough information about the lattice. To reduce the amount of computation, several scans with different grid spacing values are conducted. In addition, the calculation of the chromatic sextupole strength for the achromatic mode is included in the scan, which is useful for nonlinear lattice optimization. To better analyze the obtained solutions in the scan, the lattice properties and the variables of quadrupole strengths are statistically analyzed. The process of selecting solutions is described in detail, including the choice of the working point, the settings for the emittance and optical functions, and the restriction of maximum magnet strength. Two obtained lattices, one for the achromatic mode and the other for the non-achromatic mode, are presented, including their optical functions and optimized dynamic apertures.

The magnet design for the HLS storage ring upgrade project

In order to improve the performance of the Hefei Light Source (HLS), in particular to get higher brilliance synchrotron radiation and increase the number of straight section insertion devices, an upgrade project called HLSII will be launched soon. The storage ring lattice, which has a double bend achromatic structure with four periods, comprises eight dipoles, 32 quadrupoles and 32 combined function sextupoles. The design and analysis of the magnets are shown in this paper, along with the optimization of the multipurpose combined function magnet, which consists of three magnets: skew quadrupole, horizontal dipole and vertical dipole, with the main sextupole magnet. This type of magnet is the first one that has been designed and used in China. The mechanical design and fabrication procedures for the magnets are also presented.

Preliminary study of the higher-harmonic cavity for HLS- II

A higher-harmonic cavity will be used to increase the beam lifetime and suppress coupled-bunch instabilities for Hefei Light Source- II. In this paper, results simulated by the particle-tracking model confirm that tuning in the harmonic cavity may suppress the parasitic coupled-bunch instabilities. The factors calculated for lifetime improvement are larger than 2.5. The 3rd and 4th harmonic cavities have been designed. In particular, the absorbers and antenna couplers are applied in harmonic cavities to damp the higher order modes. Finally, the 4th harmonic cavity similar to the Dukes RF cavity will be used for HLS- II.

Physical design of a 10 MeV LINAC for polymer radiation processing

In China, polymer radiation processing has become one of the most important processing industries. The radiation processing source may be an electron beam accelerator or a radioactive source. Physical design of an electron beam facility applied for radiation crosslinking is introduced in this paper because of its much higher dose rate and efficiency. Main part of this facility is a 10 MeV travelling wave electron linac with constant impedance accelerating structure. A start to end simulation concerning the linac is reported in this paper. The codes Opera-3d, Poisson-superfish and Parmela are used to describe electromagnetic elements of the accelerator and track particle distribution from the cathode to the end of the linac. After beam dynamic optimization, wave phase velocities in the structure have been chosen to be 0.56, 0.9 and 0.999 respectively. Physical parameters about the main elements such as DC electron gun, iris-loaded periodic structure, solenoids, etc, are presented. Simulation results proves that it can satisfy the industrial requirement. The linac is under construction. Some components have been finished. Measurements proved that they are in a good agreement with the design values.

Linear Optics Compensation of the Superconducting Wiggler in HLS

Hefei Light Source is a dedicated VUV light source. A superconducting wiggler magnet, whose peak magnetic field is 6 T, was installed on the storage ring to generate hard X-ray radiation. With the compensation of tune shift due to superconducting wiggler, beam was successfully stored, while the beam lifetime was degenerated much. In order to cure the beam lifetime, some simple hardware improvement was made and linear optics compensation scheme was intensively studied by two calculation methods. Calculation results showed that focusing perturbation from wiggler can’t be eliminated completely for HLS and a new scenario of compensation, whose purpose is to remove tune shifts and to suppress large beta-function distortions, was brought forward. Experimental result has demonstrated the effectiveness of this new compensation scheme and the beam lifetime was recovered to original level without wiggler.

Extraordinary optical transmission through a subwavelength composite hole-pillar array

We numerically investigate the transmission properties of a subwavelength composite hole-pillar array. As the radius of the pillar increases, the transmission properties experience a complex evolution. It is found that the magnetic dipole resonance of the pillar suppresses the surface plasmon polariton resonance (SPPR) at the gold-air interface. There are two strong transmission peaks associated with the magnetic dipole resonance of pillar and SPPR at the gold-silica interface. A peak associated with magnetic quadrupole resonance of the pillar is observed. Moreover, there is a weak peak associated with the coupling between the whispering-gallery plasmon (WGP) mode and magnetic dipole. Our work is helpful for making a dual band optical filter.

A possible approach to reduce the emittance of HLS- II storage ring using a Robinson wiggler

In this paper, we present some preliminary studies on using a Robinson wiggler to reduce the horizontal beam emittance in the Hefei Light Source II (HLS- II) storage ring. A proof-of-principle lattice demonstrates that it is possible to reduce its emittance by 50% with a 2-meter long wiggler. This encouraging result suggests a feasible option to significantly improve the machine performance at a relatively low cost.

The upgraded scheme of Hefei Light Source

To enhance the performance of Hefei Light Source, which was designed and constructed two decades ago, an upgrade project would be carried out in the near future. The detail upgrade scheme was described in this paper. Firstly, the magnet lattice of storage ring should be reconstructed with 4 DBA cells, whose advantages are lower beam emittance and more straight section available for insertion devices. Secondly, the beam diagnostics, main power supply, transverse and longitudinal multi‐bunch feedback, beam control and manipulation system would be upgrade to improve the beam orbit stability. Finally, the injection system of storage ring and injector, which is composed of electron linac and beam transfer line, would be updated in order to assure smooth beam accumulation process under new low emittance lattice. With above improvement, it is hopeful to increase the brilliance of Hefei Light Source by two orders approximately. After three‐year upgrade project, the performance of HLS would meet the demands of advanced SR users.To enhance the performance of Hefei Light Source, which was designed and constructed two decades ago, an upgrade project would be carried out in the near future. The detail upgrade scheme was described in this paper. Firstly, the magnet lattice of storage ring should be reconstructed with 4 DBA cells, whose advantages are lower beam emittance and more straight section available for insertion devices. Secondly, the beam diagnostics, main power supply, transverse and longitudinal multi‐bunch feedback, beam control and manipulation system would be upgrade to improve the beam orbit stability. Finally, the injection system of storage ring and injector, which is composed of electron linac and beam transfer line, would be updated in order to assure smooth beam accumulation process under new low emittance lattice. With above improvement, it is hopeful to increase the brilliance of Hefei Light Source by two orders approximately. After three‐year upgrade project, the performance of HLS would meet the demands of adv...