Intra-beam scattering and beam lifetime in a candidate lattice of the soft X-ray diffraction-limited storage ring for the upgraded SSRF

New-generation synchrotron light sources are being designed and operated worldwide to provide brighter radiation by reducing the beam emittance to X-ray diffraction limits.Intra-beam scattering(IBS)and Touschek scattering in such facilities are significant and require attention because of their ultra-low emittance.Therefore,cure strategies need to be carefully studied to obtain highquality photon beams.For the Shanghai Synchrotron Radiation Facility Upgrade(SSRF-U),a candidate lattice of the storage ring,reaching the soft X-ray diffraction limit,was designed and presented for the first time in this study.The emittance growth and beam lifetime in the SSRF-U storage ring were studied using particle simulations for a series of different machine configurations.The gains with RF frequencies of 100 MHz and 500 MHz were compared.Along with a better filling pattern,a more suitable RF frequency was adopted in the SSRF-U.The variations in the equilibrium beam emittance with beam coupling and bunch-lengthening were identified using simulations.Optimal beam coupling and required bunch-lengthening for the SSRF-U storage ring were thus determined.The fitness of the beam energy in the SSRF-U was subsequently assessed using the obtained parameters.Additionally,the Touschek scattering and beam lifetime were calculated,and an acceptable total beam lifetime was obtained.

Effective improvement of beam lifetime based on radiofrequency phase modulation at the HLS-II storage ring

A radiofrequency(RF)phase modulation method is applied to the Hefei Light Source II storage ring to deeply investigate its longitudinal beam characteristics and improve the beam lifetime.A theoretical analytical model and corresponding experimental measurements of single bunch length and island phenomena are examined.From a series of online machine experiments,we demonstrate that the suitable phase modulation amplitude is 0.02 rad,corresponding to an optimum modulation frequency ranging from 19.6 to 20.7 kHz of the RF system.Furthermore,the overall beam lifetime can be increased by a factor of 2.38 as a result of the beam dilution effect.

Simulation of beam gas coulomb scattering in HALS

In conventional research on beam gas coulomb scattering （BGCS）, only the related beam lifetime using the analytical method is studied. In this paper, using the particle-in-cell Monte Carlo collisions （PIC-MCC） method, we not only simulated the beam lifetime but also explored the effect of BGCS on the beam distribution. In order to better estimate the effect on particle distribution, we study the ultra-low emittance electron beam. Here we choose the HeFei Advanced Light Source. By counting the lost particles in a certain time, the corresponding beam lifetime we simulated is 4.8482 h/13.8492 h in x/y, which is very close to the theoretic value （5.0555 h/13.7024 h in x/y）. By counting the lost particles relative to the collided particles, the simulated value of the loss probability of collided particles is 1.3431e-04, which is also very close to the theoretical value （1.3824e-04）. Besides, the simulation shows there is a tail in the transverse distribution due to the BGCS. The close match of the simulation with the theoretic value in beam lifetime and loss probability indicates our simulation is reliable.

Analysis and correction of linear optics errors,and operational improvements in the Indus-2 storage ring

Estimation and correction of the optics errors in an operational storage ring is always vital to achieve the design performance. To achieve this task, the most suitable and widely used technique, called linear optics from closed orbit（LOCO） is used in almost all storage ring based synchrotron radiation sources. In this technique, based on the response matrix fit, errors in the quadrupole strengths, beam position monitor（BPM） gains, orbit corrector calibration factors etc. can be obtained. For correction of the optics, suitable changes in the quadrupole strengths can be applied through the driving currents of the quadrupole power supplies to achieve the desired optics. The LOCO code has been used at the Indus-2 storage ring for the first time. The estimation of linear beam optics errors and their correction to minimize the distortion of linear beam dynamical parameters by using the installed number of quadrupole power supplies is discussed. After the optics correction, the performance of the storage ring is improved in terms of better beam injection/accumulation, reduced beam loss during energy ramping, and improvement in beam lifetime. It is also useful in controlling the leakage in the orbit bump required for machine studies or for commissioning of new beamlines.

Theoretical analysis of BLM system for HLS Ⅱ

Hefei Light Source （HLS） is being upgraded to HLS Ⅱ. Its emittance will be much lower than before, therefore the Touschek scattering will increase significantly and become the dominant factor of beam loss. So it is necessary to build a new beam loss monitoring （BLM） system that, in contrast to the old one, is able to obtain the quantity and position information of lost electrons. This information is useful in the commissioning, troubleshooting, and beam lifetime studying for HLS Ⅱ. This paper analyzes the distribution features of different kinds of lost electrons, introduces the operation parameters of the new machine and discusses how to choose proper monitoring positions. Based on these comprehensive analyses, a new BLM system for HLS Ⅱ is proposed.