Na Wang

The space-charge tune shift is a critical issue in circular proton, heavy-ion, and also low energy electron storage accelerators. Recently, some special electron rings with energies of several hundred MeV, nanometer-scale bunch lengths, and micrometer-scale bunch spacings have been proposed. In these novel rings, a significant longitudinal space-charge tune shift could be predicted by conventional methods. However, these methods may not be suitable when the bunches are extremely short. To address this issue, we derive a new set of formulas to calculate the longitudinal space-charge tune shift, which is applicable to arbitrary bunch lengths. These formulas incorporate the multibunch effects on the longitudinal space-charge tune shift, which have not been included in previous analyses of longitudinal space-charge tune shift calculations. The calculation results indicate that the tune shift predicted by our formulas is noticeably smaller than that obtained using the classical method. Moreover, our analysis demonstrates that the multibunch effect is not dominant in the longitudinal direction, even when the bunch spacing is extremely small.

In storage ring-based synchrotron radiation light sources, in-vacuum undulators (IVUs) are widely used considering their advantages of short period length and high field quality. The impedance of the IVU and heat load deposition due to the beam passage are among the main concerns during the design and operation of the IVU. In this work, both transverse and longitudinal trapped modes are investigated, and novel mitigation strategies to reduce the impedance are proposed. Additionally, the longitudinal broadband impedance increase introduced by the bulge flexible taper transitions is presented. To obtain comprehensive and reliable information on the impedance, laboratory bench measurements are performed to identify the longitudinal and transverse impedance of the IVU experimentally. A reasonably good agreement was reached between the numerical predictions and the measurements.

Synchrotron light sources are powerful platforms for cutting-edge, multidisciplinary research, with dozens currently in operation, construction or commissioning worldwide. It is widely recognized that different research areas have specific demands for source capabilities. For the majority of synchrotron facilities, delivering high-brightness, high-flux synchrotron radiation stably through high-current electron beams is the primary mode of operation. However, there is also a significant demand for timing experiments to study dynamic processes. In response, many synchrotron facilities offer specialized or hybrid timing modes. In this paper, we propose a novel method that combines a double RF system and deflecting cavities to generate pairs of X-ray pulses in electron storage rings with adjustable transverse separation and time delay. This approach holds the potential to enable new experimental possibilities, such as X-ray pump and X-ray probe studies, or capturing information from two temporal points in a dynamic process using two X-ray probes simultaneously. We analyze the fundamental characteristics of this method, present a conceptual design, and demonstrate through simulations that the scheme can achieve adjustable transverse separation of the two X-ray pulses with tunable time delay on the order of 100 ps.

Space-charge tune shifts can affect the beam quality in storage rings. Laslett’s method, a classical approach for calculating space-charge tune shifts, may not hold valid assumptions for rings with extremely short bunches and small bunch spacing, such as in steady-state microbunching (SSMB) storage rings. To overcome this limitation, we have developed new formulas that are suitable for arbitrary bunch lengths and spacings for calculating space-charge tune shifts. Additionally, simplified formulas have been provided for the calculations of space-charge tune shifts specifically in the context of extremely short bunch lengths. Numerical computations were carried out to demonstrate the validity of these newly derived formulas. Moreover, the formulas were applied to compute the space-charge tune shifts in an SSMB storage ring characterized by typical parameters. Published by the American Physical Society 2024

The Circular Electron Positron Collider is a double ring lepton collider covering beam energy from 45 GeV (Z) to 180 GeV (tt-bar). Beam coupling impedance and the collective effects that are triggered by the impedance are important subjects when targeting high machine performance of an electron positron collider. A robust impedance model is required for the instabilities evaluations as well as to investigate their possible mitigations. Meanwhile, a thorough investigation on the collective effects is essential to identify the critical issues on the beam instabilities. In this paper, a detailed impedance model has been built for the collider ring and dominant impedance contributors have been identified by evaluating the effective impedances. The potential collective instabilities driven by the impedance are also discussed.

Undulators with small gap have been widely used in various light sources all over the world for the demand of high brilliance. A large number of in-air undulators with small gap will be installed in the storage ring of the High Energy Photon Source, and become one of the important impedance contributors. Antechambers are adopted for the bypass of the synchrotron radiations, as well as to reach high vacuum in the beam pipe with small aperture. Due to the asymmetric structure of the vacuum chamber, monopole wakefield in the transverse planes will be excited by the beam passage. In addition, photon absorbers will be installed in the vacuum chamber of the in-air undulators to shield the downstream components, which will introduce extra resonances in the transverse planes. In this paper, a series of numerical simulations are performed to investigate the impedance of the in-air undulator vacuum chamber. The high order modes generated by the photon absorber and their mitigations are also investigated.