Impact of coherent wiggler radiation impedance in Tau-Charm factories

TL;DR

This paper investigates how coherent wiggler radiation affects beam stability in Tau-Charm factories, providing improved models and simulations relevant for next-generation collider design.

Contribution

It systematically analyzes CWR impedance effects, revisits instability thresholds, and applies models to the Super Tau-Charm Facility design.

Findings

CWR can significantly impact microwave stability thresholds.

Improved impedance models better predict beam behavior.

Simulations show potential stability issues in proposed collider configurations.

Abstract

Coherent synchrotron radiation (CSR) has long been recognized as a significant source of longitudinal impedance driving microwave instability in electron storage rings. In the pursuit of higher luminosity, next-generation circular $e^+e^-$ colliders operating in the few-GeV energy range, such as B-factories and Tau-Charm factories, are being designed with low-emittance beams and high beam currents. Damping wigglers are commonly introduced to reduce damping times and control beam emittance. In this study, we systematically investigate the impact of coherent wiggler radiation (CWR), a specific form of CSR generated within wigglers, on beam stability in Tau-Charm factories. We revisit the threshold conditions for CWR-induced microwave instability and evaluate its effects under realistic lattice configurations of collider rings. Furthermore, we examine theoretical models of longitudinal CWR impedance and identify improved formulations that better capture its influence. As an illustrative example, the developed CWR impedance models are applied to simulate beam stability in the Super Tau-Charm Facility currently under design in China.