Improvement and correction for transverse emittance diagnosis based on Q-scanning techniques

Precise transverse emittance assessment in electron beams is crucial for advancing high-brightness beam injectors. As opposed to intricate methodologies that use specialized devices, quadrupole focusing strength scanning (Q-scanning) techniques offer notable advantages for various injectors owing to their inherent convenience and cost-effectiveness. However, their stringent approximation conditions lead to inevitable errors in practical operation, thereby limiting their widespread application. This study addressed these challenges by revisiting the analytical derivation procedure and investigating the effects of the underlying approximation conditions. Preliminary corrections were explored through a combination of data processing analysis and numerical simulations. Furthermore, based on theoretical derivations, virtual measurements using beam dynamics calculations were employed to evaluate the correction reliability. Subsequent experimental validations were performed at the Huazhong University of Science and Technology injector to verify the effectiveness of the proposed compensation method. Both the virtual and experimental results confirm the feasibility and reliability of the enhanced Q-scanning-based diagnosis for transverse emittance in typical beam injectors operating under common conditions. Through the integration of these corrections and compensations, enhanced Q-scanning-based techniques emerge as promising alternatives to traditional emittance diagnosis methods.