Wakefield Studies for the Step Structure and the Skin Depth of Coated Dielectric Tubes

Wakefield issues are always important research objects in free electron laser (FEL) facilities. Since the wakefield in free electron laser facilities usually leads to a decrease of FEL performance, the research of the wakefield impacts is of great significance. Step structures are almost ubiquitous in the overall undulator section of an FEL facility, which always generate critical wakefields. In this paper, we systematically analyze and summarize the wakefield characteristics of step structures including the step-in structure and the step-out structure. In addition, the skin depth issue of the wakefield is still controversial. We study the skin depth of the wakefield field in the vacuum chamber of the kicker in the SHINE, which is made of the dielectric pipe. We proposed the conception of ¿effective skin depth¿ from two different perspectives and wrote simulation codes to calculate the ¿effective skin depth¿. We hope these methods could provide new mentalities for related research in the future.