A High Phase Advance Damped and Detuned Structure for the Main Linacs of Clic

TL;DR

This paper investigates high phase advance (HPA) structures for CLIC main linacs, aiming to reduce RF field group velocity and potentially lower electrical breakdown risks compared to standard designs.

Contribution

It introduces and studies a high phase advance (5π/6) structure for CLIC, analyzing its electromagnetic properties and mode behavior as an alternative to existing designs.

Findings

HPA structures have reduced group velocity compared to standard designs.

Fundamental and dipole modes are effectively characterized in the HPA structure.

HPA design shows potential for lower electrical breakdown risk.

Abstract

The main accelerating structures for the CLIC are designed to operate at an average accelerating gradient of 100 MV/m. The accelerating frequency has been optimised to 11.994 GHz with a phase advance of 2{\pi}/3 of the main accelerating mode. The moderately damped and detuned structure (DDS) design is being studied as an alternative to the strongly damped WDS design. Both these designs are based on the nominal accelerating phase advance. Here we explore high phase advance (HPA) structures in which the group velocity of the rf fields is reduced compared to that of standard (2{\pi}/3) structures. The electrical breakdown strongly depends on the fundamental mode group velocity. Hence it is expected that electrical breakdown is less likely to occur in the HPA structures. We report on a study of both the fundamental and dipole modes in a CLIC_DDS_HPA structure, designed to operate at 5{\pi}/6 phase advance per cell. Higher order dipole modes in both the standard and HPA structures are also studied.