Beam-based HOM Study in Third Harmonic SC Cavities for Beam Alignment at FLASH

TL;DR

This study analyzes how beam position affects higher order modes in third harmonic cavities at FLASH, aiming to improve beam alignment by using HOM signals for precise position monitoring.

Contribution

It provides the first analysis of HOM dependency on beam position in third harmonic cavities at FLASH, comparing various analysis methods for accurate beam position detection.

Findings

HOM signals vary with beam position, enabling beam alignment.

Dipole modes are effective for beam position monitoring.

Different analysis methods are evaluated for accuracy.

Abstract

An electron beam entering an accelerator cavity excites higher order modes (HOM). These are radiated to HOM couplers and subsequently damped. They can also be used to facilitate beam position monitoring. The modes excited by off-axis beams are the focus of this study. Results are presented on the first analysis of HOM dependency on the beam position for the third harmonic cavities at FLASH. The analysis is based on the beampipe and cavity dipole modes. Various analysis methods are used and compared to satisfy the needs emerging from the characteristics of those modes. The electric center of each mode is observed by looking for the minima of the HOM signals of different beam positions. A single electron bunch per RF pulse is used.