CLIC Wake Field Monitor as a detuned Cavity Beam Position Monitor: Explanation of center offset between TE and TM channels in the TD26 structure

TL;DR

This paper investigates the discrepancy between TE and TM channel measurements in the CLIC Wake Field Monitor, using simulations and measurements to understand the cause and improve beam position accuracy.

Contribution

It explains the center offset between TE and TM channels in the WFM as a detuned cavity effect, aiding future beam position measurements in CLIC.

Findings

Identified the cause of TE and TM channel offset as a detuned cavity effect.

Proposed methods to improve position resolution near the structure center.

Discussed implications for sign determination of beam offset.

Abstract

The Wake Field Monitor (WFM) system installed on the CLIC prototype accelerating structure in CERN Linear Accelerator for Research (CLEAR) has two channels for each horizontal/vertical plane, operating at different frequencies. When moving the beam relative to the aperture of the structure, a disagreement is observed between the center position of the structure as measured with the two channels in each plane. This is a challenge for the planned use of WFMs in the Compact Linear Collider (CLIC), where they will be used to measure the center offset between the accelerating structures and the beam. Through a mixture of simulations and measurements, we have discovered a potential mechanism for this, which is discussed along with implications for improving position resolution near the structure center, and the possibility determination of the sign of the beam offset.