In Situ Measurement of Mechanical Vibrations of a 4-Rod RFQ at GSI

TL;DR

This study used a laser vibrometer to directly measure mechanical vibrations of a 4-rod RFQ during operation, confirming their role in rf reflection modulations and providing insights for improved mitigation.

Contribution

First in situ laser vibrometer measurements of RFQ mechanical vibrations, enhancing understanding of vibration excitation and potential mitigation strategies.

Findings

Vibrations cause rf reflection modulations.

Vibrations are excited by rf pulses.

Insights enable better vibration mitigation.

Abstract

A new 4-rod RFQ was commissioned at the UNILAC in 2009, it went into operation in 2010. At high rf amplitudes strong modulations of the rf reflection emerge. They are attributed to mechanical oscillations of the rods, excited by the rf pulse. As these modulations could so far only be seen during the rf pulse by means of rf measurements, a direct observation of the mechanical vibrations was desirable. Such measurements have been conducted using a commercial laser vibrometer, allowing the investigation of the mechanical behavior of the RFQ in situ and independent of the presence of rf power. Results from investigations under standard operation conditions confirm the vibrations as the source of the modulations observed by rf as well as their excitation by the rf pulse. Further measurements revealed more details about the excitation process, leading to a better understanding and possibly new ways of mitigation.