Measurement of the transfer function for a spoke cavity of C-ADS Injector I

TL;DR

This paper presents a method to measure the transfer function of a spoke cavity in C-ADS, identifying mechanical eigenmodes and their impact on cavity stability, leading to improved RF system reliability.

Contribution

It introduces a measurement approach for the transfer function of spoke cavities and identifies key mechanical eigenmodes affecting cavity stability.

Findings

Identification of 206 Hz and 311 Hz eigenmodes excited by Lorentz force

Detection of 12 mechanical eigenmodes from 0 to 500 Hz via piezo tuner

Implementation of measures to mitigate pressure fluctuations and mechanical resonances

Abstract

The spoke cavities mounted in the China Accelerator Driven sub-critical System (C-ADS) have high quality factor(Q) and very small bandwidth, making them very sensitive to mechanical perturbations whether external or self-induced. The transfer function is used to characterize the response of the cavity eigen frequency to the perturbations. This paper describes a method to measure the transfer function of a spoke cavity. The measured Lorentz transfer function shows there are 206 Hz and 311 Hz mechanical eigenmodes excited by Lorentz force in the cavity of C-ADS, and the measured piezo fast tuner transfer function shows there are 12 mechanical eigenmodes from 0 to 500 Hz. According to these results, some effective measures have been taken to weaken the influence from helium pressure fluctuation, avoid mechanical resonances and improve the reliability of RF system.