Statistical Analysis of the Eigenmode Spectrum in the SRF Cavities with Mechanical Imperfections [PowerPoint]

Abstract

The superconducting radio frequency (SRF) technology is progressing rapidly over the last decades toward high accelerating gradients and low surface resistance making feasible the particle accelerators operation with high beam currents and long duty factors. However, the coherent RF losses due to high order modes (HOMs) excitation becomes a limiting factor for these regimes. In spite of the operating mode, which is tuned separately, the parameters of HOMs vary from one cavity to another due to finite mechanical tolerances during cavities fabrication. It is vital to know in advance the spread of HOM parameters in order to predict unexpected cryogenic losses, overheating of beam line components and to keep stable beam dynamics. In this paper we present the method of generating the unique cavity geometry with imperfections while preserving operating mode frequency and field flatness. Based on the eigenmode spectrum calculation of a series of randomly generated cavities, we can accumulate the data for the evaluation of the HOM statistics. Finally, we describe the procedure for the estimation of the probability of the resonant HOM losses in the SRF resonators. The study of these effects leads to specifications of SRF cavity and cryomodule and can significantly impact the efficiency and reliability of the machine operation.

C$^3$ Demonstration Research and Development Plan

“…To provide the required luminosity for a linear collider, it is critical to reduce emittance dilution in the main linac from machine tolerances such as cavity misalignments and imperfections [28,29]. For the C 3 linac, misalignments can arise from individual cavity misalignments and changes in the properties of coupled HOMs in a cryomodule with misaligned and deformed C 3 cavities.…”

Electron Beam Shaping and Its Applications

“…The input-power coupler provides the RF power to the cavity while the HOM couplers damp the harmful trapped fields potentially excited as long trains of bunches are accelerated in the SRF cavities. In addition to the introduced field asymmetry, the coupler can also impact the beam via geometrical wakefields [37,38].…”