RF-thermal-structural analysis of a waveguide higher order mode absorber

Abstract

For an ongoing high current cryomodule project, a total of 5 higher order mode (HOM) absorbers are required per cavity. The load is designed to absorb Radio Frequency (RF) heat induced by HOMs in a 748.5MHz cavity. Each load is targeted at a 4 kW dissipation capability. Water cooling is employed to remove the heat generated in ceramic tiles and by surface losses on the waveguide walls. A sequentially coupled RF-thermal-structural analysis was developed in ANSYS to optimize the HOM load design. Frequency-dependent dielectric material properties measured from samples and RF power spectrum calculated by the beam-cavity interaction codes were considered. The coupled field analysis capability of ANSYS avoided mapping of results between separate RF and thermal/structural simulation codes. For verification purposes, RF results obtained from ANSYS were compared to those from MAFIA, HFSS, and Microwave Studio. Good agreement was reached and this confirms that multiple-field coupled analysis is a desirable choice in analysis of HOM loads. Similar analysis could be performed on other particle accelerator components where distributed RF heating and surface current induced losses are inevitable. HOM ABSORBER DESIGNThe 748.5 MHz high order mode (HOM) absorber is based on the PEP-II HOM load design [1]. The basic design specifications are as follows:Fundamental mode frequency: 748.5 MHz Number of HOM loads per cavity: 5 RF power deposition per load: 4000 Watts

JLAB high-current CW cryomodules for ERL and FEL applications

“…The broad-band match of this load is shown in figure 5. The loads have also been analyzed using ANSYS multi-physics simulation to take real RF fields and calculate the losses, absorber temperature and thermal stresses in a common model [5], figure 6. A simplified lower power version has been developed for the 1497 MHz cavities using a similar absorber profile but with simplified construction and reduced cooling for the lower current requirements.…”