ERL HOM absorber development

Sawamura, Masaru; Furuya, Takaaki*; Sakai, Hiroshi*; Umemori, Kensei*; Shinoe, Kenji*

HOM absorbers are one of the key components to determine the ERL cavity performance to reduce the HOM problem for the high current operation. When a beam line HOM damper is installed inside the cryomodule, the HOM damper is cooled down to liquid nitrogen temperature. The RF absorber used for the HOM damper is required to have good frequency and temperature properties. Some ferrites and ceramics are tested for permittivity and permeability of frequency-dependence and temperature-dependence measured with a GM refrigerator from room temperature to 40 K. The HOM damper is designed by optimizing the parameters such as length, thickness and position with microwave simulation codes. Test models of the HOM damper are being designed and fabricated to test the RF, mechanical, cooling and temperature properties.