Development of HOM absorbers for SuperKEKB

Higher-order modes (HOM) absorbers are indispensable components for recent high-power accelerators to prevent beam instabilities or overheating of vacuum components. Ferrite has been found to be an excellent HOM absorber material because of its higher HOM absorbing efficiency. However, the difficulty in bonding to metals has been limiting the application to a reliable HOM absorber. We have been developing a fabrication method of ferrite-copper blocks using the spark plasma sintering (SPS) technique. Some key properties of the ferrite block, such as the RF absorbing property, and the gas desorption rate, are reported. The first test result using a high-power microwave source is also presented. Conceptual design and simulation study of HOM absorber chambers have just started. (author)