Development of wing-type HOM damper for KEKB

The KEK B-factory (KEKB) is a high-current electron–positron collider aiming at a luminosity goal of 1×1034 cm−2 s−1. The vacuum components are likely to be annoyed by the intense higher order modes (HOM) excited by the high bunch current. Some bellows near special vacuum components, for example, were heated up due to the HOM and their RF-shield fingers were damaged during the beam operation. To solve these HOM-related problems, and also to prepare for a future higher current operation, a wing-type HOM damper equipped with SiC HOM absorbers were developed to absorb the unnecessary HOM, especially TE-mode like HOM with a power of several kW. They were installed in the KEKB positron ring and relieved the heating of bellows and pump elements effectively. The maximum absorbed HOM power was about 5.4 kW for one HOM damper at the stored beam current of 1.6 A (bunch number=1284 and bunch length=7 mm). The structure and the properties of the wing-type HOM damper are reported, as are the results of beam tests in the KEKB.