Reduction of the photoelectron yield from a copper beam chamber by saw-tooth machining

One of the latest serious problems for KEKB is a beam size blow up of the positron beam. The blow up is considered to be caused by a single-beam instability due to an electron cloud around the positron beam. The seed of the electrons is mainly photoelectrons emitted from the surface of vacuum chamber. Here a surface with a sawtooth structure is proposed to reduce the photoelectron yield. Experiments using a test chamber made of copper verify its validity.